Kazuo Chachin

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.

Inhibition of loquat enzymatic browning by sulfhydryl compounds

Abstract The effectiveness of a series of sulfhydryl compounds in inhibiting polyphenoloxidase (PPO) activity in a model system (chlorogenic acid solution) and in loquat juices was evaluated. Application of different concentrations of sulfhydryl compounds to chlorogenic acid solution and fresh loquat juice showed that l -cysteine appeared to be an effective browning inhibitor. The required concentration of l -cysteine for 90% browning inhibition depended on loquat cultivars, and ranged from 0.6 mM for “Nagasaki” to 2.0 mM for “Yukawa” or “Toi”. The difference may be due to the concentration of endogenous phenolic compounds inherent in each cultivar. The results from oxidized product analysis by loquat PPO implied that the mechanism of browning inhibition by thiols involved the formation of a thiol-conjugated reaction product.

Presence of alcohol acetyltransferase in melons (Cucumis melo L.)

Abstract Of 20 genotypes of melon fruits tested, 17 were able to esterify exogenous isobutyl alcohol. Alcohol acetyltransferase involved in esterification of alcohols with acetyl CoA was extracted from melon pulp. The partially purified enzyme had pH and temperature optima of 8 and 30 °C respectively. The enzyme was relatively stable at temperatures up to 40 °C. The molecular weight was estimated by gel filtration to be about 400 kDa. The protein band corresponding to this molecular weight was absent from gels loaded with protein from a melon genotype lacking the ability to form esters.

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.

Off-flavor production in frozen strawberries

Abstract The development of off-flavor in frozen-thawed strawberries was attributed to the production of H2S. The identity of H2S was verified both chemically, through its reaction with lead acetate, and using gas chromatography-mass spectroscopy analyses. The duration of the production of H2S was longer in berries stored at −40 °C and −80 °C than in those stored at −20 °C. Because the amount of sulfide ion in frozen strawberries was lower than that in fresh berries, and because K2S addition resulted in further increases in the production of H2S, it is likely that H2S evolution is due to the decrease in pH of the cytosol caused by the disruption of cells by freezing, resulting in the release of sulfide ion as H2S. Vigorous crushing of fresh berries also gave rise to the production of H2S.

Studies on Physiological and Chemical Changes of Partially Processed Carrot. Part IX. Differences in Physiological Activity and Rate of Callus Formation in Carrot Sections with Respect to Tissue Type and Cutting Mode.

本研究では,ニンジンの師部,形成層部,ならびに木部の各組織から切断方向の異なる切片を調製し,生理特性やカルス形成速度の相違などを調べることによりカットニンジンの貯蔵性に差異の生じる理由を明らかにしようとした.切断方向にかかわらず,師部と形成層部の切片のCO2排出量とC2H4生成量は切断後10数時間まで増加し,その後は減少した.木部切片のCO2排出量とC2H4生成量は切断直後から実験終了の保持48時間まで増加を示した.形成層部切片のCO2排出量とC2H4生成量の一時的な増加ならびに木部切片が示したCO2排出量とC2H4生成量の保持に伴う経時的な増加は,いずれも縦切り切片の方が輪切り切片より多かった.木部切片における生菌数の増加は師部切片より速く,組織が異なっても縦切り切片における生菌数の増加は輪切り切片より速かった.カルス形成量は形成層部切片で最も多く,師部切片がそれに続き,木部切片におけるカルス形成量が最も少なかった.組織が異なっても輪切り切片のカルス形成量は縦切り切片より多かった.木部から調製した切片は,師部切片より生理活性が高く,微生物の繁殖が速く,カルス形成量が少なかった.また同じ組織から切片を調製するときには,維管束に直角に調製した切片の方が平行に調製した切片よりも生理活性が低く,微生物の繁殖が遅く,カルス形成量が多かった.このような組織間ならびに切断方向による諸特性の相違がカットーンジンの貯蔵性に差異を生じさせるものと思われた.

Changes in Phenol Oxidases Activity with Special Reference to Browning of Shiitake (Lentinus edodes Sing.) Mushroom during Storage

本研究では二つのシイタケ菌種を用い, 菌種間およびヒダと菌傘の部位別にフェノールオキシダーゼ活性の差を調べ, また, 密封と有孔包装したシイタケにおけるそれらの活性について褐変との関連を調べた。シイタケのフェノールオキシダーゼとしてMPO, oDPOおよびLAの3種の酵素活性が認められた。シイタケのヒダではMPOの菌傘より高く, oDPOとLAの活性は菌傘より低かった。oDPOとLA活性は褐変しやすい菌種Fで高い傾向があり, MPO活性は褐変の著しく起こったときに急激に増加した。ポリエチレンフィルム包装の貯蔵の場合, 密封包装ではMPO, oDPOおよびLA活性が抑制され, 有孔包装ではこれらの活性が褐変に伴って増加したことから, シイタケの貯蔵に伴う褐変にはoDPO, MPOとLAの3種の酸化酵素が関係するものと判断した。

Studies on maturation changes in fruits induced by ionizing radiation. II

Tomatoes (Licopersicon esculentum MILL. ) of three stages of maturity, mature green, breaker and light pink fruits were used in this experiment. Tomato fruits were irradiated with 60Co gamma rays at 0r, 5. 0×104r and 1. 0×106r at the rate of 2. 5×105r/hour. Temperatures during the irradiation and the storage were at about 20°C. The results obtained here were as follows:1. The pigmentation of tomatoes which were irradiated by gammarays at stages of breaker and light pink was delayed. The destruction of chlorophyll and the increasing of lycopene during ripening were apparently suppressed with higher doses. Gamma irradiation caused the considerable softening of the tissue immediately after irradiation. The subsequent change of softening in irradiated fruits was smaller than that in unirradiated ones. There was a decrease in protopectin in irradiated fruits immediately after irradiation. The titrative acidity and the amount of total sugar were not affected by gamma irradiation. The reduction of ascorbic acid by irradiation seemed to be greater in fruits of breaker stage than in those of light-pink.2. Carbon dioxide production of tomatoes irradiated at breaker stage increased with higher doses and this increased carbon dioxide production lowered to some extent at 24 hours after irradiation. These irradiated fruits exhibited the climacteric-like rise at the same period as that in unirradiated ones. Carbon dioxide production in tomatoes irradiated at light-pink stage was slightly greater than that in unirradiated ones, and light-pink fruits did not exhibited the climacteric like rise in both irradiated and unirradiated fruits.3. The effect of pyruvate and malate on carbon dioxide output in tissue slices increased in irradiated fruits more than in unirradiated ones. Gamma irradiation at 1.0×106r stimulated the ethylene formation. The increasing rate was higher in mature green fruits than in others. The rates of ethylene production decreased in all irradiated fruits 5 days after irradiation.4. The organoleptic evaluation showed the acceptability of the irradiated tomatoes lowered with the high dose.