Detailed Explanation of Key Points of Potato Storage and Fresh-Keeping Technology

The edible part of the potato is the tuber, which contains a large amount of carbohydrates and rich mineral elements. Potatoes are resistant to storage and transportation and can be supplied year-round. They are a popular fresh-eating vegetable and raw material for processed products that help balance market supply during off-peak and peak periods.

I. Storage and Characteristics

After harvest, potatoes generally have a dormant period of 2-4 months, and the length of the dormant period varies with different varieties. Late-maturing varieties have a short dormant period, while early-maturing varieties have a long dormant period. Different degrees of maturity also affect the length of the dormant period. The dormant period of immature potato stems is longer than that of mature ones. Storage temperature also affects the length of the dormant period; in particular, low temperatures in the early storage period are very favorable for prolonging the dormant period.

Potatoes are rich in starch and sugar, and during storage, starch and sugar can be mutually converted. When the temperature drops to 0°C, starch hydrolysis activity increases, monosaccharides accumulate in the tubers, the tubers become sweet, the eating quality is poor, and processed products undergo browning. If the storage temperature rises, monosaccharides will again synthesize into starch. When the temperature is higher than 30°C or lower than 0°C, the tuber flesh is prone to turning black.

II. Varieties and Harvest

Choosing potato varieties with a long dormant period can extend the storage period. Early-maturing varieties, varieties cultivated in cold regions, or autumn-cropped potatoes have a long dormant period, which is favorable for storage. In the late growth stage of potatoes, excessive irrigation should not be applied. Increasing the application of phosphorus and potassium fertilizers can improve the storability and disease resistance of potatoes. In northern China, spring-planted potatoes are mostly harvested before the rainy season arrives in July; summer and autumn plantings are mostly harvested in mid-September. When the aboveground stems and leaves of the potato turn yellow, lodge, and wither, the potatoes can be harvested. Harvesting should be carried out on sunny days, and the tubers should be dried in place for about half a day to release part of the moisture, so that the potato skin becomes dry, thereby reducing the incidence of disease during storage.

III. Storage Conditions

The suitable storage temperature for fresh-eating potatoes is 3-5°C, but potatoes used for making potato chips or French fries should be stored at 10-13°C. The suitable relative humidity for storage is 85%-90%. Too high humidity easily increases rot, while too low humidity increases water loss and causes the tubers to shrink. Light can promote potato sprouting and increase the solanine glycoside content in the tubers. The solanine glycoside content of normal tubers does not exceed 0.02%, which is harmless to humans and livestock, but after the tubers are exposed to light or sprout, the solanine glycoside content increases sharply and has toxic effects on humans and livestock. Therefore, potatoes should be stored away from light.

IV. Storage Methods and Management

1. Trench storage. Potatoes harvested in mid-July are pre-stored in a shade shed or empty room until they are placed in trenches for storage in October. The trench is 1-1.2 m deep and 1-1.5 m wide, with no limit on length. The tuber layer is 40-50 cm thick, and can reach 70-80 cm in cold regions. Soil is covered on top for insulation, and covering should be done in stages as the temperature drops. The potatoes piled in the trench should not be too high. Otherwise, the temperature at the bottom and middle of the trench tends to be too high, and heating of the tubers will cause rot.

2. Cellar storage. When using well cellars or cave cellars to store potatoes, each cellar can store 3000-3500 kg. Since only the cellar opening is used for ventilation to regulate temperature, the insulation effect is relatively good. However, it is not easy to lower the temperature in the early stage after being put into the cellar, so the potatoes should not be loaded too full, and attention should be paid to opening and closing the cellar opening. As long as management is proper, the storage effect for potatoes is very good. When using a shed cellar for storage, the covering layer on the top of the cellar should be thickened and the cellar body deepened to avoid freezing injury. The height of the potato pile in the cellar should not exceed 1.5 m; otherwise, it is prone to heating in the early stage after being put into the cellar, causing sprouting and rot.

3. Ventilated storehouse storage. Generally, the stack height should not exceed 2 m, and ventilation tubes should be set inside the stack. Loading into baskets and stacking for storage makes management more convenient and increases storage capacity. Regardless of which storage method is used, a certain gap should be left around the potato pile to facilitate ventilation and heat dissipation.

4. Cold storage. After the dormant period, transferring potatoes to a cold storage facility can better control sprouting and water loss. In the cold store, they can be stored in piles or packed in boxes and stacked. The temperature should be controlled at 3-5°C and the relative humidity at 85%-90%.

5. Chemical treatment. Chlorpropham (CIPC) is a post-harvest sprout inhibitor. The dosage of the powder formulation is 1.4-2.8 g/kg. The powder is scattered into the potato pile, and plastic film or canvas and other coverings are placed on top. After 24-48 hours, it is opened, and the treated potatoes will not sprout even at normal temperature. This sprout inhibitor must be used after the potatoes have healed; otherwise, it will interfere with potato healing and cause rot during storage. The sprout inhibition effect is good when used before the end of the dormant period, but if used after the dormant period, the sprout inhibition effect is significantly weakened. Treating potatoes with methyl α-naphthaleneacetate or ethyl α-naphthaleneacetate also gives a good sprout inhibition effect. The dosage is 0.4-0.5 kg per 10 tonnes of tubers, made into a powder with 15-30 kg of fine soil and placed in the potato pile. It should be carried out in the middle of the dormant period, not too late, otherwise the efficacy will be reduced. MH (maleic hydrazide) also has a sprout inhibition effect on potatoes, but it needs to be sprayed in the field 3-4 weeks before tuber harvest, with a concentration of 3%-5%, and should be re-sprayed if it rains.

6. Radiation treatment. Irradiating potatoes with 8-15 kRr-rays has a clear sprout inhibition effect, and irradiated potatoes can be stored well at normal temperature for several months.