JP2010538663A - Improving the thawing quality of rapidly frozen vegetables and fruits by low frequency ultrasound - Google Patents

Abstract

  Select, wash and cut the fruits and vegetables as raw materials, inactivate the enzyme with hot water, cool, freeze / freeze ultrasonically-freeze, ultrasonically-freeze in the quick-freeze process of fast-frozen vegetables and fruits It is a method for improving the thawing quality of rapidly frozen vegetables and fruits by using low-frequency ultrasound.

Description

  The method for improving the thawing quality of quick frozen vegetables and fruits by low-frequency ultrasonic wave according to the present invention belongs to the field of processing techniques of vegetables and fruit foods, and relates to quick freezing processing and ultrasonic techniques of vegetables and fruits.

  The frozen food storage is widely applied at home and abroad as an efficient food storage method that not only keeps the quality of food well but also avoids food contamination. However, how to effectively freeze foods and maintain good quality even after freezing and thawing the foods is one of the main issues that are widely noted.

  The quality of frozen vegetable and fruit foods is limited to freezing techniques, and the quality of vegetables and fruit foods cannot be optimized by the freezing rate and the final freezing temperature. In the freezing process, since the specific heat capacity of ice is about 9% larger than that of water, huge freezing stress is generated when freezing, and irreversible alteration or destruction occurs in the frozen product structure. Due to the presence of thermal resistance, a long time is required for the freezing process, and in particular, since ice crystals grow into relatively large ice particles, it takes too long to pass through the maximum ice crystal formation region of 0 ° C to 5 ° C. The freezing process that transfers the solidification latent heat by the outside cannot be completed instantaneously, the distribution of the generated ice crystals varies, and the ice crystal particles are relatively large, so the quality of the frozen product is still thorough It has not been improved.

  Furthermore, since the moisture content of vegetables and fruits is higher than that of general frozen foods, many ice crystals are generated in the general quick freezing cooling process, the ice crystals become too large, and the cytoplasm and cell walls are separated, The organizational structure will be severely destroyed. Also, when thawing, a lot of juice is lost, several enzyme systems are activated, and browning / yellowing phenomenon easily occurs.

Ultrasound is mainly applied in the following three aspects in the food industry. First, non-destructive inspections should be performed on food. Next, assistance in extraction with ultrasound, cleaning with ultrasound, promotion of food processing with ultrasound, for example, promotion of biochemical reaction courses with ultrasound. Finally, destruction of the tissue and structure to be treated with ultrasound, such as homogenization of the system, sterilization, enzyme inactivation, etc. As a result of extracting the oil that was strengthened by ultrasonic waves with a frequency of 25 kHz and a power of 300 W, Zhouyokin et al. Found that it has characteristics of short time, low temperature and good quality. The sound chemistry research group at the Natural Solution Laboratory at South China University of Technology has studied and experimented with ultrasonic fracturing techniques. As a result, this method is less time consuming and easier to operate than other conventional methods. It became clear that the rate was improved by 30% or more. Riera E et al. Studied the extraction of fats and oils from the seed kernels of apricot berries by strengthening the supercritical CO ₂ fluid with ultrasound. From the results, when applying ultrasonic waves to supercritical CO ₂ , the extraction time of apricot oil is reduced by 30% at the same extraction rate as compared to the case without applying ultrasonic waves, and at the same extraction time, the extraction rate is reduced. Was found to be improved by 20%.

  Acton and Morris (Patent Document 1, US Patent), in 1992, acted on a frozen sucrose solution for 30 s per 10 min by pulsed ultrasound at 25 kHz, but the tip of the branch ice crystals at the solid-liquid interface As it broke down, it was observed that small ice crystals were dispersed among the unfrozen liquid to form ice nuclei. Due to the breaking of the ice crystals, the size of the ice crystals in the sucrose solution was reduced. Although only 32% of ice crystals have a diameter of 50 mm or more, there are 77% of frozen crystals that have not been sonicated.

