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Enzymatic browning caused by polyphenol oxidases, tyrosinase and laccase, continues to be one of the main problems in winemaking. Therefore, wineries are very interested in studying the mechanisms of browning and procedures for decreasing the use sulphur dioxide. This research proposes a model to study tyrosinase activity from grape must using different substrates: one monophenol (p -hydroxybenzoic acid), two diphenols (caftaric acid and (−)-epicatechin) and one triphenol (gallic acid). The kinetic constants of tyrosinase, Vmax and K M , indicate that caftaric acid is the best substrate for tyrosinase, followed in decreasing order by (−)-epicatechin, gallic acid and p -hydroxybenzoic acid. This last acid does not appear to be susceptible to browning by the action of grape must tyrosinase. The influence of pH, temperature and ethanol on grape must tyrosinase were also determined and the results indicate that tyrosinase Vmax increases when pH and temperature are higher and that the presence of ethanol reduces it. • A method to study the grape must tyrosinase activity is proposed. • This method has been proved with caftaric, gallic and p-hydroxycinnamic acids and (−)-epicatechin. • The kinetic constants, Vmax and KM, of grape tyrosinase have been determined for different substrates. • Caftaric acid is the best substrate for grape tyrosinase of all those studied • The influence of pH, temperature and ethanol on the kinetic constants have been studied [ABSTRACT FROM AUTHOR]

Browning significantly affects consumer perception, while texture hardening due to wound healing further reduces the commercial value of fresh-cut potatoes. This study evaluated the effects of 5 g L−1 ascorbic acid (AA), sodium isoascorbate (SI), and calcium ascorbate (CA) on browning and wound healing during ambient storage. The results indicated that AA and SI were more effective than CA and the control in delaying browning and wound healing. By day 3, browning levels in the AA and SI groups were reduced to 65 % and 62 % of the control, respectively, while lignin content decreased by 35 % and 40 %. Additionally, AA and SI treatments reduced reactive oxygen species (ROS) and improved antioxidant capacity, preserving appearance and texture. This study provides insights into the mechanisms of browning and wound healing, suggesting potential strategies for extending the shelf life and improving the quality of fresh-cut potatoes. • AA and SI treatments significantly delayed browning in fresh-cut potatoes. • AA and SI treatments effectively delayed wound healing, reducing lignin accumulation. • AA and SI treatments were linked to improved ROS metabolism and antioxidant capacity. • CA was less effective than AA and SI in controlling browning and wound healing. [ABSTRACT FROM AUTHOR]

Whole white button mushrooms (WWBM) exhibit a limited shelf-life owing to the oxidative enzymatic browning. Inactivation of polyphenol oxidase-PPO and peroxidase-POD in WWBM and its kinetic behavior were studied using pulsed light(PL) treatment (0.13–1.11 J/cm2). The first-order kinetics explained PL-induced enzyme inactivation. Rate constants(k) for PPO and POD were 3.84 and 2.55 cm2/J. FTIR-analysis revealed secondary-structural changes in partially-purified enzyme. PL-treatment retarded browning, retained phenolics and enhanced vitamin D 2. PL-treatment at 1.11 J/cm2 rendered WWBM both microbially and enzymatically stable. The PL-treated WWBM's shelf-life at 4, 20, and 37 °C were 5, 3, and 1 day. At 4 °C, browning increased by 6.1 %; firmness decreased by 55.2 %, while PL-treated mushrooms retained 90.6 % phenolics, 78.9 % antioxidant capacity, and 64.2 % D 2 after 5 days. Higher activation energy value confirmed phenolics were most sensitive during storage. PL-technology supports UN Sustainable Development Goals by reducing chemical use, lowering carbon-footprints, minimizing pollution, and enhancing shelf-life, promoting sustainable global trade. • Pulsed light (PL) treatment at 1.11 J/cm2 led to microbial and enzyme stablity. • First-order kinetics effectively explains PL-induced enzyme inactivation. • PL exposure leads to alteration in secondary structure of partially-purified enzyme. • PL treatment at 1.11 J/cm2 extends mushroom shelf life to 5 days at 4 °C. • PL-treated mushrooms retain 90 % phenolics, 79 % antioxidant, 64 % vitamin D 2 at 4 °C. [ABSTRACT FROM AUTHOR]

Tyrosinase (Polyphenol oxidase), a key enzyme in enzymatic browning, is an attractive target for developing new anti-browning agents in the food industry. In this work, twenty pyrazole-1,2,4-triazole derivatives (3a-3n, 4a-4f) were synthesized and tested in vitro, most of compounds showed potent anti-tyrosinase activity. Of these, 3c (IC 50 = 1.02 ± 0.08 μM) was found to be 14 folds stronger than kojic acid (IC 50 = 14.74 ± 1.23 μM) and behaved as a mixed type inhibitor. Besides, the disappeared peak of dopaquinone in the HPLC assay intuitively validated the inhibitory effect of 3c. Copper ions chelating, fluorescence quenching and molecular docking assays showed that coordination with copper is the key to play a role. Furthermore, 3c exhibited excellent anti-browning ability for the Rosa roxburghii Tratt, the non-enzymatic browning experiment showed that 3c could prevent browning in non-enzymatic ways. It is suggested that these derivatives could serve as the leading compounds to find more efficient anti-browning agents in the future. [Display omitted] • A range of linear pyrazole-1,2,4-triazole derivatives were prepared. • The inhibitory activity of compound 3c is much stronger than that of kojic acid. • Compound 3c could effectively retard the browning of Rosa roxburghii Tratt. • Compound 3c could prevent enzymatic and non-enzymatic browning. [ABSTRACT FROM AUTHOR]

[Display omitted] • MG-BLGNPs with different unfolding structures can be induced by heating and SDS. • LN can be loaded into MG-BLGNPs without altering their MG state to form MG-BLG@LN. • Unfolding degree of MG-BLGNPs is associated with enhanced binding and loading of LN. • CMC coatings embedded with MG-BLG@LN show great mechanical and adhesive properties. • MG-BLG@LN/CMC coating effectively mitigate quality deterioration in fresh-cut apples. This investigation employed molten globule state β-lactoglobulin nanoparticles (MG-BLGNPs) for encapsulating linalool (LN) combined with carboxymethyl chitosan (CMC) coating to enhance the shelf-life of fresh-cut apples. The effect of different MG structures on the encapsulation efficiency of BLGNPs and the properties of coating was studied. Structural characterization and molecular simulation showed structural differences between heat-induced MG state (70-BLGNPs, heated at 70 °C for 1 h) and sodium dodecyl sulfate- co -heat-induced MG state (SDS/70-BLGNPs, treated with 0.192 mg/mL SDS for 10 min, then heated at 70 °C for 1 h), with the latter being more unfolded. LN self-assembles into MG-BLGNPs, among the generated particles, SDS/70-BLG@LN exhibits stronger binding effect and higher LN loading capacity. Integration of MG-BLG@LN into CMC enhanced coating's mechanical properties and adhesion to fresh-cut apples. The SDS/70-BLG@LN/CMC coating showed superior preservation on fresh-cut apples during storage, reducing enzymatic browning, membrane lipid oxidation, and microbial growth while maintaining hardness and overall quality. [ABSTRACT FROM AUTHOR]

