Effects of different drying methods on the micronutrients of four leafy vegetables traditionally consumed by some Clans in Izzi and Unwana, Ebonyi State, Nigeria

This study was carried out to evaluate the effects of different drying methods (Freeze drying, shade drying and oven drying at varied temperatures of 40^oC, 50^oC and 60^oC) on the micronutrients (mineral and vitamin) contents of L. cupanioides, F. ottonifolia, P. osun and C. pentandra. The minerals contained in both dried and fresh leafy vegetable samples were analyzed by the dry ash extraction method, while vitamins (A, B₁, B_2, B₆ and E) contents of the leafy vegetable samples were determined spectrophotometrically. Vitamin C was determined titrimetrically after homogenizing each sample in 50ml 5.6M EDTA solution. The results from the study revealed that the various drying methods affected the leafy vegetable samples within and between them in the same pattern but to different degrees resulting to moisture lose with increase in minerals and increase in vitamin concentrations when compared with the fresh leafy vegetable samples. Freeze drying and shade drying had the best micronutrients retention effects across all the leafy vegetable samples while oven drying at varied temperatures of 40^oC, 50^oC and 60^oC had gradual decrease in minerals and vitamins retention effects as the temperature increases. The difference in mineral and vitamin concentrations retention with respect to drying methods decreased in this order: Freeze drying > shade drying > oven drying at 40^oC > oven drying at 50^oC > oven drying at 60^oC. The results of the various micronutrients for both fresh and dried leafy vegetable samples in this study ranged as thus: Calcium (72.59–398.10mg/100g), magnesium (41.16–461.07mg/100g), phosphorus (79.28–306.11mg/100g), iron (2.11–32.11mg/100g), zinc (0.19–18.88mg/100g), sodium (29.10–326.51mg/100g), potassium (0.8-196.31mg/100g), vitamin B₁ (0.31– 4.22mg/100g), vitamin B₂ (0.31 –1.49mg/100g),vitaminB₆ (0.36–3.91mg/100g), vitamin A (110.01–548.22ug/g), vitamin C (159.84–818.46mg/100g) and vitamin E (0.16– 9.91mg/100g). In conclusion, the freeze drying and shade drying are the best drying methods for producing dried traditional leafy vegetables with higher micronutrients retention than oven drying at varied temperatures (40^oC, 50^oC and 60^oC).