Fractionation is a potential way to valorize under-utilized fishes, but the quality of the resulting fractions is crucial in terms of their applicability. The aim of this work was to study the quality of protein isolates and hydrolysates extracted from roach (Rutilus rutilus) and Baltic herring (Clupea harengus membras) using either pH shift or enzymatic hydrolysis. The amino acid composition of protein isolates and hydrolysates mostly complied with the nutritional requirements for adults, but protein isolates produced using pH shift showed higher essential to non-essential amino acid ratios compared with enzymatically produced hydrolysates, 0.84–0.85 vs. 0.65–0.70, respectively. Enzymatically produced protein hydrolysates had a lower total lipid content, lower proportion of phospholipids, and exhibited lower degrees of protein and lipid oxidation compared with pH-shift-produced isolates. These findings suggest enzymatic hydrolysis to be more promising from a lipid oxidation perspective while the pH-shift method ranked higher from a nutrient perspective. However, due to the different applications of protein isolates and hydrolysates produced using pH shift or enzymatic hydrolysis, respectively, the further optimization of both studied methods is recommended.
The aim of this research was to study the biochemical properties of a new protein-rich feed additive produced by the short-term intense thermal treatment and subsequent enzymatic hydrolysis of the wastes of poultry slaughter and primary processing (feathers and fluff). It was found that this feather-based fermented feed additive contained high amounts of crude protein (86.52%); and the content of easily digestible low-molecular peptides in the additive was 9% higher compared to fishmeal. The amino acid profiles of the additive and fishmeal were compared. The effectiveness of substituting the additive for fishmeal in the diet of broiler chicks was demonstrated by the in vivoexperiments. The results showed that the digestibility of the dietary nutrients was higher in broilers that were fed the new additive compared to those fed fishmeal, which resulted in higher meat productivity: the average daily weight gains in additive-fed broilers was 3.82% higher (p <0.01) compared to fishmeal-fed control broilers, the dressing was 1.4%higher, the muscle in the carcass was 2.1% higher, and the feed conversion ratio was 3.57%lower. The sensory evaluation scores of the meat and broth were also higher in the additive-fed broilers.
Keywords: feedadditive, feather wastes of poultry slaughter, enzymatic hydrolysis, distribution of molecular peptide weights, digestibility, productive performance in broilers