Functional properties of low‐fat soy flour produced by an extrusion‐expelling system

Abstract

Low-fat soy flour (LFSF) obtained by extrusionexpelling processing was investigated for functional properties. Flours with the following various levels of protein dispersibility indexes (PDI) and residual oil (RO) contents were investigated: "high" 67 ± 4/10.4 ± 1, "mid" 42 ± 3/7.4 ± 2, and "low" 14 ± 5/6.5 ± 0. The solubility of all three LFSF was minimal at pH 4.0 and increased at more alkaline and acidic pH levels. Waterholding capacity (WHC) increased with a decrease in PDI and RO content, whereas fat-binding capacity (FBC) decreased. Foaming stability increased as PDI and RO increased, with significant differences between all LFSF samples. Emulsification capacity (EC) was measured at three pH levels (5.5, 6.7, and 8.0). At each pH level, the "low" samples showed the least EC compared to the "mid" and "high" samples, with no significant difference between the "mid" and "high" samples at pH 6.7 and 8.0. Emulsification stability and activity decreased from low LFSF to high LFSF. This study showed that in general low LFSF was less functional than the other flours tested and there was no significant difference in the functionality of mid-and high-LFSF samples.Research efforts to find value-added uses for soybean protein in food and nonfood products have been going for some time. Researchers have found that soy protein is a promising substitute for animal protein in foods because it contains all of the essential amino acids required for the diet, does not negatively affect sensory attributes (except flavor), and has additional health benefits including the lowering of blood cholesterol levels and reduction of risk of some cancers (1,2). In nonfood applications, soy protein has been used in wood adhesives as a partial replacement for petroleum-based ingredients, and in other applications such as biodegradable plastics and paper coatings and sizings (3). These value-added uses for soy proteins are based on the functional properties of the protein that add key characteristics to the food or nonfood product that is being formulated. The properties include emulsification, foaming, gelation, and water and fat binding. Recently, researchers have sought to add additional value to soy protein by using alternative processing techniques, genetic engineering, or traditional plant breeding to incorporate new, desirable characteristics or alter undesirable characteristics inherent in the soybean. In this paper, the potential for adding value to soy through an alternative processing technique, namely extrusion-expelling (EE) processing, will be discussed.Traditional industrial soybean processing involves solvent extraction of the oil with subsequent desolventizing and drying of the meal. The meal is then further processed via grinding and separation steps to produce flour, meal, or grits. An alternative soybean processing technique is the EE process developed by Nelson et al. (4) at the University of Illinois. EE processing relies on the mechanical extraction of soybean oil and thus does not incorporate any chemicals in the ext...

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