Kiwifruit (Actinidia deliciosa) extract shows potential as a low-cost and efficient milk-clotting agent

Actinidin, a cysteine protease accounting for more than 50% of the soluble proteins in kiwifruit pulp, has shown promise as a milk-clotting agent. In this study, the potential use of kiwifruit pulp extract as a clotting agent was investigated. It was shown that three kiwifruit extracts made from the pulp of a single fruit have significantly different levels of active actinidin, depending on the extraction buffer employed. Kiwifruit extract prepared at pH 5.0 had the best milk-clotting properties, with a nearly 30% better ratio of clotting activity to proteolytic activity than purified actinidin. This extract produced a casein coagulum clearly separated from the whey proteins, and was shown to be stable at room temperature for up to two months. This extract has the potential to be employed as an efficient and low-cost milk-clotting agent in the production of dairy products.