Potato Storage Methods and Key Technical Points

Potato, also known as tater, yam, and earth apple, belongs to the Solanaceae family, and its edible organ is the underground tuber. It is rich in starch and protein, serving as both a vegetable and a staple food, and can also be used as feed; it is also a raw material for industries producing starch, alcohol, glucose, and the like.

The potato originated in the high mountain regions of Peru and Chile in South America and is now widely distributed throughout the world. In some European and American countries it is mostly used as a staple food. It was introduced into China in 1650. At present, it is cultivated most extensively in the high mountain areas of the Northeast, Northwest, and Southwest. The potato prefers cool conditions and avoids high temperatures, yet it is not tolerant of severe cold or frost. In cool regions, single-crop cultivation with spring planting and autumn harvest is mostly practiced, while in hot regions, double-crop cultivation with spring and autumn planting is mostly practiced.

After harvest, the potato is still a living organism, and during storage, transport, @#@136@#@, it continues to carry out metabolism, which is the main factor affecting potato storage and freshness. After the tubers are harvested, the dormancy and sprouting process is divided into three stages.

The first stage is called the tuber maturation period, that is, the early storage period. It is manifested in that the tuber skin has not yet fully suberized, and water within the tubers evaporates outward rapidly. Due to vigorous respiration and a significant increase in water evaporation, tuber weight decreases markedly, and because of the relatively high temperature, water vapor easily accumulates and causes tuber rot. After about 20-35 days of after-ripening, the skin becomes fully suberized, and as evaporation intensity and respiration intensity gradually weaken, the tubers enter a dormant state.

The second stage is called the tuber resting period, or deep dormancy period, that is, the mid-storage period. During this period, tuber respiration slows down, and nutrient consumption is reduced to a minimum. If suitable low-temperature conditions are maintained, the tuber dormancy period can be kept for a relatively long time, generally reaching about two months, and at most more than 4 months. If temperature is well controlled, rapid passage through the dormancy period can be promoted as needed, or the dormancy period can be prolonged to induce forced dormancy.

The third stage is the late dormancy period, also called the sprouting period, that is, the late stage. At this time, potato dormancy ends and respiration becomes vigorous again; meanwhile, because the heat produced by respiration accumulates and raises the storage temperature, the tubers are prompted to sprout rapidly. At this time, the degree of tuber weight loss is proportional to the degree of sprouting. If a certain low-temperature condition can be maintained during this period and ventilation of the storage facility strengthened so that the O2 and CO2 concentrations inside the packaging are kept within a certain range, the tubers can be kept in a state of forced dormancy and sprouting delayed, which is very important for extending the fresh-keeping storage period of potatoes. This is because sprouting causes a large amount of starch contained in the potato tuber tissues to be converted and causes the appearance to become wilted; at the same time, toxic substances are produced at the sprouting sites of the potato, causing losses in sales and processing, and even complete loss of edible value.

During storage, the starch and sugar contained in potatoes can be interconverted. These conversions are governed by temperature. At low temperatures, the sugar content in the tubers gradually increases. This is because respiration slows down, and the oxidation of sugar as a substrate during respiration is much slower than the hydrolysis of starch within the tissues, so the sugar formed is not consumed and accumulates in the tissues. Conversely, at high temperatures, sugar is synthesized into starch again, and the sugar consumed by respiration also increases relatively, so the sugar content continuously decreases.

Under conditions of a temperature of 15-20°C and a relative humidity of 85%-90%, the mechanical wounds of potatoes will form a dense suberized protective layer in about 1 week, preventing O2 from entering the tubers, and can also control water loss and the invasion of various microorganisms, which is beneficial for storage. Therefore, the above treatment can be carried out before potatoes are put into storage.

When pre-storing in a cool, ventilated place after harvest, select tubers that are free from disease and insect damage and not wilted and put them into baskets, with each basket holding 20-25 kg. Stack them in a cold storage facility. Gaps should be left within and between stacks to facilitate air circulation.

Within one week after being put into storage, use fans to exhaust air and exchange air 2-3 times per day until the tuber skin is dry, after which ventilation is gradually reduced. The suitable vegetable stack temperature for long-term storage is 2-3°C, and the cold storage temperature is 1-2°C.

A recently developed potato fresh-keeping measure is the use of film-forming preservatives. That is, using film-forming agents such as chitin, chitosan, maltodextrin, konjac glucomannan, sodium alginate, paraffin, and beeswax sucrose ester, with certain antibacterial agents and antioxidants added, to carry out coating preservation by soaking to form a film, brushing on a film, or spraying. Coating preservation is very effective and also has the functions of modified atmosphere and inhibiting respiration, with broad application prospects.

In the early storage period, the stacks should be turned and inspected once about every 2 weeks to remove rotten tubers. Afterward, inspect once about every one month. In order to inhibit sprouting in the late storage period, about two months after harvest, tubers may also be treated with methyl naphthaleneacetate. Use 0.4-0.5 kg of the chemical per 10 t of potatoes, add 15-30 kg of fine soil to make a powder, and sprinkle it among the tubers. Methyl naphthaleneacetate is a volatile substance, taking effect through volatilization and disappearing through volatilization.

Using 60Co gamma-ray irradiation treatment on potatoes has an obvious sprout-inhibiting effect and is currently a technique with a very good sprout-inhibiting effect in long-term potato storage. The general irradiation dose is 8-15 krad. Under the same dose, the higher the dose rate, the more obvious the effect. Radiation treatment can destroy the synthesis of auxin at the growth points of potato tubers and weaken respiration, and can significantly extend the storage period of potatoes.

Under suitable conditions, potatoes can be stored for 7-9 months.