The effects of γ-aminobutyric (GABA) on enzymatic browning, storage quality, membrane and reactive oxygen species (ROS) metabolism in fresh-cut stem lettuce were investigated. The results illustrated that GABA treatment delayed browning degree, polyphenol oxidase (PPO) activity and the expression of LsPPO. Meanwhile, higher chlorophyll and ascorbic acid contents were exhibited in GABA-treated stem lettuce, as well as the slower microbial propagation. Further investigation revealed that exogenous GABA application declined malondialdehyde content, electrolyte leakage and the enzyme activities of membrane metabolism, and the expression levels of related genes were also downregulated. In addition, GABA treatment scavenged ROS and strengthened the enzyme activities of ROS metabolism, as well as the expression levels of corresponding genes. Taken together, these findings implied that the repressed enzymatic browning and microbial propagation in GABA-treated stem lettuce were due to the inhibition of ROS accumulation, enhancement of membrane stability and increased resistance to oxidation. • Exogenous GABA inhibited the enzymatic browning of fresh-cut stem lettuce. • GABA treatment maintained the quality in fresh-cut stem lettuce. • GABA application inhibited the microbial propagation in fresh-cut stem lettuce. • GABA treated-fresh-cut stem lettuce exhibited higher membrane stability. • GABA treatment enhanced the antioxidant capacity in fresh-cut stem lettuce. [ABSTRACT FROM AUTHOR]

Fresh-cut pear fruit is greatly impacted by enzymatic browning, and maintaining quality remains a challenge. This study examined the impact of exogenous α-lipoic acid (α-LA) treatment on enzymatic browning and nutritional quality of fresh-cut pears. Results revealed that 0.5 g/L α-LA treatment effectively maintained color and firmness, and inhibited the increase in microbial number. The α-LA treatment also reduced MDA and H 2 O 2 contents, decreased PPO activity, and enhanced SOD, CAT, and PAL activities. The α-LA treatment notably upregulated phenolic metabolism-related gene expression, including PbPAL , Pb4CL , PbC4H , PbCHI and PbCHS , and then increasing total phenols and flavonoids contents. Furthermore, it also influenced carbohydrate metabolism-related gene expression, including PbSS , PbSPS , PbAI and PbNI , maintaining a high level of sucrose content. These findings indicated that α-LA treatment showed promise in reducing browning and enhancing fresh-cut pears quality, offering a potential postharvest method to prolong the lifespan and maintain nutritional quality. [Display omitted] • Flesh browning, MDA and H 2 O 2 contents were reduced by α-lipoic acid treatment. • α-Lipoic acid inhibited microbial growth and enhanced antioxidant capacity. • α-Lipoic acid maintained total phenols, flavonoids, and ascorbic acid contents. • α-Lipoic acid curbed PPO activity and enhanced PAL, CAT, and SOD activities. • α-Lipoic acid regulated genes expression in carbohydrate and phenolic metabolism. [ABSTRACT FROM AUTHOR]

The development of natural inhibitors of polyphenol oxidase (PPO) is crucial in the prevention of enzymatic browning in fresh foods. However, few studies have focused on the effect of subsequent sterilization on their inhibition efficiency. This study investigated the influence and mechanism of high hydrostatic pressure (HHP) on the inhibition of PPO by epigallocatechin gallate (EGCG), cyanidin-3-O-glucoside (C3G), and ferulic acid. Results showed that under the conditions of 550 MPa/30 min, the activity of EGCG-PPO decreased to 55.92%, C3G-PPO decreased to 81.80%, whereas the activity of FA-PPO remained stable. Spectroscopic experiments displayed that HHP intensified the secondary structure transformation and fluorescence quenching of PPO. Molecular dynamics simulations revealed that at 550 MPa, the surface interaction between PPO with EGCG or C3G increased, potentially leading to a reduction in their activity. In contrast, FA-PPO demonstrated conformational stability. This study can provide a reference for the future industrial application of natural inhibitors. • HHP treatment improved the inhibitory efficiency of PPO by EGCG or C3G • The activity of FA-PPO remained stable even at 550 MPa/30 min • TEM observed that HHP promoted the aggregation of PPO in the presence of EGCG • MD simulations showed an increase in interaction between PPO and inhibitors under HHP • FA was embedded inside the PPO to form a complex that exhibited pressure stability [ABSTRACT FROM AUTHOR]

To reduce the detrimental effects of enzymatic-browning on potato pulp quality, this study investigated the anti-browning potential of magnetic field at varying intensities. The magnetic field (4 mT) enhanced the structural integrity of potato pulp cells, with the highest hardness (119.37 g). Furthermore, the potato pulp subjected to a magnetic field treatment of 4 mT for 60 min at a temperature of 32 °C (PP-MF-4) shown an orderly macromolecular aggregation, increased viscoelastic properties of potato pulp. The PP-MF-4 demonstrated excellent anti-browning capability, as evidenced by the highest L⁎ value (59.18), reduced browning index, and lower accumulation of browning-products. Furthermore, the PP-MF-4 exhibited a significant reduction in oxidative damage, attributed to enhanced antioxidant activity and total phenolic content. Besides, the PP-MF-4 inhibited browning enzymes and improved the molecular structure orderliness. Consequently, magnetic field presents a viable approach for mitigating enzymatic-browning in potato pulp, offering a promising methods for preserving its quality. [Display omitted] • Magnetic field promoted macromolecular aggregation to inhibit enzymatic browning. • Magnetic field reduced the oxidative damage and MDA content in potato pulp. • Magnetic field effectively alleviated the browning degree of potato pulp. [ABSTRACT FROM AUTHOR]

