Fruit processed products are made by pre-processing the fruit, canning it, adding a certain concentration of sugar solution, and sealing it. It is required to achieve commercial sterility and a certain degree of vacuum. According to the sugar content, fruit shape and type of fruit in the can, canned fruit can be divided into 7 categories: canned fruit in sugar water, canned fruit in syrup, canned jam, canned juice, canned fruit puree, canned jelly, canned two-color or assorted fruit. . Generally speaking, canned fruits refer to canned fruits in sugar water.

Development Overview

Canned food was invented by the Frenchman N. Ap-pert. In 1810, he published a monograph "Method of Storing Food in Sealed Containers" and proposed a food preservation method, namely the boiling water boiling method. He pointed out that various foods that are tightly sealed in bottles can be preserved for a long time. The main foods used for canning are Meats, vegetables, fruits, etc. were once known as Abel's skills. After the Frenchman Louis Pasteur discovered microorganisms in 1864, he confirmed that the main cause of food spoilage is the growth and reproduction of microorganisms. In 1874, a high-pressure sterilizer that introduced steam from the outside and was equipped with control facilities was invented, thereby shortening the sterilization time and improving the safety of the operation. Canning technology was widely promoted. From 1920 to 1923, Bigelow and C.O. Ball proposed using mathematical methods to determine the reasonable sterilization temperature of canned food based on the heat resistance of microorganisms and the heat transfer characteristics of canned containers and food in the cans. In 1948, Stambo further proposed the F value, the theoretical basis for canned food sterilization, and the canning process gradually became more perfect.

China's canning industry began in 1906. Shanghai Taifeng Food Company, invested by overseas Chinese, was China's first canning processing factory. Since then, some canneries and empty can factories have been built in Shanghai, Ningbo and other provinces, with a maximum annual output of only more than 7,000 tons. In 1949, China's annual canned production dropped to only 484 tons. Later, with the recovery of the economy, canned production increased steadily. By 1952, the output rose to 13,000 tons. After that, a number of canned industry backbone factories were built and expanded. , by 1959 the total output rose to 159,600 tons. With the change in the export trend of canned food, we have carried out the construction of raw material bases, the selection of canned varieties, the introduction of foreign advanced technology and equipment, and the formulation of quality standards, process operation points, testing methods and factory hygiene management systems for major canned goods. etc., thereby bringing China's canning industry to a new level. By 1986, China's total canned production had reached 1.641 million tons, of which canned fruits accounted for about 40-45%, ranking first.

In the 1980s, the world's total canned production was about 40 million tons, of which the United States accounted for about 1/2. The other major producing countries include the Soviet Union, Japan, the United Kingdom, France, etc. The main canned fruits abroad include pineapples, peaches, pears and apples. China mainly produces pineapples, citrus, peaches, apples, etc. The specialty canned fruits include bayberry, loquat, lychee, longan, kiwi, kumquat, hawthorn, etc.

Principle of canned fruit

Canned fruit eliminates part of the air in the can, seals the can, and then kills the fruits and juice contained in the canned container. Harmful microorganisms are eliminated to achieve "commercial sterility", and the sealing performance of the tank container is used to prevent external microorganisms from entering the tank for infection and long-term storage. Thermal sterilization method is usually used. (See Fruit Processing). Since fruit raw materials are rich in organic acids, their pH value is often below 4.5, which is an acidic food. Under such low pH conditions, the heat resistance of microorganisms is greatly weakened. Therefore, most canned fruits are made of boiling water or below the boiling point. The sterilization temperature can kill the microorganisms that cause the spoilage of canned fruits.

Processing process of canned fruit

The processing process varies greatly depending on the type, variety, product type and product specification of the fruit, but this difference mainly occurs before canning the fruit. During the raw material pretreatment process, the processing process after canning is similar.

The main process flow is as follows:

Selection and grading of raw materials

Different canned fruits have specific requirements for raw materials, which results in certain fruits forming specific canned varieties ( See seeds for canning). In order to ensure the quality of canned fruits, facilitate processing operations, improve production efficiency, and reduce the consumption of raw materials, raw materials must be classified. There are two grading methods: size grading and quality grading. Size grading is generally divided into grades every 5 to 10 mm based on the maximum transverse diameter of the fruit. Small fruits such as cherries, bayberries, lychees, longans, strawberries, loquats, and plums are generally divided into three or two levels: large, medium, and small by visual inspection. Quality grading is divided into different quality levels based on differences in fruit color, maturity, shape, flavor, etc. Fruit grading and processing have an important impact on ensuring the quality of canned food.

Washing or blanching

Washing before fruit processing requires the removal of dust, sediment, some microorganisms and residual pesticides on the surface of the fruit. The washing method is to soak it first, and then wash it with running water or spray water. Fruits that have been sprayed with pesticides should be soaked in a dilute hydrochloric acid solution of 0.1 to 1.0, and then washed with clean water. Small fruits without skins and soft texture, such as bayberries and strawberries, should be washed in small batches or washed with compressed air in a sink. Some fruits are blanched to facilitate peeling. For example, oranges are blanched with hot water at 95-100℃ for 45-60 seconds; loquats are blanched at 85-90℃ for 5-15 seconds.

