TEMPERATURE-DEPENDENT HYDRATION KINETICS OF MUNG BEAN (VIGNA RADIATA L.) PRIOR TO SPROUTING: SIGMOIDAL, EMPIRICAL AND FICKIAN MODELLING

Abstract

Soaking is the first and often the slowest step in producing mung bean sprouts, yet there is little quantitative information on how soak-water temperature controls water uptake in this legume. Mung bean (Vigna radiata L.) grains with an initial moisture content of 9.17% d.b. were soaked at 25, 30, 35, 40 and 45 °C, and their moisture content was recorded every 0.5 h for 8 h in triplicate. Every hydration curve was distinctly sigmoidal: uptake was slow at first, accelerated to a peak rate and then levelled off at a terminal moisture content of 118.41–139.80% d.b. Raising the temperature from 25 to 45 °C increased the peak hydration rate from 38.47 to 55.62% d.b. h−1 and shortened the time needed to reach 95% of the total moisture gain from 6.31 to 2.75 h. Terminal moisture, however, did not increase steadily with temperature and was highest at 30 °C. Of five models tested, the Kaptso-type sigmoidal model described the data best (mean R2 = 0.9968; RMSE = 2.32% d.b.), closely followed by the Weibull model (R2 = 0.9961), whereas the Peleg, exponential and one-term Fick-type models, which assume a downward concave curve, performed markedly worse. The inflection time of the sigmoidal model fell from 2.88 to 1.19 h, showing that warmer water shortened the lag phase. Effective moisture diffusivity ranged from 3.59 × 10−11 to 8.20 × 10−11 m2 s−1, and the Arrhenius analysis gave an apparent activation energy of 27.84 kJ mol−1, a value consistent across four independent kinetic indicators (24.3–29.2 kJ mol−1). At 40–45 °C the grains reached a typical steeping target of about 82% d.b. (≈45% w.b.) within 1.6–2.5 h, compared with 3.8 h at 25 °C. These results offer a practical basis for choosing soaking time–temperature combinations for mung bean sprouting.