Cold Silos, Slow Clocks: Eight-Month Experiment Reveals How Temperature Rewrites the Chemistry and Fungal Fate of Stored Rice
Rice is the daily caloric anchor for nearly half of humanity, yet very little of it reaches a bowl in the year it is harvested. Between the paddy field and the plate stretches a long, largely invisible interval of storage in which the grain keeps aging chemically—lipids splitting apart, membranes failing, proteins cross-linking—while an equally invisible fungal community quietly rewrites itself across every kernel surface. A new 240-day experiment, published in Food Chemistry: X, tracked both processes simultaneously and reached a conclusion with enormous practical weight: the difference between storing rice at 15 °C and at 25 °C is the difference between a grain bulk that ages slowly while keeping its field-born microbial identity and one that deteriorates measurably faster while drifting toward dominance by storage-adapted fungi, including species of Aspergillus, a genus that contains some of the world’s most notorious mycotoxin producers. Led by Yingying Wu and colleagues in Ningbo, in China’s Zhejiang Province, the study offers some of the most detailed paired evidence yet that temperature governs not one but two intertwined clocks of grain decline.
The team built a pilot-scale, informationally controlled silo system at Liangqiao Rice Industry Co. in Ningbo, using wooden square-compartment silos subdivided into independent units of roughly 0.15 to 0.20 cubic meters, each holding 100 to 120 kilograms of grain, for a total capacity near 500 kilograms. Continuous low-airflow mechanical aeration of about 0.05 cubic meters per minute per tonne kept the bulk ventilated, while temperature was held at either 15 °C or 25 °C with a precision of ±0.5 °C and relative humidity was maintained at 65 ± 5 percent. Three commercial Yongyou-series hybrid varieties—Yongyou 15, Yongyou 1540, and Yongyou 7860—were loaded at initial moisture contents of 12.0 to 14.2 percent and sampled every 40 days across seven time points, from day 0 to day 240. At each visit, paddy was dehusked, milled, and sieved through an 80-mesh screen before a battery of standardized assays: electrical conductivity of steeped grains, amylose content by iodine colorimetry, moisture by direct drying at 105 °C, fatty acid value by potassium hydroxide titration, malondialdehyde by thiobarbituric acid reaction, polyphenol oxidase activity, and sequential extraction of the four soluble protein fractions.
The chemical story was one of steady, temperature-accelerated decay. Electrical conductivity, a classic proxy for membrane integrity, climbed from roughly 20 to 26 microsiemens per centimeter at day zero and accelerated most sharply between days 200 and 240, because compromised membranes leak intracellular electrolytes into the soaking water. Fatty acid value—the standard gauge, under China’s GB/T 20569-2006 stored-rice rules, of the free fatty acids released when lipases hydrolyze grain lipids—rose from an initial 8 to 10 milligrams of potassium hydroxide per 100 grams and climbed significantly faster at 25 °C. Malondialdehyde, the terminal product of lipid peroxidation measured spectrophotometrically at 532 nanometers after reaction with thiobarbituric acid, rose in lockstep, confirming that hydrolysis was giving way to outright oxidative attack on membrane lipids. Meanwhile, polyphenol oxidase activity collapsed to roughly 40 percent of its starting value, falling further in the warm treatment and correlating negatively with all three deterioration indices—a biochemical signature of waning seed vigor. Temperature, the authors note, governs this cascade directly by modulating endogenous hydrolytic enzymes such as lipases and amylases, setting the pace of both lipid splitting and subsequent oxidation.
Starch and proteins told parallel stories of structural reorganization. Apparent amylose content crept upward from an initial 7 to 9 percent, a shift the researchers attribute to molecular rearrangement within starch—conversion of long chains into shorter fractions and the formation of lipid–starch complexes that behave analytically like amylose. Moisture, crucially, stayed flat at 12 to 14 percent under both treatments, a range considered safe for paddy storage and generally inhospitable to active fungal growth; that stability matters for interpretation, because it implies that shifts in fungal DNA signatures reflect changes in which propagules persist and dominate rather than unchecked proliferation on wet grain. The protein system differentiated as well: readily soluble albumins and globulins declined progressively, while the structurally robust glutelin fraction swelled above 80 percent in some variety–treatment combinations by day 240. The team proposes that storage-related protein oxidation and aggregation, possibly through intermolecular disulfide bonding, locks the labile fractions out of extraction—a mechanism flagged as plausible rather than proven, since cross-linking was not measured directly.
To capture the biological half of the equation, the researchers amplified the internal transcribed spacer 1 region of fungal ribosomal DNA with the primer pair ITS1F/ITS86R and generated paired-end, 2 × 250-base-pair reads on an Illumina NovaSeq 6000. Twenty-one representative samples were sequenced: three day-zero samples taken before any temperature treatment, and eighteen stored samples spanning three varieties, two temperatures, and days 80, 160, and 240. After quality filtering, denoising, and chimera removal with the DADA2 pipeline in QIIME2, and taxonomic assignment against the UNITE reference database, valid sequence counts ranged from 45,480 to 137,780 per sample, with Good’s coverage exceeding 0.99 everywhere—deep enough to exhaust the detectable diversity. Principal coordinate analysis of Bray-Curtis dissimilarity showed day-zero samples separating cleanly from all stored samples along the first axis, and PERMANOVA confirmed that storage duration significantly reshaped community composition at both 15 °C (F = 2.5387, R² = 0.1922, p = 0.001) and 25 °C (F = 3.1205, R² = 0.2263, p = 0.001), with succession unfolding as a continuous drift rather than abrupt, stage-wise turnover.
