Mandarin fruit quality: a review

On-site analysis and rapid identification of citrus herbs by miniature mass spectrometry and machine learning

BACKGROUND

Natural medicines present a considerable analytical challenge due to their diverse botanical origins and complex multi-species composition. This inherent complexity complicates their rapid identification and analysis. Tangerine peel, a product of the Citrus species from the Rutaceae family, is widely used both as a culinary ingredient and in traditional Chinese medicine. It is classified into two primary types in China: Citri Reticulatae Pericarpium (CP) and Citri Reticulatae Pericarpium Viride (QP), differentiated by harvest time. A notable price disparity exists between CP and another variety, Citri reticulatae "Chachi" (GCP), with differences being based on the original variety.

METHODS

This study introduces an innovative method using portable miniature mass spectrometry for swift on-site analysis of QP, CP, and GCP, requiring less than a minute per sample. And combined with machine learning to differentiate the three types on site, the method was used to try to distinguish GCP from different storage years.

RESULTS

This novel method using portable miniature mass spectrometry for swift on-site analysis of tangerine peels enabled the characterization of 22 compounds in less than one minute per sample. The method simplifies sample processing and integrates machine learning to distinguish between the CP, QP, and GCP varieties. Moreover, a multiple-perceptron neural network model is further employed to specifically differentiate between CP and GCP, addressing the significant price gap between them.

CONCLUSIONS

The entire analytical time of the method is about 1 minute, and samples can be analyzed on site, greatly reducing the cost of testing. Besides, this approach is versatile, operates independently of location and environmental conditions, and offers a valuable tool for assessing the quality of natural medicines.

Identification of key sensory and chemical factors determining flavor quality of Xinyu mandarin during ripening and storage

Xinyu mandarin is popular for its good flavor, but its flavor deteriorates during postharvest storage. To better understand the underlying basis of this change, the dynamics of the sensory profiles were investigated throughout fruit ripening and storage. Sweetness and sourness, determined especially by sucrose and citric acid content, were identified as the key sensory factors in flavor establishment during ripening, but not in flavor deterioration during storage. Postharvest flavor deterioration is mainly attributed to the reduction of retronasal aroma and the development of off-flavor. Furthermore, sugars, acids and volatile compounds were analyzed. Among the 101 detected volatile compounds, 10 changed significantly during the ripening process. The concentrations of 15 volatile components decreased during late postharvest storage, among which α-pinene and d-limonene were likely to play key roles in the reduction of aroma. Three volatile compounds were found to increase during storage, associated with off-flavor development.

Comparative study on volatile compounds and taste components of various citrus cultivars using electronic sensors, GC-MS, and GC-olfactometry

Various citrus fruits' flavor compounds were analyzed using an electronic sensor (E-sensor), and odor-active compounds were identified using gas chromatography-mass spectrometry-olfactometry (GC-MS-O). In the E-tongue analysis, the intensity of sweetness, saltiness, and bitterness was highest in Citrus unshiu, while sourness and umami were highest in C. setomi. A total of 43 volatile compounds were detected in the E-nose analysis, and the compound with the highest peak area was limonene, a type of terpenoid, which exhibited a prominent peak area in C. unshiu. Principal component analysis between flavor compounds and each sample explained a total variance of 83.15% and led to the classification of three clusters. By GC-MS-O, 32 volatile compounds were detected, with limonene being the most abundant, ranging from 20.28 to 56.21 mg/kg. The odor-active compounds were identified as (E)-2-hexenal, hexanal, α-pinene, β-myrcene, limonene, γ-terpinene, nonanal, and D-carvone, respectively.

Widely metabolomic combined with transcriptome analysis to build a bioactive compound regulatory network for the fruit growth cycle in Pseudocydonia sinensis

Neglected and underutilised plants such as Pseudocydonia sinensis (Chinese quince) have garnered global interest as invaluable sources of natural bioactive compounds. Herein, a wide-targeted metabolomics-based approach revealed 1199 concurrent metabolites, with further analysis of their fluctuations across with the five stages of fruit growth. The bioactive compounds in Chinese quince primarily comprised sugars and organic acids, flavonoids, and terpenoids. Moreover, 395 metabolites were identified as having medicinal properties and rutin was the most content of them. Transcriptome analysis further provided a molecular basis for the metabolic changes observed during fruit development. By thoroughly analysing metabolite and transcriptome data, we revealed changes in bioactive compounds and related genes throughout fruit development. This study has yielded valuable insights into the ripening process of Chinese quince fruit, presenting substantial implications for industrial applications, particularly in quality control.

Assessing the Feasibility of Biorefineries for a Sustainable Citrus Waste Management in Korea

Citrus fruits are one of the most widely used fruits around the world and are used as raw fruits, but are also processed into products such as beverages, and large amounts of by-products and waste are generated in this process. Globally, disposal of citrus waste (CW) through simple landfilling or ocean dumping can result in soil and groundwater contamination, which can negatively impact ecosystem health. The case of Korea is not much different in that these wastes are simply buried or recycled wastes are used as livestock feed additives. However, there are many reports that CW, which is a waste, has high potential to produce a variety of products that can minimize environmental load and increase added value through appropriate waste management. In this study, we aim to explore the latest developments in the evaluation and valorization of the growing CW green technologies in an effort to efficiently and environmentally transform these CW for resource recovery, sustainability, and economic benefits. Recent research strategies on integrated biorefinery approaches have confirmed that CW can be converted into various bioproducts such as enzymes, biofuels and biopolymers, further contributing to energy security. It was found that more efforts are needed to scale up green recovery technologies and achieve diverse product profiling to achieve zero waste levels and industrial viability.

Enhancing citrus fruit yield investigations through flight height optimization with UAV imaging

Citrus fruit yield is essential for market stability, as it allows businesses to plan for production and distribution. However, yield estimation is a complex and time-consuming process that often requires a large number of field samples to ensure representativeness. To address this challenge, we investigated the optimal altitude for unmanned aerial vehicle (UAV) imaging to estimate the yield of Citrus unshiu fruit. We captured images from five different altitudes (30 m, 50 m, 70 m, 90 m, and 110 m), and determined that a resolution of approximately 5 pixels/cm is necessary for reliable estimation of fruit size based on the average diameter of C. unshiu fruit (46.7 mm). Additionally, we found that histogram equalization of the images improved fruit count estimation compared to using untreated images. At the images from 30 m height, the normal image estimates fruit numbers as 73, 55, and 88. However, the histogram equalized image estimates 88, 71, 105. The actual number of fruits is 124, 88, and 141. Using a Vegetation Index such as IPCA showed a similar estimation value to histogram equalization, but I1 estimation represents a gap to actual yields. Our results provide a valuable database for future UAV field investigations of citrus fruit yield. Using flying platforms like UAVs can provide a step towards adopting this sort of model spanning ever greater regions at a cheap cost, with this system generating accurate results in this manner.

