Eugenol emulsions affect the browning processes, and microbial and chemical qualities of fresh-cut Chinese water chestnut

Applications of Plant Bioactive Compounds as Replacers of Synthetic Additives in the Food Industry

According to the Codex Alimentarius, a food additive is any substance that is incorporated into a food solely for technological or organoleptic purposes during the production of that food. Food additives can be of synthetic or natural origin. Several scientific evidence (in vitro studies and epidemiological studies like the controversial Southampton study published in 2007) have pointed out that several synthetic additives may lead to health issues for consumers. In that sense, the actual consumer searches for "Clean Label" foods with ingredient lists clean of coded additives, which are rejected by the actual consumer, highlighting the need to distinguish synthetic and natural codded additives from the ingredient lists. However, this natural approach must focus on an integrated vision of the replacement of chemical substances from the food ingredients, food contact materials (packaging), and their application on the final product. Hence, natural plant alternatives are hereby presented, analyzing their potential success in replacing common synthetic emulsifiers, colorants, flavorings, inhibitors of quality-degrading enzymes, antimicrobials, and antioxidants. In addition, the need for a complete absence of chemical additive migration to the food is approached through the use of plant-origin bioactive compounds (e.g., plant essential oils) incorporated in active packaging.

Browning inhibition in fresh-cut Chinese water chestnut under high pressure CO2 treatment: Regulation of reactive oxygen species and membrane lipid metabolism

Fresh-cut Chinese water chestnut (CWC) was treated with high pressure CO₂ (HPCD) to inhibit the browning reactions, and the underlying mechanism was investigated in this study. Results showed that HPCD at 2 MPa pressure significantly inhibited lipoxygenase activity and enhanced superoxide dismutase activity, leading to decreased malondialdehyde and H₂O₂ contents in surface tissue. Moreover, HPCD could reduce total phenols/flavonoids content of surface tissue. Compare with control, homoeriodictyol, hesperetin, and isorhamnetin contents of 2 MPa HPCD-treated samples on day 10 were reduced by 95.72%, 94.31%, and 94.02%, respectively. Furthermore, HPCD treatment enhanced antioxidant enzyme activities, and improved the O₂^- scavenging ability and reducing power of inner tissue. In conclusion, by regulating ROS and membrane lipid metabolism, HPCD treatment with appropriate pressure could retard the biosynthesis of flavonoids and enzymatic oxidation of phenolic compounds in surface tissue, and enhance antioxidant activity of inner tissue, thereby, delaying the quality deterioration of fresh-cut CWC.

Integration of Metabolome and Transcriptome Profiling Reveals the Effect of Modified Atmosphere Packaging (MAP) on the Browning of Fresh-Cut Lanzhou Lily (Lilium davidii var. unicolor) Bulbs during Storage

The fresh-cut bulbs of the Lanzhou lily (Lilium davidii var. unicolor) experience browning problems during storage. To solve the problem of browning in the preservation of Lanzhou lily bulbs, we first investigated the optimal storage temperature and gas ratio of modified atmosphere packaging (MAP) of Lanzhou lily bulbs. Then, we tested the browning index (BD), activity of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD), the content of malonaldehyde (MDA) and other physiological activity indicators related to browning. The results showed that the storage conditions of 10% O₂ + 5% CO₂ + 85% N₂ and 4 °C were the best. To further explore the anti-browning mechanism of MAP in fresh-cut Lanzhou lily bulbs, the integration of metabolome and transcriptome analyses showed that MAP mainly retarded the unsaturated fatty acid/saturated fatty acid ratio in the cell membrane, inhibited the lipid peroxidation of the membrane and thus maintained the integrity of the cell membrane of Lanzhou lily bulbs. In addition, MAP inhibited the oxidation of phenolic substances and provided an anti-tanning effect. This study provided a preservation scheme to solve the problem of the browning of freshly cut Lanzhou lily bulbs, and discussed the mechanism of MAP in preventing browning during the storage of the bulbs.

Improving the nutritional quality and bio-ingredients of stored white mushrooms using gamma irradiation and essential oils fumigation

