Soaking behaviour and milky extraction performance of tiger nut (Cyperus esculentus) tubers

Three diameter sizes (D < 0.5 cm, 0.5 cm < D < 1 cm and D > 1 cm) of tiger nut (Cyperus esculentus) tubers growing in Cameroon (Central Africa) were soaked between 20 °C and 100 °C until water content equilibrium, and pressed for extraction of milky beverage (“horchata”). Application of Peleg model was investigated for predicting water absorption of tubers during soaking. The model showed to predict kinetics of the tiger nut soaking. The Peleg absorption rate constant (k1) decreased as temperature increased, indicating increase in absorption rate with temperature, with a discontinuity at 60 °C. The water absorption capacity (k2) was relatively stable, but displayed the same discontinuity at 60 °C. The extraction yield and the insoluble extract content of the milky beverage increased with temperature, while its soluble extract content decreased in the same conditions. These trends were attributed to the weakening of cell walls of the tubers at higher soaking temperature, generating high level of material transfer, as justified by the very low values of k1 at high soaking temperature.