Different Postharvest Responses of Fresh-Cut Sweet Peppers Related to Quality and Antioxidant and Phenylalanine Ammonia Lyase Activities during Exposure to Light-Emitting Diode Treatments

Modulation of Antioxidant Compounds in Fruits of Citrus reticulata Blanco Using Postharvest LED Irradiation

Phlegrean mandarin fruits are already known for health-promoting properties due to the high concentration of phytochemicals in peel, pulp, and seed. Biotic and abiotic factors, including light, may modulate their biosynthesis, metabolism, and accumulation. In this context, light-emitting diodes (LED) have recently been applied to control nutritional traits, ripening process, senescence, fruit shelf-life, and pathogenic microbial spoilage of fruits. This study investigated the effect of the seven-day exposure of Phlegrean mandarin fruits to two LED regimes, white (W) and red-blue (RB), to test the possibility that the storage under specific light wavelengths may be used as green preservation technology that enhances fruit phytochemical properties. To pursue this aim, the antioxidant activity and polyphenolic profile of the pulp and peel of mandarins under W and RB light regimes were evaluated and compared with Control fruits not exposed to LED treatment. Our results indicated that storage under W and RB treatments modulates the antioxidant content in pulp and peel differently. Compared to W, the RB regime increases the ascorbic acid, flavonoid, anthocyanin, and carotenoid concentrations, while the polyphenol profile analysis reveals that the number of important phytochemicals, i.e., quercetin rutinoside, chlorogenic acid, sinensetin, and rutin, are higher under W. The overall data demonstrated that postharvest LED irradiation is a valid tool for modifying fruit phytochemical properties, which also boosts specific bioactive compounds.

Antioxidant potential and factors influencing the content of antioxidant compounds of pepper: A review with current knowledge

The use of natural food items as antioxidants has gained increasing popularity and attention in recent times supported by scientific studies validating the antioxidant properties of natural food items. Peppers (Capsicum spp.) are also important sources of antioxidants and several studies published during the last few decades identified and quantified various groups of phytochemicals with antioxidant capacities as well as indicated the influence of several pre- and postharvest factors on the antioxidant capacity of pepper. Therefore, this review summarizes the research findings on the antioxidant activity of pepper published to date and discusses their potential health benefits as well as the factors influencing the antioxidant activity in pepper. The major antioxidant compounds in pepper include capsaicinoids, capsinoids, vitamins, carotenoids, phenols, and flavonoids, and these antioxidants potentially modulate oxidative stress related to aging and diseases by targeting reactive oxygen and nitrogen species, lipid peroxidation products, as well as genes for transcription factors that regulate antioxidant response elements genes. The review also provides a systematic understanding of the factors that maintain or improve the antioxidant capacity of peppers and the application of these strategies offers options to pepper growers and spices industries for maximizing the antioxidant activity of peppers and their health benefits to consumers. In addition, the efficacy of pepper antioxidants, safety aspects, and formulations of novel products with pepper antioxidants have also been covered with future perspectives on potential innovative uses of pepper antioxidants in the future.

The Impact of Light Wavelength and Darkness on Metabolite Profiling of Korean Ginseng: Evaluating Its Anti-Cancer Potential against MCF-7 and BV-2 Cell Lines

Korean ginseng is a source of functional foods and medicines; however, its productivity is hindered by abiotic stress factors, such as light. This study investigated the impacts of darkness and different light wavelengths on the metabolomics and anti-cancer activity of ginseng extracts. Hydroponically-grown Korean ginseng was shifted to a light-emitting diodes (LEDs) chamber for blue-LED and darkness treatments, while white fluorescent (FL) light treatment was the control. MCF-7 breast cancer and lipopolysaccharide (LPS)-induced BV-2 microglial cells were used to determine chemo-preventive and neuroprotective potential. Overall, 53 significant primary metabolites were detected in the treated samples. The levels of ginsenosides Rb1, Rb2, Rc, Rd, and Re, as well as organic and amino acids, were significantly higher in the dark treatment, followed by blue-LED treatment and the FL control. The dark-treated ginseng extract significantly induced apoptotic signaling in MCF-7 cells and dose-dependently inhibited the NF-κB and MAP kinase pathways in LPS-induced BV-2 cells. Short-term dark treatment increased the content of Rd, Rc, Rb1, Rb2, and Re ginsenosides in ginseng extracts, which promoted apoptosis of MCF-7 cells and inhibition of the MAP kinase pathway in BV-2 microglial cells. These results indicate that the dark treatment might be effective in improving the pharmacological potential of ginseng.

