Effect of Soaking and Roasting on the Physicochemical and Pasting Properties of Soybean Flour

Abstract

The effects of soaking and roasting on the physicochemical and pasting properties of soybean flour were evaluated. Soybean seeds were soaked overnight in tap water for 0–72 h, hand dehulled, dried, and part of the sample was roasted. Roasted and unroasted soy beans were milled into flour and analyzed. The results showed that the total carbohydrates (22.8–27.9 g/100 g), the ash content (3.5–3.6 g/100 g), and the total polyphenols (0.29–0.51 g/100 g) did not significantly change during both the soaking and roasting processes. However, the total proteins (35.8–46.0 g/100 g) and lipid contents (21.4–29.5 g/100 g) were significantly (p < 0.05) affected only by soaking, with a decrease in total protein and an increase in lipid contents. Phytate content (0.22–0.26 g/100 g) decreased significantly (p < 0.05) only with roasting. The tannins (0.01–0.30 g/100 g) and soluble proteins (4.0–29.0 g/100 g) significantly (p < 0.05) diminished with both treatments. There was a significant increase in the least gelation concentration (20–30 g/100 mL), a decrease in the swelling power (1.3–2.0 mL/mL), and consequently, reduction in the viscosity (range peak viscosity 18–210 cP) of the flour slurry after soaking and roasting. All these qualities—needed for producing nutritious flour for infants—highlighted the efficiency of these endogenous technologies.

Functional Properties of Select Dry Bean Seeds and Flours

“…() reported 1.32, 1.19, 1.26, 1.30, 1.14, and 1.12 g/g OHC for whole pinto, pink, Great Northern, dark red kidney, light red kidney, and small white bean flours, respectively, which are comparable to the OHC of the beans in our study. Additionally, several dry beans have been reported to have OHC values in the same range (1 to 2 g/g) as in our investigation (Adebowale & Lawal, ; Aguilera et al., ; Ai et al., ; Appiah et al., ; Du et al., ), as do certain oilseeds, including soybean (Agume, Njintang, & Mbofung, ; Makeri et al., ; Padilla, Alvarez, & Alfaro, ), lupine (Sathe, Deshpande, & Salunkhe, ), and winged bean (Makeri et al., ; Sathe, Deshpande, & Salunkhe, ). OHC found in our investigation (0.96 g/g) for soybean flour was comparable to that reported by Lin, Humbert, and Sosulski (), 84.4% (that is, 0.84 g/g) and higher than the reported oil absorption capacity for defatted soy flour, 29.59% (that is, 0.29 g/g) reported by Padilla et al.…”

“…More recently, Agume et al. () observed raw soybean flour LGC at 20% (w/v), which increased to 30% (w/v) when soaked 72 h and roasted. Ghribi, Maklouf, Blecker, Attia, and Besbes () reported LGC to be 14% and 16%, respectively, for Kabuli and Desi chickpea seeds obtained from a local market in Tunisia.…”

“…Similarly, Bambarra groundnut (Adebowale & Lawal, 2004) and adzuki bean (Tjahjadi, Lin, & Breene, 1988) flours have been reported to not form a gel when tested using concentrations up to 14% and 20%, respectively. More recently, Agume et al (2017) observed raw soybean flour LGC at 20% (w/v), which increased to 30% (w/v) when soaked 72 h and roasted. Ghribi, Maklouf, Blecker, Attia, and Besbes (2015) reported LGC to be 14% and 16%, respectively, for Kabuli and Desi chickpea seeds obtained from a local market in Tunisia.…”

The effects of different pre-treatments on the physicochemical composition and sensory acceptability of ‘Kacang Koro’ energy bar

“…The reduction in tannin was estimated at 99.9% after soaking-roasting, while soaking could reduce up to 99.8%. This result is in a close agreement with a study conducted by Agume et al (2017), who used soybean flour as a sample and showed that tannin content decreased generally using the soaking-roasting pre-treatment. It was also shown a similar result in a study by Agume et al (2016), using 48 hrs of soakingroasting of maize, and the tannin content was reduced by 22%.…”

“…The lower percentage of ash content is when using the soaking-microwave and soaking pre-treatment while the higher percentage is when using the soaking-roasting pre-treatment. The ash content in raw 'Kacang Koro' is 0.94%, however, the previous studies showed the percentage of ash content in 'Kacang Koro' after roasting is 3.6% (Akanji and Ogungbesan, 2014), and 3.5% (Agume et al, 2017), which clearly shows an increase of the percentage when using the roasting pre-treatment. Okoye and Eke-Ejiofor (2018) have obtained slightly higher ash content in his energy bar than this study which ranges between 1.54% and 1.90% and the energy bar was made of nuts, sesame seeds, and cereals.…”