The role of various amino acids in enzymatic browning process in potato tubers, and identifying the browning products

Unlocking novel biopeptides hidden in Camellia seed cake fermented by Bacillus subtilis through in silico and cellular model approaches

In this study, Bacillus subtilis was used to ferment the CSC and produce hydrolysates (CSCH), from which novel bioactive peptides were identified. The ultrafiltration fraction of CSCH under 3 kDa (CSCH-3) revealed the most efficient in vitro antioxidant and anti-tyrosinase activity. The peptide profile of CSCH-3 was further characterized using LC-MS/MS, and novel biopeptides were screened through in silico analysis and molecular docking methods. Four peptides (LPFR, WGFKPK, PFDLR, and FPGEL) were recognized as the most promising antioxidant and anti-tyrosinase peptides based on their better binding affinities (< 5 kcal/mol) with the tested receptors. Cell antioxidant assay revealed that the four peptides exhibited significant (P < 0.05) antioxidant activity against AAPH-induced oxidative damage. Meanwhile, B16F10 cell model tests revealed that tyrosinase activity was significantly (P < 0.05) inhibited by LPFR (44.62 %), WGFKPK (32.12 %), PFDLR (34.06 %), and FPGEL (33.66 %) compared to the control. The docking results suggested that the four peptides were tightly bound to antioxidant related receptors (DPPH, ABTS, CAT, SOD, and Keap1) and tyrosinase, suggesting that each peptide could exhibit multiple bioactivities via various structure-activity linkages.

Effects of delayed tuber cutting after catalytic infrared heat treatment on browning of fresh-cut potatoes and its potential mechanisms

Heat treatment, a form of thermal stress can confer anti-browning properties to potato tubers. However, the effect of delayed cutting after catalytic infrared heat treatment (DC-CIRHT) on browning inhibition remains unexplored. The study optimized catalytic infrared heat treatment conditions (55 °C for 10 min) and delayed cutting time (3 d). DC-CIRHT significantly inhibited the increase of browning index and browning degree and did not affect the quality of potato tubers. The mechanisms underlying browning inhibition involve two aspects: the reduction of phenolic-enzyme catalysis and the enhancement of the defense system. DC-CIRHT inhibits browning by suppressing polyphenol oxidase, peroxidase and phenylalanine ammonia lyase enzyme activity, reducing total phenol and flavonoid content, enhancing antioxidant activity, reducing membrane permeability and MDA, and balancing amino acid metabolism. This method offers a novel strategy for inhibiting browning during the post-harvest storage and processing of fruits and vegetables.

Characterization of differences in volatile compounds and metabolites of six varieties of potato with different processing properties

Potato is the fourth-most important food crop around the world, and most of the potatoes are used for foodstuffs and starch products. The aim of this paper is to identify the volatile compounds and metabolites in potatoes with different processing properties. The results showed large differences of volatile and metabolite compounds such as 2,4-Heptadienal and rhoifolin in potatoes and indicated the potential regulations between volatile compounds and metabolites. Moreover, the differences in volatile and metabolite compounds were compared between fresh eating and processing type potatoes. Compared to process type potatoes, fresh eating potatoes contained a higher proportion of aldehyde and alcohol compounds, but being lower in hydrocarbon, furan, and ketone compounds. Moreover, the different expressed metabolites were involved in the metabolism of amino acids, flavone and flavanol biosynthesis, and tryptophan metabolism. The Random forest showed that the fresh eating and processing type potatoes could be distinguished by the content of amino acids and phenols.

Integrative transcriptome and metabolome analyses reveal the mechanism of melatonin in delaying postharvest senescence in cowpeas

Rapid postharvest senescence and quality deterioration severely limit logistics of cowpeas. Melatonin (MEL) is a pivotal bioactive molecule that can modulate multiple physiological attributes in plants. In this study, physiological, transcriptomic and metabolomic analyses were conducted to explore the effects of exogenous MEL on cowpea senescence and its underlying mechanisms. Physiological results showed that 100 μM MEL treatment maintained sensory quality (greeness, firmness and soluble solids content), reduced weight loss as well as inhibited the degradation of chlorophyll (Chl) and protopectin. Preservation of color and firmness in cowpeas was greatly attributed to inhibition of expression of genes related to Chl and cell wall metabolism, which was based on a transcriptomic analysis. Integrated transcriptomic and metabolomic analyses revealed that MEL promoted transcription of genes associated with amino acid and carbohydrate metabolism, resulting in the accumulation of amino acid and sugar metabolites. Additionally, by integrating transcription factor-binding site analysis with cis-acting element analysis, we constructed a regulatory network of transcription factors underlying MEL-mediated antisenescence. The present study found a series of potential candidate genes and metabolites involved in regulating senescence process and provided an insight into improving postharvest quality of cowpeas.

Applications and characterization of anti-browning enzymatically modified potato starch (EPS) film associated with chitosan (CTS)/L-Cys/citric acid (CA) on fresh-cut potato slices

This study explores the influence of incorporating L-cysteine (L-Cys), chitosan (CTS), and citric acid (CA) on the enzymatic modification of potato starch (EPS) films to enhance anti-browning properties. Four types of EPS composite films were evaluated for preserving fresh-cut potato slices at low temperatures to inhibit browning. Their thermal, physiochemical, mechanical, and digestibility properties were assessed. Results indicate that the addition of CTS, CA, and L-Cys improved the anti-browning activity of the EPS films by increasing film thickness and reducing water vapor permeability (WVP), oxygen transmission rate (OTR), ultraviolet (UV) transmittance, and tensile strength (TS). Furthermore, these additives improved the film's microstructure, resulting in reinforced intermolecular interactions, increased elongation at break, heightened crystallinity, enhanced thermal stability, and favorable gastrointestinal digestibility. Overall, EPS/CTS/L-Cys/CA composite films show promise as edible packaging materials with effective anti-browning properties.

