John P. Giesy

Recently, processed foods have become an important part of human eating habits. However, several processing techniques, such as dehulling and roasting, are applied to raw foods. Roasting is a thermal process that depends on temperature and time and improves the extraction yield of oil by generating pores in the oilseed cell walls. Sesame (Sesamum indicum L.) is an annual plant belonging to Pedaliaceae and is considered to be one of the oldest oil crops. Nowadays, the cultivation of this plant is economically important in several countries. This review clarifies the botanical characteristics and nutritional importance of sesame seeds, reviews their phytochemical composition, and discusses the effects of dehulling and roasting on their nutritional quality. S. indicum, which is known to contain several classes of bioactive compounds, including fatty acids, phenolic compounds, amino acids, and lignans, has been reported to possess a wide range of biological activities such as antioxidant, anti-inflammatory, anticancer, antimicrobial, and cardioprotective activity; however, processing such as dehulling eliminates undesirable chemical constituents while roasting provides the best chemical composition at moderate temperatures.

Biochar’s agricultural and environmental benefits have been widely demonstrated; however, it may cause environmental contamination if it contains large amounts of pollutants such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs). Therefore, this study aimed to assess the contents of PAHs and HM in a range of biochars generated from different sources and pyrolysis temperatures. A range of feedstock was converted to biochar, including sewage sludge (SS), olive mill pomace (OP), feather meal (FM), soft offal meal (CSM), chicken manure (CM), and date palm residues (DPR). Each feedstock was then pyrolyzed at three temperatures of 300, 500, or 700 °C, thereby producing a total of 18 types of biochar. These biochar products were analyzed for 16 PAHs and eight metals (Cr, Mn, Fe, Ni, Cu, Zn, Cd, and Pb). Benzo[b]fluoranthene, benzo[k]fluoranthene, and benzo(a)pyrene were significantly greater in the biochar produced at 700 °C than in that produced at 300 °C, especially for CM. The concentrations of dibenz(a,h)anthracene were significantly lower at 700 °C but greater at 500 °C and 300 °C in DPR. Increasing the pyrolysis temperature from 300 to 700 °C significantly increased the concentrations of metals, including Cr in SS and OP; Mn in CM; and Fe, Ni, Cu, and Zn in SS. However, the concentration of Cd was significantly lower in the SS when biochar was produced at 700 °C than at 500 or 300 °C. The type of feedstock used and the pyrolysis temperature are key factors influencing the contents of PAHs and HMs in biochar, both of which need to be considered during the production and use of biochar. Further investigations are recommended to establish the relationships between pyrolysis temperature and types of feedstock and the formation of PAH or the concentrations of metals. Monitoring the concentrations of PAHs and HMs before applying biochar to soil is also recommended.