Enzymatic browning and microbial growth are two natural phenomena that occur when fruits and vegetables are exposed to abnormal conditions, i.e., temperatures in the range of 12–22 °C, leading to their spoilage. Controlling the temperatures during the supply chain aims to optimize the product's shelf life. Irreversible thermochromic beads were fabricated using a simple extrusion technique containing fatty acid, lecithin, and anthocyanin solution-alginate. The pigmentation durability was adjusted based on electrostatic interactions, as evidenced by the reduction in dye leaching in the case of the produced bead at pH = 6 to less than 0.007 after 45 min. Characterization shows that the chosen combination of fatty acids and the quinonoid molecule is useful for producing thermochromic beads, with a color change at 12 °C–22 °C, from blue to purple. Using the prepared thermochromic beads in the supply chain of fresh-cut salad and brussels sprouts showed a great result for monitoring their freshness after 21 ± 1 min. • Simple extrusion-based preparation of irreversible thermochromic sensors for smart packaging. • Thermosensor based on edible molecules from red cabbage, oils, and eggs. • Pigmentation was stabilized via electrostatic interaction between core-shell structure in beads. • Thermochromic beads change the color above 12 °C. • The possible color change mechanism and application in packaging were clarified [ABSTRACT FROM AUTHOR]

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. • Combinational effects of kojic acid and ELAH were probed during the storage of fresh-cut potato. • Combination of kojic acid and ELAH effectively inhibited enzymatic browning and microbial growth of fresh-cut potato. • The mechanism underlying the combinational effects of kojic acid and ELAH was elucidated at molecular level. • The study sheds light on the preservation of fresh-cut products using a combined approach. [ABSTRACT FROM AUTHOR]

• Cyrene™ is an effective anti-browning agent, preventing enzymatic food browning. • Cyrene™ is 44 % more effective than the reference compound (ascorbic acid) • Cyrene™ and its gem-diol form have the same molecular dynamics characteristics. • Cyrene™ is a biocompatible and biodegradable compound. The tyrosinase pathway takes part in the enzymatic process of food browning and is primarily responsible for food spoilage - manifesting itself from a decrease in its nutritional value to a deterioration of taste, which consequently leads to a gradual loss of shelf life. Finding safe and bio-based tyrosinase inhibitors and anti-browning agents may be of great importance in agriculture and food industries. Herein, we showed that Cyrene™ exhibits tyrosinase inhibitory activity (IC 50 : 268.2 µM), the 1.44 times higher than ascorbic acid (IC 50 : 386.5 μM). Binding mode studies demonstrated that the carbonyl oxygen of Cyrene™ coordinates with both copper ions. Surprisingly, both hydroxyl groups of Cyrene gem -diol perform a monodentate binding mode with both copper ions, at similar distances. This fact suggests that both compounds could have a similar binding mode and, as consequence, similar biological activities in tyrosinase inhibition assays and anti-browning activities. [ABSTRACT FROM AUTHOR]

• Polyphenol oxidase inactivation as a strategy to avoid fruits/vegetables browning. • MIL-53(Al)/DUT-5/MIL-110 were tested as enzyme inactivators in apple juice. • MIL-53(Al) / DUT-5 inhibited polyphenol oxidase by at least 70 % in 10 / 30 min. • MIL-110 retained its structure and completely inactivated polyphenol oxidase. • Polyphenol oxidase was inactivated/inhibited by its interaction with MOF materials. Polyphenol oxidase (PPO) is critical due to enzymatic browning in fruits and vegetables, developing economic impact in fruits industry. Metal-Organic Frameworks (MOF) have shown interesting characteristics such as water stability, low toxicity, and good adsorption yield, making them good candidates for PPO inactivation. Al-based-MOFs, MIL-53(Al), DUT-5, and MIL-110 were tested as PPO inactivators in apple juice by enzyme-MOF interactions at r.t. through two possible mechanisms, i) substrate scavengers (substrates:catechol and 4-methylcatechol) or ii) enzyme activity modifiers. The scavenging behavior of Al-based-MOFs was moderate, in the same magnitude, being catechol adsorption better than 4-methylcatechol. PPO activity was reduced by at least 70% by MIL-53(Al)/DUT-5 in 10/30 min respectively, and MIL-110 inactivated PPO in 50 min with some structural modifications. Enzyme-MOF interactions are major responsible for PPO inactivation. This could be a new applicability of MOFs, as an alternate PPO inactivation process, easily included in juice processing, retaining sensorial/nutritional properties, developed at r.t thus energy-cost-effective. [ABSTRACT FROM AUTHOR]

[Display omitted] • Outlines the mechanisms of natural color formation in aquatic products. • Summarises the discoloration mechanisms of aquatic products during storage. • Recapitulates the comprehensive factors that affect the color of aquatic products. • Discusses current cutting-edge technology in color preservation of aquatic products. • Recommends the development of high-quality prefabricated aquatic products. Color plays a pivotal role in guiding and assessing the industrial production of aquatic products due to the swift sensory perception of information through vision. This review provides a comprehensive overview of the following four aspects: (a) mechanisms governing natural color formation in aquatic products, (b) factors and mechanisms contributing to the discoloration of aquatic products, (c) cutting-edge methods for color analysis and detection, and (d) current valuable techniques for preserving color quality. The natural color of aquatic products is derived from skin chromatophores, endogenous pigment proteins, and astaxanthin. Discoloration of aquatic products can occur due to lipid oxidation, as well as enzymatic and non-enzymatic browning. Furthermore, this review examines frontier color protective technologies, encompassing physical methods like ultra-high pressure, irradiation, and low-temperature plasma, as well as chemical methods involving natural preservatives. The findings of this study offer significant insights into the development of high-quality aquatic products. [ABSTRACT FROM AUTHOR]

Highlights • Purslane extract greatly inhibited fresh-cut potato browning during 4 °C storage. • Purslane extract significantly suppressed the activities of PPO, POD and PAL. • Purslane extract could retain the membrane permeability, MDA content. • Medium concentration of purslane extract inhibited browning. Abstract Enzymatic browning is a crucial reaction affecting the quality of fresh-cut fruit and vegetables. Purslane is an edible Chinese folk medicine with extensive distribution and containing a lot of polyphenols and alkaloids. However, little research on its' anti-browning effect on fresh-cut food was reported. In this study, the effectiveness of 0.05% (w/w) purslane aqueous extract treatment efficiently inhibited the activities of polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia-lyase (PAL), the membrane integrity was effectively maintained, and malondialdehyde (MDA) content increases was retarded during whole storage period at 4 °C. Oddly, the higher purslane extract concentration, the lower endogenesis phenolic content. Additionally, thirty polyphenols and fifty-six alkaloids were found in purslane aqueous extract by LC-MS/MS. All results suggest that purslane aqueous extract is a promising nutritive anti-browning agent for fresh-cut potato. [ABSTRACT FROM AUTHOR]

