Miki Yoshimura

Gelation kinetics of konjac glucomannan in the presence of an alkaline coagulant was studied by dynamic viscoelastic measurements. The gelation time became shorter and the rate constant of gelation increased with increasing molecular weight or concentration of konjac glucomannan or heating temperature. The plateau value of the storage shear modulus increased with increasing molecular weight or concentration of konjac glucomannan. The plateau value as a function of heating temperature or pH showed a maximum at a certain temperature or pH. © 1999 Elsevier Science Ltd.

Effects of xyloglucan (XG) on gelatinization and retrogradation of corn starch (CS) were studied as a function of mixing ratio and of storage time and by measuring force-deformation curves, dynamic viscoelasticity, syneresis and differential scanning calorimetry (DSC). Total polysaccharide concentrations were 3.5 wt% or 20 wt% and CS/XG mixing ratios were 10/0, 9.5/0.5, 9.0/1.0 and 8.5/1.5. Results of dynamic viscoelasticity and DSC measurements indicated that XG did not interact synergistically with CS to promote the formation of three dimensional network structure of CS. The storage and loss Young's moduli, E′ and E″ for mixed gels of CS and XG increased with increasing XG concentration. E′ and E″ decreased with increasing temperature from 25°C-60°C, and increased slightly with decreasing temperature from 60°C-25°C, E′ and E″ did not recover the initial value at 25°C when the temperature was lowered from 60°C-25°C. E′ and E″ at 25°C increased with increasing storage time, while both moduli at 25°C after heating-cooling cycle were not so different for gels after 1 day storage and for gels after 7 or 14 days storage. Breaking stress and Young's modulus for gels increased, while breaking strain decreased with storage time. Breaking stress and retrogradation ratio by DSC for mixed gels with mixing ratio CS/XG= 8.5/1.5 proceeded faster during 7 days of storage and proceeded slower after 7 days storage than gels of corn starch (10/0). © 1999 Elsevier Science Ltd.

Rheological properties of corn starch (CS) and konjac-glucomannan (KM) mixtures (total polysaccharide concentration: 3.50 wt%, CS/KM ratios: 10/0, 9/1, 8/2, 7/3, 6/4) were studied as a function of mixing ratio and storage time by measuring storage and loss shear moduli and by observing the large deformation and fracture behaviour. The viscoelastic behaviour of dispersions of CS plus water (2.10-3.50 wt%, 3.50 wt% = 10/0) was intermediate between a weak gel and an elastic gel, and dispersions of KM plus water (0.35-1.40 wt%) showed a behaviour similar to a concentrated polymer solution. The behaviour of CS and KM mixture was intermediate between a concentrated polymer solution and a weak gel. KM does not interact synergistically with CS to promote the formation of ordered structure. The breaking stress for CS and KM mixtures increased slowly with storage time than for CS alone. KM prevented syneresis of corn starch during storage. (C) 1998 Elsevier Science Limited. All rights reserved.

Changes in the sugar content and sucrose metabolizing enzymatic activities of stored green peas were studied. Green pea seeds were removed from their pods, and the pods without seeds or whole peas were stored at 1°C or 20°C. Their sucrose content significantly decreased, especially in seeds without pods stored at 20°C, but the stachyose and verbascose contents increased. Glucose and sucrose were the major components in the pods. The pod sucrose content significantly decreased, especially in pods with seeds stored at 20°C. Sucrose synthase (sucrose synthesis, sucrose cleavage) and invertase activities in the seeds decreased during storage, but sucrose phosphate synthase activity increased after 1 or 2 days of storage and then decreased. According to these results, we suggest that sucrose might be utilized not only in the synthesis of starch, but also in the synthesis of the raffinose family of oligosaccharides such as stachyose and verbascose.

The changes of peroxide content and enzyme activities involved in hydrogen peroxide metabolism of stored mitsuba (Japanese hornwort, <I>Cryptotaenia japonica</I> Hassk. cv. Senkaku) leaves were studied to elucidate the role of peroxides in leaf yellowing. The peroxide content in mitsuba leaves decreased significantly during storage at 25°C. Glycolate oxidase activity increased for the first 2 days of storage at 25°C and then decreased with leaf yellowing, while superoxide dismutase activity showed a decline during storage. Catalase and peroxidase activities decreased in stored mitsuba leaves, the decrease being greater in catalase than in peroxidase. These results suggest that the oxidation process in which the peroxides, including hydrogen peroxide, are involved, might enhance leaf yellowing in stored mitsuba.

The effects of pods on starch and sugar contents were determined to clarify the sugar metabolism of stored green peas (<I>Pisurn sativum</I> L., cv.Kishu-usui). The quality of peas stored with pods was maintained at a longer period than peas without pods. The total sugar content of seeds stored with pods increased after 2 days of storage at 1 °C, but seeds with or without pods, especially without pods, decreased significantly during storage at 20°C. On the other hand, the total sugar contents of pods stored with seeds at 1°C and without seeds at 20°C showed almost no change, but pods with seeds at 20°C decreased markedly. The starch content of seeds stored with pods at 1 °C showed almost no change, but seeds with or without pods at 20°C increased greatly. The accumulation of the starch content of seeds stored with pods was as high as compared with seeds without pods.

