CHEMICAL COMPOSITION OF SOME FABA BEAN CULTIVARS

Abstract

Twelve cultivars of faba beans (Vicia faba L.) were analyzed for gross composition, nonprotein nitrogen, amide nitrogen, total free α-amino nitrogen, and for the presence of trypsin inhibitors (TI). In addition, protein solubility characteristics of three faba bean cultivars having low, medium and high protein contents were investigated. The gross composition of the cultivars showed variation only in protein (26 to 35%), total carbohydrate (55 to 61%), and starch (28 to 40%); ether extract, fiber and ash contents were relatively uniform. Nonprotein nitrogen, amide nitrogen, and free α-amino nitrogen contents of the cultivars were also largely similar. About 70 to 90% of the faba bean nitrogen was soluble in dilute sodium hydroxide (pH 12.0), and about 60% in dilute hydrochloric acid (pH 2.0) whereas only 8 to 10% of the nitrogen was soluble at pH 4.0 to 4.5 in a single extraction. Maximum precipitation of the extracted proteins also occurred at pH 4.0. The isoelectric points of faba bean proteins were in the region of pH 4.0 to 4.5. Protein solubility at pH 4.0 was increased threefold by extracting the meals with up to 1.0 M sodium chloride. At neutral pH, sodium chloride concentrations increased protein solubility only by 2 to 4%, whereas at the alkaline pH, protein solubility was decreased by 3 to 5%. Aqueous extracts of the cultivars contained different concentrations of TI. The range in inhibition of the standard trypsin assay was from 2 to 32%, indicating a significant difference in TI activities of the cultivars. None of the cultivars approached soybean (Glycine max Merr.) in its TI activity. The faba bean TI was heat-labile.