Prevention of enzymatic browning of pear by onion extract

Onion extract was prepared by extracting onion with water, and the effects of the extract on pear polyphenol oxidase and browning of pear were investigated. The polyphenol oxidase of pear was inhibited by onion extract, and the inhibitory effect of onion extract toward pear polyphenol oxidase was increased with the heated extract. The inhibitory effect of the extract was increased with increasing heating temperature and time. The browning of pear juice was retarded by addition of both fresh and heated onion extracts. The onion extract inhibited the pear polyphenol oxidase non-competitively. Therefore, the inhibitory effect of onion extract against pear browning seems to be due to the inhibitory effect of onion extract against pear polyphenol oxidase.     

Inhibitory effect of banana polyphenol oxidase during ripening of banana by onion extract and Maillard reaction products

The inhibitory effect of onion extract on banana polyphenol oxidase activity during ripening of banana when stored at room temperature for 10 days was investigated. The addition of the onion extract that had been heated at 100 °C for 10 min exhibited a higher inhibitory effect on the banana polyphenol oxidase activity during ripening of banana than that of the fresh onion extract. When the onion extract that had been treated at a high temperature was added, the banana polyphenol oxidase activity was markedly inhibited. It was found that heat treated onion extract inhibited the banana polyphenol oxidase non-competitively. The MRP synthesized from arginine, cysteine, histidine and lysine significantly inhibited banana polyphenol oxidase. The enzyme activity was inhibited by addition of various anti-browning agents.     

洋葱提取液对鲜切马铃薯褐变的影响

使用洋葱的磷酸缓冲溶液提取液对马铃薯PPO酶活抑制率以及鲜切片贮藏保鲜进行了研究。结果表明，洋葱提取液抑制马铃薯PPO酶活的效果分别达到了34．2％和59.3％，且经100℃水浴加热的洋葱提取液对马铃薯PPO酶活的抑制效果优于新鲜的洋葱提取液。在贮藏实验中洋葱提取物通过对贮藏过程中鲜切薯片的硬度、色度和PPO酶活力变化的测定，初步证实了洋葱提取液具有防褐变效果。     

Light exposure inhibiting tissue browning and improving antioxidant capacity of fresh-cut celery (Apium graveolens var. dulce)

Fresh-cut celery is perishable and susceptible to tissue browning during storage. In this study, the effect of continuous light exposure (2000 lux) on browning related enzyme activity of fresh-cut celery was investigated during 8 d storage at 7 °C using darkness (0.2 lux) as control. Light exposure significantly suppressed polyphenol oxidase (PPO) and peroxidase (POD) activities, and subsequently decreased soluble quinone accumulation and browning index (BI) evolution during storage. In addition, phenylalanine ammonia lyase (PAL) activity, total phenol (TP) content, and antioxidant capacity (AC) values were all higher when the fresh-cut celery samples were exposed to light than in darkness during storage. A significant positive correlation between TP and AC was observed at both light (R = 0.884, P < 0.01) and dark (R = 0.705, P < 0.01) conditions.     

苹果多酚处理对鲜切芋艿品质的影响

为了控制鲜切芋艿贮藏过程中的褐变并延长其货架期,研究（10.0±0.5）℃条件下,蒸馏水（CK）和不同质量分数（0.3%、0.5%、0.7%）苹果多酚浸泡处理对其色泽、硬度、糖类物质含量、总酚含量、丙二醛含量及褐变相关酶活力的影响。结果表明：苹果多酚处理能够延缓芋艿切片贮藏过程中的褐变进程,其中以0.5%苹果多酚处理的效果最佳;与CK组相比,0.5%苹果多酚处理可以保持芋艿切片较好的色泽和较高的硬度,延缓苯丙氨酸解氨酶活力和总酚含量的升高,抑制芋艿过氧化物酶、多酚氧化酶、脂氧合酶活力和丙二醛含量的升高,从而延缓鲜切芋艿贮藏过程褐变的发生,保持鲜切芋艿较好的贮藏品质。     

Inhibitory effects of p-alkylbenzoic acids on the activity of polyphenol oxidase from potato (Solanum tuberosum)

In order to prevent potato from browning during preservation and processing, the effects of p-alkylbenzoic acids (p-propylbenzoic acid, p-butylbenzoic acid, p-pentylbenzoic acid, p-hexylbenzoic acid, p-heptylbenzoic acid, p-octylbenzoic acid) on the activity of potato polyphenol oxidase (PPO) have been studied. The PPO was extracted with PBS (pH 6.8), fractionated with ammonium sulphate, concentrated, and purified with Sephadex G-100 (1.8 × 100 cm) filtration chromatography. The active fractions were pooled and the PPO activity was determined to be 79.83 U/mg. The results showed that p-alkylbenzoic acids could strongly inhibit the activity of potato PPO. The values of IC₅₀ of these six inhibitors were determined to be 0.213, 0.180, 0.152, 0.106, 0.075 and 0.047 mM, respectively. Kinetic analyses showed that p-alkylbenzoic acids used in this experiment were reversible and noncompetitive inhibitors to the enzyme. The inhibitory effects were potentiated with increasing lengths of the hydrocarbon chains, indicating that the inhibitory efficiency on the enzyme was influenced by the steric effect of the substituted groups.     

