A natural beverage made from fresh fruit through processes such as juice extraction and sterilization. Juice contains a lot of water, as well as fruits, sugar, acids, vitamins, pigments and inorganic salts. Its color, aroma, flavor and nutrients are very close to fresh fruits. In addition to being used for general drinking, fruit juice is also a good health food. It is different from artificially prepared hobby drinks. Concentrated and dehydrated juice products are also the main raw materials or ingredients of many beverages and foods. Juice is easily deteriorated and corrupted, and it is a type of product with the highest quality requirements and the strictest process requirements for fruit processing.
Types of juice
Juices are classified into non-concentrated juices, concentrated juices, juice syrups, and juice powders based on their processing technology and product status. Non-concentrated fruit juice, also known as raw fruit juice or direct fruit juice, is the juice extracted or extracted directly from the fruit without dilution or concentration. It contains 100% fruit juice and is a fruit product for direct consumption. There are two types of transparent and turbid. Transparent juice or clear juice, with clear and transparent appearance, such as apple juice and grape juice. Cloudy juices are in a uniformly turbid state and contain flesh particles. Nutrition is often better than transparent juices, such as various citrus juices. Concentrated fruit juice is made by concentrating the original fruit juice 3-6 times. There are two types of transparent and turbid. The content of soluble solids is 40-60%, the highest is 65%, but orange juice is usually 42-43%. The product is diluted with water for drinking, so it is often used as a base for juice or beverages. Fruit juice syrup is a product containing a large amount of sugar added to the original fruit juice. It also needs to be diluted for drinking and can also be used as a beverage base. Juice powder is a powdered product after concentrated dehydrated juice is further dehydrated. The water content is 1 to 3%. It is dissolved after reconstitution with water.
Principles of preservation
Use heat-type other sterilization methods to eliminate or inhibit the microorganisms and enzymes present in the juice, combined with vacuum and sealing to isolate the infection of external microorganisms, so that the product can be hidden for a long time. Concentrated juices and juice syrups have more preservation effects such as increased concentration resulting in strong osmotic pressure and reduced water activity. Juice powder is mainly dehydrated and preserved.
The main processing of raw juice includes raw material selection and processing, juice extraction, adjustment, coarse filtration, clarification filtration or homogeneous degassing, packaging and sterilization. Concentrated juice needs to be concentrated, and juice powder needs to be dehydrated.
It is required to have a pleasing color, unique flavor and aroma, proper sugar-acid ratio, rich in vitamin C, and can maintain these excellent properties during the processing and product preservation without obvious adverse changes. At the same time, it requires rich juice, easy juice extraction and good processing adaptability. Fruits suitable for processing juice mainly include citrus, pineapple, apple, grape, raspberry, plum, guava, passion fruit and kiwi fruit. Due to the differences in processing suitability between varieties, variety selection is even more necessary. Before the raw fruit juice is taken, it still needs to undergo preparation treatments such as washing, sterilization, grading, selection, cutting, and pre-boiling.
Juices such as apples and grapes are contained in the whole fruit, and the juice can be taken by crushing and pressing. Citrus has an outer skin, and the juice exists in the juice cells, and the cone juice machine is often used to extract the juice. The fruit juice extraction rate accounts for about 45 to 80% of the fruit weight, which varies depending on the type, variety, raw material status, juice extraction process and equipment.
It is an important process of transparent juice, used to remove suspended solids and colloidal particles that hinder quality and stability. Juice clarification includes gelatin tannin method, heating coagulation method, freezing method and enzymatic method. Some commercial pectinase preparations have the best clarification effect at pH 3 and 40 ° C, and the dosage is about 0.05% of the juice amount. After clarification, it is filtered to obtain a clear solution.
Homogeneity and degassing
Used for cloudy juice. Homogenization is a process that mechanically disperses the suspended matter in the juice to improve stability. There are two types of homogenizers: high-pressure and ultrasonic. High pressure homogenization pressure is about 150 ~ 170 kg / cm2, ultrasonic homogenization frequency is 18 ~ 22 kilohertz (kH), can induce cavitation force of about 9 tons / cm2. In addition, some colloid mills and ultra-micro mills can also be used for homogenization.
Deaeration is deoxygenation, which is the process of removing air from the juice. It can prevent the juice from oxidizing and discoloring, loss of vitamin C, container corrosion, and eliminating foam. There are several methods such as vacuum, nitrogen and enzymatic methods. Vacuum degassing vacuum degree is 79.98 ～ 93.3 kilopascals (kPa); enzymatic method uses glucose oxidase to oxidize glucose in the juice to gluconic acid and consume oxygen in the juice in the tank and in the headspace; nitrogen filling method is strongly pressed Nitrogen foam to remove oxygen from the juice.
Concentration and dehydration
Concentrated juices are often vacuum-concentrated, with a vacuum of about 93.31 kPa. Freeze concentration method and reverse osmosis concentration method can also be used. Dehydration is the main process for preparing fruit juice powder. The spray drying method is commonly used. Although the temperature is as high as 160 ℃, the drying time is extremely short, and the fruit juice powder will not be deteriorated by heat. This method has quick dehydration, continuous operation, simple labor saving, and the product quality is better than the general drying method.
The juice is also packaged in various canned containers, including various tinplate cans, aluminum cans, laminated plastic cans, and glass cans (see Canned Fruits).
Juices must be sterilized except for juice powder, the purpose is to eliminate or inhibit the presence of microorganisms and destroy the activity of enzymes. The pasteurization of fruit juice is pasteurized. Low-pH transparent juice is generally sterilized at 80 ℃ for 30 seconds. To avoid the decomposition of pectin by pectinase, turbid juice must be sterilized at 93.3 ～ 95 ℃ for 30 ～ 90 seconds Sometimes instantaneous pasteurization at higher temperatures and shorter times is used to destroy enzyme activity.