Key technologies for fruit and vegetable juice beverage production - juice extraction and coarse filtration

The juice extraction process of fruits and vegetables is another important process in the processing of fruit and vegetable juice beverages. The method of juice extraction not only affects the juice yield but also affects the quality and production efficiency of fruit and vegetable juice products.

Depending on the raw material and product form, the method of taking the juice varies greatly.

Squeeze

The squeeze juice extraction method uses external mechanical pressing force to squeeze the fruit and vegetable juice from the fruit or vegetable or vegetable pulp to obtain the juice. A method of juice extraction widely used in the production of fruit and vegetable juice beverages is mainly used for raw materials of fruits and vegetables rich in water content. According to the different temperature of the raw materials when juicing, the pressing can be divided into cold pressing, hot pressing or even freezing pressing; according to whether the slag is pressed again after leaching, the pressing is divided into secondary pressing and one pressing.

Hot pressing refers to heating the crushed raw material pulp, and then pressing the fruit pulp to extract juice. Hot pressing is determined by the biochemical properties of the raw materials after crushing and the processing technology of the juices. Before the raw material is broken, the biochemical reaction rate is quite slow in the intact cell tissue; however, when the raw material is broken, the various chemical, enzymatic and microbial processes in the raw material suddenly accelerate and interact, causing a series of chain reactions. Among them, zui is mainly various oxidation reactions catalyzed by an enzyme escaping from a raw tissue cell. Oxidation is often the main cause of the dramatic decline in the quality (color, aroma, taste and chemical composition) of fruit and vegetable juices, such as the browning reaction of polyphenols catalyzed by polyphenol oxidase, resulting in color changes in fruit pulp and fruit and vegetable juices. Therefore, in the processing of fruit and vegetable juices, effective prevention or inhibition measures must be taken for reactions that adversely affect, such as enzymatic browning reactions. Therefore, after the raw materials are broken, sometimes the fruit is heat treated and then hot pressed to inactivate the activity of the enzyme, and at the same time, the growth of the microorganisms can be inhibited, and the quality of the juice is ensured.

Cold pressing is relative to hot pressing. Cold pressing refers to the fact that after the raw material is broken, it is not subjected to heat treatment and is juiced at normal temperature or below.

The reason for the secondary pressing is that the essence of the juice is extracted from the soluble solids in the fruit, and the pomace after the *-pressing also contains a certain amount of soluble solids. In order to extract the soluble solids in the pomace as much as possible, so that the sugar content of the pomace is reduced, use normal temperature water or recover condensed water (generally not more than 80 ° C) according to the slag: water = 1: (1 ~ 2) The ratio (mass ratio) is leached for 20 to 40 minutes with or without enzyme addition, followed by secondary pressing. The secondary pressing process can increase the juice yield by 5% to 10%.

2. Leaching

Leaching is the process of transferring juice from fruits and vegetables into a liquid leaching medium (hot water). It is mainly used for the extraction of juices of fruits and vegetables (such as hawthorn) which are difficult to be juiced by dried fruits such as jujube, ebony, red dates and the like. The extraction method is divided into static extraction, countercurrent extraction, single-time extraction, multiple extraction methods, and the like. The factors affecting the juice extraction rate mainly include the extraction temperature, time, the degree of breakage of the raw materials, the concentration difference, and the flow rate.

3. Beating

The beating is to obtain the fruit (vegetable) puree by scraping and crushing the broken fruit and vegetable raw materials through a beater and separating the core, the fruit seed, the thin skin and the like. The fineness of the puree can be achieved by selecting the pore size of the different beater screens. In the processing of fruit and vegetable juices, this method is suitable for the production of fruit and vegetable pulp and pulp beverages, such as strawberry juice, mango juice, peach juice, hawthorn juice and the like. After the raw materials of fruits and vegetables are crushed, they need to be pre-cooked in the pre-cooking machine, passivate the enzyme activity in the fruits and vegetables, prevent browning, and then beat the pulp. Generally, three beatings are performed in the production. The size of the sieve aperture is 1.2, 0.8, 0.5 mm in turn, and the meat particles become smaller after the beating process, which is beneficial to the homogenization treatment. If a single pass is used, the mesh aperture should not be too small, otherwise it will easily block the mesh.

Centrifugation

Centrifugation should be done by a horizontal screw centrifuge, and the separation of fruit and vegetable juice and pulp can be achieved by the principle of centrifugal force. The slurry enters the centrifugal chamber of the rotating drum through the central feeding pipe. Under the action of high-speed centrifugal force, the poma is smashed onto the wall of the rotating drum, and the pomace is continuously sent to the tapered end of the rotating drum by the screw conveyor, and the juice is discharged. It flows out from the front end of the drum through the thread gap.

5. Coarse filtration

The coarse filtration is a process of removing larger or suspended particles dispersed in the juice. In addition to the pulping method, the juice obtained from other methods contains a large amount of suspended particles. If meat fiber, peel, fruit core, etc., their presence will affect the appearance quality and flavor of the product, and need to be removed in time, the coarse filter can be squeezed. During the juice process or click operation, the vibrating sieve is usually used in the production for coarse filtration, and the juice of the fruit and vegetable generally passes through the 0.5 mm aperture filter screen to achieve the coarse filtration requirement. It is necessary to clarify and filter after coarse filtration of fruit and vegetable juices. For turbid juice and meaty drinks, homogenization and degassing are required.

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