Peptide and peptidomimetic tyrosinase inhibitors

Melanin, which is produced by melanocytes and spread over keratinocytes, is responsible for human skin browning. There are several processes involved in melanogenesis, mostly prompted by enzymatic activities. Tyrosinase (TYR), a copper containing metalloenzyme, is considered the main actor in melanin production, as it catalyzes two crucial steps that modify tyrosine residues in dopaquinone. For this reason, TYR inhibition has been exploited as a possible mechanism of modulation of hyper melanogenesis. There are various types of molecules used to block TYR activity, principally used as skin whitening agents in cosmetic products, e.g., tretinoin, hydroquinone, azelaic acid, kojic acid, arbutin and peptides. Peptides are highly valued for their versatile nature, making them promising candidates for various functions. Their specificity often leads to excellent safety, tolerability, and efficacy in humans, which can be considered their primary advantage over traditional small molecules. There are several examples of tyrosinase inhibitor peptides (TIPs) operating as possible hypo-pigmenting agents, which can be classified according to their origin: natural, hybrid or synthetically produced. Moreover, the possibility of variating their backbones, introducing non-canonical amino acids or modifying one or more peptide bond(s), to obtain peptidomimetic molecules, is an added value to avoid or delay proteolytic activity, while the possibility of conjugation with other bioactive peptides or organic moieties can bring other specific activity leading to dual-functional peptides.

A combined approach of lauroyl arginine ethyl ester hydrochloride and kojic acid in mitigating fresh-cut potato deterioration

The combinational effects of kojic acid and lauroyl arginine ethyl ester hydrochloride (ELAH) on fresh-cut potatoes were investigated. Kojic acid of 0.6% (w/w) effectively inhibited the browning of fresh-cut potatoes and displayed antimicrobial capacity. The color difference value of samples was decreased from 175 to 26 by kojic acid. In contrast, ELAH could not effectively bind with the active sites of tyrosinase and catechol oxidase at molecular level. Although 0.5% (w/w) of ELAH prominently inhibited the microbial growth, it promoted the browning of samples. However, combining kojic acid and ELAH effectively inhibited the browning of samples and microbial growth during the storage and the color difference value of samples was decreased to 52. This amount of kojic acid inhibited enzyme activities toward phenolic compounds. The results indicated that combination of kojic acid and ELAH could provide a potential strategy to extend the shelf life of fresh-cut products.

Localization of potato browning resistance genes based on BSA-seq technology

Browning is a common problem that occurs during potato processing; it is typically resolved by adding chemicals during the production process. However, there is a need to develop potato varieties that are resistant to browning due to a growing consumer interest in healthier diets. This study initially identified 275 potato varieties that are resistant to browning; these were narrowed down to eight varieties, with four of them being highly resistant. A hybrid population was developed by crossing the highly resistant CIP395109.29 with the easily browned Kexin 23. Bulked segregant analysis (BSA) was conducted, which identified 21 potato genes associated with anti-browning properties through sequencing data analysis and organization. The findings of this study lay a solid groundwork for future research on breeding potatoes with anti-browning traits, offer molecular markers for identifying anti-browning varieties, and serve as a valuable reference for further investigations into potato browning mechanisms.

Metabolomic insights into the browning inhibition of fresh-cut apple by hydrogen sulfide

Hydrogen sulfide (H2S) is known to effectively inhibit the browning of fresh-cut apples, but the mechanism at a metabolic level remains unclear. Herein, non-targeted metabolomics was used to analyze metabolic changes in surface and internal tissues of fresh-cut apple after H2S treatment. The results showed that prenol lipids were the most up-accumulated differential metabolites in both surface and inner tissue of fresh-cut apple during browning process, which significantly down-accumulated by H2S treatment. H2S treatment reduced the consumption of amino acid in surface tissue. Regarding inner tissue, H2S activated defense response through accumulation of lysophospholipid signaling and induced the biosynthesis of phenolic compounds. We therefore propose that H2S inhibited the surface browning of fresh-cut apple by reducing the accumulation of prenol lipids, directly delaying amino acid consumption in surface tissue and indirectly regulating defense response in inner tissue, which provides fundamental insights into browning inhibition mechanisms by H2S.

DNA methylation remodeled amino acids biosynthesis regulates flower senescence in carnation (Dianthus caryophyllus)

Dynamic DNA methylation regulatory networks are involved in many biological processes. However, how DNA methylation patterns change during flower senescence and their relevance with gene expression and related molecular mechanism remain largely unknown. Here, we used whole genome bisulfite sequencing to reveal a significant increase of DNA methylation in the promoter region of genes during natural and ethylene-induced flower senescence in carnation (Dianthus caryophyllus L.), which was correlated with decreased expression of DNA demethylase gene DcROS1. Silencing of DcROS1 accelerated while overexpression of DcROS1 delayed carnation flower senescence. Moreover, among the hypermethylated differentially expressed genes during flower senescence, we identified two amino acid biosynthesis genes, DcCARA and DcDHAD, with increased DNA methylation and reduced expression in DcROS1 silenced petals, and decreased DNA methylation and increased expression in DcROS1 overexpression petals, accompanied by decreased or increased amino acids content. Silencing of DcCARA and DcDHAD accelerates carnation flower senescence. We further showed that adding corresponding amino acids could largely rescue the senescence phenotype of DcROS1, DcCARA and DcDHAD silenced plants. Our study not only demonstrates an essential role of DcROS1-mediated remodeling of DNA methylation in flower senescence but also unravels a novel epigenetic regulatory mechanism underlying DNA methylation and amino acid biosynthesis during flower senescence.

