Study On Triglyceride Hydrolysis During In Vitro Digestion

Oil provides nutrition and bioactive substances to human body and has importantinfluences on human health, so the food industry needs to design and produce food withincreasing, reducing or controling fat digestion and absorption, or control and guide thetransportation of drugs. Fat digestion is an interface reaction, the study of the effect of fatstructure on this interface properties has undoubtedly important significance on fat digestion.But most of current researches are limited to the influence of external factors and onlycompare the differences of digestion rate and degree of digestion, study on the effect of thestructure of fat are less. In this paper, the digestion rate, degree of digestion and changes ofinterfacial properties of different triglycerides (C2, C8, C12, C18, C18:1) in simple andcomplex oil system were studied by pH-stat in vitro digestion, respectively.1) The hydrolysis of these triglycerides in vitro digestion were studied. The resultsshowed that the hydrolysis rate in initial stage were: C8> C18:1> C12> C2> C18, thedegree of final digestion were: C8> C12> C18:1> C18> C2. It was suggested that theunsaturation and carbon chain length of acyl-chain had great influence on these interfacereactions.2) The diameter variations of these triglycerides in vitro digestion were studied. Beforedigestion, the median diameters (d50value) of C2, C8, C12, C18, C18:1were62.12μm，13.81μm，31.42μm，42.55μm，7.32μm, respectively. It was suggested that the extension ofcarbon chain was conductive to reducing the particle sizes of the emulsion of liquidtriglycerides, while for solid triglycerides, it might have an opposite effect. The existence ofdouble bond was conducive to a better combination with bile salts and other surfactants andthen reduced the particle sizes of the emulsion. The d32values of all samples were lower afterincreasing; The d43values of C2and C8were increasing during the process of digestion,while the d43values of C12, C18and C18:1were increasing and then decreasing, suggesttingthat short chain triglyceride hydrolysis products were easier to combine with bile salt micellesand form compounds which were difficult to be hydrolyzed, these compounds consisted ofthe main part of large particles. The large particles in long chain triglyceride emulsions mightcontained these compounds and oil droplets aggregate.3) The potential.changes of these triglycerides in vitro digestion were studied. After15min digestion, the potentials of C8and C18increased from-14.7mV and-15.5mV to-0.05mV and0.02mV, and then remained at near0mV, respectively.That of C2increased from-17.1mV to-16.4mV after15min, then reduced to-19.8mV after120min. While during120min digestion, that of C12and C18:1were decreasing from-14.9mV and-14.7mV to22.8mV and22.7mV, respectively. This suggested that the fatty acids hydrolyzed from C2,C8, C18may have larger proportion of adsorption on the surface of oil droplets than that ofC12and C18:1.4) The microstructure changes of these triglycerides during digestion were studied. Theresults showed that C2, C12, C18:1had more flocculation before digestion, and theseflocculation were decreasing during the digestion. While no obvious flocculation in C8and C18was observed before digestion, during digestion, the flocculation was increasing until60min, and then decreased gradually. This suggested that the flocculation sensitivity of saturatedtriglycerides fluctuate with the increasing of carbon chain length; double bonds were morelikely to cause flocculation before digestion. The surface of oil droplets in C8and C18mightbe adsorbed more fatty acids.5) Three different types of oil complex systems were studied, the digestion rate in initialstage, final digestive degrees and the variations of interfacial properties of these systems werecompared. The results showed that the difference of digestion rates were consistent with therules revealed from the simple systems above. But the variation of interfacial properties werenot the same with those of the difference in simple systems. This might because of thecomplicate composition of fatty acid and the superposition of their effects on the interfacialproperties.