Detailed Experimental Study on Canned Oyster Mushroom Processing Technology

Oyster mushroom is one of the main varieties of edible fungi, belonging taxonomically to the order Agaricales, family Pleurotaceae, genus Pleurotus. Oyster mushroom cultivation involves a simple process with relatively low technical difficulty, and coupled with widely available cultivation substrates, it has become the artificially cultivated variety with the highest output and largest sales volume in China's edible fungi market. It is widely cultivated in China, especially in the north, and has become a pillar industry of local agriculture in some provinces and cities. Many farmers in impoverished areas have found a path to prosperity through oyster mushroom cultivation. It is not difficult to predict that with the expansion of international and domestic markets, the improvement of urban and rural people's dietary structure, and the rise in consumption levels, oyster mushroom, as a major species of edible fungi, will inevitably see even greater development. Oyster mushroom has very high nutritional value and health benefits. Its fresh fruiting bodies are rich in amino acids and B vitamins, and also have high contents of vitamin C and ergosterol. In addition, research on the application of oyster mushroom polysaccharides and polysaccharide proteins in cancer prevention and anticancer activity has also been reported. Oyster mushrooms are mainly consumed fresh, with some used for salted processing and export. Because oyster mushroom fruiting body tissue is delicate, has high water content, and has particularly strong respiration after harvest, it is very prone to deterioration. If stored at room temperature above 16°C for 1 day, white fuzz grows on the stipe, and the cap cracks and curls at the edges, eventually leading to browning and rotting. At the same time, oyster mushroom has a large surface area and strong transpiration, and the fruiting body easily loses water, thereby causing a decrease in freshness and affecting flavor and commercial value. Therefore, the quality of fresh oyster mushrooms is very difficult to control. However, canned oyster mushrooms are safe, convenient, and hygienic to eat, can be stored for a long time at room temperature, and have stable quality, with great demand in both domestic and international markets.

1 Experimental Materials and Methods

1.1 Experimental Materials

Salted oyster mushrooms were provided by a local factory; salt and citric acid were purchased from the local market.

1.2 Experimental Instruments and Equipment

Jacketed kettle, GT4B2 vacuum seamer, steam pressure sterilizer, etc.

1.3 Experimental Methods

The process route for processing canned oyster mushrooms is: raw material selection -> desalting -> water washing -> precooking -> sorting -> cleaning -> canning -> filling with broth -> sealing -> sterilization -> cooling -> heat preservation -> inspection -> finished product.

1.3.1 Raw Material Selection Since fresh oyster mushrooms are prone to deterioration and their quality is difficult to control, salted oyster mushrooms were used as the raw material. Varieties with short stipes, thick flesh, resistance to breakage, and suitability for canning should be selected, such as excellent varieties like Pleurotus ostreatus (purple-spored oyster mushroom) and Pleurotus ostreatus (rough-skinned oyster mushroom). The raw material quality standards are: brine concentration 18°Be'-22°Be', oyster mushrooms free of off-odors, mold, pests, and mud or sand impurities, with no surface yellowing, stickiness, shrinkage, or deterioration, stipe length not exceeding 1.5 cm, and breakage rate not exceeding 5%.

1.3.2 Soaking The raw materials were placed in a soaking tank and washed with running water for desalting until the salt content of the oyster mushrooms was below 0.3%.

1.3.3 Blanching The desalted oyster mushrooms were blanched in boiling water for 2 min-3 min, then immediately cooled.

1.3.4 Sorting Impurities and oyster mushroom fragments were removed, and the mushrooms were graded according to cap size. Grade I oyster mushrooms have a cap diameter of 5 cm-8 cm, Grade II oyster mushrooms have a cap diameter of 2 cm-5 cm, and mixed-grade products contain 50% each of Grade I and Grade II oyster mushrooms.

1.3.5 Preparing the Brine The salt water mass fraction was 2.2%-2.5%, boiled for 2 min-3 min, and 0.05% citric acid was added to the boiling brine, then filtered and set aside. The brine temperature was not lower than 90°C.

1.3.6 Canning The can type selected was 7116. Empty cans were cleaned and disinfected with hot water above 85°C, drained, and then filled. The filling amount of oyster mushrooms per can was 195 g. The tissue morphology of the caps was required to be intact, and the color, size, and stipe length of the oyster mushrooms in the same can were required to be uniform and consistent. After filling the mushrooms, broth was added to each can up to 1 cm from the can opening.

1.3.7 Vacuum Sealing The can seaming machine maintained a vacuum degree of 40 kPa-53 kPa, and the center temperature of the can was not lower than 85°C.

1.3.8 Sterilization The sterilization formula was 20'-20'-counter-pressure cooling/121°C. The time from sealing to sterilization did not exceed 30 min. After sterilization, the cans were rapidly cooled to below 37°C.

1.3.9 Storage The can surfaces were wiped clean and promptly placed in a heat preservation warehouse.

2 Product Quality Requirements and Test Results

2.1 Product Quality Requirements

2.1.1 Sensory Indicators The color is light yellow, the broth is relatively clear, and a small amount of oyster mushroom fragments is allowed; it has the flavor that canned oyster mushrooms should have, with no off-odor; the cap tissue morphology is intact, uniform in size, and slightly elastic.

2.1.2 Physicochemical Indicators The product specification is a net mass of 425 g, and its physicochemical indicators are shown in Table 1.

Table 1 Physicochemical Indicators of Canned Oyster Mushrooms

Test Item|Standard Requirement|Test Result|

Net mass g|A tolerance of 3% per can is allowed|430|

Solid content g|Not less than 52% of net mass|235|

Sodium chloride content %|0.8-1.5|1.00|

Copper mg/kg|<=10|0.30|

Tin mg/kg|<=200|0.01|

Lead mg/kg|<=1|0.10|

2.1.3 Microbiological Indicators Total bacterial count not greater than 10 per mL; coliform bacteria not greater than 6 per mL; no pathogenic bacteria detected.

3 Nutritional Composition Analysis of Canned Oyster Mushrooms

After the product was stored at room temperature for 3 months, its nutritional composition was tested, and the results were: every 100 g of canned oyster mushrooms contained 89.02 g water, 3.84 g protein, 0.46 g fat, 4.58 g carbohydrates, 1.10 g fiber, and 2.10 g ash.

4 Precautions

(1) Canned oyster mushrooms are a low-acid food. If the raw materials are contaminated or sterilization during processing is incomplete, the contents are prone to acid spoilage and deterioration, which is caused by the proliferation of thermophilic spoilage bacteria (flat-sour bacteria) in the can. Therefore, in production, process operating regulations must be strictly followed, hygiene management must be strengthened, and the sealing quality of cans must be strictly controlled. In addition, the spore count of thermophilic spoilage bacteria should be regularly tested on raw materials, semi-finished products, and sealed canned products before sterilization, so as to guide and monitor the production process.

(2) During production, the operation process should be shortened as much as possible to reduce the exposure time of raw materials, so as to avoid contamination caused by the accumulation of semi-finished products.

(3) Contact between oyster mushroom raw materials and metal tools such as iron and copper should be prevented. Utensils, work tables, and the like used in processing should preferably be made of stainless steel.

(4) In addition to tinplate cans, packaging containers may also use twist-off glass jars and retort pouch flexible packaging.