Characterization of oxidative browning in flue-cured tobacco I. A method for evaluating varietal discoloration potentials
A method was developed and tested for characterizing oxidative browning in tobacco during curing, utilizing standardized procedures. Nearly identical cultural practices and curing conditions were imposed on three varieties of Nicotiana tabacum L. (Golden Wilt, Yellow Special A and Coker 139) to permit evaluation of color change phenomena as a variable of variety and leaf position. Oxidative browning was studied in vivo by thermally initiating the reaction at 80-85C and allowing it to proceed at high leaf moisture content at 25C. Tristimulus colorimetry was used to establish initial yellow color (Yi), final brown color (Ye), color change (Δ Y) and browning rate constant (k). Both Yi and Ye varied among varieties and decreased for higher leaf positions. The browning rate constant (k) varied among varieties and increased by about 100% between bottom and top leaf positions. Polyphenol concentrations decreased by 85% during oxidative browning, implying a means for rapid and extensive reduction of this class of constituents, if desired. This method appears useful in quantifying effects due to varieties, cultural practices, environmental factors, and process conditions.