|MITSUHASHI, K - Washington State University|
|CLARY, C - Washington State University|
|PITTS, M - Washington State University|
|FELLMAN, J - Washington State University|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2010
Publication Date: N/A
Interpretive Summary: Apple impact injury, also known as bruising, usually results in fruit cullage because of cell damage and tissue discoloration. To better understand the factors associated with this problem, cellular mechanisms need to be investigated. As mechanisms are understood, management practices may be devised to reduce bruising to apples during and after harvest. ‘Golden Delicious’ apples were harvested at different maturity levels based on peel color (green [immature], cream [turning] or yellow [mature]). To simulate picker-induced injury, a silicon finger was fixed to an Instron and a constant force applied to each apple. Excised samples of bruised tissue were examined 48 h after injury using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). We found that 1) cell wall rupture or damage is not required for bruise induction; 2) damaged tissue is made up of a mixture of dead and live cells; 3) cell rupture is facilitated by intercellular spaces which are the weakest point in the tissue; 4) cells adjacent to intercellular spaces are more vulnerable to damage due to the lack of cell-to-cell contact, thereby allowing them to expand and rupture more easily than cells that are tightly packed; and 5) discoloration of bruised tissue appears to come from damaged cells that have released their contents to neighboring areas.
Technical Abstract: It is important to understand how apples bruise in order to prevent or reduce bruising. Tissue from ‘Golden Delicious’ apples was analyzed to determine the bruising mechanism at different maturity levels. Bruising was induced by an artificial finger attached to an Instron machine applying an external load to fresh picked ‘Golden Delicious’ apples. To understand the bruising mechanism involved, we used fluorescence microscopy with Calcofluor fluorescent dye to identify cell walls and CDFA to identify cell membranes in the bruised and discolored tissue. Together with SEM different breakage mechanisms were observed in the bruised area. We observed that 48 hours following damage, the bruised tissue was comprised of dead and live cells, burst, crushed and intact cells. The more intercellular space there was in the tissue, the more tissue damage occurred. Airspaces were the weakest points in the tissue structure, and damage initiated in those points. As apples matured, there was an increase in damaged cells surrounding larger intercellular spaces.