Browning Of Vegetables Research Articles

Effect of intensive pulsed light on the activity, structure, physico-chemical properties and surface topography of polyphenol oxidase from mushroom

The primary aim of this study is to investigate the impact of intensive pulsed light (IPL) on the activity, structure, and physico-chemical properties of polyphenol oxidase. The results showed that the lower the concentration of PPO, the lower the intensity and fluence required inactivating 90% of PPO. With the increase of the IPL fluence, the content of ɑ-helix and β-turn decreased by 57.6% and 22.5%, and the content of β-fold and random curl increased by 58.2% and 69.0%, respectively. The endogenous fluorescence intensity decreases, which proves that IPL effectively inactivates PPO by destroying the secondary and tertiary structure of PPO. Surface hydrophobicity, free sulfhydryl content, aggregation index, and turbidity increased by 191.0%, 24.3%, 23.5%, 151.7%, respectively. The atomic force microscopy (AFM) results showed that the height distribution increased from 3 to 8 nm to 12–16 nm as the fluence increased, and the surface roughness decreased. This research provides a theoretical basis for applying IPL technology in inhibiting endogenous enzyme activity in food and controlling the browning of fruits and vegetables.

Design, synthesis, molecular modeling, and biological evaluation of novel kojic acid derivatives containing bioactive heterocycle moiety as inhibitors of tyrosinase and antibrowning agents

Tyrosinase plays an important role in melanin biosynthesis and enzymatic browning of fresh-cut fruit and vegetables. To discover potent tyrosinase inhibitors and antibrowning agents, a series of novel kojic acid derivatives containing bioactive heterocycle moiety (4a-4l) were designed and synthesized. Thereinto, 4d displayed the most potent tyrosinase inhibitory activity with IC50 of 3.23 ± 0.26 μM and behaved as a competitive inhibitor with a Ki of 1.96 μM, compared to kojic acid (IC50 = 32.23 ± 2.01 μM). Besides, copper-chelating assay, fluorescence spectrum quenching experiment, ANS-binding fluorescence quenching analysis, and molecular modeling studies indicated that 4d may inhibit tyrosinase activity by chelating with copper ions in the active site of tyrosinase. Furthermore, 4d exhibited low cytotoxic activity and significant antibrowning effects.This study suggests that these compounds may serve as lead molecules for developing novel tyrosinase inhibitors and antibrowning agents.

Disaggregating climatic and anthropogenic influences on vegetation changes in Beijing-Tianjin-Hebei region of China

The Beijing-Tianjin-Hebei (BTH) region of China is a typical area where both population and economy have been increasing rapidly in recent decades. The rapid economic development and population increase also bring severe environmental stresses. To better understand the factors that contribute to the regional ecological environment change, this study aims to disaggregate the effects of climate and human activity on vegetation dynamics based on a vegetation index derived from remote sensing for the BTH region through time. First, we implemented a linear regression analysis on the Enhanced Vegetation Index (EVI) in the BTH region from 2001 to 2015. We found vegetation greening mainly occurred in the mountainous area in the north and the west of the BTH region, where the forests and grasslands dominate, and the vegetation browning was mainly distributed in the southeast, where the built-up lands and croplands were located. Then, we used the Random Forest (RF) regression model to rank the importance of the climatic and anthropogenic factors. The results showed that temperature was the most influential factor among our climate variables while land cover dominated the anthropogenic variables. Finally, this study applied the RF model to disaggregate the climatic effects from that of the anthropogenic effects on vegetation dynamics by keeping human-activity- or climate-related variables constant. It showed that the method was capable of quantifying climatic and anthropogenic effects on vegetation changes. This study also found that the N deposition significantly negatively correlated with the vegetation growth trend in BTH. The approach this study proposed advanced our understanding of the driving factors of vegetation dynamics, and the approach is applicable elsewhere.

