Effects of Drying Methods on Organic Acid Contents of Tobacco Flowers and Discriminant Analysis

To explore the utilization of tobacco flower in tobacco flavoring applications and establish discriminant model for drying methods based on key organic acids, GC/MS was employed to analyze the differences in organic acid content across seven drying methods. Partial least squares-discriminant analysis (PLS-DA) was used to identify key differential organic acids, followed by Fisher discriminant analysis to construct a discriminant model for identifying drying methods. Results showed as the follows. (1) Volatile acids in tobacco flowers treated with different drying methods were identified as benzoic acid, phenylacetic acid and 3-methylpentanoic acid (with characteristic aroma), with total content ranging from 116 to 181 μg/g. The total content of non-volatile acids ranged from 59.7 to 77.0 mg/g, with the sum of oxalic acid, malic acid and citric acid content accounting for approximately 92.5% to 97.8% of the total. The total content of higher fatty acids ranged from 22.4 to 65.2 mg/g, with unsaturated fatty acids (oleic acid, linoleic acid, and linolenic acid) accounting for about 58.7% to 76.6% of the total. (2) Drying methods significantly affected organic acid contents: air drying achieved the highest volatile acid content, followed by programmed heating drying and sun drying, whereas freeze drying yielded the lowest. Non-volatile acids reached peak levels during freeze drying, whereas their minimum content were observed in 65 ℃ constant temperature drying. The total content of higher fatty acids was the highest in freeze drying and the lowest in air drying. (3) PLS-DA classified the seven drying methods into five categories: freeze drying, programmed heating drying, constant temperature drying, sun drying, and air drying. Based on the VIP values from the PLS-DA model, seven key differential organic acids, namely glutaric acid, oleic acid, stearic acid, oxalic acid, citric acid, myristic acid, and phenylacetic acid, were identified as characteristic markers. Subsequently, a Fisher discriminant model was established for the five categories of tobacco flower drying methods, with classification accuracies of 96.7% in the training set and 100% in the test set. In summary, the organic acid profiles of tobacco flowers subjected to air drying, sun drying, or programmed heating drying (up to 59 ℃) exhibit greater suitability for tobacco flavoring applications. Organic acids can serve as characteristic chemical components for effectively discriminating tobacco flower resources obtained from different drying methods.