Impact of soaking and cooking of soya (Glycine max L.) on the protein and oxalate content

Abstract

Aim: Soya (Glycine max L.) is a legume rich in nutrients (proteins, lipids, carbohydrates, and minerals) but also in anti-nutrients such as oxalate, which hampers the bioavailability of nutrients. The various processes used to treat it reduce the anti-nutrient content while affecting the protein content to a greater or lesser extent. This study aimed to evaluate the impact of a soaking period followed by cooking on the reduction of oxalates and enhancement of protein availability in soya flour. Methods: To achieve this, the response surface methodology with the centred composite design was used to reduce the oxalate content and increase the protein content of cooked soya flour. The factors chosen were soaking time (5–24 h), cooking time (15–50 min), and cooking temperature (70–100°C). The soya flours obtained were characterised for protein and oxalate content using standard methods. The optimal samples were also characterised. Results: The results obtained showed that cooking and soaking times, followed by the quadratic effect of soaking time, significantly (p < 0.05) increase the protein content and decrease the oxalate content. In terms of optimal conditions, a soaking time of 25.44 h, a cooking temperature of 101.05°C, and a cooking time of 61.93 min reduced the oxalate content by 87.43% and also increased the protein content from 35.98 g/100 g DM to 49.16 g/100 g DM. Optimal conditions of the different treatments also increase lipids, reducing sugar, and the main minerals like Ca, P, Mg, and Fe. Conclusions: The application of such conditions would help to combat protein deficiencies.