Compositionally, the fungal universe inside the silos belonged overwhelmingly to two phyla: Ascomycota averaged 86.5 percent relative abundance across all samples, with Basidiomycota contributing another 13.0 percent. What stands out is the tempo. Early storage was still a field world: the genus Phaeosphaeria surged to peak abundance at 80 days under both temperatures, while Fusarium, a classic field-associated genus with toxigenic members, persisted without marked enrichment. Sarocladium and Moesziomyces showed similarly staged fluctuations in both temperature regimes, evidence that fungi of field origin follow comparable ecological trajectories regardless of silo temperature. The microbial baseline carried forward from cultivation—rich in pathogens and saprobes that colonized the crop before harvest—thus persisted well into the storage period, before the community gradually pivoted toward organisms better suited to the dry, enclosed, grain-rich niche of a functioning silo. Only later, and only in the warmer bulk, did that pivot become decisive.
That pivot is the study’s sharpest finding. By day 240 at 25 °C, Aspergillus had risen to 22.4 percent relative abundance, alongside progressive enrichment of Curvularia, a thermophilic saprotroph tied to grain molding and declining eating quality, and Wallemia, an extremely xerophilic mold of stored foods. Indicator species analysis flagged Aspergillus penicillioides, Aspergillus ruber, Aspergillus restrictus, and Wallemia sebi as hallmarks of the warm, aged grain—taxa long documented in stored-grain ecosystems and, in some cases, capable of mycotoxin production under favorable conditions. Even the warm bulk’s early phase told a distinct story: at 80 days, Periconia homothallica, Curvularia hawaiiensis, and Ceratocystis fimbriata served as indicators, hinting that warm storage promoted its own succession almost immediately. The 15 °C bulk told a gentler tale: Papiliotrema was distinctly characteristic of cool storage, and cool, aged samples were rich in yeast-like taxa including Hannaella oryzae, Hannaella sinensis, and Bulleribasidium variabile. One cautionary note did surface on the cold side—Ustilaginoidea, whose member Ustilaginoidea virens produces ustiloxins, increased late in cool storage—though the authors emphasize that no toxins were quantified and relative DNA abundance cannot demonstrate toxin formation.
Connecting the two data streams, the team applied FUNGuild ecological annotation and exploratory PICRUSt2 functional prediction, then correlated dominant taxa against the chemical indices using false-discovery-rate-corrected Spearman rank statistics. FUNGuild suggested that saprotroph-associated guilds gradually gained ground at 15 °C, while pathotroph-associated guilds persisted at relatively higher levels in the 25 °C bulk. The predicted functional profile of warm, aged grain showed elevated lipid- and carbohydrate-related pathways, mirroring the observed rises in fatty acid value and amylose content. Correlation analysis found that fatty acid value, malondialdehyde, and electrical conductivity moved together—expected for coupled hydrolysis, oxidation, and membrane failure—and were positively co-associated with Wallemia sebi and Aspergillus ruber in the cool-storage comparison, and with Aspergillus penicillioides, Aspergillus restrictus, and Sarocladium strictum in the warm one. The authors are explicit that these are hypothesis-generating patterns only: because chemistry and community both shifted systematically with time, shared temporal trends cannot be excluded, and marker-gene predictions are not direct measurements of fungal metabolism.
The caveats are as instructive as the results. No mycotoxins were measured, no toxigenic genes were assayed, and amplicon sequencing reports relative abundance, never absolute fungal biomass—a 22.4 percent Aspergillus signal is an ecological flag, not a contamination verdict, and targeted toxin or culture-based analyses would be needed to establish any food-safety implication. Still, the paired design delivers a coherent mechanistic picture: cool storage simultaneously damps the enzymatic engine of lipid hydrolysis and oxidation and redirects fungal succession away from storage-adapted, risk-associated taxa and toward slower restructuring dominated by benign yeast-like lineages. For grain industries weighing the energy cost of refrigerated storage against the risk of quality loss and mycotoxin episodes, that dual leverage is precisely the evidence base that has been missing, particularly for hybrid rice varieties whose long-term storage behavior was poorly characterized. Given that rice anchors food security for billions, the study’s implicit recommendation is disarmingly simple: one of the cheapest instruments for protecting a silo’s contents may be the thermostat.
Subject of Research: Effects of storage temperature (15 °C versus 25 °C) on physicochemical quality deterioration and fungal community succession in Yongyou-series hybrid paddy rice during 240 days of simulated silo storage
Subject of Research: Chemistry
Article Title: Temperature-associated quality deterioration and fungal community succession in stored paddy rice during long-term storage
Article References: Wu, Y., Wang, Z., Liu, Y., Shi, J., Wu, Z., Shen, C., Zhang, H., & Yang, H. (2026). Temperature-associated quality deterioration and fungal community succession in stored paddy rice during long-term storage. Food Chemistry: X, 39, Article 104351. https://doi.org/10.1016/j.fochx.2026.104351
Image Credits: AI Generated
DOI: 10.1016/j.fochx.2026.104351
Keywords: paddy rice, storage temperature, fungal community succession, fatty acid value, malondialdehyde, ITS amplicon sequencing, Aspergillus, low-temperature storage, grain quality deterioration, food security
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Alan Morgan. (August 30, 2026). Temperature drives quality loss and fungal shifts in stored paddy rice. Scienmag. https://scienmag.com/temperature-drives-quality-loss-and-fungal-shifts-in-stored-paddy-rice/
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