Highlights • The effect of UV-C treatment on the quality of lotus root was investigated. • The inhibiting browning mechanism of UV-C was studied. • The optimum condition of UV-C radiation was treated for 5 min. • Low PPO, POD, PAL activities and less damage degree of the cell inhibited browning. Abstract The effect of shortwave ultraviolet (UV-C) radiation on the quality, especially browning of fresh-cut lotus (Nelumbo nucifera Gaertn.) root in relation to enzymes and phenolic metabolism was investigated. Fresh-cut lotus roots were exposed to UV-C lamp (75 W) at a distance of 30 cm above the produce tray for 1, 5, 10, 20, and 40 min, and then stored for 8 days at 4 °C. Results showed that UV-C treatments for 5 and 10 min exhibited significantly low browning degree, soluble quinone content and inactivation of polyphenol oxidase, peroxidase, and phenylalanine ammonia lyase activities, while other qualities including soluble solids content and hardness had no difference with other treatments. Prolonging treatment time had less effect on inhibiting the browning since a long time of UV-C radiation increased cell damage. In summary, UV-C treatment has the potential to maintain quality of fresh-cut lotus root. [ABSTRACT FROM AUTHOR]

Highlights • Quantify the browning of tender jackfruit slices using image analysis technique. • Comparing results from sensory test, enzyme activity and colorimeter. • Variation in rate of browning of fresh cut tender jackfruit slices with time. • Prevention of browning by using different packaging techniques. Abstract Changes in physicochemical properties of fresh cut tender jackfruit during storage is depend on its colour. Colorimeter measurements are best for the samples with homogeneous colour. However, for samples with non-homogenous colors or large sizes (like fruits and vegetables), the colorimeters are inappropriate and inaccurate. The aim for this study is to quantify the amount of browning in fresh cut tender jackfruit slices by using image analysis technique and justify the results by comparing them with existing techniques like sensory examination, enzyme activity, and colorimeter. It can be concluded from the results that browning in fresh cut tender jackfruit slices increase rapidly in control and normally packed samples. Correlation coefficient as high as 0.963, represent that image analysis system is an accurate and highly consistent method to quantify the colour of fruits and vegetables. [ABSTRACT FROM AUTHOR]

Highlights • Maclurin was treated in potato supernatant for 5 weeks. • Maclurin inhibited enzymatic browning in potato supernatant. • Maclurin may bind to and inactivate PPO. • Maclurin increases antioxidant capacity in potato supernatant. Abstract Although enzymatic browning is important for the beneficial coloration of some foods, it also causes negative effects on safety, quality, and nutritional values of fruit and vegetable. Thus, anti-browning natural compounds have gained attention in the food industry. Xanthone-related compounds have been well-known for its biological activities, but their roles in enzymatic browning are unclear. We screened xanthone-related natural compounds for their anti-polyphenol oxidase (PPO) activity and maclurin was selected for further experiments due to stronger PPO-inhibitory activity. Maclurin suppressed enzymatic browning in potato supernatant for long-term partly through direct binding to and inactivating PPO presumably by forming multiple hydrogen bonds and aromatic interactions with the binding pocket. In addition, maclurin elevated antioxidant capacity when added to potato supernatant. Considering the diverse health-promoting effects of antioxidants, maclurin can be applied as a functional food additive to block enzymatic browning and increase the antioxidant property of foods including beverages and soups. [ABSTRACT FROM AUTHOR]

This work describes a TLC-coupled bioautographic assay suitable for the separation and detection of apple polyphenol oxidase (PPO) inhibitors from natural extracts. PPO was immobilised in agar containing l -DOPA as substrate and 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) to enhance colour development. The inhibition was detected as white spots on reddish background. Minimum amount of PPO inhibitors detected was 0.0125 µg of 4-hexylresorcinol, 0.025 µg of ascorbic acid, 0.5 µg of cysteine and 1 µg of kojic acid. The assay was compatible with normal and reverse phase TLC systems and allows detecting compounds that directly had action on the enzyme as well as agents that could convert quinones back to their reduced form. The chromatographic run evidenced the different nature of enzymatic browning inhibitory compounds from garlic and onion extracts. Using natural enzymes will provide a fast and cheap alternative for target specific exploration of natural enzymatic inhibitors. [ABSTRACT FROM AUTHOR]

The enzymatic browning reaction caused by polyphenol oxidase (PPO) has a negative effect on the processing of fruits and vegetables. However, some chemical inhibitors have been used to prevent enzymatic browning reaction, although they may be toxic and potentially hazardous to use in food. In this study, PPO was isolated and purified from the Whangkeumbae pear, and four food grade inhibitors were used to prevent the enzymatic browning reaction. The results showed that the PPO activity increased by 32.93-fold; its yield was 0.2 U/100 U, and the specific activity was 519,895.73 U/mg protein. The molecular weight of the PPO was approximately 44 kDa. The most potent inhibitor was l -cysteine, which fully inhibited the PPO activity at a concentration of 0.8 mg/mL. The type of inhibition of l -cysteine was noncompetitive. It suggests that l -cysteine can be utilized to prevent enzymatic browning reaction during the processing of pear juice. [ABSTRACT FROM AUTHOR]

Enzymatic browning is a major issue that needs to be solved in the food industry. Although swertiajaponin is a flavonoid rich in the whole herb of Swertia japonica that has been clinically used, its biological functions and applicat​ion in the foods have not been fully elucidated. Here, we showed that swertiajaponin efficiently blocked enzymatic browning in potatoes possibly by direct binding to and inactivating polyphenol oxidase. Furthermore, swertiajaponin showed potent antioxidant activity proven by markedly suppressed reactive oxygen species. Swertiajaponin significantly increased antioxidant properties of potato extract when it is added since it additively elevated total flavonoid content. Considering numerous beneficial effects of antioxidants, swertiajaponin may be used as a functional food additive to suppress enzymatic browning and elevate the antioxidant capacity of foods including beverages and soups by fortification of flavonoids. [ABSTRACT FROM AUTHOR]

Enzymatic browning limits the postharvest life of minimally processed foods, thus the study selected the optimal inhibitors of polyphenol oxidase (PPO) and evaluated their effect on enzymatic browning, phenolics and antioxidant capacity of stored mung bean sprouts. The sprouts treated with 2 mM and 20 mM ascorbic acid had a lowered PPO activity; compared to the control by 51% and 60%, respectively. The inhibition was reflected in a significant decrease in enzymatic browning. The sprouts treated with 20 mM ascorbic acid had 22% and 23% higher phenolic content after 3 and 7 days of storage, respectively. Both storage and ascorbic acid treatment increased potential bioaccessibility of phenolics. Generally, there was no effect of the treatments on the antioxidant capacity; however, a significant increase in the reducing potential was determined for the sprouts washed with 20 mM ascorbic acid. In conclusion, ascorbic acid treatments may improve consumer quality of stored sprouts. [ABSTRACT FROM AUTHOR]

