| Longan pulp(dried longan)is a tonic product included in the "medicine and food homology list".Fresh longan pulp is rich in sucrose and high in total sugar.High sucrose intake results in a high blood glucose level,which could lead to several metabolic syndromes,such as obesity,cardiovascular diseases and type II diabetes.Hence,reducing sucrose content in juice is beneficial in keeping blood glucose level stable of consumers,and in preventing these metabolic syndromes.Therefore,it is necessary to develop low-sugar(low-calorie)and probiotic-rich longan processed products.In this thesis,longan pulp was firstly treated with enzyme(Viscozyme L)to convert sucrose in longan pulp into fructo-oligosaccharides(FOS),and optimized the optimum process with sucrose conversion rate and FOS content as indicators.Under the optimized conditions,the physicochemical properties and nutrient compositions of the modified longan juice(MLJ)were evaluated.Stimulation effects of the MLJ on probiotic bacteria growth were also studied,and GI value of the longan juice was test by rat experiment.The effects of MLJ on body characteristics,biochemical indicators,hormone levels and intestinal flora of rats were studied using the high-fat diet rat model.The underneath mechanisms were also discussed.1.The preparation,physicochemical properties and nutrient compositions of MLJ(1)The modified longan juice(MLJ)was prepared under the optimized conditions: enzyme addition amount 9 U/g sucrose,reaction temperature 55?,reaction time 5 h.Compared with the no-modified longan juice(NLJ),the sucrose content of MLJ decreased from 110.98 mg/g to 17.11 mg/g,the conversion rate reached 84.58%,and the FOS content reached 61.59 mg/g.Main FOS were 1-kestose and nystose,with contents of 47.52 mg/g and 14.08 mg/g,respectively.(2)Under the optimized processing conditions,the yield,clarity and total soluble solids of MLJ were significantly improved compared with NLJ,reaching 93.03%,82.07% and 20.13 oBrix,respectively.Enzyme treatment significantly reduced the content of insoluble fiber in the juice residue,while increased the content of water-soluble polysaccharide,water-soluble pectin and soluble amino acid.The molecular size distribution and monosaccharide compositions of the water-soluble polysaccharide in longan juice were also changed.2.The effect of MLJ on the proliferation of probiotics including Lactobacillus and Bifidobacterium and on the postprandial blood glucose in rats.(1)Both MLJ and NLJ effectively promoted the growth of probiotics.For Lactobacillus acidophilus,Lactobacillus delbrueckii,Streptococus thermophilus,Bifidobacterium adolescentis and Leuconostoc mesenteroides,the effects of MLJ were significantly better than NLJ.This result is mainly contributed by FOS in the MLJ.(2)NLJ had a GI value of 78.33,belonging to high GI food.The GI value of MLJ was 64.15,and therefore it belongs to medium GI food.Compared with NLJ,the MLJ could better maintain postprandial blood glucose stability in rats.3.Effect of modified longan juice on body characteristics,lipid metabolism,glucose tolerance,insulin resistance,serum hormone,and liver function of rats with high fat diet(1)MLJ,FOS and NLJ all can increase the levels of adiponectin and tyrosinein serum of rats on high-fat diet,which can control the appetite of rats,reduce the energy intake of rats and inhibit the hypertrophy of fat cells in rats,so as to reduce the accumulation of abdominal fat in rats and control the weight of rats.(2)Lipid metabolism: MLJ,FOS and NLJ effectively reduced the levels of TC,TG,LDL and nonesterified fatty acid in serum of rats with high-fat diet,improve serum HDL level,as well as LPL and HL levels in liver.The atherosclerosis index(AI)was reduced,well the lipid metabolism was improved,and therefore the risk of cardiovascular disease was decreased.Compared with NLJ,MLJ and FOS interventions showed better effects.(3)Compared with the high-fat model group,the fasting blood glucose,blood glucose peak and blood glucose curve area of MLJ and FOS intervention groups were significantly(p<0.05)lower,indicating that the MLJ and FOS have better effects on reducing the postprandial blood glucose peak and on improving the glucose tolerance in rats.Homeostasis model assessment of insulin resistance,serum GIP and GLP-1 levels in the MLJ intervention group were improved compared with the high-fat diet model group,indicating that the MLJ could inhibit the insulin resistance of rats by regulating the levels of GIP and GLP-1.(4)The liver coefficient,serum ALT and serum AST activity,the content of MDA in liver tissue were decreased,however the GSH content in liver tissue of rats were improved by MLJ,FOS and NLJ compared with HLgourp.And the MLJ effect is better than that of FOS and NLJ.This indicated that MLJ could effectively improving liver function and prevention of liver oxidative damage.In summary,MLJ,FOS,and NLJ could improve the abnormal glucose and lipid metabolism and liver function damage induced by high-fat diet,and the effect of MLJ is significantly better than NLJ.4.Effect of MLJ on intestinal flora in rats with high fat diet(1)Modified longan juice could significantly increase the abundance of Bacteroides,and probiotics of Lactobacillus and Bifidobacterium,and reduce the abundance of Firmicutes.At the same time,it promoted the production of short-chain fatty acids in the intestine of rats,thereby promoted intestinal health and inhibited the induction of obesity by high-fat diet.(2)Through the KEGG functional gene annotation and analysis,the results showed that the pathway Metabolism genes of the two intervention groups of fructo-oligosaccharide and modified longan juice were similar,and the natural longan juice intervention group was closer to the high-fat diet model group.Compared with the high-fat diet model group,the modified longan juice group samples showed increased the gene abundance of the glycerolipid metabolism(ko00561),secondary bile acid biosynthesis(ko00121),and primary bile acid biosynthesis(ko00120).They also promoted bile acid enterohepatic circulation,and thus could maintain the body's normal digestion and absorption of lipid foods.(3)The increased abundance of Lactobacillus and Bifidobacterium could improve glucose metabolism and lipid metabolism in the host and inhibit liver antioxidants,while increased abundance of Desulfovibrio and Butyricimonas species might aggravate abnormalities in host lipid metabolism and liver oxidative stress.In summary,MLJ rich in fructo-oligosaccharide could regulate intestinal flora,promote the proliferation of intestinal probiotics,and regulate the metabolic pathways and carbohydrate enzymes of the intestinal flora.It could also improve the body's decomposition,digestion and absorption of lipids and carbohydrates in food,and inhibit metabolic abnormalities induced by high-fat diet. |
PDF Full Text Request