Effect of Nitrogen Supply and Storage Temperature on Vitamin C in Two Species of Baby Leaf Rocket, and the Potential of These Crops for a Nutrient Claim in Australia

Abstract

Baby leaf crops such as rocket are popular in mixed salads and add flavor and diversity to these dishes. Rocket leaves contain many beneficial compounds to human health, including vitamin C. It is important to determine abiotic factors that influence the concentration of this compound; in order to improve the supply of quality produce with a high nutritional value. The possibility of a nutrient claim for leaves of perennial wall rocket [Diplotaxis tenuifolia (L.) DC.] and annual garden rocket (Eruca sativa Mill.) was examined under the Food Standards Australia New Zealand (FSANZ) framework. Crops were supplied with 0, 100, 200, and 300 kg · ha−1 of nitrogen (N); leaves were stored at 0, 4, and 7°C for 15 days. The cultivar and amount of nitrogen supplied to perennial wall rocket did not affect the concentration of vitamin C in leaves at harvest, with a mean of 79.6 mg 100 g−1. For annual garden rocket there was an interaction between cultivar and nitrogen supply, with higher levels of supply generally resulting in lower vitamin C concentrations at harvest. The postharvest stability of vitamin C in both crops was best maintained at the lowest storage temperature. The results of this study illustrate that if stored at 0°C, both species contain vitamin C in sufficient quantities 15 days after harvest, to result in a “good source” health claim [>25% recommended daily intake (RDI)]. However, the storage temperature in the supply chain is typically ∼7°C, still permitting a “source” health claim (>10% RDI) for both species.