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Cahu T., Larsen N., Blennow A., Saad S., Jespersen L.
University of Copenhagen, Denmark

The ability of bacterial strains to exert probiotic properties depends on their survival in the gastro-intestinal (GI) tract. There is scientific evidence that prebiotic carbohydrates exhibit a protective effect on bacterial tolerance to gastric conditions by interacting with bacterial cells. An interesting approach to characterize pro-/prebiotic interactions is based on determination of Zeta potential (Zp)-the electrical potential in the shear plane of particles in suspensions. The objective of the study was (i) to investigate the ability of selected pectins and starches to improve survival of probiotic bacteria during co-incubation in simulated GI juices and (ii) to characterize the factors involved in synbiotic interactions, such as functional groups, hydrodynamic diameter, Zp and polydispersity.

Probiotic Lactobacillus and Bifidobacterium strains (6 in total) were obtained from Chr.Hansen A/S. Survival of the strains was determined in the simulated stomach solution (SS) in the presence of nine pectins or three starches and compared to control SS without carbohydrates. Differences in reduction of viable counts (CFU) between treatments and controls were assessed by the paired two-tailed Student s t–test. Zeta potential of carbohydrates and bacterial cells was determined at pH 2.5 and pH 6.5 by dynamic light scattering with a ZetasizerZS (Malvern Instruments, UK).

L. acidophilus LA-5, L. fermentum PCC and L. reuteri RC-14 were most resistant to acid stress, followed by B. animalis BB-12. Viability of these strains in SS was either improved or consistent in the presence of carbohydrates. The highest increase of viability (10 fold) was obtained for PCC and RC-14 in combination with sugar beet pectin, harsh extracted pectin from orange, differentially extracted HM pectin from lemon and potato fiber. L. rhamnosus LGG and L. paracasei F-19 were less tolerant to SS conditions and their survival was negatively affected by pectins. Zeta-potential of bacterial cells and carbohydrates was highly affected by pH. The values of Zp in bacteria were reduced with lower pH, due to protonation of cell surface molecules; the largest shifts were observed for L. acidophilus LA-5. Zp values were positive or close to zero for Lactobacillus strains and negative for BB-12 at acidic conditions. Pectins, especially low-methoxyl, were characterized by more negative Zp than starches due to the polygalacturonic acid residues in their structure.

Viability of bacterial strains in SS incubated in the presence of pectins and starches correlated significantly (P<0.5) with Zp values of carbohydrates. Generally, carbohydrates with intermediate to lower negative Zp were more efficient to improve bacterial survival. The results of this study indicated that Zp approach might be useful to predict the extent of electrostatic interactions between polysaccharides and bacteria, thereby, promoting the ability to survive at GI conditions.

Keywords: Probiotics, Survival, Synbiotic Interactios, Zeta Potential, Prebiotics

Cahu T., et al. (2016). Effect of pectins and starches on bacterial survival in the gastro-intestinal juices and mechanisms of synbiotic interactions. Conference Proceedings of IPC2016. Paper presented at the International Scientific Conference on Probiotics and Prebiotics, Budapest (p. 87.). IPC2016

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