Geographical origin identification of mandarin fruits by analyzing fingerprint signatures based on multielemental composition

Given rising traders and consumers concerns, the global food industry is increasingly demanding authentic and traceable products. Consequently, there is a heightened focus on verifying geographical authenticity as food quality assurance. In this work, we assessed pattern recognition approaches based on elemental predictors to discern the provenance of mandarin juices from three distinct citrus-producing zones located in the Northeast region of Argentina. A total of 202 samples originating from two cultivars were prepared through microwave-assisted acid digestion and analyzed by microwave plasma atomic emission spectroscopy (MP-AES). Later, we applied linear discriminant analysis (LDA), k-nearest neighbor (k-NN), support vector machine (SVM), and random forest (RF) to the element data obtained. SVM accomplished the best classification performance with a 95.1% success rate, for which it was selected for citrus samples authentication. The proposed method highlights the capability of mineral profiles in accurately identifying the genuine origin of mandarin juices. By implementing this model in the food supply chain, it can prevent mislabeling fraud, thereby contributing to consumer protection.

Screening and Characteristics Analysis of Polysaccharides from Orah Mandarin (Citrus reticulata cv. Orah)

This study aimed to screen out polysaccharides with the ability to activate NK cells. Ten polysaccharides (OP) were isolated from orah mandarin (Citrus reticulata cv. Orah) peel using hot-water extraction combined with the alcohol precipitation method and the ultrafiltration-membrane separation method. After measuring the effects of 10 OPs on NK-92MI cell proliferation and cytotoxicity, it was found that the polysaccharide OP5 had the highest activity in vitro. OP5 can significantly promote the proliferation of and increase the gene expression of perforin, granzyme B and IFN-γ in NK-92MI cells. Its molecular weight was between 50 and 70 kDa. The identification results of monosaccharide composition indicated that OP5 was composed of arabinose (31.52%), galacturonic acid (22.35%), galactose (16.72%), glucose (15.95%), mannose (7.67%), rhamnose (2.39%), fucose (1.41%), xylose (1.30%), glucuronic acid (0.42%) and ribose (0.27%). The sugar ring of the β-configuration was the main, and that of the α-configuration was the auxiliary. These results would provide a foundation for the functional product development of OPs.

Effect of Natural Variation and Rootstock on Fruit Quality and Volatile Organic Compounds of 'Kiyomi tangor' (Citrus reticulata Blanco) Citrus

In this study, we compared the fruit quality and color of 'Kiyomi' (WT) and its mutant (MT) grafted on Ziyang xiangcheng (Cj) (WT/Cj, MT/Cj), and the MT grafted on Trifoliate orange (Pt) (MT/Pt). The differences in sugar, organic acid, flavonoids, phenols, and volatile substances of the three materials were also analyzed by high performance liquid chromatography (HPLC) and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The results showed significant differences in the appearance of WT/Cj, MT/Cj, and MT/Pt. MT/Pt, compared to WT/Cj, MT/Cj, had lower sugar, acid, phenol and flavonoid contents in the pulp. However, MT/Pt pulp was higher in vitamin C (VC), and the peel had significantly higher total phenol and flavonoid contents. In terms of pulp, WT/Cj had the greatest diversity of volatile organic compounds (VOCs). 4-methyl-1-pentanol was significantly higher in MT/Cj pulp, while MT/Pt pulp had a unique octanoic acid, methyl ester. VOCs were more diverse in the peels of the three materials. β-Myrcene and valencen were significantly higher in MT/Cj peels. In contrast, 16 unique VOCs were detected in MT/Pt, and D-limonene content was significantly higher than in WT/Cj and MT/Cj. The results suggest Trifoliate orange is a suitable rootstock for MT.

Magnesium accelerates changes in the fruit ripening and carotenoid accumulation in Satsuma Mandarin pulp

This study aims to further examine the effect of Magnesium (Mg) application on fruit quality and carotenoid metabolism in Satsuma mandarin pulp. For this, a field experiment was using 20-year-old Satsuma mandarin (C. unshiu Marc.) for two treatment; (1) CK treatment (without Mg), (2) Mg fertilizer treatment (200 g MgO plant-1). Compared with CK, Mg treatment substantially raised the Mg content in pulp at 90 to 150 DAF (the fruit expansion period), increasing by 15.69%-21.74%. Mg treatment also increased fruit TSS content by 15.84% and 9.88%, decreased fruit TA content in by 34.25% and 33.26% at 195 DAF and 210 DAF (the fruit ripening period). Moreover, at 120 to 195 DAF, Mg treatment significantly increased the levels of lutein, β-cryptoxanthin, zeaxanthin and violaxanthin in the pulp. This can be explained by the increased expression of important biosynthetic genes, including CitPSY, CitPDS, CitLCYb1, CitLCYb2, CitLCYe, CitHYb, and CitZEP, that played a role in altering the carotenoid composition. The findings of this research offer a novel approach for augmenting both the economic and nutritional worth of citrus fruits.

Comparative Analysis of Concurrent (CC), Mixed Flow (MX), and Combined Spray Drying Configurations on the Physicochemical Characteristics of Satsuma Mandarin (Citrus unshiu) Juice Powders

Satsuma mandarins are good sources of vitamin C and can be used as raw materials to produce novel plant-based food ingredients including satsuma mandarin juice powders (SJP). Food powders produced via spray drying often show thermal degradation due to the drying conditions and high drying air temperatures. The aim of this study was to evaluate the effect of using different spray drying configurations, including concurrent (CC), mixed flow (MX), and combined (CC + MX), at two inlet air temperatures (160 and 180 °C) on the physicochemical properties of SJP. Remarkably, SJP produced using the CC spray drying configuration exhibited a higher vitamin C content (3.56-4.01 mg/g) and lower moisture levels (15.18-16.35 g/100 g) than powders produced via MX or CC + MX. The vitamin C content of MX and CC + MX powders ranged from 2.88 to 3.33 mg/g. Meanwhile, all SJP had water activity values below 0.19. Furthermore, MX powders displayed the largest mean particle sizes (D50) (8.69-8.83 µm), higher agglomeration, and a rapid dissolution. Despite these differences, all SJP variants exhibited consistent color, surface area, and pore volumes. Notably, powders dried at higher inlet air temperatures (180 °C) showed less vitamin C content and increased thermal damage when compared with powders dried at 160 °C inlet air temperature. This study demonstrated the feasibility of producing high-quality SJP with an extended shelf life. SJP can be used as a novel plant-based ingredient in different food applications.

Nutritional and volatile profiles of pulp and flavedo from four local pummelo cultivars grown in Fujian province of China

The nutritional and volatile profiles of pulp and flavedo samples from four distinct local pummelo landraces ("Siji," "Pingshan," "Wendan," and "Guanxi") cultivated in Fujian province of China were investigated. "Guanxi" pummelo exhibited relatively high contents of vitamin C (42.01 mg/100 mL) and phenols (360.61 mg/L) and displayed a robust antioxidant capacity (41.15 mg/100 mL). Conversely, the red pulp from "Pingshan" demonstrated relatively high values of carotenoids (55.96 µg/g) and flavonoids (79.79 mg/L). Considerable differences were observed in volatile compositions between the two fruit tissues and among the four genotypes. A total of 166 and 255 volatile compounds were detected in the pulp and flavedo samples, respectively. Notably, limonene and β-myrcene were identified as the principal volatile compounds in flavedo, whereas hexanal was highly abundant in the pulp of "Siji," "Pingshan," and "Guanxi." "Wendan" displayed distinct separation from the other three pummelo cultivars in principal component analysis based on the pulp volatile compositions. This distinction was attributed to the higher number and content of volatile compounds in "Wendan" pulp, particularly the remarkable enrichment of β-myrcene. The newly characterized pummelo landraces and genotype/tissue-dependent variations in volatiles provide essential information for the genetic improvement of pummelo aroma, as well as for fruit processing and utilization.

