Microencapsulation Of Lactic Acid Bacteria Using The Methods Of Complex Coacervation And Anti-solvent Precipitation

The storage at room temperature and humidity of the dry product of lactic acid bacteria?LAB?has been the urgent issue of food industry to be solved.Achievement of the storage of LAB product at room temperature and humidity is more in line with actual needs,which decreases the transportation and storage cost of LAB product,and is more convenient and simple during distribution and consumption of LAB product.LAB microencapsulation could improve the stress resistance of LAB against environmental factors,such as temperature,humidity,oxygen,etc.,and has been the research focus of food science.Complex coacervation and anti-solvent precipitation are emerging microencapsulation techniques in recent years.In this research,suitability of these two techniques in LAB storage at room temperature and humidity was investigated.First,whey protein isolate / gum Arabic?WPI/GA?complex coacervate was used to encapsulate LAB and the protection of coacervation for LAB during storage at room temperature?25oC and 30oC?and certain humidity?11% and 33%?was investigated.Then a higher coacervation-pH matrix,gelatin A / gum arabic?GE/GA?,was investigated.Oil/zein microparticle with core-shell structure was constructed using the anti-solvent precipitation technique and its protection on LAB was investigated.The principal conclusions are as follows:?1?The coacervation of WPI/GA complex was optimized.The influence of encapsulation with WPI/GA coacervation on LAB survival after spray drying and during storage under different temperature and relative humidity was studied.The optimum coacervation of WPI/GA complex was carried out at pH 4.5,4:1 WPI/GA ratio and 3%?w/w?of encapsulating materials.Compared to WPI group,the protection of WPI/GA group for bacteria during spray drying and during room temperature and humidity storage was not significant.The adding of sucrose significantly improved cell survival after spray drying,from 56.3±8.0% to 78.7±5.7%,but did not improve LAB storage stability.This might be due to the low pH of coacervation of WPI/GA and WPI/GA+S,which induced acid and heat damage to cell during spray drying.Sucrose could provide certain protection to LAB,but it failed to effectively prevent deterioration of bacterial survival during storage at controlled temperature and humidity.?2?The coacervation of GE/GA complex was optimized.The influence of encapsulation with GE/GA coacervation on LAB survival after spray drying and during storage under different temperature and relative humidity was studied.The optimum coacervation of WPI/GA complex was carried out at pH 5.0 or 5.5,4:1 GE/GA ratio,2%?w/w?of encapsulating materials.Compared with WPI/GA group,the coacervation pH of GE/GA complex was enhanced.The cell protection of GE/GA_5.5 complex during spray drying and during ambient storage was statistically significant compared to GA_5.5group,while not significant compared to GE5.5.The increase of coacervation pH of WPI/GA complex from 5.0 to 5.5 improved LAB survival at all the ambient storage conditions.The adding of sucrose significantly increased cell survival after spray drying,from 102.6±5.9% to 131.3±8.0%,and also significantly improved LAB storage stability at all storage conditions.Cell count of WPI/GA/S_5.5 group only decreased 1.63 log CFU after storing for 56 d at 30 oC and 11% relative humidity.?3?The preparation of oil/zein microparticles using the method of anti-solvent precipitation was optimized.Using medium chain triglycerides?MCT?and palm oil?PO?as the typical oil,the structure and physico-chemical properties of oil/zein microparticles,the encapsulation of LAB in microcapsules and the protection for LAB were investigated.Based on the method of anti-solvent precipitation of zein and using GA as emulsifier of oil in water emulsion and as the dispersant of zein microparticles in water,MCT/Zein microparticles were made with good stability,obvious core-shell structure.Microcapsules of LAB/MCT/Zein and LAB/PO/Zein prepared with anti-solvent precipitation were good in morphology and dispersion,and achieved entrapment of LAB.However,LAB survival was extremely low due to the presence of ethanol.