[Show abstract][Hide abstract] ABSTRACT: As starter cultures are distributed worldwide by specialized suppliers, long-term stabilization becomes more important. Therefore the trend goes from liquid and frozen to dried cultures. Freeze drying is the standard process to produce dried starter cultures; however, alternative, more energy-efficient drying technologies are becoming more important. This chapter discusses the characteristics and suitability of different drying technologies for the production of starter cultures and their impact on product quality and handling. The impact of the fermentation process and the drying matrix is also reviewed.
[Show abstract][Hide abstract] ABSTRACT: There is still lack of the insight into the storage stability of dry probiotics produced by vacuum drying. Therefore, in this study we assessed the stability of a vacuum-dried Lactobacillus paracasei F19 under varying storage conditions. L. paracasei F19 was vacuum-dried with and without sorbitol and trehalose. The dried cells were stored at 4, 20 and 37°C, and at aw=0.07, 0.22 and 0.33. The survival was determined by viable counts on MRS agar plates. The inactivation rate constants were determined for each storage condition. The survival after drying of cells dried without and with trehalose and sorbitol was 29, 70 and 54%, respectively. All vacuum-dried cells were very stable at 4°C. However, high stability at non-refrigerated temperatures was obtained only in the presence of sorbitol. In contrast to sorbitol, the supplementation of trehalose did not stabilize cells during storage. This is supposedly due to the rapid crystallization of trehalose during storage. While glass transition temperatures of dry cell-sorbitol increased from −32°C to 12°C during storage at 37°C and aw=0.07, Tg of dry cell-trehalose (−15°C after drying) could not be determined after storage for only 24h. In conclusion, we showed that high stability of probiotic cells at non-refrigerated temperatures could be obtained by vacuum drying process with appropriate protectant.
No preview · Article · Apr 2012 · Food and Bioproducts Processing
[Show abstract][Hide abstract] ABSTRACT: High viability of dried probiotics is of great importance for immediate recovery of activity in fermented foods and for health-promoting effects of nutraceuticals. The conventional process for the production of dried probiotics is freeze-drying. However, loss of viability occurs during the drying and storage of the dried powder. It is believed that achieving the "glassy state" is necessary for survival, and the glassy state should be retained during freezing, drying, and storage of cells. Insight into the role of glassy state has been largely adopted from studies conducted with proteins and foods. However, studies on the role of glassy state particularly with probiotic cells are on the increase, and both common and explicit findings have been reported. Current understanding of the role of the glassy state on viability of probiotics is not only valuable for the production of fermented foods and nutraceuticals but also for the development of nonfermented functional foods that use the dried powder as an adjunct. Therefore, the aim of this review is to bring together recent findings on the role of glassy state on survival of probiotics during each step of production and storage. The prevailing state of knowledge and recent finding are discussed. The major gaps of knowledge have been identified and the perspective of ongoing and future research is addressed.
No preview · Article · Oct 2011 · Journal of Food Science
[Show abstract][Hide abstract] ABSTRACT: The high viability of lactic acid bacteria (LAB) during storage is greatly important for starter cultures used for the direct
inoculation to food matrices and for the development of probiotic products. The established methods for preservation are freezing
and freeze-drying, in which cells are maintained in frozen and dried forms. The frozen cells should be kept at a low storage
temperature, such as −80°C, and rapid thawing is recommended for cells frozen with liquid nitrogen. The dried cells should
have a low moisture content (<4%). They should be stored at a low relative humidity and temperature and rehydrated in a warm
rehydration medium. In addition to these established methodologies, dried cells can be prepared by alternative drying processes
such as spray-, fluidized bed-, and vacuum-drying. The viability of frozen and dried cells can be improved by the addition
of protectants such as skim milk and sugars. The physiological state of LAB plays a crucial role, and an increased viability
can be obtained by the sublethal stress treatment of cells. Exposing LAB cells to a mild stress triggers cells’ protective
mechanisms to subsequent stresses occurring during the preservation processes. These stresses are, for example, the entry
of cells to the stationary phase; osmotic, heat, cold, and acid shock; as well as genetic modification of genes related to
[Show abstract][Hide abstract] ABSTRACT: Although the addition of sugars to drying media is a general practice for the viability improvement of lactic acid starter
cultures during drying, the mechanism behind the protective effects is not clear. To gain insight into the protective mechanisms
of sugars, Lactobacillus helveticus was dried by vacuum drying in the presence of sorbitol, whose protective effects were shown in our previous study (Santivarangkna
et al. Lett Appl Microbiol 42:271–276, 2009). In this study, membrane phase transition temperatures (Tm) of fresh cells and cells dried with and without sorbitol were measured by Fourier transform infrared spectroscopy (FT-IR).
