Probiotics 3

Continued from Probiotics and Prebiotics As Ingredients in Functional Foods

Polydextrose is a highly branched polymer of glucose. Its unique arrangement of glycosidic linkages makes it resistant to hydrolysis by human digestive enzymes.  After ingestion it passes intact into the colon where it is partially fermented by the colonic microflora.  In this way polydextrose contributes an energy value of one calorie per gram.  It is the preferred speciality carbohydrate for a wide variety of processed food applications including baked goods, confectionery, dairy products and beverages.  Its relatively high molecular weight and slow fermentation rate contribute to polydextrose being very well tolerated at typical use rates (Flood et al, 2004).

Polydextrose is well established as a dietary fibre and complies with the recently published CODEX Alimentarius fibre definition (Anon, 2005).  Human intervention studies, combined with in vitro and metabolism data, have demonstrated that polydextrose also functions well as a prebiotic, sustaining its impact throughout the colon.

Jie et al (2000) conducted a double blind intervention study involving 120 healthy males.  This demonstrated that polydextrose enhanced both bifidobacteria and Lactobacilli in a dose dependent manner with the effect being seen with a dose as low as 4 grams per day. Increasing doses of polydextrose resulted in a reduction in fecal pH, indicative of a shift from proteolytic to saccharolytic fermentation.  The lower pH serves to inhibit pathogen growth. Fecal butyrate was also enhanced in a dose-dependent manner.

The bifidogenic effect of polydextrose was confirmed in a recent human intervention study in which polydextrose at 5 grams per day was combined with a probiotic. An almost 100 fold increase in bifidobacteria was seen from a starting level of 107 (Tiihonen et al, in press).

Colon simulation work has shown that polydextrose is fermented throughout the colon and is particularly efficient at mediating a prebiotic effect in the distal colon, where the potential for disease and disorder is particularly high (Probert et al, 2004).  Ishizuka et al (2003), using a rat model, showed that polydextrose considerably reduced the formation of aberrant crypt foci (ACF) in the presence of a carcinogen.  The effect was most pronounced in the rectum where the reduction was up to 65%.  The authors concluded that ingestion of polydextrose may prevent colorectal carcinogenesis.

A study by Hara et al (2000) showed that dietary polydextrose increased calcium absorption and bone mineralization in rats.  The effect may partly have been due to colonic acidification which would be expected to increase calcium solubility.  However, the main positive effect was, unexpectedly, seen in the small intestine.

Fermentation of polydextrose has beneficial effects for mucosal functions.  Enhanced butyrate production serves as an important energy source, not only for epithelial cells, but also for mucosal immune cells.  Polydextrose has been shown to increase production of immunoglobulin A (IgA) in the large intestine of rats and a synergistic effect was seen with a polydextrose:lactitol combination.

Balancing immune responses in the large intestine is especially important for reducing the risk of colon cancer development.  A possible mechanism for reduction in cancer development involves the regulation of mucosal gene expression.  Over-expression of the cyclo-oxygenase 2 (cox-2) gene is related to early stages of colon cancer development and chronic inflammatory diseases in the intestine.  Mäkivuokko et al (2005) combined two different in vitro systems, namely a four-stage simulator of colonic fermentation and a cell-culture based model of human intestinal epithelial function, in order to study the effects of polydextrose on colon cancer development.  A dose-dependent decreasing effect on cox-2 expression was observed in Caco-2 cells (a human colon cancer cell line).  This reduction of cox-2 expression associated with the colonic fermentation of polydextrose further suggests a protective role of polydextrose against colon cancer.  This study is a good example of the emerging science of nutrigenomics – the impact of nutrition on gene expression.

Efforts are ongoing to further elucidate the role of polydextrose in gut health.