Response of Nutritional and Phytochemical Constituents of Bitter Leaf to Some Drying Methods

Abstract

Aim: Food processing is one of the post-harvest factors that affect the quality of food products. This research was aimed at evaluating the impact of two drying methods (sun-drying and freeze-drying) on the nutritional and phytochemical contents of Vernonia amygdalina Del. Study Design: Processed vegetables of V. amygdalina were subjected to the selected drying methods and the composition of the dried samples was thereafter compared. Place and Duration of Study: The eight-month study was carried out at the Food Chemistry Research Laboratory, Chemistry Department, The Federal University of Technology, Akure, Ondo State, Nigeria. Methodology: Harvested fresh samples of V. amygdalina were first cleaned with distilled water prior to drying. The dried vegetable samples were then ground to powder and subjected to proximate analysis via the application of recommended methods of Association of Official Analytical Chemists. Other nutritional and phytochemical analyses were achieved using standard methods. Independent-samples t-test was used to compare the difference in composition. Results: The results showed that except for crude fibre content, there was a statistical significant difference (p < 0.05) in the proximate composition of the vegetable samples obtained from the two drying methods while the freeze-drying method favoured the concentration of most of the dietary minerals tested. The two drying methods were found to give a similar phytochemicals screening result with the sun-dried samples having a higher concentration of total phenols and total flavonoids. The freeze-dried samples, however, had higher vitamin A and C contents. Conclusion: The research outcome revealed the suitability of the freeze-drying method for enhanced/improved drying action on vegetables and to have the optimum level of crude protein, major dietary minerals, vitamin A and C in the dried vegetables. Further work is needed to assess the impact of the selected drying methods on antinutrients composition.