Inactivation of polyphenol oxidase by ultraviolet irradiation: Protective effect of melanins

Most of the studies about UV irradiation of fruit and vegetable derivatives have been carried out in order to assess its effect on microbial inactivation. Nevertheless, there are few references about UV influence on some enzyme activities that are important in this kind of food, especially polyphenol oxidase, which is responsible for enzymatic browning in fruit and vegetable tissues containing phenolic or polyphenolic compounds. In this work, the effect of UV–Vis irradiation on polyphenol oxidase from Agaricus bisporus was investigated. A reduction of 58.7% in enzyme activity was achieved in the first 90 s, and it was completely inactivated after 35 min of treatment. In addition, the protective effect of melanins synthesized by the action of the same polyphenol oxidase was assessed. These pigments absorbed some of the radiant energy and led to a slower inactivation of polyphenol oxidase.     

抗坏血酸与壳聚糖处理对鲜切香芋贮藏效果的研究

以湖南香芋头为试材,研究不同浓度抗坏血酸与壳聚糖处理对鲜切香芋的贮藏效果及生理生化变化的影响。结果表明,在15℃贮藏温度下,与对照相比,0、1.0、5.0、10.0g/L 抗坏血酸(VC)分别与15.0g/L 壳聚糖配合处理较好地保持了鲜切香芋的外观和营养,减少鲜切香芋的失重率和褐变度,并抑制多酚氧化酶(PPO)、过氧化物酶(POD)和淀粉酶的活性。其中,5.0g/L 抗坏血酸与壳聚糖配合处理的保鲜效果最明显。     

1-MCP处理对鲜切芋艿褐变的影响

为了延缓鲜切芋艿褐变, 延长其货架期, 研究4 ℃ 贮藏条件下, 1 0 μ L / L 1 - 甲基环丙烯 （1-methylcyclopropene,1-MCP）处理对鲜切芋艿色泽和褐变相关指标的影响。结果表明：10 μL/L 1-MCP熏蒸处理能 够有效延缓鲜切芋艿贮藏期间L*值下降,降低芋艿苯丙氨酸解氨酶活性和总酚合成速度;延缓芋艿多酚氧化酶和过氧 化物酶活性上升,抑制脂氧合酶活性,降低膜质的氧化损伤,进而延缓贮藏鲜切芋艿的褐变。而对照芋艿切片贮藏过 程中,褐变底物累积速度加快,相关酶活性迅速上升,细胞膜结构完整性遭到破坏,褐变程度明显高于处理组。     

Inhibition of polyphenol oxidase and peroxidase activities on fresh-cut apple by simultaneous treatment of ultrasound and ascorbic acid

The effects of ultrasound and ascorbic acid on activity changes of polyphenol oxidase and peroxidase, of fresh-cut apple during storage, were investigated. The combined treatment of ultrasound and ascorbic acid inactivated monophenolase, diphenolase, and peroxidase, whilst the individual treatment of ultrasound or ascorbic acid had inverse and limited inhibitory effect on the enzymes. The main protein bands had a molecular weight of approximately 63 kDa. A diffuse band, lacking the electrophoretic mobility of proteins, was observed after combined treatment. This investigation revealed that simultaneous treatment with ultrasound and ascorbic acid had synergistic inhibitory effects on several enzymes related to enzymatic browning.     

Effect of nitric oxide on pericarp browning of harvested longan fruit in relation to phenolic metabolism

The effects of nitric oxide (NO) on enzymatic browning of harvested longan fruit in relation to phenolic metabolisms were investigated. Fruits were dipped for 5 min in 1 mM sodium nitroprusside (SNP), a nitric oxide donor, then packed in 0.03 mm thick polyethylene bags, and finally stored for 6 days at 28 °C. Changes in pericarp browning and pulp breakdown were evaluated, while total phenol content, activities of phenolic-associated enzymes, polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia lyase (PAL), and concentrations of total soluble solids, titratable acidity and ascorbic acid were measured. SNP treatment delayed pericarp browning, inhibited activities of PPO, POD and PAL and maintained a high total phenol content of longan fruit during storage. Furthermore, NO showed a significant inhibition of the in vitro activities of PPO and POD, indicating that the beneficial effect of NO was direct. Moreover, application of NO resulted in a lower pulp breakdown and maintained relatively high levels of total soluble solids and ascorbic acid.     

