Fresh mushrooms must meet specific quality standards before processing. The cap diameter should be 4 cm or larger, with firm and thick flesh, a smooth surface, and no visible damage. The moisture content of fresh mushrooms should remain above 90%, and they should not be washed with water to maintain their natural hydration.
Dehydration is essential depending on the transportation method. For air transport, the moisture content must be below 90%, while for sea shipping, it should be between 65% and 70%. It's important to ensure that the mushrooms do not wrinkle due to excessive drying. There are three common dehydration methods:
1. **Cold Air Dehydration**: This method involves using a cold air blower to gently remove some moisture from the mushrooms. It’s ideal for small air shipments and is best performed in winter when temperatures are naturally low.
2. **Sun Drying and Oven Drying**: Fresh mushrooms are first placed in the sun until slightly dry, then transferred to a dryer and baked until the surface turns white. They must be removed immediately to avoid over-drying. This technique effectively lowers moisture content and is suitable for both sea and air transport in large packages.
3. **Low-Temperature Drying**: A dehumidifier is used in a high-temperature warehouse to reduce humidity, followed by the use of a refrigerator fan to dry the mushrooms at a lower temperature. After 2–3 days, the mushrooms will have a white surface and the desired moisture level. This method is versatile and suitable for both sea and air transport.
After dehydration, fresh mushrooms need to be carefully graded. For example, M-grade mushrooms have a diameter of 4–5 cm, with six per box; L-grade mushrooms measure 5–6 cm, with four per box; and 2L-grade mushrooms are 6–7 cm in diameter, with two per box. The stem length should be approximately 2 cm.
Packaging depends on the size. Small packages are placed in plastic boxes inside cartons, available in 8,000 and 10 kg sizes. Large packages are packed in big bags and placed in foam boxes, with options of 5 kg or 10 kg. When preparing large packages, the mushrooms should first be cooled to 0°C in a cold room, then vacuum-sealed in storage bags before being placed in foam boxes. The mix of mushroom grades should follow certain percentages: M-grade less than 25%, L-grade around 50%, and 2L-grade about 25%.
Finally, all packaged mushrooms should be stored in a cold room. If no cold storage is available, the warehouse temperature should be kept near 0°C. Small packages should not be stored for more than 3 days, as prolonged storage may cause the caps to darken and the stems to turn black, leading to a decline in quality and difficulty in selling.
Polyhydroxyalkanoates PHAs
Polyhydroxyalkanoates (PHAs) comprise a group of natural biodegradable polyesters that are synthesized by microorganisms. However, several disadvantages limit their competition with traditional synthetic plastics or their application as ideal biomaterials. These disadvantages include their poor mechanical properties, high production cost, limited functionalities, incompatibility with conventional thermal processing techniques and susceptibility to thermal degradation. To circumvent these drawbacks, PHAs need to be modified to ensure improved performance in specific applications. In this review, well-established modification methods of PHAs are summarized and discussed. The improved properties of PHA that blends with natural raw materials or other biodegradable polymers, including starch, cellulose derivatives, lignin, poly(lactic acid), polycaprolactone and different PHA-type blends, are summarized. The functionalization of PHAs by chemical modification is described with respect to two important synthesis approaches: block copolymerization and graft copolymerization. The expanded utilization of the modified PHAs as engineering materials and the biomedical significance in different areas are also addressed.
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