Agar films containing fish protein hydrolysate for extending fish fillets shelf-life

Abstract

The incorporation of protein hydrolysates in food is an increased commercial interest, because the resources to produce peptides are available and due to the bioactive properties that could be presented, such as the antimicrobial activity. Thus, agar films containing Argentine croaker (Umbrina canosai) protein hydrolysate were applied on flounder (Paralichthys orbignyanus) fillets in order to evaluate the effect of these films during 7 days of storage at 5 °C. Protein of Argentine croaker muscle was alkali-solubilised at pH 11.2 and recovered at pH 5.0 to obtain a protein isolate. This substrate was hydrolysed using Alcalase to 20% degree hydrolysis. The physicochemical characteristics of recovered proteins were evaluated. Thus, films with and without (control) incorporation of protein hydrolysate were prepared. Mechanical and barrier properties of the films were characterized. The microbiological and physicochemical properties of flounder fillets coated with films were monitored on zero, 3, 5 and 7 days of storage at 5°C. Results showed that the protein content of isolate was 92.13% and polar amino acids comprise approximately 59.80%. The presence of hydrolysate increased significantly (p < 0.05) the water solubility, elongation at break, when compared to control films. However, the control films showed a higher tensile strength (27.46 MPa) than the hydrolysate film (19.89MPa) (p < 0.05). The short chain peptides could act as plasticizers in films, reducing the interaction between the polymers, increasing the free volume between them and the elongation at break, and reducing the tensile strength, as verified in this study. These films decreased pH values and delay the growth of total aerobic mesophiles and Enterobacteriaceae, bacteria when compared with control films on 7 days of storage. These results suggested that fish protein hydrolysates are good source of natural antimicrobial peptides and can be utilized for improvement the shelf life of flounder fillets.