CN102150908A - Method for vacuum microwave concentration of fruit juice - Google Patents

Abstract

The invention discloses a vacuum microwave concentration method for fruit juice, which comprises the following steps: vacuumize the original fruit juice, heat it with microwaves, and monitor the temperature of the original fruit juice. When the temperature of the material starts to rise and exceeds 50°C, reduce the heating power; when the temperature of the material reaches 60°C, stop heating. The concentration temperature of the method is low, the concentration speed is fast, and the obtained fruit juice is of high quality, and basically does not lose its inherent flavor after dilution. Simultaneously, according to the method of the present invention, the equipment is not prone to fouling, and the energy consumption is low.

Description

A kind of fruit juice vacuum microwave concentration method

technical field

The invention relates to a method for concentrating fruit juice, in particular to a method for concentrating fruit juice with vacuum microwaves.

Background technique

Concentrated fruit juice is a kind of product produced by fruit juice, sterilization, concentration, filling and other processes. Concentrated fruit juice is the raw material for the production of fruit juice drinks, fruit wine and fruit vinegar. Compared with freshly squeezed unconcentrated fruit juice, concentrated fruit juice has the characteristics of small size, convenient transportation, and low packaging cost. At the same time, due to the high content of soluble solids in concentrated fruit juice, it is not easy to spoil, especially suitable for long-distance transportation. of international trade.

Concentration methods mainly include membrane concentration method, reverse osmosis concentration method and freeze concentration method. Thin-film concentration method is the most commonly used concentration method. Steam is used to evaporate the water in the fruit juice to achieve the purpose of concentration. The heat source of thin-film concentration method is usually steam, which needs to be equipped with a boiler, which requires a large investment and high energy consumption.

The reverse osmosis concentration method uses a reverse osmosis membrane to filter the water in the juice for the purpose of concentration, but the juice is usually required to go through an ultrafiltration process before reverse osmosis, otherwise the reverse osmosis membrane is easily blocked, that is, the reverse osmosis concentration method does not work It is suitable for the production of turbid concentrated fruit juice. At the same time, the reverse osmosis concentration method has the problems of low concentration end point and high operating cost.

The principle of the freeze concentration method is to lower the temperature of the dilute solution below the freezing point of water so that part of the water freezes into ice crystals, and the ice crystals are separated to obtain a concentrated solution. This method has been used in the production of instant coffee, instant tea, concentrated orange juice, etc., after vacuum The quality of the juice produced by microwave concentration is almost the same as that of freshly squeezed juice after adding water to reduce it. The vacuum microwave concentration method reported so far is the method of removing ice crystals in time after the fruit juice freezes. Freezing is the main step. At present, there are two main methods for fruit juice freezing. One is that the water in the dilute solution forms an ice layer on the cold surface. The formation of progressive layered crystals; the other is to freeze in a stirred suspension, and to achieve concentration through the growth and separation of a large number of suspended and dispersed ice crystals in the mother liquor, which is called suspension crystallization. However, the main technical difficulties of these two methods are that it is difficult to form small ice crystals, it is difficult to separate the formed ice crystals, and the separated ice crystals need to be cleaned and other steps. These make the vacuum microwave concentration equipment very complicated, expensive, with many procedures and easy production process. pollute. Domestically, many equipment researches have been carried out aiming at this principle, but the industrialization has not yet been realized.

As a new heating technology, microwave is different from traditional heating. Microwave heating does not require an external heat source, but radiates a microwave electromagnetic field to the inside of the heated material, pushing its dipoles to move, causing them to collide and rub against each other to generate heat. Water, protein, fat and carbohydrates in food are all dielectrics, which are good media for absorbing microwaves. In the alternating electric field with a frequency of 2450MHz, the direction of the electric field changes billions of times per second for these polar molecules. The polar molecules also swing billions of times accordingly, causing the polar molecules to generate heat similar to friction in a very short time. Microwave heating has the characteristics of high efficiency and rapidity, energy saving and power saving (compared with conventional methods, it can save electricity by 30% to 50%), uniform heat, clean and safe, etc. Microwave has been widely used in food thawing, drying, baking, enzyme elimination and Sterilization, etc., but the use of microwaves for concentration, especially concentration under vacuum conditions, has not been reported and applied.

Wang Wuquan, a graduate student majoring in agricultural mechanization engineering at Henan Agricultural University, carried out the work of "development of microwave energy concentration equipment for fruit juice". A circular material vehicle and a microwave energy leakage suppressor are installed to further ensure the uniformity. In order to discharge water vapor in time and ensure the concentration effect, a dehumidification device is also designed. For the steam generated by microwave concentration, the function is to discharge the water vapor evaporated from the object and to ventilate and cool the material, and connect it to the cooling holes on the inner and outer walls of the microwave heater. Due to the adoption of ventilation, cooling and dehumidification technology, the connection with the outside world cannot achieve concentration under vacuum conditions, which will inevitably lead to a higher concentration temperature, resulting in the loss of nutritional flavor of the juice during the concentration process.