This study investigated the effects of microwave power density on effective moisture diffusion coefficient ( D eff ), glass transition temperature ( T g ), gelatinization temperature ( T P ), physical and chemical qualities of lotus seeds during microwave vacuum drying. D eff increased by 42% and 127% at 15 W/g and 20 W/g, respectively, when compared with 10 W/g. T P was negatively correlated with the relaxation times of T 21 and T 22 , while T g was negatively correlated with the relative areas A 22 . The rates of change of color were observed to be divided roughly into two periods, consisting of a rapid change caused by enzymatic browning and a slow change caused by non-enzymatic browning. An equation is provided to illustrate the relationship of k 1 and k 2 of Peleg’s model depending on power density during rehydration kinetics. The samples at 20 W/g exhibited the higher content of amino acid (540.19 mg/100 g d.b.) while lower starch (17.53 g/100 g d.b.). [ABSTRACT FROM AUTHOR]

Fresh-cut lotus root slices were treated with 80 nM 24-epibrassinolide (EBR) and then stored at 4 °C for 8 days to investigate the effects on cut surface browning. The results showed that EBR treatment reduced cut surface browning in lotus root slices and alleviated membrane lipid peroxidation as reflected by low malondialdehyde content and lipoxygenase activity. EBR treatment inhibited the activity of phenylalanine ammonia lyase and polyphenol oxidase, and subsequently decreased phenolics accumulation and soluble quniones formation. The treatment also stimulated the activity of peroxidase, catalase and ascorbate peroxidase and delayed the loss of ascorbic acid, which would help prevent membrane lipid peroxidation, as a consequence, reducing decompartmentation of enzymes and substrates causing enzymatic browning. These results indicate that EBR treatment is a promising attempt to control browning at cut surface of fresh-cut lotus root slices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of kojic acid-1,3,4-oxadiazole derivatives (5a – 5n) were designed and synthesized. • All compounds showed better tyrosinase inhibitory activity than positive control kojic acid. • Compound 5f effectively reduced the enzymatic browning of fresh-cut mushrooms. • The inhibitory mechanism of compound 5f on tyrosinase has been studied. • Compound 5f exhibited low cytotoxic activity. In the food industry, inhibition of tyrosinase activity is considered as one of the main means to prevent browning. Therefore, fourteen kojic acid-1,3,4-oxadiazole hybrids (5a–5n) were prepared and tested for their tyrosinase inhibitory effects. Among them, 5f (IC 50 = 5.32 ± 0.58 μM) has the best anti-tyrosinase activity and was 9 times higher than that of kojic acid (IC 50 = 49.77 ± 1.19 μM). Additionally, the inhibitory mechanism was studied by copper-chelating assay, ultraviolet spectrophotometry, fluorescence quenching, molecular docking, etc. The results had shown that 5f could not only bind to the copper ion in the active region of tyrosinase but also change the secondary structure of tyrosinase. Combined with the outstanding anti-browning effect and low cytotoxicity of 5f , it is concluded that these title derivatives could be used as the leading molecules in the development of new anti-browning agents. [ABSTRACT FROM AUTHOR]

• Combination of physical and chemical treatments reduced polyphenol oxidase activity in wheat flour. • The brightness L* values of fresh noodles were negatively correlated with polyphenol oxidase activity. • The combination of citric acid and 75 °C heat treatment significantly delayed the darkening of fresh noodles. • The combination treatment weakened the gluten network structure and increased the peak starch viscosity. • Textural analysis showed an increase in hardness and chewiness and a decrease in adhesion of the cooked noodles. Enzymatic browning has been a significant factor affecting the sale of fresh noodles. This study used a combination of physical and chemical methods to achieve a long-lasting and effective anti-browning effect in fresh noodles. The results showed that the combinations of citric acid (CA), NaOH, and KOH with heat treatment blunted the polyphenol oxidase activity and improved the color of fresh noodles. Specifically, the L* value of fresh noodles stored at 6 °C treated by the combination of CA and 75 °C (CHFN-75) at 72 h (81.71) was significantly higher than that of the control at 72 h (74.42). Mixolab and confocal laser scanning microscopy showed that the combined treatment affected the protein and starch of the flour. However, the hardness and chewiness of the cooked noodles increased only slightly, and the adhesiveness decreased slightly. The innovative combination can be used as an effective way to delay the darkening of fresh noodles. [ABSTRACT FROM AUTHOR]

• Slightly acid electrolysed water (SAEW) inhibited PPO in a mixed-type mode. • SAEW bound to PPO by hydrogen bond and rearranged the secondary structure. • HOCl bound to the active site of PPO to inhibit its enzymatic activity. • SAEW treatment inhibited melanin related compounds formation. It has been revealed that slightly acid electrolysed water (SAEW) could delay enzymatic browning and melanin formation in food. In this work, multi-spectroscopic methods and UHPLC-Q-TOF-MS were combined to study the underlying reason. The reversible mixed-type inhibition mode of HOCl (main components in SAEW) was determined. The ground state complex formation quenched the intrinsic fluorescence of polyphenol oxidase (PPO) and it was stable at lower temperature. The PPO conformational change (transformation from α-helix to β-sheet) induced by SAEW was confirmed by 3D fluorescence and Circular dichroism (CD) spectrum. Moreover, the driving force of the interaction between HOCl and PPO was hydrogen bond, which was validated by the molecular docking result. Besides, the formation of melanin related compounds including dihydroxyphenylalanine (DOPA), dopaquinone, dopachrome, 5,6-dihydroxyindole-2-carboxylic acid (DHICA), 5,6-dihydroxyindole (DHI), and 5,6-indolequinone were significantly inhibited by SAEW treatment. These results demonstrated the potential of SAEW as a PPO inhibitor in the food industry. [ABSTRACT FROM AUTHOR]

• Established a method for identifying tyrosinase inhibitors from the complex matrix. • The method avoided false positive activity with good selectivity and sensitivity. • The method exhibited excellent tolerance to the sample matrix. • The method enabled minimal sample consumption with high analytical efficiency. • Several tyrosinase inhibitors were identified from green tea and cinnamon extracts. Tyrosinase plays a primary role in melanin biosynthesis and enzymatic browning of freshly cut fruits and vegetables. Herein, an on-line ultraperformance liquid chromatography diode array detector biochemical detection (UPLC-DAD-BCD) method was established to identify trace amount potent tyrosinase inhibitors and antibrowning agents in complex mixtures. The tyrosinase inhibition activities of some representative compounds were evaluated by using the established method and their chromatography-activity relationships were obtained. Then the proposed UPLC-DAD-BCD method was applied to screen tyrosinase inhibitors in edible herbal extracts and identified two tyrosinase inhibitors in green tea and three in cinnamon. The above active ingredients were determined by ultra-high-performance liquid chromatography linear ion trap/orbitrap high resolution mass spectrometry (UHPLC-FTMS). The on-line UPLC-DAD-BCD in combination with UHPLC-FTMS was confirmed to be a powerful technique to screen and elucidate the active ingredients in complex matrixes and could be applied to evaluate the integrated effects of multiple ingredients against corresponding targets. [ABSTRACT FROM AUTHOR]