Comparison of Some Fruit Quality Parameters of Selected 12 Mandarin Genotypes from Black Sea Region in Turkey

Mandarins are mostly preferred specie of Citrus genus, and there has been a continuous rise in consumption and global marketing due to having easy-to-peel, attractive flavor, and fresh consumption advantages. However, most of the existing knowledge on quality traits of citrus fruit comes from research conducted on oranges, which are the main products for the citrus juice manufacturing industry. In recent years, mandarin production in Turkey surpassed orange production and took the first place in citrus production. Mandarins are mostly grown in the Mediterranean and Aegean Regions of Turkey. Due to suitable climatic conditions, they are also grown in the microclimatic condition in Rize province located in the Eastern Black Sea region. In this study, we reported the total phenolic content, total antioxidant capacity, and volatiles of 12 Satsuma mandarin genotypes selected from Rize province of Turkey. Considerable differences in the total phenolic content, total antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl assay), and fruit volatile constituent were found among the 12 selected Satsuma mandarin genotypes. The total phenolic content ranged from 3.50 to 22.53 mg of gallic acid equivalent per 100 g of the fruit sample in the selected mandarin genotypes. The total antioxidant capacity was the highest in genotype HA2 as 60.40%, and followed by IB (59.15%) and TEK3 (58.36%), respectively. A total of 30 aroma volatiles were detected from the juice samples of 12 mandarin genotypes by GC/MS, which comprised six alcohols, three aldehydes (including one monoterpene), three esters, one ketone, and one other volatiles. The main volatile compounds were identified in fruits of all Satsuma mandarin genotypes as α-terpineol (0.6-1.88%), linalool (1.1-3.21%), γ-terpinene (4.41-5.5%), β-myrcene (0.9-1.6%), dl-limonene (79.71-85.12%), α-farnesene (1.1-2.44), and d-germacrene (0.66-1.37%). Limonene accounts for most of the aroma compounds (79.71-85.12%) in fruits of all Satsuma genotypes. The genotypes MP and TEK8 had the highest total phenolic content, and HA2, IB, and TEK 3 had the highest antioxidant capacity. The YU2 genotype was found to contain more aroma compounds than the other genotypes. The genotypes selected on the basis of their high bioactive content could be used to develop new Satsuma mandarin cultivars with high human health promoting contents.

Allelic haplotype combinations at the MS-P1 region, including P-class pentatricopeptide repeat family genes, influence wide phenotypic variation in pollen grain number through a cytoplasmic male sterility model in citrus

In citrus breeding programs, male sterility is an important trait for developing seedless varieties. Sterility associated with the male sterile cytoplasm of Kishu mandarin (Kishu-cytoplasm) has been proposed to fit the cytoplasmic male sterility (CMS) model. However, it remains undetermined whether CMS in citrus is controlled by interactions between sterile cytoplasm and nuclear restorer-of-fertility (Rf) genes. Accordingly, mechanisms underlying the control of the wide phenotypic variation in pollen number for breeding germplasm should be elucidated. This study aimed to identify complete linkage DNA markers responsible for male sterility at the MS-P1 region based on fine mapping. Two P-class pentatricopeptide repeat (PPR) family genes were identified as candidates for Rf based on predicted mitochondrial localization and higher expression in a male fertile variety/selected strain than in a male sterile variety. Eleven haplotypes (HT1-HT11) at the MS-P1 region were defined based on genotyping of DNA markers. Association analysis of diplotypes at the MS-P1 region and the number of pollen grains per anther (NPG) in breeding germplasms harboring Kishu-cytoplasm revealed that the diplotypes in this region influenced NPG. Among these haplotypes, HT1 is a non-functional restorer-of-fertility (rf) haplotype; HT2, a less-functional Rf; HT3-HT5 are semi-functional Rfs; and HT6 and HT7 are functional Rfs. However, the rare haplotypes HT8-HT11 could not be characterized. Therefore, P-class PPR family genes in the MS-P1 region may constitute the nuclear Rf genes within the CMS model, and a combination of the seven haplotypes could contribute to phenotypic variation in the NPG of breeding germplasms. These findings reveal the genomic mechanisms of CMS in citrus and will contribute to seedless citrus breeding programs by selecting candidate seedless seedlings using the DNA markers at the MS-P1 region.

Transcriptome Analysis and VIGS Identification of Key Genes Regulating Citric Acid Metabolism in Citrus

Citrus (Citrus reticulata) is one of the world's most widely planted and highest-yielding fruit trees. Citrus fruits are rich in a variety of nutrients. The content of citric acid plays a decisive role in the flavor quality of the fruit. There is a high organic acid content in early-maturing and extra-precocious citrus varieties. Reducing the amount of organic acid after fruit ripening is significant to the citrus industry. In this study, we selected a low-acid variety, "DF4", and a high-acid variety, "WZ", as research materials. Through WGCNA analysis, two differentially expressed genes, citrate synthase (CS) and ATP citrate-pro-S-lyase (ACL), were screened out, which related to the changing citric acid. The two differentially expressed genes were preliminarily verified by constructing a virus-induced gene-silencing (VIGS) vector. The VIGS results showed that the citric acid content was negatively correlated with CS expression and positively correlated with ACL expression, while CS and ACL oppositely control citric acid and inversely regulate each other. These results provide a theoretical basis for promoting the breeding of early-maturing and low-acid citrus varieties.

Magnetic Iron-Improved Growth, Leaf Chemical Content, Yield, and Fruit Quality of Chinese Mandarin Trees Grown under Soil Salinity Stress

Chinese mandarin fruits are an inexpensive and rich source of vitamin C. They have potential benefits in treating acute respiratory infections and mitigating inflammation in critical patients with COVID-19. In Egypt, citrus is the most important fruit tree but is sensitive to salinity stress, resulting in poor vegetative tree growth and reductions in productivity and fruit quality. Magnetic iron has emerged as a promising approach in the citrus tree industry, since it improves vegetative growth, yield, and fruit quality and alleviates salinity stress in Chinese mandarin trees grown in soils suffering from high salt stress. This research is aimed at studying the influence of adding magnetic iron (as soil treatment) on tree canopy growth, yield, and fruit quality of 'Chinese' mandarin trees. Therefore, the treatments were as follows: 0, 250, 500, and or 750 g of magnetic iron.tree^-1. Our results indicated that all applications of magnetic iron significantly improved tree canopy volume, leaf total chlorophyll, relative water content, yield (kg.tree^-1), and the fruit physical and chemical characteristics of Chinese mandarin. In contrast, leaf Na and Cl content, (%), proline, and total phenolic content were decreased by magnetic iron soil treatments. In respect to vegetative growth, our results indicated that adding magnetic iron at the concentration 750 g.tree^-1 caused the best values of tree canopy volume. A similar trend was noticed regarding yield. The increase in yield attained was nearly 19%; the best values were obtained when magnetic iron were used at 750 g.tree^-1. In conclusion, the application of magnetic iron can lead to improved fruit production and fruit quality of Chinese mandarin trees grown in salinity stress conditions.

