Lipase-catalyzed Transesterification of Lard to Produce L-ascorbyl Fatty Acid Esters
|School||Nanjing Agricultural College|
|Course||Of Food Science|
|Keywords||immobilized lipase fatty acid ascorbly ester response surface method packed bed reactor Isolation and purification emulsification ability|
There exist rich and inexpensive lard in china.But because of lard relatively high melting point, entering the human body are difficult to digest and absorb,so this resource has not got effective utilization.In order to improve the use and nutrient values,lipase catalyzed transesterification of L-ascorbic acid and fatty acid methyl esters in nonhydrous medium was investigated. The main contents are as follows:1. Lipase-catalyzed transesterification of L-ascorbic acid and fatty acid methyl esters in nonhydrous medium was investigated. One of the most troublesome problem in lipase-catalyzed transesterification of L-ascorbic acid and fatty acid methyl esters is the reactive byproduct methanol may bate the catalyze capability of lipase. In order to solve this problem, we need to eliminate methanol from the reaction medium. We chose co-solvent mixtures as reaction medium. It was composed of a high logP solvent which can provide a suitable environment for enzyme catalysis and a low logP solvent which can be used for dissolving methanol.It was found that of the lipases tested in the initial screening, immobilized lipase Novozyme 435 was the best catalyst.The effect of lipase amount, reaction time, reaction temperature and substrates mole ratio was further studied. The results showed that the optimum conditions for the conversion of L- ascorbic acid was as follows:immobilized lipase Novozyme 435 as a catalyst, the reaction medium was 30% tert-amyl alcohol (t-pentanol):70% isooctane (isooctane),10% of enzyme dosage,1:10 of mole ratio of L-ascorbic acid to lard methyl ester, at 55℃for 24h. Under these conditions, the conversion of L-ascorbic acid up to 52.7%±2.8%.2. Based on the results of one-factor-one-time experiments, response surface method was usied to optimize the reaction conditions (substrate ratio, enzyme concentration, reaction temperature and reaction time). Through regression analysis, a good quadratic polynomial mathematical model was obtained. By analyzing the response surface contour plots generated from the quadratic regression equation and solving the model equation using software of Design Expert. The result showed:substrate molar ratio 1:10.16(L-ascorbic acid to lard methyl ester), enzyme dosage15.70%, reaction temperature 54.50℃and reaction time 32.16h.Under these reaction conditions, the best conversion of the L-ascorbic acid was 71.03%±2.16%, compared with the single factor experiments increased by nearly 20 percentage points.3. In packed bed reactor, we preliminary studied the effect of substrate molar ratio, liquid flow rate and cycle reaction time on the conversion of L-ascorbic acid.The result showed:8:1 of mole ratio of lard methyl ester to L-ascorbic acid, the liquid flow rate 0.5ml/min, the conversion of 1-ascorbic acid was highest. Compared with Isolation and purification methods, I suggest using organic solvent extraction to purify product. Based on the infrared spectra of the product, further defined the purified white powder was fatty acid ascorbly ester. Mensuraed CMC value of the fatty acid ascorbly ester, we found it has good emulsification ability. Fatty acid ascorbyl esters was used in ice cream. We found that the emulsification stability was better than monoglyceride and Span60, but the effect of the form of ice crystals was worse than monoglyceride. Altogether, the emulsification stability of fatty acid ascorbyl esters was little difference of monoglyceride. Moreover, Span60 had worst performance in the application in ice cream.