Abstract: Spray drying is one of the most commonly used drying methods in the food industry. With the in-depth research and development of spray drying technology and equipment, the application of spray drying technology in the food industry will be more extensive. The main characteristics and existing problems of spray drying are briefly introduced, and the application of spray drying technology in food industry is emphatically expounded.
Key words: spray drying; food industry; application; current situation
Spray drying is one of the most commonly used drying methods in the food industry. In 1872, the American SameulPercy clearly discussed the essence of the spray drying process in his patent “Improvement of Drying Operation and Concentration of Liquid Materials by Atomization”. The birth of drying equipment has made an important contribution. Since LaMont proposed spray drying method to treat eggs in 1865, spray drying technology has been developed for more than a century, but it started relatively late in my country. In the 1950s, Jilin Dye Factory introduced the rotary spray dryer from the former Soviet Union. , for the spray drying of dyes, since then the spray drying technology has been industrialized in our country. With the improvement of spray drying technology and the deepening of research, at present, this technology has been widely used, especially in the food processing industry. In the early 20th century, it was first used in the manufacture of skimmed milk powder. Later, spray drying technology was also widely used in the manufacture of dairy industry, solid beverage and solid seasoning, so that the food industry has been greatly developed.
1 Spray drying technology Research on spray drying technology
Beginning in the early 19th century, with the wide application of spray drying technology in industry, people have also carried out in-depth research on its basic principles and characteristics.
1.1 The principle of spray drying technology
The basic principle of spray drying is that the material is pumped through the filter to the atomizer at the top of the spray dryer. The atomizer is used to disperse the liquid material into droplets. Due to the small radius of the droplets, the specific surface area and surface free energy are large, and Highly dispersed, the vapor pressure of the moisture on the surface of the droplets is larger than that of the liquid moisture on the surface under the same conditions, so the moisture evaporates very quickly and the product is dried quickly. Dai Minghe et al. derived a one-dimensional bidirectional static mathematical model of the spray drying process based on mass conservation, energy conservation and Newton’s second law, and theoretically studied the thermal drying mechanism of spray drying, which is of great significance for improving the technical level of spray drying.
1.2 Characteristics of spray drying technology
1.2.1 Dry quickly to ensure product quality. Foods contain a lot of protein and sugar, and protein is generally denatured at 60-80°C for a few minutes, and Maillard reaction will also occur when placed at high temperature [6]. Using spray drying, the product can be dried in only 3-10 seconds, which can effectively inhibit the thermal denaturation of food and the loss of aromatic components during the drying process, and ensure the quality of the product.
1.2.2 The dry product has good dispersibility, fluidity and solubility. For dry products, dispersibility, fluidity and solubility are important indicators of product quality. In the spray drying process, the drying of the product is carried out in hot air, so the product can basically maintain a spherical shape similar to the droplet [7], so it has good dispersibility, fluidity and solubility.
1.2.3 The production process is simplified, the operation and control are convenient, and it is suitable for continuous large-scale production. Most of the products obtained by spray drying do not need to be pulverized and screened, thereby reducing the production process and simplifying the production process. The particle size, bulk density and water content of the product can be adjusted by changing the operating conditions within a certain range, the control and management are very convenient, and it can meet the requirements of industrialized mass production.
1.2.4 Prevent pollution and improve the production environment. Since the spray drying is carried out in a closed container, it can avoid dust flying caused in the drying process and avoid environmental pollution.
1.3 Problems in spray drying
The advantages of spray drying technology are significant, but its disadvantages cannot be ignored. Its disadvantages are mainly manifested in large power consumption, low volumetric heat transfer coefficient and thermal efficiency, large equipment volume, prone to wall sticking, and large one-time investment. Especially the wall sticking problem, if the wall sticking material stays on the hot inner wall for a long time during the spray drying process, it may be burnt or deteriorated, which will affect the product quality. Zhou Xueyong et al. analyzed the types and causes of spray drying sticky walls, and proposed three types of spray drying sticky walls: semi-wet material sticky walls, low-melting material sticky walls and dry powder surface sticking, and proposed Solutions for various types of sticky walls.
2 Application of spray drying in food industry
2.1 Application of spray drying in the production of fruit and vegetable powder
my country is a large agricultural country, and the fruit and vegetable industry has become a pillar industry second only to grain in the country. Due to its unique advantages, fruit and vegetable powder can not only overcome the shortcomings of fruits and vegetables that are not resistant to storage and are easy to rot and deteriorate, but also can meet people’s needs for the diversification, high-end and freshness of fruits and vegetables, so it has broad development prospects. There are many techniques for preparing fruit and vegetable powder, such as spray drying, hot air drying, vacuum freeze drying, microwave drying, variable temperature and pressure difference puffing drying and ultrafine grinding technology, etc. occupies a very important position. VaibhavPatil et al. applied response surface methodology (RSM) to optimize the spray drying process of guava powder. When the inlet temperature was 185°C and the concentration of maltodextrin was 7%, guava powder was rich in vitamins. Wang Yachen and others studied the process conditions of enzyme-treated wild papaya instant solid beverages. The results showed that wild papaya was treated with enzymes and spray-dried at an inlet air temperature of 175°C to obtain a wild papaya with rich taste and suitable sweet and sour taste. Papaya instant solid drink. Di Jianbing et al. used yam as a test material, preboiled it into pulp, and then sprayed it to make powder. When the additive amount is 4%, the yam powder made is white, fine and fine, and has a high quality evaluation.
