Abstract
It is common practice to freeze dry probiotic bacteria to improve their shelf life. However, the freeze drying process itself can be detrimental to their viability. The viability of probiotics could be maintained if they are administered within a microbially produced biodegradable polymer - poly-γ-glutamic acid (γ-PGA) - matrix. Although the antifreeze activity of γ-PGA is well known, it has not been used for maintaining the viability of probiotic bacteria during freeze drying. The aim of this study was to test the effect of γ-PGA (produced by B. subtilis natto ATCC 15245) on the viability of probiotic bacteria during freeze drying and to test the toxigenic potential of B. subtilis natto. 10% γ-PGA was found to protect Lactobacillus paracasei significantly better than 10% sucrose, whereas it showed comparable cryoprotectant activity to sucrose when it was used to protect Bifidobacterium breve and Bifidobacterium longum. Although γ-PGA is known to be non-toxic, it is crucial to ascertain the toxigenic potential of its source, B. subtilis natto. Presence of six genes that are known to encode for toxins were investigated: three component hemolysin (hbl D/A), three component non-haemolytic enterotoxin (nheB), B. cereus enterotoxin T (bceT), enterotoxin FM (entFM), sphingomyelinase (sph) and phosphatidylcholine-specific phospholipase (piplc). From our investigations, none of these six genes were present in B. subtilis natto. Moreover, haemolytic and lecithinase activities were found to be absent. Our work contributes a biodegradable polymer from a non-toxic source for the cryoprotection of probiotic bacteria, thus improving their survival during the manufacturing process.
Highlights
IntroductionExtensive research has been done to determine the efficacy of probiotic foods in controlling and alleviating disorders/diseases (de Moreno de LeBlanc et al 2007, Falagas et al 2007, Garrait et al 2009, LaraVilloslada et al 2007)
Over the years, extensive research has been done to determine the efficacy of probiotic foods in controlling and alleviating disorders/diseases
Results γ-PGA as a cryoprotectant for probiotic bacteria The effect of sterilization on γ-PGA was investigated using Fourier transform infrared (FTIR) to determine whether steam sterilization alters the structure of the polymer
Summary
Extensive research has been done to determine the efficacy of probiotic foods in controlling and alleviating disorders/diseases (de Moreno de LeBlanc et al 2007, Falagas et al 2007, Garrait et al 2009, LaraVilloslada et al 2007). Some lactic acid bacteria have been shown to have antitumor activity (de LeBlanc et al 2005). One of the most important manufacturing steps for producing a probiotic food product is to introduce the bacteria into the foodstuff as dry cultures. It has been shown that the viability of lactic acid bacteria reduces by 3 log CFU/g when freeze dried (Jagannath et al 2010). There remains a need to improve the viability of probiotic microorganisms as they pass through, in particular, the freeze drying process
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