Abstract
Background: Our study was part of the large European project ISAFRUIT aiming to reveal the biological
explanations for the epidemiologically well-established health effects of fruits. The objective was to identify effects
of apple and apple product consumption on the composition of the cecal microbial community in rats, as well as
on a number of cecal parameters, which may be influenced by a changed microbiota.
Results: Principal Component Analysis (PCA) of cecal microbiota profiles obtained by PCR-DGGE targeting bacterial
16S rRNA genes showed an effect of whole apples in a long-term feeding study (14 weeks), while no effects of
apple juice, purée or pomace on microbial composition in cecum were observed. Administration of either 0.33 or
3.3% apple pectin in the diet resulted in considerable changes in the DGGE profiles.
A 2-fold increase in the activity of beta-glucuronidase was observed in animals fed with pectin (7% in the diet) for
four weeks, as compared to control animals (P < 0.01). Additionally, the level of butyrate measured in these pectinfed
animal was more than double of the corresponding level in control animals (P < 0.01). Sequencing revealed
that DGGE bands, which were suppressed in pectin-fed rats, represented Gram-negative anaerobic rods belonging
to the phylum Bacteroidetes, whereas bands that became more prominent represented mainly Gram-positive anaerobic
rods belonging to the phylum Firmicutes, and specific species belonging to the Clostridium Cluster XIVa.
Quantitative real-time PCR confirmed a lower amount of given Bacteroidetes species in the pectin-fed rats as well
as in the apple-fed rats in the four-week study (P < 0.05). Additionally, a more than four-fold increase in the
amount of Clostridium coccoides (belonging to Cluster XIVa), as well as of genes encoding butyryl-coenzyme A CoA
transferase, which is involved in butyrate production, was detected by quantitative PCR in fecal samples from the
pectin-fed animals.
Conclusions: Our findings show that consumption of apple pectin (7% in the diet) increases the population of
butyrate- and b-glucuronidase producing Clostridiales, and decreases the population of specific species within the
Bacteroidetes group in the rat gut. Similar changes were not caused by consumption of whole apples, apple juice,
purée or pomace.