| In vitro artificial gastric models are increasingly being used to replace in vivo experimental studies,providing valuable research tools for the evaluation of bioacceptability of nutrients and active ingredients of food,gastrointestinal release of drug preparations and survival rate of microbial preparations in food nutrition and health related research.Although a variety of in vitro digestive systems have been developed and utilized,such as static one-compartment model(constant physiological environment),dynamic multi-compartment model(dynamic physiological environment)and so on,but there is still a lot of room for improvement and improvement in approaching human body authenticity(such as peristalsis,pressure,pH changes in different time and space in the stomach,etc.).This study aimed to optimize the working parameters of Artificial Gastric Digestive System(AGDS),which was based on the previous research in our laboratory,and evaluate it.Besides,the digestive properties of different forms of dairy products(UHT pure milk,yogurt,cheese)was explored using optimized AGDS.The main research contents and results were as follows:(1)The gastric emptying and gastric secretion of AGDS were optimized,and the stress of gastric wall and gastric contents and the pH changes at different positions in the stomach were also investigated.In the study of the force exerted on gastric wall and gastric contents under fasting/satiety conditions,it was found the gastric motilities at the top(1/3 of gastric body)and the end(gastric antrum)were different,and the force exerted on gastric wall and gastric contents by the roller were also different.The force transferred downward was greater,and the force exerted on gastric wall and gastric contents reached the maximum value at 27 mmHg(2.67 N)in the gastric antrum part,which was similar to the force exerted on real human gastric motility,and the force exerted on gastric contents at different positions was expressed in a mathematical model.In addition,it was found that the pH value at different positions in AGDS was different when acetic acid-sodium acetate buffer solution was added to AGDS.In the early stage of digestion,the pH value of the gastric antrum was about 0.3 lower than that of the gastric body,and the difference was up to about 1.1 at 90 min,and after 180 min gastric digestion,the pH value of the gastric antrum was about 0.8 lower than the gastric body.The above results showed that AGDS can simulate the human body in the dynamic system and endocrine system,and can the digestive environment was similar to that of human stomach for food in the stomach.(2)The digestion behavior of ?-lactalbumin was evaluated using the AGDS model,and two most commonly used digestive models(static and semi-dynamic)were applied as comparision.The experimental results showed that in the static digestion process(constant pH and enzymes,water bath stirring),the protein was heavily hydrolyzed at 3 min,with the free amino nitrogen content 6.06 ?g/mL.However,the semi-dynamic model(change in pH and enzymes,water bath stirring)and AGDS(constant pH and enzymes,roller peristalsishad lower hydrolysis degree and lower free amino nitrogen content(1.55 ?g/mL and 2.22 ?g/mL,respectively).After 120 min gastric digestion,the three models showed similar content of amino nitrogen(?11 ?g/mL),and the change trend of polypeptide content was similar.By comparing the static and semi-dynamic digestions with the same power system,the dynamic environment(changes in pH and enzyme concentration)changes have a great impact on the early digestion of the food stomach.The initial digestion level(0-6 min)of static model is significantly faster than the semi-dynamic model.Compared with semi-dynamic model and AGDS,the dynamic system has an important effect on the middle of gastric digestion.The protein particles in semi-dynamic digestion with water bath shaking was smaller than that of inAGDS,which had similar human peristalsis,at the initial 12 min,indicating that the mechanical force of semi-dynamic digestion was larger than that of AGDS.The results showed that changes in gastric environment(pH and enzymes)influenced the early stage of gastric digestion,and the different mechanical forces would lead to different size chyous in the middle stage of gastric digestion.The existing static model and semi?dynamic model had a certain gap with human digestion,which AGDS could better simulate human gastric digestion.(3)The digestive performances of protein,fat and microstructure in differet dairy products(UHT pure milk,yoghurt and cheese)were studyed using AGDS.The protein of liquid pure milk and yogurt was strongly hydrolyzed during 15-30 min in the stomach,while the protein digestion of solid cheese was about 10 min slower than that of liquid milk.The results showed that the solid cheese needed to release the protein through gastric peristaltic extrusion and gastric acid crushing the cheese structure.According to SDS-PAGE and microstructure analysis,with the digestion of MFGM in pure milk,the size of milk fat globule increased from 0.61?m at the begining to 85.5 ?m at 30 min,and then decreasedto 9.1 ?m at 120 min.Due to the interaction between polysaccharides and proteins in yoghurt,it could prevent protein-encapsulated fat from being exposed during digestion,leading to the size of fat globules negligible changes.The size of cheese fat globules was similar to that of pure milk,and the fat of cheese is mainly composed of free fat in the water phase and fat produced by the digestion of MFGM.The above results showed that different forms of dairy products have an important influence on the milk fat globules and proteins structure and digestibility in the early stages of gastric digestion.In this study,we optimized the gastric secretion and emptying kinetic parameters based on human data,and confirmed that AGDS can truly simulate the digestion of human stomach,through the digestive properties esperiment of different dairy products,it was found that the digestion characteristics of the components of the food system under different processing techniques were completely different,which was similar with the experimental results of the laboratory study on the digestion of different milk(unheated whole milk,pasteurized milk and UHT milk)in mice. |
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