Assessing the Enzymatic Hydrolysis of Salmon Frame Proteins through Different By-Product/Water Ratios and pH Regimes.

Cristian Ramirez,Paula Garcia,Silvana Valdivia,Suleivys Nuñez,Paula Jimenez,Sergio Almonacid,Reza Ovissipour,Marlene Pinto,Alvaro Perez,Manuel Ruz,Pedro Valencia

doi:10.3390/foods10123045

Abstract

The enzymatic hydrolysis of fish by-product proteins is traditionally carried out by mixing ground by-products with water. In addition, pH control is used to avoid pH drops. Higher costs are involved due to the use of pH control systems and the consequent energy cost in the drying stage. This work aimed to evaluate the effect of these conditions on the hydrolysis of salmon frame (SF) proteins, including the SF hydrolysis without added water. SF hydrolysis by subtilisin at 50, 75, and 100% SF under different pH regimes were evaluated by released α-amino (α-NH) groups, total nitrogen, degree of hydrolysis, and estimated peptide chain length (PCL) at 55 °C. The concentration of released α-NH groups was higher in the conditions with less added water. However, the nitrogen recovery decreased from 50 to 24% at 50 and 100% SF, respectively. Changing the SF/water ratio had a more significant effect than changing the pH regime. Estimated PCL changed from 5–7 to 7–9 at 50 and 100% SF, respectively. The operating conditions affected the hydrolysis performance and the molecular characteristics of the hydrolysate.

Highlights

More than 50% of fishery products are discarded as wastes [1,2]
As degree of hydrolysis (DH)’ and peptide chain length (PCL) are molecular characteristics that modulate hydrolysates’ functional properties, we have found that different operating conditions will generate different hydrolysates in terms of these properties
A novel study of the Salmon frames (SF) protein hydrolysis has been performed in non-ideal conditions such as 100% SF in the reaction mixture and uncontrolled pH

Summary

Introduction

More than 50% of fishery products are discarded as wastes [1,2]. The use of fish by-products involves using zero-cost raw materials that can be converted into low-marketvalue products, such as meals for animal nutrition or fertilizers, or into high-market-value products, such as functional and bioactive protein hydrolysates for human foods. Compared to the chemical hydrolysis, the enzymatic hydrolysis of fish by-products is an efficient valorization alternative that converts the original proteins into peptides exhibiting various functional properties [4,5]. The first step is performed by mixing a certain amount of raw material with water to allow the mixture to be homogenized and, later, agitated during the enzymatic reaction step. The first goal of this study was to compare the performance of SF hydrolysis with and without added water. The novelty of our study is the enzymatic hydrolysis of SF in the condition without added water, the main challenge of which is to keep the system properly mixed. A quantitative comparison of the enzymatic hydrolysis at different water contents, including the condition without added water, and in different pH control regimes was made in this work. The condition without added water and uncontrolled pH corresponds to the main novelty of this study

Materials

Hydrolysis Reaction

Characterization of Hydrolysis

Findings

Conclusions