Effect of different drying techniques on chemical composition, color and antioxidant properties of kinnow (Citrus reticulata) peel

Preparation, Characterization and Application of Active Food Packaging Films Based on Sodium Alginate and Twelve Varieties of Mandarin Peel Powder

The industrial processing of mandarin fruits yields a large amount of peel waste, resulting in economic losses and environmental pollution. The peels of mandarin fruits are a good source of biomass and active substances that can be used to produce food packaging systems. In this study, active food packaging films were prepared based on sodium alginate and twelve varieties of mandarin peel powder. The structures, properties, and corn oil packaging performance of the films were compared. Results showed that the twelve varieties of mandarin peel powder differed in pectin, lipid, protein, crude fiber, and total phenol contents. The prepared films all exhibited a yellow color, 117.73-152.45 μm thickness, 16.39-23.62% moisture content, 26.03-90.75° water contact angle, 5.38-8.31 × 10-11 g m-1 s-1 Pa-1 water vapor permeability, 5.26-12.91 × 10-20 m2 s-1 Pa-1 oxygen permeability, 4.87-7.90 MPa tensile strength, and 13.37-24.62% elongation at break. Notably, the films containing mandarin peel powder with high pectin and lipid contents showed high moisture/oxygen barrier ability and mechanical properties. The films containing mandarin peel powder with high total phenol content exhibited high antioxidant- and antimicrobial-releasing abilities and good performance in delaying corn oil oxidation. Overall, the results suggested that the films have good application potential in active food packaging.

Evaluation of nutritional profile, phytochemical potential, functional properties and anti-nutritional studies of Citrus limetta peels

The aim of this work was to determine the proximate, mineral, amino acid composition, antioxidant activity, anti-nutritional factors, total dietary fiber, total phenolic content and technological properties of C. limetta peels. Moreover, analytical techniques including FT-IR and SEM were also conducted to study the morphological and structural properties of C. limetta peels. Considering the proximate, mineral, and amino acid composition, C. limetta peels was found to be a good source of ash (3.06 ± 0.20%), crude fiber (10.13 ± 0.30%), carbohydrate (64.08 ± 0.55%), protein (7.56 ± 0.25%), potassium (125.9671 mg/100 g), calcium (112.5861 mg/100 g), magnesium (16.43 mg/100 g), asparagine (2111.06 nmol/mg), glutamic acid (1331.96 nmol/g), and aspartic acid (1162.19 nmol/mg). Furthermore, they contain an appreciable amount of total dietary fiber (48.73 ± 0.45%), total phenolic content (14.30 ± 0.03 mg GAE/g), and antioxidant activity (52.65 ± 0.10%). Moreover, the antinutritional factors present in C. limetta peels were observed to be within the threshold limit. The results of technological properties of peels suggested that they can be potentially utilized as good emulsifying, gelling, foaming, and bulking agents in food industries. Therefore, C. limetta peels can be successfully re-utilized as natural food additive with numerous nutritive and bioactive properties in food sector, thereby achieving zero waste generation.

Evaluation of ultrasonication and carbonation-ultrasonication assisted convective drying techniques for enhancing the drying rates and quality parameters of ripe and raw banana (Musa) peel

Raw and ripe banana (Musa Cavendish) peel slices were dried by application of ultrasonication (U) and carbonation-ultrasonication (CU) as pre-treatments for tray drying (T) at 60 °C. Lesser drying time and higher diffusivity was noticed in CU + T dried samples followed by U + T and T dried samples. Model 'Wang and Singh' was identified as the excellently fitting model to experimental data. SEM images of dried samples revealed the microchannels formation due to U treatment, which were more couloir after CU treatment. Water and oil holding capacity (WHC and OHC) for raw peel powders was higher than ripened peel powders at 40, 60 and 80 °C. WHC and OHC increased significantly after U + T drying or CU + T drying as compared to T drying for ripe and raw peel powder samples. Back extrusion force (BEF) varied from 67.42 to 69.22 N and from 84.6 to 86.02 N for ripe and raw peel samples respectively. Given treatments resulted in lesser colour change and Browning Index. But U + T or CU + T treatment did not affect BEF significantly. CU + T was deemed to be the appropriate drying technique for ripe and raw banana peel drying.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05535-9.

