Nutritional characterization of millet protein concentrates produced by a heat-stable α -amylase digestion

Abstract

We prepared various millet protein concentrates by a heat-stable α -amylase (Termamyl 120L) digestion, i.e., foxtail millet (FC), proso millet (PC), Japanese white barnyard millet (WBC) and Japanese black barnyard millet protein concentrates (BBC). Nutritional characterization for these protein concentrates was performed from the aspects of chemical and protein compositions, amino acid composition, and protein digestibility, biological value and net protein utilization were determined using rats. The yield of millet protein concentrates was 10% or more, and the protein recovery of millet protein concentrates exceeded 85% irrespective to the original millet flours. Protein concentrations of FC, PC, WBC and BBC were 668, 777, 763 and 637 g · kg −1, respectively. The lower protein concentration of BBC would reflect the higher dietary fiber content in the original millet flour, because dietary fiber fraction was concentrated in the process of protein production. Although lysine contents of millet protein concentrates were slightly lower than those of the corresponding millet flours, protein compositions of millet protein concentrates were similar to those of the corresponding millet flours. Lysine was the first limiting amino acid for all millet protein concentrates. The amino acid score of FC (28) was higher than those of PC (21), WBC (23) and BBC (25), and protein digestibility of FC (90%) was also higher than those of PC (80%), WBC (71%) and BBC (61%). The net protein utilization of FC (37%) was slightly higher than those of PC (35%), WBC (32%) and BBC (33%). Repeated production of millet protein concentrates confirmed that our method using a heat-stable α -amylase would be suitable for an industrial mass-production, and that the resultant millet protein concentrates would be useful enough to sustain a protein nutrition in combination with other foods. FC, in particular, would be the most recommendable millet protein concentrate among all millet protein concentrates tested.