Mushrooms are highly perishable in nature and deteriorate within a few days after harvesting due to their high respiration rate and delicate epidermal structure. Consequently, the shelf-life of freshly harvested mushroom is limited to 1–3 days at ambient condition. Hence, the current investigation was carried out to study γ-irradiation effects (1.5 and 2.0 kGy) and essential oils (EOs) fumigation including geranium (60 and 80 μL/L) and lemongrass (40 and 60 μL/L) on nutritional quality (Vitamins C and D2) as well as bio-ingredients such as total soluble proteins, phenolic and flavonoids contents, antioxidant activity were determined as an origin of potential natural antioxidant plus the profile of phenols and flavonoids identified by HPLC. As well as activities of some enzymes (PPO, SOD, PAL, and APX) of Agaricus bisporus mushroom at 4 °C during storage time for twelve days. The findings showed that there was a reduction in the contents of Vit. C and vitamin D2 in all mushroom samples during storage, where the essential oil treatment especially 60 μL/L of geranium and 40 μL/L of lemongrass gave the least decrease (3.42 and 3.28 mg/100 g FW, respectively) of ascorbic acid content compared to the other treatments while the irradiated samples (1.5, and 2.0 kGy) gave the lowest decrease of vitamin D2 (106.30 and 114.40 mg/kg DW, respectively) at the end of storage time. The content of the bio-ingredients content was affected by the storage periods, and the samples treated with oil fumigation gave the best content and the same trend happened with the antioxidant activity. The enzymes activity increased by the storage period, especially after 4 days of storage, and then the activity decreased after that. Quantification of phenolic and flavonoid compounds affected by storage periods in all treatments and the EO-treated mushrooms gave the best amount of them. Thus, samples of mushrooms treated with oil fumigation especially 60 μL/L of geranium and 40 μL/L of lemongrass can successfully increase the nutritional value plus maintain the value of the mushrooms during storage time.

The effects of aurone on the yellowing of fresh-cut water chestnuts

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Aurone (0.6 and 1.0 %) could inhibit the yellowing of FCWCs by decreasing the yield of eriodictyol and restraining POD activity.

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The inhibition aurone to POD activity was a kind of mixed inhibition.

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PPO and PAL did not catalyze the yellowing of FCWCs.

Yellowing is the main reason for deterioration of edible quality of fresh cut water chestnuts (FCWCs). The mechanism of aurone inhibiting the yellowing of FCWCs was studied. FCWCs were treated with aurone (0.2, 0.6 and 1.0 %). The controls yellowed completely on day 9. The treatment sample with 1.0 % aurone did not yellow on day 9. Compared to the controls, aurone (1.0 %) completely inhibited the production of eriodictyol during 9 d of storage. Aurone (1.0 %) reduced peroxidase activity of FCWCs by 23 % on day 9. The effects of aurone on naringenin concentration, polyphenol oxidase activity, phenylalanine lyase activity, number of thermophilic bacteria colonies, and number of yeasts and molds colonies of FCWCS were not significant. Aurone reduced the yellowing by decreasing the yield of eriodictyol and inhibiting POD activity. Aurone (1.0 %) can be used to inhibit the yellowing of FCWCs in practice.

Effect and mechanism of eugenol on storage quality of fresh-peeled Chinese water chestnuts

The study aimed to investigate the effect and mechanism of eugenol treatment on fresh-peeled Chinese water chestnuts (CWCs). The results found that eugenol treatment maintained the appearance of fresh-peeled CWCs, accompanied by higher L* value, total solids and O₂ contents, as well as lower browning degree, weight loss rate, CO₂ content, a* and b* values. In addition, eugenol treatment significantly reduced the activities of peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase, as well as the total content of soluble quinone in fresh-peeled CWCs. Meanwhile, fresh-peeled CWCs treated with eugenol showed markedly lower content of total flavonoids, which may be related to yellowing. Furthermore, eugenol treatment suppressed the rates of O₂·^- and OH·^- production as well as the contents of H₂O₂ and malondialdehyde in fresh-peeled CWCs. During the storage, eugenol treatment not only increased the activities of catalase, superoxide dismutase, ascorbate peroxidase and glutathione reductase as well as the DPPH free radical scavenging rate, but also increased the total phenolics, ascorbic acid and glutathione contents. In summary, eugenol treatment delayed the surface discoloration of fresh-peeled CWCs by improving the antioxidant capacity, inhibiting the phenolic compound metabolism and scavenging ROS, thus effectively maintaining the quality of fresh-peeled CWCs while extending their shelf life.

Eugenol treatment delays the flesh browning of fresh-cut water chestnut (Eleocharis tuberosa) through regulating the metabolisms of phenolics and reactive oxygen species

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1.5 % EUG exhibited best inhibitory effect on browning in fresh-cut water chestnut.

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Phenylalanine ammonia-lyase of surface tissue was inhibited after eugenol treatment.

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Eugenol inhibited browning in fresh-cut water chestnut by regulating ROS metabolism.

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Eugenol enhanced ROS-scavenging enzymes and antioxidant capacity in surface tissue.

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Eugenol increased phenolic content and antioxidant capacity of inner tissue.