A Comparative Study on the Debittering of Kinnow (Citrus reticulate L.) Peels: Microbial, Chemical, and Ultrasound-Assisted Microbial Treatment

Kinnow mandarin (Citrus reticulate L.) peels are a storehouse of well-known bioactive compounds, viz., polyphenols, flavonoids, carotenoids, limonoids, and tocopherol, which exhibit an effective antioxidant capacity. However, naringin is the most predominant bitter flavanone compound found in Kinnow peels that causes their bitterness. It prohibits the effective utilization of peels in food-based products. In the present study, a novel approach for the debittering of Kinnow peels has been established to tackle this problem. A comparative evaluation of the different debittering methods (chemical, microbial, and ultrasound-assisted microbial treatments) used on Kinnow peel naringin and bioactive compounds was conducted. Among the chemical and microbial method; solid-state fermentation with A. niger led to greater extraction of naringin content (7.08 mg/g) from kinnow peels. Moreover, the numerical process optimization of ultrasound-assisted microbial debittering was performed by the Box–Behnken design (BBD) of a response surface methodology to maximize naringin hydrolysis. Among all three debittering methods, ultrasound-assisted microbial debittering led to a greater hydrolysis of naringin content and reduced processing time. The optimum conditions were ultrasound temperature (40 °C), time (30 min), and A. niger koji extract (1.45%) for the maximum extraction rate of naringin (11.91 mg/g). These debittered Kinnow peels can be utilized as raw material to develop therapeutic food products having a high phytochemical composition without any off-flavors or bitterness.

Evaluation of quality change in Salviae miltiorrhizae radix et rhizoma during drying by LF-NMR and HPLC

Salviae miltiorrhizae radix et rhizoma (Danshen, in Chinese) is one of the traditional Chinese medicines commonly used in clinical practice. In this study, low field nuclear magnetic resonance (LF-NMR) was used to detect changes in the moisture content during the drying of Danshen. Three water states (bound, immobilized, and free) in Danshen were investigated by multi-exponential fitting of the NMR data. Mass changes during drying were analyzed using high-performance liquid chromatography and partial least squares discriminant analysis. The results revealed that two components, salvianolic acid B and tanshinone, were the main chemical substances that produced the differences. Correlations were found among chemical substances, color, and moisture. LF-NMR can quickly assess the moisture content during drying. It also provides a practical tool for the production and processing of medicines or slices.

Pressurized Extraction as an Opportunity to Recover Antioxidants from Orange Peels: Heat treatment and Nanoemulsion Design for Modulating Oxidative Stress

Orange peel by-products generated in the food industry are an important source of value-added compounds that can be potentially reused. In the current research, the effect of oven-drying (50–70 °C) and freeze-drying on the bioactive compounds and antioxidant potential from Navelina, Salustriana, and Sanguina peel waste was investigated using pressurized extraction (ASE). Sixty volatile components were identified by ASE-GC-MS. The levels of terpene derivatives (sesquitenenes, alcohols, aldehydes, hydrocarbons, and esters) remained practically unaffected among fresh and freeze-dried orange peels, whereas drying at 70 °C caused significative decreases in Navelina, Salustriana, and Sanguina peels. Hesperidin and narirutin were the main flavonoids quantified by HPLC-MS. Freeze-dried Sanguina peels showed the highest levels of total-polyphenols (113.3 mg GAE·g⁻¹), total flavonoids (39.0 mg QE·g⁻¹), outstanding values of hesperedin (187.6 µg·g⁻¹), phenol acids (16.54 mg·g⁻¹ DW), and the greatest antioxidant values (DPPH•, FRAP, and ABTS^•+ assays) in comparison with oven-dried samples and the other varieties. Nanotechnology approaches allowed the formulation of antioxidant-loaded nanoemulsions, stabilized with lecithin, starting from orange peel extracts. Those provided 70–80% of protection against oxidative UV-radiation, also decreasing the ROS levels into the Caco-2 cells. Overall, pressurized extracts from freeze-drying orange peel can be considered a good source of natural antioxidants that could be exploited in food applications for the development of new products of commercial interest.

