Biochemical analysis was carried out for pH profiles, freshness in terms of K-values, amino acids profiles, total volatile bases (TVB), total volatile acids (TVA) and biogenic amines for fresh and preserved Macrobrachium rosenbergii. Results showed that pH profiles of Macrobrachium rosenbergii explain the inability of this parameter to be used to evaluate the quality of Macrobrachium rosenbergii. Thus changes in pH profiles of Macrobrachium rosenbergii should be combined with indicators such as total volatile acids and total volatile bases. Total volatile acids of the shrimps increased steadily in small amounts throughout the storage period. A rapid increase in TVB at 100C was detected due to the increase in total aerobic bacteria at elevated temperatures. The microbial activities caused the decrease in the amino acids arginine, lysine and histidine which correlated well with the increase in the corresponding biogenic amines such as putrescine, cadaverine and histamine respectively. Preservatives used in this study controlled the production of these biogenic amines without significantly altering the pH of preserved shrimp.
Lipase from a newly isolated strain of Rhizopus rhizopodifonnis was partially purified and characterized. By acetone fractionation, the enzyme was purified to about 2.8 fold, with 62.5% recovery and with specific activity of 3.2 U/mg. By gel filtration through Sephadex G-100, the enzyme was further purified to 9.7 fold and had a specific activity of 11.1 U/mg. By polyacrylamide gel electrophoresis, five protein bands were observed after acetone fractionation, white two protein bands were observed after the preparation was passed through Sephadex G-100. It has a pH optimum at 6.0 and a temperature optimum at 45°C. The enzyme is most stable at pH 7.0 and temperature of 50°C. The enzyme has a preference for short chain triglycerides and can also hydrolyse some methyl esters. The lipase is specific for 1,3 positions.
Lipase daripada satu stren Rhizopus rhizopodifonnis yang baru dipencilkan telah diseparatulen dan diciri. Melalui fraksi asiton, enzim telah ditulen lebih kurang 2.8 ganda, dengan pengutipan 62.5% dan aktiviti spesifik 3.2 U/mg. Dengan penurasan gel melalui Sephadex G-l00, enzim ditulenkan lagi hingga 9.7 ganda dengan aktiviti spesifik mencapai 11.1 U/mg. Dengan elektroforesis gel poliakritamida, 5 jalur protein didapati selepas fraksi asetone, sementara 2 jalur protein dilihati selepas penurasan gel Sephadex G-10. Enzim ini mempunyai pH optimum pada pH 6.0 dan suhu optimumnya ialah 45°C Enzim ini paling stabit pada pH 7.0 dan suhu 50°C Enzim mempunyai kepilihan pada trigliserida rantai pendek dan dapat menghidrolisiskan beberapa ester metit. Lipase ini spesifik pada posisi 1,3.