Increase In Polyphenol Oxidase Activity Research Articles

Investigating the impact of active PHBV films on the nutritional quality of minimally processed apples

The aim of the study was to study the effect of an active film, a blend of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with a derivative of ferulic acid known as bis-O-dihydroferuloyl-1,4-butanediol (BDF), on the quality decay kinetic of minimally processed apples. Due to its properties, BDF is a promising candidate to serve both as a non-toxic biobased plasticizer and as an active additive, simplifying formulation of active packaging. Molecular modelling studies were conducted to explore the interaction between polyphenol oxidase (PPO) and BDF molecule, with the aim of understanding the mechanism of inhibition. The apple slices packed in different treatments exhibited an increase in PPO activity; however, the samples packed in active films showed a significantly slower rate of PPO activity (P < 0.05). Almost 50% of the ascorbic acid content degraded in the control samples (4.95–4.97 mg/100 g fruit weight (FW)) at d7 compared with the samples packaged in BDF-releasing films (5.81–6.1 mg/100 g FW) in which the degradation was only 30%. Using molecular modelling, it was observed that BDF (−6.3 kcal/mol) exhibited a stronger interaction with PPO than catechol (−4.5 kcal/mol) in the met and oxy states. BDF-releasing films showed superior preservative potential over the control as BDF competitively inhibits the PPO active site due to π–π stacking between the aromatic cycle of the BDF molecule and the PHE259 and hydrogen bonding with the active site.

60Co γ‐radiation at low‐dose level alters volatile compounds of blueberry during storage

Summary60Co γ‐radiation was applied to blueberry fruits in an effort to investigate a safe, eco‐friendly and effective blueberry preservation technique. However, the preservation effects were variable depending on tissue tolerance to irradiation doses. Moreover, irradiation may cause off‐odour. In this study, we examined the effects of three low doses of 60Co γ‐radiation on the physical and flavour attributes of blueberry. The results showed that 60Co γ‐radiation did not significantly improve fruit quality but extend the shelf life up to 15 days at 25 °C and 30 days at 4 °C. Compared with the control group, the preservation effect of 0.5–1.0 kGy irradiation treatment on blueberry fruit was not obvious before 15 days but maintained 65% of fruit firmness and reduced the loss of nutrients afterwards at 4 °C. At 25 °C, irradiation treatment caused up to a 150% increase in polyphenol oxidase activity, which was relevant to colour changes in late storage. Headspace Gas Chromatography Ion Mobility Spectrometry (HS‐GC‐IMS) was applied, and 33 volatile organic compounds (VOCs) in blueberry treated with different radiation doses were identified, including 11 esters, 8 aldehydes, 7 alcohols, 6 ketones and other substances, which increased with increasing radiation dose. Radiation reduced the green taste of blueberry and promoted their ripening. Radiation above the level of 1.02 kGy led to the flavour deterioration of blueberry such as ethyl trans‐2‐butenoate. The side effects of radiation on the aroma of blueberry could be offset by low‐temperature storage. Blueberry stored at 4 °C contained more aldehydes with a heavier fresh/green aroma. Six aromas were proposed to be characteristic odour markers of radiated blueberry.

Effects of long-term no-tillage and different stover mulching amounts on soil carbon and nitrogen contents and enzyme activities of carbon and nitrogen cycle in Mollisols.

