Effects of combined mid-infrared and hot air (CMIHA) drying and hot air (HA) drying on the physical characteristics of beef jerky were investigated in this paper. Physical characteristic was one of the most important quality characteristics for drying food, such as beef jerky. Different drying methods had different physical characteristic. In terms of HA drying, which was often used in factory, lower drying efficiency and physical characteristics were the main problems that demanded to be resolved. CMIHA drying was a new drying method used in beef jerky, which could improve drying efficiency and reduce energy-consumption, but the reason why it could improve quality of jerky, especially the physical characteristic, were still unknown. So, the physical characteristic (color and texture characteristic) of beef jerky was studied in this paper. Firstly, for studying the color characteristic of jerky drying CMIHA and HA drying, the changed of L*, a* and b* value during drying were investigated, and then contents of myoglobin, metmyoglobin, oxymyoglobin and heme iron were studied to explain the changes of color. Secondly, the changes of shear force and TPA of jerky were determined during drying, and then the changes of microstructure, ultra microstructure and H proton density images of jerky were observed by using scanning electron microscopy (SEM), transmission electron microscope (TEM) and magnetic resonance imaging (MRI), respectively, to explain the changes of texture properties. The results showed that, compared with HA drying, CMIHA drying could significantly improve (P〈0.05) the values of L*, a* and b*, decrease the value of shear force and increase the values of spring, gumminess and chewiness of jerky during the later stage of drying. As we all known, different myoglobin could make meat have different color, myoglobin was kermesinus, oxymyoglobin was bright red and metmyoglobin was taupe brown. Compared with HA, CMIHA drying could reduce the oxidation of myoglobin, and increase the contents myoglobin, oxymyoglobin and heme iron, reduce the content of metmyoglobin, which could make jerky have better color than HA drying. SEM and TEM shown that compared with HA drying, CMIHA drying could keep the myofiber of jerky in better shape, reduce the shrinkage of myofiber and sarcomere, and increase the dissolve of Z line. This could explain why jerky dried with CMIHA had better tenderness, spring, and chewiness than HA drying. Results of MRI shown that the H proton density of jerky drying the two drying methods were all decreasing and shrinkage, but compared with HA drying, CMIHA drying could reduce the shrinkage of H proton density and make the distribution of water in surface and inside are uniformity, which could made jerky have better spring and chewiness. So, compared with HA drying, CMIHA drying could reduce the oxidation of myoglobin, and increase the contents myoglobin, oxymyoglobin and heme iron, reduce the content of metmyoglobin, so as to improve the color characteristic. Besides, CMIHA drying could make myofiber in good shape, reduce the shrinkage of myofiber and sarcomere, increase the dissolve of Z line and make the distribution of water in surface and inside are uniformity. So as to improve the physical characteristics of beef jerky, this study can offer better theoretical foundation for the application of CMIHA drying on beef jerky to improve the physical characteristics. ©, 2014, Chinese Society of Agricultural Engineering. All right reserved.