Although fruit juices are very popular, enzymatic browning occurs easily. Browning of fruit juice deteriorates nutrition value and product quality due to oxidation of polyphenol compounds. Therefore, development of natural food additives that reduce browning will be beneficial for improving quality of fruit juices. Onion has been reported to be a potent natural anti-browning agent. Here, we compared unheated and heated apple juices pre-supplemented with onion with respect to browning and nutritional quality. The unheated apple juice supplemented with onion showed reduced browning as well as increased total soluble solid, total phenol concentration, radical scavenging activities, and ferric reducing and copper chelating activities without any change in flavonoid concentration. On the other hand, heated juice supplemented with onion not only showed improved values for these parameters but also markedly increased flavonoid concentration. Thus, we conclude that application of heating and onion addition together may greatly improve quality of apple juice. [ABSTRACT FROM AUTHOR]

• The enzymatic browning of catechin is the same as that of non-enzymatic browning. • 1 mM AA had the most effective protective effect on catechin. • The effect of AA on the stability of catechin is time-dependent and dose-dependent. • The antioxidant effect of AA and the addition reaction of DHAA are two key factors affecting the stability of catechin. A series of incubation systems of (+) - catechin (Cat), ascorbic acid (AA) and polyphenol oxidase (PPO) of lotus rhizome at 40 °C were performed to investigate the effect and oxidation pathway of AA on the stability of Cat. The results showed that after the enzymatic or non-enzymatic oxidation of Cat, the products of the two reactions were the same, namely epicatechin, catechin dimer and dehydrogenated catechin dimer. After adding AA, the protective effect of AA on catechin increased first and then decreased with the increase of AA concentration. 0.1 mmolL(exp)-1 AA can inhibit PPO activity in a short time. Within 24 h, 1 mmolL(exp)-1 AA can keep Cat content at 87.88 %. At the concentration of 10 mmolL(exp)-1 AA, excessive AA is oxidized to form a large amount of dehydroascorbic acid (DHAA), which forms an adduct with Cat, promoting the consumption of Cat. The effect of AA on the stability of Cat is time-dependent and dose-dependent. [ABSTRACT FROM AUTHOR]

• Ultrasound-assisted treatment at mild heat extended shelf life from 3 to 12 d. • Combined treat inhibited microorganism and the activity of PAL, PPO and POD. • Combined treat affected cell structural integrity of lotus root. Ultrasound-assisted probiotic fermentation suspension treatment under mild heat was applied to freshly cut lotus root. Combined treatment significantly (p < 0.05) improved the bactericidal effect: S. aureus , E. coli O157:H7, A. flavus spores, and yeast were completely killed at 55℃ for 6 min, morphological and structural changes of cells were observed. Combined treatment inhibited enzymatic browning via decreasing the activities of PPO, POD, PAL, and decreasing TPC, soluble quinone content. The decrease of external resistance, capacitance and the increase of internal resistance reflected the loss of structural integrity of cells after combined treatment. For combined treatment samples, no obvious color change was observed during 12 days of storage but weight loss rate, total acid increased significantly (p < 0.05) and hardness decreased, the shelf life was extended to 12 d. Ultrasound-assisted probiotic fermentation suspension treatment under mild heat had the dual effects of sterilization and inhibition of browning. [ABSTRACT FROM AUTHOR]

• EGCG exhibited high affinity for and mixed-type inhibition on PPO. • Multispectral experiments showed the structural changes of PPO after binding with EGCG. • Molecular docking and dynamic simulation revealed EGCG directly bind to the active center of PPO. • The effect of inducing aggregation of EGCG to PPO was identified. • The PPO inhibitory mechanism of EGCG included competing with substrates and induced aggregation. Polyphenol oxidase (PPO)-mediated enzymatic browning occurs in fruit, vegetables and aquatic products and causes huge economic losses every year. In this study, epigallocatechin-3-gallate (EGCG) displayed high affinity for and efficient inhibitory capacity against PPO. To explore the inhibition mechanism, multispectroscopic methods and computational simulations were implemented. Initially, EGCG inhibited PPO activity reversibly in a mixed-type manner. Then, the conformation and secondary structure changes of PPO after binding with EGCG were discovered by fluorescence emission spectra and circular dichroism. Molecular docking and dynamic simulation results revealed that EGCG could tightly bind with the binuclear copper domain of PPO through hydrophobic stacking and hydrogen bonds. Moreover, EGCG might act as a linker to interact with different PPO molecules at another binding site. Transmission electron microscopy observation suggested that EGCG induced the aggregation of PPO. Therefore, the inhibition mechanism of EGCG on PPO included competition for catalytic centers and induced aggregation. [ABSTRACT FROM AUTHOR]

Roasting treatment increased levels of unsaturated fatty acids (linoleic, oleic and elaidic acids) as well as saturated fatty acids (palmitic and stearic acids) in almond ( Prunus dulcis ) kernel oils with temperature (150 or 180 °C) and duration (5, 10 or 20 min). Nonetheless, higher temperature (200 °C) and longer duration (10 or 20 min) roasting might result in breakdown of fatty acids especially for unsaturated fatty acids. Phenolic components (total phenols, flavonoids, condensed tannins and phenolic acids) of almond kernels substantially lost in the initial phase; afterward these components gradually increased with roasting temperature and duration. Similar results also observed for their antioxidant activities (scavenging DPPH and ABTS + radicals and ferric reducing power). The changes of phenolic acid and flavonoid compositions were also determined by HPLC. Maillard reaction products (estimated with non-enzymatic browning index) also increased with roasting temperature and duration; they might also contribute to enhancing the antioxidant attributes. [ABSTRACT FROM AUTHOR]

Full-fatted and commercially defatted rice bran extracts (RBE and CDRBE) were evaluated for their ability to inhibit enzymatic browning in potato and apple. RBE showed more effective inhibition of polyphenol oxidase (PPO) activity and browning in potato and apple as compared to CDRBE. Five phenolic compounds in RBE and CDRBE (protocatechuic acid, vanillic acid, p -coumaric acid, ferulic acid and sinapic acid) were identified by HPLC. They were then evaluated for their important role in the inhibition using a model system which found that ferulic acid in RBE and p -coumaric acid in CDRBE were active in enzymatic browning inhibition of potato and apple. p -Coumaric acid exhibited the highest inhibitory effect on potato and apple PPO ( p ⩽ 0.05). Almost all phenolic compounds showed higher inhibitory effect on potato and apple PPO than 100 ppm citric acid. [ABSTRACT FROM AUTHOR]

