Optimization of Black Plum (Vitex doniana) Foam Mat Drying for Improved Micronutrient Retention

Abstract

Black plum (Vitex doniana) is a sweet, edible perennial shrub widely distributed in tropical West Africa. The fruit is green when matured and changes to dark brown when fully ripened. They are known as a good source of phytochemicals and micronutrients. Foam mat drying is a technique whereby foam is incorporated into food material by addition of an edible foaming agent before subjecting it to drying. Foam formation increases the surface area of product which in turn increases the overall heat and mass transfer, thus reducing the drying time, minimize loss of nutrients. Optimization of foam mat drying of black plum pulp to powder using response surface methodology for micronutrients determination was studied. The fruits were thoroughly washed with distilled water and sorted to remove bad ones. The edible portions of the plum were removed with a clean kitchen knife and the pulp collected was subjected to foaming process using glycerol monostearate (5 to 15%) as foaming agents, carboxymethyl cellulose (3 to 5%) as foam stabilizer and the foamed samples subjected to drying at temperature range of 50oC to 70oC till moisture content of less than 10% was achieved. The samples were analyzed for minerals and vitamins using standard analytical procedure. Vitamin A content recorded was in the range of 401.11 to 727.03 mcg RAE, vitamin C 10.56 to 14.06 mg/100g, vitamin E 4.58 to 6.14 mg/100g, vitamin B1 0.29 to 0.72 mg/100g, vitamin B2 0.27 to 0.92 mg/100g, vitamin B6 1.27 to 2.33 mg/100g, calcium 298.77 to 349.87 mg/100g, iron 6.27 to 8.37 mg/100g, potassium 1695. 18 to 2126.74 mg/100g, magnesium 216.78 to 244.32 mg/100g, phosphorus 2.25 to 3.84 mg/100g, sodium 10.16 to 15.32 mg/100g, and zinc 18.03 to 25.88 mg/100g. All the micronutrients investigated varied significantly (P≤0.05) and samples with higher concentration of foaming agent recorded the highest values. The study shows that foam mat drying minimize the rate of loss of micronutrients during drying of the fruit powder and increase the scientific database of black plum fruit to be used as organic antioxidant agents in the management of several chronic diseases.