Citrus juice off-flavor during different processing and storage: Review of odorants, formation pathways, and analytical techniques

As the most widespread juice produced and consumed globally, citrus juice (mandarin juice, orange juice, and grapefruit juice) is appreciated for its attractive and distinct aroma. While the decrease of characteristic aroma-active compounds and the formation of off-flavor compounds are easy to occur in processing and storage conditions. This review provides a comprehensive literature of recent research and discovery on citrus juice off-flavor, primarily focusing on off-flavor compounds induced during processing and storage (i.e., thermal, storage, light, oxygen, package, fruit maturity, diseases, centrifugal pretreatment, and debittering process), formation pathways (i.e., terpene acid-catalyzed hydration, caramelization reaction, Maillard reaction, Strecker degradation, and other oxidative degradation) of the off-flavor compounds, effective inhibitor pathway to off-flavor (i.e., electrical treatments, high pressure processing, microwave processing, ultrasound processing, and chemical treatment), as well as odor assessment techniques based on molecular sensory science. The possible precursors (terpenes, sulfur-containing amino acids, carbohydrates, carotenoids, vitamins, and phenolic acids) of citrus juice off-flavor are listed and are also proposed. This review intends to unravel the regularities of aroma variations and even off-flavor formation of citrus juice during processing and storage. Future aroma analysis techniques will evolve toward a colorimetric sensor array for odor visualization to obtain a "marker" of off-flavor in citrus juice.

An integrated metabolome and transcriptome approach reveals the fruit flavor and regulatory network during jujube fruit development

The fruit flavor is a key economic value attribute of jujube. Here we compared metabolomes and transcriptomes of "Mazao" (ST) and "Ping'anhuluzao" (HK) with unique flavors during fruit development. We identified 437 differential metabolites, mainly sugars, acids, and lipids. Fructose, glucose, mannose and citric acid, and malic acid are the determinants of sugar and acid taste of jujube fruit. Based on the transcriptome, 16,245 differentially expressed genes (DEGs) were identified, which were involved in "glucosyltransferase activity," "lipid binding," and "anion transmembrane transporter activity" processes. Both transcriptome and metabolome showed that developmental stages 2 and 3 were important transition periods for jujube maturation. Based on WGCNA and gene-metabolite correlation analysis, modules, and transcription factors (ZjHAP3, ZjTCP14, and ZjMYB78) highly related to sugar and acid were identified. Our results provide new insights into the mechanism of sugar and acid accumulation in jujube fruit and provide clues for the development of jujube with a unique flavor.

Metabolomic Profiling of Citrus unshiu during Different Stages of Fruit Development

Citrus fruits undergo significant metabolic profile changes during their development process. However, limited information is available on the changes in the metabolites of Citrus unshiu during fruit development. Here, we analyzed the total phenolic content (TPC), total carotenoid content (TCC), antioxidant activity, and metabolite profiles in C. unshiu fruit flesh during different stages of fruit development and evaluated their correlations. The TPC and antioxidant activity significantly decreased during fruit development, whereas the TCC increased. The metabolite profiles, including sugars, acidic compounds, amino acids, flavonoids, limonoids, carotenoids, and volatile compounds (mono- and sesquiterpenes), in C. unshiu fruit flesh also changed significantly, and a citrus metabolomic pathway related to fruit development was proposed. Based on the data, C. unshiu fruit development was classified into three groups: Group 1 (Aug. 1), Group 2 (Aug. 31 and Sep. 14), and Group 3 (Oct. 15 and Nov. 16). Although citrus peel was not analyzed and the sensory and functional qualities during fruit development were not investigated, the results of this study will help in our understanding of the changes in chemical profile during citrus fruit development. This can provide vital information for various applications in the C. unshiu industry.

Effects of packinghouse operations on the flavor of 'Orri' mandarins

Mandarins have a delicate flavor and are easy to peel and easy to consume. However, they are relatively perishable and suffer from flavor deterioration after harvest. The goal of the current study was to examine the effects of commercial packinghouse operations on the flavor of 'Orri' mandarins. For that purpose, we collected fruit from four different points along a commercial citrus packing line: (1) directly from the harvest bin, (2) after application of a hot (53°C) fungicide treatment for 30 s, (3) after waxing, and (4) after waxing and after the fruit had passed through a hot-air drying tunnel (37°C) for 2 min. The collected fruit were stored for 3 or 6 weeks at 5°C and then kept for five more days under shelf-life conditions at 22°C. The observed results indicate that the hot fungicide treatment had no effect on flavor quality. However, the waxing and waxing +drying treatments resulted in significant increases in ethanol accumulation, lower flavor-acceptability scores, and increased off-flavors. Gas-chromatography mass-spectrometry (GC-MS) analysis revealed that the waxing and waxing +drying treatments resulted in particular increases in the levels of alcohol and ethyl ester volatiles; whereas levels of other aroma volatiles (i.e., esters, aldehydes, monoterpenes, and sesquiterpenes) decreased after storage in all fruit samples. Overall, the waxing process in commercial citrus packinghouses increased ethanol and ethyl ester volatile levels and harmed flavor acceptability. These findings demonstrate the need to identify new wax formulations that do not hamper fruit-flavor quality.

Fruit peel bioactives, valorisation into nanoparticles and potential applications: A review

Nanotechnology is a rapidly growing field with profound applications in different domains, particularly in food science and technology. Nanoparticles (NPs) synthesis, an integral part of nanotechnology-based applications, is broadly classified into chemical, physical and biosynthesis methods. Chemically sensitive and energy-intensive procedures employed for NPs synthesis are some of the limits of traditional chemical approaches. Recent research has focused on developing easy, nontoxic, cost-effective, and environment-friendly NPs synthesis during the last decade. Biosynthesis approaches have been developed to achieve this goal as it is a viable alternative to existing chemical techniques for the synthesis of metallic nanomaterials. Fruit peels contain abundant bioactive compounds including phenols, flavonoids, tannins, triterpenoids, steroids, glycosides, carotenoids, anthocyanins, ellagitannins, vitamin C, and essential oils with substantial health benefits, anti-bacterial and antioxidant properties, generally discarded as byproduct or waste by the fruit processing industry. NPs synthesized using bioactive compounds from fruit peel has futuristic applications for an unrealized market potential for nutraceutical and pharmaceutical delivery. Numerous studies have been conducted for the biosynthesis of metallic NPs such as silver (AgNPs), gold (AuNPs), zinc oxide, iron, copper, palladium and titanium using fruit peel extract, and their synthesis mechanism have been reported in the present review. Additionally, NPs synthesis methods and applications of fruit peel NPs have been discussed.

