Storage related changes of cell wall based dietary fiber components of broccoli (Brassica oleracea var. italica) stems

- Storage related changes of cell wall components of broccoli stems were investigated.
- Overall, larger effect of storage temperature than of storage time (as chosen here)
- Detailed characterization of polysaccharide and lignin structures was performed.
- Polysaccharide profiles changed during storage.
- Increases in lignin contents were accompanied by altered lignin compositions.

Storage related changes in the cell wall composition potentially affect the texture of plant-based foods and the physiological effects of cell wall based dietary fiber components. Therefore, a detailed characterization of cell wall polysaccharides and lignins from broccoli stems was performed. Freshly harvested broccoli and broccoli stored at 20 °C and 1 °C for different periods of time were analyzed. Effects on dietary fiber contents, polysaccharide composition, and on lignin contents/composition were much more pronounced during storage at 20 °C than at 1 °C. During storage, insoluble dietary fiber contents of broccoli stems increased up to 13%. Storage related polysaccharide modifications include an increase of the portions of cellulose, xylans, and homogalacturonans and a decrease of the neutral pectic side-chains arabinans and galactans. Broccoli stem lignins are generally rich in guaiacyl units. Lignins from freshly harvested broccoli stems contain slightly larger amounts of p-hydroxyphenyl units than syringyl units. Syringyl units are predominantly incorporated into the lignin polymers during storage, resulting in increased acetyl bromide soluble lignin contents. NMR-based analysis of the interunit linkage types of broccoli stem lignins revealed comparably large portions of resinol structures for a guaiacyl rich lignin. Incorporation of syringyl units into the polymers over storage predominantly occurs through β-O-4-linkages.

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