Purification and partial characterization of polyphenol oxidase from the flower buds of Lonicera japonica Thunb.

The purification and partial enzymology characteristics of polyphenol oxidase from Lonicera japonica (LjPPO) were studied in this paper. The crude enzyme solution was purified in turn by ammonium sulfate, dialysis, and DEAE-cellulose ion-exchange chromatography after preliminary treatments. Purification resulted in 31-fold enrichment and its molecular weight was estimated to be ∼49 kDa exhibited on sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). The pH for optimal conditions of LjPPO was 7.5, and the temperature was 25 °C, in addition, the inhibitive effects of inhibitors were enhanced positively with increasing of the concentration. Moreover, crude enzyme solution showed diphenolase activity toward catechol, l-dopa and chlorogenic acid rather than monophenolase and triphenolase activity, and the best substrate was catechol because of the highest V_max/K_m value. However, the oxidation of diphenol related to browning significantly, so the data obtained in this research provided theoretical basis for the prevention of enzymatic browning of L. japonica during processing.     

海藻酸钠涂膜对鲜切芋艿保鲜效果的影响

为了延缓鲜切芋艿的褐变和品质劣变,延长其保鲜期。以芋艿为原料,在(10±1)℃的贮藏条件下,研究不同浓度海藻酸钠涂膜对鲜切芋艿营养品质和酶活性的影响。结果表明:与对照组相比,不同浓度海藻酸钠涂膜可降低鲜切芋艿贮藏过程中多酚氧化酶和过氧化物酶的活性,显著抑制鲜切芋艿的褐变,减少淀粉、可滴定酸和维生素C的降解,延缓失重,维持可溶性糖和还原糖的含量,保持鲜切芋艿的营养品质。其中以2%海藻酸钠涂膜处理效果较好,与对照组相比可延长保鲜期4 d。      

Antioxidant activities and contents of polyphenol oxidase substrates from pericarp tissues of litchi fruit

The experiments were performed to extract and purify substrates for polyphenol oxidase (PPO) from pericarp tissue of postharvest litchi fruit. Two purified PPO substrates were identified as (−)-epicatechin and procyanidin A2. The antioxidant properties of two PPO substrates were further evaluated in the present study. Variation in the content of the major substrate (−)-epicatechin of litchi fruit during storage at 25 °C was analysed using the HPLC-UV method. The results showed that (−)-epicatechin exhibited stronger antioxidant capability than procyanidin A2, in terms of reducing power and scavenging activities of DPPH radical, hydroxyl radical and superoxide radical. Furthermore, (−)-epicatechin content in pericarp tissue tended to decrease with increasing skin browning index of litchi fruit during storage at 25 °C. Thus, these two compounds can be used as potential antioxidants in litchi waste and the fresh pericarp tissue of litchi fruit exhibited a better utilisation value.     

Salt effect on heat-induced physical and chemical changes of salmon fillet (O. gorbuscha)

This research studied the effect of salt on kinetics for quality changes in pink salmon fillet, during commercial sterilisation. Sample cuts from salmon fillets were placed in sealed aluminum containers and heated at 121.1 °C for 10, 30 and 60 min. Samples with 1.5% (w/w) salt addition were compared with those without added salt. Salt addition reduced cook loss, area shrinkage and shear force of the heated fillet and resulted in a slightly darker colour. Effect of salt addition in thiamin loss, degree of lipid oxidation and fatty acid profile was not significant. Peroxide (PV) and thiobarbituric acid (TBA) values slightly increased within the first 10 min of heating, followed by a significant reduction as heating progressed. No measurable loss of polyunsaturated fatty acids (PUFA) was observed. Thermally processed shelf-stable salmon investigated should be a valuable source of ω-3 PUFA, with EPA values ranging from 52 to 71 mg/100 g product and DHA ranging from 258 to 340 mg/100 g of product.     

Antimicrobial activity of essential oil extracts of various onions (Allium cepa) and garlic (Allium sativum)

Antimicrobial activity of different concentrations (50, 100, 200, 300 and 500 ml/l) of essential oil extracts of three type of onions (green, yellow and red) and garlic against two bacteria, Staphylococcus aureus, Salmomella Enteritidis, and three fungi, Aspergillus niger, Penicillium cyclopium and Fusarium oxysporum, was investigated. The essential oil (EO) extracts of these Allium plants (garlic and onions) exhibited marked antibacterial activity, with garlic showing the highest inhibition and green onion the lowest. Comparatively, 50 and 100 ml/l concentrations of onions extracts were less inhibitory than 200, 300 and 500 ml/l concentrations. However, with garlic extract, high inhibitory activity was observed for all tested concentrations. S. aureus showed less sensitivity towards EO extracts inhibition, however S. Enteritidis was strongly inhibited by red onion and garlic extracts. The fungus F. oxysporum showed the lowest sensitivity towards EO extracts, whereas A. niger and P. cyclopium were significantly inhibited particularly at low concentrations. Conclusively, where seasoning is desired, essential oil extracts of onions and garlic can be used as natural antimicrobial additives for incorporating in various food products.     