  Bing Li and Da-Wen Sun froze potato chips in 2003 using a technology that combines ultrasonic waves at 25 KHz and power of 15.85 W with immersion refrigeration (this power is converted to actual power via an ultrasonic energy converter). Is converted into actual working power when ultrasonic waves propagate through the medium). The freezing time was remarkably shortened compared with general immersion freezing. From the frozen section of potato chips, the mechanical damage to the cells due to the size and distribution of ice crystals was reduced.

  Maria Patrick A and others helped olive oil crystals by ultrasound in 2004, shortening the crystallization time and improving the quality of olive oil crystals. However, for example, a material such as fat has a very variable taste. In particular, when ultrasonic waves are introduced, free radicals are easily generated due to the cavitation effect of ultrasonic waves. In this case, unsaturated fats and oils and fats are very easily oxidized and altered.

International Publication No. 99/20420 Pamphlet

  The present invention utilizes a method of processing quick frozen vegetables and fruits combining immersion freezing and ultrasonic waves, and is used for quick freezing processing of various vegetables and fruits. The object is to provide a quality improvement method.

The present invention provides a quick-frozen vegetable and fruit quick-frozen process in which fruit and vegetables as raw materials are selected, washed, and cut, enzyme-inactivated with hot water, cooled, frozen / ultrasonic assisted freezing, and packaged. Adopt sonic assisted freezing,
The above-mentioned freezing / ultrasonic assisted freezing is performed by immersing / freezing the secondary refrigerant having a temperature of −20 to −18 ° C. as a freezing medium, and the weight / volume ratio of the fruit / vegetable material and the secondary refrigerant. Is (l: 30-1: 40) g / mL and the center temperature of the vegetable and fruit foods falls below 0 ° C., the ultrasonic frequency is 20-24 KHz, the power is 40-80 W, the ultrasonic pulse mode (ie, Ultrasonic assisted freezing is performed under the conditions of 40% to 60% and the total time of 0.8 to 2 minutes, and 45 to 50% glycol aqueous solution is used as a secondary refrigerant. The method of improving the thawing quality of quick frozen vegetables and fruits by low-frequency ultrasonic waves, characterized in that the temperature of the secondary refrigerant is −20 ° C. and the ratio of the reaction material to the liquid is 1:10. The cooling system is mainly a blower quick freezer, and by implementing convection forcibly with a fan in the quick freezer, it is possible to achieve constant temperature in the box or temperature drop / temperature rise by a program. After thawing by microwave, the percentage of free droplets of the sample is 3% to 5%.

  Quick frozen vegetables and fruit products are packaged rapidly in low temperature environments below -5 ° C.

  The thermal effect of ultrasonic waves is a problem that cannot be ignored. The ultrasonic power, the ultrasonic action time, and the ultrasonic pulse mode are directly proportional to the thermal effect of the ultrasonic wave, and the ultrasonic frequency is inversely proportional to the thermal effect of the ultrasonic wave. Accordingly, the parameters of the ultrasonic process of ultrasonic assisted immersion freezing must be selected appropriately.

  When low-frequency high-intensity ultrasonic waves are used in a food freezing process, the freezing quality and freezing speed of the food can be significantly improved. Combining ultrasonic technology with the food freezing process not only promotes the formation of ice crystal nuclei due to the physical effect (cavitation effect) of ultrasonic waves, but also the formation of microbubbles due to the ultrasonic cavitation effect. Uniform nucleation ice crystal nuclei can be formed, the nucleation temperature of water in the food is changed, rapid nucleation of ice crystals is promoted, and the degree of supercooling of the food is reduced. Compared to other nucleation techniques, such a nucleation technique has advantages such as more direct action, no need to contact the sample, and no contamination of the sample.

  Low-frequency high-intensity ultrasonic waves have the function of breaking relatively large ice crystals. In addition, microgasification due to the cavitation effect and vigorous stirring such as swirls generated in the liquid medium by ultrasonic waves can accelerate the mass transfer and heat transfer of rapidly frozen foods, thereby accelerating the food freezing rate. Since the ice crystals formed are small, the distribution is uniform, and the damage to the plant cells is weakened, the quality of the frozen product is better. Thus, not only quick freezing is realized, but the quality of the frozen product is effectively improved, and real “rapid freezing” is realized.

