Nitrogen Storage Protects Rice Until the Air Returns, Study Finds

Nitrogen-modified atmosphere storage has become one of the most widely adopted green preservation technologies in the grain industry, flooding sealed granaries with nearly pure nitrogen to suffocate insect pests and suppress molds without a single pesticide residue. For years, the technique has been celebrated as a clean, efficient way to keep paddy rice fresh through storage seasons that in China routinely stretch beyond a full year. But a new study published in Food Chemistry: X delivers an uncomfortable twist to that success story: once the nitrogen atmosphere is removed and the grain is returned to normal air, the rice appears to deteriorate faster than rice that was never treated at all.

Researchers led by Ming Chen and Chenling Qu tracked two rice varieties—a japonica cultivar called Jinjingyou and an indica cultivar called C-liangyou Simiao—through 360 days of storage under three regimes. One group sat in conventional storage at 25 degrees Celsius and 65 percent relative humidity. A second group received 99 percent nitrogen for 40 days before re-aeration, a protocol designed to mirror the industry standard for rapid pest eradication. A third received 95 percent nitrogen for 180 days, matching the long-term pest suppression guideline from the Chinese standard LS/T 1225–2022. After the nitrogen phase, both treated groups were returned to ordinary air for the remainder of the year-long experiment.

The warning signs emerged at the end of storage. Freshness, measured by a bromothymol blue assay that tracks the acidic substances that accumulate as rice ages, fell significantly below conventional-storage levels in both nitrogen-treated groups by day 360. Germination rate, a proxy for the biological vigor of the embryo, dropped in parallel. The energy chemistry inside the kernels told the same story: ATP content and the cellular energy charge were significantly depleted in the re-aerated rice, while AMP accumulated, a signature of an energy-starved cell scrambling to stay functional.

To understand why, the team zeroed in on central carbon metabolism—the interconnected network of glycolysis, the tricarboxylic acid cycle, the mitochondrial electron transport chain, and the pentose phosphate pathway that converts stored starch into energy and building blocks. Even after harvest, rice kernels remain alive, burning through their own reserves to maintain basic physiology. The researchers measured the activities of seven key enzymes that gate the flow of carbon through this network, from hexokinase at the entry point of glycolysis to ATP synthase at the final step of mitochondrial energy production.

The enzyme data revealed a striking pattern of collapse. By day 360, mitochondrial isocitrate dehydrogenase, a rate-limiting enzyme of the TCA cycle, and ATP synthase, the core engine of oxidative phosphorylation, were both significantly suppressed in the re-aerated rice compared with conventional storage. The pentose phosphate pathway enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were also significantly down, cutting the grain’s supply of NADPH, the reducing power that fuels antioxidant defense and nucleotide synthesis. Glycolytic enzymes showed dramatic fluctuations rather than the slow, stable decline seen in untreated rice, suggesting the treated grain was lurching through cycles of metabolic stress and partial recovery.

The most likely culprit, the authors suggest, is a phenomenon well known in plant physiology: the hypoxia–reoxygenation response. When plant tissues are deprived of oxygen and then suddenly re-exposed, reactive oxygen species surge, damaging mitochondrial membranes and inhibiting the very enzymes that generate cellular energy. The transient spike in isocitrate dehydrogenase and ATP synthase activity observed in the high-nitrogen group between days 40 and 180 fits this picture—a stress-repair response firing up when the air returned, followed by progressive exhaustion as the damage accumulated over the remaining months of storage.

Targeted metabolomics using UHPLC-MS/MS added molecular precision to the picture. Of 140 targeted metabolites, 95 passed quality filtering, and principal component and discriminant analyses cleanly separated the re-aerated rice from conventionally stored grain in both varieties. Five metabolites emerged as biomarkers of the accelerated decline. In the high-nitrogen group, fructose-6-phosphate, guanosine monophosphate, and AMP accumulated while cytosine was depleted—evidence of a traffic jam in glycolysis, disrupted nucleotide metabolism, and impaired capacity for DNA repair. In the low-nitrogen group, homogentisic acid, a precursor of the antioxidants tocopherol and plastoquinone, dropped sharply, signaling a weakened antioxidant shield.

The accumulation of fructose-6-phosphate is particularly telling. This glycolytic intermediate piled up in both varieties under the high-nitrogen protocol, likely because phosphofructokinase, the enzyme that should consume it downstream, was significantly inhibited. A stalled pipeline means less carbon flowing toward ATP production and fewer carbon skeletons for biosynthesis, a metabolic bottleneck that echoes findings in cold-stressed peas and nitrogen-starved apple roots, where fructose-6-phosphate likewise accumulates under duress.

The practical implications are immediate. Nitrogen treatment still does its job during the sealed phase—freshness was actually better preserved at day 180 in the long-nitrogen group than in conventional storage—but the benefits evaporate, and then reverse, once the grain meets ordinary air. The authors recommend that paddy rice be processed and consumed promptly after re-aeration rather than returned to long-term storage. They also point to possible remedies: gradual re-aeration to soften the oxidative burst, or exogenous metabolic regulators to restore carbon flux through the compromised pathways.

Caveats remain. The experiment was conducted under tightly controlled laboratory conditions of constant temperature and humidity, and the authors note that verification in real warehouses with full-scale nitrogen systems and longer storage horizons is still needed. Even so, the study reframes a technology often assumed to be purely protective. The nitrogen atmosphere, it turns out, does not simply pause the life of the grain—it reshapes its metabolism in ways that only become costly when the air comes back.

Subject of Research: Effects of nitrogen-modified atmosphere storage and re-aeration on central carbon metabolism and quality deterioration in stored paddy rice

Article Title: Nitrogen-modified atmosphere with re-aeration storage triggers deterioration in paddy rice by disrupting central carbon metabolism

Article References: Chen, M., Xue, F., Li, M., Liu, X., Zhang, Y., & Qu, C. (2026). Nitrogen-modified atmosphere with re-aeration storage triggers deterioration in paddy rice by disrupting central carbon metabolism. Food Chemistry: X, 39, Article 104524. https://doi.org/10.1016/j.fochx.2026.104524

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104524

Keywords: paddy rice, nitrogen-modified atmosphere storage, re-aeration, central carbon metabolism, glycolysis, TCA cycle, pentose phosphate pathway, ATP synthase, targeted metabolomics, grain storage quality, oxidative stress, seed germination