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The effect of wash water chlorine content on the pinking discolouration of fresh cut Iceberg lettuce

The effect of wash water chlorine content on the pinking discolouration of fresh cut Iceberg lettuce

Fisher, Lorraine H.C. and Rees, Deborah ORCID: 0000-0003-3541-0424 (2022) The effect of wash water chlorine content on the pinking discolouration of fresh cut Iceberg lettuce. International Journal of Postharvest Technology and Innovation, 8 (2/3). pp. 184-195. ISSN 1744-7550 (Print), 1744-7569 (Online) (doi:

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Iceberg lettuce is subject to pinking discolouration along cut edges during processing. Passive and active modified atmosphere (MA) packaging with very low steady state oxygen (typically < 0.2%), achieved with nitrogen flushing, limit this effect, however the industry still suffers instances of pinking. Typically, bags of processed lettuce with over 5% pinking by leaf area are rejected by the food industry. Rejections during quality assessment by suppliers, retailers and the householder, contribute to the total estimated 47% of bagged salad that is wasted across the processor to consumer supply chain in the UK. The causes of the discolouration involve complex biochemical pathways. Breeding for varieties with a reduced pinking response requires extensive resources and does not provide a short-term solution. Treatments to reduce the response, e.g., inhibitor additives and heat shock treatment, typically involve additional costs and extensions to the processing line. Minimal processors require a low-cost method to reduce pinking that can be easily incorporated into current practises. Chlorine is already used in the processing line as a sanitiser and has been previously proposed to reduce pinking. This study examined the effects of applying a range of chlorine concentrations to wash water, ≈1 mg L-1, 50 mg L-1, 100 mg L-1 and 200 mg L-1 total chlorine content, to reduce cut edge pinking. In the first part of this study lettuce was packaged in air and observed beyond the normal commercial shelf life period. For overall pinking score there was a clear U-shaped response to chorine concentration, with minimum overall pinking score for concentrations close to 100 mg L-1 chlorine. In a second trial, using controlled atmosphere chambers, samples stored in air were compared to those exposed to an initial oxygen content of 3% and 6%, followed by changes to the atmospheric concentrations to simulate the conditions to which cut lettuce is exposed within MA bags. Pinking was monitored at days 4 and 7. There was no pinking for lettuce packaged in bags with an initial oxygen concentration of 3%. For overall pinking score a clear chlorine concentration effect was apparent for lettuce stored in air and at an initial oxygen concentration of 6%. In this study the effect was linear with lowest pinking scores for lettuce washed at the highest chlorine concentration of 200 mg L-1.

Item Type: Article
Uncontrolled Keywords: chlorine; pinking; discolouration; cut-edge; lettuce; modified atmosphere
Subjects: S Agriculture > S Agriculture (General)
Faculty / School / Research Centre / Research Group: Faculty of Engineering & Science
Faculty of Engineering & Science > Natural Resources Institute
Faculty of Engineering & Science > Natural Resources Institute > Food & Markets Department
Faculty of Engineering & Science > Natural Resources Institute > Postharvest Science and Technology Research Group
Last Modified: 30 Mar 2023 01:38

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