Investigation of the effect of sterilization methods on the quality characteristics of cumin

Microbial contamination of spices and medicinal plants at various stages of the production leads to low quality and shorter shelf life. As a result, sterilization is required to decrease the microbial load. The purpose of the current study was qualitative comparison of the two methods induction heating technology (115, 135 and 155 °C for 45, 60 and 75 s) with gamma irradiation (5 and 10 kGy) for sterilization of cumin seeds. For this purpose, microbial load (total microbial count, mold and yeast and coliform), total color differences and essential oil content were studied as quality properties of cumin seeds. After examining the influence of various induction heating system treatments on the specified parameters, process optimization was carried out by using the response surface methodology. Optimal decontamination conditions were obtained with a combined treatment of 151 °C -46 s. In these conditions, total microbial count, mold and yeast, coliform, total color differences and the amount of essential oil were 3.06 CFU/g, 3.1 CFU/g, 2.28 CFU/g, 4.15 and 2.57%, respectively. The optimal points of the induction heating method were validated and compared with the gamma irradiation method. The results showed that gamma irradiation caused in the greatest decrease of microbial load (1.52 CFU/g) (10 kGy). The least amount total color differences were found at 5 kGy treatment with a value of 2.76. No significant effect on total color differences was identified between gamma irradiation (10 kGy) and induction heating system. The highest and lowest levels of essential oil were found in the induction heating treatment (151 °C -46 s) and gamma irradiation (5 kGy), with the values of 2.45 and 1.7 %, respectively. According to the results of scanning electron microscope, induction heating led to a change in the surface structure, pores and cracks in the seed surface compared to gamma irradiation.