EFFECTS OF WHITE YAM PROCESSING METHODS ON GLYCEMIC PROFILE IN TYPE-2 DIABETIC NIGERIANS AND BIOCHEMICAL VARIABLES

Abstract

Food processing methods demonstrated using apparently healthy subjects have been reported to affect Glycemic Index (GI) and Glycemic Responses (GR) in different ways with either favourable or adverse effects. However, there are limited data on the effects of food processing methods on GR and GI in diabetics. This study was carried out to determine the effects of boiling, frying, pounding, roasting and flouring (parboiling, sun-drying and grinding) processes on the Proximate of white yam (Dioscorearotundata), GI and GR in male type-2 diabetic Nigerians. The effects of low- and high-GI diets on organ weights, pancreas histoarchitecture, Glycemic Tolerance (GT) and Lipid Profile (LP) in alloxan-induced male diabetic rats (DR) were also investigated. Proximate of white yam-based meals (raw and processed) and 50g digestible carbohydrates of served portions were determined using Platt and Southgate’s standard methods of food analysis while the lipid profile of the experimental rats was analysed using a dry-chemical auto-analyser. The GI was determined in 10type-2 diabetic and 10apparently healthy subjects (control)who consumed served portions of each processed meals containing 50g digestible carbohydrates. Postprandial capillary blood glucose concentrations taken half hourly for two hours using glucometer were used to construct the mean incremental GR curve from which the GI was calculated. The product of each processing method was classified into high or low GI diet based on international GI classification of foods. Effects of low-GI (fried yam) and high-GI (roasted yam) diets on organ weights, pancreas histology, GT and LP were respectively determined and compared in the six grouped(n = 8) adultexperimental alloxan-induced (150mg/kg BW intraperitoneal) diabeticand control rats fed with test and standard diets for six weeks. Data were analysed using ANOVA and Student’s t test at p  0.05. Fiber, protein and calorie contents of the processed meals were significantly increased compared with the unprocessed raw yam, while the ash and moisture contents of the processed vii meals were affected by the degree and extent of exposure to heat of processing. Roasting of yam gave the highest GI (93.34±4.04%) frying gave the lowest GI (36.16±2.71%). Postprandial GR to low-GI diet showed significant improved glycemic tolerance over that of High-GI diet (3082.5mg/dl.minvs 8332.0mg/dl.min). An increase in body weight of rats was observed in all groups after six weeks of feeding with highest increase (24.8%) observed in DR on high-GI diet (251.00±1.61g vs 312.33±5.85g) and the lowest increase (9.2%) in DR on Low-GI diet (250.67±1.12g vs 273.17±1.72g). No significant change was observed in organ weights. Pancreas histology of diabetic rats on high-GI diet displayed degeneration with degranulation and vacuolation of the islet β cells while regeneration of some β cells was observed in rats fed with low-GI diet. Triacylglycerides (52.2±1.0mg/dL) and cholesterol (60.5±1.5mg/dL) increased in DR fed with fried yam compared to those fed with roasted yam. White yam processing methods increased glycemic index with quick glycemic response and decreased glycemic index with delayed glycemic response. Although the fried yam with low glycemic index improved glycemic profile, its recommendation for dietary control of diabetes mellitus may be considered with caution due to its associated dyslipidaemia – a known cardiovascular risk factor.