EVALUATION OF NUTRITIONAL QUALITY, PHYSICOCHEMICAL PROPERTIES AND SENSORY ATTRIBUTES OF FOUR SOYBEAN VARIETIES GROWN IN WESTERN KENYA

Abstract

Protein nutrition is important for human health because its deficiency leads to major public health problems such as Protein Energy Malnutrition. Soybean an excellent and cheap source of high quality protein has been introduced into developing countries for improved health and food security, but end use qualities may reduce its utilization. The main objective of this study was to evaluate the nutritional quality, physicochemical properties and sensory characteristics of four soybean varieties grown in Western Kenya. The physical characteristics of colour, grain size, hydration and swelling capacities and the cooking times were determined. The proximate analyses including moisture, crude protein, crude oil and ash were conducted using AOAC International approved methods. Protein nutritional quality was determined using male weanling albino rats for the indices of net protein retention, food efficiency, apparent and true protein digestibilities and faecal weight. The soybeans’ amino acid efficiency was evaluated using Protein digestibility corrected amino acid score. Sensory evaluation was conducted using a descriptive panel to characterize the four soybean varieties and a consumer panel for acceptability using a 9 point hedonic scale. The four soybean varieties had physical characteristics that ranged from pale yellow to yellow colours. Variety SB 132 had the highest length and width of 8.35 mm and 6.69 mm respectively, shortest cooking time of 128.33 minutes and best hydration and swelling capacities of 0.26 g/seed and 0.46 ml/seed, respectively. Variety SB 132 was also highest in proximate composition for the raw, roasted and boiled samples in crude protein at 40.18 g/100 g, 40.60 g/100 g and 36.71 g/100 g, fat at 23.00 g/100 g, 23.17 g/100 g and 21.83 g/100 g and energy at 1864.73 kJ, 1949.12 kJ and 1866.36 kJ, respectively. The raw soybean had the ash content between 7.83 g/100 g in SB 25 and SB 132 to 8.17 g/100 g in SB 30. Boiling reduced the ash content in comparison to the raw and roasted samples. Soybean diet SB 132 had the highest protein nutritional quality with the best protein retention of 6.29 g, Apparent Protein digestibility of 89.13%, True Protein Digestibility of 96.48%, weight gain of 5.50 g and a Net Protein Retention Ratio of 4.70. All the four soybean varieties had high amino acid profiles with a Protein digestibility Corrected Amino Acid Score of 1.0. Principal Component Analysis (PCA) revealed that of the 90% variation showed by the 26 attributes, 70% were due to the varieties and 16% due to physical characteristics. Soybean variety SB 132 was associated with positive characteristics of sweet and oily flavour, roasted soybean and sweet aromas and splitting surface by the descriptive sensory panel and the highest consumer liking rating on total quality of 7.42 in appearance, aroma, flavour and texture attributes. Soybean variety SB 132 is the most superior in digestibility, physicochemical properties, sensory characteristics and consumer acceptability and the study recommends its promotion as a food crop in Western Kenya and other developing countries for the management of Protein Energy Malnutrition and for food security.