Assessment of initial stages of Maillard reaction in dehydrated onion and garlic samples

The initial steps of the Maillard reaction in freshly laboratory-freeze-dried and commercial dehydrated onion and garlic samples have been assessed by quantitative determination of 2-furoylmethylamino acids, obtained after acid hydrolysis of the corresponding Amadori compound. In freshly prepared samples, hardly any presence of 2-furoylmethylamino acids was detected, whereas in commercial samples, onion contained much more important levels of 2-furoylmethylamino acids as compared to garlic species. 2-Furoylmethyl-gamma-aminobutyric acid (1), 2-furoylmethyl-lysine (furosine; 2), and 2-furoylmethylarginine (3) were identified in all commercial dehydrated onion samples, with compound 3 being the most abundant. All garlic samples presented slightly higher levels of 2 than 3 with no presence of 1. The observed differences between onion and garlic commercial samples may be due to their very different content of reducing sugars. Moreover, some variations found in 2-furoylmethyl derivatives within both onion and garlic species could be also attributed to different processing and storage conditions during the manufacture of these products. The findings of this study show the first evidence of important levels of Amadori compounds in dehydrated garlic and onion samples, as well as the usefulness of 2-furoylmethyl derivatives as quality indicators for the early detection of the Maillard reaction in onion and garlic products.