Detailed Explanation of the Development Method and Production Process of Oyster Mushroom Yogurt

Oyster mushroom is an edible fungus that is easy to cultivate, has high yield, and is deeply loved by the general public. Oyster mushroom has tender flesh, a delicious taste, and rich nutrition. Every 100g of dried mushroom contains 23-28g of protein and 1.42-2.87g of fat; the protein contains 18 kinds of amino acids, and the 8 essential amino acids for the human body and 2 semi-essential amino acids (arginine, histidine) account for about 40-50% of the total amino acid content. It also contains trace elements such as phosphorus, potassium, iron, zinc, and copper, as well as rich Vc. Oyster mushroom has very high medicinal value, with anti-tumor and immunity-enhancing effects. Oyster mushroom also contains taurine, gamma-aminobutyric acid, and other substances that promote human health. Regular consumption of oyster mushroom has a clear effect on reducing cholesterol in the human body, lowering blood pressure, and improving health. Yogurt is a functional food that combines nutrition and health benefits. It not only has a unique flavor, but also contains a large amount of lactic acid bacteria and their decomposition products, which can inhibit the survival of other harmful bacteria in the gastrointestinal tract, promote digestion, prevent and treat diseases, and improve health. Therefore, by adding oyster mushroom to cow's milk and subjecting it to lactic acid fermentation, a product with the dual nutritional and health benefits of both oyster mushroom and yogurt can be produced.

(1) Materials: Select fresh oyster mushrooms that are fresh, free of off-odors, free of mold, and free of mechanical damage, as well as fresh cow's milk that meets the GB6914-86 standard. Select sucrose that meets national standards. Strains: Lactobacillus bulgaricus (abbreviated as L.B) and Streptococcus thermophilus (abbreviated as S.T), each activated for 5 generations and then made into a working starter (L.B:S.T = 1:1). The equipment used includes a pulping machine, high-pressure homogenizer, drying oven, constant-temperature incubator, ultra-clean workbench, refrigerator, etc.

(2) Methods: Preparation of oyster mushroom juice: Remove the roots and impurities from fresh oyster mushrooms, wash them clean in clear water, cut them into pieces, put them into a pot with a small amount of clear water, add 0.2% citric acid and 0.1% Vc at the same time, heat at 95-100°C for 30 minutes, and cool rapidly; add an equal amount of water to the cooled oyster mushrooms and pulverize with a pulping machine, then finally filter through 120-mesh silk cloth to obtain oyster mushroom juice. Oyster mushroom yogurt process flow: ① Fresh cow's milk -> filtration and purification -> preheating -> mixing -> homogenization -> sterilization -> cooling ② Pure lactic acid bacteria culture -> mother starter -> working starter -> inoculated into the cooled semi-finished product from ① -> packaging -> constant-temperature cultivation -> refrigeration -> finished product. Process key points: Carry out according to the processing technology of ordinary yogurt, that is, when the milk temperature is 60-65°C, add 6% white sugar and different amounts of oyster mushroom juice. To prevent the addition of oyster mushroom juice from reducing the dry matter content of the milk, add 3% milk powder and mix evenly. After homogenization (pressure 18-20 MPa), raise the temperature to 90-95°C and hold for 5-10 minutes for sterilization, then rapidly cool to 40°C, add 3% working starter (L.B:S.T = 1:1), ferment at a constant temperature of 42°C until coagulation, and place in a 4-6°C refrigerator for refrigeration. (3) Test results: With the increase in the amount of oyster mushroom juice added, the coagulation time tended to shorten; especially when the amount of oyster mushroom juice added reached more than 20%, the effect was obvious. Therefore, when making fermented milk, the amount of oyster mushroom juice added can be selected at more than 15%. When the amount of oyster mushroom juice added was in the range of 5%-30%, the acidity of the product increased with the increase in the amount added; at the same addition amount, its acidity showed an upward trend during fermentation, cooling, and refrigeration, among which the acidity increased significantly during fermentation, and the change in acidity within 3 days of refrigeration was significantly greater than after 3 days. This is because the activity of the bacterial cells decreases under refrigeration conditions and, as time extends, metabolites such as organic acids cause the bacterial cells to further age or die. Moreover, when the addition amount was 15% and 20%, the acidity during refrigeration was close to that of ordinary yogurt. The highest acidity value of the finished product was 104.23°T, and the lowest was 92.19°T, meeting the provisions of GB2746-85. When oyster mushroom juice was in the range of 5%-30%, the more oyster mushroom juice added, the higher the number of viable bacteria in the product, and the decrease in bacterial count during refrigeration decreased as the addition amount increased. This may be because the nutrients in oyster mushroom juice promoted the growth of the bacterial cells, but when the amount of oyster mushroom juice added exceeded 30%, the number of viable bacteria during refrigeration tended to decrease. Oyster mushroom yogurt was refrigerated in a 4-6°C refrigerator for 24 hours. The test results showed that yogurt with 15-20% oyster mushroom juice added had good flavor, no off-odor, and a milky white color.

(4) Conclusion 1) Compared with ordinary yogurt, 15%-20% oyster mushroom juice yogurt has no off-odor, has the unique aroma of pure lactic acid fermentation, has a uniform and fine texture, and a color similar to ordinary yogurt. 2) Within 7 days of storing the yogurt in the refrigerator, the texture was good and no whey separated out; but after more than 7 days, whey separated out. It is recommended that the storage time of oyster mushroom yogurt in the refrigerator should preferably be within 7 days. 3) By adding 15-20% oyster mushroom juice, 6% sucrose, 3% milk powder, and inoculating 3% starter to fresh cow's milk, and following the production process of ordinary yogurt, high-quality oyster mushroom yogurt can be produced.