Effects of elevated CO2 on pigment metabolism of postharvest mandarin fruit for degreening

Sucrose, cell wall, and polyamine metabolisms involve in preserving postharvest quality of 'Zaosu' pear fruit by L-glutamate treatment

'Zaosu' pear fruit is prone to yellowing of the surface and softening of the flesh after harvest. This work was performed to assess the influences of L-glutamate treatment on the quality of 'Zaosu' pears and elucidate the underlying mechanisms involved. Results demonstrated that L-glutamate immersion reduced ethylene release, respiratory intensity, weight loss, brightness (L*), redness (a*), yellowness (b*), and total coloration difference (ΔE); enhanced ascorbic acid, soluble solids, and soluble sugar contents; maintained chlorophyll content and flesh firmness of pears. L-glutamate also restrained the activities of neutral invertase and acid invertase, while enhancing sucrose phosphate synthetase and sucrose synthase activities to facilitate sucrose accumulation. The transcriptions of PbSGR1, PbSGR2, PbCHL, PbPPH, PbRCCR, and PbNYC were suppressed by L-glutamate, resulting in a deceleration of chlorophyll degradation. L-glutamate concurrently suppressed the transcription levels and enzymatic activities of polygalacturonases, pectin methylesterases, cellulase, and β-glucosidase. It restrained polygalacturonic acid trans-eliminase and pectin methyl-trans-eliminase activities as well as inhibited the transcription levels of PbPL and Pbβ-gal. Moreover, the gene transcriptions and enzymatic activities of arginine decarboxylase, ornithine decarboxylase, S-adenosine methionine decarboxylase, glutamate decarboxylase, γ-aminobutyric acid transaminase, glutamine synthetase along with the PbSPDS transcription was promoted by L-glutamate. L-glutamate also resulted in the down-regulation of PbPAO, PbDAO, PbSSADH, PbGDH, and PbGOGAT transcription levels, while enhancing γ-aminobutyric acid, glutamate, and pyruvate acid contents in pears. These findings suggest that L-glutamate immersion can effectively maintain the storage quality of 'Zaosu' pears via modulating key enzyme activities and gene transcriptions involved in sucrose, chlorophyll, cell wall, and polyamine metabolism.

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.

The Effects of Poly-γ-Glutamic Acid on the Postharvest Physiology and Quality of Strawberry cv. Hongyan during Cold Storage

This study investigated the effects of poly-γ-glutamic acid (γ-PGA) on the postharvest physiology and quality of the strawberry cv. Hongyan during cold storage. The results showed that all concentrations of γ-PGA improved decay control and strawberry preservation by enhancing antioxidant capacity, delaying the softening process, and maintaining fruit quality, especially for 100 mg·L-1 γ-PGA. After 14 days of treatment, compared with control, 100 mg·L-1 γ-PGA decreased weight loss, decay rate, and index by 21.9%, 75.0%, and 66.7% and increased the total antioxidant capacity by 43.5% through antioxidant enzymes. In addition, 100 mg·L-1 γ-PGA increased fruit firmness by 53.6% by decreasing the activities of polygalacturonase, pectin lyase, cellulase, and β-galactosidase. In terms of color quality, 100 mg·L-1 γ-PGA improved the values of lightness and yellowness by 30.9% and 52.8%. As regards nutritional quality, 100 mg·L-1 γ-PGA increased the contents of protein, soluble sugars, vitamin C, and total phenols by 106.6%, 80.6%, 51.2%, and 78.4%. In terms of sensory quality, 100 mg·L-1 γ-PGA increased the soluble solids' content by 19.0% and decreased the titrated acids' content by 21.1%, which increased the sugar-acid ratio by 50.9%. Our findings suggest that 100 mg·L-1 γ-PGA can be used to improve the decay control and preservation of strawberry cv. Hongyan under cold storage.