To understand the effects of different stover mulching amounts in no-tillage on soil carbon and nitrogen contents and enzyme activities, finding a stover mulching amount which can meet the requirement of soil carbon and nitrogen accumulation while maximizing economic benefits, we conducted a long-term conservation tillage field experiment since 2007 in Mollisols area of Northeast China. We analyzed soil carbon and nitrogen contents, enzyme activities and economic benefits under conventional tillage (Control, CT), no-tillage without stover mulching (NT0), no-tillage with 33% stover mulching (NT33), no-tillage with 67% stover mulching (NT67), and no-tillage with 100% stover mulching (NT100) before planting in May 2020. The results showed that compared with CT, NT0 did not affect soil organic carbon (SOC) and total nitrogen (TN) contents, but increased soil organic carbon recalcitrance and decreased the availability of dissolved organic nitrogen (DON) and ammonium nitrogen. Compared with NT0, no-tillage with stover mulching significantly increased SOC contents in 0-10 cm layer and increased with the amounts of stover. In addition, NT67 and NT100 significantly increased SOC stocks, facilitating the accumulation of soil organic matter. The effects of different stover mulching amounts on soil nitrogen content in 0-10 cm layer were different. Specifically, NT33 increased DON content and DON/TN, NT67 increased DON content, while NT100 increased TN content. Compared with CT, NT0 decreased peroxidase (POD) activity in 0-10 cm layer. Compared with NT0, NT33 increased β-glucosidase (βG), cellobiase (CB), 1,4-β-N-acetylglucosaminidase (NAG), polyphenol oxidase (PPO) and POD activities, while NT67 only increased CB, NAG and POD activities in 0-10 cm soil layer, both alleviated microbial nutrient limitation. NT100 increased PPO activity in 10-20 cm layer. NT33 increased carbon conversion efficiency of stover compared with NT100, and had the highest economic benefit. In all, no-tillage with 33% stover mulching was the optimal strategy, which could promote nutrient circulation, boost stover utilization efficiency, improve the quality of Mollisols, and maximize guaranteed income.

Different responses of lipids and lignin phenols to nitrogen addition in meadow grassland soil

PurposeNitrogen (N) enrichment can affect the composition and stability of soil organic carbon (SOC) pools by altering vegetation and soil properties. However, the response of plant-derived carbon components in soil to different N addition levels is unclear. We investigated the changes and potential driving processes of plant-derived carbon components (especially lignins and lipids) in meadow grassland soils under long-term N addition in eastern Inner Mongolia, China.Materials and methodsBiomarker technology was utilised to analyse changes in plant-derived carbon components (C>20 free lipids, bound lipids, and lignin phenols) in soil under different N addition levels, including changes in soil chemical properties, enzyme activity, plant biomass, and diversity under N addition, as well as the specific pathways involved.Results and discussionWe found that high levels of N addition significantly reduced the concentration of soil lignin phenols whereas increased the accumulation of lipids (free and bound lipids). Compared with changes in plant biomass and diversity, soil chemical properties and enzyme activity play a more significant role in regulating the accumulation and degradation of plant-derived carbon. Structural equation modelling (SEM) showed that decreases in lignin phenol concentration were related to specific biochemical decomposition processes (increased polyphenol oxidase activity and decreased C/N). The increase in lipids associated with the protective effects of minerals mediated by pH.ConclusionsIn general, plant-derived carbon components showed inconsistent responses to N addition, lignin phenol concentration decreased and lipid concentration increased, which was mainly related to the change of soil biochemical properties. Plant-derived carbon components only showed significant changes under high N addition levels. Furthermore, our research indicates that SOC sequestration and functioning are highly dependent on soil biochemical properties, which weakens the influence of changes in plant carbon input on soil carbon storage.

A Novel Sodium Alginate-Carnauba Wax Film Containing Calcium Ascorbate: Structural Properties and Preservative Effect on Fresh-Cut Apples

In order to improve the mechanical properties, nutritional value and fresh-keeping ability of conventional sodium alginate edible composite membranes, a new type of edible composite film was prepared by adding water-blocking agent carnauba wax, plasticizer glycerin, antioxidant and nutritional enhancer sodium ascorbate on a basis of traditional sodium alginate composite film. In this study, the physical, mechanical and structural properties of different film components were investigated. The results showed the components did not simply combine, but produced interaction forces which improved the stability and mechanical properties of composite film. When the amount of calcium ascorbate was 0.4%, the water vapor transmittance of the composite film reached a minimum of 0.65 g·mm/(cm2·d·kPa), and the tensile strength and elongation at break reached the maximum, which were 398.64 MPa and 17.93%, respectively. Additionally, the sodium alginate-carnauba wax film exhibited better performance on the preservation of fresh-cut apples. Compared with other composite films, the color and hardness of fresh-cut apples coated with this composite film were better maintained, and the losses of titration acid content and soluble solid content were reduced. Moreover, the weight loss rate, increase in polyphenol oxidase activity and total colony count were inhibited. All results determined that the edible film has good application value in the field of fresh-cut fruit preservation, which provides a theoretical basis for further research on edible film.