Post-Harvest Red- and Far-Red-Light Irradiation and Low Temperature Induce the Accumulation of Carotenoids, Capsaicinoids, and Ascorbic Acid in Capsicum annuum L. Green Pepper Fruit

Environmental factors, such as light of different spectral compositions and temperature, can change the level of activated photoreceptors which, in turn, can affect the biosynthesis of secondary metabolites in the cells of green fruit. By briefly irradiating the harvested fruit of Capsicum annuum L. hot peppers with red light (RL, maximum 660 nm) and far-red light (FRL, maximum 730 nm) and by keeping them at a low temperature, we attempted to determine whether the state of phytochromes in fruit affects the biosynthesis of secondary metabolites. Using HPLC, we analysed the qualitative composition and quantitative content of the main carotenoids and alkaloids and the chlorophylls and ascorbate, in pepper fruit exposed to the above factors. We measured the parameters characterising the primary photochemical processes of photosynthesis and the transcript levels of genes encoding capsaicin biosynthesis enzymes. The total carotenoids content in the fruit increased most noticeably after 24 h of RL irradiation (more than 3.5 times compared to the initial value), and the most significant change in the composition of carotenoids occurred when the fruit was irradiated with FRL for 72 h. The capsaicin alkaloid content increased markedly after 72 h of FRL irradiation (more than 8 times compared to the initial value). It was suggested that decrease in the activity of phytochromes due to a low temperature or FRL may result in an increase in the expression of the PAL and CAM genes.

Application of chitosan nanoparticles in quality and preservation of postharvest fruits and vegetables: A review

Chitosan is an interesting alternative material for packaging development due to its biodegradability. However, its poor mechanical properties and low permeability limit its actual applications. Chitosan nanoparticles (CHNPs) have emerged as a suitable solution to overcome these intrinsic limitations. In this review, all studies regarding the use of CHNPs to extend the shelf life and improve the quality of postharvest products are covered. The characteristics of CHNPs and their combinations with essential oils and metals, along with their effects on postharvest products, are compared and discussed throughout the manuscript. CHNPs enhanced postharvest antioxidant capacity, extended shelf life, increased nutritional quality, and promoted tolerance to chilling stress. Additionally, the CHNPs reduced the incidence of postharvest phytopathogens. In most instances, smaller CHNPs (<150 nm) conferred higher benefits than larger ones (>150 nm). This was likely a result of the greater plant tissue penetrability and surface area of the smaller CHNPs. The CHNPs were either applied after preparing an emulsion or incorporated into a film, with the latter often exhibiting greater antioxidant and antimicrobial activities. CHNPs were used to encapsulate essential oils, which could be released over time and may enhance the antioxidant and antimicrobial properties of the CHNPs. Even though most applications were performed after harvest, preharvest application had longer lasting effects.

LED Technology Applied to Plant Development for Promoting the Accumulation of Bioactive Compounds: A Review

