Visible and Ultraviolet Absorption and Fluorescence Excitation and Emission Characteristics of Florida Orange Juice and Orange Pulpwash: Detection of Adulteration

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Abstract
Visible and ultraviolet absorption and room temperature fluorescence excitation and emission spectra, obtained from alcoholic solutions of Florida orange juice and pulpwash, were investigated to characterize citrus products, and thereby detect adulteration and approximate orange juice content. Absorption shoulders and maxima were observed at 465, 443, and 425 nm of the visible spectrum and at 325, 280, and 245 nm of the ultraviolet spectrum. The spectral curves for orange juice and pulpwash were similar. However, orange pulpwash had weaker visible and stronger ultraviolet absorption than did orange juice. It was determined (416 frozen concentrated orange juice and 206 orange pulpwash samples obtained from Florida commercial processors) that the average sum and standard deviation of absorbance at 443, 325, and 280 nm was 2.410 ± 0.164 for orange juice and 3.781 ± 0.473 for orange pulpwash (based on reconstituted 12.8° Brix products). Average absorbance 443/325 nm ratio was 0.144 ± 0.026 for orange juice and 0.048 ± 0.020 for orange pulpwash. Simple dilutions of orange juice with water and/or sugar solutions resulted in a linear decrease in absorbance sum while the absorbance ratio remained essentially the same. Orange juice and pulpwash systems resulted in a linear increase in absorbance sum and a decrease in absorbance ratio (natural log function). The investigation enabled the derivation of equations, using absorption data, to approximate orange juice and/or pulpwash contents and/or dilution of a sample. The constants used in the equations were based on results obtained from commercially produced Florida citrus products and may vary with other citrus-producing regions. Fluorescence excitation and emission spectra complemented the absorption spectra. Fluorescence excitation for orange juice was maximum at 283 nm with a shoulder at 291 and inflections at 270 and 302 nm with maximum emission at 333 nm. Excitation was also maximum at 291 nm with a shoulder at 283 and inflections at 270 and 302 with maximum emission at 343 nm. Pulpwash excitation was maximum at 270 and 302 nm with a minimum at 283 nm and emission at 353 nm. Peaks or pronounced shoulders at 270 and 302 nm have been indicative of the presence of orange pulpwash.

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