Olfactory impact of guaiacol, ortho‐vanillin, 5‐methyl, and 5‐formyl‐vanillin as byproducts in synthetic vanillin

To better control the quality of synthetic vanillin obtained by using the guaiacol synthesis method, the olfactory impacts of byproducts on the aroma of the synthetic vanillin samples were evaluated and their optimum concentration ranges were determined. Four byproducts (guaiacol, ortho-vanillin, 5-methyl-vanillin, and 5-formyl-vanillin) were identified by gas chromatography-mass spectrometry (GC-MS) and quantified by gas chromatography-flame ionization detection (GC-FID) in the synthetic vanillin samples with different degrees of purity. The aroma intensities (AIs) of the four byproducts obtained by gas chromatography-olfactometry (GC-O) were: guaiacol (AI: 3.5-4.0, smoke), ortho-vanillin (AI: 1.6-2.5, almond), 5-methyl-vanillin (AI: 2.5-3.3, aldehyde), and 5-formyl-vanillin (AI: 3.2-3.8, green). The aroma perceptual interactions of the four byproducts and the vanillin in the synthetic vanillin samples were determined by S-curve analysis. Guaiacol and 5-methyl-vanillin showed synergistic effects by Feller's additive model. Combined with the results of an addition experiment, when the contents of guaiacol, ortho-vanillin, 5-methyl-vanillin, and 5-formyl-vanillin were within 50, 10, 400, and 1,000 mg/kg respectively, the byproducts had no effects on the aroma quality of the synthetic vanillin samples. PRACTICAL APPLICATION: Synthetic vanillin is one of the most commonly used food additives. Currently, the purity of synthetic vanillin can reach 99.9%, but trace byproducts are still present. Continuing to improve the purity of synthetic vanillin will significantly increase its production costs. Therefore, it is necessary to determine whether the presence of these byproducts affects the aroma quality of the synthetic vanillin samples or not. If they have a negative effect on its aroma, it will be important to reduce their content. If they have no influence or positive role, there is no need to control the content of these byproducts to very low levels. This study determined the content of the byproducts produced during the synthesis of vanillin by guaiacol glyoxylic acid method, judged the perceptual interaction between the byproducts and the vanillin in the synthetic vanillin samples, and determined the optimum range within which the byproducts had no effects on the aroma quality. This study provides a theoretical basis for improving the aroma quality of synthetic vanillin while controlling the production costs.