The structural composition and thermal properties of the products of enzymatic interesterification of triolein and tristearin were investigated. The biocatalyst for the reaction was an immobilized Candida antarctica lipase, SP435. Enzyme load of 10% (w/w reactants) produced 72% of desired total products. Oleoyl-distearoyl triglycerides (SSO, OSS) had higher melting points than dioleoyl-stearoyl triglycerides (OOS, SOO) because the sample contained larger amounts of stearic acid than oleic acid residues. SOS and OSO were hardly produced (0.2 to 1.2%), which indicates that SP435 acted as a nonspecific lipase when catalyzing the interesterification of triolein and tristearin. The maximal yield of OSS and SSO (46.9%) was achieved with a 1:2 mole ratio of triolein to tristearin. As the proportion of tristearin was increased, the production of SOO and OOS decreased, the melting profile of the interesterified triglycerides shifted toward higher melting forms, and the solid fat content increased, indicating formation of hard fats. JAOCS 75, 711-716 (1998). FIG. 2. Differential scanning calorimetry (DSC) heating thermograms of interesterified triolein and tristearin. Pretreatment: heated to 80°C at 200°C/min; cooled to −40°C at 10°C/min; held for 30 min; heating program: heated to 80°C at 5°C/min.FIG. 3. Percentage yield of products from interesterification of triolein with various mole ratios of triolein to tristearin by SP435 lipase. Each mixture was incubated at 55°C for 24 h. Total product: OSS + SSO + SOS + SOO + OOS + SOS, where OOO = triolein, OOS, SOO, and DSD = dioleoyl-stearoyltriglycerides; SSO, OSS, and SOS = oleoyldistearoyl triglycerices; SSS = tristearin.