Discover the science behind preserving pear quality during cold storage
Imagine biting into a perfectly ripe, juicy pear only to find its skin marred by unsightly brown patches. This common postharvest disorder, known as superficial scald, has plagued pear growers and distributors for decades, causing significant economic losses worldwide.
The 'Wujiuxiang' pear, a popular hybrid variety known for its exquisite aroma and delicate flavor, is particularly susceptible to this condition after long-term cold storage. But recent scientific advances have revealed a powerful weapon against this disorder: 1-methylcyclopropene (1-MCP), an ethylene action inhibitor that's revolutionizing postharvest management of fruits.
Without treatment, scald incidence can reach 78-97% in certain pear varieties after just four months of cold storage 4 .
Superficial scald is a physiological disorder that affects apples and pears during and after cold storage. It manifests as irregular brown or black patches on the fruit's skin, making it visually unappealing and significantly reducing its market value 7 .
Contrary to what one might think, this isn't caused by pathogens or mechanical damage but rather by a complex interplay of biochemical processes within the fruit itself triggered by cold storage conditions.
The economic implications of superficial scald are substantial. For popular varieties like 'Wujiuxiang' pears, which are particularly susceptible to this disorder, losses can be devastating.
This represents not just a loss of the fruit itself but also wasted resources in harvesting, storage, and transportation—a serious concern for the agricultural industry striving for sustainability.
To understand how 1-MCP works its magic, we must first appreciate the role of ethylene in fruit ripening and disorder development. Ethylene is a natural plant hormone that regulates fruit ripening, senescence, and various metabolic processes.
1-methylcyclopropene (1-MCP) is a cyclic hydrocarbon that acts as a potent inhibitor of ethylene action. It works by binding irreversibly to ethylene receptors in plant tissues, effectively blocking ethylene perception and response 3 .
For 'Wujiuxiang' pears, researchers have found that fumigation with 1-MCP at concentrations of 0.5-1.0 μL/L before cold storage can significantly reduce scald incidence 1 .
The treatment is typically applied in sealed containers for 18-24 hours at room temperature before the fruits are transferred to cold storage facilities 5 .
In a comprehensive study investigating the effects of 1-MCP on 'Wujiuxiang' pears, researchers designed a meticulous experiment to unravel how this compound confers protection against superficial scald 1 2 :
'Wujiuxiang' pears were harvested at commercial maturity and carefully selected for uniform size and absence of defects.
The pears were divided into three groups:
Fruits were periodically analyzed for:
The findings from this and similar studies have revealed a multifaceted mechanism through which 1-MCP protects 'Wujiuxiang' pears from superficial scald 1 2 5 .
1-MCP treatment dramatically reduced scald incidence in 'Wujiuxiang' pears. After 180 days of cold storage plus shelf life, control fruits showed severe scald symptoms, while 1-MCP-treated fruits remained largely unaffected 5 .
| Parameter | Control | 0.5 μL/L 1-MCP | 1.0 μL/L 1-MCP |
|---|---|---|---|
| Scald Index (%) | 78-97% | <20% | <15% |
| Firmness Retention | Low | High | Higher |
| Storage Life | Shortened | Extended | Maximized |
1-MCP treatment significantly reduced the accumulation of both α-farnesene and its oxidation products, conjugated trienols (CTols), which are directly responsible for cell membrane damage and scald development 1 8 .
| Parameter | Control | 1-MCP Treatment | Change (%) |
|---|---|---|---|
| α-Farnesene content | High | Low | -60 to -70% |
| Conjugated trienols | High | Low | -65 to -75% |
| AFS1 gene expression | Upregulated | Downregulated | -50 to -60% |
1-MCP treatment enhanced the activity of key antioxidant enzymes in pear peel, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) 1 .
At the molecular level, 1-MCP treatment downregulated genes involved in ethylene synthesis, perception, and signal transduction 5 .
While the ethylene-dependent pathway explains much of 1-MCP's protective effect, recent research suggests additional mechanisms may be at play.
Studies comparing 1-MCP with lovastatin (a compound that reduces scald without inhibiting ethylene action) have revealed that both treatments repress PPO gene expression and increase sorbitol content, suggesting the existence of non-ethylene-mediated processes in scald prevention 4 .
1-MCP appears to activate cold-acclimation mechanisms within the fruit, including the biosynthesis of very-long-chain fatty acids that help stabilize cellular membranes under cold stress 4 .
| Reagent/Technology | Primary Function | Application in Scald Research |
|---|---|---|
| 1-MCP | Ethylene action inhibitor | Blocking ethylene receptors to study its role in scald development |
| Ethylene producers | Stimulate ethylene response | Positive controls for scald induction studies |
| Lovastatin | HMG-CoA reductase inhibitor | Studying non-ethylene scald pathways |
| qPCR technology | Gene expression analysis | Measuring changes in stress-related gene expression |
| HPLC-MS | Phenolic compound analysis | Quantifying changes in phenolic metabolism |
| GC-MS | Volatile compound analysis | Measuring α-farnesene and CTols levels |
The research on 1-MCP's effects on 'Wujiuxiang' pears represents a fascinating convergence of postharvest physiology, molecular biology, and practical agriculture. By unraveling the intricate mechanisms through which 1-MCP prevents superficial scald, scientists have not only solved a practical problem but also deepened our understanding of fruit biology under cold stress.
Perhaps most excitingly, the molecular insights gained from these studies may inform breeding programs aimed at developing new pear varieties with natural resistance to superficial scald, reducing the need for postharvest treatments altogether. Until then, 1-MCP remains a powerful tool in the ongoing effort to minimize food waste and maximize the enjoyment of one of nature's most delightful fruits—the perfect pear.
Acknowledgement: The research highlighted in this article was made possible by the dedicated work of scientists at the Institute of Genetics and Physiology, Hebei Academy of Agriculture and Forestry Sciences, and the Plant Genetic Engineering Center of Hebei Province, Shijiazhuang, China.