Determination of Bioactive Components in Mandarin Fruits: A Review

During the last decade, there has been a continuous rise in the consumption of fresh easy-to-peel mandarins. However, the majority of the knowledge comes from other citrus fruit, like orange, while there are relatively few studies about mandarins and no comprehensive research on literature data about them. One of the most important steps in the analytical process is sample preparation. Its value is evident in analyzing the samples with complex matrices, such as in mandarin fruit. In addition, mandarin contains hundreds to thousands of various compounds and metabolites, some of them present in extremely low concentrations, that interfere with the detection of one another. Hence, mandarin samples are commonly pretreated by extraction to facilitate analysis of bioactive compounds, improve accuracy and quantification levels. There is an abundance of extraction techniques available, depending on the group of compounds of interest. Finally, modern analytical techniques, have been applied to cope with numerous bioactive compounds in mandarins. Considering all the above, this review aims to (i) list the most valuable procedures of sample preparation, (ii) highlight the most important techniques for extraction of bioactive compounds from mandarin fruit, and (iii) summarize current trends in the identification and determination of bioactive compounds in mandarin.

Dissecting Breeders' Sense via Explainable Machine Learning Approach: Application to Fruit Peelability and Hardness in Citrus

"Genomics-assisted breeding", which utilizes genomics-based methods, e.g., genome-wide association study (GWAS) and genomic selection (GS), has been attracting attention, especially in the field of fruit breeding. Low-cost genotyping technologies that support genome-assisted breeding have already been established. However, efficient collection of large amounts of high-quality phenotypic data is essential for the success of such breeding. Most of the fruit quality traits have been sensorily and visually evaluated by professional breeders. However, the fruit morphological features that serve as the basis for such sensory and visual judgments are unclear. This makes it difficult to collect efficient phenotypic data on fruit quality traits using image analysis. In this study, we developed a method to automatically measure the morphological features of citrus fruits by the image analysis of cross-sectional images of citrus fruits. We applied explainable machine learning methods and Bayesian networks to determine the relationship between fruit morphological features and two sensorily evaluated fruit quality traits: easiness of peeling (Peeling) and fruit hardness (FruH). In each of all the methods applied in this study, the degradation area of the central core of the fruit was significantly and directly associated with both Peeling and FruH, while the seed area was significantly and directly related to FruH alone. The degradation area of albedo and the area of flavedo were also significantly and directly related to Peeling and FruH, respectively, except in one or two methods. These results suggest that an approach that combines explainable machine learning methods, Bayesian networks, and image analysis can be effective in dissecting the experienced sense of a breeder. In breeding programs, collecting fruit images and efficiently measuring and documenting fruit morphological features that are related to fruit quality traits may increase the size of data for the analysis and improvement of the accuracy of GWAS and GS on the quality traits of the citrus fruits.

Five Rootstocks for "Emperor" Mandarin Under Subtropical Climate in Southern Brazil

Rootstocks modulate several characteristics of citrus trees, including vegetative growth, fruit yield and quality, and resistance or tolerance to pests, diseases, soil drought, and salinity, among other factors. There is a shortage of scion and rootstock cultivars among the combinations planted in Brazil. "Ponkan" mandarin and "Murcott" tangor grafted on "Rangpur" lime comprise the majority of the commercial mandarin orchards in Brazil. This low genetic diversity of citrus orchards can favor pest and disease outbreaks. This study aimed to evaluate the agronomic performance, Huanglongbing (HLB) tolerance, and fruit quality of "Emperor" mandarin on five different rootstocks for nine cropping seasons under the subtropical soil-climate conditions of the North region of the state of Paraná, Brazil. The experimental design was a randomized block, with six replications, two trees per block, and five rootstocks, including "Rangpur" lime, "Cleopatra," and "Sunki" mandarins, "Swingle" citrumelo, and "Fepagro C-13" citrange. The evaluations included tree growth, yield performance, fruit quality, and HLB disease incidence. "Emperor" mandarin trees grafted on "Rangpur" lime and "Swingle" citrumelo had early fruiting and high yield efficiency. "Rangpur" lime also induced the lowest tree growth, but low fruit quality. Trees on "Swingle" citrumelo and "Fepagro C-13" citrange showed low scion and rootstock affinity and produced fruits with high total soluble solids (TSS), with a lower number of seeds for those from trees on "Fepagro C-13" citrange. "Cleopatra" and "Sunki" mandarins induced higher juice content, while fruits from trees on "Cleopatra" also had higher TSS/titratable acidity (TA) ratio. "Emperor" mandarin trees were susceptible to HLB regardless of the rootstocks. Overall, "Cleopatra" and "Sunki" mandarins, "Swingle" citrumelo, and "Fepagro C-13" are more suitable rootstocks for "Emperor" mandarin under Brazilian subtropical conditions than "Rangpur" lime.

Effect of information about mandarin internal maturity on consumer hedonic and sensory expectations: a cross-cultural study in Spain and Mexico

BACKGROUND

Under certain climate conditions, citrus fruit may reach optimum internal maturity while the rind is still green. It is therefore customary to enhance skin colour changes by submitting early citrus varieties to ethylene degreening treatment, which implies a cost and may result in external disorders. In this study, the effect on consumer expectations (sensory and hedonic) of providing them with information about the internal maturity of non-degreened mandarins (greenish-coloured rind) was evaluated.

RESULTS

Mandarins with three different external colour indices (CI), CI = -6, CI = +1 and CI = +5, and three ways of conveying information, were investigated: (i) No information (NoInfo), (ii) The text 'Mandarins ready to eat' (Text) and (iii) Text + Visualisation of mandarin flesh (orange-coloured in all cases) (Text+Flesh). Consumer expected liking, purchase intention and sensory expectations were markedly affected after receiving the different information types. The greatest effect was detected when Text+Flesh information was provided. Rind mandarin colour was also a determinant factor of how consumer expectations were modified by the received information. Moreover, our results revealed some differences among Spanish and Mexican consumers, since maturity information had a stronger effect on hedonic expectations of Mexican consumers.

CONCLUSIONS

When mandarins reach CI = +5 (pale orange-coloured rind with small areas still green), letting consumers know that mandarins are ready to eat by means of Text+Flesh information may be a non-cost strategy to avoid degreening treatment or to shorten its length. © 2021 Society of Chemical Industry.

