Abstract

Many fruits and vegetables suffer from unwanted discolorations that reduce product quality, leading to substantial losses along the supply chain. Witloof chicory (Cichorium intybus L. var. foliosum), a specialty crop characterized by its unique bitter taste and crunchiness, is particularly sensitive to various types of red and brown discolorations. The etiolated vegetable suffers from three predominant color disorders, i.e., core browning, internal leaf reddening, and leaf edge browning. Additionally, several less frequently observed color disorders such as hollow pith, external red, and point noir can also negatively affect crop quality. In this article, we bring together fragmented literature and present a comprehensive overview of the different discoloration types in chicory, and discuss their potential underlying physiological causes, including laticifer rupture, calcium deficiency, and a disturbed water distribution. We also describe the role of environmental cues that influence discoloration incidence, including cultivation and postharvest storage conditions such as forcing and storage temperature, root ripeness and the duration of the forcing process. Finally, we zoom in on the underlying biochemical pathways that govern color disorders in witloof chicory, with a strong emphasis on polyphenol oxidase.

Highlights

  • In Europe, chicory has a long history of cultivation for its taproot and leaves, but the particular method that produces the etiolated buds known as witloof chicory, was only introduced in the 19th century in the region of Brussels in Belgium

  • Production of witloof chicory is mainly localized in Western Europe, with the Netherlands, Belgium, France, Italy, and Germany as main producers

  • We bring together the current knowledge to categorize and illustrate the different types of discolorations in witloof chicory, and we provide insight into the physiological and biochemical factors that govern these disorders

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Summary

INTRODUCTION

Witloof chicory (Cichorium intybus L. var. foliosum, syn. Belgian endive, chicon) is a leafy vegetable with firm white-yellow leaves and a characteristic bitter taste. In Europe, chicory has a long history of cultivation for its taproot and leaves, but the particular method that produces the etiolated buds known as witloof chicory, was only introduced in the 19th century in the region of Brussels in Belgium (van Kruistum and Zwanepol, 1997; Lucchin et al, 2008). C. intybus shows a broad genetic diversity, harboring a wide range of different ecotypes and numerous cultivated varieties (Lucchin et al, 2008; Ghanaatiyan and Sadeghi, 2016, 2017) In accordance with their different uses, chicory cultivars can be divided into three subtypes, i.e., root chicory, leaf chicory, and witloof chicory, which show a clear genetic diversion (Raulier et al, 2016). Discolorations already occurred in traditionally grown soil chicory, a lot of color defects arose upon the introduction of high-yielding cultivars bred for hydroponic systems (Den Outer, 1989; Reerink, 1994). We bring together the current knowledge to categorize and illustrate the different types of discolorations in witloof chicory, and we provide insight into the physiological and biochemical factors that govern these disorders

OVERVIEW OF DISCOLORATION TYPES
Leaf Reddening
Pith Disorders
Leaf Edge Browning
Less Frequently Encountered Discolorations
EXTERNAL FACTORS INFLUENCING COLOR DISORDERS
Cultivation Practice and Postharvest Storage
Storage temperature Storage duration Atmosphere
GENETIC DETERMINANT OF COLOR DISORDERS
PHYSIOLOGICAL CAUSES OF COLOR DISORDERS
Laticifer Rupture
Calcium Deficiency
Water Distribution
Tissue Tension
BIOCHEMISTRY OF DISCOLORATION IN CHICORY AND RELATED SPECIES
PPO in Plants
PPO Reaction Mechanism and Phenolic Substrates in Chicory
Findings
Strategies to Reduce Enzymatic Discoloration
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