Evaluation of some phytochemicals in raw and cooked Ipomea batatas (Lam), (Sweet potato), Solanum tuberosum (Irish potato) and Dioscorea cayenensis (Yellow yam)

Abstract

Cooking induces numerous phytochemical changes in food. This study is aimed at determining the amount of phytochemicals present in raw and cooked sweet potato, Irish potato and yellow yam. The amount of tannin, alkaloids, saponin, flavonoids and phenol were determined in raw and cooked samples of each food crop. The result showed that tannin, alkaloids, saponin, flavonoids, phenol contents was high in Irish potato and sweet potato but was far much present in Irish potato, while it was seen in minute quantity in yellow yam. The values obtained for each phytochemicals in each food sample raw and cooked respectively, in mg/100g were; Yellow yam: Tannins (0.10 and Nil), Alkaloids (2.00 and 0.51), Flavonoids (1.18 and 0.87), Saponins (2.00 and 1.02) and Phenols (0.72 and 0.10). Sweet potato: Tannins (0.32 and 0.28), Alkaloids (2.17 and 0.62), Saponins (2.10 and1.58), Flavonoids (1.28 and 0.97) and Phenols (1.42 and 0.72). Irish potato: Tannins (0.55 and 0.49), Alkaloids (2.17 and 0.81), Saponins (4.00 and 2.13), Flavonoids (5.00 and 2.91) and Phenols (2.00 and 0.91). The % loss of phytochemicals after cooking were; Yellow yam: Tannins (Nil), Alkaloids (74.5), Saponins (49.0), Flavonoids (26.3) and Phenols (86.1). Sweet potato: Tannins (12.5), Alkaloids (71.4), Saponins (24.8), Flavonoids (24.2) and Phenols (49.3). Irish potato: Tannins (10.0), Alkaloids (62.7), Saponins (46.8), Flavonoids (41.8) and Phenols (54.5). These results indicate that boiling of the samples seems to reduce their phytochemical contents as the raw samples showed higher amounts of the phytochemicals. The results also revealed that Tannins are more stable to heat across the 3 food samples, followed by Flavonoids, Saponins, Phenols and Alkaloids. The loss in some of the phytochemicals after cooking did not significantly affect the nutritional quality of the food samples.