Maillard Reaction Intermediates and Related Phytochemicals in Black Garlic Determined by EPR and HPLC Analyses

Abstract

The Maillard reaction intermediates and related phytochemicals in garlic (Allium sativum L.), which was heated for various lengths of time, using X-band (9 GHz) electron paramagnetic resonance (EPR) and high performance liquid chromatography (HPLC) were investigated. Non-spin-trap and non-destructive EPR detected the total reaction intermediates (radicals). The g-value of the signal was 2.004. The signal with a peak-to-peak linewidth (ΔHpp) was approximately 0.67 milli Tesla (mT). The values of the intermediates are suggestive of organic compounds. The garlic darkened in color with the increasing number of heating days. Melanoidin, responsible for darkening of the garlic, was detected at an absorbance of 400 nm. Analysis of the correlation between the EPR intensity and melanoidin absorbance showed a good correlation coefficient (0.98). In addition, 5-hydroxymethyl furfural (5-HMF) and total phenolic compounds increased with the increasing number of heating days. Moreover, trace amount of Fe3+ was observed in the black garlic by EPR. Non-destructive EPR is a useful method for evaluating not only Maillard reaction intermediates, but also the pigment associated with the reaction processes.

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“…Therefore, when the pH decreased with increasing incubation time, 5-HMF increased. This is consistent with the research of Nakagawa et al 19 , who found that the 5-HMF level of garlic heated at 70 °C increased as the number of heating days increased. In addition, extensive research reported that 5-HMF has antioxidant activity, anti-ischemic functions, and other beneficial effects on the human body 20 .…”

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“…Therefore, when the pH decreased with increasing incubation time, 5-HMF increased. This is consistent with the research of Nakagawa et al [31], who found that the 5-HMF level at the 70 °C heating of garlic increased as the number of heating days increased. However, it is noted that there was a continued increase of HMF in garlic produced at 60 °C; meanwhile, in garlic produced at 80 °C, there was a continuous decrease in HMF after week 3, possibly due to moisture content [21].…”

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“…The typical EPR settings were as follows: microwave power, 5 mW; time constant, 0.1 s; sweep time, 4 min; magnetic field modulation, 0.32 mT; and sweep width, 10 mT. The details were described in the previous report [42].…”