Predicting moisture and chemical changes during bulk curing of flue -cured tobacco

The objective of this research was to develop models to predict moisture content, chlorophyll, starch, and reducing sugar concentrations at any time during flue-curing of tobacco as a function of curing conditions, initial moisture, and initial chemical concentration. Chlorophyll degradation during the yellowing stage of a curing process is used as an important indicator of curing progress, while the degradation of starch is crucial to induce the accumulation of reducing sugar. Reducing sugar has a positive impact on tobacco quality, while high starch concentration is often associated with bitter taste.;The effects of yellowing temperature and yellowing relative humidity (wet-bulb depression) on chlorophyll, starch, reducing sugar, and total alkaloid concentrations were investigated. The chemical concentrations as well as moisture content in the leaves were measured periodically during the cure. The data were collected (for model development purposes) and statistically analyzed. Varying a yellowing temperature from 30°C to 40°C, did not have any significant effects on chlorophyll and starch, but it significantly affected reducing sugar concentration; the highest yellowing temperature resulted in the lowest reducing sugar. Yellowing relative humidity (wet-bulb depression), which was varied from 70% to 89% (5°C to 1.67°C wet-bulb depression) did not have any significant effects on chemical concentrations, but it significantly affected moisture content at the end of the yellowing stage.;Mathematical models to predict moisture content, chlorophyll, starch, and reducing sugar were developed as a function of curing conditions and initial chemical concentrations. The moisture removal model was based on a two-term (liquid and vapor diffusion) thin layer drying equation. The chlorophyll, starch, and respiration models were based on first order rate equations. The models called TCURE6 were regressed to the experimental data collected in the first year of the experiment to determine the value of the parameters. Then the models were verified using the experimental data collected in the second year of the experiment. In general, TCURE6 predicted moisture content, chlorophyll, starch, and reducing sugar fairly well, although the chlorophyll and starch model tended to predict higher chlorophyll and starch concentration than those of experimental data.;The model TCURE6 was utilized to investigate the behavior of the curing factors such as temperature, relative humidity (wet-bulb depression), airflow rate, and time in relation to moisture content and chemical concentrations. The results were used to improve a curing schedule as a function of initial moisture and chemical concentrations. Different green leaf conditions suggest the utilization of different curing schedule to optimize quality. TCURE6 has potential and provides a means for improving a curing schedule, which in turn will improve cured tobacco quality when initial moisture and chemical concentrations are readily available.