Characterization of Polyphenol Oxidase (PPO) from Blackberry Thorny Wild Rubus Fruticosus and its Inhibition using Natural Extracts

The Polyphenol oxidase (PPO) leads to the enzymatic browning of fruits and vegetables and needs to be prevented in food browning and quality. The present study aimed to investigate the use of natural extracts and chemical inhibitors to prevent browning of the PPO of blackberries. Purification, characterization, and kinetics of PPO of blackberry parameters for five substrates, namely, pyrocatechol, 4-methylcatechol, Pyrogallol, Gallic acid, and tyrosine, were described. The results showed that the DEAE-Sepharose and Superdex G-200 purification methods, which achieved electrophoretic purity, increased PPO activity by 556 fold. Purification with Sephadex GE-200 and SDS-PAGE reveals two PPO isoenzymes with an apparent molecular weight of 22 kD and 70 kD. The optimum pH and temperature values indicated were 6.6 and 25°C, respectively. The PPO showed variable affinity towards o-dihydroxy phenolic substrates with catecholase activity but without any activity observed with phenol, a monohydroxy substrate, and it was very effective towards pyrocatechol, pyrogallol, and 4-methyl catechol. The results revealed that inhibition of the PPO using both synthetic inhibitors and natural extracts was the most effective method. Quercetin and ascorbic acid showed higher inhibition with the lowest Ki values. Fresh onion (Allium cepa) and wild Arbutus unedo extract were able to inhibit the blackberry PPO activity up to 50% and 60%, respectively. Therefore, the use of natural extracts from Arbutus unedo L as anti-browning agents on the blackberry PPO may provide new insight to overcome the enzymatic browning.

Influence of germicidal ultraviolet radiation UV-C on the quality of Apiaceae spices seeds

BackgroundSpices are susceptible to surface microbial contamination. Countries’ ban on ethylene oxide fumigation due to possible residual toxicity encouraged the usage of irradiation. Surface sterilization with low doses of ultraviolet radiation has been extensively researched as a safe, eco-friendly, and fast route. This study examines the quality of Apiaceae spices for consumption, including anise, fennel, caraway, and cumin, in response to germicidal ultraviolet radiation using a developed sterilization unit.MethodsThe influence of UV-C (254 nm, 10.5 mW/cm2) on the fungal and microbial count, germination percentage, respiration rate, phenolic content, essential oil, and the activity of antioxidant enzymes was investigated at exposure durations of 0–45 min in increments of 5 min. The treated seeds were packed in polyethylene bags in a naturally aerated storage room for 30 days before the inspection.ResultsThe obtained data showed that UV-C stimulated seeds germination and increased respiration rate for all studied types. The 25 min of exposure exhibited the highest significant values compared to the control, considered a good indicator of seed vigor. In addition, UV-C exposure between 20 and 35 min promoted the accumulation of phenolic compounds and increased the oil content as a defense mechanism against radiation. Conversely, higher exposure to UV-C led to a significant reduction in phenolic and oil contents. Furthermore, the exposure to UV-C radiation enhanced the activity of antioxidant enzymes in terms of peroxidase and catalase, which progressively increased with increasing exposure durations, reached their peak at 25–30 min, and subsequently declined with extended exposure time was extended. In a similar pattern, exposure to UV-C radiation increased polyphenol oxidase activity to its highest level at 25 min, owing to the development of antioxidant protective mechanisms against oxidative stress.ConclusionUV-C irradiation in the range of 25–30 min is the most appropriate pretreatment to maintain the vitality of the examined seeds.Graphical

