Comparison of properties of mung bean (Vigna radiata) protein isolate films at different pH

M.N. Nasriyanti, Noor Aziah, A.A. and R. Ahmad

Abstract

Mung bean protein isolate was prepared from mung bean (Vigna radiata) flour by extraction with 1N NaOH and precipitated at pH 4 with 1N HCl. Glycerol 3% (w/v) was added to the mung bean protein isolate 5% (w/v) solution to form a transparent edible film. The films were then adjusted to pH 8, 10 and 12 with 2N NaOH and dried at 60 °C for 12 h. The water vapour permeability of the films was evaluated using the ASTM Method E96-80, the tensile tests of the films were evaluated using the ASTM Method D882-80a, with some modifications. The water vapour permeability of protein (5%) films at three different pH did not differ significantly (p <0.05). The protein film at pH 8 has a higher moisture sorption isotherm than those made at pH 10 and 12 as a function of a_w. The elastic modulus differed significantly (p <0.05) between the protein films at a_w 0.22. The tensile strength of protein film at pH 8 was significantly lower (p <0.05) than those of protein films at pH 10 and 12 at a_w 0.22–0.84. Protein film at pH 12 was significantly higher (p <0.05) on elongation percentage than at pH 8 and 10 at a_w 0.22–0.84.

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