Comparative study of the effect of dry and wet ginger (Zingiber officinale Roscoe) spice on the proximate and microbial safety of soybean beverage

Abstract

Soybean beverage, most common nutritious local beverages in Nigeria and other nations of the world, is a high protein beverage used as a dairy milk substitute with limited utilization due to natural or ambient conditions that serves as growth medium for micro-organisms, hence a short shelf life. This study examines the shelf life of soybean beverage preserved with ginger spice (dried at 70 ˚C, 80 ˚C, 90 ˚C and 100 ˚C and 2 g and 4 g of fresh/wet ginger respectively) over 7-week period. The samples were (A: plain soybean beverage; B: 200 ml soybean beverage + 2 g of ginger dried at 100 ˚C; C: 200 ml soybean beverage + 2 g ginger dried at 90 ˚C; D: 200 ml soybean beverage + 2 g ginger dried at 80 ˚C; E: 200 ml soybean beverage + 2 g ginger dried at 70 ˚C; F: 200 ml soybean beverage + 2 g fresh ginger; and G: 200 ml soybean beverage + 4 g fresh ginger respectively). The proximate, pH, microbial and sensory analyses of samples ranged as follows: 87.35% - 90.83% for moisture content; 0.58% - 0.65% ash content; 4.65% - 4.96% protein; 0.10%-0.26% fibre content; 2.06% - 2.98% crude fat and 1.68% - 4.17% carbohydrate and pH values ranged from 6.2 - 6.5. Microbiological analysis over storage period showed the control sample ranged from 0.4×106 -8.3×106 cfu/ml and treated samples 0.4×106 to 2.4×106 cfu/ml. Low values of the treated samples probably due to preservative and anti-microbial properties of the spice, with samples treated with dry ginger spice better preserved than others. Sensory evaluation by twenty eight persons showed that sample E: (200 ml soymilk+ 2 g ginger dried at 70 ˚C) was most preferred (for taste, aroma and overall acceptability), while there was significant difference in appearance of the samples.