Liao Zisu, a postgraduate student majoring in mechanical design and theory of Guangxi University, carried out the "Design and Process Research of Microwave Heating Evaporation and Concentration Experimental Device for Sugar Juice in Sugar Factory", and proposed to use microwave as the evaporation heat source of sugar factory. Experimental research was carried out on the process of concentrating sugar juice to verify the feasibility of this method. It fully proves that the microwave heating and concentration method has the characteristics of high evaporation efficiency, energy saving and environmental protection, and good economic benefits. The convective heat transfer coefficient is small and easy to scale during wall heat transfer. The equipment also adopts some vacuum methods. The vacuum system chooses the Midea vacuum cleaner produced by Midea Group. Its vacuuming capacity is about 20-40kPa. Between 10lkPa, the boiling point of water is around 92°C under this vacuum condition, and the boiling point of fruit juice is higher because it contains sugar and other substances, which will also cause the loss of nutritional flavor of fruit juice during the concentration process.

Contents of the invention

The object of the present invention is to provide a kind of fruit juice concentration method.

The technical scheme that the present invention takes is:

A fruit juice vacuum microwave concentration method, comprising the following steps:

1) Vacuum the fruit juice until the absolute pressure is lower than 15kpa, and use a 10-50kw microwave to heat the fruit juice;

2) Monitor the temperature of the fruit juice, when the temperature of the material exceeds 50°C, adjust the microwave heating power to 2-20kw;

3) When the temperature of the material reaches 60°C, stop heating.

Preferably, a water ring vacuum pump is used to evacuate the fruit juice to an absolute pressure lower than 15kpa.

Preferably, during the microwave heating process, the material rotates at a constant speed in the cavity at a speed of 3-30 rpm.

The concentration temperature of the method is low, the concentration speed is fast, and the obtained fruit juice is of high quality, and basically does not lose its inherent flavor after dilution. Simultaneously, according to the method of the present invention, the equipment is not prone to fouling, and the energy consumption is low.

Detailed ways

A fruit juice vacuum microwave concentration method, comprising the following steps:

1) Vacuum the fruit juice until the absolute pressure is lower than 15kpa, and use a 10-50kw microwave to heat the fruit juice;

2) Monitor the temperature of the fruit juice, when the temperature of the material exceeds 50°C, adjust the microwave heating power to 2-20kw;

3) When the temperature of the material reaches 60°C, stop heating.

Preferably, a water ring vacuum pump is used to evacuate the fruit juice to an absolute pressure lower than 15kpa.

Preferably, during the microwave heating process, the material rotates at a constant speed in the cavity at a speed of 3-30 rpm.

Below in conjunction with embodiment, further illustrate the present invention.

Example 1:

The vacuum microwave drying equipment produced by Guangzhou Rongxing Industrial Microwave Equipment Co., Ltd. is used for concentration, and 3 glass containers are placed on each of 6 rotating baskets, each with a capacity of 2L, and 1.5L of lychee juice (initial sugar content 16bx) ), put a total of 27L lychee juice, close the furnace door, turn on the water ring vacuum pump to make the vacuum of the chamber reach 10kpa, start the rotating basket, rotate 10 times per minute, set the upper limit of the microwave heating temperature to 60°C, and turn on the microwave heating Switch, microwave power is set to 12kw, after 10 minutes of microwave heating, when the temperature rises to 50°C, stop the rotation of the material basket, put a vacuum, and when the temperature in the cavity reaches normal temperature, open the oven door, there is still 13L of lychee juice left, the sugar content of lychee juice up to 32bx.

Example 2:

The vacuum microwave drying equipment produced by Guangzhou Rongxing Industrial Microwave Equipment Co., Ltd. is used for concentration, and 3 glass containers are placed on each of 6 rotating baskets, each with a capacity of 2L, and 1.5L of lychee juice (initial sugar content 16bx) ), put a total of 27L lychee juice, close the furnace door, turn on the water ring vacuum pump to make the vacuum of the chamber reach 10kpa, start the rotating basket, rotate 10 times per minute, set the upper limit of the microwave heating temperature to 60°C, and turn on the microwave heating Switch, set the microwave power to 12kw, after microwave heating for 10 minutes, when the temperature rises to 50°C, adjust the microwave power to 4kw, and heat for about 10 minutes. When the temperature reaches above 60°C, turn off the microwave, stop the rotation of the material basket, and put a vacuum. When the temperature in the cavity reaches normal temperature, open the oven door, there is still 6.3L of lychee juice left, and the sugar content of lychee juice reaches 65bx.

Claims (3)

1. fruit juice vacuum microwave method for concentration may further comprise the steps:

1) fruit juice is evacuated down to absolute pressure and is lower than 15kpa, use the heating using microwave fruit juice of 10～50kw;

2) temperature of monitoring fruit juice when material temperature surpasses 50 ℃, transfers to 2～20kw with the power of heating using microwave;

3) after material temperature reaches 60 ℃, stop heating.

2. a kind of fruit juice vacuum microwave method for concentration according to claim 1 is characterized in that: use water-ring vacuum pump that fruit juice is evacuated down to absolute pressure and be lower than 15kpa.

3. a kind of fruit juice vacuum microwave method for concentration according to claim 1, it is characterized in that: in the microwave heating process, material is uniform rotation in cavity, 3～30 rev/mins of rotating speeds.