Use of different food additives to control browning in fresh-cut potatoes

Fresh-cut potato browning is a severe problem in the potato processing industry. Ascorbic acid, L-cysteine, hydrogen sulfide (H2S), and nitric oxide (NO) have been reported to reduce the browning in fresh-cut vegetables and fruits. We compared the effect of each food additive at its commonly used concentration on fresh-cut potato browning in order to choose a highly efficient treatment and explore its mechanism. Fresh-cut potato slices were immersed in 0.3 mmol L-1 ascorbic acid, 0.7 mmol L-1 L-cysteine, 0.7 mmol L-1 H2S, or 2.0 mmol L-1 NO for 10 min and stored at 4°C until the measurements finished. Results showed that the ascorbic acid and L-cysteine treatments showed less browning than the control treatment, while the H2S and NO treatments did not. Ascorbic acid increased total phenolic content, polyphenol oxidase (PPO) and peroxidase (POD) activities, while L-cysteine decreased PPO and POD activities with no change in total phenolic content. In addition, these two treatments did not influence respiration rate, weight loss, or rot index. In conclusion, ascorbic acid (0.3 mmol L-1) and L-cysteine (0.7 mmol L-1) can be valuable means to control fresh-cut potato browning. Ascorbic acid inhibits the browning mainly by reducing quinones back to phenolic compounds, but L-cysteine inhibits the browning mainly by decreasing PPO and POD activities.

Enzymatic browning: The role of substrates in polyphenol oxidase mediated browning

Enzymatic browning is a biological process that can have significant consequences for fresh produce, such as quality reduction in fruit and vegetables. It is primarily initiated by polyphenol oxidase (PPO) (EC 1.14.18.1 and EC 1.10.3.1) which catalyses the oxidation of phenolic compounds. It is thought that subsequent non-enzymatic reactions result in these compounds polymerising into dark pigments called melanins. Most work to date has investigated the kinetics of PPO with anti-browning techniques focussed on inhibition of the enzyme. However, there is substantially less knowledge on how the subsequent non-enzymatic reactions contribute to enzymatic browning. This review considers the current knowledge and recent advances in non-enzymatic reactions occurring after phenolic oxidation, in particular the role of non-PPO substrates. Enzymatic browning reaction models are compared, and a generalised redox cycling mechanism is proposed. The review identifies future areas for mechanistic research which may inform the development of new anti-browning processes.

Structural and expression analysis of polyphenol oxidases potentially involved in globe artichoke (C. cardunculus var. scolymus L.) tissue browning

Globe artichoke capitula are susceptible to browning due to oxidation of phenols caused by the activity of polyphenol oxidases (PPOs), this reduces their suitability for fresh or processed uses. A genome-wide analysis of the globe artichoke PPO gene family was performed. Bioinformatics analyses identified eleven PPOs and their genomic and amino acidic features were annotated. Cis-acting element analysis identified a gene regulatory and functional profile associated to plant growth and development as well as stress response. For some PPOs, phylogenetic analyses revealed a structural and functional conservation with different Asteraceae PPOs, while the allelic variants of the eleven PPOs investigated across four globe artichoke varietal types identified several SNP/Indel variants, some of which having impact on gene translation. By RTqPCR were assessed the expression patterns of PPOs in plant tissues and in vitro calli characterized by different morphologies. Heterogeneous PPO expression profiles were observed and three of them (PPO6, 7 and 11) showed a significant increase of transcripts in capitula tissues after cutting. Analogously, the same three PPOs were significantly up-regulated in calli showing a brown phenotype due to oxidation of phenols. Our results lay the foundations for a future application of gene editing aimed at disabling the three PPOs putatively involved in capitula browning.

Whole-transcriptome RNA sequencing reveals changes in amino acid metabolism induced in harvested broccoli by red LED irradiation

Whole-transcriptomic profiling combined with amino acid analysis were conducted in order to gain a better understanding of global changes in amino acid metabolism induced in broccoli by red LED irradiation. The results showed that the contents of almost all 16 amino acids in postharvest broccoli were maintained under red LED illumination. The red LED irradiation enhanced the anabolism of amino acid, including the biosynthesis of aromatic amino acids by upregulating the genes' expression in the shikimate pathway, as well as by upregulating the genes' expression which encoding biosynthetic enzymes in the branched-chain amino acid biosynthesis pathway. Red LED irradiation induced the expression of genes encoding aspartate aminotransferase, which plays a role in Asp synthesis, aspartate kinase, which functions in aspartate metabolism, and a cytoplasmic aspartate aminotransferase that converts 2-Oxoglutarate into Glu. Genes encoding imidazole glycerol-phosphate synthase and histidinol-phosphatase, which function in the His biosynthesis pathway, were also upregulated. According to our results, red LED irradiation delays broccoli's yellowing and senescence by regulating amino acid metabolism. These results enhance our understanding of the role of amino acid metabolism in the senescence of broccoli and the mechanism of red LED irradiation to alter amino acid metabolism in harvested broccoli.

Inhibitory mechanism of sodium hexametaphosphate on enzymatic browning in yellow alkaline noodles

The effect and mechanism of sodium hexametaphosphate (SHMP) on polyphenol oxidase (PPO) enzymatic browning in yellow alkaline noodles (YAN) were investigated. The browning degree and PPO activity in YAN or PPO solutions decreased with the SHMP concentrations increased. Variations in pH values (pH 7-8.5) adjusted by HCl or acetic acid slightly affected the PPO activity, but SHMP inhibited PPO activity more pronounced. The inhibition of SHMP on PPO activity was irreversible. SHMP formed coordinate covalent bonds with Cu²⁺ to make PPO inactive. HPLC analysis revealed that SHMP reduced the browning products and led to the color of PPO-catechol systems being lightened. Furthermore, SHMP inhibited browning by hampering the auto-oxidization of intermediate products due to the change in pH value. Besides, the HPLC chromatogram, UV-vis spectrum, and mass spectrometry revealed that SHMP could convert melanin (m/z 248.97, 723.5, and 836.58) to light-colored substances (m/z 137.11).

