Abstract
The objective of this study was to provide the optimum drying conditions to produce high-quality dried tiger nuts using hot-air drying. For this, we evaluated the effect of the whole, halved, and pulverized tiger nuts and air temperature (50 to 70°C) on the drying kinetics and quality of tiger nuts. The drying process generally followed a constant rate in the first 3 hours and a falling regime. We found the optimum drying conditions for tiger nuts to be crushed before convective hot-air drying at a temperature of 70°C. At this optimum condition, the predicted drying time, vitamin C content, reducing sugars, browning, brightness, redness, and yellowness was 780 min, 22.9 mg/100 mg dry weight, 157.01 mg/100 g dry weight, 0.21 Abs unit, 56.97, 1.6, and 17.0, respectively. The tiger nut's reducing sugars increased from the 130.8 mg/100 dry weight in the raw tiger nuts to between 133.11 and 158.18 mg/100 dry weight after drying. The vitamin C degradation rate was highest in the uncut tiger nuts (32-35%) while in the halved and the pulverized samples, it was between 12 and 17%. The crushed samples' effective moisture removal increased between 5.6- and 6.75-fold at the different air temperatures than that of the intact tiger nuts. The activation energy was 18.17 kJ/mol for the unbroken, 14.78 kJ/mol for the halved, and 26.61 kJ/mol for the pulverized tiger nut samples. The model MR = 0.997 exp(−0.02t1.266) + 0.0000056t was the most suitable thin-layer drying model among the models examined for convective hot-air drying of tiger nuts. It is advisable to crush tiger nut before hot-air drying to produce better-quality flour for making milk beverages, cakes, biscuits, bread, porridge, and tiger nut-based breakfast cereals.
Highlights
Tiger nuts (Cyperus esculentus) are a tuber crop belonging to the family Cyperaceae, which is cultivated worldwide [1] The black, brown, and yellowish-brown tubers are the cultivars commonly produced in many parts of the world including Ghana
The effective moisture removal rate was highest for the pulverized samples, followed by the split and the intact tiger nut tubers
The drying rate potential was significantly affected by the state of the tiger nut and the air temperature for all the drying models tested
Summary
Tiger nuts (Cyperus esculentus) are a tuber crop belonging to the family Cyperaceae, which is cultivated worldwide [1] The black, brown, and yellowish-brown tubers are the cultivars commonly produced in many parts of the world including Ghana. It is in the same family as the sedges and usually called earth almond, yellow nut sedge, and rush nut in many parts of the world [2]. The phytosterols that distinguish tiger nuts from olive are much richer in tiger nuts [7]. In Ghana, tiger nut tubers are typically consumed fresh or as tiger nut milk, which substantially affects its storage
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