Characterisation of potential milk coagulants from Calotropis gigantea plant parts and their hydrolytic pattern of bovine casein

Abstract

The steady increase in world cheese demand keeps the search for appropriate coagulating enzymes as rennet substitutes in the scientific focus. This work reports the milk-clotting activities of aqueous crude enzyme (CE) from different parts of Calotropis gigantea using skim milk as substrate. CE from latex exhibited high caseinolytic (86.445 ± 1.055 U/ml) as well as milk-clotting activity (450 U/ml) when compared to other parts. Significant milk clotting index (MCI) was presented by crude enzyme of latex followed by stem, flower and leaf in the decreasing order (p < 0.05). CE from all parts showed an optimum activity at 37 °C, pH 5.5 and 10 mM calcium chloride concentration with excellent pH (4.5–6.5) and thermal stability (30–60 °C). Hydrolysis pattern of casein components by CE during 1 h incubation, as assessed by Tricine–SDS-PAGE, and subsequent peak analysis revealed CE from stem to be closely similar to that of rennin. However, extensive casein hydrolysis was observed when incubated with crude latex enzyme. Casein bands of CE and rennin tended to disappear as incubation progressed to 24 h. Proteolytic degradation was found to be advanced and resulted in complete breakdown of casein fractions unravelling the importance of incubation time as a possible essential requisite for controlled and appropriate casein hydrolysis. The study provides evidence of rennin-like activity associated with C. gigantea plant parts which may serve as a promising source of vegetable milk coagulant.