Yoshihiro Imahori

Effects of storage temperatures on physiology and quality of loquat fruit

Abstract Loquat fruit (Eriobotrya japonica Lindl. cv. Mogi) were harvested at the ripe stage, packaged in perforated polyethylene film bags (0.15% perforation) and stored under different temperatures (1, 5, 10, 20 and 30°C) for 20 and 60 days. The rates of respiration and ethylene production at 20°C were 62 ml CO2 kg−1 h−1 and 1.4 μl kg−1 h−1, respectively, on the first day of storage, and were significantly lower with lower storage temperatures. Weight loss and the incidence of breakdown increased significantly with increasing storage temperatures. There was a significant decline in malic acid and sucrose contents during storage, with a more rapid decrease at higher temperatures. Skin colour and carotenoids progressively developed during the first 30 days of storage, and then remained steady for the remainder of the storage period. The cryptoxanthin content increased 2.4-fold in fruit stored at 20 and 30°C, but increased only slightly or underwent a small decrease in fruit stored at ≤10°C. There was little change in total phenolics in fruit stored at ≤10°C. The fruit stored at 1 and 5°C retained their initial quality and chemical components for 30 days.

Regulation of fermentative metabolism in tomato fruit under low oxygen stress

Summary Tomato fruit was stored under a continuous flow of 0% and 3% O2 (balance N2) or air for 7 d at 20°C to study the regulation of fermentative metabolism. The concentrations of ethanol and acetaldehyde were very low during storage at 3% O2 and air. At 0% O2, ethanol and to a lesser extent acetaldehyde, rapidly accumulated in the tissue. However, lactate concentration did not change during the experiment and was not significantly influenced by O2 concentration. Pyruvate decarboxylase (PDC) activity greatly increased in fruit exposed to 3% O2, while activity in fruit exposed to 0% O2 was the same level as the control. Alcohol dehydrogenase (ADH) activity greatly increased in fruit exposed to 3%, but at 0% O2 was the same level as the control. Lactate dehydrogenase (LDH) activity greatly increased in fruit exposed to 3%, but at 0% O2 was the same level as the control. The ADH activity in tomato fruit was about ten times greater than that of PDC activity and about 100 times greater than that of LDH activity during storage. Concentration of NADH in fruit exposed to 3% O2 was greater than that in fruit exposed to 0% O2 and air. Concentrations of pyruvate did not change during storage at 1% O2 and air. At 0% O2, pyruvate rapidly accumulated in its tissue. The K m of ADH in tomato fruit was 0.28 mM for acetaldehyde, and 0.058 mM for NADH. The Km of PDC in tomato fruit was 0.38 mM for pyruvate. The Km of LDH in tomato fruit was 0.18 mM for pyruvate. Possible regulation of fermentative metabolism is briefly considered.

Physiological responses and quality attributes of Japanese pear 'Kosui' fruit kept in low oxygen atmospheres

Summary Japanese pear ‘Kosui’ fruits were stored under a continuous flow of 0%, 1%, 3%, 5% and 10% O2 (balance N2) or air for 7 d at 20°C to study the effects of low O2 on their physiological responses and quality attributes. Low O2 treatments did not significantly influence changes in skin colour and soluble solids content. However, weak off-flavours were detected in the fruits stored at 0% O2 on day 3, and the intensity of these off-flavours increased as storage progressed. The concentrations of acetaldehyde in fruit increased throughout the storage period. The ethanol concentration was greatly increased in fruits stored at 0% O2. Moreover, ethanol concentrations were much higher than those of acetaldehyde and remained very low during storage in air, but their concentration were just slightly increased in fruits exposed to 1%, 3%, 5% and 10% O2. Pyruvate decarboxylase activity was greatly increased in fruits exposed to 1% and 3% O2, while its activity in fruits exposed to 5% and 10% O2 were only slightly higher than that of the control and at 0% O2 at the same level as the control. Alcohol dehydrogenase (ADH) activity greatly increased in fruit exposed to 0%, 1%, 3% and 5% O2, while at 10% O2, ADH was only slightly higher than the control. Changes in ADH isozymes correlated well with changes in ADH activity. The homogenate pH of fruits exposed to 1%, 3%, 5% and 10% O2 and air remained constant, while in fruit stored at 0% O2 their pH increased. The potential for using low O2 atmospheres to help in maintaining the quality of Japanese pear ‘Kosui’ is discussed.

Postharvest Stress Treatments in Fruits and Vegetables

Fresh fruits and vegetables are living tissues subject to continuous changes after harvest. While some changes are desirable, most are not. Their commodities are perishable products with active metabolism during the postharvest period. Proper postharvest handling plays an important role in increasing food availability. Postharvest stress treatments have been shown to be generally effective in controlling both insect and fungal pests, reducing physiological disorder or decay, delaying ripening and senescence, and maintaining storage quality in fruits and vegetables. In addition, a moderate stress not only induces the resistance to this kind of severe stress, but also can improve tolerance to other stresses. Postharvest stress treatments can, therefore, be very important to improving shelf life and quality retention during postharvest handling of fruits and vegetables.

Effect of ascorbic acid onin vivoorganogenesis in tomato plants

Summary To promote shoot formation, ascorbic acid (AsA) was applied to the leaves of tomato stock plants treated using the complete decapitation method in which multiple shoots regenerate from the cut surfaces of the main and lateral stems. Treatment with AsA at 1, 10, 100, or 1,000 mg l–1 significantly increased the number of regenerated shoots ≥ 5 cm in length. AsA levels and the activities of anti-oxidant enzymes in plants treated with AsA were higher than those in control plants. H2O2 concentrations and malondialdehyde contents in plants treated with AsA were lower than those in control plants. Cells in the calli formed at the cut surfaces re-differentiated earlier in AsA-treated plants than in control plants. Our results indicate that foliar application of AsA promotes shoot formation at the cut surface of tomato stems.