Long-term partial substitution of chemical nitrogen fertilizer with organic fertilizers increased SOC stability by mediating soil C mineralization and enzyme activities in a rubber plantation of Hainan Island, China

The partial substitution of chemical nitrogen (N) fertilizer with organic fertilizers is widely used to maintain soil fertility and enhance crop yield, although its effects on soil organic carbon (SOC) composition, mineralization and stability are not fully understood. For this study, a 12-year field experiment was conducted in a rubber plantation field of Hainan Island, China. Three fertilizer treatments included no fertilizer application as control (CK), chemical fertilizer application (NPK), and half of the chemical N fertilizer plus manure application equivalent to half of chemical N fertilizer (NPKM). We determined the soil physicochemical properties, four labile SOC compositions (microbial biomass carbon (MBC), light fraction organic carbon (LFOC), dissolved organic carbon, dissolved organic carbon extracted by hot water (HOC), particulate organic carbon (POC)), four C-associated soil enzymes (β-1, 4-glucosidase (BG), polyphenol oxidase (POX), catalase (CAT) and cellulase), and SOC mineralization (from a 46-day aerobic incubation experiment) in two soil layers (topsoil layer (0–10 cm) and subsoil layer (10–20 cm)). Compared with NPK, NPKM significantly increased soil pH, total nitrogen, total phosphorus, available phosphorus and potassium, NH4+-N, and NO3−-N contents, and SOC, LFOC, POC, HOC, and MBC concentrations. NPKM had higher cumulative CO2 production but lower SOC mineralization potential (Cp) than NPK, although the difference was not significant. In both soil layers, NPKM significantly increased POX activity, but decreased BG and CAT activities. Soil pH can regulate enzyme activities and synthesis in acidic soil in a tropical region with a significantly positive correlation with POX activity. Compared with NPK, the relatively lower Cp/SOC and higher carbon quality index (CQI) indicated higher SOC stability (Cp/SOC) in NPKM. The redundancy analysis results revealed that the dominant factors affecting SOC stability were NH4+-N, pH, POC and MBC in NPK, and available phosphorus, BG, and pH in NPKM. In the three fertilization treatments, the POX was the dominant factor affecting the CQI. Conclusively, half of the chemical N fertilizer plus half of the manure application could facilitate SOC stability by mediating soil C mineralization and enzyme activities in the rubber plantation of Hainan Island, China.

Effect of Prolonged Cold Storage on the Dynamics of the Enzymatic and Non-Enzymatic Antioxidant System in the Mesocarp of Avocado (Persea americana) cv. Hass: Relationship with Oxidative Processes

This work evaluated the enzymatic and non-enzymatic antioxidant defense systems of avocados cv. Hass stored at 7 ± 0.5 °C for 10, 20, and 30 d, and at the stage of edible ripeness. The enzymatic antioxidant enzyme system included superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and the non-enzymatic antioxidant system was composed of total phenolic compounds (TPC), total carotenoids (TC), α-, β-, and γ-tocopherols, as well as hydrophilic (H-AOX) and lipophilic (L-AOX) antioxidant activities. In addition, polyphenol oxidase (PPO) and lipoxygenase (LOX) activities, TBARS values and pulp browning area were determined. At edible ripeness, low SOD and POD but higher CAT activities were evidenced in response to their joint participation in the oxidative stress developed. In addition, low content of γ-tocopherol and higher contents of TPC and TC were evidenced and suggest their individual or joint participation in defense against oxidation. The other compounds and activities evaluated tended to remain constant. Oxidative damage was evidenced by the increase in PPO activity and TBARS values, while LOX did not play a significant role. Pulp browning area did not surpass 6% in affected fruit. The results indicate that under these conditions oxidative stress was largely restrained by the endogenous fruit antioxidant defense system.

Comparison of the Effect of Hydrostatic and Dynamic High Pressure Processing on the Enzymatic Activity and Physicochemical Quality Attributes of 'Ataulfo' Mango Nectar.

