Distillers' Dried Grains with Solubles (DDGS) is the major by-product of bioethanol and distillery plants. Due to its high content of proteins, water-soluble vitamins and minerals, DDGS has been long marketed as animal feed for livestock. EU legislation on liquid biofuels could raise the demand on bioethanol production in Europe, with a resulting increase in DDGS availability. DDGS contains a spectrum of complex organic macromolecules, particularly polysaccharides, in addition to proteins and vitamins, and its use as a starting raw material within a biomass-based biorefining strategy could lead to the development of multi-stream processes for the production of commodities, platform molecules or speciality chemicals, with concomitant economic benefits and waste reduction for bioethanol plants. The present review aims to outline the compositional characteristics of DDGS and evaluate its potential utilisation as a starting material for the production of added-value products. Parameters of influence on the chemical and physical characteristics of DDGS are discussed. Moreover, various pre-treatment strategies are outlined in terms of efficient DDGS fractionation into several added value streams. Additional processing steps for the production of medium and high added value compounds from DDGS are evaluated and their potential applications in the food and chemical industry sector are identified.

Wheat Distillers' Dried Grains with Solubles (DDGS) and in-process samples were used for protein extraction. Prolamins were the predominant protein components in the samples. The absence of extractable α- and γ-gliadins in DDGS indicated protein aggregation during the drum drying processing stage. Prolamin extraction was performed using 70% (v/v) ethanol or alkaline-ethanol solution in the presence of reducing agent. DDGS extracts had relatively low protein contents (14-44.9%, w/w), regardless of the condition applied. The wet solids were the most suitable raw material for protein extraction, with recovery yields of ∼ 55% (w/w) and protein content of ∼ 58% (w/w) in 70% (v/v) ethanol. Protein extracts from wet solids were significantly rich in glutamic acid and proline. Mass balance calculations demonstrated the high carbohydrate content (∼ 50%, w/w) of solid residues. Overall, the feasibility of utilising in-process samples of DDGS for protein extraction with commercial potential was demonstrated.

Polymer films were developed utilising proteins extracted from wheat distillers' dried grains with solubles (DDGS) and in-process samples (wet solids), both by-products of bioethanol production process. Structural characterisation of DDGS and wet solids films indicated a change in the secondary structure of the proteins, reflecting the impact of DDGS production process such as effect of enzyme on protein properties and consequently on the film properties; whereas the developed films exhibited a rough surface with voids.Determination of moisture sensitivity indicated that DDGS films exhibited more hydrophilicity than wet solids films, with the same trend being observed for their water solubility and water uptake. The moisture content and solubility of DDGS films ranged from 10.2-14.2 % and 32.3-41.8 % respectively whereas those for wet solids' film ranged from 18.9-19.8 % and 23.8-24.2 % respectively. The mechanical properties of DDGS and wet solids (ranging from 0.27-0.32 MPa) were comparatively lower than commercial wheat gluten film (0.6 MPa). The poor mechanical properties and high water vapour permeability of DDGS and the wet solids films limit their application as biodegradable packaging materials.However, based on their hydrophilicity, the developed films have potential applications in agriculture and horticulture as controlled release matrices and soil conditioners.

HighlightsAX was determined in wheat grain after commercial and laboratory alcohol production.Samples from laboratory scale production were similar to those from commercial processing.The concentration, solubility and dynamic viscosity of AX increased during processing.AX in DDGS was less variable in composition and properties than that in whole grain.DDGS has potential to provide a source of AX for novel products.

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