A review of chemical constituents and health-promoting effects of citrus peels

Citrus is one of the main fruits processed worldwide, producing a lot of industrial by-products. As the main part of citrus "residue", citrus peels have a wide application prospect. They could not only be directly used to produce various food products, but also be used as promising biofuels to produce ethanol and methane. Additionally, functional components (flavonoids, limonoids, alkaloids, essential oils and pectin) extracted from citrus peels have been related to the improvement of human health against active oxygen, inflammatory, cancer and metabolic disorders. Therefore, it is clear that the citrus peels have great potential to be developed into useful functional foods, medicines and biofuels. This review systematically summarizes the recent advances in current uses, processing, bioactive components and biological properties of citrus peels. A better understanding of citrus peels may provide reference for making full use of it.

Evaluation of dynamic changes in the bioactive components in Citri Reticulatae Pericarpium (Citrus reticulata 'Chachi') under different harvesting and drying conditions

BACKGROUND

The Citrus reticulata 'Chachi' pericarp (CRCP) is one cultivar of Citri Reticulatae Pericarpium (Chenpi), which is widely applied in medicine and food. To determine the potential value of CRCP harvested at different stages and subjected to different drying processes, the dynamic changes in the bioactive components were profiled and evaluated in this study.

RESULTS

The contents of all non-volatile components, i.e. synephrine, limonin, phenolic acids and flavonoids, decreased with delayed harvest time. The volatiles thujene, α-pinene, β-pinene, d-citronellol, d-citronellal, decanal, linalool, geraniol, l-cis-carveol, terpinen-4-ol, α-terpineol, carvacrol, perillaldehyde, methyl 2-(methylamino)benzoate and d-limonene were considered the characteristic components for distinguishing CRCP harvested at different stages. Phenolic acids, synephrine and limonin were stable at different drying temperatures; however, high-temperature drying at 60 °C induced a significant transformation in the flavonoids (especially polymethoxyflavones) and volatile substances in CRCP.

CONCLUSIONS

The results suggested that most of the bioactive components declined with the growth of Citrus reticulata 'Chachi'. And it is believed that the fresh peel should be naturally sun-dried or dried at low temperature (30 or 45 °C) rather than at high temperature (60 °C) to prevent excessive loss of nutrients. © 2020 Society of Chemical Industry.

Processing Factors Affecting the Phytochemical and Nutritional Properties of Pomegranate (Punica granatum L.) Peel Waste: A Review

Pomegranate peel has substantial amounts of phenolic compounds, such as hydrolysable tannins (punicalin, punicalagin, ellagic acid, and gallic acid), flavonoids (anthocyanins and catechins), and nutrients, which are responsible for its biological activity. However, during processing, the level of peel compounds can be significantly altered depending on the peel processing technique used, for example, ranging from 38.6 to 50.3 mg/g for punicalagins. This review focuses on the influence of postharvest processing factors on the pharmacological, phytochemical, and nutritional properties of pomegranate (Punica granatum L.) peel. Various peel drying strategies (sun drying, microwave drying, vacuum drying, and oven drying) and different extraction protocols (solvent, super-critical fluid, ultrasound-assisted, microwave-assisted, and pressurized liquid extractions) that are used to recover phytochemical compounds of the pomegranate peel are described. A total phenolic content of 40.8 mg gallic acid equivalent (GAE)/g DM was recorded when sun drying was used, but the recovery of the total phenolic content was higher at 264.3 mg TAE/g when pressurised liquid extraction was performed. However, pressurised liquid extraction is costly due to the high initial investment costs and the limited possibility of carrying out selective extractions of organic compounds from complex peel samples. The effects of these methods on the phytochemical profiles of pomegranate peel extracts are also influenced by the cultivar and conditions used, making it difficult to determine best practice. For example, oven drying at 60 °C resulted in higher levels of punicalin of 888.04 mg CE/kg DM compared to those obtained 40 °C of 768.11 mg CE/kg DM for the Wonderful cultivar. Processes that are easy to set up, cost-effective, and do not compromise the quality and safety aspects of the peel are, thus, more desirable. From the literature survey, we identified a lack of studies testing pretreatment protocols that may result in a lower loss of the valuable biological compounds of pomegranate peels to allow for full exploitation of their health-promoting properties in potentially new value-added products.

