Effect of air velocity, temperature, and relative humidity on drying kinetics of rubberwood

Spondias purpurea L. (Anacardiaceae) fruits flours at different maturation stages: Drying kinetics, mathematical modelling, characterization and correlation analysis

The aim of this study was to examine the drying kinetics of Spondias purpurea L. fruits at various maturation stages (I to V) using a range of mathematical models (Henderson and Pabis, Lewis, Logarithmic, Midilli, and Page). Additionally, an assessment of the resulting flours' quality was conducted. The stabilization phase of S. purpurea fruit drying kinetics commenced at 420 min for maturation stages I and III, and at 480 min for the remaining stages. All employed mathematical models effectively characterized the drying process, exhibiting R 2 values exceeding 0.99, MSD below 0.03, and X 2 below 0.0009. Flours demonstrated increased color intensity with higher levels of flavonoids and anthocyanins, showing a positive correlation. Immature fruits yielded flours with elevated titratable acidity, total chlorophylls, phenolic compounds, and density. In contrast, fruits in the final maturation stages produced flours with higher yield, levels of reducing sugars, total carotenoids, flavonoids, and anthocyanins. The results indicate that flours derived from ripe fruits exhibited higher yield, moisture content, pH, soluble solids, and reducing sugars, while titratable acidity was higher in green fruits. Bioactive compounds such as total chlorophyll, ascorbic acid, and phenolic compounds decreased with ripening, whereas total carotenoids increased due to chlorophyll degradation and carotenoid biosynthesis. Anthocyanin and total flavonoid levels increased in the final stages of ripening. Thus, the developmental stage directly influences the physicochemical and functional characteristics of S. purpurea fruit flours. This comprehensive analysis offers valuable insights into the drying kinetics of S. purpurea fruits and underscores the influence of maturation stages on the quality attributes of the resultant flours.

Integrated drying model of lychee as a function of temperature and relative humidity

Drying is a universal method applied for food preservation. To date, several models have been developed to evaluate drying kinetics. In this study, lychee was dried employing a hot air dryer, and the drying kinetics was evaluated by comparing the Newtonian model, Henderson and Pabis model, Page model, and Logarithmic model. However, temperature and relative humidity, the key driving forces for drying kinetics, are not considered by these models. Thus, an integrated drying model, as a function of temperature and relative humidity, was developed to predict the hot air-drying kinetics and mass transfer phenomena of lychee followed by the calibration and validation of the model with independent experimental datasets. The model validation consisted of Nash- Sutcliffe model coefficient (E ), coefficient of determination ( R 2 ) and index of agreement ( d ) and all of them were found close to 1 indicating perfect model fit. Besides, the developed model was applied for process optimization and scenario analysis. The drying rate constant was found as a function of temperature and relative humidity that was high at high temperature and low relative humidity. Interestingly, temperature showed a higher effect on the drying rate constant compared to relative humidity. Overall, the present study will open a new window to developing further drying model of lychee to optimize quality its quality parameters.