Biochemical characterisation of the northern Australian-grown black sesame as a source of bioactive compounds

Sesame, an emerging crop of interest in Australia, has been widely investigated for its numerous health benefits. These health-promoting effects of sesame are associated with a rich source of various bioactive compounds, including lignans, phytosterols, and polyphenols naturally present in sesame seeds. Sesame production is emerging in Northern Australia, facing high temperatures and prolonged periods of moisture stress which often leads to high levels of environmental stress on crops. Plant stress (lack of moisture) is often associated with increased bioactive content in plant products. There is a lack of data on the typical levels of bioactive compounds found in crops such as sesame, particularly for the Australian-grown environment. Products derived from the oil processing in sesame (i.e. pressed cake and sludge) may be considered as economic resources with great food potential; however, they are poorly investigated. Amongst different analytical techniques the Folin-Ciocalteu (FC) assay was selected to estimate total phenolic content (TPC), while the ferric-reducing antioxidant power (FRAP) and cupric-ion reducing antioxidant capacity (CUPRAC) methods were selected to assess the total antioxidant capacity. Moreover, high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) analyses were used to separate, identify, and quantify the lignans (sesamin and sesamolin) and the major fatty acids in the sesame, respectively. This investigation focused on profiling the typical levels of of TPC, lignans, fatty acids and TAC present in whole seeds of selected lines of Australian-grown sesame under two irrigation treatments: water deficit (WD) and well-watered (WW). A mechanical oil extraction method was used to partition the seed into oil and yielded two distinct by-products. Using spectrophotometric methods, moderate differences were found in the TPC and TAC between the different varieties of sesame. This was particularly evident in the WD treatment, which also contained the highest TPC of most of the sesame varieties investigated. HPLC and GC-MS analyses revealed key lignans (sesamin and sesamolin) in all four sesame products, and nine individual fatty acids in seeds, oil and cake from sesame, respectively. Most field-grown samples exhibited superior adaptation to WD treatment with higher levels of sesamin and sesamolin contents, particularly with higher concentrations in sesame seeds than in the other three derived products from sesame. Moreover, lignan contents showed minor differences across all field-grown sesame samples. Meanwhile, linolenic and oleic acids were the most prominent fatty acids, with a higher content in sesame seeds than the oil and cake. ii Deficit irrigation is slightly associated with low yield in sesame crops. This study postulates that sesame traits subjected to deficit irrigation strategies could be potentially cultivated to influence the bioactive compounds, particularly lignans, fatty acids, and phenolics.