Preparation Of Alginate Microcapsules By Emulsification/Internal Gelation And Their Protection For Lactobacillus Acidophilus CGMCC1.2686

The microencapsulation of lactic acid bacteria (LAB) has long been a researchfocus in the area of food science and technology. However, effective methods toencapsulate and protect LAB are still less developed, due to the high sensitivity of LABagainst adverse environments and the diversity in LAB strains. Emulsification/internalgelation is a useful method for LAB encapsulation, and results in capsules withcontrollable particle size and is easy to scale up. In the study, alginate (Alg) and konjacglucomannan (KGM) were used as wall materials to encapsulate Lactobacillusacidophilus CGMCC1.2686using the emulsification/internal gelation method. Physicalproperties and protection efficiency of LAB microcapsules were determined. The mainconclusions were as follows:(1) Microcapsules of L. acidophilus CGMCC1.2686were prepared byemulsification and gelation of alginate solutions with slow release of Ca2+ions fromcalcium carbonate (CaCO3) and calcium disodium ethylenediaminetetraacetate(Ca-EDTA). Particle size analysis and optical microscope showed thatCa-EDTA-alginate microcapsules had a more uniform size distribution, compared withCaCO3-alginate microcapsules. Mechanical test and scanning electron microscopepointed to a denser structure, a higher fracture force and a larger elasticity forCaCO3-alginate microcapsules than Ca-EDTA-alginate microcapsules. Encapsulationyields of CaCO3-alginate and Ca-EDTA-alginate microcapsules were37.9%and36.9%,respectively. LAB survivals of CaCO3-alginate and Ca-EDTA-alginate microcapsules insimulated gastric juice (SGJ) were22.2%and7.1%, respectively, while those ofCaCO3-alginate and Ca-EDTA-alginate microcapsules in bile salts solution (BS) were2.6%and0%, respectively. Thus, CaCO3seemed to a more suitable calcium source thanCa-EDTA to solidify alginate for the encapsulation of L. acidophilus CGMCC1.2686.(2) Correlation of LAB survivability with the mechanical properties ofmicrocapsules was investigated. Mechanical strength of microcapsules was manipulatedby using different alginate concentrations and different calcium alginate monomer molarratios. Five formulae of microcapsules with increasing mechanical strengths (normalforce at0.15mm:4.3,13.1,26.9,31.8and35.1N, respectively) were chosen toencapsulate Lactobacillus acidophilus CGMCC1.2686. Particle size analysis and opticalmicroscope showed that the particle diameter of the five LAB microcapsules rangedfrom294.2to406.9μm. LAB encapsulation yields of the five microcapsules were11.6%,17.7%,42.3%,44.4%and55.5%, respectively. Cell survivals in SGJ were5.4%,19.4%,23.5%,25.4%and26.3%, respectively, while those in BS were6.3*10-4%,1.4*10-4%,7.0*10-4%,4.3*10-4%,3.6*10-4%, respectively. Regression analysis showedthat cell viability in SGJ was positively correlated with the mechanical strength of themicrocapsules. However, increasing mechanical strength did not effectively enhance thecell survival in bile salts solution. (3) KGMs of different molecular weights were prepared by enzymatic degradation.Mixture of KGM and alginate was used as composite wall material to encapsulate L.acidophilus CGMCC1.2686and the effect of KGM molecular weight on LABprotection studied. Compared to alginate microcapsules, all the Alg-KGMmicrocapsules had superior physical properties and better protection efficiency, in termsof mean diameter, mechanical strength, viscoelasticity, encapsulation yields, andsurvivals in SGJ and BS. As for the effect of KGM molecular weight, Alg-KGMmicrocapsules prepared using KGMs of intermediate molecular weights exhibitedhigher values of mechanical strength and better LAB protection efficiency in SGJ andBS. Regression analysis showed that cell survivals in SGJ and BS were positivelycorrelated with the mechanical strength of the Alg-KGM composite microcapsules.