Encapsulation And Release Characteristics Of Geotrichum Candidum LG-8 From Kefir As A Novel Curcumin Cell-Based Microcarrier

Curcumin(Cur)is a diketone polyphenol commonly extracted from the rhizome of turmeric,which has antioxidant,anti-tumor,anti-inflammatory and anti-viral activities,and has been widely applied in some disease therapy,such as cancer,cardiomyopathy,diabetes,and Alzheimer’s.For all the above advantages,curcumin is considered as a promising drug in chemotherapy.However,the application of curcumin faces severe challenges because of its low water solubility,poor chemical stability,and low bioavailability.Therefore,research efforts towards improving the stability and bioaccessibility of curcumin have intensified in recent times.At present,encapsulation of curcumin into carriers has been considered as an effective solution.The common encapsulation carriers include liposomes,emulsions,polymer nanoparticles and cell-based carriers.However,the encapsulation process is often time-consuming and complex,which involves the addition of organic solutions(including glutaraldehyde and acetone)and high temperature treatment,that limits its application to food industry.In this study,Geotrichum candidum LG-8 isolated from kefir were prepared as microcarrier for curcumin encapsulation.The main findings are as follows:1.Evaluation of curcumin encapsulation capacity of GNCs and GCWPs and optimization of encapsulation conditionsG.candidum LG-8 native cells(GNCs)and G.candidum LG-8 cell wall particles(GCWPs)were prepared as microcarriers for encapsulation.The G.candidum LG-8 native cell-Curcumin(GNCs-Cur)and G.candidum LG-8 cell wall particles-Curcumin(GCWPs-Cur)were prepared by vacuum infusion process.The encapsulation efficiency of GNCs and GCWPs were 38.6%±1.23% and 26.06%±1.07% respectively,which showed a better encapsulation capacity than other cell-based microcarriers.Laser scanning confocal microscope and transmission electron microscope images showed that the encapsulated curcumin was dispersed uniformly in encapsulation microcarriers.Due to the presence of cytoplasm,GNCs maintained the intact cell structure after encapsulation process,and had higher encapsulation efficiency than GCWPs.By studying the influence of different factors on encapsulation efficiency,the best encapsulation condition for GNCs and GCWPs was obtained as follows: p H 6,encapsulation medium with 40% ethanol(v/v),and vacuum infusion treatment for 10 minutes.2.Stability and in vitro release of curcumin encapsulated in GNCs and GCWPsIn this study,the storage,p H,thermal stability and antioxidant capacity stability of curcumin in GNCs-Cur and GCWPs-Cur were determined.The release processes were monitored during in vitro simulated digestion.Compared with free curcumin,the storage stability of curcumin was significantly enhanced after encapsulating by GNCs and GCWPs.After 30 days of storage in dark place and at room temperature,the retention rates of curcumin in GNCs-Cur and GCWPs-Cur were 70.41%±1.17% and 55.97%±1.73%respectively,which were relatively high.For p H and thermal stability,curcumin in GNCs-Cur showed better acid,neutral and weekly alkaline stability,while curcumin in GCWPs-Cur showed better stability under strongly alkaline condition.Curcumin in GNCs-Cur was more stable at heat treatment below 60°C,while curcumin in GCWPs-Cur possessed better stability at heat treatment above 80°C.Besides,because of encapsulation process,the stability of antioxidant capacity of curcumin was significantly improved.After24 hours,GNCs-Cur and GCWPs-Cur still had excellent scavenging ability of DPPH and hydroxyl radical.Moreover,the antioxidant capacity of GNCs-Cur was always better than that of GCWPs-Cur,mainly due to the presence of antioxidant substances in cytoplasm such as glutathione.Compared with GCWPs,GNCs showed better curcumin release ability during in vitro simulated digestion.GNCs protected curcumin against the harsh acid environment of gastric digestion,and the main release of curcumin occurred in intestinal digestion,which resulted in better absorption and utilization of curcumin.Furthermore,the results of sequential digestion showed that more curcumin could be released during intestinal digestion after the pretreatment of gastric digestion.3.Effect of G.candidum LG-8 polysaccharide on curcumin encapsulationIn this study,the function of G.candidum LG-8 polysaccharide(GPS)in curcumin encapsulation was characterized.Crude G.candidum LG-8 polysaccharide(c-GPS)was extracted from G.candidum LG-8 by ultrasonic extraction and was purified by anion exchange column.After the purification process,there were three purified polysaccharides:GPS-1,GPS-2 and GPS-3.Through the component analysis,UV spectra,and FTIR analysis,it was found that the purified polysaccharides had similar composition and structure with c-GPS,but the purification process could effectively eliminated protein and other impurities in c-GPS.HPLC analysis showed that c-GPS and purified polysaccharides had the same monosaccharide composition,which included mannose,glucose and galactose,but their proportions were different.Scanning electron microscope images showed that GPS had a compact spherical structure,which provided more binding sites and larger surface for curcumin binding.After formation of complex,the scanning electron microscope images of crude G.candidum LG-8 polysaccharide-Curcumin(c-GPS-Cur)was more compact with layered structure,which indicated the tight binding between c-GPS and curcumin,and better stability of c-GPS-Cur.FTIR analysis showed that the hydroxide radical and α-pyranose of c-GPS were involved in the binding with curcumin,and the characteristic functional groups of curcumin were masked after binding.c-GPS and three purified polysaccharides all had great curcumin binding ability,and all the values of binding efficiency were higher than 70%.Besides,curcumin in c-GPS-Cur showed great storage,p H and thermal stability,which proved that GPS played an important role in the encapsulation and delivery of curcumin by G.candidum LG-8.