The effects of hydrostatic (HHP) and dynamic (HPH) high-pressure treatments on the activity of pectin methylesterase (PME) and polyphenol oxidase (PPO) as well as the physicochemical quality attributes of ‘Ataulfo’ mango nectar were assessed. HHP reduced PME relative activity by 28% at 100 MPa for 5 min but increased PPO activity almost five-fold. Contrarily, HPH did not affect PME activity, but PPO was effectively reduced to 10% of residual activity at 300 MPa and at three passes. Color parameters (CIEL*a*b*), °hue, and chroma were differently affected by each type of high-pressure processing technology. The viscosity and fluid behavior were not affected by HHP, however, HPH changed the apparent viscosity at low dynamic pressure levels (100 MPa with one and three passes). The viscosity decreased at high shear rates in nectar samples, showing a shear-thinning effect. The results highlight how different effects can be achieved with each high-pressure technology; thus, selecting the most appropriate system for processing and preserving liquid foods like fruit beverages is recommended.

Kinetic analysis of PGA/PBAT plastic films for strawberry fruit preservation quality and enzyme activity

The strawberry fruit is delicious and sweet; it is very popular among consumers. However, its high water content makes it susceptible to mechanical injury and microbial infestation, leading to spoilage and deterioration. Therefore, proper post-harvest preservation methods play an important role in enhancing its economic value. We conducted a scientific analysis on the influence of different films packaging on strawberry fruit quality, to provide a technical basis and theoretical support for the storage and preservation of strawberries during the post-harvest shelf life and the industrial production of environmentally friendly plastic films. A twin-screw extruder and films blowing machine were used to prepare polyglycolic acid (PGA)/polybutylene adipate (PBAT) biodegradable composite membranes. The effect of composite films on the fresh-keeping quality of strawberry was studied. We observed that the 80 % PGA/20 % PBAT group could effectively inhibit the increase in polyphenol oxidase activity and H2O2 content; delay the decrease in superoxide dismutase, catalase, and ascorbate peroxidase activities, total phenol, total flavonoid, soluble solid contents and sensory scores. Additionally, PGA group could delay POD activity and pH decrease. Thus, biodegradable plastic films with a high PGA content are highly conducive to strawberry preservation, especially the 80 % PGA/20 % PBAT plastic films.

Transcriptional, secondary metabolic, and antioxidative investigations elucidate the rapid response mechanism of Pontederia cordata to cadmium

Pontederia cordata is previously demonstrated a cadmium (Cd) tolerant plant, and also a candidate for the phytoremediation of heavy-metal-contaminated wetlands. A hydroponic experiment was used to investigate variations in photosynthetic gas exchange parameters, antioxidative activities, chlorophyll and secondary metabolite contents, and transcriptome in leaves of the plant exposed to 0.44 mM Cd2+ for 0 h, 24 h, and 48 h. Under Cd2+ exposure for 24 h, the plant presented a favorable photosynthesis by maintaining relatively higher antioxidant activity. Cd2+ exposure for 48 h accelerated membrane peroxidation, declined photosynthetic pigment content, and increased polyphenol oxidase activity, thus interfering with photosynthesis. The phenylpropane pathway served as a chemical rather than physical defense against Cd2+ in the plant leaves. A total of 20,998, 4743, and 4413 differentially expressed genes (DEGs) were identified in the groups of 0 h vs 24 h, 0 h vs 48 h, and 24 h vs 48 h, respectively. The primary metabolic pathways of the DEGs were mainly enriched in nitrogen metabolism, starch and sucrose metabolism, fructose and mannose metabolism, as well as pentose-phosphate pathway, contributing to a stable cell structure and function. Flavonoid biosynthesis directly or indirectly played an antioxidative role against Cd2+ in the leaves. Forty-nine transcription factor (TF) families were identified, and 8 TF families were shared among the three groups. The present study provides a theoretical foundation for investigating tolerance mechanisms of wetland plants to Cd stress in terms of secondary metabolism and transcriptional regulation.