Comprehensive insight into an amino acid metabolic network in postharvest horticultural products: a review

Amino acid (AA) metabolism plays a vital role in the central metabolism of plants. In addition to protein biosynthesis, AAs are involved in secondary metabolite biosynthesis, signal transduction, stress response, defense against pathogens, flavor formation, and so on. Besides these functions, AAs can be degraded into precursors or intermediates of the tricarboxylic acid cycle to substitute respiratory substrates and restore energy homeostasis, as well as directly acting as signal molecules or be involved in the regulation of plant signals to delay senescence of postharvest horticultural products (PHPs). AA metabolism and its role in plants growth have been clarified; however, only a few studies about their roles exist concerning the postharvest preservation of fruit and vegetables. This study reviews the potential functions of various AAs by comparing the difference in AA metabolism at the postharvest stage and then discusses the crosstalk of AA metabolism and energy metabolism, the target of rapamycin/sucrose nonfermenting-related kinase 1 signaling and secondary metabolism. Finally, the roles and effect mechanism of several exogenous AAs in the preservation of PHPs are highlighted. This review provides a comprehensive insight into the AA metabolism network in PHPs. © 2023 Society of Chemical Industry.

Protective Effect of Peptides from Pinctada Martensii Meat on the H2O2-Induced Oxidative Injured HepG2 Cells

Pinctada martensii is a major marine pearl cultured species in southern China, and its meat is rich in protein, which is an excellent material for the preparation of bioactive peptides. In this study, the peptides from Pinctada martensii meat were prepared by simulated gastrointestinal hydrolysis, and after multistep purification, the structures of the peptides were identified, followed by the solid-phase synthesis of the potential antioxidant peptides. Finally, the antioxidant activities of the peptides were verified using HepG2 cells, whose oxidative stress was induced by hydrogen peroxide (H₂O₂). It was shown that the antioxidant peptide (S4) obtained from Pinctada martensii meat could significantly increase the cell viability of HepG2 cells. S4 could also scavenge reactive oxygen species (ROS) and reduce the lactate dehydrogenase (LDH) level. In addition, it could enhance the production of glutathione (GSH) and catalase (CAT) in HepG2 cells, as well as the expression of key genes in the Nrf2 signaling pathway. Three novel antioxidant peptides, arginine-leucine (RL), arginine-glycine-leucine (RGL), and proline-arginine (PR), were also identified. In conclusion, peptides from Pinctada martensii meat and three synthetic peptides (RGL, RL, PR) showed antioxidant activity and could have the potential to be used as antioxidant candidates in functional foods.

Enzymatic browning in apple products and its inhibition treatments: A comprehensive review

Apple (Malus domestica) is widely consumed by consumers from various regions. It contains a high number of phenolic compounds (majorly hydroxybenzoic acids, hydroxycinnamic acids, flavanols, flavonols, dihydrochalcones, and anthocyanins) and antioxidant activity, which are beneficial for human health. The trends on healthy and fresh food have driven the food industry to produce minimally processed apple, such as fresh-cut, puree, juice, and so on without degrading the quality of products. Enzymatic browning is one of the problems found in minimally processed apple as it causes the undesirable dark color as well as the degradation of phenolics and antioxidant activity, which then reduces the health benefits of apple. Proper inhibition is needed to maintain the quality of minimally processed apple with minimal changes in sensory properties. This review summarizes the inhibition of enzymatic browning of apple products based on recent studies using the conventional and nonconventional processing, as well as using synthetic and natural antibrowning agents. Nonconventional processing and the use of natural antibrowning agents can be used as promising treatments to prevent enzymatic browning in minimally processed apple products. Combination of 2-3 treatments can improve the effective inhibition of enzymatic browning. Further studies, such on as other potential natural antibrowning agents and their mechanisms of action, should be conducted.

Tyrosinase inhibitory effects of the peptides from fish scale with the metal copper ions chelating ability

Tyrosinase inhibitors have important applications in the cosmetics, medical and food industries due to they can effectively inhibit the synthesis of melanin. In this study, tilapia scale polypeptides were used as raw materials, and high-purity polypeptides with metal copper ions chelating ability were obtained by enzymatic hydrolysis, column chromatography, and EDTA elution. In vitro cell model analysis showed that the fish squamous peptides could strongly inhibit the activity of tyrosinase. When the sample concentration was 5 mg·mL^-1, its inhibition rate of tyrosinase reached to 59.73%, which had a better inhibition of enzyme activity compared with the positive control of the same concentration. The comprehensive results showed that the fish scale polypeptide with metal copper ions chelating ability could be a strong tyrosinase inhibitor, and might be used to prevent food browning in food-related fields, and could also be used for skin whitening in the fields of medicine and cosmetics.

Effects of negative air ions treatment on the quality of fresh shiitake mushroom (Lentinus edodes) during storage

Fresh shiitake (Lentinus edodes) is prone to brown, pileus-opening and flavor-loss during storage. Therefore, it is important to find an effective preservation method for fresh shiitake. Negative air ions (NAI) are negatively-charged molecules or atoms in the air, and can affect the physiological metabolism of live cells and be conveniently used with low cost. In this study, NAI treatment was performed at different times and the physico-chemical characteristics, microstructure, membrane potential and energy metabolism of shiitake were determined during storage. Results showed that NAI treatment for 40 min could reduce 29% of browning index and maintain the hardness of shiitake. NAI treatment groups had higher content of sweetness amino acids, umami amino acids, 5'-IMP, eight-carbon alcohols compounds and cyclic sulfides compounds than the control, and comprehensive quality of the group being treated for 40 min was the best. The mitochondria of shiitake swelled and the membrane potential decreased after being treated by NAI. However, NAI treatment for 40 min could improve the contents of ATP and ADP, maintain a relatively stable energy charge level, and promote energy utilization of shiitake during storage. The results demonstrated that NAI treatment had the potential to improve the quality shiitake during storage.

