Abstract
Plants represent an attractive source of milk-clotting proteases with potential use for chymosin substitution in cheesemaking process. A crude enzymatic extract from B. pinguin fruit showed capacity to clot milk efficiently in a short time. It showed a maximum milk-clotting activity around 4 U/mL in the range of 70-80 ºC. This value indicated that one mL of the extract was capable to clot around 400 mL of milk in 40 min at the specified condition. B. pinguin extract presented only 25% of its maximum activity under standard temperature (30-35 ºC) for cheese-making. Proteases inhibitors indicated that cysteine and serine proteases were present in the extract and could be responsible for the milk-clotting activity found. SDS-PAGE analysis of casein hydrolysis indicated that proteases in B. pinguin extract were more proteolytic than chymosin. The high presence of milk-clotting proteases in B. pinguin fruit offers an alternative new source of proteases for biotechnological processes.
Highlights
Rennet or milk coagulants are enzymatic preparations employed in cheesemaking process for thousand years
Milk-clotting activity is reported as a % relative to the maximum observed at the different temperatures
The milk-clotting characteristics of proteases are related with their activity and hydrolytic preference on kappa-casein (κ-CN) over others milk proteins during early stages of milk coagulation
Summary
Rennet or milk coagulants are enzymatic preparations employed in cheesemaking process for thousand years. Calf rennet contains a high concentration of chymosin (EC 3.4.23.4), which can represent up to 95% of total proteases in young calves abomasum extracts This proportion decreases with animal age, becoming pepsin the predominant enzyme in adult cattle abomasum extracts (Chitpinityol and Crabbe 1998). The worldwide increase in cheese consumption and the reduction in natural rennet supply has induced to look for new alternative sources of milk coagulants such as those obtained from microbial fermentation or genetically modified microorganisms. Some specific genera such as Mucor baciliformis and Rhizomucor miehei can produce, by fermentation, chymosin-like enzymes with similar milk-clotting properties (Chitpinityol and Crabbe, 1998; Machalinski et al 2006). Leaves, stems, fruits, flowers and some plant secretions (e.g. latex) have been commonly researched for protease characterization, exploring their proteolytic and milk-clotting properties
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