Preservation of the Nutritional Quality of Soymilk by Heat Treatment

Abstract

Household soymilk preparation is labor intensive and time consuming, hence, in order to encourage soymilk consumption there is need for safe, easy, available, accessible and affordable measure of preserving the nutritional and safety quality for at least a few days after preparation even in areas of poor power supply that makes refrigeration unreliable. This experimental study was therefore designed to determine the effect of boiling for three consecutive days on the nutritional, physical, sensory and microbial properties of soymilk with a view of preserving the milk for consumption within the first three days after preparation. Soymilk was prepared using standard procedure. A sample was taken on the day of production (SM0) and set as control. This was subjected to boiling for 5 minutes twice a day (morning, 7a.m. and evening, 5p.m.) without covering the pot for three consecutive days and samples were designated as SM1, SM2 and SM3 respectively. Proximate composition, thiamine, riboflavin, niacin, vitamin C, mineral composition as well as pH, viscosity, specific gravity, microbial status and sensory properties were assayed using standard analytical methods. Mean data were compared using analysis of variance at p ≤ 0.05. Nutritional components of the soymilk sample increased with increase in days of preservation by boiling but the moisture content reduced significantly relative to control. Similarly specific gravity and viscosity increased while the pH reduced, though not significantly, throughout the experimentation period. The soymilk samples were free of coliforms throughout the preservation period while the microbial load fell within acceptable range for safe consumption. The sensory scores for taste, mouth feel, aroma and overall acceptability throughout the experimentation period was 8 which denotes ‘like very much’ except for color which reduced significantly to 7.79 in SM3 which is still acceptable. Boiling of soymilk for three consecutive days after production did not adversely alter its nutritional, physical, microbial and sensory properties except color which was impaired at the third day. Household preservation of soymilk by boiling should encourage its consumption especially in areas where refrigeration is not easily available.