Effects Of Heat-induced Ca-aggregated Milk On The Viability Of Probiotics During Single Droplet Drying,Storage And Digestion

Probiotic bacteria have been defined as "live microorganisms which when administered in adequate amounts confer a health benefit on the host" by FAO/WHO.However,probiotics often lose their viability during the processes of production,storage and digestion.In order to prolong the shelf-life of probiotic products,drying technology is generally used to produce dried form probiotics.Nowadays,freeze drying is most frequently used to produce dried probiotics.Spray drying is expected to be an alternative method of freeze drying due to its low production cost and high energy efficiency.The bottleneck of spray drying in probiotic application addresses the thermal and dehydration-related inactivation of bacteria during process.In this work,a protective drying matrix was designed by modifying skim milk with the principle of calcium-induced protein thermal aggregation.The well-defined single-droplet drying technique was used to monitor the droplet-particle conversion and the protective effect of this modified Ca-aggregated milk on Lactobacillus rhamnosus GG.The Ca-aggregated milk exhibited a higher drying efficiency and superior protection,in comparison with commercial UHT skim milk,on L.rhamnosus GG during thermal convective drying.The mechanism was explained by the aggregation in milk,causing the lower binding of water in the serum phase and,conversely,local concentrated milk aggregates involved in bacteria entrapment in the course of drying.This work may open a new avenue for the development of probiotic products with high bacterial viability and calcium enrichment via spray drying.Besides,Ca-aggregated milk had no significant effect on the storage stability and digestion resistance of LGG.Last but not least,the effects of commercial beverage Cola,Coffee,Spirit and alcohol drinks on stabilization of probiotic Lactobacillus casei Zhang were also investigated in this work.The alcohol drinks with ethanol concentration higher than 20%(v/v)were found to significantly damage LCZ cells.This result provides helpful information for improvement of dietary habit.