Effects of aqueous chlorine dioxide treatment on browning of fresh-cut lotus root

Effect of aqueous chlorine dioxide (ClO₂) treatment on browning of fresh-cut lotus root (FLR) was investigated to explore the feasibility to apply ClO₂ for browning inhibition of fresh-cut products. Cut lotus roots were treated in ClO₂ solutions at different concentrations (10, 50 and 100 mg/l) for different time (5, 10 and 15 min), followed by chilled storage for 8-10 days at 4 °C. Color parameters (L^∗, a^∗ and b^∗), polyphenol oxidase (PPO) activity and overall visual quality (OVQ) were measured at one-day interval during storage. Results showed that higher ClO₂ concentration and longer treatment time can provide better inhibitory effects on the browning of FLR. ClO₂ concentration, treatment time and storage time were three significant factors (P < 0.05) and some significant interactions were observed. PPO activities were largely inhibited by 100 mg/l ClO₂ treatment for 10 min. The 100 mg/l ClO₂ treatment maintained high OVQ scores during 10-day storage; while 50 mg/l ClO₂ treatment was acceptable for maintaining OVQ during 4-day storage. ClO₂ treatment was demonstrated to be a promising alternative approach to control browning and improve OVQ of FLR.     

Dual effectiveness of sodium chlorite for enzymatic browning inhibition and microbial inactivation on fresh-cut apples

The dual effectiveness of sodium chlorite for browning inhibition and microbial inactivation on fresh-cut apples was investigated and compared to other anti-browning and antimicrobial agents. Results indicate that sodium chlorite significantly (P < 0.001) inhibited the browning reaction of fresh-cut Red Delicious apples stored at 5 °C for 14 days. This treatment also significantly reduced polyphenol oxidase activities. Treatments with acidified sodium chlorite, calcium chloride, or calcium ascorbate exhibited strong inhibition on apple browning during the early storage, these treatment effects diminished after 7 days in storage. Combining calcium chloride with sodium chlorite further significantly (P < 0.001) improved the firmness of apple slices, and browning inhibition during storage. Additionally, treatments with acidified sodium chlorite, sodium chlorite, or the combination of sodium chlorite and calcium chloride significantly (P < 0.001) reduced Escherichia coli populations on fresh-cut apples by 3.0, 3.6, and 3.9 log cfu g⁻¹ over the water control. The dual effectiveness of sodium chlorite to inhibit enzymatic browning and inactivate E. coli may allow this compound to achieve a prominent role in improving the quality and safety of products in the fresh-cut apple and other food industries.     

Biochemical and Structural Changes of Taro (Colocasia esculenta) Tubers During Simple Thermal Treatments (Low Temperature) or in Combination with Chemicals

The present study set out to study the structural and biochemical modification of taro (Colocasia esculenta) grown in Cameroon, through simple heating or in association with chemicals. Both techniques are known to inactivate the reactions of polyphenol oxidase. The textural analysis was performed on tubers heated in water, 0.5% NaCl and 1% NaCl solution at various times from 0 to 105?min. The result showed optimum pH and temperature for taro polyphenol oxidase (PPO) activity at pH?6.0 and t?=?40?°C with 10?mM catechol in 0.1?M phosphate buffer as substrate. K _m and V _max values were about 7.317?±?0.012?mM and 0.148?±?0.0003 OD_{430 nm}/minute. Seven inhibitors were tested in this study, and the most effective inhibitors were found to be NaCl, CaCl2 and KCl. Kinetic studies showed that the thermal inactivation of taro PPO followed first-order kinetics, with an activation energy of E _a?=?422.79?±?0.52?kJ/mol. The textural modification of taro tubers during heating follows the kinetic of the fractional model. It was noticed that the activation energy increased with the concentration of NaCl.     

Inhibition of browning on the surface of peach slices by short-term exposure to nitric oxide and ascorbic acid

The effect of 0.2% ascorbic acid (AA), 5 μM nitric oxide (NO), and the simultaneous use of 0.2% AA and 5 μM NO solutions on inhibiting surface browning of fresh-cut peach slices stored at 10 °C and RH 95% was investigated. The browning index, relative leakage rate, microstructure, total phenol content, and activity of the phenol metabolism-associated enzymes phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) were evaluated. The results indicate that treatment with 0.2% AA, 5 μM NO and simultaneous use of 0.2% AA and 5 μM NO resulted in higher total phenol content, inhibition of PPO and POD activity, reduced membrane permeability and protection of cell microstructure to maintain compartmentation between enzymes and their substrates. In addition, NO increased PAL activity. The causes of inhibition in the browning of peach slices by NO are discussed.