The effect of fumigation with hydrogen sulfide (H 2 S) gas on inhibiting enzymatic browning of fresh-cut lotus root slices was investigated. Browning degree, changes in color, total phenol content, superoxide anion production rate (O 2 − ), H 2 O 2 content, antioxidant capacities (DPPH radical scavenging ability, ABTS radical scavenging activity and the reducing power) and activities of the phenol metabolism-associated enzymes including phenylalanine ammonialyase (PAL), catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO) were evaluated. The results showed that treatment with 15 μl L −1 H 2 S significantly inhibited the browning of fresh-cut lotus root slices ( P < 0.05), reduced significantly O 2 − production rate and H 2 O 2 content, and enhanced antioxidant capacities ( P < 0.05). PPO and POD activities in the fresh-cut lotus root slices were also significantly inhibited by treatment with H 2 S ( P < 0.05). This study suggested that treatment with exogenous H 2 S could inhibit the browning of fresh-cut lotus root slices by enhancing antioxidant capacities to alleviate the oxidative damage. [ABSTRACT FROM AUTHOR]

In this study, a process for the production of premium quality yellowish, cloudy pear juice from low-quality fruit under low-oxygen conditions was developed. The production process consisted of (1) shredding, (2) pressing with spiral-filter technology including a vacuumised extraction cell, (3) holding in an inert gas buffer tank, (4) pasteurisation, (5) and refrigerated storage. First, the system parameters of a spiral-filter press were optimised with the aim of producing a yellowish, cloudy pear juice with the highest possible juice yield. A maximum juice yield of 78% could be obtained. Enzymatic browning during juice extraction could be suppressed as a result of the fast processing and the low air (oxygen) levels in the extraction chamber of the spiral-filter press. Furthermore, we observed that instantaneous pasteurisation at 107 °C for 6 s, subsequent aluminium laminate packaging and cold storage had only a minimum effect on the phenolic composition. [ABSTRACT FROM AUTHOR]

In this study, advantages and disadvantages of the innovative, low-oxygen spiral-filter press system were studied in comparison with the belt press, commonly applied in small and medium size enterprises for the production of cloudy apple juice. On the basis of equivalent throughput, a higher juice yield could be achieved with spiral-filter press. Also a more turbid juice with a higher content of suspended solids could be produced. The avoidance of enzymatic browning during juice extraction led to an attractive yellowish juice with an elevated phenolic content. Moreover, it was found that juice produced with spiral-filter press demonstrates a higher retention of phenolic compounds during the downstream processing steps and storage. The results demonstrates the advantage of the use of a spiral-filter press in comparison with belt press in the production of a high quality cloudy apple juice rich in phenolic compounds, without the use of oxidation inhibiting additives. [ABSTRACT FROM AUTHOR]

Gamma-radiation induced browning inhibition in minimally processed shredded cabbage stored (10 °C) for up to 8 days was investigated. γ-irradiation (2 kGy) resulted in inhibition of browning as a result of down-regulation (1.4-fold) in phenylalanine ammonia lyase (PAL) gene expression and a consequent decrease in phenylalanine ammonia lyase (PAL) activity. Activity of polyphenol oxidase and peroxidase, total and individual phenolic content as well as o -quinone concentration were, however, unaffected. In the non-irradiated samples, PAL activity increased as a consequence of up-regulation of PAL gene expression after 24 and 48 h by 1.2 and 7.7-fold, respectively, during storage that could be linearly correlated with enhanced quinone formation and browning. Browning inhibition in radiation processed shredded cabbage as a result of inhibition of PAL activity was thus clearly demonstrated. The present work provides an insight for the first time on the mechanism of browning inhibition at both biochemical and genetic level. [ABSTRACT FROM AUTHOR]

The inhibitory effect and associated mechanisms of salicylic acid (SA) on the browning of fresh-cut Chinese chestnut were investigated. Shelled and sliced chestnuts were immersed in different concentrations of an SA solution, and the browning of the chestnut surface and interior were inhibited. The activities of polyphenol oxidase (PPO) and peroxidase (POD) extracted from chestnuts were measured in the presence and absence of SA. SA at concentrations higher than 0.3 g/L delayed chestnut browning by significantly inhibiting the PPO activity ( P < 0.01), and the POD activity was not significantly affected ( P > 0.05). The binding and inhibition modes of SA with PPO and POD, determined by AUTODOCK 4.2 and Lineweaver–Burk plots, respectively, established SA as a competitive inhibitor of PPO. [ABSTRACT FROM AUTHOR]

• Developing new tyrosinase inhibitors is very important in food and agriculture. • New derivatives were synthesized from phenolic compounds used in food industry. • They had potent inhibitory effects on mushroom tyrosinase in low concentrations. • They might be as anti-browning candidates for food and agriculture industries. • The compound, 4-(4-Hydroxyphenyl)butan-2-one (1b) was the most potent inhibitor. Tyrosinase plays determinant role in enzymatic browning of vegetables and fresh-cut fruits. Development of new tyrosinase inhibitors is of great concern in food and agriculture. To discover new inhibitors, novel phenolic derivatives were synthesized and their inhibitory effects were investigated on activity of mushroom tyrosinase. All compounds showed potent inhibitory activities in their low concentrations and compound 4-(4-hydroxyphenyl)butan-2-one (1b) was found to be the most potent inhibitor (73.75% inhibition, IC 50 value 5.6 μmol L−1). This ligand inhibited enzyme activity in a mixed pattern and kinetic parameters were also determined. In vitro assays revealed that this compound has not cytotoxicity/hemolytic effects and can be considered as safe for further investigations. Analysis of fluorescence spectra showed that all ligands quenched enzyme intrinsic fluorescence. The quenching mode and important binding parameters were also calculated. Enzyme-ligands interactions were also theoretically analyzed by molecular docking and results showed that the ligands interact with structurally/functionally critical residues. [ABSTRACT FROM AUTHOR]

Highlights: [•] Polyphenol oxidase from “Rojo Brillante” persimmon fruits has been characterized. [•] Maximum enzyme activity was reached at pH 5.5 and 55°C. [•] PPO stability decreased sharply at pH 4.0, even at 60°C. [•] At least four PPO isoforms from the “Rojo Brillante” variety were detected. [ABSTRACT FROM AUTHOR]

