Researchers in China identified 4ºC as the optimal temperature for short-term storage of olives, particularly for periods exceeding 24 hours after harvesting.
A new study has investigated the impact of different refrigeration methods on the quality of olives and the resulting olive oil after milling.
The researchers found that frozen storage of olives may be detrimental to the crucial qualities of the fruit.
They also identified 4ºC as the optimal temperature for short-term storage of olives, particularly for periods exceeding 24 hours after harvesting.
While the study focused on Chinese varieties, including Fuao and Laixing, grown in the Gansu Valley, the researchers believe their findings could support olive farming in many other countries.
Specifically, the study published by Food Chemistry compared the olive oil profiles resulting from seven days of storage under three different conditions: room temperature (approximately 23ºC), refrigeration at 4ºC, and freezing at ‑20ºC.
According to the scientists, previous studies primarily focused on the long-term storage of olives or assessments at fixed points in time.
“The reason for this study, based on a real-life production problem, was the difficulties experienced by a Chinese company in storing olives,” Xiuzhu Yu, professor at the College of Food Science and Engineering at Northwest A&F University in Yangling, told Olive Oil Times.
Challenging production conditions included occasional machinery breakdowns and the need to harvest olives early in response to adverse weather.
“This resulted in a short-term influx of olives into the mill, which far exceeded the mill’s capacity for immediate oil production,” Yu noted.
This situation is common in many olive oil-producing countries, particularly in regions where olive farming is rapidly developing.
These conditions prompted the researchers to search for a storage solution that would preserve olives’ unique qualities in the short term.
“The olive fruit is highly susceptible to deterioration during storage, such as oxidation or microbial growth,” Yu said. “That might lead to losing olive oil quality, such as increased acidity or a vanishing flavor.”
The researchers found that different short-term storage conditions produce different results.
“If olives are stored for more than 24 hours, then refrigeration is recommended,” Yu said. “Under refrigerated conditions, the respiration of the olives is slowed down, enzymatic activity is inhibited and microbiological growth is effectively controlled.”
Under these conditions, crucial antioxidants such as alpha-tocopherols are retained, along with the olives’ complete phenolic profile and chlorophyll content.
“At the same time, refrigeration reduces the production of undesirable flavors such as ‘fermentation’ and ‘mold,’ and maintains the quality of aromas such as ‘grassy,’” Yu remarked.
The researchers found that at room temperature, the high activity of fat oxidative enzymes accelerates the oxidation of fatty acids, leading to an increase in acidity and peroxide values while destroying volatile aldehydes, such as E‑2-hexenal. More