Elevated CO2 exposure induces core browning in Yali pears by inhibiting the electron transport chain

Pears may be affected by core browning during storage, reducing their commercial value. The effect of CO2 stress on the core browning process in Yali pears was investigated. Exposure to a 4% CO2 atmosphere significantly increased the core browning and reduced titratable acidity and soluble solids content. The activity of succinate dehydrogenase and peroxidase was reduced in CO2-stressed pears, whereas the levels of H2O2 and malondialdehyde were increased. Transmission electron microscopy revealed significant damage to cellular membrane structure in the core tissues of CO2-stressed pears. In addition, CO2-stressed pears showed increased polyphenol oxidase activity. These results suggest that high concentrations of carbon dioxide can accelerate core browning in pears by inhibiting the activities of enzymes in the electron transport chain, resulting in increased levels of free radicals that damage cellular membranes.

Lachancea thermotolerans acts as a resistance inducer in soybean infected with Meloidogyne incognita

The worldwide interest in sustainable agriculture has contributed to the development of alternative methods for the control of plant pests and diseases. This study aimed to assess the efficiency of Lachancea thermotolerans CCMA 0763 and its metabolites in controlling Meloidogyne incognita in soybean and their effects on plant defense enzymes and glyceollin synthesis. The following treatments were applied as foliar spray 4 days before nematode inoculation: fermentation broth, broth filtrate, yeast cells, sugarcane juice, acibenzolar-S-methyl (ASM). An inoculated untreated control and an absolute control were also included. The same treatments were used in the glyceollin assay. For analysis of resistance induction, the treatments were fermentation broth, broth filtrate, yeast cells, ASM, and water (control). Fermentation broth and yeast cells reduced total nematode number, population density and reproduction factor. Yeast-based treatments and ASM enhanced glyceollin synthesis compared with sugarcane juice and water. Peroxidase activity was highest at 4 and 10 days after treatment in plants treated with yeast-based treatmentss. Broth filtrate and yeast cells increased polyphenol oxidase activity at 4 days after treatment. Phenylalanine ammonia-lyase and glucanase activities were not influenced by treatment. L. thermotolerans stimulated phytoalexin synthesis in soybean cotyledons and defense enzyme activity in soybean roots, showing potential as a biopesticide.

Biochemical characteristics of urban maple trees.

The study, which covers the period between 2014 and 2018, was carried out in the city of Naberezhnye Chelny, Republic of Tatarstan, Russia. The aim of the study was to examine the biochemical response of maple trees growing in the anthropogenic environments. Leaf samples from 600 trees (Acer platanoides L. and Acer negundo L.) were collected at monthly intervals from June through August. Sampling was performed early in the morning (11 a.m.) in the middle of the month. The study offers statistical data on the tannin content, determined via permanganometry; the ascorbic acid concentration, found via titration with 2.6-dichlorophenolindophenol; the ascorbate oxidase activity determined by absorbance at 265 nm; and the polyphenol oxidase activity, found by the spectrophotometric method. Relatively higher ascorbate oxidase activity was detected in August among ash-leaved Acer platanoides L. and Acer negundo L. in areas with strong anthropogenic impact. Due to increased air pollution, maple trees were found to exhibit an increase of polyphenol oxidase activities. The condensed tannin content in Norway maple trees dropped over time: by 1.24 in July (avenue); by 0.94 (buffer area) and 0.76 (avenue) in August. The condensed tannin content in the ash-leaved maple trees also decreased: by 0.69 (buffer area) and 0.22 (avenue) in July; by 0.37 (buffer area) and 0.61(avenue) in August.

Long-Term Effect of Heavy Metal–Polluted Wastewater Irrigation on Physiological and Ecological Parameters of Salicornia europaea L.

