Fumio Hashinaga

ELECTROHYDRODYNAMIC (EHD) DRYING OF APPLE SLICES

ABSTRACT Conventional dryings at high temperatures often produce undesirable changes in the physical-chemical properties of materials. This paper describes the relatively novel technique of electrohydrodynamic (EHD) drying of apple slices, which did not cause any observable product degradation and extensive color changes. Multiple point-to-plate electrodes with AC high voltages, accelerated the initial drying rates to almost 4.5 times over the ambient air drying control. The size of the point electrode, electric field strength, electrode gap, and interelectrode separation were the determinant factors in EHD drying which could be maximized by optimizing these variables. A theoretical consideration showed the principal driving force behind EHD drying to be due to the generation of an electric wind which produced turbulence and thereby enhanced the drying rate of the slices. EHD drying is basically non-thermal and convective, and hence could provide an advantage to industries involved in manufacturing heat-s...

HIGH ELECTRIC FIELD DRYING OF JAPANESE RADISH

Japanese radish (Raphanus sativus L.) slices were dried under an alternating current (AC) high electric field (HEF) of 430 kV/m using a multiple point electrode and a grounded copper mesh. HEF with multipoint to a mesh electrode system could evaporate 87.5% of the total moisture from fresh radish slices on 7 h exposure. Oven-drying at 60°C and ambient air at 25°C for 7 h could dry 86.9% and 26.5% of the total moisture from the fresh radish slices respectively. The average rate of HEF drying from second hour to sixth hour was 0.025 g/min which was 0.0012 g/min higher than the oven-drying. Quality factors for HEF-dried radish exhibited less shrinkage, high absorption of water, better rehydration, less solids loss and better color than the oven-drying.

Chlorophyll degradation in Wase satsuma mandarin (Citrus unshiu Marc.) fruit with on-tree maturation and ethylene treatment

Abstract Changes in chlorophylls content and their derivatives were determined to elucidate the differences in chlorophyll degradation of Wase satsuma mandarin (Citrus unshiu Marc. cv. Miyagawa-Wase) fruit with on-tree maturation or ethylene treatment. Chlorophylls content in the ethylene-treated fruit decreased markedly after 2 days of storage at 20 °C. 132-hydroxychlorophyll a and pheophorbide a also decreased during storage, whereas chlorophyllide a did not decrease for the first 5 days of storage. Chlorophylls, 132-hydroxychlorophyll a, chlorophyllide a and pheophorbide a in on-tree matured fruit decreased with degreening. A small amount of pyropheophorbide a was detected in on-tree matured fruit, but the content showed almost no change during on-tree maturation. These results suggest that the acceleration of chlorophyll degradation by ethylene treatment could be due to the enhancement of chlorophyllide a formation by chlorophyllase.

DRYING OF SPINACH WITH A HIGH ELECTRIC FIELD

An alternating current high electric field (HEF) of 430 kV/m generated by multiple point-to-plate-electrodes was used to dry spinach (Spinacia oleracea L). Point electrodes distributed above a layer of fresh spinach were effective in removing moisture. Drying continuously for 7 h removed 80.1% of the total moisture compared with 79.8% and 19.3% when dried in an oven (60°C) and in ambient air (25°C), respectively. The Hunter ‘a’ value for HEF-dried samples maintained most of the original green color compared with oven-drying, during which the spinach turned brown. Total chlorophyll (Chl), Chl a and Chl b contents in spinach were substantially higher after HEF-drying than oven-drying. The ascorbic acid content after six weeks of storage of the dried material was almost three times higher in HEF-dried samples than those oven-dried. HPLC determinations of organic acids and sugars indicated no formation of by-products in post-HEF-dried spinach.

Inhibition of postharvest decay of fruits by nitrous oxide

Abstract Nitrous oxide (N 2 O) was tested for its potential to control the postharvest decay of fruits. Both climacteric and non-climacteric fruits were inoculated with high and low N 2 O-sensitive groups of fungi. Fruits included apple cv. Fuji, inoculated with Alternaria alternata and Penicillium expansum , strawberries cv. Toyonoka with Botrytis cinerea, Fusarium oxysporum f. sp. fragariae and Rhizopus stolonifer, Satsuma mandarin with Geotrichum candidum , tomato cv. Momotaro with F. oxysporum f. sp. lycopersici , persimmon cv. Fuyu with Colletotrichum acutatum and seedling guava with R. stolonifer . Inoculated fruits were exposed to 80:20% (N 2 O:O 2 ) and stored at 20°C. In addition, strawberries were inoculated with B. cinerea and exposed to 10, 30, 50 and 80% N 2 O with 20% O 2 and stored at 2°C. Our results showed that regardless of the physiological nature of the fruits or group of fungi, N 2 O delayed the appearance of disease and reduced the lesion growth rate. This response to N 2 O was dose and time dependent. This suppression of decay by N 2 O treatment is thought to be a direct inhibitory effect on fungal growth rate and/or increased resistance of host tissue.

Antioxidant Activity of Sugar-Tolerant Yeast Zygosaccharomyces Rouxii

Functional foods have been increasingly popular in Japan and are widely claimed to be beneficial for health. Among many kinds of such food, one distinct type is fermented food employing osmophilic or osmo-tolerant yeasts under high concentration of salt or sugar. We are the first to investigate the antioxidant activities of a strain of sugar-tolerant yeast isolated from high-sugar fermented food. In search of novel natural antioxidants, we screened 17 strains of yeast, including 7 sugar-tolerant strains, 4 salt-tolerant strains and 6 conventional strains, based on DPPH-scavenging (2,2-diphenyl-1-picrylhydrazyl) capacity of their ethyl acetate extracts. A sugar-tolerant strain of Zygosaccharomyces rouxii (MAFF 237555) yielded a maximum amount of extract which exhibited the strongest activity of 66.3% at 2 mg ml−1. The yeast was cultured under various conditions at different pH and different glucose concentrations for different numbers of incubating days and the antioxidant activity of each solvent extract was determined using different assay methods of DPPH, FRAP (Ferric reducing/antioxidant power), NBT (nitro blue tetrazolium) and the capacity for inhibiting linoleic acid oxidation, in comparison with natural and synthetic standard compounds. In most cases, while the activity of the extract was lower than that of BHA, it was higher than or comparable to that of ascorbic acid or α-tocopherol, tested under the same concentration range of 1 mg ml−1 to 5 mg ml−1. The results suggested that the yeast had a wide spectrum of moderately strong antioxidant activity and it could be utilized as a source of natural antioxidant.