Lentil Starch Content and its Microscopical Structure as Influenced by Natural Fermentation

Dry lentils seeds are a good source of high quality protein, vitamins, and a balanced range of minerals. They are also an excellent source of complex carbohydrates and dietary fibres [1]. Lentil seeds, which are highly accepted in most parts of the world, provide one of the best means of fighting malnutrition among people in developing countries [2]. In several countries, reduction in the consumption of legumes in general, and lentils in particular, has been related to the presence of antinutritional factors in these legumes. Cheap methods are required to improve nutritional quality, by either removing antinutritional compounds or by raising the levels of nutritional enhancers. Traditional methods such as germination and fermentation tend to improve the nutrient quality of foods. Fermentation is generally achieved by native microflora. Fermented food is a widely exploited source of valuable protein. Among the legumes, soybeans have been extensively used for this purpose [3], although other legumes such as beans and chickpeas are also occasionally used [4]. Fermentation is associated with many chemical changes that enhance organoleptic response, contents of free sugars and vitamins, as well as bioavailability of minerals [5, 6], and results in the breakdown of some of the antinutritional endogenous compounds [7–11]. Ikenebomeh [12] found that the levels of reducing sugars and soluble nitrogen in African locust bean gum increased dramatically as a result of natural fermentation. Beuchat et al. [13] proposed peanuts and cowpeas as acceptable substrates for the preparation of natto-like products. In lentils, Ragaee et al. [14] observed that natural fermentation for 4 days at 32 °C increased the availability of total amino acids and improved in-vitro protein digestibility. These authors [15] also reported a good consumer acceptance of products formulated from fermented lentils, while Mahaja and Chauhan [16] noted that natural fermentation improved the HCl-extractability of minerals including calcium, magnesium and copper in pearl milled flour. VidalValverde et al. [8, 17] have also shown that natural fermentation of lentils caused an increase in vitamin content and an improvement in the available starch:total starch ratio. Tabera et al. [9], Frias et al. [10] and Kozlowska et al. [11] reported that fermented lentil flour is an excellent source of protein and that natural fermentation removed a high amount of trypsin inhibitor activity, tannins, α-galactosides and phytic acid. Although most studies reported on natural fermentation have been related to protein quality and the elimination of some antinutritional factors, the full potential of natural fermentation on legumes is still unknown. The present work investigates the modification in starch content and starch’s microscopical structure that occurs during natural fermentation of lentils at different times, temperatures and concentrations of flour.