Chemical and physicochemical characterisation of co-products from the vegetable food and agro industries

Six co-products from the vegetable food and agro industres in Denmark – brewer's spent grain, pea hull, seed residue (rye grass), potato pulp, sugar beet pulp and pectin residue – were collected eight times during two seasons (four samples from each season) (n = 8; N = 48). The samples were analysed for dry matter (DM), ash, sand, protein, amino acids, ether extract (EE), carbohydrate constituents, enzyme digestible organic matter (EDOM) and physicochemical properties—water binding capacity (WBC) and swelling. The co-products in general had a low DM (142–216 g/kg as is), EE (6–54 g/kg DM) and protein (61–116 g/kg DM) content and a high content of non-starch polysaccharide (430–743 g/kg DM). Exceptions, however, were seed residue and pea hull which had a DM content of 896–923 g/kg as is, and brewer's spent grain which had a EE and protein content of 117 and 215 g/kg DM, respectively. The sugar beet pulp and potato pulp had a high content of soluble fibre, which resulted in high WBC and swelling. Even though pectin residue had a high content of insoluble fibre constituents, WBC and swelling were high. Seed residue, brewer's spent grain and pea hull had high content of insoluble fibre, which was responsible for the relatively low EDOM. There was a variation from year to year in the concentration of ash (P<0.0001) and sand (P=0.003) in seed residue and for protein (P=0.04) and EDOM (P=0.003) in pea hull. In conclusion, co-products from the vegetable food and agro industries are characterised by a high DF content resulting in high swelling and WBC and relatively low EDOM. The variability in chemical composition of most co-products was in the same relative range as found for barley and wheat in other national and Scandinavian studies.