(1) Dehumidification: Freshly harvested or purchased shiitake mushrooms typically have a moisture content ranging from 85% to 95%, which is not suitable for cryogenic storage, transportation, and export. To meet these requirements, it is essential to perform dehumidification—removing excess moisture from the mushrooms. The ideal moisture level for exporting fresh shiitake depends on the packaging type and refrigeration duration. For small packages, moisture should be controlled between 80% and 90%, while large packages require moisture levels of 70% to 80%. Dehumidification methods include drying with air, using dehumidifiers, or combining hot air drying with dehumidifying machines.
(2) Sorting and Slicing: After cooling, fresh mushrooms must be sorted and graded based on size to ensure uniformity in appearance and ease of packaging, storage, and sale. Proper grading helps in clearly marking prices and highlighting premium qualities. Grading standards usually divide mushrooms into large (L), medium (M), and small (S) based on cap size, and into special grades (A and B) depending on openness and appearance. Some systems further categorize caps into four sizes: 3 cm, 4 cm, 6 cm, and 8 cm. In China, grading standards are not yet standardized and often depend on merchant preferences. A common three-tier system divides caps by diameter: over 5.5 cm as L, 4.5–5.5 cm as M, and 3.5–4.5 cm as S. Some also use weight as a criterion. For export, mushrooms should be round, with thick stems, neat edges, dark brown color, and a cap diameter of at least 3.5 cm. They must have low moisture, no debris, disease, or insect infestation, and maintain their natural shape. The sorting process involves removing unsuitable mushrooms and classifying them according to established standards, either manually or using mechanical screens.
(3) Pre-cooling and Cold Storage: Pre-cooling and refrigeration are crucial steps in maintaining the freshness and quality of shiitake mushrooms. Without pre-cooling, direct packaging and low-temperature transport can reduce shelf life and increase energy consumption. Pre-cooling reduces respiration, nutrient loss, and enzyme activity, preventing browning and delaying physiological changes. It also ensures optimal moisture levels for efficient cold storage. Air cooling is the most common method, with forced ventilation being widely used due to its simplicity and cost-effectiveness. This method relies on refrigerants to cool the air inside the storage facility. Fixed-type small refrigerators are commonly used, featuring mechanical refrigeration systems that maintain temperatures between 1°C and 4°C. During pre-cooling, mushrooms should be placed in plastic baskets, avoiding stacking and ensuring proper airflow. The temperature must remain above 0°C to prevent freezing. Proper humidity control is also essential, with relative humidity kept around 75% to avoid condensation and spoilage. Regular ventilation is necessary to remove gases like carbon dioxide and ethylene, which can cause deterioration if left unchecked.
(4) Scientific Packaging: Scientific packaging plays a vital role in preserving the quality of fresh shiitake mushrooms during transport. It involves using appropriate materials such as vacuum-sealed plastic bags, net bags, or tray-style stretch films. These materials help regulate oxygen and carbon dioxide levels, creating an environment that slows down respiration and microbial growth. By reducing oxygen concentration and increasing CO₂, the preservation period is extended, and the risk of spoilage is minimized. Additionally, scientific packaging enhances product aesthetics, improves shelf display, and increases market competitiveness. Common packaging dimensions include 15 cm x 11 cm x 2.5 cm for 100 g, 15 cm x 11 cm x 3 cm for 200 g, and 15 cm x 11 cm x 4 cm for 300 g. Stretch film used is typically 300 mm wide, with a thickness of 10–15 micrometers. Materials like low-density polyethylene (LDPE) and polypropylene (PP) are commonly used for trays and cling films, offering good water resistance and breathability.
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