Soaking water composition

Abstract

Soaking legumes is necessary for consumption, but nutritional losses occur during this process. Partial explanation to the altered nutritional profile of soaked legumes could be leaching in the processing water. Therefore, this chapter examines recent publications and discusses new experimental findings on the composition of legume soaking water. Studies have shown that the soaking water of legumes contained 0.26–2.38 g-100 mL of dry matter. Seeds geometry (size, shape) and structure (whole, split) affects leaching, with the highest losses for haricot beans and split yellow peas. Soluble and insoluble carbohydrates each constitute about 30% of the leached material, followed by lower levels of protein (20–30%) and minerals (15–20%). Iron, magnesium, potassium and phosphorous were present in nutritionally relevant quantities: 100 mL of legume soaking water contained up to 200% of the recommended daily intake. On the contrary, phenolic compounds and saponins were found in modest amounts: 0.3 and 3.0 mg/g, respectively. Similarly, antinutritional factors such as phytic acid and trypsin inhibitors represented minor fractions of the solids. Only soybean soaking water contained about 3 TUI/mg of trypsin inhibitors, well below values of processed legume foods (1.6–14 TUI/mg). In closing, legume soaking water is an interesting source of oligosaccharides and minerals.