Impact of microwave-assisted heating and enzymatic treatment on functional and antioxidant properties of rainbow trout (Oncorhynchus mykiss) by-product hydrolysates
Fish protein hydrolysates (FPH) have been widely used as a mean to better utilize fishery by-products through the use of proteolytic enzymes to produce a wide range of functional peptides that can be used as food ingredients. Studies have shown that these functional peptides have enhanced interface-stabilizing properties (e.g. functionality) and antioxidant activity. FPH production can be accelerated by using rapid heating methods (e.g. microwave) compared to slower conventional heating (CH). The objective of this study was to investigate the effects of microwave heating (MW) during enzymatic hydrolysis on functionality and antioxidant properties of FPH. Treatments consisted of adding Alcalase™ to rainbow trout by-products (frames) at 0.5%, 1.7% and 3.0% (w/v) enzyme substrate ratio (E:S). Hydrolysis was for 3, 5 and 15 minutes, respectively, using a microwave system (1200W, 20% power with 50% duty cycle at 50-55°C) and a CH method (water bath at 50°C). Degree of hydrolysis (DH), protein solubility (PS), emulsifying activity index (EAI), emulsion stability (ES), foam capacity (FC), foam stability (FS), 2,2-Diphenyl-1-picryhydrazyl (DPPH) radical-scavenging activity and ferric ion reducing capacity (FIRC) were evaluated. MW-assisted hydrolysis increased the number of peptide bonds broken (DH) by alcalase compared to hydrolysis of CH treatments. Protein solubility of MW-FPH was higher than CH-FPH at pH 3 and 7. MW-FPH (hydrolyzed 5 min with 0.5% E:S) showed higher (P < 0.05) EAI and ES compared to CH-FPH. Foaming capacity and stability were also higher (P < 0.05) for MW-FPH samples that were hydrolyzed for 15 min (0.5% E:S) compared to CH FPH. Antioxidant activity (DPPH and FIRC) of MW-FPH was overall higher (P < 0.05) than CH-FPH. Hence, MW-assisted hydrolysis is an alternative method to produce FPH in shorter amount of time (higher DH) with improved solubility, emulsifying activity, foaming properties and antioxidant activity. By-product hydrolysates derived from microwave-assisted hydrolysis show great potential as value-added food ingredients.
Liceaga, Purdue University.
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