Effects of konjac-glucomannan (KM) on retrogradation and gelatinization of corn starch (CS) were studied as a function of mixing ratio and of storage time by measuring force-deformation curves, dynamic viscoelasticity, and differential scanning calorimetry (DSC). Total polysaccharide concentration for the rheological experiments was 15 wt % and CS/KM ratios were 15/0, 14.25/0.75, 13.50/ 1.50, and 12.75/2.25. A mixed gel with a CS/KM ratio of 13.50/1.50 showed a larger breaking strain and Young's modulus than a gel of CS plus water (15/0) stored for 1 day. Mixed gels of CS and KM stored for 14 days showed a smaller breaking stress than a gel of CS plus water. The DSC endothermic peak accompanying the gelatinization shifted slightly to higher temperatures with increasing KM concentration. A CS-KM-water mixture (total polysaccharide concentration, 33 wt %) retrograded faster than CS plus water during short storage. Enthalpies of CS-KM-water mixtures stored for 14 days were smaller than that of CS plus water. From the rheological and DSC changes it is suggested that KM promoted CS retrogradation during short-term storage and then retarded it slightly during longer storage times.

Changes in levels of chlorophyll (Chi) and its derivative and Chi degrading enzyme activity were examined to elucidate the pathway of Chi degradation in stored mitsuba (Japanese hornwort, Cryptotaenia japonica Hassk, cv Senkaku) leaves. Chi content decreased markedly concurrent with the yellowing of leaves, Chlorophyllide (Chlide) a and 13(2)-hydroxychlorophyll a eluted as a Chi derivative, but their levels were low and did not increase during storage at 25 degrees C. Chlorophyllase activity increased significantly with the yellowing of leaves. In contrast with its activity, peroxidase activity decreased markedly with the senescence of leaves. Additionally, lipoxygenase activity increased during storage at 1 degrees C and 25 degrees C. The activities of enzymes relating to Chi degradation, such as chlorophyllase, peroxidase, lipoxygenase and Chi oxidase, were found in the chloroplasts of mitsuba leaves. These results suggest that Chi is degraded by chlorophyllase to Chlide and then the oxidative degradation of Chlide to a colorless compound occurs inside chloroplasts of mitsuba leaves.

Quality changes of sous vide processed mitsuba were evaluated in relation to the differences of processing temperatures (100, 90 or 80 degrees C) and degrees of vacuum (30 or 100 mmHg) in chamber of packing machine. Surface color of sous vide processed mitsuba at 100 or 90 degrees C was superior than that of other processings. There were no considerable differences among processing temperatures on total chlorophyll content. However, absorption spectrum of acetone extract at the region of 415 nm differed due to the formation of pheophytins a and b during processing. Results of sensory evaluation showed that the sous vide processed mitsuba had more inherent aroma and flavor than those of the usual processing. Surface color of processed mitsuba changed to yellow during storage, especially at 20 degrees C. Pheophytins a and b were formed significantly with yellowing of processed mitsuba. L-ascorbic acid content decreased sharply during storage at 20 degrees C, but was slowly at 5 degrees C. Anaerobic bacteria increased after 2 days at 20 degrees C and 6 days at 10 degrees C when the mitsuba were stored, but did not increase even after 8 days at 5 degrees C. These results indicated that processing under reduced pressures at 90 degrees C or higher temperatures provided good quality of mitsuba. And that the storage at 5 degrees C or low temperature gave microbiological safety condition.

Effects of addition of pumpkin paste on the physical properties of pumpkin jellies by using three kinds of gel agents which were κ-carrageenan, agar, and gelatin were investigated by measuring texture properties, rupture properties, dynamic viscoelasticity, melting points, syneresises, friction coefficients. Sensory evaluation was also performed to clarify the palatability of pumpkin jellies. 1) Addition of pumpkin paste resulted in the increase of rupture stress on carrageenan jellies, the slight decrease of agar jellies, no effect on gelatin jellies. 2) Addition of pumpkin paste resulted in the increase of dynamic viscoelasticities and melting temperatures, and the suppression of syneresises on the three kinds of jellies. 3) The results of sensory evaluation indicated which the youth panel showed that carrageenan jellies were more tasty, but gelatin jellies were not, and elder panel were not showed significant difference between three kinds of jellies.

Quality of sous vide processed potatoes was studied in relation to the differences of processing temperatures (70, 80, 90 or 100°C) and degrees of vacuum (30 or 100Torr) in packaging. In addition, quality changes in sous vide processed potatoes during storage was also investigated. When processed at 80°C or higher temperatures, potatoes showed no changes in surface color in all treatments. Browning, however, occurred in processing at 70°C. There were no appreciable differences between the hardness of potatoes and the degree of vacuum during processing at 80 or 90°C. In the processing at 100°C, potatoes remained harder with a lowering of the degree of vacuum while those packaged under atmospheric pressure remained hardest. The content of total ascorbic acid in potatoes was kept higher during processing at 90 and 100°C. The content in packaged potatoes was higher than that in the conventional processing potatoes. Dehydroascorbic acid content showed almost the same value in all the treatments. There was no considerable difference between the sugar content and the degree of vacuum in packaged potatoes. The sugar content in the conventional processing, however, was lower when compared with that of the processing at 80 or 90°C of packaged potatoes. Anaerobic bacteria were detected after 3 days of storage at 20°C. Potatoes were putrefied after 3 days of storage at 20°C. No bacteria were detected for 7 days of the storage when stored at 5 or 10°C. Dehydroascorbic acid content increased during storage at all temperatures. Changes of reducing sugar content showed a similar tendency at all of the storage temperatures and increased slightly during storage. It is suggested that sous vide processing at 90°C or higher temperatures is good for the storage of potatoes and that storage at 5°C or a lower temperature is good for quality.

