Development and test of continuous combined mid-infrared with hot air drying equipment

Abstract: Drying efficiency was always considered to be the most important factor by factories, however, low thermal conductivity and case hardening of the material slowed the moisture migration in hot air drying, and resulted in more time and energy consumption. So to solve the existing problems of present drying equipment, a continuous drying equipment of combined mid-infrared and hot air (CMIHA) was developed in this paper. This drying equipment included feed section, heating sections and cooling section, of which each heating section was made up of four parts, i.e. conveying system, heating system, convective circulation system and control system. As we all know, since infrared energy is converted into heat only when material absorbs the radiation, it was essential to select a heat source emitting radiation with the range in which the material to be processed had maximum absorption. So, the radiation wavelength of infrared was selected by the infrared spectra of meats, and the radiation intensity could be controlled by changing the amount of working lamps to make good use of the radiation energy. At the same time, this equipment was developed by calculating the main technological parameters of convection system, cooling system and heating system, and then the production verification test was also done to compare the difference between CMIHA drying and hot air drying on beef jerky. Results showed that, in the same conditions (heating power 105 kW, heating temperature 70℃, wind velocity 1 m/s, cooling wind velocity 3 m/s, heating distance 8 cm), compared with hot air drying, the continuous CMIHA drying equipment could speed up muscle protein denaturation, reduce activation energy, reduce the energy that jerky needed to accelerate moisture migration, and improve drying efficiency. The time consumption that the beef samples in the first row on the conveyor dehydrated from raw to weight reduction by 50% for CMIHA drying equipment was 120 min, and the production efficiency was 120 kg/h, if the working time of equipment was more than 10 h every day. However, the time consumption and production efficiency of hot air drying equipment were 280 min and 40 kg/h, respectively. Besides, compared with hot air drying equipment, CMIHA drying equipment could reduce the case hardening of jerky, significantly decrease (P<0.05) the value of shear force and shrinkage rate, and increase (P<0.05) the values of chewiness of jerky, and the chewiness, shear force and shrinkage rate were 44.79 N, 143.59 N and 45.48%, respectively, but those of hot air drying were 35.87 N, 182.69 N and 55.0%, respectively. As we all know, different kinds of myoglobin can make meat have different colors, of which myoglobin is kermesinus, oxymyoglobin is bright red and metmyoglobin is taupe brown. Compared with hot air drying equipment, CMIHA drying equipment could increase the content of oxymyoglobin, and reduce the content of metmyoglobin, which made jerky have better color. The values of a* (redness value), C* (chroma value) and H* (hue value) of jerky dried with CMIHA were significantly higher (P<0.05) than hot air. Besides, the sensory evaluation of jerky dried with CMIHA drying had higher scores than hot air drying. This study can provide valuable information for designing and developing this new continues combined mid-infrared and hot air drying equipment that can be used for solving the problems that low drying efficiency and poor quality of jerky.