Effects of micronization on viability and thermotolerance of probiotic freeze-dried cultures

摘要

Three strains of probiotic freeze-dried bacteria, Bifidobacterium breve R070 (BB R070), B fidobacterhun longum R023 (BE R023), and Lactobacillus acidophilus R335 (LA R335), were micronized using a spiral jet mill as grinding system, in order to decrease the powder particle size for incorporation in multiphase low-diameter microcapsules produced by emulsification and spray-drying. The effects of grind air pressure (1. 2. 4 or 5.5 bar) and product feed rate (150 or 300 g h(-1)) on powder particle-size distribution and bacterial viability were evaluated. The D(v, 0.9) of the micronized powder was found to be only affected by grind air pressure (P < 0.05). Survival of the micro-organisms to the particle-size reduction process was essentially related to the final powder particle size. A grind air pressure of 4 bar with a product feed rate of 300 g h(-1) was selected as the least destructive treatment (survival rate of 25.5 +/- 5.2%) to produce powders of probiotic freeze-dried cultures with particle-size distribution suitable for the microencapsulation technology (D(v, 0.9)< 25 mum). Heat susceptibility of the two micronized bifidobacteria, strains prepared using these operating conditions was compared with that of the unprocessed cultures by means of various thermotolerance parameters (E-a D-45degreesC, D-65degreesC D-80degreesC) Results indicated that BE R023 displayed intrinsic low heat resistance whereas particle-size reduction dramatically increased the thermosensitivity of BB R070. Micronization is an effective way of reducing powder particle size of freeze-dried bacterial cultures for subsequent use in cell immobilization applications with low heat treatment.