Upgrading Food Processing Side Streams

Wheat-derived Distillers’ Dried Grains with Solubles (DDGS) and wet solids (in-process sample) were utilised as raw material for the production of biopolymers and oligosaccharides. The protein content of samples was extracted under aqueous ethanol conditions (70%, v/v) at 70 °C, in the presence of 1% (w/w) sodium metabisulfite as reducing agent. DDGS protein extracts had a protein content of ∼45% (w/w) and the wet solid-derived extracts ∼58% (w/w). The achieved protein yield for DDGS was 30.1% (w/w) whereas 55.3% (w/w) of the total protein was recovered from wet solids. The lower protein extractability from DDGS could be attributed to the decreased solubility of protein aggregates formed during the intensive thermal treatment of the drum drying stage. Protein extracts from both samples were utilised for the development of biodegradable films, with DDGS protein-derived films exhibiting a darker colour compared to wet solid ones, possibly due to heat-induced Maillard reactions during the DDGS production process. DDGS and wet solids protein films showed higher moisture sensitivity, compared to films produced using commercial gluten. This feature could be advantageous for using the films for agricultural and horticultural applications, e.g. as fertiliser release matrices and soil conditioners. Moreover, the solid residues of DDGS and wet solids after protein extraction had high carbohydrate content (49%, w/w) consisting primarily of water unextractable arabinoxylans. Enzymatic treatment of the residues with a food-grade endo-xylanase led to the production of potentially prebiotic xylo-oligosaccharide (XOS) mixtures with a degree of polymerisation (DP) of up to 7, and a XOS purity (DP≥2) of 70.2% in the DDGS hydrolysates and 51.8% in the wet solids hydrolysates.