Determination of Protease Activity of Koji based on the Extruded Broad Bean Paste and Its Process Optimization

In this paper,broad bean(faba)was as the main material,with the addition of wheat flour in appropriate proportion,the extrusion technology was adopted for pretreatment of faba and wheat flour,which could improve protease activity in koji-making technique for broad bean paste. The Box-Behnken central combination design was applied and the response surface methodology was used to study the effects of the speed of screw,the proportion of wheat flour,the temperature of barrel,the moisture of material on the protease activity of koji for broad bean paste. The optimum koji-making technique in the paste production using swelling materials was determined. Results showed that,the optimum parameters of extrusion process were as follows:the speed of screw was 120 r/min,the proportion of flour was 17%,the temperature of barrel was 130℃,the moisture of material was 45%. In that condition,protease activity was(1331.91±8.22) U/g,which was increased by 33.57% compared with traditional cooking method. The fermentation was conducted with the koji of higher protease activity. The broad bean paste became reddish-brown in color and showed good flavor. The contents of amino acid nitrogen and moisture were 0.720 g/100 g and 50.75%,respectively.