Physicochemical Characterization and Effect of Thermal Treatments on the Enzymatic Browning Inhibition of Violet Eggplant (Solanum melongena L.) Cultivated in Daloa (Côte d’Ivoire)

Background: The polyphenol oxidase (PPO) responsible for the enzymatic browning of fruits and vegetables, has been involved in the undesirable brown discolouration of food products that resulted in negative effects on colour, taste, and nutritional value. This is a generally undesired process and needs to be prevented in food technology.
 Objective: The present work was carried out to evaluate the effect of chemical and thermal treatments on browning inhibition of eggplant fruit (Solanum melongena L.).
 Materials and Methods: A screening of PPOs activities from eggplant was carried out. The physicochemical characteristics and thermal stability of main PPOs activities were determined in order to develop methods of anti-browning.
 Results: Dopamine oxidase and pyrocatechol oxidase activities were the most active main eggplant fruit PPO activities. Maximal PPO activity was found at 30°C, pH 7.0 for dopamine and 25°C, pH 6.6 for pyrocatechol. The enzymes were stable and retained almost all of their catalytic activity at their optimum temperature (30 and 25°C) for 120 min and their pH stability was in the range of 5.0 - 7.0. Polyphenol oxidases (dopamine oxidase and pyrocatechol oxidase) remained their full activity in the presence of ion Na+, Cu2+, Pb2+ (1 mM) but were inhibited strongly by the ion Fe2+ and Pb2+ (5 mM). On the other hand, the ion K+, Ba2+ and chemical agents, EDTA, citric acid have virtually no effect on dopamine oxidase and pyrocatechol oxidase activities. Energy for inactivation (Ea) obtained using dopamine and pyrocatechol were 30.8 kJ/mol and 7.1 kJ/mol from respective substrates.
 Conclusion: Ascorbic acid was a better inhibitor where 82.32% of PPOs inhibition was achieved. At 65°C, their D-values ranged from 44.72 to 72.72 min. Hence, heat treatment at 65°C for 30 min reduced browning of eggplant fruit. These data regarding the properties of PPO should enhance understanding of the browning reaction in eggplant and lead to the development of techniques for controlling this undesirable process.

In silico investigation and assessment of plausible novel tyrosinase inhibitory peptides from sesame seeds

Tyrosinase, the copper containing enzyme is responsible for undesirable browning in various fungi, fruits and vegetables during their post-harvest storage and processing. Currently available tyrosinase inhibitors have limitations leading to their restricted applications in the food sector. There is an indispensable need for unravelling new, natural, efficient and non-toxic inhibitors to address enzymatic browning. This study, hence focussed on the identification of bioactive peptides from sesame seed proteins for inhibition of tyrosinase activity using in silico methodologies. Proteins, 11S Globulin and 2S Albumin were chosen for proteolytic digestion using the BIOPEP tool. Eight peptides, namely AH, ECA, EL, IR, LK, RHF, VY and WDR with antioxidant potential were obtained. Based on molecular docking analysis, the peptide inhibitors were found to have higher binding affinities to mushroom tyrosinase in comparison to kojic acid and inhibited the enzyme by chelating the copper ions at the active site. The peptides IR, LK and VY were found to be the most effective inhibitors and were non-toxic as well as non-carcinogenic according to toxicity analysis. The findings of this study indicate that the small peptides obtained from sesame seeds hold promise as novel and safe tyrosinase inhibitors to mitigate post-harvest losses in the food industry.

Antityrosinase Mechanism and Antimelanogenic Effect of Arbutin Esters Synthesis Catalyzed by Whole-Cell Biocatalyst.

