What Modified Atmosphere Packaging Does to Kiwifruit Over 150 Days
Kiwifruit is one of the most ethylene-sensitive crops in commercial storage. UC Davis’s Postharvest Research and Extension Center notes that as little as 5–10 ppb (parts per billion) of ethylene is enough to induce softening in kiwifruit — a threshold far lower than most fruit, and low enough that even trace contamination in a cold room can start the clock (UC Davis PREC, Kiwifruit produce facts sheet). That extreme sensitivity, combined with rapid post-harvest softening and significant weight loss, makes kiwifruit a demanding long-storage crop. A university trial on the premium G3 Sungold cultivar tested how well modified atmosphere packaging manages all three problems across a full five months of cold storage.
The Postharvest Challenge for Kiwifruit
Kiwifruit is harvested firm, unripe, and starch-rich, and its storage life ends when it softens past the point of marketability. Research published in Postharvest Biology and Technology describes softening as a multi-phase process, with the fruit’s own autocatalytic ethylene production only beginning once flesh firmness has already dropped to around eating-firmness — meaning by the time the fruit is producing its own ethylene in quantity, quality is already declining fast. Earlier UC Davis work found that kiwifruit can lose roughly 40% of its firmness within the first three months of storage, closely tied to the breakdown of fruit starch into sugars.
Temperature and atmosphere control dramatically slow this. UC Davis cooperative extension trials on Hayward kiwifruit found that air-stored fruit softened approximately 2.6 times faster than fruit held in controlled atmosphere (5% CO₂ + 2% O₂) at 0°C over 16 weeks (UC Davis, Central Valley Postharvest Newsletter). But atmosphere control introduces its own risk: if ethylene accumulates inside a sealed environment, it can trigger a serious disorder.
Why Ethylene Control Is Non-Negotiable for Kiwifruit
The specific danger for kiwifruit in sealed storage is white-core inclusions (WCI) — distinct white patches of hardened core tissue that appear in ripe fruit and render it unmarketable. UC Davis directly links this disorder to ethylene presence in controlled-atmosphere storage, and recommends keeping ethylene below 20 ppb to avoid both accelerated softening and WCI (UC Davis PREC, Kiwifruit produce facts sheet). Research in the New Zealand Journal of Crop and Horticultural Science confirmed the dose-dependence: Hayward kiwifruit developed white-core inclusions after 8 weeks of exposure to 100 and 1000 nL·L⁻¹ ethylene in CA, while the lowest concentration tested (≤10 nL·L⁻¹) did not affect quality. In other words, kiwifruit storage succeeds or fails on how well ethylene is held down — which is exactly what a well-designed MAP system is built to do.
The Trial: G3 Sungold Over 150 Days
Researchers at Çanakkale Onsekiz Mart University (Faculty of Agriculture, Department of Horticulture) ran a storage trial on G3 Sungold gold kiwifruit, harvested in October 2018 and held at 1°C with 90–95% relative humidity. In the modified atmosphere arm of the study, fruit was packed in LDPE and polypropylene-based MAP material on the second day of cold storage and assessed at 30, 60, 90, 120, and 150 days, directly against unpackaged control fruit under identical conditions. Quality was tracked through firmness, weight loss, soluble solids, titratable acidity, and ethylene production, with three replicates of 30 fruit each analysed by ANOVA.
Weight Loss: The Clearest Result
Weight loss showed the most dramatic separation between the two groups. This matters because kiwifruit shows visible shrivelling once weight loss passes roughly 3–4% (McDonald, 1990, as cited in the trial). By 150 days, the control fruit had lost roughly twice as much weight as the MAP-packed fruit — the control climbing well past the shrivelling threshold while the MAP fruit stayed far below it. The MAP bag’s humidity control kept moisture around the fruit, directly protecting against the weight loss that drives shrivelling and downgrade.
Firmness: MAP Held the Fruit Together
Firmness is the make-or-break quality trait for kiwifruit — UC Davis research suggests a minimum of around 5.0 lbf is needed to prevent bruising during packing and shipment (Crisosto & Garner, UC Davis). In the Sungold trial, the MAP fruit outperformed the control at every checkpoint from 60 days onward. Where the control softened steadily toward unmarketable levels, the MAP-packed fruit retained substantially more firmness through to 150 days — consistent with the broader finding that atmosphere control slows the starch-to-sugar and cell-wall breakdown that drive softening.
Ethylene: Suppressed Under MAP
Ethylene production climbed steadily in both groups as the fruit aged, but the MAP fruit consistently produced less than the control — most visibly at the 90 and 120 day marks. Given that kiwifruit responds to ethylene at the parts-per-billion level, holding this accumulation lower is precisely what slows the softening and internal breakdown the hormone drives. This is the mechanism behind the firmness result: less ethylene, slower softening, and a lower risk of the white-core disorder that ethylene accumulation causes.
What This Means for Packaging
The trial’s own conclusion was direct: modified atmosphere packaging significantly affected every quality measure assessed, and made six months of cold storage achievable for G3 Sungold kiwifruit. That result aligns with the wider research base — kiwifruit needs the firmness protection of atmosphere control, but only if ethylene is kept low enough to avoid triggering white-core inclusions. The Life Pack MAP bag works on all three fronts at once: humidity control to hold weight and prevent shrivelling, gas modification to slow respiration and firmness loss, and a lower-ethylene environment to suppress the hormone driving kiwifruit’s softening.
The Practical Takeaway
Kiwifruit is unforgiving of ethylene and quick to soften, which is exactly why packaging has to work on all three problems together. The control fruit in this trial lost firmness, lost weight, and produced more ethylene at every stage; the MAP fruit held quality across the board and reached a full five months in saleable condition. For exporters moving Sungold or other kiwifruit varieties by sea, this trial — backed by decades of independent postharvest research — supports MAP as the difference between arriving firm and arriving soft.
Download the full G3 Sungold kiwifruit trial report (PDF)
- UC Davis Postharvest Research and Extension Center — Kiwifruit produce facts sheet (ethylene sensitivity 5–10 ppb; CA below 20 ppb; white-core inclusions).
- UC Davis Central Valley Postharvest Newsletter — Hayward kiwifruit softening 2.6× faster in air vs CA.
- Crisosto, C.H. & Garner, D., UC Davis — kiwifruit size, firmness thresholds and softening rate during storage.
- The responses of ‘Hayward’ kiwifruit to ethylene during regular and controlled atmosphere storage, New Zealand Journal of Crop and Horticultural Science — dose-dependent white-core inclusions.
- Temperature, length of cold storage and maturity influence the ripening of ethylene-preconditioned kiwifruit, Postharvest Biology and Technology — softening phases and climacteric onset.
- Sakaldas, M., Çanakkale Onsekiz Mart University — G3 Sungold kiwifruit MAP storage trial (primary trial data).
