The Effect of Oxygen Absorbers on Extending the Storage Life of Dried Fruits

When we talk about “waste,” we usually picture moldy fruit or wilted vegetables. For dried fruits and nuts—pistachios, walnuts, almonds, raisins, and dried figs—the greatest threat takes a different form: a product that still looks sound but has developed a sharp, unpleasant rancid flavor, causing its market value to fall sharply. The main cause of this hidden deterioration is an element that is present everywhere: oxygen.

1. Why the Dried-Fruit Industry Is Worth Protecting

Dried fruits and nuts are among Iran’s most valuable agricultural export categories. According to a report from the Islamic Republic of Iran Customs Administration, approximately 515,000 tonnes of various dried-fruit products, worth nearly US$1.1 billion, were exported from the country over a ten-month period[1]. Pistachios in shell accounted for 103,300 tonnes worth more than US$621.5 million, while pistachio kernels accounted for 15,300 tonnes worth more than US$170.7 million. Dried figs also featured in the list, with 11,200 tonnes valued at US$33.9 million[1].

This position, however, is vulnerable. Dried-fruit industry representatives have warned that quality problems and exchange-rate fluctuations have, in some years, contributed to a sharp decline in exports—by as much as 70% during one period[2]. The value of Iran’s pistachio exports, which once reached US$2.5 billion, has also fallen to less than US$1 billion in recent years[3]. Preserving quality—and especially preventing oxidative deterioration—is one of the few levers that producers and exporters can directly control.

2. Why Oxygen Is the Main Enemy of Dried-Fruit Shelf Life

Pistachios, walnuts, almonds, and many other dried-fruit products are rich in unsaturated fatty acids—the same compounds that give them much of their nutritional value. However, when these fatty acids come into contact with oxygen, they undergo a reaction known as lipid oxidation. Peroxide values and a compound called hexanal increase, the flavor gradually becomes sharp and unpleasant, and eventually consumers or quality inspectors may reject the product[4]. Unlike microbial spoilage, which is often visible, this process progresses invisibly. That is precisely why managing it requires a more active tool than conventional packaging alone.

3. What Scientific Research Shows About Oxygen Absorbers

Evidence in this field is extensive and supported by research. One review reports that pistachios stored at an oxygen concentration below 2% and a temperature of 5°C have a considerably longer storage life than pistachios stored at 8% oxygen at the same temperature[4]. An atmosphere consisting of 83% nitrogen, 15% carbon dioxide, and only 2% oxygen has also been shown to preserve the quality of fresh pistachios effectively[4].

For walnut kernels, one study found that using an oxygen absorber together with packaging that has low oxygen permeability could maintain kernel quality for up to 13 months without noticeable change[5]. Another study reported a similar 13-month result for walnut kernels stored at 11°C using multilayer EVOH films combined with nitrogen flushing[7].

In a more recent study published in 2025, packaging equipped with an oxygen scavenger made from a special polymer called trans-polyoctenamer (TOR) reduced residual oxygen inside walnut-kernel packages from approximately 3% to below 0.1%, significantly improving product stability during the first two months of storage[6]. This illustrates what an oxygen absorber can do: not merely reduce oxygen, but practically remove it from the environment surrounding the product.

4. A Lesser-Known Additional Benefit: Controlling Stored-Product Pests Without Pesticides

One interesting finding in the scientific literature concerns raisins. A study reported that in 500-gram packs of sun-dried raisins packaged in metallized polyester film, the stored-product pest red flour beetle (Tribolium castaneum) was completely eliminated (100% mortality) after 9, 20, and 45 days at temperatures of 30°C, 22.5°C, and 15°C, respectively. The combined use of an oxygen absorber and a low temperature of 15°C also preserved fruit color[7].

This finding is important because it suggests that oxygen absorbers may serve not only as a tool against chemical deterioration but also as an effective, residue-free alternative for managing stored-product pests. This can be especially relevant for exports to markets with strict pesticide-residue standards.

5. From the Laboratory to the Warehouse: Turning These Findings into Real Profit

The link between these scientific findings and Iran’s dried-fruit economy is direct. A substantial share of the export value of pistachios and other dried-fruit products depends on consistent quality and the absence of unpleasant flavors during long periods of transportation and storage. For an exporter whose shipment may remain in a warehouse or at sea for months before reaching its destination, the difference between a product that retains its original quality and one whose flavor has deteriorated can mean the difference between selling at full price and accepting a forced discount—or even having the shipment rejected.

Given that exported pistachios and pistachio kernels alone generated more than US$792 million over a ten-month period[1], even a modest improvement in shipment acceptance rates can preserve a substantial amount of foreign-exchange revenue at the industry level.

For dried fruits and nuts, unlike many other products, the greatest threat to quality is something that is always present around the product: air. Scientifically managing this one factor can make the difference between an ordinary shipment and a premium export consignment.

Conclusion

Dried fruits and nuts, generating nearly US$1.1 billion in export revenue over a single ten-month period[1], are a key pillar of Iran’s agricultural exports. However, because they are rich in unsaturated fats, they are highly vulnerable to oxidation. Multiple scientific findings—from reducing residual oxygen in walnut-kernel packaging to below 0.1%[6], to preserving pistachio quality at oxygen concentrations below 2%[4], and even controlling stored-product pests in raisins without pesticides[7]—show that oxygen absorbers are a scientifically grounded tool for extending the storage life of dried fruits and nuts.

For an industry whose profitability depends heavily on preserving quality through months of storage and export transportation, this technology is moving beyond the category of an “optional expense” and becoming a strategic investment.