Tyrosinase is a key enzyme responsible for enzymatic browning of fruits and vegetables and skin disorders due to overproduction of melanin. Arbutin is an inhibitor of tyrosinase; however, its high polarity and weak transdermal absorption capacity limit its applications. In this paper, a green solvent system was developed to successfully synthesize arbutin esters with improved liposolubilities (Clog P values = 0.27-5.03). Among the obtained esters, arbutin undecenoate (AU) showed the strongest tyrosinase-inhibiting activity (15.6%), which was 9.0 times higher than that of arbutin. An enzyme kinetics study indicated that AU was a competitive inhibitor with reversible inhibition. The esters inhibited tyrosinase by making the secondary structure of tyrosinase looser and less stable; moreover, the interactions between tyrosinase and AU driven by metal interactions and hydrogen bonds also offered a mechanism for inhibition of AU on tyrosinase. In addition, AU (100 μM) reduced the melanin content of B16 mouse melanoma cells to 61.3% of the control group.

Recent Advancement in Fluorescent Probes for Sensing and Imaging Tyrosinase Activity in Living Cells

Tyrosinase, a multi-copper oxidase enzyme, is widely distributed in different organisms and plays a vital role in the melanogenesis and enzymatic browning in fruits and vegetables. An abnormal level of tyrosinase in the living system is often associated with different kinds of skin diseases including albinism, vitiligo, skin hyperpigmentation etc. Moreover, overexpressed tyrosinase has become a prognostic biomarker for melanoma. Therefore early detection of tyrosinase activity both in vivo and in vitro has a potential diagnostic and therapeutic application. Small-molecule fluorescent probes have become a powerful device over the traditional biochemical method for the detection and imaging of enzymatic activities in biological systems by virtue of their superior sensitivity, nondestructive fast analysis, spatiotemporal resolution and real-time detection abilities. Moreover, due to their structural tunability, several small-molecule fluorescent probes have been developed to meet various aspects such as enhancing sensitivity, selectivity, cell permeability, real-time monitoring and easy imaging in biological systems. This review article sums up the recent progress of small-molecules fluorescent probes for tyrosinase activity, including their synthesis strategies, mechanistic paths and potential applications based on reports mainly in the past five years. The rapid advancement in this field suggests that fluorescence detection and imaging is a promising technology and widen up new horizons for early diagnosis of melanoma.

Intensified Drought Enhances Coupling Between Vegetation Growth and Pregrowing Season Precipitation in the Drylands of the Silk Road Economic Belt

AbstractDryland ecosystems cover approximately 40% of terrestrial land surfaces and form a major component of global biogeochemical cycles, which are sensitive and vulnerable to climate change. Rapid climate change observably threatens vegetation growth and profoundly affects the global carbon cycle. However, interannual variations in vegetation growth, and changes in coupling between vegetation growth and precipitation in response to drought are not fully understood in the dryland ecosystems of the Silk Road Economic Belt (SREB). By combining remote sensing normalized vegetation indexes from GIMMS (GIMMS NDVI), simulated net primary productivity levels from TRENDYv2 (TRENDY NPP), terrestrial water storage change data (△TWS) derived from GRACE, and climate grid datasets, we investigated climate change, vegetation growth and nonlinear changes in coupling between vegetation growth and precipitation in the pregrowing and current seasons during 1982–2015. The results show intensified drought and extensive vegetation browning in all seasons, especially the summer, across the drylands of the SREB from 1993 to 2015. Precipitation in the pregrowing season significantly contributed to vegetation growth in the subsequent spring and summer, showing that the effects of precipitation in the pregrowing season on subsequent vegetation growth lags by almost two seasons. We also found that intensified drought significantly strengthened the coupling between vegetation growth and precipitation in the pregrowing and current seasons. These results highlight the nonlinear response of vegetation growth to intensified drought, and can be referenced to improve the coupling of land‐atmospheric models for drylands.

Complex anthropogenic interaction on vegetation greening in the Chinese Loess Plateau.

