Date Published: July 24, 2017
Publisher: Springer Berlin Heidelberg
Author(s): Mingzhan Toh, Shao Quan Liu.
This study evaluated the influence of three inactivated yeast derivatives (IYDs) used in wine production, namely OptiRed®, OptiWhite® and Noblesse®, on the viability of the probiotic strain Lactobacillus rhamnosus HN001 in an acidic environment. Addition of the IYDs at 3 g/L significantly enhanced the survival of the probiotic bacteria by 2.75–4.05 log cycles after 10-h exposure in a pH 3.0 buffer. Acid stress assay with IYD components obtained after centrifugation and filtration revealed that water-soluble compounds were responsible for improving the acid tolerance of L. rhamnosus HN001 for all three preparations. Differences in protective effect amongst the IYDs on L. rhamnosus HN001 were observed when permeates and retentates of the water-soluble extracts, obtained through ultrafiltration with a 2 kDa membrane, were assayed against the lactic acid bacterium. Chemical analysis of the water-soluble components suggests that low molecular weight polysaccharides, specific free amino acids and/or antioxidants in the 2 kDa permeates could have contributed to the enhanced survival of L. rhamnosus HN001 during acid stress. The contrast amongst the 2 kDa retentates’ viability enhancing property may have been attributed to the differences in size and structure of the higher molecular weight carbohydrates and proteins, as the survival of the probiotic did not relate to the concentration of these compounds. These results suggests that oenological IYDs could potentially be applied to probiotic foods for enhancing the acid tolerance of the beneficial microorganisms, and consequently prolonging the shelf life of these products.
Enhancing the survival of probiotic bacteria in acidic environments such as fermented food carriers and gastric juice is crucial for ensuring their optimal function as health promoting agents. As defined by the FAO/WHO working group, probiotics are “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” (FAO/WHO 2001). It is generally accepted that the minimum level of these microorganisms in probiotic foods or supplements at the point of consumption is 1 × 109 CFU per serving, or 1 × 107 CFU/g, for delivering sufficient viable cells required to colonize the host’s gut (Hill et al. 2014).
The present study served as a follow-up to previous studies involving the L. rhamnosus HN001 and S. cerevisiae EC-1118 pairing (Suharja et al. 2014; Lim et al. 2015). These studies demonstrated the potential of using viable and non-viable yeast as a means to enhance the acid tolerance of L. rhamnosus HN001. In the current study, we used three IYDs as sources of non-viable yeast and compared its efficacy against live S. cerevisiae EC-1118. We proposed several reasons for IYDs viability enhancing properties with reference to established mechanisms, based on results involving other strains of probiotics and lactic acid bacteria.