Prevention of Enzymatic Browning by Natural Extracts and Genome-Editing: A Review on Recent Progress

Fresh fruits and vegetable products are easily perishable during postharvest handling due to enzymatic browning reactions. This phenomenon has contributed to a significant loss of food quality and appearance. Thus, a safe and effective alternative method from natural sources is needed to tackle enzymatic browning prevention. The capabilities of natural anti-browning agents derived from plant- and animal-based resources in inhibiting enzymatic activity have been demonstrated in the literature. Some also possess strong antioxidants properties. This review aims to summarize a recent investigation regarding the use of natural anti-browning extracts from different sources for controlling the browning. The potential applications of genome-editing in preventing browning activity and improving postharvest quality is also discussed. Moreover, the patents on the anti-browning extract from natural sources is also presented in this review. The information reviewed here could provide new insights, contributing to the development of natural anti-browning extracts and genome-editing techniques for the prevention of food browning.

Purification, Characterization, and Inhibition of Tyrosinase from Jerusalem Artichoke (Helianthus Tuberosus L.) Tuber

Background

Because it tends to cause deterioration in the quality of food and appearance, food browning is unacceptable. Tyrosinase, which catalyzes the transformation of mono phenolic compounds into o-quinones, has been associated with this phenomenon. Natural anti-browning agents were used to help avoid the enzymatic browning that occurs in many foods.

Methods

Tyrosinase of Jerusalem Artichoke tubers was purified through (NH4)2SO4 sedimentation, dialysis, chromatography, and finally gel electrophoresis. The purified enzyme was characterized and inhibited by rosemary extracts.

Results

Purification of tyrosinase from Jerusalem Artichoke tuber were accomplished. The specific activity at the final step of purification increased to 14115.76 U/mg protein with purification fold 32.89 using CM-Cellulose chromatography. The molecular mass was evaluated by electrophoresis and found to be 62 KDa. Maximum tyrosinase activity was found at 30 °C, pH 7.2, and higher affinity towards L-tyrosine. Inhibition percentage of heated extracts for leaves and flowers on tyrosinase activity was better than nonheated with 29.65% and 23.75%, respectively. The kinetic analysis exposed uncompetitive inhibition by leaves and flowers heated extracts.

Conclusion

In this study, we concluded the usage of natural anti-browning inhibitors like rosemary extract be able to be castoff to substitute the chemical agents which might be dangerous to social healthiness. Natural anti-browning agents can be used to prevent the browning of many foods.

Ergothioneine: a potential antioxidative and anti-melanosis agent for food quality preservation

The global population increase has increased the demand for food products. However, post-harvest deterioration due to oxidation and discoloration results in a drastic loss of food quality and supply. Thus, research has focused on developing strategies to minimize such losses. One of those strategies includes the application of ergothioneine (ET), a potent hydrophilic antioxidant, to several food products so as to overcome their short shelf-life. ET can be synthetic or derived from several species of edible mushrooms and their extracts, which are known sources of natural ET. Given the reported potential of ET in food quality preservation, this review compiles the recent applications of ET as a preservative for maintaining the quality of food commodities.

Benzothiazines as Major Intermediates in Enzymatic Browning Reactions of Catechin and Cysteine

The course of melanin formation is yet not thoroughly resolved on a mechanistic level. With the present study, incubations of catechin (CA)- and cysteine-derived dihydro-1,4-benzothiazine carboxylic acid derivatives were investigated for colored products during enzymatic browning. Analyses by high-performance liquid chromatography (HPLC)-mass spectrometry revealed the formation of two novel decarboxylated dihydro-1,4-benzothiazine derivatives [8-(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-5-hydroxy-3,4-dihydro-2H-benzothiazine and 7-(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-5-hydroxy-3,4-dihydro-2H-benzothiazine] preferentially under acidic conditions. Furthermore, in model reactions under neutral pH, a colored phenazine dimer intermediate was isolated by high-performance countercurrent chromatography and preparative HPLC when conducting the incubations in the presence of o-phenylenediamine (OPD). Mass spectrometry and nuclear magnetic resonance spectroscopy unequivocally verified the structure as (12E)-5,5'-dioxo-11a,11a'-bis(3,5,7-trihydroxy-3,4-dihydro-2H-chromen-2-yl)-3,3',4,4',5a,5a',6,6',11,11',11a,11a'-dodecahydro-2H,2'H,5H,5'H-12,12'-bi[1,4]thiazino[2,3-b]phenazine-3,3'-dicarboxylic acid. Enzymatically catalyzed incubations under aeration starting from the initial CA-cysteine adducts and their follow-up dihydro-1,4-benzothiazine carboxylic acids, respectively, proved that the unstable colored compound was a trichochrome-like reaction intermediate of the browning reaction cascade which can be trapped by postincubation with OPD, thus verifying their direct mechanistic relationship.

