Kiwifruit is what botanists call a climacteric fruit, meaning it continues to ripen after harvest by producing its own ethylene, a gaseous plant hormone that orchestrates softening, sweetening, and aroma development. Global production of the fruit has surpassed four million tons annually since 2017, reaching roughly 4.4 million tons by 2024, with the green-fleshed Hayward cultivar dominating commercial markets thanks to its characteristic flavor. Because kiwifruit is typically picked while still firm and physiologically mature but far from ripe, its flavor, sweetness, and aroma remain underdeveloped at harvest and must be coaxed along with ethylene treatment before it reaches consumers.

The research team, led by Inhwan Kim and Eunyoung Park of Chung-Ang University and Seoul National University along with colleagues at the Korea Food Research Institute, set out to answer a question that has lingered in postharvest science: how exactly do ethylene and 1-methylcyclopropene alter not just the quantity of aroma compounds in kiwifruit, but their actual sensory impact? Previous studies had catalogued volatile changes during ripening, but raw concentrations can be misleading, because odor thresholds vary enormously between compounds. A chemical present in large amounts may barely register to the human nose, while a trace compound can dominate the aroma experience.

To capture the full picture, the researchers subjected Hayward kiwifruit imported from New Zealand to three treatments in sealed chambers at 20 degrees Celsius: an ethylene exposure of 1000 microliters per liter for 22 hours, a 1-methylcyclopropene treatment at 1.4 microliters per liter, and an untreated control. Calcium hydroxide was included in each chamber to absorb carbon dioxide and keep conditions consistent. Fruit from each group was then analyzed at days zero, three, five, seven, and ten of storage, yielding a time-resolved portrait of aroma chemistry under each regime.

The analytical workhorse of the study was headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry, a technique that allows volatile compounds released from the fruit pulp to be captured on an absorbent fiber and then separated and identified with high precision. Using isotopically labeled internal standards, the team quantified 27 distinct volatile compounds: nine aldehydes, seven esters, four alcohols, five terpenes, one ketone, and one furanone. Ten of these, including hexanal, hex-2-enal, nonanal, benzaldehyde, methyl hexanoate, and the pinenes, were confirmed against authentic reference standards, while the rest were identified through mass spectral libraries and retention indices.

The headline numbers are striking. Over ten days of storage, total volatile content in untreated control fruit climbed from 761 to 6335 micrograms per kilogram, an 8.32-fold increase, while ethylene-treated fruit surged even further, from 927 to 8771 micrograms per kilogram, a 9.46-fold rise. In stark contrast, fruit treated with 1-methylcyclopropene, which jams the ethylene receptors on cell membranes and prevents the ripening signal from being received, saw its volatile content fall to just 71.5 percent of its starting level by day ten. The fruit had essentially been frozen in an immature aromatic state.

But raw abundance tells only half the story, so the researchers calculated relative odor activity values, or rOAVs, which compare each compound’s concentration to its known odor threshold and express it relative to the most potent odorant in the sample. Compounds with rOAV values of one or higher are considered critical to the characteristic aroma, those between 0.1 and one contribute to overall flavor, and those below 0.1 are merely potential aroma players. This sensory-weighted lens revealed a clear narrative arc: early in storage, the aroma of all three groups was dominated by aldehydes, particularly hexanal and hex-2-enal, the C6 compounds responsible for the fresh, green, grassy notes characteristic of freshly cut kiwifruit.

As storage progressed, a dramatic shift occurred in the control and ethylene-treated fruit. Esters, the class of compounds responsible for fruity and sweet aromas, began to accumulate explosively. Methyl isobutyrate in stored control fruit reached 1067 micrograms per kilogram, a staggering 97-fold increase over fresh fruit, and in ethylene-treated samples it climbed 370.9-fold. Ethyl benzoate, undetectable in fresh ethylene-treated fruit, reached 2401 micrograms per kilogram after storage and ultimately displayed the highest odor activity of any compound identified by day ten in the ethylene group. Methyl butyrate, methyl isobutyrate, and ethyl benzoate all crossed the critical rOAV threshold of one by day seven in controls and by day five in ethylene-treated fruit, marking the point at which the kiwifruit’s aroma pivots from green to genuinely fruity.

Interestingly, the study punctured a long-standing assumption. Ethyl acetate is routinely monitored as the signature ester of fruit ripening, and its concentration did indeed rise during storage. But its odor threshold is exceptionally high at 6200 micrograms per kilogram, so its rOAV remained below 0.01 throughout the experiment, meaning it contributes almost nothing to the aroma humans actually perceive. The real aromatic powerhouses, the authors argue, are the short-chain esters like methyl isobutyrate and the benzoates like ethyl benzoate, which should be considered the true indicators of fruity aroma development in ripe kiwifruit. The biochemistry behind this shift involves the lipoxygenase pathway, which generates aldehyde precursors, and the enzyme alcohol acyltransferase, which esterifies acyl-CoA molecules with alcohols to form esters; prior work has shown that genes encoding these enzymes are positively correlated with ester accumulation and are suppressed by 1-methylcyclopropene treatment.

The practical implications are considerable. Principal component analysis showed that 1-methylcyclopropene-treated fruit retained an early-stage aroma profile throughout the entire storage period, clustering with fresh samples rather than progressing toward the ripe, ester-rich profile of the other groups. This confirms that blocking ethylene perception preserves shelf life and firmness but comes at the cost of aroma development, a trade-off that distributors must weigh depending on their timeline. Conversely, ethylene treatment accelerates the arrival of full fruity aroma, making it a tool for preparing ready-to-eat fruit on demand. By combining quantitative volatile profiling with odor activity analysis, the Korean team has provided the industry with a sensory-meaningful framework for deciding exactly when and how to intervene, transforming what was once an art of guesswork into a science of precision flavor control during the long journey from vine to table.

Subject of Research: Effects of ethylene and 1-methylcyclopropene on aroma volatile profiles of Hayward kiwifruit during postharvest storage

Article Title: Ethylene and 1-methylcyclopropene modulate aroma volatile profiles in kiwifruit (Actinidia spp.) during postharvest storage

Article References: Kim, I., Park, E., Lee, H., Ahn, D., Choi, J. H., Park, K.-J., Lim, J.-H., & Lee, J. (2026). Ethylene and 1-methylcyclopropene modulate aroma volatile profiles in kiwifruit (Actinidia spp.) during postharvest storage. Food Science and Biotechnology. https://doi.org/10.1007/s10068-026-02248-z

Image Credits: AI Generated

DOI: 10.1007/s10068-026-02248-z

Keywords: kiwifruit, ethylene, 1-methylcyclopropene, aroma volatiles, postharvest storage, esters, aldehydes, odor activity value, climacteric fruit, HS-SPME-GC-MS, food science, fruit ripening