CHARACTERIZATION OF THREE NOVEL ALKALINE SERINE PROTEASES FROM TOMATO ( LYCOPERSICUM ESCULENTUM MILL.) FRUIT AND THEIR POTENTIAL APPLICATION

In order to quest new potential plant protease and make it industrially applicable and cost‐effective, three novel proteases were detected in tomato ( Lycopersicum esculentum Mill.) fruit by sodium dodecyl sulfate (SDS)–gelatin–polyacrylamide gel electrophoresis. All three proteases were isolated and partially purified by heat treatment (70C, 5 min) and ethanol precipitation (0–33%, v/v), with ninefold increase in specific activity and 31.6% recovery. These proteases exhibited the highest specificity for gelatin substrate and were indentified as serine protease. The optimum pH and temperature of proteolytic activity were pH 8–10 and 37–60C, respectively. They were stable at high pH (up to 12) and temperature (up to 70C) and in the presence of 20 mM metal ions (Na + , Ba 2+ , Ca 2+ , Mg 2+ , Mn 2+ ), surfactants (SDS and 80 mM Triton X‐100) and denaturants (urea and dithiothreitol). These results suggested that proteases from tomato fruit had potential application in food, detergent, tannery and medical industries.PRACTICAL APPLICATIONS Plant cysteine proteases such as papain, bromelain and ficin are extensively applied in many industries. Recently, several plant serine proteases, which were more stable under demanding conditions than cysteine proteases, were exploited for industrial applications. Tomato is one of the highest produced and consumed vegetables in the worldwide. Alkaline serine proteases from tomato fruit in this paper were stable at high pH and temperature and in the presence of metal ions and oxidation. Enzyme activity against a wide variety of nature protein substrates indicated that they would be investigated for a range of potential commercial applications especially for gelatin and casein hydrolysis in the food processing industry as well as for the dissolution of casein and bovine hemoglobin in detergent industry.