Peel and remove the core

Peeling the fruit can improve the color, flavor and quality of the product. The method of peeling should be different according to the type and maturity of the fruit. There are three commonly used peeling methods: manual, mechanical and chemical peeling. The mechanical peeling method generally uses a peeling machine, such as pineapples, apples, pears, etc. Chemical peeling method usually uses a hot solution of sodium hydroxide to peel fruits such as peaches, apricots, plums, kiwis, etc. Some more ripe peaches can be peeled using steam jet heat. No matter which peeling method is used, the principle is to remove all the outer skin and keep the fruit's appearance smooth, so as to prevent excessive peeling and increase the loss of raw materials. Most fruits will undergo enzymatic browning quickly after peeling, so the peeled fruits should be immediately immersed in dilute acid, dilute salt water or a mixture of acid and salt to protect their color. For varieties that need to be cored or cored, you can use a corer or corer to remove the core or core manually. The concentration and time of lye peeling should vary according to the type, variety, maturity of the fruit and the temperature of the lye. For varieties that need to be pre-cooked, they should be quickly boiled in boiling water and cooled quickly after peeling and pitting to inactivate enzyme activity and remove air from the pulp tissue. The time from peeling to canning, sealing and sterilization should be shortened as much as possible. .

Slicing and trimming

Large fruits must be sliced ??or diced according to the type and size of the raw materials and the specifications of the products. Pineapples are generally cut into ring-shaped discs, fans or pieces; peaches, apples and pears can be cut into halves or quarters. After the fruit is cut, the scars, pit tips, bruises, discoloration and burrs on the fruit pieces should be removed. The pulp tissue of pineapples and apples contains a lot of air, which can cause discoloration of the product, corrosion of the metal can wall, and reduced vacuum of the can, so vacuum degassing must be used to prevent it.

Canning

It includes two parts: filling the fruit and adding sugar liquid. The fruits or fruit pieces that have been trimmed and meet the canning requirements can be canned separately according to their size, shape, and color. The fruits in the same can are required to be uniform in color, size, and shape. The weight of the fruit in each can should be accurately measured according to product specifications to ensure a stable quantity. Then add sugar liquid. The amount of sugar liquid added is generally controlled to be slightly higher than the specified net weight to avoid insufficient net weight of the can, but there must be a top gap of 6 to 8 mm (that is, the distance between the surface of the can's contents and the bottom of the lid). The concentration of sugar solution to be added can be determined based on the soluble solids content of the fruit itself before canning, the weight of pulp in each can, the net weight of the product, the concentration of sugar solution required when opening the can, and the actual amount of sugar solution added to each can. calculate.

Exhaust and seal

After canning, the cans must be vented and then quickly sealed. There are two exhaust methods: heating exhaust method and vacuum exhaust method.

The former is heated through the exhaust box after canning, so that when the center temperature of the can reaches the specified requirements, the seal is taken out immediately; the latter is carried out simultaneously by extracting air from the vacuum sealing machine and sealing the can. The vacuum degree of the vacuum sealing machine is generally controlled between 300 and 500 mm of mercury, depending on the temperature of the can during sealing, the size of the can and the type of product. The can sealing machines used for sealing include semi-automatic, fully automatic and vacuum automatic can sealing machines. The sealed cans must be rolled up to meet the specified dimensions and specifications, and the surface must be flat and smooth without defects such as chips, ribs, snaps, and wrinkles. Otherwise, the sealing performance will not meet the requirements.

Sterilization and cooling

Canned fruits are acidic foods, and the sterilization conditions (ie, sterilization temperature and sterilization time) should be based on the type of product, the pH value of the canned content, and the size of the can. , the thermal conductivity of the packaging container, the tightness of the arrangement of the fruit pieces in the tank, the presence or absence of soup in the tank, and the sanitary conditions of the process. There are two sterilization methods: water bath heating and steam heating sterilization. Water bath heating transfers heat more evenly and quickly than steam heating, so it is widely used. It is better to use a rotating atmospheric pressure continuous sterilization cooler as the sterilization equipment. The sterilization intensity is enough to kill the microorganisms in the can and cook the fruit pulp properly to improve the tissue state and flavor. Excessive heat sterilization will damage the quality of the fruit. Therefore, under the premise of ensuring the safe storage of cans, the sterilization should be done to the maximum extent possible. Reduce the sterilization temperature and shorten the sterilization time. After cans are sterilized, they must be cooled promptly and quickly to prevent the cans from continuing to be heated and affecting their quality. The cooling method can be to immerse the can directly in flowing cold water, or to cool it by pouring cold water on it. Cooling water should be kept clean and hygienic. Generally, after the can is cooled to a uniform temperature, the temperature inside the can should be between 37 and 40°C. Glass jars should be cooled in stages at 80°C, 60°C, and 40°C to prevent sudden cooling that may cause bursting. After cooling, the water droplets on the outside of the can should be wiped off in time to allow the lukewarm temperature of the can to evaporate and dry the water on the surface of the can. Then it is put into storage for inspection at a temperature of 35 to 37°C. One week later, after passing the inspection and sampling inspection, the product is labeled and packaged into pieces, which is the finished product.