A COMPARATIVE ASSESSMENT OF HYDROLYSIS METHODS USED TO OBTAIN FISH COLLAGEN PEPTIDES AND INVESTIGATION OF THEIR AMINO ACID BALANCE

Abstract

Biotechnological methods for obtaining peptides of unique composition by means of protein hydrolysis are widely used in the food, agricultural and medical industries. One promising source of active peptides is considered to be collagen-rich solid byproducts, obtained from the fish-processing industry, whose proteins contain valuable amino acids. For the extraction of proteins, high-temperature processing (thermolysis) with preliminary fermentation is frequently recommended. The resulting dispersion is further divided into peptide, lipid and mineral protein fractions, which are used for various purposes. This method was proposed by the ANiMOX GmbH company (Germany) and tested in the Kaliningrad State Technical University (KSTU, Russia). At the fish product canning enterprises of the Kaliningrad region, about 50% of fish solid wastes (heads, ridges, bones, scales, entrails), which approximately equals to 10 tons per day, remains unprocessed. This work is aimed at comparing the quality of hydrolysis products obtained from collagen-rich solid fish wastes by the thermal, fermentative and combined methods. A series of experiments was carried out using waste product samples from the RosKon fish cannery complex. Proteins were obtained by three methods: fermentolysis, thermolysis and the combination of fermentolysis and thermolysis. Using centrifugation, the obtained suspensions were divided into the upper (fat), medium (water) and lower (sedimentary) fractions. The aqueous (medium) fraction presents a solution of peptides. Depending on the modes of the method used, peptide mixtures with a molecular weight (MW) from 0,1 kDa to 100 kDa were obtained. Low-molecular weight peptides with a MW lower than 10 kDa are considered to possess a high nutritional value, since they exhibit a high biological activity and are easily digested. During the hydrolysis of sardinella heads, the highest and the lowest yields of peptides with a MW lower than 10 kDa were achieved by fermentolysis (97,7%) and thermolysis (40,6%), respectively. The composition of amino acids in peptides is shown to depend on the type of both raw material and hydrolysis; however, all peptide fractions contain essential amino acids (leucine, lysine, phenylalanine, threonine, valine, etc.). Glycine, aspartic and glutamic acids, which are characteristic of collagen proteins, are established to prevail among other acids. The lyophilized peptide solutions obtained by all hydrolysis methods are demonstrated to contain more than 82% of proteins (calculated with reference to dried substance), less than 6% of mineral substances and less than 5% of fat. It should be noted that the peptides obtained by thermal hydrolysis exhibit the lowest amount of impurities. The obtained peptides can be used in the composition of animal feed (aquaculture, cattle, poultry), food additives, specialized nutrition for athletes and the elderly, as well as in microbiological media, cosmetic and medical preparations.