Novel alternative for controlling enzymatic browning: Catalase and its application in fresh-cut potatoes

Surface browning is a vital phenomenon that adversely reduces the quality of fresh-cut potatoes. Although many anti-browning methods have been explored, it is unclear whether exogenous catalase (CAT) treatment influences the enzymatic browning. Our results showed that 0.05% CAT immersion for 5 min alleviated browning during cold storage (4°C, 8 days), which was accompanied by a higher lightness and lower redness; additionally, lower H₂ O₂ and O₂ ·- contents were found. The activities of CAT, ascorbate peroxidase, and glutathione peroxidase and the scavenging efficiency of 2,2-diphenyl-1-picrylhydrazyl were also increased. Moreover, CAT treatment inhibited the activities of polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase and reduced phenol accumulation. Treatment with 0.1% hydrogen peroxide (H₂ O₂ ) achieved the opposite results. This is the first report of CAT application reducing fresh-cut potato browning, providing a safe treatment alternative for enzymatic discoloration and preliminarily revealing the underlying mechanism with insight into antioxidant regulation. PRACTICAL APPLICATION: This research is helpful for fresh-cut potato producers because a novel, safe, easy-to-carry out anti-browning solution was proposed. Dipping in 0.05% catalase solution for 5 min revealed color improvement in the quality of fresh-cut potato slices. The mechanism may rely on enhancing antioxidant ability (ascorbate peroxidase, and glutathione peroxidase, and 2,2-diphenyl-1-picrylhydrazyl scavenging), reducing reactive oxygen species (H₂ O₂ , O₂ ·-, malondialdehyde) and controlling enzymatic browning reaction factors (polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase, and phenol accumulation). This method shows promise for better meeting the requirements and demands of consumers for fresh quality products.

Selection of appropriate post-harvest processing methods based on the metabolomics analysis of Salvia miltiorrhiza Bunge

Post-harvest processing is a leading cause of metabolic changes and quality loss in food products. An untargeted metabolomics approach based on UHPLC-QTOF-MS was conducted to explain metabolic changes during post-harvest processing of Salvia miltiorrhiza. A rapid identification method was established for comprehensive characterization of 56 phenolic acids and 45 tanshinones. Enzymatic browning was found to be the primary factor impacting the metabolic profile. A decreasing in free phenolic acids along with increasing in bound polyphenols was observed correlated with the deepening of browning degree. The various substructures of bound polyphenols were explored to interpret the composition of browning-associated products. It has also been found that the steaming process and control of the moisture content during slicing can effectively reduce the influence of enzymatic browning. This metabolomics study will contribute to select the optimal post-harvest processing methods for S. miltiorrhiza and provide information for post-harvest processing of similar products.

Inhibition of L-Cysteine on the Browning of Fresh Wet Noodles

This research explored the effect of L-cysteine on the browning of fresh wet noodles (FWN). With the increasing addition of L-cysteine (0.02–0.1%), the ΔL* decreased and Δa*, Δb* increased. The L-cysteine could reduce the pH value and polyphenol oxidase (PPO) activity and increase the retention rate of polyphenol of FWN. It suggested that L-cysteine could inhibit the browning of FWN by decreasing pH value, PPO activity, and the oxidation of polyphenols. In the in vitro PPO solution, the inhibitory effect of L-cysteine on PPO activity was related to the decrease in pH and the ability of chelating Cu²⁺. According to UPLC-TOF-MS analysis, L-cysteine could reduce the generation of browning products, which suggested that L-cysteine could react with the browning intermediate product (quinone) and generate a light-colored substance (-C₉H₁₀NO₄S). L-cysteine effectively inhibited the browning of FWN and had the potential to be used in noodle industry.

Plant-derived antioxidants incorporated into active packaging intended for vegetables and fatty animal products: a review

Nowadays, the food industry is focused on improving the shelf life of products by controlling lipid oxidation using natural antioxidants. The study of natural antioxidants is a field that attracts great interest because of their greater safety compared to synthetic ones. Plant-derived antioxidants being eco-friendly and effective are increasingly playing an important role in food preservation. When incorporated into active packaging, plant-derived antioxidants have no direct contact with foods, and will not change the colour or taste of the foods. They will, however, inhibit the development of rancidity, retard formation of toxic oxidation products, maintain nutritional quality, and prolong the shelf life of products. This review summarises research on the development of plant-derived antioxidants in food packaging. Antioxidants are found in plants such as green tea, olive leaves, ginkgo leaves, rosemary, Indian gooseberry, cinnamon, savoury, bay leaves, mango leaves, sage and clove etc. Antioxidants can scavenge free radicals and inhibit the activity of polyphenol oxidase. Therefore, they can inhibit lipid oxidation and browning of fruit and vegetables. These active substances can be obtained through extracting the plants using solvents with different polarities. The oxidation resistance of active substances can be determined by DPPH radical scavenging capacity, oxygen radical absorbance capacity, PPO enzyme inhibition capacity and other methods. In recent years, research on the preparation of food packaging with plant-derived antioxidants has also made significant progress. One development is to encapsulate plant-derived antioxidants such as tea polyphenols with capsules containing inorganic components. Thus, they can be blended with polyethylene granules and processed into active packaging film by industrial production methods such as melting, extrusion and blowing film. This research promotes the commercial application of active packaging incorporated with plant-derived antioxidants.

Effects of Isochoric Freezing Conditions on Cut Potato Quality

Isochoric freezing is a pressure freezing technique that could be used to retain the beneficial effects of food storage at temperatures below their freezing point without ice damage. In this study, potato cylinders were frozen in an isochoric system and examined using full factorial combinations of three processing procedures (immersed in water, vacuum-packed and immersed in ascorbic acid solution), four freezing temperatures/pressures (−3 °C/37 MPa, −6 °C/71 MPa, −9 °C/101 MPa and −15 °C/156 MPa) and two average compression rates (less than 0.02 and more than 0.16 MPa/s). The effects of process variables on critical quality attributes of frozen potatoes after thawing were investigated, including mass change, volume change, water holding capacity, color and texture. Processing procedure and freezing temperature/pressure were found to be highly significant factors, whereas the significance of the compression rate was lower. For the processing procedures, immersion in an isotonic solution of 5% ascorbic acid best preserved quality attributes. At the highest pressure level of 156 MPa and low compression rate of 0.02 MPa/s, potato samples immersed in ascorbic acid retained their color, 98.5% mass and 84% elasticity modulus value. These samples also showed a 1% increase in volume and 13% increase in maximum stress due to pressure-induced hardening.

