Cold Treatment of Fruits

Henry H. Richardson.

Hundreds of tons of fresh grapes, pears, and other deciduous fruits are imported into the United States in late winter and spring each year to replenish our own supplies. Practically all of it comes from the Southern Hemisphere, where the season is the reverse of ours and where many localities are infested with the Mediterranean and other fruit flies.

Rather than deny ourselves the fruit and eliminate this foreign trade, quarantine treatments have been developed to rid the fruits of the fly maggots that might be present in a few of them. The fruit is given a cold treatment, with regular commercial cold storage or refrigerator facilities. As a result, no live maggots were present in the 285,000 boxes of South African and Argentine grapes, pears, plums, and apples that we imported in 1951, mostly into New York City markets.

The cold treatment was found effective against the Mediterranean fruit fly more than 40 years ago. Exposing the fly larvae, eggs, or pupae to temperatures of 36 F. or below for varying periods will do the job. The first large-scale commercial use of the treatment was in Florida in 1928. A large part of the citrus fruit within the area where a Medfly eradication campaign was being waged was allowed to move to market after holding it at 34 or below for 12 days.

Grapes and other fruits from Medfly-infested areas later were allowed entry if they were treated in approved cold-storage plants on arrival in New York. Finally in 1937 the treatment was approved for application to fruit on shipboard during the voyage.

In order that the period at the selected temperature can be measured accurately, the fruit must be brought down to the treatment temperature, a process called precooling. Therefore the cold treatment consists of two steps precooling the fruit to its very center to the desired temperature and holding the fruit at or below that temperature for 12 to 20 days, depending on the species of fruit fly involved and the treatment temperature selected, whether 33 , 34 , 35 , or 36 F.

Precooling must be completed before the shipment leaves the country of origin, so that an inspector of the department of agriculture of that country may so determine it and officially designate the beginning of the second step of the treatment. As the voyage from South Africa or Argentina takes 18 to 20 days or more, the cold treatment fits in very well. with shipping schedules. During the voyage a continuous record of the air and fruit temperatures in each compartment is kept by an automatic temperature-recording instrument. On arrival in the United States, officials of the Bureau of Entomology and Plant Quarantine review the temperature charts. If they find no irregularities, they declare the fruit to be cold-treated and release it from quarantine.

The entire procedure always is under careful supervision. Shipments may only be made on ships previously tested and approved by representatives of the Department of Agriculture. Approval is based on proper circulation of air in the refrigerated compartments, adequate cooling capacity and insulation, proper operation of the temperature-recording instrument, and identification of the temperature-sensitive elements that are placed in the compartment. Before the fruit is loaded for the trip, the operation of the temperature recorders is checked and the temperature - sensitive elements are tested to determine whether they register the correct temperature. The elements are at the ends of long extension cords that extend into the compartments. Their correct placement there, in the air stream and in the fruit, is supervised also by the agricultural inspector. When the fruit is properly precooled that is, all of the fruit-pulp temperatures are down to the desired treatment level the inspector issues a certificate of precooling, which is forwarded to the port of entry in the United States.

The temperature-recording instruments are mostly of the multiple-point electronic type and usually are accurate down to one- or two-tenths of a degree Fahrenheit. One instrument may record the temperatures from as many as 16 locations. The records are printed one at a time on a roll chart. Each record is identified by a number printed beside it. The instrument may be adjusted to print at 1 or 2 minute intervals, so that each point can be recorded at least once every 16 minutes, or oftener if there are fewer than 16 points. Each sensitive element is labeled with the same code number that is printed on the chart. Usually each compartment has at least four elements, two to measure the air temperature and two for the fruit. The roll chart is about 128 feet long, enough to record the temperatures for a voyage of 30 days.

In South Africa all the fruit is exported by a government control board and consequently is all handled at one point. It is precooled to 30 F. in a dockside cold-storage plant and is transferred to the holds of the vessel so quickly that the temperature rises only 1 or 2 . Thus the cold treatment can be started as soon as the fruit is on board.

Dockside precooling facilities are not available in Argentina. Fruit is usually loaded from refrigerated railroad cars or must be transported by truck from cold-storage plants at considerable distances from the docks. Hence the fruit is only at 38 to 40 by the time it is loaded aboard ship, and precooling must be finished there. The fruit must be stacked in a more open manner to permit air to pass between all fruit boxes to insure uniform cooling. As the process usually takes 2 or 3 days or more, the fruit must be loaded several days before the ship is to leave. All fruit boxes are stamped with an identification mark to preclude mixing treated and untreated fruit. That is necessary because some untreated fruit is imported for treatment after its arrival in New York.

The cold treatment of fruit by itself would be relatively expensive as a method of killing fruit flies. But because imported fruit must be kept under refrigeration anyhow to prevent spoilage, its use during the voyage as a quarantine treatment has proved to be practical. Most modern ships have adequate refrigeration, so that usually it is necessary only to install the temperature recorders and to control the temperatures more carefully. The fact that the fruit is completely clean or disinfested on its arrival in this country removes the risk of disseminating fruit flies.

As a result of the uniform precooling and temperature regulation during the voyage, the fruit arrives in better condition than it used to. The efficiency of the treatment often has been demonstrated upon inspection of cold-treated fruit for other insects. Dead fruit fly larvae have been found evidence of the hazard involved in the importation of untreated fruit, of the positive effect of the treatment, and the need for continued careful supervision to protect our own fruit industry.

HENRY H. RICHARDSON studied at Massachusetts State College and Iowa State College and joined the Bureau of Entomology and Plant Quarantine in 1926. He worked on fumigants and other insecticides at the Agricultural Research Center at Beltsville, Md. During the Second World War he served in the Army Sanitary Corps. Since then he has worked at Hoboken, N. J., developing treatments for plants and products regulated by plant quarantines. In 1949 he was sent to Argentina to help that government in the treatment he here describes.