Valorization of Aquaculture By-Products of Salmonids to Produce Enzymatic Hydrolysates: Process Optimization, Chemical Characterization and Evaluation of Bioactives.

José Antonio Vázquez,Noelia Sanz,Jesus Valcarcel,Isabel Rodríguez-Amado,Ricardo I Pérez-Martín,Carmen G Sotelo

doi:10.3390/md17120676

Abstract

In the present manuscript, various by-products (heads, trimmings, and frames) generated from salmonids (rainbow trout and salmon) processing were evaluated as substrates for the production of fish protein hydrolysates (FPHs), potentially adequate as protein ingredients of aquaculture feeds. Initially, enzymatic conditions of hydrolysis were optimized using second order rotatable designs and multivariable statistical analysis. The optimal conditions for the Alcalase hydrolysis of heads were 0.1% (v/w) of enzyme concentration, pH 8.27, 56.2°C, ratio (Solid:Liquid = 1:1), 3 h of hydrolysis, and agitation of 200 rpm for rainbow trout and 0.2% (v/w) of enzyme, pH 8.98, 64.2 °C, 200 rpm, 3 h of hydrolysis, and S:L = 1:1 for salmon. These conditions obtained at 100 mL-reactor scale were then validated at 5L-reactor scale. The hydrolytic capacity of Alcalase and the protein quality of FPHs were excellent in terms of digestion of wastes (Vdig > 84%), high degrees of hydrolysis (Hm > 30%), high concentration of soluble protein (Prs > 48 g/L), good balance of amino acids, and almost full in vitro digestibility (Dig > 93%). Fish oils were recovered from wastes jointly with FPHs and bioactive properties of hydrolysates (antioxidant and antihypertensive) were also determined. The salmon FPHs from trimmings + frames (TF) showed the higher protein content in comparison to the rest of FPHs from salmonids. Average molecular weights of salmonid-FPHs ranged from 1.4 to 2.0 kDa and the peptide sizes distribution indicated that hydrolysates of rainbow trout heads and salmon TF led to the highest percentages of small peptides (0–500 Da).

Highlights

The production of aquaculture fish around the world achieved 80 million tons in 2016, supposing48% of the total fish captured, transformed, and marketed [1]
The aims of this work are (1) optimization of the experimental conditions to produce fish protein hydrolysates (FPHs), using Alcalase, of salmonid by-products by response surface methodology (RSM), (2) mathematical analysis of hydrolysis kinetics by Weibull equation, (3) chemical characterization of products obtained from salmonid hydrolysis, (4) identification of average molecular weights and peptide size distribution of the hydrolysates, and (5) determination of two bioactives from FPHs
The moisture of these samples ranged between 66% and 70% and the organic matter was higher in salmon than rainbow trout and superior in trimmings + frames compared to heads by-products

Summary

Introduction

The production of aquaculture fish around the world achieved 80 million tons in 2016, supposing. 48% of the total fish captured, transformed, and marketed [1]. Rainbow trout (Oncorhynchus mykiss) and mainly Atlantic salmon (Salmon salar), is the most important in economic. Mar. Drugs 2019, 17, 676; doi:10.3390/md17120676 www.mdpi.com/journal/marinedrugs. Mar. Drugs 2019, 17, 676 and volume terms in the European fish farming system. More than 1.78 MTm of both were produced in 2016 generating more than € 15 billion [1]. Huge amounts of by-products (about 35–45% of the total weight of salmonids) are generated in processing plants, mainly heads, trimmings, viscera, and frames that have to be managed efficiently to reduce environmental health problems and to improve the sustainability of such farming productions [2,3]

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Conclusion