Factors, physiology, and genetics associated with the deterioration of fresh-cut lettuce in modified atmospheres

Authors: PENG, HUI - University Of California; LAVELLE, DEAN - University Of California; TRUCO, MARIA - University Of California; MICHELMORE, RICHARD - University Of California; Simko, Ivan

Submitted to: Meeting Abstract
Publication Type: Other
Publication Acceptance Date: 2/14/2020
Publication Date: 3/16/2020
Citation: Peng, H., Lavelle, D., Truco, M., Michelmore, R., Simko, I. 2020. Factors, physiology, and genetics associated with the deterioration of fresh-cut lettuce in modified atmospheres. Future of Lettuce Conference, March 16, 2020, Pismo Beach, California.

Interpretive Summary: Lettuce is one of the most economically important leafy vegetables. Majority of freshly harvested lettuce is cut to pieces and stored in modified atmosphere packaging (MAP) bags for convenient consumption. MAP reduces oxidative discoloration and wilting of processed tissue but may not prevent tissue deterioration which leads to substantial food waste and economic loss. Understanding the deterioration process of fresh-cut lettuce in MAP is thus important to the industry. This study investigated the impact of many factors on the deterioration of fresh-cut lettuce and found that high temperature, physical wounding, ethanol, hexanal, leaf maturity, the ratio of tissue to package volume, and oxygen level could significantly affect deterioration. Under low oxygen level (< 2%), cultivars with genetic predisposition for rapid deterioration displayed faster deterioration and respiration than cultivars known for slow deterioration. Consistently, many respiration related genes had higher expression in the rapidly deteriorating cultivar La Brillante (LaB) than in the slowly deteriorating cultivar Salinas 88 (Sal88), in the early stage of deterioration, suggesting deterioration is high associated with cellular respiration . The loci (qSL4) that was previously identified as the main genetic factor consistently associated with the rate of deterioration in several populations was placed into a region of 5.1 kbp by genetic analyses. The target region was predicted to have a gene encoding a toll/interleukin-1 receptor (TIR) domain-containing protein. Findings regarding major environmental, physiological, and genetic factors associated with the deterioration of fresh-cut lettuce can be used to improve length of shelf life and postharvest quality of lettuce salad in MAP.

Technical Abstract: Lettuce is one of the most economically important leafy vegetables. Majority of freshly harvested lettuce is cut to pieces and stored in modified atmosphere packaging (MAP) bags for convenient consumption. MAP reduces oxidative discoloration and wilting of processed tissue but may not prevent tissue deterioration which leads to substantial food waste and economic loss. Understanding the deterioration process of fresh-cut lettuce in MAP is thus important to the industry. We documented that high temperature, physical wounding, ethanol, and hexanal could accelerate deterioration in MAP by investigating the effects of plant physiology, processing approaches, storage conditions, and exogenous stimuli on fresh-cut lettuce,. Reducing humidity inside MAP bags can slow down deterioration process, while leaf maturity and the ratio of tissue to package volume showed genotype-dependent responses. Oxygen rather than carbon dioxide or ethylene was the major atmosphere component associated with deterioration. The optimal oxygen level for maintaining product quality was cultivar dependent. Under low oxygen level (< 2%), cultivars with genetic predisposition for rapid deterioration displayed faster deterioration and respiration than cultivars known for slow deterioration. Many respiration related genes had consistently higher expression in the rapidly deteriorating cultivar La Brillante (LaB) than in the slowly deteriorating cultivar Salinas 88 (Sal88), in the early stage of deterioration. Deterioration rates of F1 hybrids developed from reciprocal crosses between Sal88 and LaB fell between those of parental lines, suggesting an additive effect of qSL4, the locus previously identified as the main genetic factor consistently associated with the rate of deterioration in several populations. The position of this locus on linkage group 4 was placed into a region of 5.1 kbp by fine-mapping using a F2 population from a cross between RIL79 (a slowly deteriorating recombinant inbred line) and LaB. In silico analysis revealed that the target region carries a putative gene encoding a toll/interleukin-1 receptor (TIR) domain-containing protein. Findings regarding major environmental, physiological, and genetic factors associated with the deterioration of fresh-cut lettuce can be used to improve length of shelf life and postharvest quality of lettuce salad in MAP.