• Galla rhois water extract inhibited the enzymatic browning of apple juice for 16 days. • Galla rhois water extract bind to and inactivate polyphenol oxidase. • Galla rhois water extract is a strong antioxidant that decreases DPPH radicals and elevates ferric reducing antioxidant power. • Gallotannin derivatives are major compounds in Galla rhois water extract. • Among the major compounds of Galla rhois water extract, penta-O-galloyl-β- d -glucose, tetragalloylglucose, epicatechin gallate, methyl gallate, ellagic acid, ethyl gallate, and trigalloylglucose showed anti-PPO activities. Although Galla rhois has been used as a traditional medicine in Asian countries, there was no application of it in anti-browning food additives. Here, we tested whether Galla rhois inhibits apple juice browning. Apple juice browning was blocked at 250–1000 µg/ml of Galla rhois for 16 days but the effect of vitamin C did not last until a day. In vitro assays showed that the antioxidant capacity of Galla rhois was stronger than that of vitamin C. Further analysis by UPLC-MS/MS identified 17 phytochemicals containing gallotannin derivatives. Docking simulation and polyphenol oxidase activity assay indicate that the mechanisms underlying Galla rhois-mediated inhibition of the enzymatic browning include but are not limited to the combined effects of multiple compounds including galloylglucose- and gallate-derivates. Although marketability and long-term toxicity of Galla rhois should be tested, it may be applied as a food additive to elevate food quality. [ABSTRACT FROM AUTHOR]

Highlights: [•] Discolouration of Jerusalem artichokes was measured by instrumental colour analysis. [•] Sensory analysis of colour attributes of raw and boiled tubers was performed. [•] Contents of total phenolics, phenolic acids, iron and organic acids were analysed. [•] Enzymatic browning was the same independent of variety and harvest time. [•] Analysed constituents could not explain discolourations of raw and boiled tubers. [ABSTRACT FROM AUTHOR]

Abstract: Oats were subjected to treatments like defatting, hydrothermal cooking and kilning, milled into flour and then the control and treated flours were incorporated into wheat flour at 25% and 50% levels and chapatti making behaviour and antioxidant properties were studied. The treatments significantly affected the antioxidant properties of oats. Incorporating oat flours to wheat increased total phenolic content but lowered the antioxidant activity however both were decreased significantly upon baking. The reducing power of the oat blended flour was higher than the wheat flours and ranged from 8.0 to 15.5μmol AAE/g and was further increased upon baking. The metal chelating activity of flour blends varied from 62.0% to 73.8% and further increased upon baking. After baking the total flavonoid content was lowered and ranged from 308 to 389μg CE/g. The non-enzymatic browning index significantly increased up to 27.6% upon baking. [Copyright &y& Elsevier]

Abstract: Effects of oxidative browning inhibitors on sweet potato protein (SPP) recovery and quality were studied. Oxidative browning inhibitors successfully decreased sweet potato oxidative browning, but reduced both SPP extractability and recovery. Ultrafiltration/diafiltration processed sweet potato (UDSP) protein (at pH 4, 6 and 7) showed significantly (p <0.05) higher yield, purity, solubility, thermal stability and amino acid constituents than that of isoelectrically precipitated sweet potato (IPSP) protein (at pH 4). The yield of UDSP proteins was more than twice that of IPSP protein. Denaturation temperature (T d), enthalpy change (ΔH) and solubility (at pH 3 and 8) of UDSP proteins were in the ranges 82.89–90.29°C, 6.34–11.35 (J/g) and 71.4–94.2%, respectively, while that of IPSP protein were 85.27°C, 2.35 (J/g) 31.2% and 55.5%, respectively. Ratio of SPP essential amino acid to the total amino acid ratio ranged from 0.49 to 0.51. SPP in vitro digestibility and digestibility-corrected amino acid score (PDCAAS) ranged 70–80.7% and 44.79–51.08%, respectively. [Copyright &y& Elsevier]

Abstract: The mechanism of browning involving enzymatic browning was investigated in the pericarp of water caltrop, an Asian vegetable popular for its taste and medicinal properties. Polyphenol oxidase (PPO) and peroxidase (POD) activities were determined in pericarp at various times and temperatures. Water caltrop consisted of 44.22% moisture content, 37.23% crude fibre, and 2.63% crude protein. PPO and POD activities dropped from 62 and 38units/g sample, respectively, as water temperature was increased from 30 to 80°C. Optimum pH and temperature for PPO activity was at pH 5.0, 25–45°C, and POD activity peaked at 60°C. High PPO and POD activities at 40–50°C resulted in degradation of phenolic compounds, which led to increased aggregation of browning pigments and discolouration (lower L-values) of the pericarp. Enzymatic browning was determined as the major factor in the browning discolouration of heat-treated water caltrop pericarp. [Copyright &y& Elsevier]

Abstract: As the Maillard reaction is known to occur in heat-treated foods, unheated and heated honey samples were subjected to the activity-guided fractionation and size-exclusion chromatography to compare the degree of browning, radical scavenging activity (ORAC) and molecular size of the fractions obtained. Heat-treatment increased browning in the fractions of light- and medium-coloured honeys (p <0.002), accelerated the formation of high molecular weight melanoidins (85–232kDa) and significantly increased ORAC values (p <0.0001). In contrast, melanoidin content and ORAC decreased in the fractions of heat-treated dark buckwheat honey (p <0.001). Unheated dark honey contained a significantly higher amount of melanoidins than other honeys (p <0.007). Together, results showed that at low initial concentration of melanoidins, heat-treatment accelerated formation of new melanoidins and increased ORAC, while at high concentration it caused decrease and a reduction of radical scavenging activity. This study emphasises the importance of non-enzymatic browning in the prediction of the antioxidant pool in thermally processed honeys. [ABSTRACT FROM AUTHOR]

Abstract: This study describes the extraction and characterisation of cashew apple polyphenol oxidase (PPO) and the effect of wounding on cashew apple phenolic acid composition, PPO activity and fruit browning. Purification factor was 59 at 95% (NH4)2SO4 saturation. For PPO activity, the optimal substrate was catechol and the optimum pH was 6.5. PPO K m and V max values were 18.8mM and 13.6Umin−1 ml−1, respectively. Ascorbic acid, citric acid, sodium sulphite and sodium metabisulphite decreased PPO activity, while sodium chloride increased PPO activity. Wounding at 2°C and 27°C for 24h increased PPO activity but storage at 40°C reduced PPO activity. Gallic acid, protocatechuic acid and cinnamic acid (free and conjugate) were identified in cashew apple juice. Cutting and subsequent storage at 40°C hydrolysed cinnamic acid. 5-Hydroxymethylfurfural content in cashew apple juice increased after injury and storage at higher temperatures, indicating non-enzymatic browning. [ABSTRACT FROM AUTHOR]