Strengthen the efficiency of vacuum pre-cooling of Taiwan's agricultural products

In order to strengthen the local and international production and transportation quality of Taiwan's agricultural products and the international competitiveness after China's accession to the WTO, the plan is to integrate the school's vacuum and refrigeration and other related technologies to complete fully automated mass production and laboratory vacuum precooling. The equipment was developed and tested with many agricultural production cooperatives in Taiwan. The test subjects included liquid water, leafy vegetables (pakchoi, shallots, water spinach, and spinach), and pears. The main applications of freezing in the food industry are preventing and delaying the growth of microorganisms, inhibiting chemical changes in foods and maintaining food safety supplies. The general microorganisms can be divided into four categories: bacteria, yeasts, microbes and viruses, of which the bacteria are the most important cause of food spoilage. The types include spherical, rod-shaped and screw-shaped, etc. Their sizes range from 0.3 mm to 10 mm. between. The best adaptation phase for microbial growth occurs when the microorganism first starts to grow and adapt to a new growth environment. This phase has a direct relationship with the maximum shelf life of the food. Once the adaptation period occurs, the microorganism will enter the maximum growth rate (logarithm In the long-term), under the right conditions, the amount of growth is about 1 times every 20 to 30 minutes.

The production of food toxins usually occurs at the end of logarithmic growth. When external nutrients are depleted, microorganisms enter the death phase, and their rates are related to microbial species, propagation media, and environmental characteristics. The function of freezing is to prolong the growth time of microorganisms, reduce the activity of enzymes and inhibit the production of poisons. For fruits and vegetables, their respiration rate and respiratory heat are closely related to their own temperature. However, if the stored temperature is too low, ice crystals will be produced inside the fruits and vegetables, resulting in cell damage or death. Using sweet corn as the test object, the method of vacuum pre-cooling will reduce the temperature of sweet corn to less than 4°C in 20 minutes, whereas in ordinary cold-preserved sweet corn that has not been pre-cooled, its temperature will only be after 60 minutes. The drop is about 6 to 7°C. Therefore, it can be seen that vacuum precooling is better than cold water precooling and air precooling.

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