Processing a maize germ side stream: de-oiling as key to dry fractionation and foam stability

Maize grain processing usually starts with degerming to lower its oil content. The created maize germ-enriched fraction (MGF) represents up to 15 % of the kernel mass. Oil recovered from the MGF is valuable, but the non-oil fraction is underutilized. We separated MGF (14 % protein, 40 % starch, 18 % oil; db) into enriched fractions via dry processing, and reflect on the energy efficiency in combination with additional aqueous extraction. Dry fractionation requires mechanical pressing and oil extraction with hexane or food-safe 2-methyltetrahydrofuran, which yields cakes having residual oil contents of 0.4 w/dw% or 3.1 w/dw%, respectively. Both cakes could be milled, and air classification enriched protein in the fine fraction from 19 % to 27 % by deflecting larger starch granules. The protein yield relative to MGF was 15 %, mainly due to milling losses. CLSM revealed the protein to be in a fibrous matrix, hence it was not enriched further by electrostatic separation. Due to the moderate protein contents and yields, aqueous protein extraction was more energy efficient from de-oiled flour than from fine fractions. Extracts from hexane-processed fractions foamed better than whey protein at 0.5 mg protein/mL. Processing with 2-methyltetrahydrofuran did not enable stable foaming, which requires optimization towards lower residual oil contents.