Light is an important environmental factor for plants. The quality of light and the wavelength stimulate enzyme activation, regulate enzyme synthesis pathways and promote bioactive compound accumulation. In this respect, the utilization of LED light under controlled conditions in agriculture and horticulture could be the most suitable choice for increasing the nutritional values of various crops. In recent decades, LED lighting has been increasingly used in horticulture and agriculture for commercial-scale breeding of many species of economic interest. Most studies on the influence of LED lighting on the accumulation of bioactive compounds in any type of plants (horticultural, agricultural species or sprouts) and also biomass production, were carried out in growth chambers under controlled conditions, without natural light. Illumination with LED could be a solution for obtaining an important crop with maximum efficiency, with a high nutritional value and minimum effort. To demonstrate the importance of LED lighting in agriculture and horticulture, we carried out a review based on a large number of results cited in the literature. The results were collected from 95 articles and were obtained using the keyword LED combined with plant growth; flavonoids; phenols; carotenoids; terpenes; glucosinolates; food preservation. We found the subject regarding the LED effect on plant growth and development in 11 of the articles analyzed. The treatment of LED on phenol content was registered in 19 articles, while information regarding flavonoid concentrations was revealed by 11 articles. Two articles we reviewed debate the accumulation of glucosinolates and four articles analyzed the synthesis of terpenes under LED illumination and 14 papers analyzed the variation in content of carotenoids. The effect of LED on food preservation was reported in 18 of the works analyzed. Some of the 95 papers contained references which included more keywords.

Phototreatment (below 1100 nm) improving quality attributes of fresh-cut fruits and vegetables: A review

The emerging area of phototreatment technology has shown a significant potential to enhance the quality of fresh-cut fruit and vegetable products (FFVP). This review critically evaluates relevant literatures to address the potential for phototreatment technology (Red, blue, green, ultraviolet and pulsed light) applied to FFVP, outline the key to the success of phototreatment processing, and discuss the corresponding problems for phototreatment processing along with research and development needs. Base on photothermal, photophysical and photochemical process, phototreatment displays a great potential to maintain quality attributes of FFVP. The operating parameters of light, the surface properties and matrix components of the targeted material and the equipment design affect the quality of the fresh-cut products. To adapt current phototreatment technology to industrial FFVP processing, it is necessary to offset some limitations, especially control of harmful substances (For example, nitrite and furan) produced by phototreatment, comparison between different phototreatment technologies, and establishment of mathematical models/databases.

Controlled Atmosphere Improves the Quality, Antioxidant Activity and Phenolic Content of Yellow Peach during the Shelf Life

Controlled atmosphere (CA) has been demonstrated to maintain the shelf-life quality of fruits, but its effect on the antioxidant activities and phenolic content of yellow peach is not comprehensive. This study analyzed the role of CA on the quality of shelf period, phenolic content and antioxidant activity of "Jinxiu" yellow peach. Yellow peach was left under specific aeration conditions (3.5-4% CO2, 2-3% O2, 92-95.5% N2, 1 ± 0.5 °C) and the control (1 ± 0.5 °C) for 21 d, to observe changes in physiological parameters of the fruit during 10 d of the shelf life (25 ± 1 °C). The result showed that CA reduced the weight loss rate (WLR), decay rate (DR), and browning index (BI) of yellow peaches. Furthermore, the CA held a high level of total flavonoid content (TFC), total phenol content (TPC) and phenolic content in the fruit. Antioxidant analysis showed that polyphenol oxidase (PPO) enzyme activity was lower and free radical scavenging capacity (DPPH, ABTS, and FRAP) and antioxidant enzyme activities (POD and PAL) were higher in the CA group. Combining the results of significance analysis, correlation analysis, principal component analysis (PCA) and hierarchical cluster analysis (HCA) clearly identified the differences between the CA group and the control group. The results showed that the CA could maintain higher phenolic content and reduce the oxidation of yellow peach fruit and enhance fruit quality by affecting the antioxidant activities of yellow peach.

Supplemental Blue Light Frequencies Improve Ripening and Nutritional Qualities of Tomato Fruits

Tomatoes (Solanum lycopersicum L. Micro-Tom) were grown in a plastic greenhouse. When plants anthesis, the 100 μmol m^-2 s^-1 blue light-emitting diode (LED) light (430 ± 10 nm) was supplemented from 6:00 to 18:00. There were 5 treatments, which contained different blue light frequencies with the same intensity: S6 (30 min blue light and 30 min pause), S8 (30 min blue light and 15 min pause), S10 (30 min blue and 8 min pause), S12 (continuous blue light for 12 h), and control (CK) (natural light, without any supplemental light). Agronomic traits and nutritional qualities of tomato fruits were measured at 30, 34, 38, 42, and 46 days after anthesis (DAA), respectively. Different frequencies of supplemental blue light could accelerate flowering of tomato plants and promote fruit ripening about 3-4 days early via promoting ethylene evolution of fruits, which significantly facilitated the processes of color change and maturity in tomato fruits. The contents of lycopene, total phenolic compounds, total flavonoids, vitamin C, and soluble sugar, as well as the overall antioxidant activity of tomato fruits were significantly enhanced by all the supplemental blue light treatments. In all, different frequencies of supplemental blue light prominently reinforced the antioxidant levels and nutritional qualities of tomato fruits, especially lycopene content, and S10 was more optimal for tomato fruits production in a plastic greenhouse.

