ARTICLE 64 FEED & ADDITIVE MAGAZINE January 2023 at 118 °C in 6 M HCl. Due to the low cost of processing and the consequent widespread hydrolysis, this method is often used to convert secondary raw material from fish into fertilizer (Elavarasan et al., 2019). However, during acid hydrolysis important amino acids such as tryptophan, methionine, cystine are normally lost. In addition, asparagine and glutamine are converted into aspartic acid and glutamic acid respectively. Due to the formation of salts during the neutralization process, acquired hydrolysates have weak functional properties. Therefore, many methods of separation of salt have been suggested, such as nano filtration and the use of ion exchange resins with excellent performance. ALKALINE HYDROLYSIS Wide water-soluble polypeptides are easily broken in the alkaline hydrolysis process. Sodium hydroxide is mainly used in the alkali hydrolysis process. A high pH of 12.5 at 95 °C for 20 minutes was used in the small-scale batch system developed to hydrolyze the fish protein concentrates to increase functionality (Elavarasan et al., 2019). The key drawback of this process is the development of low amino acid content in hydrolysates such as cystine, lysine, arginine, serine, threonine, isoleucine and produce residues such as lanthionine and lysinoalanine. FERMENTATION PROCESS It uses natural or cultured microorganisms (starter cultures). During the growth of the organism, they hydrolyze the nutrients particularly carbohydrate and proteins. The extracellular microbial proteases hydrolyze the proteins into peptides of varied molecular size. Depend upon the microorganism species used for fermentation, the property and quality of protein hydrolysate differs. NUTRITIONAL PROPERTIES The protein contents of FPH vary between 60.0% and 90.0% depending on the types and sources of raw material and hydrolysis protocol (Kristinsson & Rasco, 2000; Bhaskar et al., 2008). Due to the solubilisation of protein during enzymatic hydrolysis and removal of lipid after hydrolysis increase the protein content of FPH. However, the protein content of the FPH also varies with the temperature during drying process. The raw materials having higher percentage of lipids that produce lower amount of solubilized protein. Reduced lipid content in FPH may increase the stability of the final product towards lipid oxidation, which may increase the shelf life of FPH in storage condition. The high ash contents in FPH may be due to the addition of alkali for pH adjustment and breakdown of bones in the raw material. The moisture content of FPH should be below 10% of total composition to retain its quality (Bhaskar et al. 2008; Chalamaiah et al. 2010). FUNCTIONAL PROPERTIES Solubility Protein solubility is referred to as the quantity of protein that goes into the solution under identified settings. Hydrophobic interactions promote protein-protein interactions which decreases their solubility whereas ionic interactions support protein water interactions favoring the solubility characteristics. The potential applications of proteins in FPH can be expanded with higher solubility. The level of degree hydrolysis (DH), pH, temperature, ionic strength, type of solvent and processing conditions strongly influence the solubility of protein. Long time hydrolysis leading to a high degree of hydrolysis resulting in protein solutions with smaller molecular weights of higher solubility. Emulsifying properties Emulsions are thermodynamically unstable systems as a result of the large positive energy at the inSr. No 1 2 3 4 Nutritional component Protein Moisture Fat Ash Composition (%) 60-90 < 10 < 5 0.45 - 27 Table: Nutritional components of FPH (Marchbank et al., 2008)
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