HPLC Profiles of Onion Fructooligosaccharides and Inulin and their Prebiotic Effects on Modulating Key Markers of Colon Function, Calcium Metabolism and Bone Mass in Rat Model

The objective of this study was to purify and characterize the fructooligosaccharides (FOS) and inulin (INU) contents in local onion varieties. Vigorous extraction of the onion with hot water recovered over 93% of the initial non digestible carbohydrates (NDC). HPLC separation and quantitation showed that total FOS accounted for 20% and INU for 16% of the dry onion NDC extract. The prebiotic effect of onion NDC was tested by incorporating the freeze dried onion NDC at 13% in semisynthetic diet fed to Sprague Dawley rats for 5 weeks. Commercial FOS and INU were run in parallel and served as references. Key markers of colon function included measuring enlargement in colon weight as criteria of bifidogenic effect and colonization, activities of the caecal glycolytic enzymes, lowering in the activity of the glucuronidase and lowering of caecal pH value. The effect of dietary onion NDC on different aspects of calcium metabolism and bone mass was studied as well. The consumption of dietary onion NDC, FOS and INU for 5 weeks was associated with significant shifting in the fecal pH value towards the acidic direction, increase in the caecal weight due to colonization with beneficial bacteria and significant increases in the activities of caecal α- and β-glucosidases and α- and β- galactosidases compared with respective results obtained with the control group. The enzyme activity of the caecal glucuronidase was reduced compared with the respective control group. Parameters of calcium metabolism included % absorption, balance, retention, femur and tibia calcium contents were significantly improved compared to the respective control group. Conclusion: Adaptation to a diet containing prebiotic from onion led to positive physiological changes in the gut biomarkers of microbial activity This study provides direct evidence that onion (NDC) can act as an orally active agent for preserving bone mass in a growing rat model (aged 3-6 months),which has great implication on good health. Accurate quantitation of FOS and INU will allow the development of functional food formulations in human diets.