Characterization of physicochemical properties, flavor volatiles and phenolic compounds of feijoa fruit varieties

Thirteen varieties of feijoa (Feijoa sellowiana) fruit were collected and the physical and chemical properties of feijoa peel, flesh, seed, and leaf were analyzed. Large diversities in the physicochemical characteristics and phenolic and volatile composition among various parts and between different varieties of feijoa were observed. Degrees Brix of whole fruits ranged from 10.1 (Anatoki) to 18.0 (No. 2) °Brix. Procyanidin B-type tetramer, procyanidin B-type dimer, and procyanidin C-type trimer had the highest concentrations in all parts and varieties of feijoa. Caffeoyl glucose, dihydroferulic acid 4-O-glucuronide, galloyl glucose, and lariciresinol-sesquilignan were detected in feijoa fruits and leaves. A total of 105 esters, 68 terpenes, 20 alcohols, 31 hydrocarbons, 12 aldehydes, and 11 ketones were related to aromatic attributes of fruits and leaves. Early season and mid-season varieties had larger variations in the chemical properties than late-season varieties. Anatoki, Kakariki, and No.1, have the potential to be developed for attractive flavor and functional properties.

The flavonoid profiles in the pulp of different pomelo (Citrus grandis L. Osbeck) and grapefruit (Citrus paradisi Mcfad) cultivars and their in vitro bioactivity

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Fourteen flavonoid compounds were detected in pomelo and grapefruit pulp.

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The flavonoid profiles in pomelo and grapefruit pulp had varietal difference.

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Flavonoids of pomelo and grapefruit showed strong cellular antioxidant activity.

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Flavonoids of pomelo and grapefruit are good inhibitors of pancreatic lipase.

Previous results indicated that the flavonoid profiles might have varietal differences in pomelo, but detailed information is unknown. We previously isolated 4 new flavonoids, cigranoside C, D, E, F, in Citrus grandis Shatianyu pulp. However, their distribution in different pomelo cultivars remains to be explored. Therefore, the flavonoid profiles and in vitro bioactivity of the pulp from 5 pomelo and 1 grapefruit cultivars commonly consumed in China were investigated. Fourteen flavonoids were identified, cigranoside C, D, E were detected in these pomelo and grapefruit. Naringin and cigranoside C were the major flavonoids in grapefruit, Guanximiyu-W, Guanximiyu-R and Liangpingyu, while melitidin and rhoifolin was the predominant flavonoid in Shatianyu and Yuhuanyu, respectively. Pomelo and grapefruit showed strong antioxidant activity, and were potent inhibitors of pancreatic lipase with IC₅₀ values of 11.4–72.6 mg fruit/mL except Shatianyu. Thus, pomelo and grapefruit are natural antioxidants and possess anti-obesity potential.

Exogenous Ethylene Promotes Peel Color Transformation by Regulating the Degradation of Chlorophyll and Synthesis of Anthocyanin in Postharvest Mango Fruit

Due to geographical location and climatic factors, postharvest storage and preservation of tropical fruits and vegetables are still facing huge challenges. Ethephon (ETH) is widely used as an ethylene donor to achieve the commercial color and flavor of climacteric fruits. However, the effect of ETH on fruit coloration was affected by many factors, such as fruit species, plant hormones, and storage conditions. In this study, the main mango variety “Guifei” in Hainan, China, was used to study the effects of different concentrations of ETH on fruit ripening and coloration during storage at 25°C. Results showed that postharvest treatment with ETH (300, 500, and 900 mg·L⁻¹) enhanced the activities of ACS and ACO, stimulated the release of endogenous ethylene, and accelerated fruit softening and color transformation. Compared with control, ETH treatment not only accelerated the breakdown of chlorophyll with higher activities of Chlase and MDCase but also induced the synthesis of carotenoid and anthocyanin with higher activities of PAL, CHI, DFR, and UFGT. Moreover, the changes in DFR and UFGT activities coincided with the increase in ETH concentration. Further, correlation analysis showed that the production of endogenous ethylene induced by ETH was significantly negatively correlated with firmness and chlorophyll content, whereas positively correlated with MDA content and anthocyanin content. This study suggests that the positive effect of ETH on “Guifei” mango color transformation is concentration-dependent within a certain concentration range. Anthocyanin is the main pigment for the red formation of “Guifei” mango, and DFR and UFGT may play critical roles in anthocyanin synthesis. ETH promoted the red coloration by promoting the release of endogenous ethylene and enhancing the activities of anthocyanin synthesis enzymes.

