Accelerated storage testing of freeze-dried immobilized lactobacillus acidophilus-fermented banana media

Freeze-drying was applied as a drying method for the production of dehydrated immobilized Lactobacillus acidophilus-fermented banana medium containing high levels of probiotics and appropriate prebiotic (mainly fructooligosaccharides) contents in an attempt to develop dried synbiotic products. Ca-alginate and kappa-carrageenan were used for the immobilization of L. acidophilus, and the immobilized bacteria were employed directly in the banana media fermentation. The fermented products were then freeze-dried. Results indicated that cell immobilization could provide effective protection to L. acidophilus, and reduce the damage caused by freezing and freeze-drying. Meanwhile, accelerated storage testing using temperatures of 50, 60 and 70C was applied to the dehydrated products. Gel-entrapped L. acidophilus appeared to have lower decimal reduction, and Ca-alginate immobilized cells had a better survival than kappa-carrageenan. Results of accelerated storage test showed that immobilization could effectively increase the thermal resistance of entrapped microorganisms, and Ca-alginate showed a better effect than kappa-carrageenan, and the beneficial effects increased with the decrease of the storage temperature. The freeze-dried products exhibited little hygroscopicity because of the consumption of monosaccharides during fermentation. Results revealed that freeze-drying could be used as a proper method for the development of dried product of immobilized L. acidophilus-fermented banana media, and accelerated storage test could be used to evaluate the storage stability of the dried products.