| The aim of this paper was to isolate, select and identify the Staphylococcus with protease activity in Rugao ham and Jinhua ham. Besides the factors influencing on protease secretion and the application of supernatant in fermented sausage were also studied.184 strains were isolated from the hams and 78 strains belonged to Gram positive Staphylococcus. 15 strains were screened for the capability of hydrolyzing casein. According to the physiological and biochemical identification, the selected strain C8 with highest protease activity was S.epidermidis.KH2PO4, CaCl2 and Beef Extract, the three significant variables were screened from eight nutritional constituents mainly affecting the protease production by Seriatim-Factorial Experiment and Plackett-Burman design. The three components were optimized by Response Surface Methodology and the concentrations were as follows: KH2PO4 2.24 g/L, CaCl2 0.34 g/L, Beef Extract 8.86 g/L. Inoculum volume, initial pH and shaking speed all had an obvious effect on protease secretion. Optimum condition (Inoculum volume 16%, initial pH 5.5, shaking speed 180rpm) was gained through L9 (34) orthogonal design. The protease activity raised from the original 12.60 U/mL to 34.52 U/mL, enhanced nearly two times.The moisture, pH and water activity (aw) all declined during the entire fermentation. Compared with the control batch, the final moisture of protease-added batch was lower. The pH in the batch with protease changed obviously, while the control was stable relatively during the fermentation.In the protease-added batch, the contents of free amino acid were all enhanced and the total increased 791.07 mg/100g. The aspartate were added more than two times. Besides the essential and fresh amino acid increased 106.49% and 134.96% respectively. In the aspect of volatile compounds, the kinds of them reached 69 in the protease-added batch. The content of aldehydes increased from 25.78% to 44.98%, but the alcohols were reduced. |
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