Irrigation of Salicornia europaea with heavy metal–polluted wastewater is a promising alternative method for risk mitigation of the Urmia Lake ecosystem from uncontrolled sewage. The objective of the study was to evaluate morphological and physicochemical responses of Salicornia europaea under wastewater irrigation at different growth stages. A field experiment was conducted in a split-plot experiment based on randomized complete block design with four replications. Treatments included control and wastewater irrigation (containing zinc (Zn), iron (Fe), copper (Cu), cadmium (Cd), lead (Pb), and nickel (Ni)) at three stages (vegetative, flowering, and reproductive) of plant growth and two times (two and 4 days in each stage). The result showed that the wastewater application at reproductive stage resulted in higher biomass production than that of the control plants. Wastewater irrigation at the flowering stage caused a significant increase in the amount of total chlorophyll and chlorophyll-a, while chlorophyll-b content was decreased at both flowering and reproductive stages. The amount of the total soluble protein was also affected, with wastewater irrigation showing the most significant increase at the reproductive stage. There was significant enhancement of osmolytes in leaves of plant under heavy metal stress, and the increased rate of proline was higher than soluble sugar at the flowering stage. Relative water content in Salicornia was not duration- and time-dependent. A 154% increase in catalase activity, 32% increase in peroxidase activity, and 57% increase in polyphenol oxidase activity were observed in the plant exposed to long-term wastewater duration. Based on the observed positive effect of wastewater on shoot length and weight, total soluble protein, proline, soluble sugar, enzyme activities, and plant biomass of Salicornia europaea, long-term effect of heavy metal–polluted wastewater irrigation can be approved for Salicornia crops in coastal areas.

Effects of simultaneous ultrasonic and cysteine treatment on antibrowning and physicochemical quality of fresh-cut lotus roots during cold storage

Abstract The effects of ultrasound (US) power of 200 w at a constant frequency of 40 kHz for 2 min, 0.01 % cysteine (Cys) and combinative application of US and Cys (US + Cys) on browning prevention and quality of lotus root slices were compared during storage at 4 °C for 12 d. The visual appearance, colour attributes including L*, b*, hue, chroma, whiteness index (WI), browning index (BI) and colour difference (ΔE*), browning enzymes activities such as polyphenol oxidase (PPO) and peroxidase (POD), total phenols concentration, texture, total sugars concentration and antioxidant activities were evaluated. US + Cys retarded browning incidence being greater than Cys, US and control treatments, respectively. The browning retardation was concomitant with the retention of high L* and WI values and low b*, chroma, BI and ΔE* value. Cys and US + Cys controlled the increased PPO activity rather than US. All treatments delayed the increased total phenols concentration compared to control. All treatments maintained hardness of lotus root slices, especially US, and did not affect total sugars concentration. Both sonication treatment enhanced ferric reducing antioxidant potential (FRAP) whilst free radical scavenging activity was enhanced by Cys. In conclusion, both of the Cys and US could prevent browning and maintain physicochemical quality of lotus root slices and the simultaneous US and Cys treatment exhibited synergistic antibrowning effect.

Physiological and Biochemical Aspects of Frost Resistance in Оlea europaea L.

