Changes in β-carotene Content of Thermally Processed Sweet Potato (Ipomoea batatas) Cultivar

Abstract

This research was conducted to evaluate the changes in β-carotene (the major pro-vitamin A) associated with processing of sweet potatoes, Total β-carotene of a sweet potato cultivar (Ex-Igbariam) was quantified using High Performance Liquid Chromatography (HPLC). The level of retention (%R) of β-carotene was calculated. The all-trans and cis isomers of β-carotene were also quantified. Processing methods used were boiling, roasting, deep fat-frying and oven drying. β-carotene retention after oven drying and roasting was highly significant (P<o.o5) when compared to boiling and deep fat-frying. The total β-carotene concentration for the oven dried (29.25 µg/g) and roasted samples (23.53 µg/g) were about twice the concentration of the unprocessed (13.08 µg/g). Processing by boiling showed low β-carotene retention (38%) when compared with the unprocessed (100%). It also showed higher levels of the cis isomers of β-carotene which has less vitamin A activity. The all-trans geometrical isomer of β-carotene was greater than the cis geometrical isomer fractions in both the oven dried and roasted samples. The overall results show that oven drying and roasting improved the retention of pro-vitamin A activity in this sweet potato cultivar and that the all-trans configuration which is associated with higher nutrient value is still largely retained even after using these processing methods. There is the need to develop an appropriate method of identifying the isomers formed after processing by frying since the method applied in this research could not separate different isomers of fried samples.