What is the application of frying technology in prepared foods?

Prepared foods (Prepared foods), also known as convenience prepared foods, refers to agricultural, livestock, aquatic products as raw materials, after appropriate conditioning, properly packaged, in the frozen (18 ℃), refrigerated (7 ℃ or below) or by the gas conditioning and other treatments can be stored at room temperature, trafficking, and can be directly consumed or eaten before a simple processing or heat treatment can be consumed products.

Conditioned food is in essence a convenience food, with convenience, speed, delicious flowers, nutrition, safety and other characteristics. Because of its high value-added products and the demand for localized tastes, it is recognized as one of the products with development potential in the domestic food industry. With the innovation of technology, the improvement of cold chain circulation system, the updating of packaging materials and the development of high-efficiency defrosting equipment, the new type of prepared food has an unlimited market prospect.

Deep-fried seasoned food has a unique flavor, simple seasoning can be eaten, can be stored at room temperature and other advantages, can be accepted by the majority of consumers. In today’s fast-paced life, although people have mixed feelings about it, but one thing is indisputable, fried instant noodles, French fries and fruit and vegetable crisps and other representative of the bulk of fried seasoned food has become indispensable to people’s food.

Frying technology can be divided into three categories: atmospheric pressure frying, reduced pressure frying and high pressure frying.
Atmospheric pressure deep-frying kettle pressure and environmental atmospheric pressure is the same, usually open, is the most common way of deep-frying, applicable to a wider range, but the food in the process of atmospheric pressure deep-frying nutrients and natural pigment loss is greater, so the atmospheric pressure deep-frying is more suitable for grain food deep-frying. Such as fried pastries, fried bread, fried instant noodles dehydration.

Low-pressure deep-frying, also known as vacuum deep-frying, food in the edible oil for deep-frying dehydration and drying, so that the water in the raw material is fully evaporated off the process. The frying temperature in the frying kettle is generally below 100 ℃, and the vacuum degree is 92~98.7 kPa. This method can make the products maintain good color, shape and crispness, and due to the low-oxygen environment, the products as well as the degradation of fats and oils will be reduced accordingly, and the loss of nutrients will be less.

High-pressure deep-frying is a method of deep-frying in which the pressure in the frying kettle is higher than the normal pressure. High-pressure deep-frying can solve the problem of affecting the quality of food due to the need for long-time deep-frying, this method of high temperature, water and oil volatilization loss is less, the product is crispy on the outside and tender on the inside, which is most suitable for the deep-frying of meat products, such as deep-fried chicken thighs, deep-fried steak and so on.

Microwave heating compared with conventional heating has significant differences, mainly due to the heating form, heating speed of the different, resulting in different distribution of heat energy and moisture in the food, thus affecting the intrinsic quality of food. Conventional heating requires heating environment and heat medium, it takes a relatively long time to reach the required heating temperature, while microwave heating can make the food directly absorb microwave and can be heated immediately.

Microwave heating of food is through the microwave electric field and magnetic field alternating cycle changes, so that the dipole molecules in the food (such as water, proteins, etc.) with the magnetic field changes continue to turn back and forth, molecules and molecules of friction, collision, vibration, extrusion and other roles to generate heat, so that the food is heated, and the heating speed, time-consuming short, high quality products. The combination of microwave and vacuum deep-frying, not only in a very short period of time and rapid dehydration, but also in the negative pressure conditions can be very good to maintain the quality of the product, so as to realize the microwave efficient deep-frying of seasoned foods.

Atmospheric Frying Conditioned Food

1、Normal pressure deep-frying
Atmospheric pressure frying as a means of food processing can be traced back to 1600 BC and the ancient Egyptian era. Although there is no clear record of the time when deep-frying was actually used as a means of food processing, the word “frying” is derived from the Latin and Greek word “roasting”, which suggests that deep-frying may have been developed by the roasting technique. Normal pressure deep-frying because of its earlier origin, domestic and foreign research on the deep-frying technology and equipment is more mature, and is now more popular at home and abroad.

