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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]

Lanzhou lily (Lilium davidii var. willmottiae) are known for its medicinal and culinary attributes and has gained popularity among consumers due to its distinct regional characteristics. However, the bulbs of Lanzhou lily are prone to browning during storage at room temperature, thus adversely affecting their quality and value. X-ray irradiation, a chemical residue-free, and energy-efficient physical technology, emerges as a promising solution for preserving freshly harvested the bulbs of Lanzhou lily. In this study, different doses of X-ray irradiation (0–400 Gy) were applied to the bulbs of freshly harvested Lanzhou lily stored at room temperature, aiming to explore the impact of irradiation on browning development, total phenolic content, and the activity of related antioxidases. The results revealed that X-ray irradiation, especially at the dose of 50 Gy, can effectively maintain the appearance and reduce the browning index (BI) of freshly harvested Lanzhou lily bulbs during storage. The 50 Gy X-ray treatment is found to significantly suppress the activity of polyphenol oxidase (PPO) and peroxidase (POD) in the bulbs of freshly harvested Lanzhou lily, thereby reducing enzymatic browning. Additionally, the X-ray irradiation can elevate the activity of phenylalanine ammonia-lyase (PAL), superoxide dismutase (SOD) and catalase (CAT) while decreasing the accumulation of malondialdehyde (MDA). This led to the preservation of cell membrane integrity, mitigation of lipid peroxidation (LOP), and a delay in browning process. These findings suggested that treating with 50 Gy X-ray irradiation can effectively slow down the color changes of Lanzhou lily bulbs during the storage under the room temperature, which is beneficial to extend the shelf-life of freshly harvested Lanzhou lily bulbs. • X-ray irradiation reduced the browning index of freshly harvested Lanzhou lily bulbs. • The process of membrane peroxidation of lily bulbs after X-ray irradiation was slowed down. • X-ray irradiation increased the activities of SOD and CAT. • X-ray irradiation (50 Gy) can extend the shelf-life of freshly harvested Lanzhou lily bulbs. [ABSTRACT FROM AUTHOR]

Litchi, a tropical and subtropical fruit with substantial commercial value, is prone to browning after harvest. Phytosulfokine (PSK), a plant peptide hormone, plays a significant role in postharvest fruit preservation by affecting various biological processes. However, its specific effects on litchi browning have not been fully elucidated. This study demonstrates that PSK application effectively delays litchi pericarp browning, maintains a higher TSS/TA ratio, and reduces electrical conductivity. PSK treatment inhibits the degradation of anthocyanins, flavonoids, and phenolics, while also decreasing the accumulation of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and superoxide anions (O₂⁻). Additionally, PSK enhances the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR), while reducing the activities of ascorbate peroxidase (APX), polyphenol oxidase (PPO), and peroxidase (POD) compared to the control. Transcriptome analysis reveals that PSK upregulates genes involved in plant hormone signaling and biosynthesis of anthocyanins and flavonoids, while downregulating genes associated with glutathione metabolism and autophagy. RT-qPCR confirms that PSK treatment decreases the expression levels of APX , LAC7 , PPO , POD1 , POD5 , POD51 , and PODX , while increasing the expression of GPX4 , contributing to the delayed browning. These findings suggest that PSK mitigates litchi browning by modulating oxidative enzymatic reactions and suppressing the expression of browning-related genes. • PSK application delays senescence and reduces pericarp browning in litchi fruits. • PSK boosts SOD, CAT, and GR activities, but reduces APX, PPO, and POD activities. • PSK enhances hormone signaling and anthocyanin biosynthesis genes expression. • PSK downregulates genes linked to glutathione metabolism and autophagy. • PSK delays litchi browning by regulating antioxidant enzymes and browning genes. [ABSTRACT FROM AUTHOR]

