Detailed Explanation of Key Points of Post-harvest Fresh-keeping Technology for Mushrooms
Freshly harvested mushrooms are prone to discoloration, off-flavors, deformation, weight loss and quality decline at room temperature, which reduces the selling price and edible value of fresh mushrooms. In order to extend the fresh-keeping time of fresh mushrooms, the following techniques can be adopted for fresh-keeping storage.
?I. Low-temperature fresh-keeping technology:
Low-temperature storage inhibits the metabolism of fresh mushrooms and the activity of spoilage microorganisms by lowering the ambient temperature, maintaining the freshness, color and flavor of mushrooms within a certain period of time. Low-temperature storage is a commonly used fresh-keeping storage technology for mushrooms. There are generally 2 methods.
1. Ice storage: In cold seasons, naturally frozen ice is collected and stored in a centralized ice storage site. In warm seasons, mechanical refrigeration is used to obtain ice blocks for fresh-keeping storage. Air conditioning can also be used to cool down the cultivation of mushrooms, with machine ice for fresh-keeping. The specific method is as follows: use silicon window bags for packaging, with a suitable loading amount of 1-2.5 kg per bag, adjust the oxygen concentration inside the bag to 1% and the carbon dioxide concentration to 2.5%, then pack them into cartons with ventilation holes, with 10 kg per box, to facilitate ventilation.
2. Cold storage: After mushrooms are harvested, trim the mushroom stems, grade them, and rinse them clean with clean water. If color protection is needed, rinse with a 0.01% sodium metabisulfite aqueous solution for 3-5 min, then use vacuum cooling or ice water for pre-cooling treatment, so that the mushroom body temperature drops to 3-5°C, drain and put into the warehouse, in order to reduce the pressure of a large amount entering the warehouse at one time and avoid too large temperature fluctuations in the cold storage. Generally, the cold storage temperature should be kept at 1-3°C, and the relative humidity at 90%-95%. At the same time, attention should also be paid to frequent ventilation, controlling the carbon dioxide concentration in the cold storage to no more than 0.3%, so that mushrooms stored in the cold storage can be kept fresh for about 1 week.
????II. Modified atmosphere fresh-keeping technology:
After the picked fresh mushrooms are rinsed and graded, drain the water, and pack them separately in plastic bags or put them into ventilated plastic boxes. Adjust the oxygen concentration in the bags or in the cold storage to 1% and the carbon dioxide concentration to 2.5%, so that the oxygen concentration is moderately reduced and the carbon dioxide is increased. In this environment, the mushroom caps open and the stipes elongate extremely slowly, growth is obviously inhibited, very few caps open, and the mushrooms remain white. Modified atmosphere fresh-keeping can be used in mushroom sales activities.
?III. Irradiation fresh-keeping technology:
Place the rinsed fresh mushrooms in porous polyethylene plastic bags and irradiate with 66Co rays at a dose of 2000-3000 gray. After irradiation, store at 10°C. Irradiated mushrooms evaporate less water, and browning, membrane rupture and cap opening of fresh mushrooms are obviously inhibited. After irradiation with 3000 gray, at room temperature 16-18°C and relative humidity 65%, they can be stored for 4-5 days; if stored at a lower temperature, the storage time will be longer. Irradiation fresh-keeping is a new technology for mushroom fresh-keeping and has many advantages compared with other preservation technologies. It can better maintain the fresh state of the mushroom body, has no chemical residues, saves energy, has a high processing rate, can operate continuously, and is suitable for automated production. It is a fresh-keeping method with broad prospects.
?IV. Chemical fresh-keeping technology
Chemical fresh-keeping storage of mushrooms is only used for short-term storage or color protection of mushrooms. The commonly used ones are as follows:
1. Dilute hydrochloric acid fresh-keeping: Soak mushrooms in a 0.05% dilute hydrochloric acid solution. The acid liquid gradually penetrates into the mushroom tissue, bringing the pH value inside the mushroom body below 6, in order to inhibit enzyme activity, lower the metabolic level of mushrooms, slow down the speed of browning and cap opening, and at the same time also inhibit the reproduction and growth of spoilage microorganisms.
2. Brine treatment: After washing the fresh mushrooms clean, put them into 0.6% brine and soak for 10 min, then remove and drain the water. Under conditions of 10-25°C, after 4-6 h, the mushrooms can turn white, which can reduce cap opening.
3. Rinse the mushroom bodies with a 0.05% sodium metabisulfite aqueous solution for 3-5 min, then soak with 0.1% sodium metabisulfite for 30 min, remove and drain, put into plastic bags for storage. Under conditions of room temperature 10-15°C, the fresh-keeping effect is good, and the color can remain white for a long time. However, note that when eating or processing mushrooms that have been fresh-kept and color-protected with sodium metabisulfite solution, they should first be washed with clean water 2-3 times, until the sulfur content is below 20 mg/kg.