Study On The Co-encapsulation Of Lactobacillus Plantarum And Curcumin By Alginate-Gelatin Hydrogel Beads

Probiotics have the function of regulating and promoting the health of intestinal flora and can be used to prevent and treat different diseases.Most probiotics are sensitive to temperature,oxygen,acids,enzymes,resulting in low survival rate during processing,storage and transportation.Curcumin is a common polyphenol with a variety of bioactive functions.However,curcumin has poor water solubility and rapid degradation rate,which limits its application in the field of food and medicine.The encapsulation technology can help to solve the problems of poor stability and low bioavailability of probiotics and curcumin.The encapsulation technology using polysaccharide,protein and other biological macromolecules as wall material is one of the hot issues in current research.Hydrogels based on the interaction between polysaccharides and proteins can form a three-dimensional network structure,and the active substances can be captured in the network structure to achieve the protection for active substances.It provides an important theoretical basis for the wide application of co-encapsulation system of probiotics and prebiotics in food.In this paper,alginate（ALG）and gelatin（GE）were used as wall materials to co-encapsulate Lactobacillus plantarum JYLP-326 and curcumin（CUR）,and the ALG-LP-CUR-GE hydrogel beads were obtained by extrusion.The physicochemical properties and simulated digestion behavior of hydrogel beads were studied,and the formation mechanism of the hydrogel beads was explored.The hydrogel beads were applied in the mimic milk tea system.The main results are as follows:（1）Alginate-gelatin（ALG-GE）composites with different mass ratios were prepared by changing the ratio of alginate to gelatin.The particle size and zeta potential of the composites were measured by laser particle sizer.When the ratio of sodium alginate to gelatin was 4:1,the maximum particle size of ALG-GE composites was 1709.33 nm and the maximum zeta potential was-59.43 m V.The interaction between alginate and gelatin was studied by multi-spectroscopy.Fourier transform infrared spectroscopy（FTIR）showed that there was hydrogen bonds and electrostatic interactions between alginate and gelatin.Fluorescence spectroscopy showed that the quenching mechanism of the interaction between ALG and GE was static quenching.A composite was formed between them mainly through hydrophobic interaction,and electrostatic interaction also existed.Scanning electron microscopy（SEM）images showed that the ALG-GE composite was formed,and laser scanning confocal microscope（CLSM）images showed that ALG and GE formed a complex network structure.（2）Alginate-gelatin（ALG-GE）hydrogel beads were prepared by extrusion with a cross linker of Ca Cl2,and used for encapsulating Lactobacillus plantarum JYLP-326（LP）.According to the growth curve of LP,the incubating time of 18 h was chosen as the harvest time for subsequent study.The images of SEM proved that LP was encapsulated inside the hydrogel beads.The viable counts of LP,ALG-LP,and ALG-LP-GE decreased by 2.1 log CFU,1.5 log CFU,and 1.4 log CFU,respectively,after storage at 4℃ for 6 d.The storage stability of ALG-LP and ALG-LP-GE was better than that of free LP.The results of thermal stability showed that when the temperature increased to 50℃,the viable number of free LP decreased by 5.7 log CFU,while the viable number of LP encapsulated by ALG and ALG-GE decreased by 0.8 log CFU and 0.2 log CFU,respectively.Only 8 Log CFU viable LP were found in ALG-LP-GE sample at 55℃,and no viable LP were detected in LP and ALG-LP.This indicated that ALG-GE hydrogel beads had better protection for LP.According to the in vitro simulated digestion,the survival rate of LP in ALG-LP-GE beads during simulated gastric digestion was 97.8%,and it reached sustained release（10⁸ CFU/m L）in simulated intestinal digestion.The results of rheology,FTIR and X-ray diffraction（XRD）showed that ALG and GE formed composite through electrostatic and hydrogen bonding interactions.LP was wrapped inside the hydrogel beads and was protected by the wall materials formed by ALG and GE.The ALG-LP-GE hydrogel beads were applied in the mimic milk tea system,and the number of viable LP in the simulated milk tea was greater than 10¹⁰ CFU/m L after soaking for 2 h.（3）Based on the preparation of ALG-LP-GE hydrogel beads,the concentration of CUR was optimized by single factor analysis with the encapsulation efficiency of LP and curcumin as indexes,and the ALG-LP-CUR-GE co-encapsulating hydrogel beads were prepared by extrusion method.When the concentration of CUR was 0.5 mg/m L,the maximum encapsulation efficiency of LP was 84.6%,and the encapsulation efficiency and loading capacity of CUR were 94.7%and 2.6%,respectively.The DPPH radical scavenging rate was53.8%.The SEM results showed that LP was encapsulated in ALG-GE hydrogel beads,and the FTIR and XRD results showed that CUR was encapsulated in ALG-GE hydrogel beads.In vitro digestion analysis of ALG-LP-CUR-GE hydrogel beads showed that the release rate of CUR in simulated gastric fluid was 8%,while its release rate in simulated intestinal fluid was90%.Release kinetics experiments showed that CUR was mainly released as Fickian release in simulated gastric fluid and non-Fickian release in simulated intestinal fluid,accompanied by relaxation of gel network structure.ALG-LP-CUR-GE was applied in the mimic milk tea system,and the number of viable LP in the milk tea at room temperature was higher than the minimum recommended intake of 10⁷ CFU/m L.