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The present work aimed to search for a released peptide from proteolytic action on a silver barb fish muscular protein that confers health benefit through antioxidation activity. Changes in the physicochemical, microbiological, and protein characteristics of plaa-som samples during eight days of both spontaneous traditional fermentation (Batch 1; B1) and spontaneous fermentation with the addition of pineapple (Batch 2; B2) were determined. Results showed a correlation between an increase in the total acidity and bacterial counts with the length of fermentation duration, where the pH gradually decreased at the end of fermentation. Protein hydrolysis during fermentation was indicated by an increase in the amount of TCA-soluble peptide contents that peaked on day 5 (D5) in both batches (B1D5 and B2D5), which displayed their highest DPPH radical-scavenging inhibition of plaa-som protein hydrolysates (PSPHs). Twelve peptide fractions of the best PSPH were separated by ultrafiltration using molecular weight cut off (MWCO) at 3 and 10 kDa, and they were also purified by size exclusion chromatography. Results demonstrated that stronger peptides B2D5 - 3 kDa - F1 and B1D5 - 10 kDa - F1 were arranged in 12 peptides, which exhibited the highest reducing power, more than their radical-scavenging inhibition (p < 0.05). Therefore, it was concluded that both peptides obtained from PSPH have released antioxidative peptides that could be beneficial towards consumer's health, particularly the spontaneous plaa-som fermented with the addition of pineapple.

Stereoselective ethanolysis of monoacid TAG by immobilized Rhizomucor miehei lipase (RML) was studied for preparation of optically pure sn-2,3-DAG. Trioctanoylglycerol (TO) was used as a model substrate. The enantiomeric purity of the product, sn-2,3-dioctanoylglycerol (sn-2,3-DO), was very high (percent enantiomeric excess > 99%) when an excess of ethanol was used. The result indicated that RML was highly stereoselective toward the sn-1 position of TO under conditions of excess ethanol. The stereoselectivity of RML depended on the amount of ethanol. The larger the amount of ethanol was, the higher the stereoselectivity became. After optimizing the parameters such as reactant molar ratio, water content, and temperature, (ethanol/TO molar ratio = 31:1 and water content = 7.5 wt% of the reactants at 25°C), optically pure sn-2,3-DO was obtained at 61.1 mol% in the glyceride fraction in 20 min. The above conditions were further applied for ethanolysis of monoacid TAG with different acyl groups such as tridecanoylglycerol (C10:0), tridodecanoylglycerol (C12:0), tritetradecanoylglycerol (C14:0) and trioctadecenoylglycerol [triolein, (C18:1)]. The yields and enantiomeric purities of 1,2(2,3)-DAG were dramatically reduced when TAG with FA longer than decanoic acid were used.Paper no. J11267 in JAOCS 83, 603-607 (July 2006).KEY WORDS: sn-2,3-Diacylglycerols, ethanolysis, monoacid triacylglycerols, Rhizomucor miehei lipase.DAG are widely used as emulsifiers in the food, cosmetics, and pharmaceutical industries. Frequently, mixtures of MAG and DAG are exploited because they are cheap and give appropriate performance (1). At present, DAG are regarded as healthful oils owing to their activity in preventing obesity (2). In addition, pure isomers of DAG have great potential as intermediates for the organic synthesis of phospholipids, glycolipids, prodrugs, and structured lipids (3-6). DAG exist in three isomers: sn-1,3-, sn-1,2-, and sn-2,3-DAG. For monoacid DAG, sn-1,2-and sn-2,3-DAG are enantiomers of each other. Although pure isomers of DAG are difficult to synthesize by traditional chemical synthetic methods, lipase-catalyzed regio-and stereoselective reactions would provide alternative routes. For example, preparation of sn-1,3-DAG at high yield and purity was successfully achieved by direct esterification of glycerol and FFA using 1,3-regiospecific lipase (6-8) and by direct transesterification of glycerol and vinyl esters of medium-chain FA using Candida antarctica lipase B (9).In contrast to the preparation sn-1,3-DAG, chemoenzymatic methods are used for the preparation of optically pure sn-1,2-DAG or sn-2,3-DAG. Some recent publications describe syntheses of enantiomerically pure sn-1,2-DAG by lipase-mediated sequential transesterification of the racemic O-alkyl glycerols (10,11). In another synthetic route, the chiral sn-1,2-DAG are chemically synthesized from (R)-and (S)-enantiomers of O-(4-methoxyphenyl)-glycidol, which are obtained from a onepot reduction of ketone and in situ lipase-mediated resolution (12). Altho...

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