Physicochemical characteristics and molecular structures of gelatin extracted from bovine skin: effects of actinidin and papain enzymes pretreatment

Two plant enzymes, namely actinidin (A) and papain (P), were used to pretreat bovine skin at the respective optimum pH and temperature of the enzymes for 48 h at the level of 0, 5, 10, 15, 20, and 25 unit/g of skin, and gelatin extraction was done at 60 degrees C for 6 h. Gelatin yield from actinidin at level 20 (A20) (22.67%) and papain at level 20 (P20) (23.59%) were significantly (P < 0.05) higher than control (17.90%). The gel strength values for gelatin extracted using actinidin enzyme (GEA) were significantly (P < 0.05) higher than the control (283.35 g), and the gel strength for A20 was 366.39 g. However, gelatin extracted using papain enzyme (GEP) showed relatively lower gel strength. The GEA sample viscosities were significantly (P < 0.05) higher than control (12.10 mPa.s). GEA samples revealed overall degradation of beta chains and presence of alpha chains and lower molecular weight peptides, whereas beta and alpha chains were completely absent and lower molecular weight peptides were seen in all the GEP samples. Fourier-transform infrared (FTIR) spectra indicated a greater loss of molecular order and more disruption in the alpha helical structure of P20 compared to A20 and control gelatins. Scanning electron microscopy (SEM) revealed interconnected bigger particle size and denser structure with least number of voids in A20 than P20 and control gelatin samples. Thus, it was concluded that actinidin, particularly at level 20 unit/g of skin, could be used to improve the yield and properties of gelatin from bovine skin.