Functional and Rheological Profile of LAB-fermented Bambara Groundnut (Vigna subterranean (L)) Flour

Abstract

Lactic fermentation is commonly employed to improve protein digestibility and overall nutritional quality of grains foods. This study evaluated the functional and rheological properties of flour samples from Bambara groundnut fermented with Lactobacillus plantarum [NRRL B-4306] and Lactobacillus fermentum [NRRL B-1932] obtained from the United States Department of Agriculture. Functional profile such as particle size index, water absorption capacity, swelling capacity, and least gelation concentration of the flour were determined; as well, amylograph and maturograph evaluations were used to determine the rheological properties and the results presented as average, minimum, and maxi­mum values. Particle size determination observed that 150, 125, 105 µ orifice did not readily accommodate particles from the non-inoculated samples while the inoculated samples passed through 150 and 125 µ but did not readily pass through 105 µ orifice. Bioprocess with lactic acid bacteria increased the water absorption capacity of the flour samples from 346.5 to 386.4%, the least gelation concentration decreased from 5.3 to 4.1%, while swelling capacity increased from 14.9 to 23.2 mg/100 g for non-inoculated and inoculated flours, respectively. Rheological investigations show evaluations for amylograph and maturogram determinations. Values obtained for amylograph indicate that temperature at start of gelatinization was peak at 63.8 and 63.00C for non-fermented and LAB-fermented flour with no significant (p ˂ 0.05) difference, while temperature at maximum viscosity and maximum viscosity had significant (p ˂ 0.05) values of 92.1 and 76.00C, as well as 730 and 265 brabender units (BU), respectively. Thus, amylograph quality of the fermented flour sample was indicated by the maximum viscosity which is significantly higher in the case of non-inoculated flour sample. The maturograph evaluation also recorded the maturation behavior of the dough prepared from the test flours after the proofing time (fermentation rest) by means of a sensing probe which records the elasticity of the mature dough every 2 min and produces the typical zigzag form of the maturogram. This action was recorded in maturograph units (MU) on the strip-chart with values of 44 and 28 min for final proof time, 750 and 610 MU for dough level, 210 and 220 MU for dough elasticity, as well as 10 and 12 min for proofing stability, determined respectively for non-fermented and LAB-fermented flour samples. LAB-fermentation demonstrated to improve the functionality and rheology of Bambara groundnut flour and the production process could be further controlled to achieve products of optimal quality.