Enzymatic Pretreatment Of Soybean Oil Deodorizer Distillate For Concentration Of Natural Tocopherols

Natural tocopherols are recovered from vegetable oil deodorizer distillate,which is a by-product of the deodorization step of vegetable oil refining.Soybean oil is the most important commercial vegetable oil worldwide and its deodoriser distillate represents 0.15-0.45%(w/w) of the oil to be deodorised.The price of this distillate is based on its tocopherol content,which is normally between 6.0 and 12.0%of the distillate weight. In the process of preparing tocopherol concentrates,the fatty acids present in the soybean oil deodoriser distillate(SODD) are esterified using chemical or enzymatic means in order to reduce their boiling points, thereby facilitating their separation from the desired compounds.First,we measure some property of SODD,and its acid value(AV) was 75.03±0.34 mg KOH/g,saponification value was 159.65±1.14 mg KOH/g,water and volatile contents were 1.976±0.018%,tocopherol contents was 6.02±0.08%.Otherwise,the SODD was hydrolysis by Candida rugosa lipase,the optimal reaction conditions achieved were as follows:water content 30%(pH 7.32),lipase amounts 25 U/g-mixture, temperature 45℃and rotate speed 200 rpm/min,with acid value of mixture about 102.74 mg KOH/g after reaction for 12h. In general,Candida rugosa lipase recognized FFAs as substrates but not tocopherols,and that esterification of FFAs with methanol(MeOH) could be processed in organic solvent-free system.Several factors affecting esterification of FFAs were investigated in details and optimized by Plackett-Burman and central composite design.The optimal reaction conditions achieved were as follows:water content 21.05%(pH 7.32), lipase amounts 115.45 U/g-mixture,temperature 28.95℃and methanol/free fatty acid molar ratio 4:1 by four-step addition,with degree of decrease of acid value above 93%in 18 h which was a much efficient process.No significant tocopherol losses were observed during the process. In conclusion,enzymatic esterification of free fatty acids in soybean oil deodoriser distillate for concentration of tocopherols was shown to be a technically viable process.Finally,lipase from Candida rugosa was immobilization by physical adsorption onto macroporous resins.The results showed that the weak polar resin AB-8 was the best carrier used in polar media(Tris-HCl buffer). Several factors affecting immobilization of lipase were investigated in details and optimized by Plackett-Burman and Box-Behnken design.The optimal reaction conditions achieved were as follows:0.5 g resin,5 mL buffer(pH 7.32),temperature 24.9℃,time 3.86 h,enzyme loading 50 mg/g-resins,rotate speed 150 rpm/min,with hydrolytic activity of mmobilized lipase was 112.58 U/g.The catalytic properties of immobilized lipase for esterification of FFAs with methanol(MeOH) in organic solvent-free system were studied.After 3 consecutive batches,the degree of decrease of acid value remained above 85%when the water content was law.