Effect of calcium chloride and 1-methylcyclopropene combined treatment on pectin degradation and textural changes of Eureka lemon during postharvest storage

During post-harvest storage, the cell wall properties are closely associated with the physical, chemical, and biological properties of the fruit. The degradation of pectin in the cell walls and middle lamella is critical to these properties. The effects of calcium chloride (CaCl₂) and 1-methylcyclopropene (1-MCP) combined treatment on the pectin degradation, texture, and peel color of Eureka lemon were investigated during post-harvest storage. The in-situ light microscope analysis, rapid method, and FTIR test were used to investigate the spatial distribution, the pectin content, and its degradation. The results showed a reduction in pectin degradation, by 42 d the CaCl₂ and 1-MCP combined treated fruits presented a 36.7% pectin content loss which was lower than the control which was 48.3%. The treated fruits significantly exhibited enhanced textural properties, delayed weight loss, higher total acids, and improvement of other physicochemical properties in comparison to the control. The treatment deaccelerated the fruit peel color change from green to yellow and also had a better visual appearance on the final day. Overall, the results suggest that the control treatment for pectin degradation can reduce the fruit texture decline and peel color change and maintain a good visual appearance. The influence of pectin degradation on the texture and physicochemical properties of lemon provides a theoretical basis for fruit storage optimization, quality control, and shelf-life extension.

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Combined CaCl₂ and 1-MCP treatment delayed lemon postharvest degeneration.

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Treatment suppressed pectin degradation and improved the visual appearance.

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Treatment greatly delayed softening, reduce decay rate, and extended the shelf life.

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Methylesterified pectin was localized and visualized by qualitative microscopic analysis.

Elevated CO2 Enhanced the Antioxidant Activity and Downregulated Cell Wall Metabolism of Wolfberry (Lycium barbarum L.)

Modified atmosphere packaging (MAP) has been widely known to delay the postharvest fruit senescence; nevertheless, its effect on antioxidant activity and cell wall metabolism of wolfberry fruit is largely unknown. The present study investigated the impact of elevated CO₂ on the quality attributes and cell wall degradation of wolfberry fruit during storage. The results showed that 10% CO₂ better maintained the physiological quality and conferred the reduction in weight loss, decay index, and color change. Higher 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 1,1-diphenyl-1-picrylhydrazil (DPPH) radical scavenging activity, total phenol and flavonoid content, and superoxide dismutase (SOD) and catalase (CAT) activity of wolfberry were detected at elevated CO₂ concentrations. Elevated CO₂ atmosphere contributed to the maintenance of the cell integrity, the decrease of cell wall degradation (polygalacturonase, pectate lyase, cellulase, and β-glucosidase), and the increase of cellulose and proto pectin content. Overall, we revealed the potential mechanism of elevated CO₂ on the antioxidant activity enhancement and cell wall homeostasis of fresh berry fruit.

Postharvest UV-C Irradiation Influenced Cellular Structure, Jasmonic Acid Accumulation, and Resistance Against Green Mold Decay in Satsuma Mandarin Fruit (Citrus unshiu)

Green mold caused by Penicillium digitatum is an important factor limiting the shelf life of mandarin fruit. In this study, the effect of ultraviolet-C (UV-C) irradiation on cellular structure, endogenous jasmonic acid (JA), and development of P. digitatum in satsuma mandarin fruit was investigated. UV-C treatments included 0 (untreated control), 3, and 10 kJ m−2 or the exposure time of 0, 1.18, and 4.52 min, respectively. The UV-C dose of 10 kJ m−2 significantly reduced the development of P. digitatum both in vitro and in vivo, resulting in the maintenance of the cellular structure of the albedo tissue. The production of malondialdehyde (MDA) was decreased upon UV-C treatment of 10 kJ m−2. The concentration of JA increased in the treatment of 10 kJ m−2 compared to the treatment of 3 kJ m−2 and the control. UV-C irradiation increased total phenolic and total flavonoid concentrations and DPPH radical scavenging capacity. These results suggest that UV-C at 10 kJ m−2 has a potential to control green mold caused by P. digitatum, maintain cellular structure, stimulate the accumulation of JA, and induce biochemical compounds in satsuma mandarin.