Changes in Functional Compounds, Volatiles, and Antioxidant Properties of Culinary Herb Coriander Leaves (Coriandrum sativum) Stored Under Red and Blue LED Light for Different Storage Times

This study evaluated the influence of red (630–640 nm) and blue (450 nm) light-emitting diodes (LED) lights on the changes in antioxidant constituents, activity, volatile compounds, and overall acceptability of Coriander leaves (Coriandrum sativum) during post-harvest storage. Coriander leaves are harvested at commercial maturity, packed in polyethylene terephthalate punnets, and exposed for 2 h to the red LED or blue LED lights separately during storage at 5°C and 85% RH up to 9 days. Coriander leaves exposed to the white light (2 h) and continuous darkness served as controls. Samples were removed from cold storage at 3, 6, and 9 days to determine the antioxidant constituents, their activity, retention of volatile compounds, and overall acceptance. Coriander leaves exposed to red and blue LED lights for 2 h showed a commercially allowable mass loss of up to 9 days compared to the other treatments. Compared to those exposed to red LED light (2 h) and the control, leaves exposed to blue LED light for 2 h and stored for 3–9 days showed a reduction in colour change (ΔE). The β-carotene content significantly peaked at 44.55% on day 6 in coriander leaves exposed to the red LED light. However, leaves exposed to blue and red LED light showed an increase in total phenolic content by 9.34 and 6.39% on day 9, respectively. Exposure to blue LED lights increased the antioxidant activities (DPPH, ABTS, and FRAP), quercetin content, and the concentration of typical coriander aroma, 2-tridecenal, 2-dodecenal, (E), and Z-9-19 hexadecenal on day 9. Coriander leaves exposed to blue LED light (2 h) and stored up to day 9 scored a higher acceptance level by the panellists. Thus, blue light LED treatment during post-harvest storage can be recommended to retain the antioxidant property of coriander leaves.

Light-emitting diodes (below 700 nm): Improving the preservation of fresh foods during postharvest handling, storage, and transportation

In order to maintain the original taste, flavors, and appearance, fresh foods usually do not go through complex processing prior to sale; this makes them prone to deterioration due to external factors. Light-emitting diodes (LEDs) have many unique advantages over traditional preservation technologies leading to their increasing application in the food industry. This paper reviews the luminescence principles of LED, the advantages of LED compared with traditional lighting equipment, and its possible preservation mechanism, and then critically summarizes the beneficial effects of LED irradiation on the ripening and aging process of various fruits and vegetables (climacteric and non-climacteric). The activity changes of many enzymes closely related to crop development and quality maintenance, and the variation of flavor components caused by LED irradiation are discussed. LED illumination with a specific spectrum also has the important effect of maintaining the original color and flavor of meat, seafood, and dairy products. For microorganisms attached to the surface of animal-derived food, both 400-460 nm LED irradiation based on photodynamic inactivation principle and UV-LED irradiation based on ultraviolet sterilization principle have high bactericidal efficacy. Although there is still a lack of useful standards for matching optimal LED irradiation dose with wavelength, perhaps in the near future, the improved LED irradiation system will be applied extensively in the food industry.