Heated plant extracts as natural inhibitors of enzymatic browning: A case of the Maillard reaction

Enzymatic browning is the second largest cause of quality loss in fruits, vegetables, and seafood. Methods to prevent browning are the subject of great research interest in the field of Food Science and Technology. Numerous strategies for inhibiting enzymatic browning have been proposed in literature. Recent research is focused on finding alternative anti-browning agents to synthetics such as sulfites. Amongst natural antioxidants, Maillard reaction products (MRPs) have proven to be effective. Although reviews have been published on the antioxidant and anti-browning activity of MRPs, none of these focused solely on enzymatic browning inhibition mechanism of MRPs generated via heated plant extracts. Therefore, this review explores the common factors associated with the Maillard reaction (temperature, time, and concentration) and enzymatic browning inhibition (enzyme, substrate and reaction time) in order to confirm the activity and presence of MRPs in heated plant extracts. PRACTICAL APPLICATIONS: Chemical food additives applied in prevention of enzymatic browning are subjected to scrutiny. Therefore, alternative natural compounds are sought after. Plant extracts have been applied, however, they tend to impart their characteristic natural flavor into the product. Heating of these plant extracts have been proven to reduce the "planty, herby" flavors, whilst producing Maillard reaction. Maillard reaction products are known to exhibit anti-browning activity, and they are a cheap alternative to these chemical inhibitors. Therefore, these can be applied as potential anti-browning agents in food products.

Polyphenol oxidase browning in the formation of dark spots on fresh wet noodle sheets: How dark spots formed

The role of polyphenol oxidase (PPO) in the browning of fresh wet noodle sheets (FWNS) was discussed. To release the chemical formation mechanism of the dark spots formed on FWNS, the reconstituted FWNS and PPO-catechol reaction systems were prepared. Different from the overall color change of FWNS, almost all the melanins in dark spots were indirect products of PPO catalysis. The PPO catalytic dehydrogenation was an essential step for the formation of dark spots, but once the phenol dehydrogenation products were formed, the dark spots could still form through a further polymerization process, even though the PPO was completely deactivated. The optimum pH for the phenolic dehydrogenation in FWNS was about 7, and the alkaline condition was advantageous to the progress of the polymerization. Comprehensively, the maximum amount of dark spots was formed at about pH 9.

Aquatic polymer-based edible films of fish gelatin crosslinked with alginate dialdehyde having enhanced physicochemical properties

Fish-derived gelatin (FG), a raw material for edible films, has recently been spotlighted as an alternative source of mammalian gelatin. However, its low stability under moisture conditions and weak mechanical properties limit its application. In this study, a water-stable and mechanically robust FG film was prepared using alginate dialdehyde (ADA) as an eco-friendly crosslinking agent. The crosslinking process of FG with ADA was easily recognized by the change in the color of the FG/ADA composite film, and the browning index of the FG/ADA film could be correlated well with the actual crosslinking degree. The mechanical strength and Young's modulus of the FG/ADA composite film increased significantly with an increase in the content of the ADA crosslinker. In the case of FG/ADA10, the tensile strength and Young's modulus increased by 400 and 600 %, respectively, compared to those of FG. Remarkably, the FG-ADA crosslinking process greatly decreased the vulnerability of FG in moisture environments. Consequently, the FG/ADA10 film remained stable for 30 days under wet environment. In addition, the FG-ADA crosslinking process could enhance the antioxidative capacity of the FG/ADA edible film. According to this study, FG/ADA composite films fabricated in an effective manner using polymers derived from aquatic species like gelatin from fish and ADA from algae could have practical applications in the edible film-based packaging industry.

Antibrowning effect of commercial and acid-heat coagulated whey on potatoes during refrigerated storage

Potato color turns to brown after some process such as peeling, cutting, and slicing. In this research, the effect of acid-heat coagulated whey and commercial whey solutions on the color, polyphenol oxidase, phenylalanine ammonia-lyase activity, malondialdehyde, hydrogen peroxide content of potatoes were compared with pure water (control) immersion and sodium hydrogen sulfide solution. According to color results, there was no significant (P > 0.05) difference was found in the L^* and b^* values, browning index, and whitening index of the treatment groups. The polyphenol oxidase activity of the sulfide and commercial whey solution groups decreased from the initial values on day 3 then increased over that value. The use of the whey solution in preventing polyphenol oxidase activity showed a similar curve with the use of the sulfide solution. A rapid increase was observed in the malondialdehyde and hydrogen peroxide values of all treatment groups during the first 3-day storage. PRACTICAL APPLICATION: Immersion of potato cubes to whey protein solution prevents the browning and inhibits polyphenol oxidase activity. The browning index of the samples was not affected by the immersing water or whey solutions.

Beneficial impact of exogenous arginine, cysteine and methionine on postharvest senescence of broccoli

This study examined the ability of l-arginine, l-cysteine and l-methionine, to inhibit postharvest senescence of broccoli. Florets were dipped in aqueous solutions of the amino acids at concentrations from 1.0 to 100 mM and stored at 10 °C. A 5 mM dip was found to be optimal in delaying senescence as measured by retention of green colour, vitamin C and antioxidant activity, and a lower level of ethylene production, respiration, weight loss, phenylalanine ammonia lyase (PAL) activity and ion leakage with the benefits being similar for all three amino acids. Arginine, cysteine and methionine have Generally Recognised As Safe (GRAS) status and should have few impediments in obtaining regulatory approval for commercial use if similar effects were found for other leafy vegetables.

