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The application of spray drying to produce probiotic or synbiotic preparation

The objective of this work was to evaluate the applicability of spray drying in the production of skim milk-based preparations containing probiotic bacteria. Furthermore, oligofructose-based or polydextrose-based prebiotic substances were also included in the carrier matrix to assess their protection capacity and to examine the possibility of generating synbiotic powder products. Initially, the thermal tolerance, an indicator of probiotic survival during spray-drying, of three strains of probiotic lactobacilli were compared. L. rhamnosus E800 was the most heat resistant strain, followed by L. salivarius UCC 500, with L. rhamnosus GG being least heat resistant. Although L. rhamnosus GG exhibited the poorest thermal tolerance of the three Lactobacillus strains studied, it was the best survivor during spray-drying, indicating that thermal tolerance alone is not an accurate predictor of performance during spray-drying and that other phenomena, such as dehydration affect cell viability during drying. When reconstituted skim milk was used as spray drying carrier, a microbial survival rate of 60% to 80% was achieved at an outlet temperature of 80°C. This results in probiotic powders harbouring high numbers of viable microorganisms (~1E9CFU/g) generated with stationary phase cultures.

The incorporation of commercial prebiotic substances such as Raftilose®P95 or polydextrose in the skim milk powder did not exert any adverse effect on bacterial survival upon spray drying. Probiotic cultures retained good viability during storage in powders containing skim milk/prebiotics at 4 and 15°C. However, stability of bacteria during long term storage at 37°C was impaired by partial substitution of skim milk with either of the prebiotic substances evaluated. This might be caused by the inability of the oligosaccharides in these prebiotic substances in adequately replacing water molecules on dehydration. The spray drying media were also calorimetrically characterised in terms of their glass transition temperatures so as to evaluate the contribution of glassy state on the maintenance of bacterial survival during storage.

Although all evaluated carriers were in the glassy state, differences were still observed in their capacity to confer protection on the probiotic bacteria. The presence of the dried medium in the glassy state appeared to have had only little effect on bacterial stability in the spray dried powder and thus is not sufficient for preservation. Moreover, storage survival was affected by the phase of growth of the spray-dried culture with stationary phase best, followed by lag and log phase. Flow cytometric assessment in combination with functional dyes (carboxyflurescein diacetate and propidium iodide) was applied as a diagnostic tool to evaluate the type of cellular injuries which occurred upon spray-drying. Cell death was caused mainly by damage to cell membranes and the degree of membrane disintegration increased progressively as the outlet temperatures increased.

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Berlin University of Technology (TUBER LMT)
Koenigin-Luise-Str. 22
14195 Berlin
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