Improvement Of Stress Resistance Of Encapsulated Probiotics

As important functional food ingredient,probiotics are widely used in various foods.However,probiotics are sensitive to the environmental stresses,in which they are easily inactivated during processing,storage and digestion.Microencapsulation is reported to be effective in improving the stress tolerance of probiotics.In this paper,the effects of the hydrophobicity of encapsulating matrix,the encapsulating method of complex coacervation,the core-shell structure of microcapsules and the charge of encapsulating matrix on the survival of microencapsulated probiotics were studied.Probiotics survivals under stress conditions?drying,simulated gastrointestinal fluid,heat treatment and room temperature storage?and some physiochemical properties were measured.The main conclusions are as follows.?1?Protection of hydrophobic encapsulating materials on probiotics and the related protection mechanism were investigated through adding two hydrophobic materials?shellac and whey protein isolate?as encapsulating materials.Microcapsules alginate/sucrose?namely ALG?,alginate/shellac/sucrose?namely ALG/LAC?,alginate/whey protein isolate/sucrose?namely ALG/WPI?and alginate/whey protein isolate/shellac/sucrose?namely ALG/WPI/LAC?were prepared using the method of external emulsification/freeze drying.Compared with ALG microcapsule,ALG/LAC microcapsules increased probiotic survival by 0.99 and 2.08 log CFU/g during freeze drying and simulated intestinal fluid,respectively.Compared with ALG/WPI microcapsule,ALG/WPI/LAC microcapsules increased probiotic survival by 2.30 and1.22 log CFU/g during freeze drying and heating treatment,respectively.The above results indicated that the addition of LAC in encapsulating material significantly improved probiotic survivals in freeze drying,simulated digestive juices,heating treatment and ambient storage,and that LAC and WPI had a synergistic protection effect on probiotics.After characterizing the hygroscopicity and wettability of four microcapsules,the protection mechanism for probiotics of LAC was revealed that LAC could reduce the hygroscopicity of microcapsules and slow down the disintegration rate of microcapsules in simulated digestive juices.?2?In this work,matrixes of type-A gelatin/sodium caseinate?GE/Cas?and type-A gelatin/gum arabic?GE/GA?coacervated at neutral pH were designed and constructed based on the alkaline isoelectric point of type-A gelatin?GE?.Probiotic protection of the above two kinds of coacervates,protein/protein and protein/polysaccharide,was compared and the protection mechanism was elucidated.Based on heteroprotein complex coacervation,coacervating pH and GE/Cas ratio were optimized and the best pH and ratio was pH 6.0 and 4,respectively.Survivals of coacervating microcapsules?GE/Cas and GE/GA?during ambient storage,simulated digestion and heating treatment were higher than those of the corresponding control?GE and Cas?,which confirmed the cell protection effect by the encapsulation coacervate.The cell viability of the GE/Cas microcapsule treated with simulated gastric juice,intestinal juice and heating was higher than those of GE/GA by log2.06,log0.47,log1.58,respectively.And all the cell inactivation constants of GE/Cas under four amibient storage conditions were lower than those of GE/GA.Therefore,the cell protection by protein/protein coacervates was significantly better than that of protein/polysaccharide coacervate.The experiments of dynamic vapor sorption,dissolution and wettability of microcapsule particles showed that GE/Cas microcapsule based on heteroprotein coacervtion reduced the hygroscopicity and wettability and slowed down the disintegration rate of microcapsules in simulated digestive juices.?3?The method of spray drying was used to construct the core-shell microcapsules,with coacervating GE/Cas microcapsules as the core and other encapsulating material?shellac or chitosan?as the shell.Protection of the core-shell microcapsules on probiotics and the related protection mechanism under environmental stresses were investigated.Compared with GE/Cas microcapsule,Core-shell microcapsules had low hygroscopicity and slower wettability.At relative humidity of 90%,GE/Cas/LAC,GE/Cas/CHI and GE/Cas/LAC?Ca2+?microcapsules decreased the moisture content by6.9%,12.5%and 16.2%,respectively,than that of GE/Cas microcapsule.However,the core-shell microcapsules did not provide the expected protection for probiotics during spray drying,simulated digestive juices,heating treatment and ambient storage.This might be related to the antibacterial activity of the charged encapsulating material on the probiotics.?4?Effects of the type and charge of polysaccharide on probiotic protection and the related protection mechanism during freeze drying and ambient storage were investigated using two types of pectin?same molecular weight but different degree of esterification?and three types of carboxymethyl cellulose?CMC,same molecular weight but different degree of substitution?as typical polysaccharides.The results showed that polysaccharide with higher charge accelerated the deactivation of probiotics during freeze-drying and ambient storage,and the decrease in the number of CMC_1.2 microcysts was 2.83 d faster than that of LMP microcapsules by comparing CMC_1.2 microcapsules and LMP microcapsules,but there was no significant difference in the charge between CMC_1.2 and LMP.This indicated that the survival of the cells during storage is not only affected by the charge of the wall material,but also by the type of wall material.Cell membrane integrity and cell membrane fluidity experiments indicated that probiotic inactivation by highly-charged polysaccharides might be due to their larger change in membrane integrity and fluidity of probiotics.