Oyster Mushroom Heat Pump Drying at 50°C
A preliminary process study comparing drying time, final moisture and selected nutritional indicators with conventional hot-air drying.
This preliminary study evaluated oyster mushroom heat pump drying using fresh Xiuzhen mushrooms collected in Luoyuan County, Fuzhou. At a reported 50°C setpoint, heat pump drying reduced moisture to 5.01% in 6 hours, while the conventional hot-air comparison reached 12.96% after 18 hours.
Study objective and raw material
The work was conducted by Cheng Lin of the Fuzhou Municipal Bureau of Agriculture and Rural Affairs. Its objective was to test whether a programmable heat pump dryer could shorten drying time while maintaining appearance and selected nutritional indicators in Xiuzhen mushroom products.
Fresh mushrooms were transported from Luoyuan County to the laboratory in an ice-cooled insulated box within 2 hours of harvest. Samples with disease, insect damage, abnormal odor or mechanical injury were excluded. The source does not provide a scientific name for Xiuzhen mushroom. This edition therefore uses the commercial name and the broader oyster mushroom group rather than assigning an unverified species.
Dryer and analytical equipment
The experimental dryer combined PLC control with an MCGS touchscreen. It recorded drying-room and ambient temperature and humidity, displayed process curves and alarms, stored historical data, and allowed manual intervention when automatic operation required correction.
| Equipment | Model or control system | Primary use |
|---|---|---|
| Intelligent heat pump drying cabinet | PLC and MCGS control, self-developed | Controlled drying and environmental logging |
| Moisture analyzer | MA35 | Hourly moisture measurement |
| Microplate reader | SpectraMax i3x | Colorimetric assays |
| Dual-beam spectrophotometer | UV-6100PC | Absorbance measurements |
| Refrigerated centrifuge | J2-MC | Sample preparation |
| Analytical balance and water bath | BSA223S and HWS24 | Weighing and controlled reactions |
Reported heat pump drying process
- Remove the root base and spread the mushrooms on trays.
- Set the heat pump dryer to 50°C. The manuscript also reports a 5°C temperature differential or control band.
- Measure material mass or moisture once every hour.
- Continue drying until moisture is approximately 5%.
- Cool the product before sealed storage or further quality assessment.
The moisture curve showed a rapid phase followed by a slower phase. Moisture fell from 87.50% to 9.02% during the first 4 hours, then declined more gradually to 5.01% at 6 hours. This transition is consistent with the progressive depletion of readily removable water, but the source does not fit a kinetic model or report air velocity, relative humidity, tray loading or mushroom size distribution.
Laboratory analysis
The study compared fresh mushroom material with heat-pump-dried and hot-air-dried products. Analyses were repeated three times according to the manuscript, but replicate-level values and measures of dispersion were not reported.
| Indicator | Extraction or reaction | Reported reading | Interpretive caution |
|---|---|---|---|
| Moisture | Approximately 2 g dried sample | Moisture analyzer | Water activity was not measured. |
| Ascorbic acid | Trichloroacetic-acid extraction and colorimetric reaction | 534 nm for samples; an earlier passage lists 540 nm | The wavelength discrepancy should be resolved before replication. |
| Soluble sugars | Water extraction followed by anthrone colorimetry | 630 nm | Results are concentration values, not nutrient-retention yields. |
| Reducing sugars | Water extraction followed by 3,5-dinitrosalicylic-acid colorimetry | 540 nm | Extraction recovery and dry-basis conversion were not reported. |
Laboratory teams should use validated institutional methods, certified standards, blanks, calibration acceptance criteria and appropriate chemical-safety controls. AOAC Official Methods provide a recognized framework for food-composition testing, but the exact applicable method must be selected for the matrix and analyte.
Drying efficiency and product quality
| Indicator | Fresh sample | Heat pump dried | Hot-air dried |
|---|---|---|---|
| Final moisture | 87.50% initial | 5.01% after 6 h | 12.96% after 18 h |
| Ascorbic acid | 35.52 mg/100 g | 220.21 mg/100 g | 63.29 mg/100 g |
| Soluble sugars | 6.38% | 86.48% | 86.07% |
| Reducing sugars | 4.95% | 25.94% | 25.19% |
The heat pump process was substantially faster in this test. Heat pump drying reached 5.01% moisture in 6 hours, while conventional hot-air drying reached 12.96% after 18 hours. The manuscript also states that approximately 10% moisture was reached after about 4 hours with the heat pump.
Dried mushrooms retained good cap color and mushroom aroma. The stipe and lower cap were described as slightly yellow. Compared with the hot-air product, the heat pump product was reported to have better color retention.
How to interpret the nutrient values
Ascorbic acid was reported at 220.21 mg/100 g in the heat pump product and 63.29 mg/100 g in the hot-air product. The heat pump value was 3.48 times the hot-air value. Soluble sugar values were similar between dried treatments at 86.48% and 86.07%, while reducing sugars were 25.94% and 25.19%.
These figures should not be read as evidence that drying created nutrients. Fresh mushrooms contained close to 90% water. Removing water concentrates solids on a wet-weight basis, so dried samples can show much higher values per 100 g even when some nutrient loss occurs. A true retention comparison requires matched dry-matter calculations, total batch mass, extraction recovery and uncertainty estimates.
Recommendations for a production pilot
- Confirm the mushroom species or commercial strain and define harvest maturity.
- Standardize trimming, tray loading, cap size and product depth.
- Log dry-bulb temperature, relative humidity, airflow and product-core temperature.
- Measure final moisture and water activity at several tray positions.
- Record electricity consumption and calculate specific moisture extraction rate.
- Compare color, shrinkage, texture, rehydration, aroma and microbial stability.
- Report means, variability, sample size and statistical tests.
- Validate packaging and shelf life before commercial release.
Author and provenance
Original Chinese study: Cheng Lin, Fuzhou Municipal Bureau of Agriculture and Rural Affairs. “Preliminary Study on the Application of Heat Pump Drying Technology to Xiuzhen Mushrooms,” published in the technical section of the 2024 China Edible Mushroom Industry Yearbook.
Editorial note: This English edition is a technical adaptation of the supplied printed pages. The original tabulated values are preserved, while methodological ambiguities and limits are stated explicitly. Product names and instrument models are reported for reproducibility, not as endorsements.
References
- Lin C. “Preliminary Study on the Application of Heat Pump Drying Technology to Xiuzhen Mushrooms.” 2024 China Edible Mushroom Industry Yearbook, pp. 178-182. Source pages supplied for this article.
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- AOAC INTERNATIONAL. Official Methods of Analysis, 22nd edition. Official methods overview.
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