Effect Of Controlled Fermentation Of Some Traditional Foods On The Glycaemic Response Of Diabetic Adult Rats

Abstract

Effect of controlled fermentation with Candida tropicalis on glycaemic index of cassava, maize and sorghum flours and blood glucose response, protein utilization, mineral and vitamin bioavailability of their blends in diabetes induced adult rats was studied. Candida tropicalis was isolated and used in semi-solid state controlled fermentation of the starchy foods at 0, 24, 48 and 72h. Physicochemical composition of the fermented starchy flours and two under-exploited unfermented legume seed flours of Bielschmeidia gabonensis (BG) and Cola gigantean (CG) used as soup thickeners were determined. Standard techniques and statistical methods were adopted to generate data, separate and compare means of preliminary results. Three diets based on 24h fermented cassava (CA24h), maize (MA24h), sorghum (SO24h) and unfermented Cola gigeantea (CG) were used for the rat study. These test diets provided 1.6g nitrogen daily and 20g total dietary fibre/1000kcal in a ratio of 1:2, soluble: insoluble dietary fibre to mimic traditional diets. Rat chow (RC) served as the control. Sixteen adult rats (160-196g) were allotted to both control and 3 test diets in groups of 4 on the basis of body weight. The rats were individually housed in metabolism cages, induced diabetes with streptozotocin and fed ad libitum in a14-day balance study. Food intake, body weight, fasting blood glucose (FBG), plasma proteins, blood urea nitrogen (BUN), carcass nitrogen (CN), liver composition, protein, vitamin and mineral bioavailability were determined. All analyses were done using standard techniques to generate data. Completely randomized design was adopted for the bioassay. Students’ t-test, Duncan’s new multiple range test and Fisher’s least significant difference test were employed to separate and compare means statistically (p<0.05). CG had significantly (p<0.05) lower GI (68.30% versus 85.82), Ca and Fe and significantly (p<0.05) higher oxalate than BG (13.86g versus trace). The CA24h, MA24h, SO24h flours had the best chemical value for viscosity (4.21cps, 2.49cps and 3.01cps, respectively), TDF (6.24%, 6.36% and 5.69%, each); TS (67.17%, 56.35% and 56.96%, each) and GI (44.01%, 47.43% and 46.68%, respectively). These GI values were significantly (p<0.05) lower relative to their controls (93.06%, 94.76% and 84.66%, respectively). Calcium (Ca), zinc (Zn), magnesium (Mg) and riboflavin in fermented flours increased significantly (p<0.05) while Iron (Fe) significantly (p<0.05) decreased relative to the controls (0.64-0.73mg versus 0.0-0.40mg). Test diets had significantly (p<0.05) high oxalate relative to the safe level (3.75g versus 6.0g, 8.0g and 11.5g for CA24h CG, MA24hCG and SO24hCG, respectively). Test diets significantly (p<0.05) reduced blood glucose (BG) in all groups of rats (420-465mg/100ml to 82.0-83. 50mg/100ml). N balance was positive for all groups of rats. Rats fed MA24hCG diet had significantly (p<0.05) higher food intake and biochemical profile over those of both control and other test diets. Thiamin, riboflavin and niacin retentions were negative for all rats (-0.003 to -0.012mg; -0.40 to -0.88mg and -39.22 to -53.25mg, respectively). Calcium retention was positive for both test and control diets (101.89mg –188.80mg). Mg retention was positive for CA24hCG (4.12mg) and MA24hCG (5.48mg) test diets alone. Fe retention was negative for all the groups (-30.35 to -68.07mg). Zn content of the diet was negligible, as well as in the metabolic waste. Candida tropicalis fermentation reduced GI of the traditional high GI starchy staples from 84-94% to 45-47%. C. gigeantea had lower GI than B. gabonensis. The novel diets based on blends of these low GI starchy flours and Cola gigeantea (a leguminous soup thickener) (in 1:2 ratio of soluble to insoluble dietary fibre) produced high dietary fibre diets which attenuated the high blood glucose in diabetic adult rats but compromised their protein utilization as well as mineral and vitamin balance. Further investigations on diabetic rats fed varying ratios of these low GI fermented traditional starchy staples and Cola gigeantea are needed to clearly establish safer levels of the blends with regard to food intake, weight loss and glycaemic control.