Formation of Maillard Reaction Products in Heat-Treated Torreya grandis cv. Merrilli Seed Oil and Their Effects on Two Analytical Methods for the Determination of Total Phenolics

The occurrence of Maillard reaction in heated Torreya grandis cv. Merrilli seed oil was verified by detecting browning index and the contents of the Maillard reaction products (MRPs) 3-deoxyglucosone, methylglyoxal and 5-(hydroxymethyl)furfural, and the effects of the MRPs on the quantification of total phenolics using the Folin-Ciocalteu and Fast Blue BB assays were explored. The Folin-Ciocalteu assay showed that the content of total phenolics in the oil increased after treatment at 150 ℃ for 90 to 120 min, while the Fast Blue BB assay showed the opposite result. It was also observed that the absorbance of the oil at a wavelength of 294 nm increased after long-term low-temperature or high-temperature heat treatment. 3-Deoxyglucosone (0.21–0.47 μg/g) and 5-(hydroxymethyl)furfural (0.06–0.40 μg/g) were detected only in the 150 ℃ treated oil, while methylglyoxal (0.67–1.73 μg/g) existed in both oil samples. In the Folin-Ciocalteu assay, the absorbance at a wavelength of 765 nm of 3-deoxyglucosone and methylglyoxal linearly increased with an increase in their concentrations, and the decreasing order of the absorbance of the MRPs at the same concentration was 3-deoxyglucosone > methylglyoxal > 5-(hydroxymethyl)furfural. In the presence of 3-deoxyglucosone, the Folin-Ciocalteu result was greater than the actual value, and the degree of interference was not related to the content of total phenolics in samples, but instead was positively correlated with the concentration of 3-deoxyglucosone. In the Fast Blue BB assay, there was no significant difference in absorbance at 420 nm among the three MRPs. For food matrices prone to the formation of 3-deoxyglucosone and methylglyoxal during processing, the Fast Blue BB assay can be selected instead of the Folin-Ciocalteu assay to mitigate the interferences from the two substances in the quantification of total phenolics