Effects of soybean pre-treatment on the performance of the alcoholic extraction process: yield, functionalities of the protein fraction and volatile fraction characterization

Abstract

Notably, soybean is known for the high nutritional value of its protein fraction and the high content of polyunsaturated fatty acids and beneficial bioactive components, such as tocopherols, phytosterols and isoflavones. The extraction of soybean oil is one of the main steps involved in the valorization process of this raw material. Usually, in a step prior to the extraction process, the soybean undergoes treatments such as lamination and/or expansion, which modify the raw material in terms of its structural characteristics and surface properties. These treatments, which will originate the soybean flakes or the soybean expanded mass, are applied to increase the oil extraction yield.The solvent industrially employed for extracting vegetable oils is a mixture of isomers of hexane, derived from petroleum. Despite its higher stability and extraction capacity, hexane presents high toxicity, flammability and high polluting capacity. Due to the potential health and environmental risks associated with the use of hexane, several alternative solvents have been studied, among them short-chain alcohols, especially ethanol, are widely cited because of their lower toxicity and superior operational safety. Due to their higher polarity, alcoholic solvents can extract a greater amount of unsaponifiable material from the solid matrix, thus increasing the nutritional value of the oils. In addition, ethanol is partially miscible with vegetable oils at room temperature, while hexane is completely miscible. This characteristic of partial miscibility with oils allows recovery of part of the alcoholic solvent only by cooling the solvent-oil solution from the solid-liquid extractor, leading to a reduction of the energetic demand in the desolventization step.On the other hand, despite its high nutritional quality, adequate functional properties and its low cost, the use of soy protein products in human food has been limited due to its characteristic odor. In this context, in general, studies report that the extraction of vegetable oils using ethanol as a solvent makes it possible to obtain defatted material of better sensory quality in relation to those obtained with hexane.According to the considerations listed, the main aim of the research project is to evaluate the performance of the process of alcoholic extraction of oil from soybean submitted to different industrial pre-treatments such as flaking and/or expansion, aiming to increase its competitiveness in substitution of the traditional process, in which hexane is used as solvent, and seeking its application on an industrial scale. In addition to the pre-treatment of the raw material, the impact of the different variables of the alcoholic extraction process, type of solvent (ethanol absolute or azeotropic, containing 0 or 6 mass % water, respectively) and temperature, will be studied in terms of oil extraction yield and protein fraction functionalities. As for the defatted solid from alcoholic extraction, besides the protein fraction, the volatile fraction will also be characterized in terms of its aroma profile.