  The low frequency ultrasonic assisted refrigeration technology has a frequency application range of 20-25 KHz. By combining low frequency ultrasound with existing refrigeration equipment, ultrasound can assist in various refrigeration systems. There are two main types of ultrasonic assisted refrigeration. One of them is to act directly. For example, combined with immersion refrigeration. When combined with the refrigeration equipment, the ultrasonic probe head may act directly on the secondary refrigerant, or the ultrasonic energy converter may be installed on the wall of an immersion refrigerated stainless steel outer tub. The other is to use air conduction by combining ultrasonic with refrigeration equipment such as a blower freezer. The effect of the latter ultrasonic wave is lower than the combination method like the former. Ultrasound-assisted freezing technology is mainly applied to low fat materials such as fruit and vegetable materials, sucrose, crystal solutions such as MSG (Monosodium glutamate; Ajinomoto (registered trademark)), etc. The quality is improved, i.e. the vegetables and fruits after thawing can hold the maximum amount of nutrients, reduce the loss of juice, and the crystallization time of solutions such as sucrose is shortened and the desired crystal form Thus, the density after crystallization is improved and the addition of other crystal types is reduced. Since ultrasonic waves act physically, they have certain advantages in controlling microorganisms over other crystal types, contribute to environmental protection, and are good for the health.

  The present invention performs rapid freezing by combining low-frequency ultrasonic waves with the immersion refrigeration method, the ultrasonic waves directly act on the secondary refrigerant, and the action of promoting the cavitation effect by ultrasonic waves becomes even more significant. The efficiency of heat conduction and mass transfer of the secondary refrigerant is remarkably increased.

  In the present invention, the thawing quality of quick-frozen vegetables and fruits is improved by combining the sonication process in the immersion freezing step of vegetables and fruits, the freezing time is shortened, the initial shape is good, and the running cost is reduced. It has characteristics such as low.

  In addition to maximizing the freezing speed of quick frozen vegetables and fruits, the ultrasonic assisted immersion freezing method can achieve the purpose of energy saving. The disadvantage that the conventional refrigeration technique has a long freezing time and a large energy consumption is solved. This method has the characteristics that the effect of quick freezing is excellent, the action time is short, the quality of the quick frozen food is good, and the running cost is low.

  In short, compared to the background art, the present invention reduces the freezing time of the material by assisting the freezing technique with ultrasonic technology and improves the overall quality of frozen vegetable and fruit foods. The free droplet after thawing (water retention of the frozen sample) is 5% or less. The quality scoring of vitamin C, which is a nutritional component, is improved almost twice as much as that of the reference sample (a general immersed frozen sample not subjected to ultrasonic waves). The retention of vitamin C and chlorophyll reaches 85% or more. The hardness of vegetables and fruits is over 80% of their fresh vegetables and fruits.

Example 1: Assisted method for soaking and freezing green soybeans by ultrasonic wave 40g green soybeans are selected, washed, enzyme-inactivated by hot water (100 ° C, 1 minute), cooled with ice water for 2 hours, and the precooled sample is made of metal Into the reaction vessel, 1500 mL of a 50% aqueous glycol solution as a secondary refrigerant was added, and the soybean was soaked and frozen by combining ultrasonic waves. The condition of ultrasonic treatment is that the frequency is 20 to 24 KHz, power 80 W, pulse mode 50%, total time 1 min, secondary refrigerant temperature is −20 ° C., green soybean center temperature is −18 ° C. It was something to do. The freezing time was 3.1 min. Samples were packaged at low temperature (temperature -5 ° C, power 40W). The final sample was packed in a high density polyethylene bag (99.99% purity) as necessary to obtain a quick frozen edamame product. -18 ° C and stored frozen at low temperature. After thawing by microwave, the free droplet ratio of frozen green soybean becomes 3% or less.

