The fermentability and pattern of short-chain fatty acids (SCFA) formed in the hindgut of rats given various combinations of dietary fibers (DF) and resistant starch (RS) were investigated. Highly fermentable indigestible carbohydrates, i.e., guar gum (GG), pectin (Pec) and high amylose cornstarch (HAS), and a DF with a relatively high resistance to fermentation, i.e., wheat bran (WB), were included. The substrates were studied individually or as mixtures (GG + Pec, GG + WB and HAS + WB, 1:1, wt/wt indigestible carbohydrate basis) at a total concentration of 100 g indigestible carbohydrates/kg diet and fed to rats for 13 d. Rats fed Pec had a high proportion of acetic acid in the cecum (76 +/- 2% of total SCFA), whereas those fed GG had the highest proportion of propionic acid (31 +/- 4%, P <0.0005). Rats fed GG and Pec had low proportions of butyric acid (6 +/- 1 and 10 +/- 1%, respectively), whereas those fed both had a higher proportion of butyric acid (15 +/- 3%, P < 0.05). Consequently, the cecal butyric acid pool was twice as high in rats fed the GG + Pec mixture (44 +/- 9 micro mol) as in those fed the individual components (19 +/- 2 and 21 +/- 3 micro mol, respectively, P < 0.05). Rats fed HAS with WB had a greater fecal excretion of SCFA (184 +/- 19 micro mol/d) than those fed the individual components (77 +/- 10 and 116 +/- 12 micro mol/d in rats fed HAS and WB, respectively P < 0.05), suggesting that incorporation of WB delayed the site of fermentation of HAS to the distal part of the hindgut. In conclusion, the combination of indigestible carbohydrates may affect both SCFA patterns and the site of SCFA release in the rat hindgut.

Short chain fatty acids (SCFAs; acetic, propionic and butyric acid) are formed during bacterial fermentation of carbohydrates in the colon. The interest in SCFA production is related to an increasing body of knowledge of the physiological effects of these acids. SCFAs are important anions in the colonic lumen and serve locally as nutrients for the mucosa cells, stimulating mucosal proliferation and blood flow. Especially butyric acid has been cmphazised. It is the main energy substrate for the colonocytes and has been suggested to play a role in the prevention and treatment of diseases of the colonic mucosa, such as distal ulcerative colitis and cancer. SCFA production decreases the luminal pH, and may thereby stimulate mineral absorption and reduce secondary bile acid formation in the colon. Colonic generation of SCFAs has also been related to systematic and metabolic effects, e.g. SCFAs may influence the motility along the gastrointestinal tract and propionic acid has been suggested to inhibit the cholesterol synthesis from acetic acid in the liver. The SCFAformed at fermentation is quantitatively and qualitatively influenced by the type and amount of carbohydrate substrate. Further, certain combinations of carbohydrates may have synergistic effects on the SCFA pattern and may also shift the site of fermentation. This opens possibilities to design foods with tailored features regarding SCFA release in the human colon with potential health implications. There is apotential that in the future it will be possible to control SCFAproduction in the colon regarding pattern and place for release.

