![]() Tilapia is one of the major farmed species in China with a production over 1.62 million tons in 2018. ![]() However, there is no detailed information on hydrothermal pretreatment for the extraction of gelatin from fish scales. Recently, hydrothermal pretreatment has been successfully used to generate protein hydrolysates or free amino acids from different protein sources, including plant materials, fish by-products, animal by-products and even pure protein like β-casein and bovine serum albumin. The autoclave batch reactor is one of the most widely used tools for hydrothermal processing because there is no need for a pumping system, in spite of the relatively long heating and cooling period time. The increase in ionic product drives the formation of H 3O + and OH − ions, which facilitates water to appear as an acid or base catalyst. Under hydrothermal conditions, water has unique features, such as increased ionic products and a structural change in the hydrogen bond. Recently, application of hydrothermal pretreatment in hydrolysis of macromolecule substance has been investigated. A simple and efficient extraction technology for gelatin hydrolysates is thus needed. Taken together, the conventional methods used for the preparation of gelatin hydrolysates are generally reactant-, cost- and time-consuming and even bad for the environment. In addition, the overall extraction efficiency of gelatin is typically low, limiting industrial output. Nevertheless, chemical pretreatment is often harmful to the environment. Gelatin hydrolysates are then produced by enzymatic hydrolysis of the extracted gelatin based on the commercial proteases’ specificity. Firstly, gelatin is extracted from raw materials by a chemical pretreatment with dilute acid or alkali, which destabilizes the triple-helix through a disruption in hydrogen bonding and some covalent cross-links, thus enhancing protein solubilization. Gelatin hydrolysates from aquatic by-products are generally obtained by two separate operations. Although the nutritional value of gelatin is quite low for humans due to the lack of some essential amino acids, once it is hydrolyzed, gelatin hydrolysates have good process suitability and bioavailability, making them potential sources for value-added foods. Correspondingly, fish processing by-products containing a large amount of collagen, such as fish skin, fin, bone and scale, are becoming potential alternative sources for gelatin production. Fish gelatin has received increasing attention, because of the safety and religious concern of the mammalian analogue. Gelatin is widely used in biomedical, cosmetic, leather, food and pharmaceutical industries. Hydrothermal treatment followed by enzymatic hydrolysis offers a potential solution for preparation of gelatin hydrolysates for food ingredients from fish processing by-products. The ACE inhibitory activity of gelatin hydrolysates was stable under high temperature, pH and gastrointestinal proteases. The obtained gelatin hydrolysates mainly distributed in the range of 200–2000 Da with an angiotensin I-converting enzyme (ACE) IC 50 value of 0.73 mg/mL. The hydrothermal treated scales showed a better protein recovery (84.81%) and DH (12.88%) and released peptides more efficiently than that of the conventional treated samples. Results showed that hydrothermal treatment could enhance protein recovery of tilapia scales without demineralization and dramatically improve the DH of the hydrolysates. The effect of the hydrothermal process on protein recovery, degree of hydrolysis (DH) and structural properties of the hydrolysates was investigated. The objective of this work was to develop a method for protein recovery from fish scales and evaluate the hydrolysis of the scale protein. ![]() Protein hydrolysates from fish by-products have good process suitability and bioavailability in the food industry.
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