Vegetation greening steered by land use management in the Chinese Loess Plateau has been widely reported, however studies that quantitatively assessing and explicitly linking the anthropogenic forcing on vegetation greening and browning are scarce. Here in this study, we calculate the increment and rate of change of fractional vegetation cover (FVC) from 1998 to 2018 in the Loess Plateau, and compare the results with changing rainfall, soil types, and Gross Domestic Product (GDP), to detail a systematic assessment of the role of the climate-vegetation-human nexus. We have observed that nearly 80% of the study area has undergone greening, and noticed that rainfall was not the main driver of rapid vegetation change, instead of human land use management such as, irrigation along the Yellow River, snowmelt-runoff irrigation, and irrigation from reservoirs formed by check dams contributed the most for the increased FVC in the Chinese Loess Plateau. Concurrently, rapid vegetation browning is almost fully driven by urban expansion. Our findings show that GDP growth promotes both browning and greening, indicative of sustainable development in the Loess plateau region. These contrasting trends reveal that the relationship between human activities and greening is very complex.

In vitro anti-melanogenic effects of chimeric compounds, 2-(substituted benzylidene)-1,3-indanedione derivatives with a β-phenyl-α, β -unsaturated dicarbonyl scaffold

Tyrosinase is considered a key contributor to melanogenesis, and safe, potent tyrosinase inhibitors are needed for medical and cosmetic purposes to treat skin hyperpigmentation and prevent fruit and vegetable browning. According to our accumulated SAR data on tyrosinase inhibitors, the β-phenyl-α,β-unsaturated carbonyl scaffold in either E or Z configurations, can confer potent tyrosinase inhibitory activity. In this study, twelve indanedione derivatives were synthesized as chimeric compounds with a β-phenyl-α,β-unsaturated dicarbonyl scaffold. Two of these derivatives, that is, compounds 2 and 3 (85% and 96% inhibition, respectively), at 50 μM inhibited mushroom tyrosinase markedly more potently than kojic acid (49% inhibition). Docking studies predicted that compounds 2 and 3 both inhibited tyrosinase competitively, and these findings were supported by Lineweaver-Burk plots. In addition, both compounds inhibited tyrosinase activity and reduced melanin contents in B16F10 cells more than kojic acid without perceptible cytotoxicity. These results support the notion that chimeric compounds with the β-phenyl-α,β-unsaturated dicarbonyl scaffold represent promising starting points for the development of potent tyrosinase inhibitors.

Reduction of enzymatic browning of fresh-cut Chinese yam (Dioscorea opposita) by UV-C treatment

Herein, we studied the effect of UV-C (shortwave ultraviolet) irradiation on the quality and inhibition of the browning of fresh-cut Chinese yam (Dioscorea opposita). The irradiation of 0, 4, 8, 12, and 24 kJ m-2 were applied to fresh-cut Chinese yam, and quality characteristics were evaluated during 16 days of storage at 4°C. The results indicated that UV-C treatment (8 KJ m-2) effectively decreased the browning degree, polyphenol oxidase (PPO) and peroxidase (POD) activities, and total bacteria count (TBC). However, the phenylalanine ammonia lyase (PAL) activity, PAL gene expression, respiration rate, and total phenol content increased. The UV-C treatment of 8 kJ m-2 resulted in a lower degree of membrane damage, as evidenced by the lower soluble quinone accumulation and browning index (BI), and retained the soluble solid content and hardness during storage. Increasing irradiation intensity would enhance cell damage while did not reduce browning. The results also showed that UV-C treatment alone had great potential to inhibit the browning of fresh-cut vegetables.

Bioevaluation and molecular docking analysis of novel phenylpropanoid derivatives as potent food preservative and anti-microbials.

The online version contains supplementary material available at 10.1007/s13205-020-02636-0.