Generally, an increase in membrane phase transition temperature (Tm) is believed to cause membrane damage during drying. Lactobacillus helveticus cells exhibited the transitions at the temperatures of 15.5 and 37.5°C. Drying of cells without sorbitol increased the transition
temperatures to 16.5 and 41.5°C, while it was depressed by 6 and 10.5°C when dried with sorbitol. The interaction between
membrane phospholipids and sorbitol was observed from hydrogen-bonding sensitive C = O and P = O stretching bands. The position
of the P = O band was shifted to the lower frequency in cells dried with sorbitol, which reflects the hydrogen bonding interaction.
We suggest that sorbitol protects cells during drying by depressing Tm via the interaction with phosphate groups of membranes.
KeywordsSugar- Fourier transform infrared spectroscopy (FT-IR)-Vacuum drying-Sorbitol-Lactic acid bacteria-
No preview · Article · Jun 2010 · Annals of Microbiology
[Show abstract][Hide abstract] ABSTRACT: To examine changes in membrane fatty acid profile attributed to the physiological adaptation of Lactobacillus helveticus during vacuum drying.
The viability and membrane integrity of the cells after vacuum drying were measured by plate counts and DNA fluorescence dyes. The physiological adaptation of cells dried in the presence of sorbitol was observed by determining changes in membrane fatty acid composition using gas chromatography. Results showed that viability and membrane integrity of Lact. helveticus cells increased when drying in the presence of sorbitol. The occurrence of the very low melting point polyunsaturated fatty acids linoleic and arachidonic acid was observed in cells dried in the presence of sorbitol.
The physiological adaptation of cells occurred with cell membrane of Lact. helveticus during vacuum drying of cells in the presence of sorbitol.
The study showed that physiological adaptation with membrane of the cells occurred during the drying process. The insight implies that instead of viability improvement of dried cells by the conventional stress induction during cultivation, the induction may be exercised thereafter without compromising growth of the cells.
Full-text · Article · Aug 2009 · Letters in Applied Microbiology
[Show abstract][Hide abstract] ABSTRACT: The preservation of lactic acid starter cultures by drying are of increased interest. A further improvement of cell viability is, however, still needed, and the insight into inactivation mechanisms of the cells is a prerequisite. In this present work, we review the inactivation mechanisms of lactic acid starter cultures during drying which are not yet completely understood. Inactivation is not only induced by dehydration inactivation but also by thermal- and cryo-injuries depending on the drying processes employed. The cell membrane has been reported as a major site of damage during drying or rehydration where transitions of membrane phases occur. Some drying processes, such as freeze drying or spray drying, involve subzero or very high temperatures. These physical conditions pose additional stresses to cells during the drying processes. Injuries of cells subjected to freezing temperatures may be due to the high electrolyte concentration (solution effect) or intracellular ice formation, depending on the cooling rate. High temperatures affect most essential cellular components. It is difficult to identify a critical component, although ribosomal functionality is speculated as the primary reason. The activation during storage is mainly due to membrane lipid oxidation, while the storage conditions such as temperature moisture content of the dried starter cultures are important factors.
