Effect of roasting condition and ventilation on reduction of benzo(a)pyrene generation in sesame oil

Abstract

Sesame oil is a preferable seasoning having lots of usage in Korea. However, highly carcinogenic benzo(a)pyrene (BaP) was often detected exceeding the regulation level for sesame oil. Therefore, there have been many tries attempted to reduce BaP in sesame oil. BaP increases through manufacturing process especially during roasting or pressing at high temperature by incomplete combustion of hydrocarbons. To reduce BaP production in the manufacture of sesame oil, improved equipment and optimized conditions are necessary. New equipment for production of sesame oil in this study consists of automatic washing machine, roaster, filter, cyclone, and oil press, and the process conditions to reduce BaP were explored. Water content of sesame seeds, roasting temperature, ventilation speed, and dust removal were the main investigated factors. Raw sesame seeds had 5% of water content but increased to 25% after washing. Water content was controlled to 30, 25, 15, and 10% by repeated washing and drying. As water content of sesame seeds increased, BaP content in oil also increased by having high chance of generating incomplete combustion during roasting. Meanwhile, roasting without washing resulted in slightly high concentration of BaP in oil, indicating that washing had an effect of removing dust which can burn and increase BaP content. In case of roasting, roasting temperature and ventilation was important factors related to BaP generation. Roasting temperature is classified as heater temperature (220 and 250°C) and completing seed temperature (150, 180, and 210°C) which varies roasting time. Roasting at heater temperature 250°C spent less than 40 min until seed temperature reaches 210°C, but roasting at 220°C spent more than 1 hr to reach 150 and 180°C and generated more BaP. It indicated that total roasting time was more important than temperature for BaP generation. Also, ventilation during roasting was another effective factor for reduction of BaP. The smoke was eliminated by diverse ventilation speed (0, 15, 30, 45, and 60 Hz). Higher ventilating speed tended to reduce more BaP generation, however, too high speed (60 Hz) of ventilation increased BaP making air circulate faster around sesame seeds causing cooling effect. Correspondingly, sesame seeds were heated longer, which led the part near the heater burnt more. Finally, the dust removal process also affected BaP concentration. Foreign materials which went through the roasting process would cause high BaP content in oil and need to be removed. The removing process was separated by size of the material. A filter was used for bigger material than sesame seed, and a cyclone was used for fine dusts to be removed. Between these two, cyclone was more effective to reduce BaP in oil, but operating together made synergetic effect decreasing more BaP. In conclusion, low water content, short roasting time, adequate ventilating speed, and removing dust with a filter and a cyclone made 35, 59, 46, and 38% of BaP reduction in sesame oil, respectively. Throughout these process, BaP content was reduced by 67% in sesame oil. From this study, BaP reduced sesame oil can be manufactured by using the remodeled equipment and applying optimal condition of process, and it could be used for studies constructing production process for other types of pressed oil.