Litchi fruit is extremely vulnerable to postharvest browning due to its perishable physiological characteristics, which seriously restricts the shelf-life and industrial development of products. Trehalose is a natural product with excellent biological activity and safety. In this work, the ability of trehalose to mitigate the browning of 'Feizixiao' litchi fruit stored at 25 °C and its physio-biochemical mechanisms were evaluated. The application of trehalose at 2.5 g L−1 to litchi fruit delayed browning and redness loss. Trehalose treatment alleviated oxidative stress-induced impairment of membrane system, as indicated by reduced generation of O 2 -., H 2 O 2 and malondialdehyde (MDA) and lowered relative electrolyte leakage (REL), which was a result of increased activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR). Compared to control fruit, repressed activities of polyphenol oxidase (PPO) and peroxidase (POD) coincident with higher contents of total phenolics, flavonoids, anthocyanins, procyanidin B2 and cyanidin-3-O-glucoside were observed in fruit receiving trehalose, indicating an amelioration of enzymatic browning by trehalose treatment. Furthermore, trehalose treatment stimulated the expression of anthocyanin biosynthetic genes (LcPAL , Lc4CL , LcCHS , LcCHI , LcANS , LcDFR and LcUFGT) and their transcriptional activator genes (LcMYB43435 , LcMYB18362 , LcMYB30086 and LcMYB2539), while suppressing the transcription of microRNAs (miR159 , miR319 , miR828 and miR858) that mediate MYB degradation. Additionally, trehalose treatment increased content of adenosine triphosphate (ATP) and expression of LcPGK and LcCa 2+ -ATPase , while repressing the transcription of miR2118 that can target and negatively regulate LcPGK and LcCa 2+ -ATPase , which facilitated the synthesis and utilization of energy. These findings suggest that trehalose could retard postharvest browning in litchi fruit by enhancing antioxidant capacity, promoting anthocyanin synthesis and maintaining energy homeostasis. • Trehalose (2.5 g L−1) delays browning in litchi fruit during ambient storage. • Trehalose reinforces antioxidant capacity in litchi fruit during storage. • Trehalose inhibits enzymatic browning in litchi fruit during storage. • Trehalose positively regulates anthocyanin synthetic pathway in stored litchi fruit. • Trehalose promotes energy production and utilization in litchi fruit during storage. [ABSTRACT FROM AUTHOR]

Enzymatic browning is a major problem that seriously impacts the quality of fresh-cut potatoes. Our previous study found that glutamic acid (Glu) treatment could repress the discoloration of fresh-cut potatoes, but the molecular mechanism was still unknown. Herein, it was found that the content of total phenolic, H 2 O 2 , O 2 .- and the activities of PPO, POD and PAL were repressed, but the activities of CAT, APX, SOD and GPX were improved by Glu treatment. Moreover, transcriptomic analysis showed that an abundant number of differentially expressed genes (DEGs) were selected from fresh-cut potatoes browning between Glu and control groups. A comprehensive functional enrichment analysis showed that the metabolic pathways of glutathione metabolism, flavonoid biosynthesis, phenylalanine metabolism, phenylpropanoid biosynthesis, starch and sucrose metabolism, and plant hormone signal transduction were markedly enriched, which transcriptional levels were markedly altered by Glu treatment. RT-qPCR confirmed the results of RNA-Seq that Glu repressed the transcription of StPPO2 , StPPO3 , StPPO7 , and StERF-BR1-like. More importantly, as a nuclear protein, StERF-BR1-like activated the transcription of StPPO2 by directly binding with its promoter. Overall, these data indicate that Glu could repress the browning of fresh-cut potatoes by regulating the pathways mentioned above, and StERF-BR1-like may involve this process by stimulating the expression of StPPO2. • Glutamic acid (Glu) treatment inhibits the activities of PPO, POD and PAL. • Plant hormone and antioxidant enzyme play an important role in fresh-cut potatoes. • Glu treatment severely affects the transcription level during browning in potatoes. • StERF-BR1-like4 mediates the browning of fresh-cut potatoes by regulating StPPO2. [ABSTRACT FROM AUTHOR]

Enzymatic browning occurs rapidly in fresh-cut apples and can lead to economic losses. Although various methods have been developed to prevent this browning, physical methods are costly, and chemical methods are controversial, suggesting the potential usefulness of an endogenous natural browning inhibitor. In this study, the effects of ursolic acid (UA), a natural endogenous compound, on apple browning were investigated. It was found that UA inhibited the activity of polyphenol oxidase through Cu2+ chelation. Molecular docking indicated that the inhibition was reversible and mixed-type. Moreover, UA treatment promoted the scavenging of reactive oxygen species in fresh-cut apple and reduced the proliferation of microorganisms on the apple surface. Similar effects were observed on the browning of chestnut, eggplant, potatoes, and pears. In conclusion, the findings demonstrate the efficacy of UA on inhibiting browning in fresh-cut apple, together with an analysis of the mechanism involved. • A new function of UA, delaying browning of fresh-cut apple, was discovered. • UA treatment inhibits PPO activity and enhances ROS scavenging. • UA reduces breeding of microorganisms in fresh-cut apple surface. • UA has broad-spectrum anti-browning property in fresh-cut vegetables and fruits. [ABSTRACT FROM AUTHOR]