The potential mechanism behind the browning inhibition in fresh-cut water chestnuts (FWC) after eugenol (EUG) treatment was investigated by comparing the difference in browning behavior between surface and inner tissues. EUG treatment was found to inactivate browning-related enzymes and reduce phenolic contents in surface tissue. Molecular docking further confirmed the hydrophobic interactions and hydrogen bonding between EUG and phenylalanine ammonia-lyase (PAL). Moreover, EUG also enhanced reactive oxygen species (ROS)-scavenging enzyme activities, ultimately decreasing the O₂^- generation rates. Regarding inner tissue, EUG induced the accumulation of colorless phenolic compounds and increased the antioxidant capacity. In conclusion, 1.5 % EUG exhibited the best inhibitory effect on FWC browning, which partly attribute to the direct inhibitory effects on PAL activity. Furthermore, EUG could also enhance the enzymatic/non-enzymatic antioxidant capacity and alleviate the ROS damage to membranes, thereby, preventing the contact between oxidative enzymes and phenols and indirectly inhibiting the enzymatic browning in FWC.

Eleocharis dulcis corm: phytochemicals, health benefits, processing and food products

Eleocharis dulcis, an aquatic plant belonging to Cyperaceae family, is indigenous to Asia, and also occurs in tropical Africa and Australia. The edible corm part of E. dulcis is a commonly consumed aquatic vegetable with a planting area of 44.46 × 10³ hm² in China. This work aims to explore the potential of E. dulcis corm for use as a new food source for sufficient nutrients and health benefits by reviewing its nutrients, phytochemicals, functions, processing and food products. Eleocharis dulcis corm contains starches, dietary fibers, non-starch polysaccharides, proteins, amino acids, phenolics, sterols, puchiin, saponins, minerals and vitamins. Among them, phenolics including flavonoids and quinones could be the major bioconstituents that largely contribute to antioxidant, anti-inflammatory, antibacterial, antitumor, hepatoprotective, neuroprotective and hypolipidemic functions. Peel wastes of E. dulcis corm tend to be enriched in phenolics to a much higher extent than the edible pulp. Fresh-cut E. dulcis corm can be consumed as a ready-to-eat food or processed into juice for beverage production, and anti-browning processing is a key to prolonging shelf life. Present food products of E. dulcis corm are centered on various fruit and vegetable beverages, and suffer from single categories and inadequate development. In brief, underutilized E. dulcis corm possesses great potential for use as a new food source for sufficient nutrients and health benefits. © 2021 Society of Chemical Industry.

Melatonin maintains the storage quality of fresh-cut Chinese water chestnuts by regulating phenolic and reactive oxygen species metabolism

Fresh-cut Chinese water chestnuts (CWCs) are prone to quality deterioration during storage, which does not meet consumer demand. In this study, the effect of exogenous melatonin (5 mM) on the quality and potential mechanisms in fresh-cut CWC was investigated. The results showed that melatonin treatment alleviated the cut-surface discoloration of CWCs. Not only did this treatment significantly slow down the increase in browning degree and b* as well as the decrease in L*, but also significantly delayed the loss of weight and total soluble solids. Further investigations indicated that melatonin-treated fresh-cut CWCs exhibited significantly lower total phenolics and soluble quinones and suppressed the activities of phenylalanine ammonia-lyase, polyphenol oxidase, and peroxidase. Meanwhile, when fresh-cut CWCs were treated with melatonin, the total flavonoid concentration was significantly decreased compared to the control. Additionally, melatonin significantly inhibited the accumulation of H2O2 and malondialdehyde (MDA) as well as enhanced the activities of superoxide dismutase and catalase by promoting the production of O2 -·. In summary, melatonin treatment may delay the surface discoloration of fresh-cut CWCs by inhibiting phenolic compound metabolism and improving antioxidant capacity, thereby effectively maintaining the quality, and prolonging the shelf life of fresh-cut CWCs.

Melatonin treatment improves postharvest quality and regulates reactive oxygen species metabolism in "Feizixiao" litchi based on principal component analysis

Postharvest quality of litchi reduces rapidly during storage at room temperature. This study aimed to investigate the effect of melatonin treatment on postharvest quality and oxidative stress markers of litchi fruit during cold storage. The "Feizixiao" litchi was treated with melatonin solution concentrations of 0.2 and 0.6 mmol·L^-1 and then stored at 4°C for 12 days. The results confirmed that the melatonin treatment effectively maintained the appearance and color of the litchi fruit, suppressed the peel browning, and improved the litchi quality. The treatment also significantly enhanced the levels of endogenous melatonin, antioxidant components (total phenolics, flavonoids, and anthocyanin), and antioxidant enzyme activities of the fruit. It also inhibited the other oxidative stress markers, such as O 2 - , H₂O₂, MDA, and protein carbonyl content, and upregulated the expressions of antioxidant and Msr-related genes. Correlation and principal component analyses further confirmed that the melatonin treatment effectively delayed the fruit senescence by enhancing the antioxidant enzyme activities and modulating peel browning and reactive oxygen species metabolism of the litchi fruit via regulating gene expression of the related enzymes (SOD and PPO). These findings suggested that the exogenous application of melatonin to litchi during the postharvest is an ideal way to preserve the fruit quality and delay fruit senescence.