Example 2: A method for assisting immersion and freezing of potatoes using ultrasonic waves 50 g of potato serving as a material is selected, washed, shaved, cut into an elongated shape of 70 mm × 15 mm × 15 mm, and enzyme-inactivated with hot water (100 ° C., The sample was cooled with ice water for 2 hours, and the precooled sample was put in a metal reaction vessel, and a 50% glycol aqueous solution (150 OmL) as a secondary refrigerant was added, and the temperature was controlled with a thermocouple. After the center temperature of the potato chips dropped to 0 ° C. or lower, the immersion freezing treatment was performed by combining ultrasonic waves. The conditions for ultrasonic treatment are that the frequency of 25 KHz, power 40 W, pulse mode 60%, total time 2 min, secondary refrigerant temperature -20 ° C, potato chips center temperature -18 ° C, and freezing end point. there were. The freezing time was 14 min. Samples were packaged at low temperature (temperature -5 ° C). The final sample was packaged in a high density polyethylene bag (99.99% purity) as necessary to obtain a quick frozen potato chips product. -18 ° C and stored frozen at low temperature. After thawing by microwave, the free droplet ratio of the frozen potato sample is 4% or less.

Example 3: Auxiliary method of immersion freezing of kiwifruit slices by ultrasonic wave Select kiwifruit 45g as a raw material, scrape the skin, cut into 1cm thick kiwifruit slices, scrape the skin, remove the center, Enzyme inactivation with hot water (100 ° C., 15 s), put into a low-temperature anti-coloring solution, and simultaneously prevent coloring and pre-cooling for 2 hours, put the pre-cooled sample in a metal reaction vessel, 50% of the secondary refrigerant Glycol aqueous solution 1500mL was added and temperature control was performed with a thermocouple. After the center temperature of the kiwifruit slice dropped to 0 ° C. or lower, immersion freezing treatment was performed by combining ultrasonic waves. The ultrasonic treatment conditions are a frequency of 25 KHz, power of 40 W, pulse mode of 40%, total time of 2 min, secondary refrigerant temperature of −20 ° C., kiwifruit cut center temperature of −18 ° C. and freezing end point. Met. The freezing time was 7.5 min. Samples were packaged at low temperature (temperature -5 ° C). The final sample was packaged in a high density polyethylene bag (99.99% purity) as needed to obtain a quick frozen kiwifruit cut product. -18 ° C and stored frozen at low temperature. Since the formation of ice crystals was accelerated by ultrasonic waves, the destruction of the cells by the crystals was reduced, and the nutrient components and color of kiwifruit were well maintained. The quality scoring of vitamin C, which is a nutritional component, improved nearly twice as much as that of the reference sample (a general immersed frozen sample not subjected to ultrasonic waves). After thawing by microwave, the free droplet ratio of the frozen kiwifruit sample is 5% or less.

Claims (2)

Select, wash, and cut fruit and vegetables as raw materials, inactivate enzymes with hot water, cool, freeze / freeze ultrasonically-freeze, and use supersonic-freeze freezing in quick-frozen vegetables and fruits Adopted
In the freezing / ultrasonic assisted freezing, a secondary refrigerant having a temperature of −20 to −18 ° C. is used as a refrigerating medium to perform immersion / freezing treatment, and the weight / volume ratio of the raw fruits and vegetables to the secondary refrigerant is used. Is (l: 30-1: 40) g / mL, and when the center temperature of the vegetable and fruit foods falls below 0 ° C., the ultrasonic frequency is 20-24 KHz, the power is 40-80 W, the ultrasonic pulse mode is 40%- Ultrasonic-assisted freezing is performed under the conditions of 60% and the total time of 0.8 to 2 min, and 45 to 50% glycol aqueous solution is used as a secondary refrigerant, and the ratio of free droplets of the sample after thawing by microwave is 3 A method for improving the thawing quality of quick-frozen vegetables and fruits by low-frequency ultrasonic waves, characterized in that the content is 5% to 5%.   The method of claim 1, wherein the packaging of the quick frozen vegetables and fruit products is rapidly packaged in a low temperature environment below -5C.