Bioactive Molecules of Mandarin Seed Oils Diminish Mycotoxin and the Existence of Fungi

Mandarin is a favorite fruit of the citrus family. Mandarin seeds are considered a source of nontraditional oil obtained from byproduct materials. This investigation aimed to assess the biomolecules of mandarin seeds and evaluated their antimycotic and antimycotoxigenic impact on fungi. Moreover, it evaluated the protective role of mandarin oil against aflatoxin toxicity in cell lines. The two types of extracted oil (fixed and volatile) were ecofriendly. The fatty acid composition, tocopherol, sterols, and carotenoids were determined in the fixed oil, whereas volatiles and phenolics were estimated in the essential oil. A mixture of the two oils was prepared and evaluated for its antimicrobial impact. The reduction effect of this mixture was also investigated to reduce mycotoxin secretion using a simulated experiment. The protective effect of the oil was evaluated using healthy strains of cell lines. Fixed oil was distinguished by the omega fatty acid content (76.24%), lutein was the major carotenoid (504.3 mg/100 g) and it had a high β-sitosterol content (294.6 mg/100 g). Essential oil contained limonene (66.05%), α-pinene (6.82%), β-pinene (4.32%), and γ-terpinene (12.31%) in significant amounts, while gallic acid and catechol were recorded as the dominant phenolics. Evaluation of the oil mix for antimicrobial potency reflected a considerable impact against pathogenic bacteria and toxigenic fungi. By its application to the fungal media, this oil mix possessed a capacity for reducing mycotoxin secretion. The oil mix was also shown to have a low cytotoxic effect against healthy strains of cell lines and had potency in reducing the mortality impact of aflatoxin B₁ applied to cell lines. These results recommend further study to involve this oil in food safety applications.

External Quality of Mandarins: Influence of Fruit Appearance Characteristics on Consumer Choice

In a pre-purchase situation, consumer perception of mandarin quality is almost exclusively based on fruit appearance. Determination of consumer requirements in this regard is needed to preserve the current success of this crop in markets worldwide. In this study, the effect on consumer choice of different appearance characteristics that can occur mainly in early-season mandarins was quantified. Two independent Choice-Based Conjoint Analyses were performed to evaluate the effect of different external mandarin factors: (1) two factors linked mainly with harvesting practices: ‘Leaf’ (no leaves but sound calyx/fresh leaf/dehydrated leaf) and ‘Rind Colour’ (orange colour/rind with slightly greenish areas); (2) three factors related to postharvest handling: ‘Calyx Condition’ (sound/blackening/detached),’Waxing’ (absence/presence of wax), and ‘Rind Condition’ (dehydrated/turgid). A total of 280 consumers participated in each study. The evaluation of the factors linked with harvesting revealed four different choice patterns. Leaf presence was appreciated only by a small group of consumers (20%), and the presence of greenish areas on the rind was perceived mostly as a negative characteristic. Among the evaluated postharvest-related factors, ‘Waxing’ and ‘Calyx condition’ had the strongest effect on consumer choice. Consumers showed marked preferences for mandarins that had been waxed and presented shine and gloss. Calyx blackening and detachment had a negative effect mainly on waxed fruit, while rind dehydration more negatively affected the fruit that had not been waxed. Consumer perception of mandarin quality is importantly affected by external mandarin characteristics. The information herein reported can be very useful for the citrus industry for adapting quality control criteria that respond to consumer demands.

Evaluation of the Health-Promoting Properties of Selected Fruits

In this study, the health-promoting benefits of different fruits grown in Madeira Island, namely lemon (Citrus limon var. eureka), tangerine (Citrus reticulata var. setubalense), pitanga (Eugenia uniflora var. red), tomato (Solanum lycopersicum var. gordal) and uva-da-serra, an endemic blueberry (Vaccinium padifolium Sm.), were investigated. The phenolic composition (total phenolics and total flavonoids content) and antioxidant capacity (assessed through ABTS and DPPH assays) were measured revealing a high phenolic potential for all fruits, except tomato, while uva-da-serra is particularly rich in flavonoids. In relation to the antioxidant capacity, the highest values were obtained for pitanga and uva-da-serra extracts. The bioactive potential was also assessed through the ability of the extracts to inhibit digestive enzymes linked to diabetes (α-amylase, α- and β-glucosidases) and hypertension (angiotensin-converting enzyme, ACE). The results obtained point to a very high bioactive potential with the selected samples exhibiting very important ACE anti-enzymatic capacities. A statistical analysis of the obtained data reveals a very strong correlation between ABTS and TPC, and a strong contribution of the fruit polyphenols for enzyme inhibition, and thus, presenting high antihypertensive and antidiabetic capacities. Overall, the results obtained clearly show a high bioactive potential of the selected fruits that should be further studied, in terms of specific phenolic composition. Moreover, these results strongly support the valorisation of pitanga seeds usually discarded as a waste, and uva-da-serra, an endemic and wild bush, as potential bioresources of bioactive compounds with impact in human diet.

Citrus decoction by-product represents a rich source of carotenoid, phytosterol, extractable and non-extractable polyphenols

This study aimed to carry out an exhaustive chemical characterization of citrus (orange, mandarin, and grapefruit) decoctions as well as the residues obtained during the decoction process (by-products). The citrus decoctions were rich in hesperidin, naringin, and narirutin, but carotenoids and phytosterols were not detected. Interestingly, these flavanones were found in a higher concentration in the extractable polyphenol fraction of the citrus decoction by-products. Moreover, the greatest content of hesperidin and naringin was found bound to the food matrix by ether/ester bonds. Violaxanthin and β-cryptoxanthin were found as major carotenoids in the orange and mandarin decoction by-products, respectively, whereas the grapefruit decoction by-product showed a low content of carotenoids. All citrus by-products showed β-sitosterol as the major phytosterol, followed by β-campesterol. Therefore, the by-products obtained during the elaboration of citrus decoctions are rich sources of bioactive compounds that can be used for the development of functional foods or dietary supplements.

The combined effect of pomegranate extract and tangeretin on the DMBA-induced breast cancer model

The aim of this study was to investigate the protective effects of pomegranate extract and tangeretin alone or in combination in DMBA-induced rat breast cancer model. A total of 68 female rats were randomly divided into 8 groups. The first 4 groups were designed as controls for cancer and treatment groups, and the control groups were composed of only control (C), Pomegranate (P), Tangeretin (T), and Pomegranate+Tangeretin (P+T) groups. The other four groups were designed as cancer and treatment groups and were composed of DMBA (D) and DMBA+Pomegranate (D+P), DMBA+Tangeretin (D+T), DMBA+Pomegranate+Tangeretin (D+P+T) groups. Tumor markers and angiogenesis parameters were studied from plasma samples obtained from rats. Histopathological, immunohistochemical, and TUNEL analyses and expressions of proteins affecting apoptosis and cell cycle were determined in breast tissue samples. In the DMBA group, plasma CA15-3, CEA, VEGF, MMP-9, and NF-κB levels were significantly increased compared to the controls, but significant decreases were observed in these parameters except MMP-9 in the treatment groups. It was observed that p53 and Bax expressions significantly increased in both D+P and D+P+T groups compared to the DMBA group, and these findings were supported by Tunel and immunohistochemical findings. Cyclin D1 expressions were found to be significantly decreased only in the D+T group and supported by TUNEL and immunohistochemical findings. Immunohistochemical ER-α and Ki-67 immune reactivities were significantly decreased in all treatment groups compared to the DMBA group. Our results showed that combined application of pomegranate extract and tangeretin may be more beneficial in preventing breast cancer development.

