Preparation Of Medium And Long Chain Triacylglycerols By Lipase-catalyzed Interesterification

Medium and long chain triacylglycerols(MLCT)are defined as structured triacylglycerols that contain medium chain fatty acids and long chain fatty acids on the same glycerol molecule.MLCT are widely used in food and clinical nutrition with various beneficial effects on health and nutrition.The objective of this study was to optimize the conditions of lipase-catalyzed interesterification reaction between soybean oil and medium chain triacylglycerols(MCT)to produce MLCT.The main contents of this paper were as follows:Firstly,four commercial lipases were selected for interesterification reaction between soybean oil(SO)and MCT in a solvent-free system.The data showed that the type of lipase had a significant effect on MLCT yield,and the effect of lipases followed this order: Lipozyme 435>Novozym 435>Lipozyme RM IM>Lipozyme TL IM.Taking both the MLCT yield and the costs into consideration,Lipozyme 435 was considered as an optimum lipase for further reactions.The recycle of Lipozyme 435 showed it had good thermal stability,and the content of MLCT could be kept above 70% after 8 batchs,which was 91.7% of the initial catalytic ability.Subsequently,single factor and response surface optimization methods were used for optimization of several variables such as lipase loading,substrate weight ratio of MCT to soybean oil,temperature and time.The optimum conditions for preparation of MLCT by Lipozyme 435 catalyzed interesterification were as follows: Lipozyme 435 of 9% as catalyst,substrate ratio of 40:60,heating temperature of 94.5oC,reaction time of 7.4 h.Under the optimal conditions,three parallel experiments were carried out,and the average MLCT yield was 76.31%.The fatty acid compositions and TAG species of the physical mixed oil and interesterified product were analyzed.After the interesterification reaction,the type of triglycerides in the product changed significantly,and the CyLL,OOCy,LOCy,LPCy and LLnCy became the main triglyceride species of MLCT.Compared with the physical mixed oil,the prevalence of several TAG species(i.e.,LLL,LLnP,LLP and CyCyCa)that originated from SO and MCTs was decreased in the interesterified product and LLLn was completely disappeared.Finally,after the interesterification,acid value,peroxide value and DAGs content present in the crude product were 2.6 mg KOH/g,8.7 mmol/kg and 4.5%,higher than the national standard JX20070100 requirements.The free fatty acid was reduced by the neutralization with NaOH aqueous.The optimum conditions were as follows: the total amount of alkali is the theoretical amount of alkali with 0.3% of the excess alkali,miscella concentration of 60%,alkali refining temperature of 55oC,alkali concentration of 8%.The resulting product was treated with silica gel to decrease peroxide value and DAG content.The optimum conditions were as follows: macroporous silica gel dosage 10%,temperature 40oC,and time 1.5 h.Under these conditions,acid value,peroxide value and DAGs content present in the crude product were 0.13 mg KOH/g,1.5 mmol/kg and 1.2%.The appearance,physical and chemical properties of MLCT met the requirements of the standard.The smoke point of MLCT was 187oC,which was higher than the blends of MCT and soybean oil(132oC).The oxidation stability of MLCT structural lipids was determined by Rancimat method.It was found that the oxidation stability of MLCT was significantly better than that of soybean oil.The shelf life of MLCT was estimated 343.3 days at 25oC.