EFFECT OF SOAKING PRE-TREATMENTS ON NUTRITIONAL COMPOSITION AND FUNCTIONAL PROPERTIES OF BAMBARA GROUNDNUT (VIGNA SUBTERRANEA) FLOUR

Abstract

Bambara groundnut (Vigna subterranean) is one of the underutilised legumes in Nigeria. The protein content of the seeds is high with a good balance of essential amino acids, especially lysine and methionine. Bambara groundnut is a particularly hardy crop, being extremely drought resistant, and can be grown under extreme climatic conditions; hence, it is a promising crop against global climatic changes. However, the legume contains certain anti-nutrients which hinder the efficient utilisation, absorption or digestion of nutrients and thus reduce their bioavailability and their nutritional qualities. This study investigated the effect of soaking pretreatments on the nutritional composition and functional properties of flour from black and cream Bambara groundnut with a view to provide information that will enhance the end use of the legume. Soaking the seeds in hot water for 4 h resulted in the highest reduction in the tannin, phytate, trypsin inhibitor, oxalate and heamagglutinin contents of the flour compared to 24 h soaking in cold water and 3 h soaking in hot water. Soaking does not have significant (P>0.05) effect on the proximate composition of the flours, irrespective of cultivar. Moisture, ash, fat, protein and crude fibre contents ranged from 9.9-11.5%, 2.7-3.1%, 7.6-9.4, 18.4-19.7% and from 1.1-2.3%, respectively. The mineral composition of the flour was significantly (P<0.05) affected by the soaking treatment. Soaking in hot water resulted in a greater reduction in mineral content than soaking in cold water. Water absorption capacity ranged from 69.6-90.8% while dispersibility ranged from 70.5-75.5%. Swelling power and solubility ranged from 4.9-5.9 and from 22.7-31.9%, respectively. Emulsion stability, foaming capacity and foaming stability of the flours ranged from 59.8-78.5%, 10.0-18.0 foam volume/ml and from 50-66%, respectively. The study concludes that soaking pretreatment led to significant reduction in the anti-nutritional factors and mineral content (copper, manganese and zinc) of Bambara groundnut flour.