The results of studies on the frost resistance of Olea europaea L. varieties and its subspecies O. europaea subsp. cuspidata (Wall. and G. Don) Cif. under the conditions of the Southern Coast of Crimea (SCC), as well as the influence of temperature close to the absolute minimum value (–15°С) on the state of the photosynthetic apparatus, catalase activity, polyphenol oxidase, and the content of proline and phenolic compounds, are shown. It was established that a relatively high frost resistance is characteristic of the Nikitskaya variety under the conditions of the SCC. Varieties Ascoliano, Coregiolo, and Razzo turned out to be slightly frost-resistant. Minimum resistance was detected in the subspecies O. europaea subsp. cuspidata. The temperature of –15°C led to irreversible disruptions in the photosynthetic apparatus of weak varieties Razzo, Coregiolo and O. europaea subsp. cuspidata, which manifested in a significant decrease in photosynthetic activity immediately after the end of low-temperature exposure (by 80.19, 50.0, and 89.78%, respectively) as well as a fluorescence decay coefficient below the vital norm. After 24 h, a slowdown in the decrease in the parameters of chlorophyll fluorescence induction (CFI) was noted in the Ascoliano and Nikitskaya varieties. It was revealed that negative temperatures contribute to a decrease in the activity of catalase in weakly resistant O. europaea genotypes (by 40–60% on average) in contrast to the frost-resistant variety Nikitskaya, in which the activity of this enzyme remained almost unchanged. The change in polyphenol oxidase activity was multidirectional. In the Razzo and Coregiolo varieties, an increase in polyphenol oxidase activity was noted (19 and 24%, respectively). A decrease (by 8 and 37%, respectively) was noted in the subspecies O. europaea subsp. cuspidata and Nikitskaya variety. It was shown that, under the influence of negative temperatures, representatives of O. europaea decrease proline concentration in leaf tissues (by 17–55%). The most significant changes were detected in the variety Coregiolo (by 45.09%). The total content of phenolic compounds decreased in all weakly frost-resistant varieties and O. europaea subsp. cuspidata by 7–42% and remained unchanged in the frost-resistant variety Nikitskaya. It has been established that negative temperatures cause irreversible changes in the photosynthetic apparatus in weakly resistant representatives of O. europaea. The correlation of the degree of frost resistance of the studied genotypes with the activity of catalase and with the content of proline and phenolic compounds in leaf tissues was revealed.

Physicochemical changes in the discoloration of dried green tea noodles caused by polyphenol oxidase from wheat flour

The color of dried green tea noodles (DGTN) is a crucial determinant of consumer acceptance. Although polyphenol oxidase (PPO) is a key factor inducing the darkening of noodles, its contributions on the discoloration mechanism of DGTN requires clarification. Results revealed that PPO induced the decreased of lightness L value and greenness |a| value via its effects on polyphenol compounds and chlorophyll during the processing of DGTN. The increase of PPO activity significantly accelerated the discoloration rate and the degradation of chlorophyll during storage of the DGTN. Correlation analysis found that the changes of chlorophyll among DGTN made from different PPO activities of wheat flour played a major role in the discoloration. These findings indicated that the control of the negative effects of PPO on polyphenol compounds and chlorophyll could be an effective method to retard discoloration in DGTN.

Aspartic Acid Can Effectively Prevent the Enzymatic Browning of Potato by Regulating the Generation and Transformation of Brown Product

Abstract Enzymatic browning is a crucial factor affecting the quality of fresh-cut potatoes. In this study, the effects of aspartic acid (Asp) on browning, polyphenol oxidase (PPO) activity, and phenolic substrates were investigated. The results showed that all the Asp solution treatments significantly reduced the browning of fresh-cut potato chips. At 2–4 °C, control chips had lost saleability on day 1, while 1.0 % Asp treated chips were still acceptable on the day 7 evaluation. Asp can prevent the discoloration of potato pulp completely and also partly decolorize the brown color. Addition of Asp decreased the PPO activity of potato pulp. At the same pH, the PPO activities of potato pulps treated with Asp were lower than those treated with phosphoric acid (H3PO4). With the recovery of pH to the control level, the activity of the Asp-treated pulp did not improve completely like those treated with H3PO4. Moreover, the addition of copper acetate solution to the Asp-treated pulp significantly increased PPO activity. As browning progressed, tyrosine and chlorogenic acid content in the Asp-treated potato pulp was higher than that of the control, but caffeic acid, gallic acid, and protocatechuic acid content did not increase. In vitro simulation experiments demonstrated that Asp prevented the discoloration of tyrosine and chlorogenic acid solution, and also caused the fading of the discoloration to a certain degree. These results indicated that Asp is a promising anti-browning agent for fresh-cut potato and the mechanism involves the reduction of PPO activity via a decrease in pH and chelating Cu2+ by Asp, inhibiting the formation of brown color from tyrosine and chlorogenic acid solution and enhancing the fading of the brown color.