Increasing the performance of Passion fruit (Passiflora edulis) seedlings by LED light regimes

Due to progress in the industrial development of light-emitting diodes (LEDs), much work has been dedicated to understanding the reaction of plants to these light sources in recent years. In this study, the effect of different LED-based light regimes on growth and performance of passion fruit (Passiflora edulis) seedlings was investigated. Combinations of different light irradiances (50, 100, and 200 µmol m⁻² s⁻¹), quality (red, green, and blue light-emitting LEDs), and photoperiods (10 h/14 h, 12 h/12 h and 14 h/10 h light/dark cycles) were used to investigate the photosynthetic pigment contents, antioxidants and growth traits of passion fruit seedlings in comparison to the same treatment white fluorescent light. Light irradiance of 100 µmol m⁻² s⁻¹ of a 30% red/70% blue LED light combination and 12 h/12 h light/dark cycles showed the best results for plant height, stem diameter, number of leaves, internode distance, and fresh/dry shoot/root weights. 14 h/10 h light/dark cycles with the same LED light combination promoted antioxidant enzyme activities and the accumulation of phenols and flavonoids. In contrast, lower light irradiance (50 µmol m⁻² s⁻¹) had negative effects on most of the parameters. We conclude that passion fruit seedlings' optimal performance and biomass production requires long and high light irradiances with a high blue light portion.

Phenylalanine, Tyrosine, and DOPA Are bona fide Substrates for Bambusa oldhamii BoPAL4

Phenylalanine ammonia-lyase (PAL) links the plant primary and secondary metabolisms, and its product, trans-cinnamic acid, is derived into thousands of diverse phenylpropanoids. Bambusa oldhamii BoPAL4 has broad substrate specificity using L-phenylalanine, L-tyrosine, and L-3,4-dihydroxy phenylalanine (L-DOPA) as substrates to yield trans-cinnamic acid, p-coumaric acid, and caffeic acid, respectively. The optimum reaction pH of BoPAL4 for three substrates was measured at 9.0, 8.5, and 9.0, respectively. The optimum reaction temperatures of BoPAL4 for three substrates were obtained at 50, 60, and 40 °C, respectively. The Km values of BoPAL4 for three substrates were 2084, 98, and 956 μM, respectively. The kcat values of BoPAL4 for three substrates were 1.44, 0.18, and 0.06 σ−1, respectively. The major substrate specificity site mutant, BoPAL4-H123F, showed better affinity toward L-phenylalanine by decreasing its Km value to 640 μM and increasing its kcat value to 1.87 s−1. In comparison to wild-type BoPAL4, the specific activities of BoPAL4-H123F using L-tyrosine and L-DOPA as substrates retained 5.4% and 17.8% residual activities. Therefore, L-phenylalanine, L-tyrosine, and L-DOPA are bona fide substrates for BoPAL4.

Study of Postharvest Quality and Antioxidant Capacity of Freshly Cut Amaranth after Blue LED Light Treatment

Freshly cut vegetables are susceptible to microbial contamination and oxidation during handling and storage. Hence, light-emitting diode technology can effectively inhibit microbial growth and improve antioxidant enzyme activity. In this paper, the freshly cut amaranth was treated with different intensities of blue light-emitting diode (LED460nm) over 12 days. Chlorophyll content, ascorbic acid content, antioxidant capacity, antioxidant enzymes activity, the changes in microbial count, and sensorial evaluation were measured to analyze the effects of LED treatment on the amaranth. Blue LED460nm light irradiation improved the vital signs of the samples and extended the shelf life by 2-3 days. The AsA-GSH cycle was effectively activated with the irradiation of 30 μmol/(m2·s) blue LED460nm light. According to the results, the LED460nm light could retard the growth of colonies and the main spoilage bacteria, Pseudomonas aeruginosa, of freshly cut amaranth.

Vitamin C alleviates hyperuricemia nephropathy by reducing inflammation and fibrosis

