EFFECT OF GAMMA IRRADIATION ON SOFTENING CHANGES AND ENZYME ACTIVITIES DURING RIPENING OF PAPAYA FRUIT

The aim of this work was to study the role of cell wall and ethylene related enzymes to papaya fruit firmness. Irradiation treatment was used as an imposed stress to cause changes in firmness. Physiologically mature papaya fruits were irradiated (500 Gy) and allowed to ripen at 22C and 90% RH. Polygalacturo‐nase (PG), pectinmethylesterase (PME), βgalactosidase, cellulose and 1‐aminocyclopropane‐1‐carboxylate oxidase (ACC‐oxidase) activities were followed during ripening and correlated to changes in firmness, skin and pulp color, respiration and ethylene production. The firmness of irradiated fruits was retained at least 2 days longer than in normal fruits and also had a slower rate of softening. Total soluble solids (d?Brix), cellulase activity and ethylene production were not altered by irradiation treatment. The activity patterns of PG, PME and β‐galactosidase were related to pulp softening and affected by irradiation. ACC‐oxidase activity was influenced by irradiation treatment, but its changes were not temporally related to those in firmness. It was concluded that irradiation had no direct effect on firmness but it acted by altering the ripening induced synthesis of cell wall enzymes, mainly PME.     

QUALITY ATTRIBUTES, PECTOLYTIC ENZYME ACTIVITIES AND PHYSIOLOGICAL CHANGES DURING POSTHARVEST RIPENING OF NECTARINE

The postharvest ripening at 20C and 90–95% RH for 10 days of ‘Armking’ nectarine grown in a greenhouse was investigated over two seasons. Firmness, titratable acidity, ascorbic acid, pH and maturity index were all adequate to stablish the rate of ripening. However, soluble solids content and reducing and non-reducing sugars showed no significant changes. It took about 10 days for very early ripening fruit (100 g weight and 82 N firmness) and 6 days for normal early ripening fruits (115 g weight and 46 N firmness), both harvested at preclimacteric stage, to become eating ripe (near 20 N). Total weight loss and decay after 10 days was approximately 11%. During ripening there was a temporal coincidence among higher rates of ethyleneproduction, higher pectinmethylesterase (PME) and polygalacturonase (PG) activities, lower firmness and acidity and higher maturity index. PME and PG activities increased during ripening, with a highly negative linear correlation between activities of the two enzymes and firmness. In very early ripening fruit, PME activity was more closely related to softening than PG, whereas in normal early ripeningfruit, PG activity was slightly more closely linked to the loss offirmness than PME.     

OXIDATIVE STRESS AND ANTIOXIDANT SYSTEMS IN TOMATO FRUITS DURING STORAGE

Tomato varieties ARTH‐3 (long shelf‐life; 14–15 days) and Sel‐7 (short shelf‐life; 5–7 days), harvested at color turning stage, were stored in open trays at 10, 25 and 35C and sampled at two day intervals until complete deterioration. Variety ARTH‐3 could be stored at all the temperatures for ten days, while Sel‐7 could tolerate 35C only for four days. However, at 10 and 25C, it could be stored for six days. In both varieties, lipoxygenase (LOX) activity, malondialdehyde (MDA) value and H₂O₂ content increased during storage. Increase in storage temperature further enhanced the activity of LOX, and also increased MDA value and H₂O₂ content. Sel‐7 had higher values for these parameters than ARTH‐3. Activities of enzymes responsible for scavenging reactive oxygen species (ROS) viz., superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione reductase and catalase decreased continuously during storage. With increase in temperature, the activities of these enzymes further decreased significantly in both varieties. Sel‐7 had significantly lower activities of ROS scavenging enzymes than ARTH‐3 throughout the storage period. These results suggest that fruits stored at higher temperature are subjected to severe oxidative damage leading to extensive membrane damage and loss of tissue structure.     

PATTERNS OF SOLUBLE PEROXIDASE IN RIPENING BANANA FRUIT

SUMMARY— Total peroxidase activity and the spectrum of isoperoxidases solubilized from the pulp of banana fruit were relatively constant when the extraction procedure was most efficient. When casein dispersion was present during extraction of green fruit, high levels of activity were detectable. Other scavengers of condensed polyphenols were less effective in yielding activity in the soluble and particulate fractions. When collagen fibers were included with buffer during tissue maceration, no peroxidase was solubilized at all stages of ripening; however, the particulate fraction contained very high levels of peroxidase. Previous reports showing a concomitant change in peroxidase activity with the respiratory upsurge of climacteric fruit may be anomalous because of differential phenol inhibition.     

OXIDATIVE STABILITY OF BRINED ANCHOVIES WITH EXTRACTS FROM BLUEBERRY (VACCINUM SP.) FRUITS AND LEAVES

The hot-water extracts from blueberry ( Vaccinum sp.) fruits and leaves were examined for their total phenolic content, ferric reducing antioxidant power and 2,2-diphenyl-1-picrylhydrazyl–scavenging activity. It was observed that water extracts from blueberry leaves contained higher total phenolic content, ferric reducing antioxidant power and lower 2,2-diphenyl-1-picrylhydrazyl–scavenging activity than those from blueberry fruits. Oxidative stability of brined anchovies with extracts obtained from blueberry fruits and leaves was investigated during storage at 4C for 28 days. Brining with blueberry fruit and leaf extracts slowed down the lipid oxidation of anchovies. The highest antioxidant effect (peroxide value, thiobarbituric acid reactive substance and oxidative rancidity) was observed with brined anchovies with blueberry leaf extracts. The antioxidant potency of blueberry fruit extract was approximately equal to that of blueberry leaf extract. The highest polyunsaturated fatty acid percent was observed in the brined anchovies with blueberry leaf extract, but no significant difference with blueberry fruit extract was observed ( P >  0.05). These results suggest that brining with blueberry fruits and leaves extracts could enhance oxidative stability of fish.

