Study On Co-microencapsulation Of Highland Barley β-glucan And Probiotics And Its Application In Chocolate

Probiotics are a kind of beneficial active microorganisms in the host.They have the functions of improving the balance of the intestinal microecological environment,controlling cholesterol levels,inhibiting the growth of pathogenic bacteria and improving immunity,and play an important role in maintaining the health of the host and preventing and treating diseases.In this study,Lactobacillus plantarum 550 was co-embedded with highland barleyβ-glucan in isolated whey protein（WPI）and gum Arabic（GA）matrix to study and analyze the effects of highland barleyβ-glucan on the survival rate of probiotics during spray drying,in vitro simulated digestion and storage.Finally,the probiotic microcapsules were added to chocolate,and the water content,apparent viscosity,in vitro simulated digestion,storage characteristics and sensory evaluation of the probiotic chocolate were analyzed by determining the optimal amounts of probiotic microcapsules.The main experimental contents and conclusions are as follows:（1）First,the purified highland barleyβ-glucan（HBBG-20）with high purity,narrow molecular weight distribution and good homogeneity was obtained by hot water extraction and fractional alcohol precipitation.The chemical composition of HBBG-20 is mainly neutral sugar（97.69±5.06%）and uronic acid（6.89±0.99%）,the protein content is low（0.33±0.01%）,and the purity ofβ-glucan reaches 79.05±4.18%,and did not contain starch,The average molecular weight of HBBG-20 is 5.64±0.01（×10⁵g/mol）.HBBG-20 is primarily composed of glucose,with lower levels of rhamnose and mannose.SEM found that the solid morphology was mainly flake-like structure,and the surface was smooth and dense.FT-IR showed that HBBG-20 had a characteristic peak ofβ-glucan(897 cm^-1).Thermogravimetric analysis showed that HBBG-20 had the highest mass loss rate ofβ-glucan（68.7%）in the range of300～355°C.HBBG-20 was fermented in vitro with human feces for 48 h.The prebiotic activity of HBBG-20 was analyzed by combining OD₆₀₀ value,gas production,p H value,change of sugar content and release of short-chain fatty acids（SCFAs）.The results showed that HBBG-20 could be quickly utilized by intestinal flora,which could increase the concentration of bacteria liquid,produce gas,reduce the p H value of fermentation liquid and produce SCFAs during the fermentation process,and the SCFAs produced were mainly acetic acid,propionic acid and butyric acid.（2）The probiotic Lactobacillus plantarum 550 was microencapsulated with different proportions of WPI and GA as the wall material,and it was found that it has obvious protective effect on probiotics during spray drying,in vitro simulated digestion and storage.All free probiotics died after spray drying.Among the formulas,the highest survival rate of probiotics reached 78.38%.Compared with encapsulation of probiotics with WPI or GA alone,the survival rate of probiotics encapsulated with WPI and GA was significantly improved due to the complex coagulation of WPI and GA at p H 3.75,which increased the protection of probiotics.Different proportions of WPI and GA have different protective effects on probiotics.The formula with the best effect is WPI:GA=3:1.After 6 h of in vitro simulated digestion,the concentration of live probiotics only decreased by 1.95 Log CFU/g.It is due to the electrostatic interaction between WPI and GA,which can better resist the decomposition of gastric acid and bile salts.After 8 weeks of storage at 4°C,the viability of the probiotics remained essentially unchanged.（3）Based on the optimal formulation of probiotic microcapsules prepared by WPI and GA,by adding different concentrations of highland barleyβ-glucan and probiotics to co-microencapsulate in WPI and GA,which can improve the viable bacteria concentration of probiotics in vitro simulated digestion process.For the 3%highland barleyβ-glucan sample,only 0.84 Log CFU/g of viable bacteria concentration was lost after the entire in vitro simulated digestion process.This may be because highland barleyβ-glucan has a prebiotic effect,which can provide nutrients for the growth of probiotics,so that probiotics can pass and multiply in the simulated gastrointestinal tract.On the other hand,the SEM results showed that the higher the concentration of highland barleyβ-glucan added,the smoother the surface of the obtained microcapsules and the less wrinkles,resulting in smaller specific surface area,reducing the contact between probiotics and adverse factors such as gastric acid,bile salts and enzymes in the gastrointestinal environment,and greatly improving the survival rate of probiotics during in vitro simulated digestion.At the same time,the viability of probiotics remained basically unchanged after 8 weeks of storage at 4°C.（4）In the process of preparing probiotic chocolate,firstly,taking the taste as an index,the optimal addition amounts of microcapsules were determined to be 2%,and then the probiotic chocolate was prepared according to the optimal addition amount.The results showed that adding probiotic microcapsules to chocolate had no effect on the moisture content of chocolate,but increased the apparent viscosity of chocolate.Probiotics in WPI-GA microencapsulated chocolate with highland barleyβ-glucan added,the survival rate of probiotics decreased by only 0.53%after in vitro simulated digestion for 6 h,showing higher tolerance to gastric acid and bile salts.Meanwhile,the survival rate of probiotics decreased by only 4.12%after 12 weeks of storage at4°C.In addition,adding probiotic microcapsules to chocolate has no significant effect on the shape and organization of chocolate,and can also increase the sweetness and sourness of chocolate.