Abstract:
This study was conducted to determine the effects of different traditional cooking methods on the nature of starch in some Nigerian starchy staples. The staples used were yam (Dioscorea spp), cocoyam (Colocasia esculenta spp), cassava (Manihot esculenta crantz),and plantain (Musa paradisiaca spp). Yam and plantain were cooked into boiled and roasted forms. Cocoyam was prepared as cocoyam chips, while cassava was used to produce cassava dough, tapioca, and cassava foo foo and gari paste. The proximate composition, total starch and resistant starch were done using the approved methods. However, soluble starch was obtained by difference. Determination of carbohydrate digestion was achieved using Spectophometric procedure. The moisture content ranged from 21.04 % in roasted white yam to 41.00%% in gari paste. The protein content of the staples was low; ranged from 0.55g/100g in cassava foo foo to 2.25g/100g in cassava dough. The fat, ash, and crude fibre contents were also low. The boiled hybrid plantain ranked highest (3.01g) in fat, while roasted local plantain had highest ash (4.20g) and crude fibre (3.30g) values. Roasted white yam (Dioscorea spp) had highest carbohydrate 73.25g. Loss of moisture caused increases in nutrient density. Processing caused significant differences (P<0.05) in different forms of some the foods .For example the protein content of roasted white yam was 4.29g/100g and this was significantly different (P<0.05) from both the raw (2.33g/100g) and the boiled (2.72g/100g) samples, respectively). However, in cocoyam (Colocasia esculenta) varieties (esculenta var. esculenta,esculenta var. antiquorum (small corm) and esculenta var. antiquorum (large corm)), processing caused no significant difference (P>0.05) in all the proximate parameters except for esculenta var. antiquorum (large corm) where the crude fibre content of cocoyam chips (3.08g) was significantly different (P<0.05) from raw (0.6g).Total starch content of the carbohydrates ranged from 20.36g/00g in raw local plantain to 50.95/100g in boiled water yam. The resistant starch content of the carbohydrates ranged from 9.25g/100g in cassava dough to 32.15g/100g in boiled water yam. The resistant starch content of carbohydrates was affected by heat. Processing increased the resistant starch, solubility and digestibility of the carbohydrates. For example, the local plantain had resistant starch of 20.65g/100g and 23.05g/100g for boiled and roasted samples as against the raw 10.35g/100g. The roasted water yam had more resistant starch than the roasted white yam (22.85g vs 20.15g). The solubility of raw cassava was 14.82g and the processed samples had 33.30g/100g, 34.00g/100g, and 19.50g/100g for cassava dough tapioca, cassava foo foo, and gari paste, respectively. Digestibility of the carbohydrate foods increased from 27.17% in raw white yam to 71.92% in boiled white yam. Digestibility correlates positively and closely with the total starch content of the foods (r=0.9545; p<0.05), while the resistant starch content of the carbohydrates correlates positively but poorly with digestibility (r=0.6184; p=0.0017). The result of multiple regression analysis showed that moisture, protein, fat, ash and total carbohydrate as well as total and resistant starch of the foods influenced digestibility. Thus digestibility of a food depends on the interplay of many factors However, in conditions that require less energy dense foods (diabetes and obesity) emphasis should be on the processing method with highest amount of resistant starch.
