Optimisation of ultrasound-assisted enzymatic extraction conditions of umami compounds from fish by-products using the combination of fractional factorial design and central composite design.

In this work, ultrasound-assisted enzymatic extraction (UAEE) conditions of umami compounds from Labeo rohita head (LRH) was optimised using the combination of fractional factorial design (FFD) and central composite design (CCD). Six factors that can potentially influence the degree of hydrolysis (DH), equivalent umami concentration (EUC), and extraction yield (EY) of umami extract were screened through FFD. The three most significant variables were further optimised using the CCD. The developed models were successfully fitted to the experimental data and used to determine optimal extraction conditions. The optimum DH (22.73%), EUC (6.61 g MSG/100 g protein), and EY (76.34%) of umami extract were achieved with a liquid-solid ratio of 3 (v/w), ultrasonication time of 19.20 min and hydrolysis time of 140.45 min. Besides, UAEE umami extract exhibited higher DH, EUC, EY, and umami taste compared to that of the conventional enzymatic extraction (CEE).

Effects of different pretreatments and proteases on recovery, umami taste compound contents and antioxidant potentials of Labeo rohita head protein hydrolysates.

Effects of the pretreatments namely heating, microwave (MW), and ultrasound (US), followed by the enzymatic hydrolysis using different proteases (flavourzyme, neutrase, and protamex) on the protein recovery, umami taste compound content, and antioxidant activities of the Labeo rohita head (LRH) protein hydrolysate was investigated. US and MW pretreatments increased the protein recovery, MSG-like amino acid and flavour 5'-nucleotide contents, equivalent umami concentration (EUC) and antioxidant activities of LRH protein hydrolysates significantly (p < 0.05). The type of enzyme influenced the protein recovery and EUC significantly but did not influence the flavour 5'-nucleotide content of LRH protein hydrolysate (p > 0.05). The highest recovery yield of LRH protein hydrolysate (69.75%) was obtained with the MW pretreatment followed by the protamex hydrolysis, while the highest EUC (41.82 g monosodium glutamate (MSG)/kg) was yielded with the combination of the US pretreatment and the flavourzyme hydrolysis. These results indicate that US and MW pretreatments can help to enhance the recovery yield, umami taste compound content and antioxidant activities of the LRH protein hydrolysate.