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Enzymatic Production Of Human Milk Fat Substitutes

Posted on:2003-12-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:T K YangFull Text:PDF
GTID:1101360065462174Subject:Food Science
Abstract/Summary:PDF Full Text Request
Human milk is naturally the only source of food for infants in their early life. The unique structure of human milk fat,i.e. most of palmitic acid (16:0) is located at the sn-2 position of the triacylglycerol backbone,is important for the absorption of tats and some minerals in infants. The objective of this study is to produce human milk fat substitutes,which mimic tatty acid and triacylglycerol compositions found in human breast milk,as fat ingredients of infant formula. The approach should be carried out using enzymatic interestenfication with high specificity and rnild reaction conditions. During this study,the basic theorio and mathematical models of enzymatic reactions should also be studied.Kinetic models of thermal deactivation have been established for reaction enzymes (sn-1.3 specific lipases:porcine pancreatic lipase and Lipozyme RM IM) in order to find the optimal temperature for the en/ymatic acidolysis. Porcine pancreatic lipase easily deactivated at more than 50 and fitted the "one-step" deactivation mechanism. Lipo/ymc RM IM was stable in 50 - 90. The "two-step series" deactivation model presented its behavior of thermal deactivation. The first step deactivation uas significantly taster than the second step in Lipozyme RM IM. To quantify the thermal stability of lipases. other parameters such as free energy (AC) and activation energy were determined in the deactivation of lipases.Lard has a similar structure to human milk fat at the sn-2 position. Lard and specially chosen tatty acids were interesterified in a solvent-free system catalyzed by Lipozyme RM IM. Fimc courses of acyl incorporation at different temperatures,reaction times,water contents,en/yme loads and substrate ratios together with enzyme reusability were investigated. Expressions of the initial rate of acyl incorporation (Inc h) versus temperature (T. K) were found for linoleic acid: and for linolenicacid:. Response surface methodology (RSM) was used to obtain areliable polynomial model and to locate the optimum conditions of the reaction. The characteristics of the product (HMFS). produced in the scale-up acidolysis at optimal conditions,were similar to those of Chinese mothers milk.Eicosapentaenoic acid (EPA. 20:5co3) and docosahexaenoic acid (DHA,22:6co3) are very important nutrients for the infant growth and mature of their brain,nervous system,and visual process. Through the interesterification of tripalmitin with ethyl esters of EPA and DHA under RSM optimization,human milk fat substitutes containing EPA and DHA were produced by the catalysis of inexpensive Lipozyme TL IM. The product would be used as a nutritious supplement for the HMFS from lard. The model generated from RSM satisfactorily represented the real relationships between factors and the response. Furthermore,catalytic functions of Lipozyme TL IM and Lipozyme RM IM was compared in different interesteritlcations.Conjugated linoleic acids (CLA) were claimed to have potential biological functions in humans. During the production of the structured lipid,i.e. conjugated-linoleoylstearin,it was found that the different positions of double bonds and their different geometrical configurations between CLA and linoleic acid resulted in the different acyl incorporation and migration rates in the lipase-catalyzed acidolysis.Specific lipase-catalyzed interesterification,especially acidolysis is reversible reaction,leading to equilibrium. Higher yields of final products are not available in the reaction because of the chemical equilibrium. The feasibility of shifting the equilibrium by the programmed change of reaction temperature was investigated to produce more desirable products by increasing acyl incorporation and decreasing migration,based on the acidolysis of tripalmitin with CLA and tripalmitin with caprylic acid. The programmed temperature of reaction produced little difference in acyl incorporation during the acidolysis of PPP and CLA and PPP and caprylic acid because of inefficient crystalli/ation. However,migration was successfully inhibited to...
Keywords/Search Tags:human milk fat substitutes, structured lipids, interesterification, lipase, deactivation, lard, temperature-programmed acidolysis, conjugated linoleic acids (CLA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA)
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