Effect of hermetic storage technology on insect infestation and grain quality of stored wheat

Introduction

Global post-harvest grain losses to insects and microorganisms amount to roughly 35 million tonnes each year, worth an estimated USD 9.4 billion In Japan, where wheat imports and domestic storage both play key roles in food security, maintaining grain quality during warehousing is a persistent challenge Traditional storage methods relying on chemical fumigants like phosphine face growing resistance among major storage pests, and consumer demand for pesticide-free grain has risen steadily Hermetic storage works by creating an airtight environment where insect respiration depletes oxygen and raises carbon dioxide levels, eventually killing or suppressing pest populations without chemicals the technology has shown promising results for rice and maize in tropical regions, but data on its performance for wheat storage under temperate-humid conditions like those in Japan remain scarce. Key questions include whether the modified atmosphere develops fast enough to prevent damage during the warm months and whether grain quality parameters like protein and germination hold up over extended periods Fat acidity serves as a sensitive indicator of grain deterioration because lipid breakdown occurs early in the degradation process and correlates with overall quality loss Germination rate reflects seed viability and is closely tied to baking quality in wheat This research compared hermetic and conventional storage systems over 10 months, measuring insect population dynamics alongside grain quality changes to provide a practical assessment of hermetic technology for Japanese wheat storage conditions.

Research facility description

The storage trial was conducted at the University of Tokyo Agricultural Research Station in Nishitokyo City, Tokyo Prefecture (35.7275°N, 139.5384°E). The research warehouse measured 12 × 8 m with corrugated steel roofing and concrete flooring. Two storage zones were established: hermetic bags (SuperGrain™, 1-tonne capacity) and conventional woven polypropylene bags (50 kg each) placed on wooden pallets. Each treatment had four replicates. The facility had no active climate control, representing typical small-scale farm storage conditions in the Kanto region.

Storage environmental conditions

The trial ran from April 2022 to January 2023. Warehouse temperatures ranged from 8.3°C in January to 33.7°C in August, with relative humidity between 54.2% and 88.6%. The warmhumid summer months (June-September) presented the greatest risk for insect proliferation and grain deterioration. Temperature and humidity were logged hourly using HOBO U23 Pro v2 data loggers placed inside both storage types and in the ambient warehouse space

Material and Methods Material

Freshly harvested wheat (variety Norin 61) was obtained from the university's experimental farm. Initial grain moisture was 11.8%, and samples were free of visible insect infestation at the start. Super Grain hermetic bags were sourced from GrainPro Inc. (Philippines). Standard polypropylene woven bags served as conventional storage. Laboratory reagents for quality analysis included petroleum ether (Wako Pure Chemical), potassium hydroxide (Kanto Chemical), and phenolphthalein indicator Methods Sampling occurred at months 0, 2, 4, 6, 8, and 10. At each interval, 1 kg sub-samples were drawn from each replicate using a grain probe. Insect counts were determined by sieving 500 g samples through No. 10 and No. 20 mesh screens, with species identification under stereomicroscope Moisture content was measured using a Kett PM-450 grain moisture meter. Germination rate was assessed by placing 100 seeds on moist filter paper in Petri dishes at 25°C for 7 days. Protein content was determined by micro-Kjeldahl method (N × 5.7) Fat acidity was measured by extracting lipids with petroleum ether and titrating with 0.05N KOH following AACC Method 02-01.02 Oxygen and CO₂ concentrations inside hermetic bags were monitored using a Dansensor CheckMate 3 headspace analyzer. Data were analyzed using R software (v4.2.1) with repeated measures ANOVA and Tukey's HSD test at p<0.05. Sitophilus oryzae dominated both storage systems but was substantially suppressed in hermetic bags (Figure 1). The heatmap (Figure 2) shows that quality decline in hermetic storage was gradual and modest compared to initial values.

Results

Discussion

The 78.3% reduction in insect populations under hermetic storage aligns with reports from tropical trials. Njoroge et al. documented 82-91% insect mortality in hermetic bags storing maize in Kenya, and Baoua et s. recorded similar suppression for cowpea in Niger. The mechanism is straightforward: insect respiration drives O₂ below 5% and CO₂ above 10%, creating conditions lethal to most stored-product beetles in our trial, O₂ dropped to 3.7% by month 10, consistent with this threshold.

The better preservation of germination rate (78.4% vs 52.1%) has practical value. Japanese wheat millers increasingly require germination above 70% as a proxy for baking suitability Hermetic bags met this threshold at 10 months while conventional storage fell well below it by month 6. Fat acidity data reinforce this finding the lower oxidative stress inside hermetic bags slowed lipid breakdown, which directly affects flour flavor and shelf life One point worth noting is that hermetic storage didn't eliminate insects entirely. Small populations persisted, likely from eggs already present in grain at loading this suggests that combining hermetic technology with initial grain cleaning or brief lowtemperature treatment could push infestation levels even lower.

Conclusions

Hermetic storage technology proved effective at reducing insect infestation and maintaining wheat grain quality over 10 months under Japanese warehouse conditions. Insect numbers were reduced by 78.3%, and grain quality parameters including germination rate, protein content, and fat acidity were significantly better preserved compared to conventional polypropylene bag storage. The modified atmosphere that develops naturally inside sealed bags low oxygen and elevated carbon dioxide accounts for the insect suppression without any chemical inputs. These results support hermetic storage as a practical, chemical-free option for small to medium-scale wheat storage in temperate-humid climates. Wider adoption could reduce both post-harvest losses and pesticide residue concerns in stored grain.

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