Identification of the Key Aroma Compounds in Gluten-Free Rice Bread

Rice flour is commonly used as a raw material in the preparation of gluten-free bread. However, compared to wheat bread, its aroma is different and often not accepted by consumers. Aroma profile analyses of the crumb and crust of freshly baked rice bread indicated a strong rice-like flavor but lower intensities of the typical roasty wheat bread odor qualities. By application of aroma extract dilution analyses (AEDA), the most odor active compounds in both rice and wheat bread samples were characterized. In addition, two batches of rice flour were used. In particular, 2-aminoacetophenone and 4-vinylphenol reached high flavor dilution (FD) factors in the rice bread samples but were not detected in wheat bread. In the rice bread crust 1-octene-3-one, (E)-2-nonenal, and 4-methylquinazoline reached significantly higher FD factors than in the wheat bread crust, while those of maltol and 2-methoxy-4-vinylphenol were significantly lower. In a stored rice flour and in the corresponding rice bread, lipid degradation products such as hexanal were more intense compared to fresh rice flour. Finally, five aroma-active compounds, namely, 2-butyl-2-heptenal, 2-propyl-2-octenal, 4-hydroxy-2-octenoic acid lactone, 4-hydroxy-2-nonenoic acid lactone, and 4-methylquinazoline, were identified for the first time in rice-containing products.