Studies on integrated processes for the recovery of mucilage, hull, oil and protein from solin (low linolenic acid flax)

Abstract

The proportions of testa, endosperm, cotyledon and soluble solids (principally mucilage) in solin seed were determined to be 10, 21, 57 and 11%, respectively, by manual dissection of soaked seed. Endosperm/cotyledon contained 17.4 and 81.6%, respectively, of the total seed oil, and 16.3 and 75.6%, respectively, of the total seed protein. The testa and soluble solids fraction contained 24.6 and 26.3%, respectively, of the total seed dietary fibre. The yield, composition and physicochemical characteristics of mucilage were influenced by both extraction temperature and alcohol precipitation. Ethanol and isopropanol were equally suitable for mucilage precipitation. A prototype, wet dehulling system was developed. The system consisted of a blender, with its blades covered with latex tubing, in which degummed solin seed was slurried in water. Optimum dehulling conditions resulted in the recovery of 75% of the testa, and a loss of 8% of endosperm/cotyledon in the hull fraction. Extraction of oil from dehulled solin presscake with azeotropic isopropanol was slower than with hexane. Isopropanol-extractedmeal was lower in total lipid and lighter in colour than hexane extracted meal. Optimum azeotropic isopropanol oil extraction conditions resulted in an oil recovery of 96%, with less than 2% oil in the alcohol phase after chilling of miscella. Isopropanol recovered by chilling was suitable for precipitation of mucilage. Studies on aqueous extraction of oil from dehulled seed were discontinued due to the high residual oil content in meal and the formation of a stable oil-water emulsion. Concentrated protein products were prepared from azeotropic-isopropanol-extracted and hexane extracted solin meal by alkali extraction and acid and aqueous alcohol washing. The aqueous alcohol effluent from mucilage precipitation was suitable for use in the production of protein products. None of the protein products contained 65% or more of protein on a moisture-free basis. Protein products prepared by acid or aqueous alcohol washing were similar in functionality, but generally inferior to soy flour controls. Functionalities of solin hull and the hull fraction were similar to those of pea hull and wheat bran. Hydrocyanic acid, trypsin inhibitor and phytic acid were associated with endosperm/cotyledon and, therefore, present in higher concentration in dehulled seed than in the hull fraction. The opposite was true for phenolics. Concentrated protein products were lower in HCN, trypsin inhibitor and phenolics compared to oil-free meals, but were enriched in phytic acid.