Soaking and cooking modify the alpha-galacto-oligosaccharide and dietary fibre content in five Mediterranean legumes

Abstract

The effects of soaking and cooking on soluble sugars, alpha-galacto-oligosaccharides (α-GOS) and soluble dietary fibres (SDF) and insoluble dietary fibres (IDF) were assessed in five legumes (lentil, chickpea, fenugreek, faba bean and Egyptian faba bean). In raw seeds, total α-GOS content ranged from 2500 mg/100 g (chickpea) to over 4000 mg/100 g (fenugreek). Stachyose was predominant in fenugreek, lentil and chickpea, whereas verbascose was the main α-GOS in faba bean and Egyptian faba bean. IDF represented 69–87% of the total dietary fibres in all studied legumes, while SDF content varied noticeably. During soaking, total α-GOS content decreased between 10% (lentil and faba bean) and 40% (chickpea). In fenugreek, soaking reduced IDF and increased SDF concentration, possibly due to partial IDF solubilisation from the cell wall. Cooking further decreased α-GOS and increased total dietary fibre content. The different behaviours of these five legumes during processing illustrate the high biodiversity within legume species.