Changes in Browning Degree and Reducibility of Polyphenols during Autoxidation and Enzymatic Oxidation

In the present study, the browning degree and reducing power of browning products of catechin (CT), epicatechin (EC), caffeic acid (CA), and chlorogenic acid (CGA) in autoxidation and enzymatic oxidation were investigated. Influencing factors were considered, such as pH, substrate species and composition, and eugenol. Results show that polyphenols' autoxidation was intensified in an alkaline environment, but the reducing power was not improved. Products of enzymatic oxidation at a neutral pH have higher reducing power than autoxidation. In enzymatic oxidation, the browning degree of mixed substrates was higher than that of a single polyphenol. The reducing power of flavonoid mixed solution (CT and EC) was higher than those of phenolic acids' (CA and CGA) in autoxidation and enzymatic oxidation. Eugenol activity studies have shown that eugenol could increase autoxidation browning but inhibit enzymatic browning. Activity test and molecular docking results show that eugenol could inhibit tyrosinase.

Packaging of Fresh Sliced Mushrooms with Essential Oils Vapours: A New Technology for Maintaining Quality and Extending Shelf Life

The use of vapour of essential oils (EOs) through an innovative pilot-plant packaging device was studied to preserve the quality of sliced mushrooms during storage. A mix of EOs (eugenol, bergamot EO, and grapefruit EO) was vaporized (100 and 125 µL L⁻¹) and applied during packaging of sliced mushrooms under modified atmosphere packaging (MAP); then, the product quality was studied during cold storage up to 12 days. The highest colour changes of EOs125 samples, which were observed in the mushroom stipe, were not observed with the EOs100 atmosphere. Thus, the high polyphenoloxidase activity observed in untreated samples after 5–7 days was highly controlled with the vapour EOs atmospheres. Furthermore, the visual appearance scores of EOs100 samples were still over the limit of usability, while untreated samples were already below this threshold after 5 days of storage. A strong bacteriostatic effect was achieved with vapour EOs, reducing the Pseudomonas spp. (the main microbial genus in cultivated mushrooms) growth by ≈1.7 log CFU g⁻¹, regardless of the EOs dose, after 12 days. The activity of phenyl ammonia lyase was also reduced up to ≈0.4 enzymatic units with the EOs100 treatment. Conclusively, packaging of sliced mushrooms under an atmosphere enriched with 100 µL L⁻¹ EOs vapour highly controlled the quality loss of sliced mushrooms owing to their enzymatic inhibition and high bacteriostatic effect.

Active Paper Sheets Including Nanoencapsulated Essential Oils: A Green Packaging Technique to Control Ethylene Production and Maintain Quality in Fresh Horticultural Products-A Case Study on Flat Peaches

Plant essential oils (EOs) have several bioactive properties, highlighting their high antimicrobial and antioxidant capacities. As such, the use of EOs in active packaging has received special attention in the last few years. Nevertheless, the inhibitory effect of EOs on quality-degrading enzymatic systems of plant products during postharvest life has not been deeply studied. The effects of an EO active paper sheet on ethylene biosynthesis and quality (and related quality-degrading enzymes) of flat peach (Prunus persica var. platycarpa) samples were studied during 5 days (continental terrestrial transport) or 26 days (long maritime transport) storage at 2 or 8 °C, both followed by commercialization simulations (4 days at 22 °C). EOs released from active packaging reduced ethylene production by 40–50%, and by up to 70% after commercialization periods. These results were correlated with lower 1-aminocyclopropanecarboxylic acid (ACC) content and ACC-oxidase activity. Physicochemical fruit quality (as indicated by soluble solids content, titratable acidity, color, and firmness) was also better preserved by EO active sheets due to enzymatic inhibition (polygalacturonase and polyphenoloxidase). Furthermore, phenolic compounds (mainly catechin and cyanidin-3 glucoside) and total antioxidant capacity were increased (by up to 30 and 70%, respectively) in EO-packaged samples after 8 °C storage and the subsequent commercialization period. Conclusively, EO active paper sheets controlled ethylene production in flat peaches, maintained fruit quality, and even increased health-promoting bioactive compounds.