# Evaluation of Atlantic cod hydrolysate properties in innovative freeze concentration techniques

## TL;DR

This study examines the properties of Atlantic cod hydrolysate to develop an energy-efficient freeze concentration process using a high-temperature heat pump system.

## Contribution

A novel freeze concentration process for fish protein hydrolysates is introduced, aiming to reduce energy consumption in drying.

## Key findings

- Cod hydrolysate protein content ranged from 43.38% to 87.77% on a dry basis.
- Fish protein hydrolysates showed Newtonian behavior at low concentrations and Bingham behavior at high concentrations.
- Glass transition temperature of hydrolysates was as low as −32.45°C, indicating suitability for freeze concentration.

## Abstract

This study investigates Atlantic cod's (Gadus morhua) physicochemical and rheological properties throughout various stages of the hydrolysis process to assess the feasibility of integrating a high-temperature heat pump system for hydrolysis and freeze concentration. This approach will significantly reduce the energy consumption of the current drying processes. The total protein content of cod hydrolysate ranged from 43.38 % ± 0.07 to 87.77 % ± 0.2 on a dry basis, progressing from the initial fish protein hydrolysates mixture to the refined fish protein hydrolysates. The free and total amino acid profiles were analyzed, confirming the presence of all essential amino acids in the samples. Rheology test assessments indicated that fish protein hydrolysates exhibited Newtonian fluid behaviour at lower concentrations, shifting to Bingham fluid behaviour at higher concentrations. Viscosity values spanned from 0.0023 to 1.41 Pa s across concentrations ranging from 3.75 % to 44.42 %. However, deviations in viscosity were observed at elevated temperatures due to decomposition. Differential scanning calorimetry (DSC) determined the FPH's thermal properties and phase transitions concerning water contents. The lowest recorded glass transition temperature was −32.45 °C.

•Investigating the thermophysical and rheological properties of Atlantic cod fish protein hydrolysates.•Employing differential scanning calorimetry to examine the phase change of fish protein hydrolysates.•Introducing a novel concentration process for fish protein hydrolysates.•Highlighting the optimal properties of fish protein hydrolysates for freeze concentration.•Addressing the limitations associated with freeze concentration.

Investigating the thermophysical and rheological properties of Atlantic cod fish protein hydrolysates.

Employing differential scanning calorimetry to examine the phase change of fish protein hydrolysates.

Introducing a novel concentration process for fish protein hydrolysates.

Highlighting the optimal properties of fish protein hydrolysates for freeze concentration.

Addressing the limitations associated with freeze concentration.