Faster Fermentation of Cooked Carrot Cell Clusters Compared to Cell Wall Fragments in Vitro by Porcine Feces Li Day,* ,† Justine Gomez, † Sofia K. Øiseth, † Michael J. Gidley, ‡ and Barbara A. Williams ‡ † CSIRO Food and Nutritional Sciences, 671 Sneydes Road, Werribee, Victoria 3030, Australia ‡ ARC Centre of Excellence in Plant Cell Walls, Centre for Nutrition and Food Sciences, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia ABSTRACT: Plant cell walls are the major structural component of fruits and vegetables, which break down to cell wall particles during ingestion (oral mastication) or food processing. The major health-promoting effect of cell walls occurs when they reach the colon and are fermented by the gut microbiota. In this study, the fermentation kinetics of carrot cell wall particle dispersions with different particle size and microstructure were investigated in vitro using porcine feces. The cumulative gas production and short-chain fatty acids (SCFAs) produced were measured at time intervals up to 48 h. The results show that larger cell clusters with an average particle size (d 0.5 ) of 298 and 137 μm were more rapidly fermented and produced more SCFAs and gas than smaller single cells (75 μm) or cell fragments (50 μm), particularly between 8 and 20 h. Confocal microscopy suggests that the junctions between cells provides an environment that promotes bacterial growth, outweighing the greater specific surface area of smaller particles as a driver for more rapid fermentation. The study demonstrates that it may be possible, by controlling the size of cell wall particles, to design plant-based foods for fiber delivery and promotion of colon fermentation to maximize the potential for human health. KEYWORDS: Plant cell wall, particle size, cumulative gas production, short-chain fatty acids (SCFAs) ■ INTRODUCTION It is well-accepted that regular consumption of fruits and vegetables can provide positive health benefits to consumers, such as reducing the risk of cardiovascular diseases, colorectal cancer, type 2 diabetes, and obesity. 1-4 This impact is derived from a combination of the physical and physiological func- tionality of cell wall materials and a range of health beneficial micronutrients, including vitamins, minerals, polyphenols, carotenoids, etc. Plant cell walls are the major structural com- ponent of fruits and vegetables, consisting primarily of cellulose, hemicellulose, and pectin, which form a scaffold matrix with an intertwined connected structure. Plant tissue foods are broken down to small particles during food processing and/or after oral mastication. Because there are no mammalian enzymes within the stomach or small intestine that are capable of hydrolyzing the main components of plant cell walls, they pass along the gastrointestinal tract without being digested, absorbed, or metabolized, until they reach the terminal ileum and colon, where they may be used as fermentation substrates by the gut microbial community. 5,6 The continued emphasis on the importance of fruit and vegetable intake in the Western diet, in conjunction with consumer demand for natural ingredients in manufactured food products, has led to a significant increase in the use of plant cellular materials as functional food ingredients, in particular from the byproduct of industrial fruit and vegetable pro- cessing. 7,8 Our recent work has shown that the size and morphology of cell wall particles are important in determining their rheological properties, 9,10 their interaction with other food ingredients, 11 their ability to structure foods, 12 and the bioavailability of carotenoids. 13 The ability of plant cell and cell wall structures to hold water and provide high viscosity at a relatively low particle concentration can provide positive physiological benefits, such as slowing the gastric emptying rate and reducing the gastrointestinal transit time, as shown for individual polysaccharides. 14,15 Some cell walls or constituent polysaccharides may also bind bile acids and impede micelle formation, thus increasing fecal excretion of bile acids and cholesterol or influencing the absorption of nutrients. 16 How- ever, the major health-promoting effect of cell walls occurs when they reach the colon and are fermented by the gut microbiota. Dietary polysaccharides that reach the human large intestine have a major impact on gut microbial ecology and health. 17 This is partly due to their ability to increase the activity and growth of some health-promoting bacteria (prebiotic effect) by providing an energy source (selective substrate), which can thus alter the gut bacterial community composition. 3,18,19 Fermen- tation in the large intestine also leads to the production of short-chain fatty acids (SCFAs), gas (hydrogen, carbon dioxide, and methane), and other metabolites (ammonia, phenols, etc.). The primary SCFAs generated by fermentation are acetate, propionate, and butyrate, accounting for 83-95% of the total SCFA concentration in the large intestine. 20 Butyrate is absor- bed by the colonic mucosa, used as its major energy source, and plays a key role in the health of the colon. 21,22 It affects both the stimulation of cell division and the regulation of apoptosis and has been shown to increase apoptosis in human colonic tumor cell lines. 23,24 The SCFAs absorbed into the portal blood Received: December 4, 2011 Revised: February 27, 2012 Accepted: March 5, 2012 Published: March 5, 2012 Article pubs.acs.org/JAFC © 2012 American Chemical Society 3282 dx.doi.org/10.1021/jf204974s | J. Agric. Food Chem. 2012, 60, 3282-3290