Biofuel derived yeast protein concentrate (YPC) as a novel feed ingredient in carp diets

A novel yeast co-product obtained from a bio-ethanol process in which wheat was the predominant feedstock was tested in a series of iso-nitrogenous (38% crude protein) and iso-lipidic (8%) diets for juvenile mirror carp (Cyprinus carpio). The fishmeal protein component of a basal diet (control treatment) was effectively replaced by a yeast protein concentrate (YPC) at 7.5, 15, 20, and 50% of total dietary protein. After an 8 week feeding trial all fish fed YPC showed better (P<0.05) growth performance than the control fed fish, with diets containing 15% and 20% YPC being optimal. Proximate composition analysis revealed that body protein, lipid and NFE levels were unaffected by dietary treatment (P>0.05), however, ash levels were elevated in fish fed >= 15% YPC (P<0.05). Subsequently, body gross energy was significantly reduced at 50% YPC inclusion. Both alanine aminotranferase (ALAT) and aspartate aminotranferase (ASAT) were measured as indicators of hepatic function in carp. Liver ASAT activity was significantly lower in fish fed 20% and 50% YPC, but no effects were seen in ALAT activities. Additionally, preliminary histological assessment of liver and intestinal tissues gave no indication of impairment to health, but high YPC inclusion (>= 15%) elevated the number of goblet cells present in the posterior intestine (P<0.05). Molecular microbiological analysis using DGGE revealed no distinctive changes in intestinal microbial communities. This study reveals the potential benefits of utilising a biofuel derived YPC on the growth and feed utilisation performance of carp, with no apparent detrimental impacts on general health and physiological status as determined by gut and liver function and related metabolism. (C) 2011 Elsevier B.V. All rights reserved.