The effects of strawberry, black currant, and chokeberry extracts in a grain dietary fiber matrix on intestinal fermentation in rats

The objective of this work was to study the composition, hydration properties and oil holding capacity, antioxidant properties and the physiological effects on the digestive system of dietary preparations containing wheat or oat fiber enriched with polyphenol extracts from strawberry, chokeberry, and black currant pomace. By the addition of black currant, strawberry and chokeberry polyphenol extracts to grain fibers preparations with corresponding polyphenol content of 0.7%–0.8%, 1.1%–1.2%, and 2.5%–2.9% were obtained. The preparations were used as part (8%) of a modified AIN-93 diet given to growing Wistar rats (8 animals per group) over a period of 4weeks. The highest antioxidant potential had grain–chokeberry preparations with the greatest polyphenol content, while grain–black currant preparations exhibited the lowest antioxidant potential with the smallest polyphenol content. The addition of strawberry and chokeberry extracts caused a decrease in the activity of bacterial β-glucosidase and α-galactosidase, while black currant extract led to increased activity of β-galactosidase and β-glucuronidase. The production of short chain fatty acids (SCFAs) in the caecum of rats fed the grain–strawberry preparation, rich in ellagitannins, was considerably higher than the grain–black currant preparation, rich in proanthocyanidins and anthocyans, or the grain–chokeberry preparation with the highest polyphenol content (78.3 vs. 64.7 vs. 56.3μmol/100g body weight, p=0.012). In comparison to preparations without polyphenols only chokeberry extract significantly decreased SCFA concentration. The grain–strawberry preparations were characterized by a higher antioxidant potential per unit of polyphenol content and exhibited a more beneficial influence on the fermentation processes in the caecum of rats than the grain–black currant and grain–chokeberry preparations.