Red kidney beans (Phaseolus vulgaris ) processed to differ in distribution and content of indigestible carbohydrates were used to study hindgut fermentability and production of shortchain fatty acids (SCFA). Bean flours with low or high content of resistant starch (RS), mainly raw and physically-inaccessible starch, were obtained by milling the beans before or after boiling. Flours containing retrograded starch and with a high or low content of oligosaccharides were prepared by autoclaving followed by freeze-drying with or without the boiling water. Six diets were prepared from these flours yielding a total concentration of indigestible carbohydrates of 90 or 120 g/kg (dry weight basis). The total fermentability of the indigestible carbohydrates was high with all diets (80-87 %). Raw and physically-inaccessible starch was more readily fermented than retrograded starch (97 -99 % v. 86 -95 %; P , 0 : 05). Non-starch glucans were fermented to a lesser extent than RS, but the fermentability was higher ðP , 0 : 05Þ in the case of autoclaved (50 -54 %) than boiled beans (37 -41 %). The distribution between acetic, propionic and butyric acid in the caecum was similar for all diets, with a comparatively high percentage of butyric acid (approximately 18). However, with diets containing the high amounts of RS, the butyric acid concentration was significantly higher in the distal colon than in the proximal colon (P ¼ 0 : 009 and P ¼ 0 : 047 for the high-and low-level diets respectively), whereas it remained constant, or decreased along the colon in the case of the other diets. Furthermore, the two diets richest in RS also promoted the highest percentages of butyric acid in the distal colon (24 and 17 v. 12 and 12 -16 for the high-and low-level diets respectively).Short-chain fatty acids: Red kidney beans: Indigestible carbohydrates Short-chain fatty acids (SCFA; acetic, propionic and butyric acid) formed during bacterial fermentation of carbohydrates in the colon, have been suggested to have specific physiological effects. Thus, butyric acid, the main energy substrate for the colonocytes (Roediger, 1982), may play a role in the prevention and treatment of various colonic diseases (McIntyre et al. 1993;. In colonic tumour cell lines, butyrate has been shown to inhibit growth (Whitehead et al. 1986), differentiation (Siavoshian et al. 2000) and to induce apoptosis . Further, patients with distal ulcerative colitis given rectal infusions with SCFA mixtures (Breuer et al. 1991;Vernia et al. 1995) or butyrate alone (Scheppach et al. 1992) improved, regarding symptoms and/or, histological and endoscopic scores. However, lower concentrations of SCFA or butyrate enemas had no effect on diversion colitis (Guillemot et al. 1991) or distal ulcerative colitis (Steinhart et al. 1996). Propionic acid is discussed as beneficial in relation to lipid metabolism (Venter et al. 1990;Wright et al. 1990;Todesco et al. 1991). It has thus been proposed that propionate may lower plasma cholesterol concentrations by inhibiting hepatic cholesteroge...

The effect of adaptation time on the concentration and pattern of short-chain fatty acids (SCFA) formed in the hindgut of rats given resistant starch (RS) in the form of raw potato starch (RPS) or high-amylose maize starch (HAS) was evaluated. Each starchy material was tested in diets containing 100 g indigestible carbohydrates/kg DM, and fed for 13, 28 and 42 d. At the end of each period, the content of SCFA was determined in caecum, distal colon and faeces. The caecal concentration of total and individual SCFA increased for both diets with increasing adaptation time. The concentration of butyric acid was higher in the group fed RPS than in that fed HAS at all adaptation times. The caecal proportion of butyric acid was low both in rats fed RPS and HAS (6 and 4 %, respectively) following 13 d of adaptation. However, after 28 d of adaptation, the proportion of butyric acid had increased to 19 % in rats given RPS. A longer adaptation period (42 d) did not increase the proportion of butyric acid further. With HAS, there was also a significant (P,0·01) increase in the proportion of butyric acid with longer adaptation time. However, the increase was much slower and the proportion of butyric acid reached 6 and 8 % after 28 and 42 d respectively. It is concluded that the pattern of SCFA formed from RS in rats is dependent on adaptation time. It cannot be excluded that the different patterns of SCFA reported in the literature for RS may be due to the time of adaptation.

The fermentability of indigestible carbohydrates and content of short-chain fatty acids along the hindgut of rats were investigated using plant materials of importance in the Swedish diet (instant potato powder, apples and oat¯akes). Results with the composite food products were compared with commercial ®bre fractions obtained from similar sources, ie potato ®bre, apple pectin and b-glucanenriched oat ®bre. The materials were incorporated into diets yielding a concentration of 60 or 70 g kg À1 indigestible carbohydrates. The fermentability of indigestible carbohydrates was high with all diets, between 79 and 90%. All substrates except the pure apple pectin generated intermediate to high proportions of butyric acid in the caecum (15±22 vs 8%). The potato products gave high concentrations of butyric acid in the distal colon. The potato powder, ie the diet with the highest content of resistant starch (22 g kg À1 ), also gave the highest proportion of butyric acid in the distal colon (19%), which was higher than the proportion in the caecum with the same substrate (15%) (P < 0.005). The composite foods promoted a higher proportion of butyric acid in the distal colon as compared with the commercial ®bre fractions (P < 0.05).