Purification and biochemical characterization of polyphenol oxidase from seeds of melon (Citrullus colocynthis)

Polyphenol oxidase (PPO) is an enzyme that is responsible for the enzymatic browning of fruits and vegetables. This is generally undesired process and need to be prevented in food technology. PPO from seeds of Citrullus colocynthis was purified, the physicochemical properties such as effects of pH and temperature, substrate specificity, effects of inhibitors and cations on PPO activity and the kinetic parameters for four substrates namely, catechol, L-DOPA, gallic acid and tyrosine, were determined. The purification steps resulted in 41-fold with 10 % yield, and the optima pH and temperature values for PPO from C. colocynthis were found to be pH 7.0 and 60 °C, respectively using catechol as substrate. About 9 % enzyme initial activity was retained after 60 min of incubation at 80 °C, and the apparent molecular weight was determined as 42 kDa by partially denaturing SDS-PAGE. PPO activity was inhibited by ascorbic acid, SDS and certain divalent (Ca2+, Zn2+, Mg2+ and, Fe2+) and monovalent (Na+) metal. Moreover, purified enzyme solution showed diphenolase activity toward catechol, gallic acid, L-DOPA and monophenolase activity toward tyrosine, therefore, tyrosinase was identified as the only one PPO in C. colocynthis seeds. This study revealed the use of temperature above 80 °C to inhibit PPO activity during processing and storage of melon seeds.

Novel postharvest intervention using rice bran wax edible coating for shelf‐life enhancement of Solanum lycopersicum fruit

The edible coating is considered as one of the most-effective and safer ways to prolong the shelf-stability of the horticultural crops. Utilization of rice bran wax (RBW) as a coating substrate can be an excellent shelf-life extension strategy by transforming secondary by-product from rice processing into a useful coating substrate. This research was an attempt to use RBW as an edible coating and its effects on the shelf-life extension of Marutham CO3 variety tomatoes. Crude RBW refined in laboratory-scale was undergone for free fatty acid profile analysis and found that contains 18 health-beneficial free fatty acids. RBW was made into an emulsion with different concentrations used for coating the tomatoes. Physiological loss weight, lycopene content, TSS, firmness, respiration rate, SEM structure, and thickness of the coatings were analyzed and observed that 10% emulsion coated tomatoes had shown a shelf-life of 27 days, compared to 18 days of the control samples. Practical applications The concept of edible coating is one of the current global research trends that involve in the formulation of primary packaging material for food products that can be ingested safely along with the food. It is a cost-effective and sustainable solution to reduce the environmental pollution caused by conventional polymer packaging solutions. Rice bran wax is a secondary by-product separated from the rice bran oil during refining. It has good applicability in the formation of lipid-based edible coatings, after refining and removal of crude resinous matter. It is a hydrophobic substance and avoids moisture loss from the product during storage. Due to its water repellency, it also avoids microbial infestation. It can be beneficially used for horticultural crops, owing to their low shelf life due to high moisture content and metabolic activity. The rice bran wax-based coating can also delay the ripening process by modifying the immediate environment of the product. This coating can be used for high valued horticultural produce that tends to ripen or shrivel sooner. It can also be used as an obstruction against enzymatic browning in cut fruits and vegetables and for minimally processed and packaged foods. Rice bran wax-based edible coating can be used for shelf-life extension of horticultural produce and also for milk (e.g., Cheese) and meat (e.g., Cut meat) products.

Inhibitory effect of Malaysian coastal plants on banana (Musa acuminata colla "Lakatan"), ginger (Zingiber officinale Roscoe) and sweet potato (Ipomoea batatas) polyphenol oxidase.

Undesired browning reaction catalyzed by polyphenol oxidase (PPO) has reduced the nutritional quality and customer acceptance of the products. The inhibitory effects of six coastal plants including Sonneratia alba, Rhizophora apiculata, Syzygium grande, Rhizophora mucronata, Hibiscus tiliaceus and Bruguiera gymnorhiza on PPO in banana, sweet potato and ginger were studied based on oxidation of pyrocatechol. Banana exhibited the highest PPO activity (141,600 U), followed by sweet potato (43,440 U) and ginger (26,880 U). Banana PPO was strongly inhibited by R. apiculata (70.87%) and sweet potato PPO was strongly inhibited by S. alba (82.00%). In general, most banana PPO was the most susceptible to inhibition with all inhibitors having inhibition higher than 60.00% at 0.5mg/ml and ginger PPO was the least susceptible with all inhibitors showing less than 50.00% inhibition at 0.5mg/ml. Coastal plant extracts are potentially to be developed as natural inhibitors for preventing enzymatic browning of fruits and vegetables.

