Structure and function of cell wall polysaccharides in relation to tuber mechanical properties and bruise susceptibility

Samples of three varieties were studied during the project. Each variety presented different mechanical and biochemical profiles associated with bruising:

Russet Burbank presented the highest incidence of bruising at early harvests (September). Bruising was associated with low mechanical strength and deformability and higher tyrosine content.

Lady Rosetta presented a higher incidence of bruising when harvested in later season (October) and the highest incidence of bruising during storage, particularly for potatoes harvested later. Bruising was associated with increased deformability of tubers and levels of phenolics (but not necessarily tyrosine).

Maris Piper appeared to show moderate bruising until later harvests (October). It appeared to have tissue with strong mechanical properties that protected tubers from impact and intermediate levels of phenolics and tyrosine.

The project results bring into question some previous assumptions about bruise susceptibility. For example, tyrosine levels or specific gravity were not always associated with highest bruising incidence. No relationship between mechanical properties and cell wall properties (pectin linearity or branching) was found with defoliation, harvest or storage. There was a decrease in methylation of pectin along harvest time, which is expected during cell wall maturation. However, the changes were not significant enough to explain differences in bruising incidence between varieties.

Overall, the observations from the study suggest that at early stages of tuber maturation, mechanical properties may be important in protecting tubers, but this is overridden at later stages by high phenolic/tyrosine contents in mature tubers which promote tuber bruising regardless of mechanical properties.