Acetylated hemicelluloses and esterified pectin alterations in apple cell walls during the development of two apple cultivars: Insights from FT-IR, Raman spectroscopy, and imaging

FT-IR and Raman spectroscopy combined with Raman imaging provided insight into the characteristics of structural changes in polysaccharides and their distribution in the cell walls of two different apple varieties during their development. The fractions of pectin and hemicellulose polysaccharides extracted directly from the cell wall of apples were analyzed. FT-IR results for acetylated hemicelluloses (LiCl-DMSO) were grouped by term using PCA, and were influenced by bands associated with the acetyl group and mannan. Acetylated glucomannan content increased in cell walls during ripening and post-harvest storage. Raman imaging with True Component Analysis distinguished the distribution of acetylated and deacetylated hemicelluloses in the plant cell wall. In general, hemicelluloses did not form specific clusters in the cell wall, but a more pronounced uniform distribution along whole cell walls was observed for acetylated hemicelluloses. Moreover, acetylated hemicelluloses predominated at the post-harvest storage, especially in Idared apples.