Comparison of characterization and composition of melanoidins from three different dried apple slices.

The composition of melanoidins in dried apple that affects quality remains unclear. The composition and structure of melanoidins in dried apple slices by hot air drying (HAAM), instant controlled pressure drop drying (DICAM), and vacuum freeze-drying (FDAM) were investigated. It showed that the melanoidins were highly heterogeneous mixtures with a light-yellow color and blue-green fluorescence, belonging to polysaccharide-type melanoidins. Specifically, HAAM had a large molecular weight (929.5 g/mol) and wide molecular weight distribution, with more double-bond conjugated systems. DICAM (610.9 g/mol), possessing the strongest fluorescence intensity, was mainly composed of compounds with fewer π-conjugated structures and more electron-donating groups. As a control, the low level of Maillard reaction in FDAM resulted in the formation of the smallest molecular weight (458.6 g/mol) with weak fluorescence intensity. Moreover, 10 compounds were tentatively identified in apple melanoidins. This study provides the foundation for the future functional preparation of apple melanoidins. [Display omitted] • The composition of dried apple melanoidins varied from that of coffee and bread. • The apple melanoidins had distinctive chemical bonds similar to coffee melanoidins. • The structural character of melanoidins in dried apple varied from the drying methods. • The Mw of FDAM, DICAM and HAAM increased sequentially. • Pyridine and pyrrol were the main differences between apple melanoidins and others. [ABSTRACT FROM AUTHOR]