Changes in Various Ingredients, <i>Escherichia coli</i>, Taste and Texture of Blade Vegetables as a Result of Low Temperature Steam-Heating Process

Abstract

To research wider uses of the low temperature steam heating process, blade vegetables were heated by steam of temperature adjusted from 55°C to 80°C for 5-30 min. The treated vegetables were used for analysis of various ingredients, measurement of color tone and texture, and evaluation of taste. To determine possible sterilizing effect of the process on E. coli, broccoli soaked in nutrient broth with the germ was treated at 60 and 65°C. The breaking stress of Chinese cabbage leaf stalk increased when treated for 30 min at 60°C. The color tone of leaves heated for 10 min at 65°C scarcely changed during storage for 48h at 5°C. The E. coli adhering to broccoli declined from 10 CFU/g to <30 CFU/g after steaming for 5 min at 60°C. The desirability of cabbage steamed for this same period and temperature showed little difference from the fresh sample. Total vitamin C in both Chinese cabbage and cabbage steamed for 5 min at 60°C remained over 90%, while there was augmentation of the γ-amino butyric acid in the samples at this temperature. The water soluble pectin in Chinese cabbage at 60°C decreased and NaOH soluble pectin increased. Consequently, we would like to propose that the low temperature steam heating process is a very useful way to prepare blade vegetables, because the color tone and taste of the treated samples were almost the same as those of the fresh sample, and E. coli was sterilized if condition of treatment were adequate.