Hyperuricemia contributes to chronic kidney disease development. However, it has been historically viewed with limited research interest. In this study, we mimicked the development of hyperuricemic nephropathy by using a potassium oxonate-induced hyperuricemia rat model. We found that administering vitamin C at 10 mg/kg/day effectively ameliorated hyperuricemic nephropathy. Compared to the control group, rats with hyperuricemia had significantly increased serum uric acid level, xanthine oxidase activity, and urine microalbumin level, by 5-fold, 1.5-fold, and 4-fold, respectively. At the same time, vitamin C supplementation reverted these values by 20% for serum uric acid level and xanthine oxidase activity and 50% for microalbumin level. Vitamin C also alleviated renal pathology and decreased the expression of pro-inflammatory and pro-fibrotic markers. A further mechanistic study suggested that vitamin C might attenuate hyperuricemic nephropathy in renal tubular epithelial cells induced by monosodium urate (MSU) crystal, at least in part, by directly inhibiting IL-6/JAK2/STAT3 signaling pathway. Meanwhile, in macrophages, vitamin C inhibited the expression of TGF-β, and reduced ROS level induced by MSU by about 35%. In short, our results suggest that vitamin C supplementation delay the progression of hyperuricemic nephropathy.

Postharvest UV-B and Photoperiod with Blue + Red LEDs as Strategies to Stimulate Carotenogenesis in Bell Peppers

Background: Our objective was to evaluate carotenoid accumulation in bell peppers during shelf life under different light conditions. Methods: Fruit stored for 6 d at 7 °C received a 9 kJ m−2 UV-B treatment, while non-UV-treated were used as control (CTRL). Subsequently, all peppers were disposed for a retail sale period of 4 d at 20 °C with a photoperiod of 14 h under fluorescent light (FL) + 10 h under darkness (D), FL, or blue + red LEDs (BR LED). Results: Total antioxidant capacity (TAC) was increased by the UV-B treatment and the photoperiods supplemented with FL and BR LED, which was directly related to the carotenoid content. In fact, CTRL peppers (225 mg β-carotene kg−1) under FL+BR LED showed an increase of ~33% of 13-cis-β-carotene, ~24% of all-trans-β-carotene, and ~27.5% of 9-cis-β-carotene compared to FL + D and FL + FL. Capsaicinoids showed an increase by ~22%, ~38%, and ~27% in the content of capsanthin, capsanthin laurate, and capsanthin esters, respectively, after the UV-B treatment, which was even enhanced after the LED-supplemented photoperiod by ~18% compared to FL+D. Conclusions: Illumination with BR LEDs + UV-B during the retail sale period nights is recommended to increase the bioactive content of bell peppers via carotenoid accumulation to 270 mg β-carotene kg−1.

Challenges and Opportunities of Light-Emitting Diode (LED) as Key to Modulate Antioxidant Compounds in Plants. A Review

Plant antioxidants are important compounds involved in plant defense, signaling, growth, and development. The quantity and quality of such compounds is genetically driven; nonetheless, light is one of the factors that strongly influence their synthesis and accumulation in plant tissues. Indeed, light quality affects the fitness of the plant, modulating its antioxidative profile, a key element to counteract the biotic and abiotic stresses. With this regard, light-emitting diodes (LEDs) are emerging as a powerful technology which allows the selection of specific wavelengths and intensities, and therefore the targeted accumulation of plant antioxidant compounds. Despite the unique advantages of such technology, LED application in the horticultural field is still at its early days and several aspects still need to be investigated. This review focused on the most recent outcomes of LED application to modulate the antioxidant compounds of plants, with particular regard to vitamin C, phenols, chlorophyll, carotenoids, and glucosinolates. Additionally, future challenges and opportunities in the use of LED technology in the growth and postharvest storage of fruits and vegetables were also addressed to give a comprehensive overview of the future applications and trends of research.

Introduction to the Special Issue: Foods of Plant Origin

Plant food is usually rich in health-promoting ingredients such as polyphenols, carotenoids, betalains, glucosinolates, vitamins, minerals and fibre. However, pre- and post-harvest treatment, processing and storage can have significant effects on the concentration and composition of these bioactive ingredients. Furthermore, the plant food matrix in fruits, vegetables, grains, legumes, nuts and seeds is very different and can affect digestibility, bioavailability, processing properties and subsequently the nutritional value of the fresh and processed food. The Special Issue ‘Foods of Plant Origin’ covers biodiscovery, functionality, the effect of different cooking/preparation methods on bioactive (plant food) ingredients, and strategies to improve the nutritional quality of plant food by adding other food components using novel/alternative food sources or applying non-conventional preparation techniques.