Inhibition of hexose oxidase on the dark spots in fresh wet noodle sheets: A feasible prevention of dark spots

Hexose oxidase was a feasible prevention for the dark spots in the fresh wet noodle sheets (FWNS). The chemical mechanism that hexose oxidase recucing the melanins of dark spots was discussed basis on the UPLC-TOF-MS analysis of the polyphenol oxidase (PPO)-catechol system. In the process of PPO browning, hexose oxidase catalyzed the oxidation of o-benzoquinone derivatives and their oligomers, hindering the formation of melanins. Hexose oxidase was efficient in FWNS with low ash content when water addition was 24%~44% or pH range was 4 ~ 7.5. Hexose oxidase could inhubit dark spots in the presence of 10 metal ions. The recommended addition amount was 40 ~ 60 ppm, by which the dark spots could be compolitely inhibited. Hexose oxidase was also suitable for wholewheat and oat FWNS, ΔL_6d of wholewheat and oat FWNS were reduced by 4 and 7.98, respectively.

Effect of isochoric freezing on quality aspects of minimally processed potatoes

The enhanced interest in greater convenience foods has recently led to the expansion of minimally processed potato products. This study investigated the effects of isochoric freezing on pre-peeled potato cubes, including quality attributes (microstructure, texture, and color), nutritional value (ascorbic acid (AA) content, total phenolic content, and antioxidant capacity), and polyphenol oxidase activity. Isochoric freezing (-3 °C/30 MPa) was compared with isobaric freezing (-3 °C/0.1 MPa) and individual quick freezing followed by frozen storage at -20 °C for 4 weeks. The isochoric sample had lower drip loss and volume shrinkage as well as better preserved texture and microstructure than the other samples. All freezing methods caused an increase in total phenolic content and antioxidant capacity, but a decrease in AA content. Also, all freezing methods caused browning of the thawed potatoes, but isochoric freezing delayed its onset for more than 1 week. PRACTICAL APPLICATION: Results showed that isochoric freezing of pre-peeled and cut potatoes caused less freeze damage than isobaric and individual quick freezing, which might find application in the commercial preservation of minimally processed food products.

Sequencing, assembly, annotation, and gene expression: novel insights into browning-resistant Luffa cylindrica

Luffa is a kind of melon crop widely cultivated in temperate regions worldwide. Browning is one of the serious factors affecting the quality of Luffa. Therefore, the molecular mechanism of Luffa browning is of great significance to study. However, the molecular diversity of Luffa cultivars with different browning-resistant abilities has not been well elucidated. In our study, we used high-throughput sequencing to determine the transcriptome of two Luffa cylindrica cultivars '2D-2' and '35D-7'. A total of 115,099 unigenes were clustered, of which 22,607 were differentially expression genes (DEGs). Of these DEGs, 65 encoding polyphenol oxidase, peroxidase, or ascorbate peroxidase were further analyzed. The quantitative real-time PCR (RT-qPCR) data indicated that the expression levels of the LcPPO gene (Accession No.: Cluster-21832.13892) was significantly higher in '35D-7' compared with that in '2D-2'. Several POD genes (Accession No.: Cluster-21832.19847, Cluster-21832.30619 and Cluster-48491.2) were also upregulated. Analysis of the plantTFDB database indicated that some transcription factors such as WRKY gene family may also participate in the regulation of Luffa browning. The results indicated that the divergence of genes expression related to enzymatic reaction may lead to the different browning resistances of Luffa. Our study will provide a theoretical basis for breeding of browning-resistant Luffa.

Combined Effect of Dipping in Oxalic or in Citric Acid and Low O2 Modified Atmosphere, to Preserve the Quality of Fresh-Cut Lettuce during Storage

Leaf edge browning is the main factor affecting fresh-cut lettuce marketability. Dipping in organic acids as well as the low O₂ modified atmosphere packaging (MAP), can be used as anti-browning technologies. In the present research paper, the proper oxalic acid (OA) concentration, able to reduce respiration rate of fresh-cut iceberg lettuce, and the suitable packaging materials aimed to maintaining a low O₂ during storage, were selected. Moreover, the combined effect of dipping (in OA or in citric acid) and packaging in low O₂ was investigated during the storage of fresh-cut iceberg lettuce for 14 days. Results showed a significant effect of 5 mM OA on respiration rate delay. In addition, polypropylene/polyamide (PP/PA) was select as the most suitable packaging material to be used in low O₂ MAP. Combining OA dipping with low O₂ MAP using PP/PA as material, resulted able to reduce leaf edge browning, respiration rate, weight loss and electrolyte leakage, preserving the visual quality of fresh-cut lettuce until 8 days at 8 °C.

Bioavailability and antioxidant potentials of fresh and pasteurized kiwi juice before and after in vitro gastrointestinal digestion

The aim of the present work was to find the changes in the chemical composition, chemical structure and antioxidant activity of bioactive nutrients of kiwi juices upon pasteurization and in vitro gastrointestinal digestion. Results showed that fresh kiwi juice (FKJ) contains total phenols, 162 mg GAE/mL, total flavonoids 1.44 mg QE/mL, ascorbic acid 4.5 mg/mL and fiber 60%; these contents were marginally affected by pasteurization (PKJ) to be 122, 1.02, 2.6 and 47 respectively. On the other hand, gastrointestinal digestion severely lowered total phenols, total flavonoids and ascorbic acid in digested fresh kiwi juice (DFKJ) to 49 mg GAE/mL,0.16 mg GE/mL and 2.2 mg/mL, and in digested pasteurized kiwi juice (DPKJ) to 42, 0.07 and 1.2 respectively; however fiber contents increased upon digestion as a result of decreasing other nutrients. The antioxidant and reducing power activities followed the same order of decreasing total phenols, total flavonoids and ascorbic acid contents i.e. FKJ > PKJ > DFKJ > DPKJ. The major flavonoid found was apigenin in the form of various glycosides differ in the number (1-3) and position of the sugar units. Pasteurization showed minor effects on the chemical composition of fresh juice while digestion, as a result of gastrointestinal enzymes had more effect but mainly on the number and position of the sugar units rather than affecting the flavonoid moiety which preserve the main nutritive values.