Properties Of Lotus Seed Cross-linked Resistant Starch And Its Application In Probiotics Microcapsules

Lactiplantibacillus plantarum（L.plantarum）,a representative probiotic,is widely used in food,health products and pharmaceuticals.However,the high temperature environment during production and processing and the acidic environment of the stomach during digestion and usage are the reasons for the reduced survival rate of probiotics,so maintaining the activity and bioavailability of probiotics in the host body has become a hot topic of research nowadays.Microencapsulation is a promising technology for probiotic protection,where resistant starch can be used as a microcapsule wall material to protect probiotics exposed to harsh environments and deliver probiotics to the colon.Microencapsulation is a promising technology to protect probiotics,and resistant starch can be used as its wall to protect probiotics exposed to harsh environments and to deliver probiotics to the colon.Type IV-resistant starch prepared by chemical modification is one of the more studied types of RS,and cross-linking treatment is the most widely used method in chemical modification of natural starch.Therefore,the structural properties and physicochemical characteristics of lotus seed cross-linked resistant starch（LSCS）with different degrees of cross-linking were studied,and LSCS with low,medium and high degrees of cross-linking were screened,and the probiotic microcapsules（PM）were prepared with lotus seed cross-linked resistant starch（LSCS）and lotus seed cross-linked resistant starch-sodium alginate（LC-SA）as wall materials,respectively,to investigate their properties and elucidate the relationship between probiotic tolerance and structural changes of PM wall materials,which provide theoretical basis for developing starch industry and probiotic microcapsules in China.The main conclusions are as follows.（1）Study on the effect of sodium trimetaphosphate/sodium tripolyphosphate（STMP/STPP）addition on the properties of lotus seed cross-linked resistant starchThe lotus seed cross-linked resistant starch（LS-0CS,LS-1CS,LS-2CS,LS-4CS,LS-6CS,LS-8CS,LS-10CS,LS-12CS）with different additions（0%,1%,2%,4%,6%,8%,10%,12%of dry weight of starch）of mixed cross-linking agents（STMP/STPP,99:1）were prepared separately under alkaline conditions,and their structural properties,physicochemical and digestive properties were determined to construct the relationship between cross-linking degree and properties.The results showed that the crosslinking degree of LSCS increased with the increase of crosslinker addition,and the LSCS particles gradually agglomerated with each other after adhesion.The occurrence of crosslinking reaction was confirmed by Fourier transform infrared spectroscopy and ³¹P nuclear magnetic resonance spectroscopy.Compared with LS-0CS,the solubility and swelling of LSCS were significantly lower and decreased with the increase of cross-linking degree,and the thermal stability and anti-digestion properties were positively correlated with the cross-linking degree.The covalent bond formed by the phosphate group in LSCS was mainly composed of distarch monophosphate（DMSP）,so specific gravity of DSMP is closely related to the physicochemical properties and in vitro digestive characteristics of LSCS.Therefore,LS-12CS had the highest cross-linking degree,with more DMSP content,which led to more covalent bonds formed by phosphate groups to"bind"more starch chains together,significantly improving the enzymatic resistance of LS-12CS,so LS-12CS had the highest RS content.（2）Study on Characteristics of lotus seeds cross-linked resistant starch probiotic microcapsulesLotus seeds cross-linked resistant starch probiotic microcapsules（LSCS-PM）were prepared by emulsification method to investigate the protective and releasing effects of LSCS structure on Lactobacillus plantarumin（L.plantarumin）in simulated gastrointestinal digestion under the wrapping of low,medium and high cross-linked lotus seeds cross-linked resistant starch（LS-2CS,LS-6CS,LS-12CS）.The results showed that the higher the degree of microcapsule wall LSCS cross-linking,the better the encapsulation rate,heat resistance,tolerance under simulated gastric juice and release in sequential exposure to simulated gastric juice and simulated intestinal juice of LSCS-PM.LS-12CS-PM had an encapsulation rate of 48.81%,and the viable count released by LS-12CS-PM under sequential exposure to simulated gastric juice and simulated intestinal juice reached 6.26 Lg CFU/g（>10⁶ CFU/g）,which could colonize and exert probiotic effects in the intestine.The starch LSCS in LSCS-PM remained in a C-shaped crystalline structure after simulated gastrointestinal digestion,but the agglomeration between starch granules in LS-2CS-PM and LS-6CS-PM was significantly weaker compared to LS-12CS-PM,resulting in a greater degree of hydrolysis in the amorphous regions of LS-2CS-PM and LS-6CS-PM,which in turn led to a significant increase in their crystallinity.Therefore,LS-12CS,as an effective oral probiotic carrier,protecting probiotics to reach the intestine smoothly to exert their probiotic effects.（3）Study on Characteristics of lotus seeds cross-linked resistant starch-sodium alginate probiotic microcapsulesBased on the study of lotus seed cross-linked resistant starch probiotic microcapsules（LS-2CS-PM,LS-6CS-PM,LS-12CS-PM）,lotus seed cross-linked resistant starch-sodium alginate probiotic microcapsules（LC-2SA-PM,LC-6SA-PM,LC-12SA-PM）were prepared by emulsification method to investigate the protective and releasing effects of LSCS and SA composite wall structure on Lactobacillus plantarum in simulated gastrointestinal digestion under the wrapping of low,medium and high cross-linked Lotus seeds cross-linked resistant starch（LS-2CS,LS-6CS,LS-12CS）and sodium alginate（SA）.The results showed that the higher the degree of microcapsule wall LSCS cross-linking,the better the encapsulation rate,heat resistance,tolerance under simulated gastric juice and release in sequential exposure to simulated gastric juice and simulated intestinal juice of LC-SA-PM,which was consistent with the research rule of LSCS-PM,but the difference was that the effect of LC-SA-PM was stronger than that of LSCS-PM.The encapsulation rates of LC6-SA-PM and LC12-SA-PM were 81.08%and 94.22%,and the viable count released by LC6-SA-PM and LC12-SA-PM under sequential exposure to simulated gastric juice and simulated intestinal juice reached 6.22 and 7.01 Lg CFU/g（>10⁶ CFU/g）,both of which could colonize and exert probiotic effects in the intestine.The agglomeration phenomenon between starch granules in LC-SA-PM was enhanced after simulated gastrointestinal digestion compared with LSCS-PM.The crystalline structure of starch LSCS in LC-SA-PM did not change and remained a C-type crystalline structure,and the interaction between both LSCS and SA still existed,and the intensity was positively correlated with the cross-linking degree of LSCS.Therefore,based on the composite wall structure of LSCS and SA,both LS-6CS and LS-12CS served as effective oral probiotic carrieies to protect probiotics from reaching the intestine smoothly to exert their probiotic effects.