Assessing the changes in protein content during the ensilage of the Indian Mackerel (Rastrelliger kanagurta) by biological method

Abstract

Fish silage is a liquefied product resulting from tissue hydrolysis and the richness of the silage is characterized by its nutritional profile comprising of proteins, amino acids, and fats. For the production of fish silage of high nutritional value, a precise assessment of the degree of hydrolysis, particularly proteolysis becomes a paramount importance. The goal of this study is to assess the changes in protein content in fish silage prepared from the Indian mackerel (Rastrelliger kanagurta) waste using 10% (v/w) sugarcane molasses, during 8 days of fermentation (DoF). The resultant ensiled product was evaluated for changes in titratable acidity, nutrients, total protein, total carbohydrate, total lipids content, and amino acid composition. Altogether, 17 types of amino acids were identified. Concentrations of total amino acids (TAAs, 15.627 ± 0.03 mg/g) and free amino acids (5.556 ± 0.08 mg/g) peaked at the end of 6 DoF with the predominance of histidine, arginine, alanine, asparagine, aspartic acid, and glutamic acid. Results of the non-metric multidimensional scaling (nMDS) plots and one-way analysis of similarities (ANOSIM) test indicated significant differences in the composition of TAAs at different DoF were discernible (nMDS, stress 0.03162, one-way ANOSIM R = 1; p < 0.0001). Similarity percentage (SIMPER) analysis indicated that the maximum content of amino acids (TAA and FAA) were released in silage during 4–6 DoF. A significant difference was observed in concentrations of most amino acids except cysteine, serine, and tryptophan (ANOVA, p < 0.05) at 2, 4, 6 and 8 DoF. Considering the vital role played by amino acids in providing resistance to plant pathogens as well as contributing to animal nutritional supplements, the results of the present study are highly noteworthy.