Towards an optimal hybrid solar method for lime-drying behavior

Lime is one of the most commonly consumed medicinal plants in Indonesia, which must be dried to preserve its quality, but mostly by using traditional, ineffective drying method. Therefore, this study aims to investigate lime drying process a hybrid solar drying method. The hybrid solar dryer consisted of a solar dryer and Liquefied Petroleum Gas as the supplementary heater. The drying process was conducted until there was no significant weight decrease, with the drying temperature of 40, 50, 60, 70, and 80 °C. Thin-layer modeling and quality analysis were also conducted. The experimental results indicated that 5 h was required to sufficiently dry the lime at 80 °C, while drying at 40 °C took 24 h to finish. The drying rate curve of lime suggested that lime drying mostly happened during the falling-rate period. Moreover, the average efficiency of the hybrid solar dryer ranged from 5.36% to 38.61%, which increased with temperature. From the 10 thin-layer drying models used, the Wang and Singh model was the most suitable to describe the drying behavior of lime. The effective diffusivity values of the limes and the activation energy value during hybrid solar drying were within their respective acceptable range for agricultural products. However, as the drying temperature was increased from 40 to 80 °C, the total phenolic content and vitamin C content decreased, from 87.3 to 27.8 mg GAE/100 g dry limes and 0.118 to 0.015 ppm, respectively. It can be concluded that hybrid solar dryer is able to sufficiently dry the lime, with acceptable drying time and dryer efficiency, although using high drying temperature will decrease the quality of dried lime. Further modifications and improvements to the hybrid solar dryer are required to maximize the quality of dried lime while still maintaining fast and effective drying process.

Application of non-isothermal simulation in optimization of food drying process

The application of numerical methods on one hand and simulation of various food processing techniques on the other hand could be effective methods in the process optimization such as reducing energy consumption and processing time and increasing product quality. The objective of this study was to apply variable air temperatures during drying process of garlic slices while reducing the drying time and maintaining the highest possible quality of the dried product. Therefore, drying process was simulated based on the numerical methods, and the proper time to change the air temperature was predicted using the product temperature profile. A high air temperature was applied at the beginning of the drying process (70 °C) and then during the process the temperature was decreased (50 °C) in a way that that the product surface temperature was never increased more than the critical temperature of 50 °C. The result of simulation was validated based on experiments at various drying conditions such as air temperature of 50, 60 and 70 °C and slice thickness of 2.5 mm. Based on the results of the study, by applying the variable air temperatures during drying process on samples, the drying time was reduced by 24% and the color quality of the samples was preserved. The final product produced by this method had higher quality (total color changes is 3.278) compared to the products dried at the higher constant temperature of 70 °C (total color changes is 6.71).

Influence of drying techniques on bioactive properties, phenolic compounds and fatty acid compositions of dried lemon and orange peel powders