2.2 Application of spray drying technology in instant tea beverage
Instant tea beverage is a solid beverage tea that can be quickly dissolved in water. It has many characteristics such as easy to carry, instant dissolving in water, no residue, less pesticide residue, easy to adjust the concentration or easy to mix with other foods, etc. More and more people of all ages. Bi Qiuyun used Ganoderma lucidum and black tea as raw materials, and used spray drying technology to study the production process conditions of Ganoderma lucidum black tea solid beverage. The addition amount of citric acid is 1%, the addition amount of white sugar is 8%, and the addition amount of maltodextrin is 15%. 25ml/min. Cheng Jianbo et al. used black tartary buckwheat as the main raw material and adopted spray drying technology to study the processing technology of making instant red dates and black tartary buckwheat milk tea, and determined that the inlet air temperature of the key process spray drying was 185°C, and the outlet air temperature was 90°C.
2.3 Application of spray drying in food additives
Food additives can not only improve the sensory qualities of food such as color, aroma, and taste, but also meet the needs of product preservation and processing technology to a certain extent, which greatly promotes the development of the food industry and is known as the soul of the modern food industry. However, because some food additives are easily affected by factors such as light, oxygen, temperature, and moisture in the environment, and the odor, odor, and spicy taste of the food additive itself have bad odors, which seriously affect its application in food and hinder the development of food products. Industrial development. With the birth of microcapsule technology in the 20th century, these problems were all solved, and the key of microcapsule technology is spray drying. NgLayTze et al. studied the effects of different maltodextrin concentrations and spray drying inlet temperatures on the content of betatin in dragon fruit. The optimal spray drying conditions obtained were inlet temperature 155°C and 20% maltodextrin concentration. Liu Nannan used gelatin and gum arabic as wall materials to embed scallion oil essence by composite coacervation method. Taking microcapsule embedding rate as an evaluation index, the main factor affecting the embedding rate was optimized by response surface methodology: wall material concentration , core-to-wall ratio, and pH. The study found that the optimal process parameters for the preparation of scallion oil flavor microcapsules by complex coacervation method are: the wall material concentration is 1.82%, the core wall ratio is 1:1.87, and pH4.16, and on this basis, the spray drying method The white powder product of scallion oil flavor microcapsules can be prepared, the particle size of the microcapsules is relatively uniform, and the volume average particle size is 65.54 μm.
2.4 Application of spray drying in health food
In recent years, with the continuous improvement of residents’ economy and living standards, some diseases of modern civilization, such as hypertension, hyperlipidemia, and diabetes, have also emerged. Fish oil is rich in omega-3 polyunsaturated fatty acids (DHA and EPA), which has anti-inflammatory and blood lipid regulation effects, and is known as the “evergreen tree” in health food. With the continuous development of my country’s national economy, the continuous improvement of the living standards of urban and rural residents, and the continuous aggravation of population aging, the fish oil market has continued to expand, and fish oil consumption has also begun to grow rapidly. However, because the polyunsaturated fatty acids (DHA and EPA) in fish oil are easily oxidized [23], their application in health food and market demand are seriously hindered, and the microencapsulation of fish oil can not only effectively prevent its oxidative deterioration, but also cover up fishy smell. SriHaryaniAnwar et al. studied microencapsulated fish oil prepared by various drying methods, and compared the stability of microencapsulated fish oil prepared by spray granulation drying (SG), spray drying (SD) and freeze drying (FD). Propolis contains rich and unique biologically active substances, which have various functions such as antibacterial, anti-inflammatory, anti-itching, anti-oxidation, enhancing immunity, lowering blood sugar, lowering blood fat, and anti-tumor. It has a wide range of medical and health effects on the human body. It is a kind of Products with higher health functions. Zhang Yingxuan used the spray drying method to microencapsulate the propolis extract, and discussed the microencapsulation process of propolis by spray drying method by measuring the activity of total flavonoids, the main active substance in the microencapsulated propolis. The test shows that the wall material is mixed with gum arabic and dextrin in a ratio of 1:1, the solid content is 20%, the ratio of core material to wall material is 1:4, the injection volume is 20ml/min, and the air inlet pressure is 0.2MPa , the activity of total flavonoids in microencapsulated propolis is the highest.
2.5 Application of spray drying technology in other food fields
With the deepening of the research on spray drying technology and the continuous improvement of people’s requirements for the flavor and nutritional value of food, more and more foods produced by spray drying method appear on the market, such as egg yolk powder, miscellaneous grain powder, seasoning powder] Wait. Due to the development of the economy and the improvement of people’s lives, the intake of miscellaneous grains and grains has decreased in many areas, and miscellaneous grains and grains are rich in dietary fiber, minerals, etc. These substances are indispensable to the body, so grain flour Much loved by consumers. Li Junan used spray drying technology as the main carrier to process yam, black rice, corn, buckwheat, orange and other grains and fruits into powder, and evaluated the effect of spray drying treatment on the functional active ingredients; The spray-dried powder was used as the base material, and 4 kinds of ready-to-use functional drinks were prepared. In addition, spray drying technology is also commonly used in the processing of infant nutritional food, the most common is the processing of infant milk powder. Shen Guohui etc. adopt the research of spray-drying technology to prepare microencapsulated infant milk powder to show that the optimal process conditions of infant milk powder adding DHA microcapsules are: homogeneous pressure is 40MPa, homogeneous temperature is 40 ℃, spray drying inlet air temperature is 170 ℃, the air outlet temperature is 80 ℃, under this condition, the milk powder added with DHA microcapsules is prepared, and the quality index is extremely stable during the product shelf life, without any adverse reactions.
3 Conclusion
Spray drying has been used in the food industry for many years. It was only used in the manufacture of milk powder at the earliest, and it has been widely used in the food industry. Nutritional value provides better protection for people’s health. With the in-depth research and development of spray drying technology and equipment, as well as the continuous improvement of people’s requirements for the flavor and nutritional value of food, more and more spray drying products will appear in the market, and the food industry will surely develop rapidly and have a bright future.