Mineral Elements, Lipoxygenase Activity, and Antioxidant Capacity of Okara as a Byproduct in Hydrothermal Processing of Soy Milk

Abstract

Minerals and antioxidative capacity of raw okara that was obtained as a byproduct from six soybean varieties during hydrothermal cooking (HTC) of soy milk were assessed. Lipoxygenase (Lox), an enzyme deteriorating the sensory characteristics of okara, was also investigated. All genotypes had very similar concentrations of Lox (4.32-5.62%). Compared to raw soybeans, the applied HTC significantly reduced Lox content in okara (0.54-0.19%) and lowered its activity to 0.004-0.007 μmol g(-1) min (-1). Correlation between the content of Lox in soybeans and that in okara (r = 0.21;p < 0.05) was not registered. This indicates that the content of this enzyme in okara depended much more on the technological process than on soybean genotype. Very strong correlation (r = 0.99; p < 0.05) between okara Lox content and its activity was found. The most abundant minerals in raw okara were potassium (1.04-1.21 g/100g), phosphorus (0.45-0.50 g/100 g), calcium (0.26-0.39 g/100 g), and iron (5.45-10.95 mg/100 g). A very high antioxidant capacity (19.06-29.36 mmol Trolox kg(-1)) contributes to the nutritional value of raw okara.

Comparative assessment of antioxidant, nutritional and functional properties of soybean and its by-product okara

“…A significant (p<0.01) difference was observed in iron and zinc contents of soybean and okara with total iron and zinc contents in okara as 6.82 and 7.04 mg/100 g, respectively, while in soybean the respective values were 8.28 and 7.86 mg/100 g. The values in present study are within the range of those reported earlier by Varsha Rani et al (2008) for Ca, Fe and Zn of soybean. Similar results were reported by Stanojevic et al (2014) for Ca, P, Fe and Zn of okara. However, Lu et al (2013) reported higher values for Ca and Fe and lower values for K and Zn in okara.…”

Distribution of β-amylase and lipoxygenase in soy protein products obtained during tofu production

“…After extracting soymilk from soybeans, okara remained in the precipitate (Figure 4). Lox content in okara protein extracts from investigated genotypes was low ranging from 0.02 to 0.53% (Table 2), which is in agreement with literature data [34].…”

“…Therefore, the aim of this study was to assess the distribution of the two enzymes: β-amylase and lipoxygenase, during the preparation of soy protein products by hydrothermal cooking of soybeans. This research is a continuation of our previous studies on the characteristics of soy protein products obtained by the HTC process [4,7,33,34].…”

“…Content of Lox in tofu whey as well as in okara protein extracts was in traces ( Figure 5; Table 2). This low content of Lox in tofu whey indicated that the activity of this enzyme was negligible and similar to Lox activity in okara protein extracts [34]. Namely, Lox is denatured at 69-74 °C [39].…”

Okara (soybean residue) biotransformation by yeast Yarrowia lipolytica

“…5A, 5B and 5C). When raw soybeans are ground, soybean lipoxygenases catalyse the hydroperoxidation of unsaturated fatty acids, such as linoleic and linolenic acids, and the intermediates are then lysed by soy hydroperoxide lyases to form aldehydes (Stanojevic et al, 2014). Therefore, the fresh okara contained the greatest amount of hexanal, although it decreased after autoclaving.…”