Tangerines Cultivated on Madeira Island-A High Throughput Natural Source of Bioactive Compounds

Tangerines (Citrus reticulata) are popular fruits worldwide, being rich in many bioactive metabolites. The setubalense variety cultivated on Madeira Island has an intense aroma easily distinguishable from other tangerines, being traditionally used to enrich several foods and beverages. Nonetheless, setubalense volatile composition has never been characterized, and we aimed to unveil the bioactive potential of peels and juices of setubalense tangerines and compare them with the murcott variety grown in Portugal mainland. Using headspace solid-phase microextraction coupled to gas chromatography mass spectrometry (HS-SPME/GC-MS), we identified a total of 128 volatile organic metabolites (VOMs) in the juice and peels, with d-limonene, γ-terpinene, β-myrcene, α- and β-pinene, o-cymene, and terpinolene, the most dominant in both cultivars. In contrast, setubalense juices are richer in terpenes, many of them associated with health protection. Discriminant analysis revealed a pool of VOMs, including β-caryophyllene and E-ocimene, with bioactive properties able to differentiate among tangerines according to variety and sample type (peel vs. juice). This is the first report on the volatile composition of setubalense tangerines grown on Madeira Island revealing that its pungent aroma is constituted by secondary metabolites with specific aroma notes and health properties. This is strong evidence of the higher nutraceutical value of such fruit for the human diet.

Impact of processing on the nutritional and functional value of mandarin juice

BACKGROUND

Although phenolic compounds have a role in the health benefits of fruit juice consumption, little is known about the effect of processing on their bioaccessibility. The release of phenolic compounds from the food matrix during digestion is an important pre-requisite for their effectiveness within the human body, and so it is fundamental to identify technological treatments able to preserve not only the concentration of phytochemicals, but also their bioaccessibility. In the present study, we investigated the impact of high-pressure homogenization (HPH), alone and in the presence of 100 g kg^-1 trehalose or Lactobacillus salivarius, on the bioaccessibility of flavonoids in mandarin juice. In addition, digested mandarin juices were supplemented to liver cultured cells in basal and stressed conditions to evaluate their protective effect in a biological system.

RESULTS

HPH reduced the concentration of total phenolics and main flavonoids but increased their bioaccessibility after in vitro digestion (P < 0.001). In the basal condition, supplementation with all digested juices significantly reduced intracellular reactive oxygen species (ROS) concentration (P < 0.001). Thiobarbituric acid reactive substances concentration in the medium was also reduced by supplementation with HPH-treated juices. Although pre-treatment with juices did not completely counteract the applied oxidative stress, it preserved cell viability, and cells pre-treated with juices submitted to HPH in the presence of probiotics showed the lowest ROS concentration.

CONCLUSION

The present study represents an important step ahead in the evaluation of the impact of processing on the nutritional and functional value of food, which cannot simply be assessed based on chemical composition. © 2020 Society of Chemical Industry.

Comparative Studies on Different Citrus Cultivars: A Revaluation of Waste Mandarin Components

Peel, pulp and seed extracts of three mandarin varieties, namely Phlegraean mandarin (Citrus reticulata), Kumquat (Citrus japonica), and Clementine (Citrus clementina) were compared and characterised in terms of photosynthetic pigment content, total polyphenols amount, antioxidant activity and vitamin C to assess the amount of functional compounds for each cultivar. The highest polyphenols content was found in the Phlegraean mandarin, especially in peel and seeds, whereas Kumquat exhibited the highest polyphenols amount in the pulp. The antioxidant activity was higher in the peel of Phlegraean mandarin and clementine compared to Kumquat, which showed the highest value in the pulp. The antioxidant activity peaked in the seeds of Phlegraean mandarin. The vitamin C in the Phlegraean mandarin was the highest in all parts of the fruit, especially in the seeds. Total chlorophyll content was comparable in the peel of different cultivars, in the pulp the highest amount was found in clementine, whereas kumquat seeds showed the greatest values. As regards total carotenoids, peel and pulp of clementine exhibited higher values than the other two cultivars, whereas the kumquat seeds were the richest in carotenoids. Among the analysed cultivars Phlegraean mandarin may be considered the most promising as a source of polyphenols and antioxidants, compared to the clementine and Kumquat, especially for the functional molecules found in the seeds. Moreover, regardless of cultivars this study also highlights important properties in the parts of the fruit generally considered wastes.

Consumer Description by Check-All-That-Apply Questions (CATA) of the Sensory Profiles of Commercial and New Mandarins. Identification of Preference Patterns and Drivers of Liking

In the last few years, the interest in developing new mandarin cultivars of superior quality has grown as a response to the increasing consumer demand of this appreciated fruit. This study evaluated the sensory profiles of five new late-season mandarin cultivars (‘Alborea‘, ’Coral‘, ’Omet‘, ’Matiz‘ and ’Tri-703‘) and six commercial cultivars found contemporarily in stores (‘Clemenules‘, ’Nova‘, ’Tango‘, ’Nadorcott‘, ‘Orri’ and ‘Ortanique’). The sensory profiles of the cultivars were described by consumers through CATA questions. Consumers’ acceptability and the main physico-chemical properties were also evaluated. Twenty-two out of 23 CATA terms differed significantly for the sensory profiles of the studied cultivars. The new cultivars shared a similar profile, described mainly as “very intense taste”, “refreshing taste”, “very aromatic” and “juicy”, and these characteristics were quite different from those of the commercial cultivars. By combining acceptability and CATA questions, drivers of liking for segments of consumers with different preference patterns were identified. This is the first time that the sensory profiles of mandarin cultivars have been described by consumers. A significant number of consumers preferred the new mandarin cultivars to the commercial ones, which allows them a promising introduction on the market.

Assessment of sugar and sugar accumulation-related gene expression profiles reveal new insight into the formation of low sugar accumulation trait in a sweet orange (Citrus sinensis) bud mutant

The accumulation of soluble sugars in fleshy fruits largely determines their sweetness or taste. A spontaneous sweet orange mutant 'Hong Anliu' (HAL, Citrus sinensis) accumulates low soluble sugar content in fruit juice sacs than its wild type, 'Anliu' (AL) orange; however, the cause of reduced sugar content in 'HAL' fruit remains unclear. In this study, sugar content and expression profiles of genes involved in sugar metabolism and transport were compared between 'HAL' and 'AL' fruit juice sacs. In both cultivars, fructose and glucose displayed the increasing trends with significantly lower contents in 'HAL' than 'AL' after 160 DAF; moreover, sucrose had a declining trend in 'HAL' and increasing trend in 'AL' with fruit development. On the other hand, transcript levels of VINV, CWINV1, CWINV2, SUS4, SUS5, SPS1, SPS2, VPP-1, VPP-2, and some sugar transporter genes were significantly decreased in 'HAL' compared with 'AL' after 100 DAF or 160 DAF. Interestingly, the transcript levels of SPS2 and SUT2 exhibited a similar trend as it was found for sucrose content in both cultivars. These results suggested that the low sugar accumulation in 'HAL' fruit JS is accompanied by the reduced sink strength, sucrose-synthesis ability, and vacuolar storage ability compared with 'AL'; reduction of CWINVs, VINV, SPS2, SUT2, VPP-1, and VPP-2 transcript levels possibly plays a key role in the low storage of soluble sugars in the vacuoles of mutant juice sacs.