PRACTICAL APPLICATIONS

Lipid oxidation is one of the main problems during the storage of salted anchovies. One of the methods for protection against oxidation is using antioxidants. Brining with blueberry fruit and leaf extracts slowed down the lipid oxidation of anchovies. According to these results, blueberry fruit and leaf extracts can be used to extend the shelf life of brined anchovies.     

乙醇处理对桃果实贮藏期间POD、PPO活性的影响

以“大久保”和“绿化9”桃果实为试材,研究了在10℃±2℃和2℃±2℃贮藏条件下,不同浓度的乙醇蒸汽处理(1mL/kg、2mL/kg、4mL/kg)对桃果实POD、PPO活性的影响。结果表明“,大久保”用4mL/kg浓度的乙醇在10℃±2℃下处理3d,“绿化9”用4mL/kg浓度的乙醇在2℃±2℃下处理5d,有效提高了桃果实POD的活性,加强了机体的抗氧化系统,保持膜的完整性,减少冷害发生,同时抑制了果实PPO活性,减少果实褐变和腐烂病的发生,延长了贮藏期。     

POLYPHENOLOXIDASE ACTIVITY, BROWNING POTENTIAL AND PHENOLIC CONTENT OF PEACHES DURING POSTHARVEST RIPENING

Changes in the polyphenoloxidase (PPO) activity and the phenolic content of peaches (Prunus persica cv. Premier) during postharvest ripening were studied. The fruits were stored at 12 or 25C for up to 15 days. The quantity of extractable proteins was maximum at 6–10 days storage at 25 and 12C, coinciding with the onset of the yellowness in the fruits. The PPO activity increased up to the ripening stage, showing a maximum value at 8 days of storage. This was coincident with the maximum degree of browning as evaluated by the absorbance at 440 nm. The amount of total phenolics and chlorogenic acid in the fruits decreased during storage; however, the differences were not significant. The browning potential closely correlated with the enzyme activity, but not with the phenolic content.     

STABILITY OF A PANCREATIC ENZYME COCKTAIL DURING IN VITRO PROTEIN DIGESTIBILITY ASSAYS

To maximize the efficiency of utilization of a pancreatic enzyme cocktail and estimate the contamination for in vitro protein digestibility assays, the specific activity losses of trypsin and chymotrypsin and the digestion of the enzyme proteins were studied. In the absence of protein substrate, increase of enzyme concentration augmented the half‐lives of trypsin and chymotrypsin and decreased the digestion of enzymatic proteins. In contrast, in the presence of substrate, increase of enzyme concentration decreased trypsin's half‐life. Increase of pH augmented the digestion of enzymatic proteins. The results indicated the optimum time for utilization of the enzymes depended on pH, enzyme concentration and presence of substrate. At the time when digestion of the proteins ceased, the average size of the hydrolysates was calculated between 3.1 and 5.4 amino acid residues, suggesting most proteins in the enzyme cocktail would be detected as digestible proteins.     

DEVELOPMENT OF POLYGALACTURONASE ACTIVITY AND SOLUBILIZATION OF PECTIN IN PEACHES DURING RIPENING

SUMMARY –Polygalacturonase activity, water-soluble pectin, total pectin, molecular weight distribution of water-soluble pectin, and fruit firmness were determined during ripening of freestone peaches. Polygalacturonase activity was not present in unripe peaches, but it developed during both tree and postharvest ripening. The development of activity paralleled the formation of water-soluble pectin characteristic of freestone peaches. Fruit firmness began to decrease before polygalac-turonase was detected, but the peaches softened rapidly after the appearance of the enzyme. Application of gel filtration revealed that the molecular weights of peach pectin range from about 100,000 to several million and decrease progressively during ripening. The results indicate a role for polygalacturonase in pectin solubilization during ripening of peaches.     

DEVELOPMENTAL REGULATION OF THE EXPRESSION OF ALCOHOL DEHYDROGENASE IN RIPENING TOMATO FRUITS

In each of 5 tomato (Lycopersicon esculentum Mill) cultivars examined, alcohol dehydrogenase (E.C.1.1.1.1) specific activity decreased during the early stages of ripening and then increased in the postclimacteric period. Alcohol dehydrogenase specific activity also increased when immature, mature or pink fruit were placed in an atmosphere of 3% (V/V) oxygen. Measurements of oxygen in the internal tissues and the respiratory quotient throughout ripening established that fruit ripening in air does not suffer an oxygen stress. Increases in alcohol dehydrogenase activity were also observed in pink fruit exposed to 10% (V/V) carbon dioxide. Such atmospheres are known to result in a lowering of the cytoplasmic pH in plants and it is suggested that alcohol dehydrogenase activity is induced during ripening in response to cytoplasmic acid stress. The increased ADH activity during ripening may contribute to flavor development.     

甘薯叶可溶性蛋白提取工艺研究

以甘薯鲜叶为原料，研究了碱提酸沉法提取甘薯叶可溶性蛋白的工艺，通过单因素和正交实验，确定出提取甘薯叶可溶性蛋白的最佳工艺条件：提取液（0．05％NaHSO3）pH8．0，料液比（w／v）1：4，打浆时间3min，酸沉pH4．5。该优化条件下可以得到纯度为50％一65％的甘薯叶可溶性蛋白，可溶性蛋白提取率为14％-18％。