Effect of Processing Methods on Nutrient Contents of Six Sweet Potato Varieties Grown in Lake Zone of Tanzania

Abstract

A study was carried out to evaluate the effect of processing methods on nutrient contents of six fresh sweet potato varieties namely Carrot Dar, Japon, Zapallo, Mafuta, Polita and Sekondari commonly grown in three
districts (Meatu, Sengerema and Missungwi) located along the lake zone of Tanzania. Fresh samples of sweet potato from these districts were harvested packed in cool box and immediately transported to the Department of Food Science and Technology at Sokoine University of Agriculture, Morogoro. Nutrient content of the samples was evaluated before and after processing, using three different methods namely boiling (moist heat), roasting (dry heat) and sun drying. The results showed that there were significant (p.0.05) differences between varieties in protein, fat, reducing sugars, carbohydrates, total carotenoids, calcium, iron and magnesium content. Total carbohydrate between varieties ranged from 23.91 to 41.46 g/100g, total carotenoids (49.321 to 994.02 mg/100g), crude protein (1.44 to 2.50 g/100g), ash (0.87 to 0. 98 g/100g), fat (0.03 to 0.95%) and reducing sugars (102.04 to 145.60 mg/100g). Processing of sweet potato varieties by boiling, roasting and sun drying did not have any significant effect on the carbohydrate, protein, fat, ash, calcium, iron, and magnesium contents. However, significant (p.0.05) effect was observed on
reducing sugars and total carotenoids, when processed by these methods. Losses of reducing sugars between varieties ranged from 27.04 to 46.49% and total carotenoids (42.88 to 64.94%). The results showed that there is a need to choose processing methods that cause minimum nutrient losses. Also, selection of sweet potato varieties with high nutrient content could compensate likely nutrient losses occurring during processing.

Key words: sweet potato varieties, nutrient content, processing methods