Reduction in Nitrogen Prior to Harvest Increases Phenolic Content of Baby Red Lettuce Leaves

Dario Stefanelli,Christine Frisina,Sonja Winkler,Rod Jones

doi:10.4236/as.2014.56057

Abstract

This study investigated baby red lettuce leaves grown in an inert media and fertigated with 300 or 1000 mg∙L−1 CaNO3-N (19% Ca; 15.5% N), and the effects of altering CaNO3-N concentrations in the last 7 days prior to harvest on yield, antioxidant capacity, TPP and vitamin C content. Plants re- ceiving 1000 mg∙L −1 CaNO3-N had a significantly higher leaf FW than those fertilized with 300 mg∙L −1 CaNO3-N after both 21 and 28 days. Pulsing plants with 1000 mg∙L −1 CaNO3-N for 7 days af- ter 21 days at 300 mg∙L−1 CaNO3-N resulted in a significant increase in FW of 14%, compared with plants receiving 300 mg∙L−1 CaNO3-N. After 28 days plants fertilized with nitrogen at 300 mg∙L−1 CaNO3-N were significantly higher in TPP than those fertilized with 1000 mg∙L −1 CaNO3-N. While there was no significant effect on TPP of a 7-day 1000 mg∙L −1 CaNO3-N pulse added to 300 mg∙L −1 CaNO3-N, a 7-day pulse of 300 mg∙L−1 CaNO3-N added to 1000 mg∙L−1 CaNO3-N resulted in a signifi- cant increase in TPP. These results indicate that reducing the N availability for 7 days prior to har- vest can result in a significant increase in plant phenolic content with no adverse effect on yield.

Highlights

In recent years there has been much interest in the study of the health benefits involved with regular consumption of fresh fruits and vegetables
This study investigated the effects of altering CaNO3-N concentrations in the last seven days prior to harvest on yield, antioxidant capacity and vitamin C content in immature red lettuce leaves
Leaf fresh weight (FW) per plant was significantly affected by N fertilization with plants receiving 1000 mg∙L−1 CaNO3-N having a significantly higher FW than those fertilized with 300 mg∙L−1 CaNO3-N after both 21 and 28 days respectively (Table 2, Figure 1)

Summary

Introduction

In recent years there has been much interest in the study of the health benefits involved with regular consumption of fresh fruits and vegetables. Lettuce is one of the most economically important leafy vegetable crops in the world and is widely consumed in Western diets [1]. It is an important source of dietary vitamin C and antioxidants, primarily in the form of phenolic compounds such as caffeic acid derivatives and flavonols [2]. The major flavonols contributing to antioxidant activity found in lettuce are quercetin and kaempferol derivatives [5]. The closely related compound, kaempferol, has been shown to possess antioxidant activity in its own right, albeit lower than quercetin [8]

Methods

Results

Discussion

Conclusion