Lemon peel powder (LPP) obtained after drying (microwave, infrared, and oven) showed the lowest (58.72%) DPPH-radical scavenging activity in oven-dried and the highest (67.84%) in infrared-dried LPP while that of fresh lemon peel remained 63.22%. Orange peel powder (OPP) showed the lowest DSA (61.65) after microwave and the lowest (63.54%) after infrared-drying while that of fresh orange peel was 63.48%. Total phenolics were between 114.58 (fresh) and 179.69 mgGAE/100 g (oven) in LPP and between 158.54 (fresh) and 177.92 mgGAE/100 g (infrared) in OPP. The total flavonoid contents were 380.44 (fresh)-1043.04 mg/100 g (oven) in case of LPP and 296.38 (fresh)-850.54 mg/100 g (oven) in case of OPP. The gallic acid contents were 2.39 (fresh)-14.02 mg/100 g (oven) in LPP. The (+)-catechin contents were 1.10 (fresh)-49.57 mg/100 g (oven) for LPP and 0.82 (fresh)-7.63 mg/100 g (infrared) in case of OPP. The oleic acid content was 22.99 (infrared)-58.85% (fresh) in LPP-oil and 28.59 (microwave)-61.65% (fresh) in OPP-oil. The linoleic acid contents were 13.76 (fresh)-36.90% (oven) in LPP-oil and 14.14 (fresh)-37.08% (infrared) in case of OPP-oil. The drying techniques showed profound but variable effects on radical scavenging activity, total phenolics, flavonoid, carotenoids, phenolic compounds and fatty acid composition of both LPP and OPP and oven-drying (60 °C) was the most effective in improving these bioactive constituents.

Comprehensive evaluation of physicochemical properties and antioxidant activity of B. subtilis-fermented polished adlay subjected to different drying methods

The physicochemical properties and antioxidant activity of B. subtilis-fermented polished adlay (BPA) subjected to different drying methods (hot-air drying, HAD; infrared-radiation drying, IRD; vacuum drying, VD; microwave-vacuum drying, MVD; and freeze-vacuum drying, FVD) were evaluated in this study. Results showed FVD was ideal for maintaining the natural appearance and higher contents of proximate compositions, free fatty acids, tetramethylpyrazine (6.91 mg/g DW), coixol (0.62 mg/g DW), coixenolide (4.21% DW), coixan (35.10% DW), and triterpenoids (17.41 mg/g DW). The higher contents of total phenolics and flavonoids, stronger antioxidant activity, and higher color differences were observed in HAD and IRD samples. MVD displayed the shorter drying time, higher γ-aminobutyric acid content, and higher retention ratios of tetramethylpyrazine (75.54%), coixol (87.10%), coixenolide (98.57%), and coixan (99.11%). Pearson's correlation coefficient exhibited that the positive correlation between the contents of phenolics and flavonoids and the antioxidant activities of all dried BPA samples was observed (R 2 > 0.881, p < .05). Principal component analysis showed that the top three categories of comprehensive quality were FVD-, MVD-, and VD-treated BPA samples. In conclusion, MVD should be a potential preservation method to obtain high-quality dried BPA for short drying time and high comprehensive quality.

Post-harvest processing and valorization of Kinnow mandarin (Citrus reticulate L.): A review

Kinnow is a prevalent fruit crop of the mandarin group and belongs to the Rutaceae family. It is nutritionally rich in vitamin C, vitamin B, β-carotene, calcium, phosphorous and other health beneficing compounds. The fruit is grown commercially for fresh consumption and since the processing techniques are less prominent, a plentiful amount of harvested fruit goes for waxing and grading operations. To reduce the post-harvest losses, appropriate processing techniques need to be followed as considerable fruit waste is generated while processing. The foremost fruit wastes viz. peel and seeds are rich source of bioactive compounds and can be utilized for the extraction of aromatic compounds, essential oils and low-methoxyl pectin. Overall utilization of kinnow and its components through various technological interventions will not only enhance the profitability of processing industries but also assist in reducing the pollution load on the environment. The prevailing bitterness in kinnow juice has constrained its processing, value-addition, popularity and acceptability. Limited work has been done on kinnow processing leaving scarce relevant literature published on the post-harvest management. Efforts made by researchers worldwide, regarding the post-harvest application of kinnow and its by-products for product development, value addition and waste utilization is presented and discussed in this paper. This compiled information is envisioned to encourage the cottage food processing units in order to improvise the overall benefits along with achieving complete utilization of kinnow.