Quality of sous vide processed green peas were studied in relation to the differences of processing temperatures (80, 90 or 100°C) and degrees of vacuum (30 or 100 Torr) in packaging.Additionally, changes in quality during storage were also investigated. The surface color of sous vide processed green peas at 100°C was better than that with other processings. There were no considerable differences among processing temperatures on the total chlorophyll content. The content of total ascorbic acid, total sugar and soluble nitrogen compounds in sous vide processed green peas was higher than those in the green peas by conventional processing. Anaerobic bacteria increased after 4 days of storage at 20°C. The green peas were putrefied after 7 days of storage at 20°C. No bacteria were detected after 11 days of storage when the green peas were stored at 5°C. The surface color was discolored during storage, especially at 20°C, with a degradation of chlorophyll a. The ascorbic acid content showed no change during storage at 5 or 20°C. The total sugar content showed almost the same value at 5 or 20°C, and slightly decreased during storage. These results indicated that cooking under reduced pressures at 90°C or higher temperatures is good for the quality of green peas. Furthermore, it is also suggested that storage at 5°C or lower temperatures is good for maintaining quality.

Quality changes in vacuum-packaged Japanese radish during cooking were studied in relation to the difference of cooking temperatures (65, 70, 80 or 100℃ and the degree of vacuum (30 or 100 Torr) in packaging. The cooking of Japanese radish packaged under reduced and normal pressures and the non-packaged cooking were used as cooking methods. Japanese radish was softened in the cooking at 70℃ or higher temperatures, but not completely softened at 65℃. Japanese radish cooked at 100℃ or 80℃ show, ed no changes in surface colour. However, at 70℃, browning occurred in the cooking of Japanese radish packaged under normal and 100 Torr pressures, but not 30 Torr pressure and in the non-packaged cooking. There were no apparent differences observed in the hardness of Japanese radish and the degree of vacuum during cooking at 70 or 80℃. However Japanese radish remained hard with lowering of the degree of vacuum and hardest under the normal pressure at 100℃. The content of total ascorbic acid in Japanese radish showed no difference with the change of vacuum at 100℃. On the other hand, in the cooking at the temperature below 100℃, the content of Japanese radish packaged at 30 Torr showed a higher content of ascorbic acid than that of the usual coo-king. The higher the degree of vacuum was, the lower dehydroascorbic acid content became at 100℃. There were no considerable differences between sugar content and the degree of vacuum in the cooking of packaged Japanese radish. However, the sugar content of the usual cooking was lower as compared with that of the cooking of packaged Japanese radish at all the temperatures. These results described here indicate that the cooking at 80℃ or higher temperatures and under reduced pressures is better for keeping quality of Japanese radish.

Quality changes of cooking in hypobaric-packaged winter squash fruits were studied in relation to the differences of cooking temperature (70, 80 or 100°C) and degree of vacuum (30 or 100 Torr) in packaging. The cooking of winter squash fruits packaged under reduced and normal pressures with the usual cooking methods was investigated.<BR>Winter squash fruits cooked at 100°C or 80°C showed no changes in surface colour.In Winter squash fruits which were packaged under reduced pressure at 100 Torr or normal pressure, browning occured with cooking at 70°C, but the browning did not occur in winter squash fruits packaged under reduced pressure at 30 Torr and in ordinary cooked winter squash fruits.<BR>There were no appreciable differences between hardness of winter squash fruits and degree of vacuum during cooking at 70 or 80°C. In the cooking at 100°C, winter squash fruits remained harder with the lowering of the degree of vacuum while those packaged under normal pressure remained hardest.<BR>The content of total ascorbic acid in winter squash fruits was kept higher during cooking at 100°C. On the other hand, at temperatures below 100°C, the content in hypobaric-packaged winter squash fruits showed higher than that in winter squash fruits packaged under normal pressure or in ordinary cooked winter squash fruits. The higher degree of vacuum, the lower became dehydroascorbic acid content at all the temperatures. Winter squash fruits cooked under normal pressure at 100°C showed highest value of dehydroascorbic acid among all the treatments.<BR>There were no considerable differences between sugar content and degree of vacuum in packaged winter squash fruits. However, sugar content in ordinary cooking was lower when compared with that of the cooking of packaged winter squash fruits except when cooked at 100°C.<BR>It is suggested that cooking at 80°C or higher temperatures and under reduced pressures is good for keeping quality of winter squash fruits.