Full-text · Article · Aug 2008 · Journal of Applied Microbiology
[Show abstract][Hide abstract] ABSTRACT: Sugars are recognized protectants used in the preparation of dried starter cultures for fermented food industries, particularly as additives for the drying media. They increase viability of the starter cultures during drying and storage. This review intends to summarize and discuss their roles in each step of the preparation process. The main topics cover the role of sugars in the induction of compatible solutes and alteration of fermentation metabolites during growing of cells, the reduction of cryo- and thermal injuries and membrane damage during drying, as well as the formation of sugar glass matrices and the prevention of oxidation during storage. In some topics, proposed protective mechanisms together with corresponding inactivation mechanisms have been discussed. The protective hypotheses as such are preferential exclusion, water replacement, hydration force explanation, and vitrification of sugars.
No preview · Article · Jun 2008 · Food Microbiology
[Show abstract][Hide abstract] ABSTRACT: The preservation of lactic acid starter cultures by alternative drying processes has attracted increasing attention due to the high costs and energy consumption of freezing and freeze drying. This review thus aims to provide a survey regarding the state of knowledge of starter culture production at high levels of viability. The results from numerous studies on various drying processes and lactic acid bacteria are summarized. The alternative drying processes considered, such as spray drying, fluidized bed drying, and vacuum drying, are mainly of industrial interest. The features, advantages, and disadvantages of these drying processes are described. In conclusion, the important factors that need to be considered, standardized, or optimized to achieve high levels of viability include intrinsic tolerance of cultures, growth media and conditions, stress induction, cell harvesting conditions, protective agents, rehydration conditions, enumeration of cells, and storage conditions.
No preview · Article · Apr 2007 · Biotechnology Progress
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to gain insight into the inactivation mechanisms of Lactobacillus helveticus during vacuum drying.
Early stationary phase cells of L. helveticus were dried in a vacuum drier. Viability, cell integrity and metabolic activity of cells were assessed over time by plate counts on de Man Rogosa and Sharpe broth agar medium and cytological methods employing fluorescent reagents and nucleic acid stains. The cell envelope damage was visualized by atomic force microscopy (AFM). Fourier transform infrared spectroscopy (FT-IR) was used to indirectly observe changes in cell components during drying. Viability, metabolic activity and cell integrity decreased during vacuum drying, and different inactivation curves, characterized by the loss of ability to resume growth, and cell injuries were found. AFM images showed cracks on the surface of dried cells. Main changes in FT-IR spectra were attributed to the damage in cell envelope.
The cell envelope was the main site of damage in L. helveticus during vacuum drying.
Inactivation mechanisms of L. helveticus during vacuum drying were partly elucidated. This information is useful for the improvement of the viability of vacuum-dried starter cultures.
[Show abstract][Hide abstract] ABSTRACT: To assess four carbohydrates for the protective effect against Lactobacillus helveticus cells inactivation during vacuum drying, and to study the effect of selected carbohydrate on changes of inactivation kinetics.
Early stationary phase L. helveticus cells grown in MRS media were recovered from fermentation broth, washed with PBS buffer (pH 7.0), and then mixed with different concentrations of four carbohydrates, namely lactose, sorbitol, inulin, and xanthan gum. Cells were dried in a vacuum drier at 100 mbar, 43 degrees C for 12 h. Only cells with 1% sorbitol addition showed higher survival (18%) over cells without added carbohydrate (8%). Using in situ microbalance technique whereby cell weight during vacuum drying was continuously monitored via precision balances integrated into the vacuum chamber, drying and inactivation kinetics of cells and cells mixed with sorbitol were established.
Survival of L. helveticus during the vacuum drying could be improved by the addition of optimal concentration of 1% sorbitol. Addition of sorbitol did not cause drastic changes in drying rate, water content and water activity of samples. The protection mechanisms of sorbitol seemed not to be due to a direct physical effect, which could be related to drying rate.
The increase in survival of cells after vacuum drying by the addition of a protective carbohydrate may provide an alternative mean to preserve starter cultures at a higher level of activity.