Basic nutritional investigationCecal parameters of rats fed diets containing grapefruit polyphenols and inulin as single supplements or in a combination
Introduction
Grapefruit is a rich source of polyphenols that can be consumed as fresh fruits and juice or as special byproducts derived from seeds and skin. An extract of grapefruit seed and skin, which provides health benefits similar to those of grapefruit beverages, would be an alternative way of adding grapefruit polyphenols to a diet. It is common knowledge that the metabolism and absorption of polyphenols in the gastrointestinal tract play an important role in local and systemic effects of these substances [1]. In the past decade, as a result of previous investigations, knowledge on the absorption, bioavailability, and metabolism of dietary polyphenols has been widely disseminated [2], [3], [4], [5]. Polyphenols are potential modulators of digestive fermentations because, in part, they escape absorption in the small intestine and reach the large intestine, where they or their metabolites affect cecal bacteria. Intestinal microbial flora and its consistency apparently play a central role in the metabolism of plant phenolics, the mechanism of which is largely unknown thus far [6]. Under common dietary conditions, polyphenols exist in a diet beside other compounds such as non-digestible carbohydrates, which can also alter the cecal ecosystem. Numerous reports have addressed the effects of polyphenols and low-digestible carbohydrates as single dietary supplements on the large bowel ecosystem [4], [7], [8], [9], [10], [11], [12], but information on their influence when applied in a dietary combination remains scarce [3], [13], [14]. In the large bowel, both compounds can serve as substrates for the complex indigenous microflora, which contain species and genera that can exert different effects on the host’s health.
In the present study, the following hypothesis was advanced: the presence in a diet of a prebiotic constituent, which affects bacterial fermentation, may influence the action of dietary polyphenols. Because the main site of bacterial fermentation in rats is the cecum, a flavonoid extract and fermentable inulin were added to diets as single supplements or in combination to investigate their effects on cecal physiology: bulk effect, pH, microbial enzyme activity, and short-chain fatty acid (SCFA) production.
Section snippets
Preparations
A lyophilized extract from the hard parts of grapefruit (stone, peel, white coats) containing 52.8% polyphenols (flavonoids), 25% silicon dioxide, 17.8% glycerol, and 4.4% ascorbic acid was used in the study. Characterization of flavonoid composition in the extract was performed with high-performance liquid chromatographic analysis using a Waters system equipped with a photodiode-array detector (Waters Corporation, Milford, MA, USA). The column was a reversed-phase Nova Pak C18 (30 cm × 3.9 mm
Diet intake, body weight, and cecal parameters
Compared with the control group, food intake and body weight of rats were insignificantly lower when a diet was separately supplemented with a flavonoid extract or inulin in addition to a dietary combination of 5% inulin with a grapefruit extract, and significantly lower when 10% inulin and a grapefruit preparation were used together as a dietary combination (Table 2). Feed efficiency ratio did not differ between the control and experimental groups. The addition to a diet of the investigated
Discussion
The present experiment showed that consumption of grapefruit flavonoids and inulin as single dietary supplements caused a tendency to decrease diet intake and final body weight of rats (Table 2). In similar experiments by other investigators, supplementation of diets with polyphenols and easily fermentable fiber did not affect feed intake but increased body weight gain of rats [4], [7], [13], [21]. In our experiment, the lowest diet intake and final body weight were observed in the case of the
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