Purification, kinetic parameters, and isoforms of polyphenol oxidase from “Xushu 22” sweet potato skin

We purified and compared the polyphenol oxidase (PPO) isoenzymes present in "Xushu 22," a sweet potato. A membrane-bound form (mPPO) and two soluble forms (sPPO1 and sPPO2) were identified and purified using ammonium sulphate precipitation, ion exchange chromatography, gel filtration chromatography, and mass spectrometer. The three PPO isoforms were characterized enzymatically. The specific activity of mPPO was significantly higher than that of the two sPPO isoforms, being 24.55- and 13.89-fold higher than sPPO1 and sPPO2. The preferred substrates for mPPO and the two sPPOs were catechol and chlorogenic acid, respectively. They can be efficiently and safely applied to phenolic wastewater treatment after being immobilized. Both mPPO and the two sPPOs were rapidly inactivated under acid or base conditions and were unstable at 65°C. The most effective inhibitors of mPPO, sPPO1, and sPPO2 were glutathione, ascorbic acid, and L-cysteine, respectively. PRACTICAL APPLICATIONS: According to incomplete statistics, about 5% of sweet potatoes in china are wasted due to enzymatic browning every year. PPO was regarded as a key molecule contributing to enzymatic browning in fruits and vegetables during ripening, processing, and storage and responsible for economic and industrial loss. It's great importance to characterize the PPO from "Xushu 22" sweet potato and provide data on its inactivation. The three PPO isoforms were purified and identified by chromatography and mass spectrometer. This study will provide useful informations to have a better command of PPO from "Xushu 22" sweet potato and give ideals to solve the browning of sweet potato.

Comparison of the biochemical properties and thermal inactivation of polyphenol oxidase from three lily bulb cultivars.

The biochemical properties and thermal inactivation of polyphenol oxidase (PPO) from three main planted lily cultivars in China, namely, Lilium lancifolium Thunb, Lilium brownie var. viridulum, and Lilium davidii var. unicolor cotton were evaluated. Data indicate that the PPO from three cultivars showed two optimum pH levels of 4.0 and 6.5-7.0 and temperature of 15°C and exhibited the highest affinity toward 4-methylcatechol. However, this enzyme did not exhibit monophenolase activity. Thiourea and L-cysteine were more effective than other inhibitors. The enzymatic activity of L. lancifolium Thunb PPO crude extract was higher than that of L. brownie var. viridulum and L. davidii var. unicolor cotton. For thermal inactivation, L. davidii var. unicolor cotton PPO showed the best thermal resistance at 65-75°C, and L. lancifolium Thunb showed stability at 45°C. The deactivation of the three types of PPO followed the first-order reaction kinetics, and the activation energy (Ea) was 144.28, 138.00, and 107.12kJ/mol for L. lancifolium Thunb PPO, L. brownie var. viridulum PPO, and L. davidii var. unicolor cotton PPO, respectively. PRACTICAL APPLICATIONS: Lilium is an ornamental and edible plant typically used for food and traditional Chinese medicine. Its flowers are used for decoration, and its underground bulbs are rich in various bioactive substances. Fresh lily bulbs easily turn brown and lose economic value during storage and processing. Polyphenol oxidase (PPO) is a crucial molecule involved in the enzymatic browning of fruit and vegetables. In this study, PPO was extracted from three main planted lily cultivars in China. Namely, Lilium lancifolium Thunb, Lilium brownie var. viridulum, Lilium davidii var. unicolor cotton and was partially characterized. The results are of considerable importance to further understand the PPO of lily bulbs and provide guidance for the inactivation of enzymes and the processing of lily bulb juice.

Biological evaluation of Keggin-type polyoxometalates on tyrosinase: Kinetics and molecular modeling.

