A Detailed Guide to the Application of Fresh-keeping Technology for Exported Garlic

Garlic is one of the main varieties of agricultural products exported from China, with an annual export volume of about 300,000 tonnes. Of this, refrigerated (fresh-keeping) garlic accounts for about 60% of total exports. Therefore, whether the fresh-keeping technology is mature has a direct impact on the quality of exported fresh-keeping garlic.

I. The fresh-keeping principle of garlic

After the cloves of a garlic bulb develop and mature, the bulb immediately enters a dormancy period of 1-2 months, during which it will not sprout even under suitable environmental conditions such as temperature, humidity and gas composition. After the dormancy period, the bud sheath and bud primordium begin to grow and become active, and under suitable conditions the young sprouts gradually germinate. In practice, the storage and fresh-keeping of garlic means that after the dormancy period of the bulb, necessary measures are taken to create unsuitable growing conditions and thereby force it to remain dormant. That is, through appropriate low-temperature, low-oxygen and other measures, its intensity of life activity is inhibited, the rate of consumption of its substances is reduced, and its original fresh state is maintained.

II. Common methods for garlic storage and fresh-keeping

(1) High-temperature storage. Placing garlic in a relatively high temperature environment of between 28-32°C can keep it from sprouting and thereby prolong its storage time, but this method is only suitable for shorter storage periods, because the bulbs easily lose water, become spongy and shrivel.

(2) Low-temperature storage. Mechanical refrigeration (storage in a constant-temperature cold store) is used to lower the temperature, inhibit its life activity and control the germination of the cloves. This method is currently widely used.

(3) Controlled-atmosphere storage. Making use of the inhibitory effect of the gaseous environment on life activity, the gas composition is adjusted under suitable low-temperature conditions to achieve the purpose of fresh-keeping.

(4) Irradiation fresh-keeping. Co gamma rays are used to irradiate the garlic bulbs, inhibiting the young sprouts and killing insects and microorganisms, and it is suitable for storing garlic for a relatively long time.

III. The main technical conditions for constant-temperature storage and fresh-keeping

(1) The quality and grade of the garlic. The quality of garlic used for storage should be strictly controlled: choose bulbs with no mechanical injury, no insect damage, no mildew, normal outer skin colour, uniform size and no separating of the cloves, and they must be fully sun-dried until dry.

(2) Time of storage and storage temperature. Garlic should be put into storage before its physiological dormancy period ends, that is, by the end of July or the beginning of August. At the time of storage, high-density plastic woven bags are generally used, which can both reduce knocking and bruising and have a certain moisture-retaining and gas-retaining effect. Garlic is highly tolerant of low temperatures and will not suffer freezing injury even at -7°C for a short time; generally the storage temperature for garlic should be controlled between -2.5 and 3.5°C, and later between -3.5 and 4.5°C. The temperature difference should be controlled within 1°C; too great a temperature difference easily stimulates enzyme activity, triggers life activity, and consequently leads to sprouting or shrivelling.

(3) Humidity. The relative humidity for garlic storage and fresh-keeping is generally between 70% and 80%; too high a humidity easily leads to mould, while too low a humidity easily leads to water loss and weight loss, causing "sponginess". During storage, owing to reasons such as frost formation on the condenser, the ambient humidity inside the store gradually decreases, so some water needs to be added frequently, commonly known as "topping up with water". The commonly used "topping up with water" method is to spray the floor with saturated limewater or salt water; this kind of water has a low freezing point and also has a certain sterilising effect.

(4) Gas composition. Garlic has a relatively strong tolerance for carbon dioxide, up to 16%. During storage it can generally be controlled between 12%-15%, and the oxygen concentration must not be lower than 1%, otherwise the garlic will suffer poisoning and deterioration.

IV. Routine management

(1) Measure the gas composition regularly and irregularly, arrange ventilation time reasonably, and prevent the garlic from carbon dioxide poisoning and deterioration.

(2) The store door must be managed by a designated person, and random entry and exit are prohibited, so as to prevent the spread of pathogens and the phenomenon of "cold leakage".

(3) Pay attention to the temperature near the fans and air ducts to prevent the garlic from freezing injury, and when problems are found, timely measures must be taken to cover it with straw curtains or gunny sacks.