Soyabean meal versus soyabean protein isolate: A comparative study of the nutritive and functional attributes

Author: Oluwatoyin Aletor

Received 17 December 2009, accepted 22 April 2010.

Abstract

Soya bean meal (SBM) and soya bean protein isolate (SPI) were both prepared from soya bean seeds. The two samples were comparatively characterized with respect to their proximate constituents, energy values, mineral constituents, amino acid profile and functional properties. The crude protein (CP), ether extract (EE), crude fibre (CF), ash, nitrogen-free extract (NFE) and gross energy of the SMB averaged 42.0, 1.2, 5.6, 5.9, 31.9 g/100 g DM and 486.2 kcal/100 g, respectively. The corresponding values for the SPI were 85.8, 0.6, 0.2, 1.0, 4.4 g/100 g DM and 512.4 kcal/100 g, respectively. One of the major nutritive minerals analysed, potassium was the most abundant in SBM followed by phosphorus and calcium while sodium was the least one. Among the trace minerals, iron had the highest concentration and manganese the least one. A similar trend was found in SPI except that phosphorus was the most abundant among the major minerals. The amino acid profile of the SMB and SPI showed a favourable balance of both the essential and the non-essential amino acids. For example in SBM, values for lysine, valine, phenylalanine, aspartic acid, glutamic acid, proline and serine were 25.6, 20.2, 21.0, 48.0, 74.5, 20.9 and 21.1 g/16 g N while the corresponding values for SPI (which were higher) were 50.0, 42.5, 42.2, 43.4, 98.4, 160.8, 45.4 and 43.0 g/16 g N, respectively. From the scores, the 1^st limiting amino acid was methionine for both SMB and SPI at 41.7 and 47.2%, respectively. The SBM had fat absorption capacity (FAC), water absorption capacity (WAC), emulsion capacity (EC) and emulsion stability (ES) of 200, 310, 45.7 and 46.8% while the SPI had 1000, 1000, 46.3 and 0%, respectively. High variations were found in FAC and WAC which was indicated by high coefficient of variation (CV) of 94.3 and 74.8%, respectively. The foaming capacity (FC) and foaming stability (FS) of SMB and SPI were 63, 108% and 3.3, 120%, respectively. The two samples had varying solubilities with change in pH. The proteins generally had multiple maxima and minima in their solubilities. Isolation of protein from soya bean to get SPI, generally brought about increased nutritive and functional attributes when compared with soya bean meal (SBM).

Key words: Soya bean meal (SBM) and soya bean protein isolate (SPI), proximate constituents, energy values, mineral constituents, amino acid profile and functional properties.