Effect of High CO2 Treatment and MA Packaging on Sensory Quality and Physiological-Biochemical Characteristics of Green Asparagus (Asparagus officinalis L.) during Postharvest Storage

Green asparagus is vulnerable to thrips that carry microorganisms and cause deterioration in quality. The effects of 60% CO2 treatment, which is used to kill thrips, combined with perforated (P) or modified atmosphere (MA) packages during cold storage, on the sensory quality and physiological–biochemical characteristics of asparagus were investigated. MA packaging yielded an asparagus shelf-life five days longer than P packaging. The 60% CO2 treatment for 48 h at 4 °C packaged with MA film (CO2-48 h-4 °C-MA) showed a lower number of aerobic bacteria, yeast, and mold. Yellowing of asparagus was retarded, as shown by higher hue angle and chlorophyll content and lower chlorophyllase activity. Also, CO2-48 h-4 °C-MA treatment inhibited the reduction of soluble solids content in asparagus. Likewise, all high CO2 treatments showed lower electrolyte leakage (EL), with CO2-48 h-4 °C-MA demonstrating the minimum EL. The effectiveness of high CO2 on maintaining sensory qualities was observed, with a score higher than 3.0. In conclusion, CO2-48 h-4 °C-MA treatment during cold storage was effective for maintaining post-harvest sensory qualities and physiological–biological traits of asparagus, and provided strong inhibition of microflora growth during the storage period.

High Carbon Dioxide Treatment Modulates Sugar Metabolism and Maintains the Quality of Fresh-Cut Pear Fruit

The purpose of this study is to explore the effect of 10% carbon dioxide (CO₂) on the fruit quality and sugar metabolism of fresh-cut pear during storage. The results indicated that carbon dioxide treatment maintained fruit quality by delaying the decline of firmness and promoting the accumulation of total soluble solids (TSS). Moreover, carbon dioxide enhanced activities of sucrose synthase (SS), and sucrose phosphate synthase (SPS). The activities of amylase, acid invertase (AI), neutral invertase (NI), SS-cleavage, fructokinase (FK), hexokinase (HK), sorbitol oxidase (SOX), NAD-dependent sorbitol dehydrogenase (NAD-SDH), and NADP-SDH in CO₂-treated fruit were inhibited. Expression levels of key genes were found to correspond with the related enzyme activities. As a result, the accumulation of glucose, fructose, sorbitol, and sucrose were accelerated by CO₂, which were 12.58%, 13.86%, 24.7%, and 13.9% higher than those of the control at the end of storage, respectively. The results showed that CO₂ could maintain the quality of fresh-cut pears by regulating the conversion of various sugar components to enhance soluble sugars content.

Terpinen-4-ol Enhances Disease Resistance of Postharvest Strawberry Fruit More Effectively than Tea Tree Oil by Activating the Phenylpropanoid Metabolism Pathway

This study aimed to reveal the effects and possible mechanism of terpinen-4-ol, the main component of tea tree oil (TTO), on the disease resistance of strawberry fruit. When the effects of TTO and its components were compared on the decay development in fruit inoculated with Botrytis cinerea after treatment, strawberry treated with terpinen-4-ol showed the lowest disease incidence (44.4%) after 48 h and also the smallest lesion diameter during the whole storage. This indicates that terpinen-4-ol induces the highest disease resistance in strawberry compared with TTO and other components. Untargeted metabolomic analysis showed that terpinen-4-ol treatment strongly activated phenylpropanoid biosynthesis and flavonoid metabolism pathway by increasing the accumulation of cinnamaldehyde, coniferyl aldehyde, naringenin, taxifolin, quercetin, and quercitrin in fruit at 12 h after treatment. In addition, terpinen-4-ol treatment also caused the accumulation of total phenolics and lignin by enhancing activities and relative gene expression of key enzymes in the phenylpropanoid metabolism pathway. These results suggest that terpinen-4-ol, as the key component of TTO, is the most important contributor to the effectiveness of TTO in improving disease resistance of strawberry fruit through activating the phenylpropanoid metabolism pathway.