Abstract
The strain Streptococcus thermophilus are widely used in the ways of probiotic formulations form or starter culture powder depending on the function of the strain and viability during production process. The pros and cons of freeze-drying on the viability and storage of starter lactic acid bacteria are well documented. In the present study, we focused on the optimization of freeze-drying medium with addition of cryoprotectants for Streptococcus thermophilus. The interactive effects of sucrose, soluble starch and ascorbic acid on the survival rate as well as the viable counts of S. thermophilus during freeze-drying were investigated by Box-Behnken experimental design. The results showed that, with the mixture of 17 g/100mL sucrose, 17 g/100mL soluble starch and 0.4 g/mL ascorbic acid, the viability could be well preserved when freeze-drying was employed. Moreover, the survival rate and viable counts of S. thermophilus were observed to (69.93±0.07) % and (2.79±0.03) ×1011 cfu/g during freeze-drying using the optimal compound cryprotectants, respectively, which verified the adequacy of predicted value 70.19 % and 2.81×1011 cfu/g. Our results demonstrated that the mixture of the cells in the presence of above three cryprotectants before freeze-drying protected S. thermophilus cells from the adverse freeze-drying environment efficiently.
Highlights
Probiotics are microorganisms that, when administered in adequate amounts, confer a health benefit on the host (FAO/WHO, 2001)
The aim of this study was to optimize the levels of the significant factors(sucrose, soluble starch and ascorbic acid) for cryoprotectants of Streptococcus thermophilus to maximized viable counts as well as survival rate during freeze-drying, and to research the mutural interactions between selected factors using BoxBehnken experimental design
Survival rate of Streptococcus thermophilus was represented by Y1 (%) and the viable counts of freeze-dried powder was represented by Y2 (×1011cfu/g)
Summary
Probiotics are microorganisms that, when administered in adequate amounts, confer a health benefit on the host (FAO/WHO, 2001). The commercial significance to the dairy fermentation industry with probiotics, which include cheese, yogurt and sour cream, is recognized worldwide(Carvalho et al, 2004). Streptococcus thermophilus, which are characterized as thermophilic gram-positive microorganism, is widely used for fermented products in combination with Lactobacillus bulgaricus (Gezginc et al, 2013). The food process and storage challenged and diminished the viability and number of probiotics in the products (Wang et al, 2016). Consideration of maintaining or enhancing the viability of probiotics, the appropriate methods such as drying processes or encapsulation technology must be taken
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