This study was devised to elucidate whether soused shrimp exhibits a digestive action on boiled pork meats, and the mechanism by which sousing with a high concentration of sodium chloride preserves nutrients in foods for a prolonged period.
Protease was isolated from soused shrimp using a combination of ammonium sulfate fractionation, DEAE - cellulose ion exchange chromatography and gel filtration. The isolated protease had specific activity of 1,560 units, 210 purification fold with an yield of 38%. Its optimum pH and temperature were 8.0 and 43 C, respectively. The molecular weight of - the enzyme was 35,000. The Km value of the enzyme for casein was ´1.6 x 10 -6 M. The enzyme required the presence of cupric ion to exhibit its full activity. Eighty eight percent of the enzyme activity was inhibited by 3.5 M NaCl showing a reversibly linear decrease of the enzyme activity as NaCl concentration increased. The nature of the inhibition by NaCl was reversible and noncompetitive. The protease activity in soused shrimp was well preserved with the elapse of time at least in part due to NaCl induced suppression of autodigestion. The enzyme was denatured by acid easily, i.e. 1% of the original activity remained after staying at pH 2 for 10 minutes, which is within the norm-al range of pH of the human stomach. Soused shrimp was observed to be one of those containing the highest protease activity compared with the other soused foods such as soused oyster, squid, clam, and Pollack intestine with respect to specific activities of dialized 1:4 whole homogenates (w /v) in 5 mM sodium phosphate-2.4 mM P - mercaptoethanol buffer, pH 8.0. Casein and boiled meats including pork, beef, and chicken appeared to be the good substrates for the protease. Cas-
ein was the best.
Therefore, the ingestion of boiled meats including pork together with soused shrimp would help digestion of boiled pork in human not only by increasing appetite also by the direct proteolytic digestion of boiled meats by soused shrimp to some extent. And a high concentration of sodium chloride inhibited the protease activity reversibly in a remarkable degree, which ensued in a significant retardation of autodigestion of protein in foods by proteases, and hereby contributed to the preservation of foods for an extended period.
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