The objective of this study was to digest okara in high yield by food-processing enzymes. Autoclaving of okara was effective in increasing cellulase digestion for the primary cell wall, and the digestion was accelerated by the formation of single cells by stirring. Most of the residual okara after autoclaving and cellulase digestion was found to be the secondary cell walls compared with the cellulase-treated soybean single cells. The secondary cell wall was found to be composed of galacturonic acid, neutral sugars, and protein and was considered to be a complex of these compositions. Many cellulolytic and proteolytic enzymes could not digest the secondary cell wall; however, it was found that two pectinases could digest the secondary cell wall. A series of digestions resulted in yields of 83-85% from the raw okara, and the final residues were identified as oil body complexes in the soybean cells and fiber-like organ between the cells.
A newly developed 1,3-positionally specific thermostable lipase from Fusarium heterosporum (named R275A lipase) was immobilized on Dowex WBA for the production of structured lipid by acidolysis of tripalmitin (PPP) with oleic acid (OA). The immobilized catalyst was fully activated by pretreatment at 50°C in a PPP/OA mixture containing 2% water. The pretreatment caused concomitant hydrolysis, but the hydrolysis was repressed using a substrate without water in the subsequent reactions. The optimal reaction conditions were determined as follows: A mixture of PPP/OA (1:2, w/w) and 8% immobilized lipase catalyst was incubated at 50°C for 24 h with shaking at 130 oscillations/min. The acidolysis reached 50% under these conditions, and the contents of triolein, 1,3-dioleoyl-2-palmitoyl-glycerol, 1(3),2-dioleoyl-3(1)-palmitoyl-glycerol, 1(3),2-palmitoyl-3(1)-oleoyl-glycerol, 1,3-dipalmitoyl-2-oleoyl-glycerol, and PPP in the reaction mixture were 8, 36, 4, 28, 1, and 6 mol%, respectively. The stabilities of immobilized R275A lipase catalyst and two immobilized catalysts containing Rhizopus delemar or Rhizomucor miehei lipases were compared under the conditions mentioned above, with the catalysts being transferred to fresh substrate every 24 h. The half-life of the R275A lipase catalyst was 370 d, which was significantly longer than those of Rhizopus and Rhizomucor lipase catalysts.Paper no. J9657 in JAOCS 78, 167-172 (February 2001).KEY WORDS: Acidolysis, Fusarium heterosporum, immobilized lipase, oleic acid, palmitic acid, structured lipid, thermostable lipase, tripalmitin.Human milk fat contains 20-25% palmitic acid (PA, 16:0), and about 70% of this fatty acid is esterified to the 2-position of triacylglycerols (TAG) (1,2). In addition, the main component of the milk dienoic TAG is 1,3-dioleoyl-2-palmitoylglycerol (OPO). Gastric and pancreatic lipases hydrolyze TAG to free fatty acids and 2-monoacylglycerols (2-MAG), and the absorption of free PA liberated from the outer positions is lower than that of free unsaturated fatty acids (3). It has been therefore hypothesized that fat absorption is higher in infants fed fats with PA at the 2-position of TAG than the 1,3-positions (4). For this reason, OPO has been used as an ingredient of infant formula. OPO can be produced by acidolysis of tripalmitin (PPP) with oleic acid (OA, 18:1) by using immobilized 1,3-positional specific lipase or by interesterification of PPP with ethyl oleate. In general, lipases act strongly on liquid-state substrates, but weakly on solid-state ones. If conducted in an organic solvent-free system, therefore, the reaction must be conducted above 50°C. Reactions in a system containing organic solvent progress efficiently even at lower temperatures because all substrates are in the liquid state. Because an organic solvent-free system is preferable from the industrial viewpoint, a thermostable 1,3-positional specific lipase is strongly desired.Fusarium heterosporum produces a lipase that hydrolyzes ester bonds at the 1,3-positions of TAG (5). When the ...
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