Time-temperature tolerance for keeping quality of fresh fruits and vegetables

Abstract

In previous report it was suggested that peas and broad beans should be held at strictly low temperature immediately after harvest to keep the quality. Present study was carried out to investigate the time-temperature tolerance of these materials for keeping the taste and to find out the factors concerning deterioration of taste. Peas and broad beans with pods were packed in perforated polyethylene bags, and treated at 1°C, 6°C and 20°C with scheme shown in Fig. 1.1. Organoleptic test showed that the taste of peas markedly deteriorated in a day at 20°C. Even at 6°C the deterioration was considerably rapid and the difference from 1°C-storage was detected 5 days after. Delayed cooling, transferring to 20°C from 1°C-storage, and fluctuation between 1°C and 6°C resulted in hastening of deterioration in comparison with steady 1°C-storage. With broad beans, such tendency was approximately the same as peas.2. While total sugar content of peas and broad beans showed some increase at 1 °C, it decreased markedly at upper temperatures, i.e., the content became a half or a quarter of initial in a day at 20°C, about a half in 2 days at 6°C and 10°C. Transferring to 20°C from 1°C resulted in rapid decrease. Fluctuation between 1°C and 6°C showed the value between steady 1°C and steady 6°C, then gradually reached to the level of 6°C. When the materials were transferred from 20°C to 1°C, the sugar content which had once decreased was recovered to the extent of steady 1°C, however, in taste test significant recovery was not observed.3. Neutral and acidic amino acids were determined using TLC and automatic analyzer. Threonine, glutamic acid, alanine, valine, iso-leucine, leucine, tyrosine, phenylalanine and other ninhydrin-positive products were detected in both peas and broad beans at harvest. They decreased drastically at upper temperatures. For example, alanine which was found abundantly in both materials decreased by 1/12 in peas and 1/5 in broad beans in 2 days at 20°C. At 1°C the decreasing rate was slowed down considerably, but 6°C of storage temperature was insufficient to prevent the rapid change.4. Sucrose-U-14C and alanine-U-14C were applied by vacuum infiltration to the slices of broad bean cotyledons and incubated for 10 and 24 hours at 20°C. They were incorporated rapidly into alcohol-insoluble fractions, presumably starch from the sucrose and protein from the alanine. Incorporation into alcohol-soluble cationic and anionic fractions was also observed to some extent.5. Hardening of cotyledons took place rapidly in both materials at 20°C. At 1°C the texture was kept soft for considerable period. Hardness of cotyledon measured by Curd meter paralleled with organoleptic test to considerable degree with peas, however, good correlation was not obtained with broad beans.6. It is concluded that three factors as decrease of sugar and amino acid contents and hardening would largely concern with the rapid quality deterioration of peas and broad beans. For keeping the quality, strictly low temperature is needed.