Novel insights into ascorbate retention and degradation during the washing and post-harvest storage of spinach and other salad leaves

- Salad leaves lost 35-86% of their ascorbate during 10 d storage at 4 °C.
- Water-washing of spinach leaves and leaf discs increased ascorbate loss.
- Washing in presence of hypochlorite did not significantly increase ascorbate loss.
- Mechanical agitation of spinach leaves during washing exacerbated ascorbate loss.
- Oxalate was the major [14C]ascorbate by-product, indicating oxidative stress.

Post-harvest treatments of pre-packaged salad leaves potentially cause l-ascorbate loss, but the mechanisms of ascorbate degradation remain incompletely understood, especially in planta. We explored the extent and pathways of ascorbate loss in variously washed and stored salad leaves. Ascorbate was assayed by 2,6-dichlorophenolindophenol titration, and pathways were monitored by 14C-radiolabelling followed by high-voltage electrophoresis. All leaves tested showed ascorbate loss during storage: lettuce showed the greatest percentage loss, wild rocket the least. Spinach leaves were particularly prone to losing ascorbate during washing, especially with simultaneous mechanical agitation; however, washing in the presence of hypochlorite did not significantly increase ascorbate loss. In spinach, [14C]oxalate was the major product of [14C]ascorbate degradation, suggesting that commercial washing causes oxidative stress. This study highlights that ascorbate/dehydroascorbic acid are lost via the oxidative pathway during washing and post-harvest storage of salad leaves. Thus changes to washing procedures could potentially increase the post-harvest retention of ascorbate.