1. Spray drying technology
The research of spray drying technology began in the early 19th century. With the wide application of spray drying technology in industry, people have also conducted 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 transported by the pump to the atomizer at the top of the spray dryer through the filter, and the liquid material is dispersed into droplets by the atomizer. Due to the small radius of the droplet, the specific surface area and surface free energy are large, and Highly dispersed, the vapor pressure of the moisture on the surface of the droplet is higher than the vapor pressure of the plane liquid moisture under the same conditions, so the moisture volatilizes very quickly, and the product is quickly dried.
Dai Minghe et al. deduced a one-dimensional two-way static mathematical model of the spray drying process according to the conservation of mass, 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. Food contains more protein and sugar, and protein is generally denatured when kept at 60-80 °C for several minutes, and Maillard reaction will also occur when placed at high temperature. Using spray drying, the product can be dried in only 3-10s, which can effectively inhibit the thermal denaturation of the 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 process of spray drying, the drying of the product is carried out in hot air, so the product can basically maintain a spherical shape similar to the droplet, so it has good dispersibility, fluidity and solubility.
1.2.3 The production process is simplified, the operation control is 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, thus 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 large-scale production.
1.2.4 Prevent pollution and improve production environment. Since the spray drying is carried out in a closed container, it can avoid dust flying during the drying process and avoid environmental pollution.
1.3 Problems existing in spray drying
The advantages of spray drying technology are significant, but its shortcomings cannot be ignored. Its shortcomings are mainly manifested in large power consumption, low volumetric heat transfer coefficient and thermal efficiency, large equipment volume, easy wall sticking phenomenon, and large one-time investment.
Especially the sticky wall problem. If the sticky wall material stays on the hot inner wall for a long time during the spray drying process, it may be scorched or deteriorated, which will affect the product quality. Zhou Xueyong et al. analyzed the types and causes of spray drying sticking, and proposed three types of spray drying sticking: semi-wet material sticking, low-melting material hot-melt sticking and dry powder surface sticking, and proposed Solutions to 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
China is a big agricultural country, and the fruit and vegetable industry has become a pillar industry second only to grain in China. Because of its unique advantages, fruit and vegetable powder can not only overcome the shortcomings of fruits and vegetables such as intolerant storage, easy to rot and deteriorate, but also meet people’s needs for diversification, high-grade and freshness of fruits and vegetables, so it has broad development prospects.
There are many preparation techniques for fruit and vegetable powder, such as spray drying, hot air drying, vacuum freeze drying, microwave drying, temperature-variable pressure differential puffing drying and ultra-fine pulverization technology. occupies a very important position.
2.2 Application of spray drying technology in instant tea beverage
Instant tea beverage is a kind of solid beverage tea that can be quickly dissolved in water. It has many characteristics, such as easy to brew and carry, instant soluble in water, no residue, less pesticide residue, easy to adjust the thickness or easy to mix with other foods, etc. more and more popular.
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 granulated sugar is 8%, and the addition amount of maltodextrin is 15%. 25ml/min.
2.3 Application of spray drying in food additives
Because some food additives are easily affected by factors such as light, oxygen, temperature, moisture in the environment, and the peculiar smell, odor, pungent smell and other bad odors of the food additives themselves, their application in food is seriously affected and the food industry is hindered. development of.
In the 20th century, with the birth of microencapsulation technology, these problems were solved, and the key of microencapsulation technology is spray drying. NgLayTze et al. studied the effects of different maltodextrin concentrations and spray-drying population temperature on the betaene content of pitaya, and the optimal spray-drying conditions were human inlet temperature 155°C and 20% maltodextrin concentration.
2.4 Application of spray drying in health food
Because the polyunsaturated fatty acids (DHA and EPA) in fish oil are easily oxidized, which seriously hinders their application and market demand in health food, microencapsulation of fish oil can not only effectively prevent its oxidative deterioration, but also mask the fishy smell.
2.5 Application of spray drying technology in other food fields
With the in-depth research of 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, grain powder, seasoning powder, etc. . Due to the development of the economy and the improvement of people’s lives, the intake of grains in many areas has decreased, and grains are rich in dietary fiber, minerals, etc., which are indispensable to the body, so grain flour Popular with consumers.
Using spray drying technology as the main carrier, Li Junan conducted flour milling on various grains and fruits such as yam, black rice, corn, buckwheat, orange, etc., and evaluated the effect of spray drying on the functional and active components. The spray-dried powder was used as the base material, and 4 kinds of prepared functional beverages were prepared. In addition, spray drying technology is also commonly used in the processing of infant nutritional foods, the most common of which is the processing of infant milk powder.