Role of resistant starch from different sources on in vitro production of short-chain fatty acids in a pig model

There is growing interest in incorporating nutrients that may act as potential prebiotic sources in pig diets, including resistant starch (RS). Pig colonic bacteria ferment RS to short-chain fatty acids (SCFA) that can exert several physiological effects related to energy supply and renewal of intestinal cells (Bach Knudsen et al., 2012). The aim of this work was to evaluate whether the fermentation of RS obtained from different starch sources may influence SCFA fermentation patterns and related kinetics, in an effort to modulate fermentation end products by the pig microbial community. An in vitro experiment based on enzymatic digestion followed by fermentation was conducted. Five native purified starches were tested (Table 1). Each ingredient was pre-treated with a pepsin-pancreatin hydrolysis (Boisen and Fernàndez, 1997). Then, 200 mg of each hydrolysed RS residue was incubated in triplicate in glass bottles in a buffered mineral solution inoculated with pig faeces (Giuberti et al., 2013). Two fermentation runs were set up in two different days and bottles within runs were considered repetitions, with bottles between runs as replicates. Aliquots were carefully removed by a 2-ml plastic syringe at 0, 4, 8, 24, 48 and 72 h for SCFA (total and individual) determination by gas chromatography. Total SCFA profiles were fitted to a monophasic model and the maximum rate of production (Rmax) and the time at which it occurs (Tmax) were calculated (Giuberti et al., 2013). Data were subjected to ANOVA using the mixed procedure (SAS®; USA) and the minimum significant difference (MSD) was generated from Tukey’s test and used for multiple comparisons among means. The significance level was P<0.05.The average SCFA productions, as well as the molar ratios (MR) of acetate, propionate and BCFA, were similar (P>0.05) between RS sources. On the contrary, the MR of butyrate was affected by the RS sources, showing that different types of RS may favour butyrate production. In particular, the highest MR of butyrate was produced by fermentation of RS from wheat and low amylose maize starches (on average 0.21; P<0.05), whereas RS from normal amylose maize yielded the lowest MR (0.15; P<0.05). Butyrate is the major fuel for colonocytes and can inhibit apoptosis of colon crypt cells in vivo (Bach Knudsen et al., 2012). Differences were recorded for Rmax and Tmax values (P<0.05). Combined with information on the transit time, fermentation kinetics may give an indication about the site of fermentation in the gastrointestinal tract (Giuberti et al., 2013). In conclusion, current data could facilitate the selection of ingredients to manipulate the fermentation in the intestine of pigs and to potentially enhance butyrate production.