Polyphenolic profiles in lettuce (Lactuca sativa L.) after CaCl2 treatment and cold storage

Małgorzata Materska,Milena Masullo,Łukasz Pecio,Barbara Chilczuk,Barbara Pacholczyk-Sienicka,Katarzyna Olszówka,Sonia Piacente,Anna Stochmal,Cosimo Pizza

doi:10.1007/s00217-018-3195-0

Abstract

Lettuce (Lactuca sativa L.) is a popular vegetable with the health-enhancing properties determined by high levels of antioxidant polyphenols as chlorogenic acids and other derivatives of caffeic acid or flavonoids. In this study, changes in the phenolic compound profiles in the lettuce leaves induced by application of CaCl2 before harvest and cold storage were studied. For the first time quantitative analysis of individual phenolic compounds on the basis of standards isolated from lettuce leaves was performed. Compounds were identified using HPLC, LC-MS, 1H and 13CNMR techniques. The dominant compounds were 2,3-dicaffeoyltartaric (2,3-diCTA), 5-O-caffeoylquinic (5-OCQA) and caffeoyltartaric (CTA) acids, with content of 5.7, 2.5 and 0.981 mg/g DM, respectively. The levels of individual phenolic compounds, total phenolics and antioxidant activity (DPPH assay) in plants treated by CaCl2 were determined throughout the storage period (7 and 14 days) at 4 °C. To ascertain the relationship between the content of individual compounds, total phenols, antioxidant activities and storage time, Pearson’s correlation analysis was used. The best correlation between the storage length and compound concentration was observed for 2,3-diCTA (R2 = 0.866) and caffeoylmalic acid (CMA) (R2 = 0.750). Application of CaCl2 (0.05M) on lettuce resulted in an increase in the levels of CTA, 2.3-diCTA and 5-OCQA about 120, 65 and 57%, respectively, compared to the control stored for 7 days in the same conditions and had a favourable effect on the antioxidant activity (R2 = 0.985). The present paper shows that CaCl2 may be used as an agent that influences the stability of health-promoting compounds of cold-stored lettuce.

Highlights

Lettuce is a representative of the family Asteraceae and is a popular vegetable used in salads, which are being increasingly consumed as ‘healthier’ food
The use of High-performance liquid chromatography (HPLC)-diode array detection (DAD), LC-MS, 1H-NMR and 13C-NMR techniques resulted in the identification of five caffeic acid and two flavonoid derivatives in the leaves of lettuce of cv
The quantification of these compounds during cold storage of lettuce treated with CaCl2 before harvest was evaluated for the first time on the basis of isolated standards

Summary

Introduction

Lettuce is a representative of the family Asteraceae and is a popular vegetable used in salads, which are being increasingly consumed as ‘healthier’ food. The health-enhancing properties of these products are determined by their high levels of antioxidant compounds, primarily vitamin C and polyphenols, as well as fibre [1]. The primary reason that lettuce is thought to have strong antioxidant activity is its large amount of phenolic compounds. They are synthesised during normal plant growth or are produced in response to environmental stress and other stresses such as UV, radiation, injuries and processing techniques, including postharvest treatment [3]. Phenolic compounds play an important role in plant–plant and plant–pathogen signalling [4].

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