Study On Medium-and Long-chain Triacylglycerol Oil System For Retarding Digestion And Its Application

At present,meal replacements for weight management are becoming more and more popular.As an important factor affecting the quality of meal replacements,satiety has become a research hotspot.Activating the "ileal brake" by retarding lipid digestion is an effective way to increase postprandial satiety,that is,when there are unabsorbed free fatty acids(FFAs)presenting in the ileum,they can activate a feedback loop to generate satiety signal,including inhibiting gastric emptying and small intestinal transit.And the strength of satiety signal is based on the concentration of FFAs.It provides a new idea for the research and development of foods for weight management.This paper constructed multilayer emulsions using the layer-by-layer deposition technique,and optimized their interfacial compositions by emulsion stability analysis and in vitro experiment to delay lipid digestion effectively;in view of the nutritional advantages of medium-and long-chain triacylglycerol(MLCT),the transesterification reaction conditions were optimized to prepare MLCT oil,and then the MLCT multilayer emulsion which could delay lipid digestion was constructed;prepared MLCT powdered oil by spray drying,and added it into meal replacement powder to evaluate its satiety effect.The main research contents are as follows:Through emulsion stability analysis,it was determined that secondary emulsions were composed of 5% flaxseed oil,0.5% whey protein with 0.2% pectin or 0.3% alginate or 0.15%chitosan(mass fraction).In vitro digestion experiments showed that only the secondary emulsion embedded by pectin had good stability in the simulated gastric environment.Then,tertiary emulsion was constructed for further decreasing the digestion rate of flaxseed oil,and its composition was 2.5% flaxseed oil,0.25% whey protein,0.1% pectin and 0.2% chitosan(mass fraction).The flaxseed oil-whey protein emulsion,flaxseed oil-whey protein-pectin emulsion and flaxseed oil-whey protein-pectin-chitosan emulsion were subjected to three consecutive stages of in vitro simulated digestion,including mouth,stomach and small intestine,and their FFAs release rules in the intestinal phase were monitored.The results showed that the amount of FFAs released by primary,secondary,and tertiary emulsions in the ileal segment were 3.26±1.91%,8.38±1.09%,13.53±1.27% respectively,which indicated that this interfacial composition of tertiary emulsion could significantly delay lipid digestion.Medium-chain triglycerides(MCT oil),coconut oil,rapeseed oil,soybean oil,flaxseed oil and palm oil were used to prepare different kinds of multilayer emulsions.After analyzing their FFAs release rules in the intestinal digestion phase,it was found that MCT oil and coconut oil were nearly completely digested before the ileal segment,while rapeseed oil,soybean oil,flaxseed oil and palm oil could still release 8.47±1.09%,12.93±1.90%,13.53±1.27% and 15.72±1.54% FFAs respectively in the ileal segment.Among them,palm oil was digested significantly slower than other oils,so it was used as one of the substrates for synthesizing MLCT oil by transesterification.MLCT was prepared by transesterification of palm oil with coconut oil or MCT oil.The yield of MLCT and their FFAs release rules in the intestinal digestion phase were taken into account to determine the optimum transesterification reaction conditions.The results demonstrated that when the molar ratio of palm oil to MCT oil was 1:1,the yield of MLCT reached the maximal(77.44%),and the tertiary emulsion of this transesterification product had a slower rate in digestion,which could release 14.68±0.36% FFAs in the ileal segment.Powdered oil of MLCT tertiary emulsion was prepared by spray drying.According to embedding rate and oil content,the optimum process conditions were defined as maltodextrin addition amount 7.5%(mass fraction)and inlet air temperature 190℃.After adding the MLCT powdered oil into meal replacement powder,its satiety effect was evaluated by visual analogue scoring method.The results showed that the areas under curve of satiety in control group and test group were 3998.70 and 5651.85 respectively,and there were significant differences between two groups.These findings prove that this MLCT powdered oil can improve the satiety effect of meal replacement powder,so it is a suitable choice to be used in foods for weight management.