Comparative Evaluation of Drying Methods on the Rehydration Kinetics and Quality Attributes of Gnetum africanum Leaves
Amonyeze AO*, Aremu KO1, Ocholi SS and Agwu CH
ABSTRACT
This study investigated the effects of drying methods on the rehydration characteristics of okazi (Gnetum africanum) leaves. Fresh okazi (Gnetum africanum) leaves were purchased, sliced and dried using shade drying, food dehydrator drying, and freeze-drying methods. Fresh samples served as the control sample. Results from the proximate analysis showed that moisture, protein, fat, fiber, ash and carbohydrates contents ranged from 9.71- 32.68%, 14.98 – 19.92 %, 6.63 - 11.04 %, 31.24 - 35.15%, 5.38 - 6.93 %, 8.92 - 17.27 %, respectively. There were significant (p < 0.05) difference in moisture content across all drying methods, with freeze-drying producing the lowest moisture level and the highest concentrations of protein, fat, fiber, ash, and carbohydrate. Vitamin analysis revealed significant increases in betacarotene after drying, especially in freeze-dried samples, while vitamin C declined in all dried samples, with the greatest loss occurring
in the freeze-dried samples. Mineral contents such as calcium, magnesium, and potassium showed significant (p < 0.05) difference across all dried samples, with the freeze-dried samples yielding the highest concentrations. Phytochemical evaluation showed enhanced levels of flavonoids, phenols, and saponins after drying, with the freeze-dried samples producing the highest concentrations; however, tannin content increased only under shade drying. Rehydration studies demonstrated that dehydrator-dried and freeze-dried leaves absorbed water more, especially at higher temperatures of 70 - 80◦C. Rehydration progressively improved with increase in temperature and soaking time for all sample demonstrating temperature dependent hydration kinetics. Overall, the results showed that while all drying methods improves nutrient density, freeze-drying provides the most effective method for preserving nutrients and rehydration performance.
