Abstract
To enrich the diet, soybean plays great role by reducing protein malnutrition by substituting animal protein. However, the major problems in raw soybeans are off flavor and anti-nutritional factors. Processing also affect nutritional value unless optimum processing methods are used. Thus, this investigation was carried out to evaluate the effect of soaking temperature and time on anti-nutritional factors (phytic acid and condensed tannins) made from soybean variety AFGAT (Glycine max). Two soaking temperatures hot water (40 ° C) and ambient temperature (25 ° C) and three soaking times (8, 12 and 16 hrs) were considered in the experiment. The study revealed that soaking time and temperature had significantly (p<0.05) affected on anti-nutritional factors. Soy flour condensed tannin was significantly (p<0.05) higher (0.23 mg CE g -1 ) at 16 hrs soaking time with 40 ° C. The values exhibited reduction in condensed tannin (0.03±0.01 mg CE g -1 ) soaking at 8 hrs for 40 ° C. The soaking time and temperature showed reduction in condensed tannins from 0.29 mg CE g -1 (raw) to 0.02 mg CE g -1 . Higher (9.17mg g -1 ) soy flour phytic acid was observed at 12 hrs soaking time with 40 ° C. Increased in the level of phytic acid from 4.11 mg g -1 (raw) to maximum 9.17mg g -1 (soaked for 12 hr at 40 ° C) in flour was observed. Soy milk condensed tannin was also affected by soaking time and temperature and ranged from 0.07 to 0.24 mg CE g -1 for soybean soaked for 8 hrs at 25 ° C and 40 ° C and for soybean soaked for 16 hrs at 25 ° C, respectively. The higher soy milk phytic acid was 8.31 mg g -1 for soybean soaked for 8 hrs at 25 ° C. The phytic acid was decreasing when the soaking time increases at lower temperature. In conclusion the anti-nutritional factors of soybean flour and milk were influenced by soaking time and temperature. The result obtained suggests that good quality soybean flour and soybean milk can be obtained from soybean soaked for 8 hrs at 40 ◦ C. Keywords: Anti-nutritional factors, Soaking time, temperature, Soybean, Soy flour, Soy milk DOI : 10.7176/FSQM/85-02 Publication date :March 31 st 2019
Highlights
The soybean (Glycine max (L) Merrill, family Leguminosae) is important source of high quality, inexpensive protein than other legumes and about 35 -38 % of its calories are derived from its protein as compared to 20 – 30% in most other beans
Raw soya flour condensed tannins content was 0.29 (±0.01) mg CE g1. This value was higher compared to the value reported by Yimer and Admassu (2008) for raw Awassa soybean variety (0.19 mg CE g1) and Belessa variety (0.08 mg CE g1)
The phytic acid in raw soybean flour was 4.11 (±0.23) mg g-1. This value was less than the phytic acid contents of raw Belesa soybean variety (12.33 mg g-1) reported by Yimer and Admassu (2008)
Summary
The soybean (Glycine max (L) Merrill, family Leguminosae) is important source of high quality, inexpensive protein than other legumes and about 35 -38 % of its calories are derived from its protein as compared to 20 – 30% in most other beans. Soy flour had protein content between 35 and 40% and a fat level between 15 and 20% It is extremely nutritious and high in fiber and contains all of the vitamins, minerals, and phytochemicals of soybeans. Soy milk containing good quality protein, fat, isoflavones, vitamins, minerals and carbohydrate has attracted a great deal of public attention as a healthy food and a good choice for people who are lactose intolerant, in which 75% of the world population have no ability to digest lactose that causes stomach cramp, flatulence and diarrhea (Riaz, 2006). The ANFs can be fully or partially removed by pretreatments (Harmuth-Hoene, et al, 1987), including blanching, soaking, dehuling, germination, fermentation and cooking can greatly influence protein digestibility and palatability and improve nutritive value of soybean products (Wang, et al, 2003). Search for suitable soy milk and soy flour processing methods that can be locally adapted, improve the nutritional quality through suppressing the anti-nutritional factors and off flavor nature coupled with better nutrient extraction are required for proper utilization of soybean flour and milk in Ethiopia
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