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The aim of this research effort was to investigate the role of various sugar substrates in the growth medium upon thermotolerance and upon survival during storage after freeze-drying of Lactobacillus bulgaricus. Addition of the sugars tested to the growth medium, and of these and sorbitol to the drying medium (skim milk) was investigated so as to determine whether a relationship exists between growth and drying media, in terms of protection of freeze-dried cells throughout storage. The lowest decrease in viability of L. bulgaricus cells after freeze-drying was obtained when that organism was grown in the presence of mannose. However, L. bulgaricus clearly survived better during storage when cells had been grown in the presence of fructose, lactose or mannose rather than glucose (the standard sugar in the growth medium). A similar effect could not be observed in terms of thermotolerance; in this case, the growth medium supplemented with lactose was found to yield cells bearing the highest heat resistance. Supplementation of the drying medium with glucose, fructose, lactose, mannose or sorbitol led in most cases to enhancement of protection during storage, to a degree that was growth medium-dependent.

-The effects of sorbitol and monosodium glutamate upon survival during storage of freeze-dried Lactobacillus bulgaricus, Lactobacillus plantarum, Lactobacillus rhamnosus, Enterococcus durans and Enterococcus faecalis were examined. There were no significant differences in survival during freeze-drying after addition of sorbitol or monosodium glutamate. However, these compounds were found to increase the stability of most strains during long-term storage. Various survival patterns were observed among the strains considered. However, for most of them, both compounds were proven effective in maintaining high degrees of viability over long periods of storage.Starter culture / preservation / additive / processing / viability Résumé -Effet protecteur du sorbitol et du glutamate monosodique pendant le stockage de bactéries lactiques lyophilisées. Les effets du sorbitol et du glutamate monosodique sur la survie des souches lyophilisées de Lactobacillus bulgaricus, Lactobacillus plantarum, Lactobacillus rhamnosus, Enterococcus durans et Enterococcus faecalis pendant le stockage ont été étudiés. On n'a pas trouvé de différences significatives pendant la lyophilisation, après l'addition de sorbitol ou de glutamate monosodique. Cependant, l'addition de ces composés a augmenté la stabilité de la plupart des souches pendant le stockage prolongé. Différents profils de survie ont été observés parmi les souches considérées ; toutefois, pour la plupart des souches les deux composés étaient efficaces dans le maintien de degrés élevés de viabilité pendant de longues périodes de stockage. Levain / conservation / additif / traitement / viabilité

BACKGROUND Blueberry juice powder was developed via foam‐mat freeze‐drying (FMFD) and spray‐drying (SD) via addition of maltodextrin (MD) and whey protein isolate (WPI) at weight ratios of MD/WPI = 0.4 to 3.2 (with a fixed solids content of 5 wt% for FMFD and 10 wt% for SD). Feed rates of 180 and 360 mL h−1 were tested in SD. The objective was to evaluate the effect of the drying methods and carrier agents on the physical properties of the corresponding blueberry powders and reconstituted products. RESULTS Ratios of MD/WPI = 0.4, 1.0 and 1.6 produced highly stable foams most suitable for FMFD. FMFD gave high yields and low bulk density powders with flake‐like particles of large size that were also dark purple with high red values. SD gave low powder recoveries. The powders had higher bulk density and faster rehydration times, consisting of smooth, spherical and smaller particles than in FMFD powders. The SD powders were bright purple but less red than FMFD powders. Solubility was greater than 95% for both FMFD and SD powders. CONCLUSION The FMFD method is a feasible method of producing blueberry juice powder and gives products retaining more characteristics of the original juice than SD. © 2017 Society of Chemical Industry

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