Sous vide processing of seasoned spinach soup

Abstract

Spinach soup seasoned with fermented soybean paste, red pepper paste and other minor ingredients was processed into 600 g plastic pouch package by the sous vide method. The process involved hot filling, pasteurization based on the inactivation of psychrotropic Clostridium botulinum, and rapid chilling. The processed products were stored at 3 and 10°C with periodic sampling for quality measurements. The seasoned spinach soup processed by the sous vide method exhibited a sensory quality comparable to that of fresh soup. The pasteurized product showed a high microbial load of total aerobic bacterial count greater than 5 log CFU/g in the soup brine and 2 log CFU/g in the vegetable solids, caused by the use of fermented soybean and red pepper pastes in the seasoned brine. However, coliform bacteria, lactic acid bacteria and yeasts/moulds were not detected in the product. The product was stable in microbial quality during storage for 35 days at 3°C, while it was so only up to 10 days at 10°C. The surface colour, total chlorophyll, ascorbic acid content and texture of the spinach in the soup showed gradual changes toward less green colour, lower nutrient retention and softer vegetables with their changes being faster at higher temperature. The seasoned spinach soup may be stored for appropriate time periods under chilled conditions and used in the food service industry with good quality characteristics.