2、Normal pressure deep-frying equipment
Atmospheric pressure deep-frying equipment mainly includes electrically heated deep-frying equipment, gas type deep-frying equipment, continuous deep-fryer, oil and water mixing type deep-frying equipment and microwave atmospheric pressure deep-frying equipment.

When the electric heating frying equipment is in operation, the material will be placed in the material net basket and put into the oil for frying. After frying, the basket is taken out together. This frying method has the following disadvantages:

1) The oil is at high temperature during the frying process, the oil oxidizes and deteriorates very quickly, the viscosity rises, and the oil becomes black-brown after repeated use for several times, which is inedible.

2) the bottom of the ash accumulation residue, with the prolongation of the frying time. The oil becomes more turbid, and the residue attached to the surface of the product will accelerate the deterioration of food, seriously affecting the health of consumers.

3) high temperature for a long time repeatedly frying food oil will generate a variety of forms of toxicity of different oil polymers, these substances can lead to nerve paralysis, stomach tumors and even death.

Gas frying equipment with gas as the energy source of a frying equipment, equipped with automatic ignition and manual ignition, flame control, frying time, temperature control, air pressure adjustment, etc., the use of safe, convenient, hygienic, is the more ideal frying equipment.

Continuous deep fat fryer equipment is characterized by no frying cage, but can make the material all submerged in the oil for continuous frying.

The heating of the oil is carried out outside the pot, with a hydraulic device that can raise the whole conveyor frame and its accessory parts and components from the oil tank, easy maintenance. The oil-water mixing fryer completely changes the structure of the traditional atmospheric pressure frying equipment. Scientifically adopting oil-water mixing technology, through the use of a new type of burner. Sealed heating, in the process of warming up the lower oil temperature is effectively controlled, slowing down the oxidation of deep-frying, prolonging the service life of the frying oil and improving the quality of the products. Greatly enrich and revolutionize the deep-frying technology.

3、Research progress of atmospheric pressure deep-frying
Atmospheric pressure for deep-frying process, the oil temperature above 160 ℃, in the case of high temperature, will produce a special flavor. Some scholars have studied the oil intake and textural changes in fried potato chips, potato chips blanched in hot water at 85 ℃ for 3.5 min and untreated samples at 120, 150, 180 ℃ oil temperature for deep-frying. The results showed that the frying temperature and pretreatment method could significantly affect the final fat content of fried potato chips, and the higher the temperature, the lower the fat intake of potato chips. However, the frying temperature and pretreatment method had no significant effect on the final texture of fried potato chips.

In recent years, the use of microwave heating instead of traditional frying methods has become increasingly popular. Some scholars have studied the effect of pre-drying time on microwave low-oil potato chips. In order to potato chips have the flavor of fried food, while avoiding the low fat content of atmospheric pressure frying, the surface of the potato chips before baking with a brush coated with a layer of oil, so that the potato chips in the microwave treatment process to produce a “fried” environment. The purpose of microwave treatment is to dry and cook the potato chips, and the chips are baked in a microwave oven after being coated with oil until they are cooked. The results showed that the use of microwaves in the production of potato chips reduced the oil content to less than 20%. Microwave frying can be regarded as a suitable alternative to traditional frying.

4, atmospheric pressure deep-frying problems
Normal pressure deep-frying due to the high temperature will bring a lot of problems, such as food nutrients are damaged at high temperatures, color, aroma, taste and so on are affected. In addition, the high temperature makes the oil fuming, pollution of the environment, increasing oil consumption, while repeated use of deep-frying at high temperatures, will produce thermal oxidation reaction, the generation of unsaturated fatty acid peroxides, which can directly impede the body on the absorption of fats and proteins, reduce the nutritional value of food.

The components in the oil undergo many chemical reactions, leading to acidic degradation of the fried oil, thickening of the oil, producing bad taste. Even produce some harmful and even carcinogenic substances, affecting the health of consumers, such as acrylamide. Atmospheric pressure and high temperature fried food oil content are very high, so that some special groups (such as obese people, cardiovascular patients, etc.) want to eat and do not dare to eat, so that the scope of atmospheric pressure deep-fried food processing and sales have been greatly restricted. Therefore, reducing the oil content of atmospheric pressure frying products is also an urgent problem.