Resistance of Fruits From a Mandarin Cultivar to Feeding by Fork-Tailed Bush Katydids

Plants use a variety of mechanisms to defend against herbivore damage, each with different consequences for agricultural production. Crops relying on tolerance strategies may need different pest management approaches versus those relying on resistance strategies. Previous work suggested that densities of fork-tailed bush katydids (Scudderia furcata Brunner von Wattenwyl [Orthoptera: Tettigoniidae]) that generated substantial scarring on cultivars of sweet oranges (Citrus sinensis, (L.) Osbeck [Sapindales: Rutaceae]) produced only low levels of scarring on cultivars of Citrus reticulata Blanco mandarins. We used field experiments in representative cultivars of these species to test non-mutually exclusive hypotheses regarding the mechanisms underlying this observation: 1) katydids are averse to feeding on mandarin fruits, 2) damaged mandarin fruits preferentially abscise, 3) damaged mandarin fruit tissue recovers during development, and 4) katydid scars on mandarins have a different morphology that may result in misclassification. We found strong support for the first hypothesis, demonstrating that katydids reject opportunities to feed on C. reticulata fruit. Instead of chewing deep holes in the fruit, as was commonly observed for C. sinensis, the katydids only scratched the surface of the C. reticulata fruits. The hypotheses of preferential abscission of damaged fruits and of recovery of damaged tissue were not supported. The low incidence of damage to the mandarins prevented a comprehensive assessment of the scar morphology; however, at harvest, the superficial cuts in C. reticulata were not easily distinguishable from background damage. This indicates that in contrast to C. sinensis, C. reticulata has substantial natural resistance to fork-tailed bush katydids making them a non-pest in this crop.

Citrus Taste Modification Potentials by Genetic Engineering

Citrus fruits are mainly consumed as fresh fruit and processed juice products. They serve as nutritional and a tasty diet in our daily life. However, the formidable bitterness and delayed bitterness significantly impact the citrus industry attributable to the two major bitter compounds naringin and limonin. The extremely sour and acidic also negatively affects the sensory quality of citrus products. Citrus breeding programs have developed different strategies to improve citrus quality and a wealth of studies have aimed to uncover the genetic and biochemical basis of citrus flavor. In this minireview, we outline the major genes characterized to be involved in pathways shaping the sweet, bitter, or sour taste in citrus, and discuss briefly about the possible approaches to modify citrus taste by genetic engineering.

Comparative proteomics of two citrus varieties in response to infection by the fungus Alternaria alternata

Alternaria brown spot (ABS) is a disease caused by the necrotrophic fungus Alternaria alternata, which induces necrotic lesions on fruits and young leaves due to the production of the host-specific ACT toxin by the fungus. To better understand the citrus-A. alternata interaction and to identify putative resistance proteins, as well as the receptor of the ACT toxin, citrus plants susceptible ('Minneola' mandarin) and resistant ('Clemenules' tangor) to A. alternata, infected or not (control) with the pathogen were analyzed by proteomics. Protein changes were observed between citrus genotypes after infection, and 150 candidate proteins were obtained. A general scheme of the metabolic processes involved in susceptible and resistant citrus-A. alternata interactions was designed. Susceptible plants presented a high level of proteins involved in stress response at the final stages of the infection, whereas resistant plants presented high level of ROS proteins, metabolic proteins, and proteins involved in the immune system process. Proteins like ferredoxin and cyclophilin are specific to the susceptible variety and may be good candidates as fungal effector-interacting proteins. This is the first citrus-A. alternata proteomics analysis, which has allowed a better understanding of the molecular bases of the citrus response to ABS disease.

Development of a Microbial Decontamination System Combining Washing with Highly Activated Calcium Oxide Solution and Antimicrobial Coating for Improvement of Mandarin Storability

A new microbial decontamination system combining washing with a natural antimicrobial solution and coating with a carnauba wax (CW)-based antimicrobial coating was developed and its effects on mandarin storability were investigated. Mandarins were washed with an antimicrobial solution and/or coated with grapefruit seed extract-CW (GSE/CW). Values for the disease incidence of Penicillium digitatum in untreated mandarins; mandarins coated with GSE/CW without washing; and mandarins coated with GSE/CW after washing with a fumaric acid (FA) solution of slightly acidic electrolyzed water, a highly activated calcium oxide (CaO) aqueous solution, or CaO solution followed by FA solution were 96.0, 70.0, 78.8, 50.0, and 72.2%, respectively. GSE/CW coating after CaO washing was most effective in inhibiting P. digitatum growth during storage at 25 °C. Compared to untreated samples, GSE/CW coating alone or after CaO washing retained CO₂ generation, firmness, and total polyphenol content of mandarins at 25 °C. Such treatments also effectively maintained mandarin pH, ascorbic acid concentration, and antioxidant capacity at both 4 and 25 °C. Moreover, GSE/CW coating after CaO washing more effectively inhibited P. digitatum growth at 25 °C and maintained ascorbic acid concentration and antioxidant capacity at 4 and 25 °C than GSE/CW coating alone. The microbial decontamination system integrating CaO washing and GSE/CW coating demonstrates potential for improving mandarin storability by inhibiting P. digitatum growth and improving the preservation of quality properties and sensory characteristics. PRACTICAL APPLICATION: This is the first study to develop a microbial decontamination system involving both washing with a natural antimicrobial solution and carnauba wax coating containing grapefruit seed extract to improve the storability of fruits. This system demonstrated a primary effect of inhibiting fungi that cause mandarin surface decay at 25 °C via the highly activated calcium oxide wash and secondary effects of delaying quality degradation and inhibiting fungal growth by the action of the antimicrobial coating. These effects led to improvements in mandarin storability, along with enhanced visual appeal while not affecting taste, flavor, or texture.

Development of a computer vision system to estimate the colour indices of Kinnow mandarins

Maturity of a citrus fruit is generally expressed by a numerical value called citrus colour index (CCI). The success of methods employed in estimating the maturity depends on the cultivar and climatic conditions of growing regions. In this work, an image processing based method using CIELAB color model has been developed to estimate the CCI of Kinnow mandarin fruits. A polynomial transformation based camera characterization method was employed to reduce the number of transformations required for RGB to L ∗ a ∗ b ∗ colour space transformation, which resulted into a colour difference of 2.191 with CIELAB Δ E ∗ 2000 colour difference formula. In order to analyse the performance of this method, linear regression and partial least square (PLS) models were built on a dataset of 271 Kinnow fruit images wherein spectrophotometer was used for the validation of computed CCI values. The proposed method achieved a high adjusted R 2 value of 0.9660 using PLS regression, which ascertain the feasibility of image processing based system in estimating the maturity of Kinnow fruits. Additionally, a correlation analysis between colour coordinates and physicochemical properties was conducted to analyze the relation between the fruit's external peel colour and its internal characteristics.