Abnormal overexpression of tyrosinase activity can lead to the production of hyperpigmentation in human skin and enzymatic browning in fruits and vegetables. Herein, the inhibition and mechanism of the H3 PMo12 O40 and two transition metal-substituted Keggin-type polyoxometalates (Na7 PMo11 CoO40 and Na7 PMo11 ZnO40 ) on tyrosinase were studied by kinetics and molecular modeling. Kinetic studies indicated that all compounds had more potent inhibitory activities than standard arbutin, and H3 PMo12 O40 (IC50 =0.443±0.006mm) is ~15-fold stronger inhibition than arbutin. Additionally, all compounds inhibited tyrosinase in a reversible competitive manner. Intriguingly, molecular modeling elucidated that three compounds competitively bind to tyrosinase mainly through more interactions with Cu2+ ions and the amino acid residue capable of forming cation-π and hydrogen bonding, forming a reversible non-covalent complex. Molecular simulation study correlated well with the biological activity of three compounds in vitro. This work provided new insights into design and synthesis of polyoxometalates as tyrosinase inhibitors in the field of medicine, cosmetic, and food.

A Series of Benzylidenes Linked to Hydrazine-1-carbothioamide as Tyrosinase Inhibitors: Synthesis, Biological Evaluation and Structure-Activity Relationship.

Tyrosinase is a type 3 copper enzyme responsible for skin pigmentation disorders, skin cancer, and enzymatic browning of vegetables and fruits. In the present article, 12 small molecules of 2-benzylidenehydrazine-1-carbothioamide were designed, synthesized and evaluated for their anti-tyrosinase activities followed by molecular docking and pharmacophore-based screening. Among synthesized thiosemicarbazone derivatives, one compound, (2E)-2-[(4-nitrophenyl)methylidene]hydrazine-1-carbothioamide, is the strongest inhibitor of mushroom tyrosinase with IC50 of 0.05 μM which demonstrated a 128-fold increase in potency compared to the positive control. Kinetic studies also revealed mix type inhibition by this compound. Docking studies confirmed the complete fitting of the synthesized compounds into the tyrosinase active site. The results underline the potential of 2-benzylidenehydrazine-1-carbothioamides as potent pharmacophore to extend the tyrosinase inhibition in drug discovery.

Postharvest application of thiol compounds affects surface browning and antioxidant activity of fresh-cut potatoes.

The aim of this study was to compare the effects of sodium metabisulphite and the thiol compounds, glutathione (GSH), L-cysteine (CYS), and N-acetylcysteine (NAC), on the enzymatic browning, antioxidant activities, total phenolic, and ascorbic acid content of potatoes after 1, 24, and 48hr. Three different concentrations (0.5%, 1.0%, and 2.0%) of each thiol compound were tested. While sulphite solution inhibited polyphenol oxidase as expected, NAC and CYS also decreased its activity. CYS-treated samples exhibited the highest residual thiol content, while the amount of residual thiol in GSH-treated samples was the lowest. The 2.0% NAC and 2.0% CYS solutions were the most effective at increasing antioxidant activity and ascorbic acid content; however, the results of total phenolic content assays were complicated. In summary, solutions containing 2.0% NAC, 1.0% CYS, and 2.0% CYS prevented enzymatic browning and increased the residual thiol content, ascorbic acid, and antioxidant activities of fresh-cut potatoes significantly, but GSH did not significantly inhibit browning. PRACTICAL APPLICATIONS: Fresh-cut potatoes are susceptible to enzymatic browning, which significantly reduces their commercial value. In literature, there have been several methods to protect the enzymatic browning of fruits and vegetables. Among these methods, thiols are good inhibitors of enzymatic browning. So, GSH, CYS, and NAC were used in this study. The outcomes of current work may help to inhibit polyphenol oxidase activity and increase the ascorbic acid content, residual thiol content, and antioxidant activity of fresh-cut potatoes. Both CYS and NAC may be useful alternatives to sulphite anti-browning agents, which may have adverse health effects.