Chemical and structural transformations of lignin in sesame seed hull during roasting.

To investigate the mechanism of lignin degradation during sesame roasting, structural transformations of milled wood lignin (MWL) from sesame seed hull samples roasted at 190-250 °C for 30 min were investigated. The findings revealed that, with increasing temperature, the degradation extent of carbohydrates from lignin carbohydrate complex in the fractions deepened, which reduced total sugar content (from 8.59 % to 0.45 %). Compared to that of the original sesame seed hull lignin (LSSH), the molecular weight of MWL fractions showed a tendency to decline (Mw 4377-2235 Da) with the rise of roasting temperature (210-250 °C). During roasting, lignins in the sesame seed hull underwent degradation and condensation. Due to demethoxylation, the H-type lignin proportion increased from 2.7 % to 26.1 %. Compared to G- and C-type lignin, S-type lignin was more stable. The ß-O-4 linkages decreased from 5.8 to 1.2/100 Ar due to CO bond breaking, and ß-ß linkages from 26.3 to 9.6/100 Ar decreased due to condensation of CC. As the roasting temperature increased, more chemical bonds between lignin structural units were broken, resulting in the generation of more phenolic hydroxyl groups (1.80-2.53 mmol/g). This study helps to elucidate the contribution of lignin degradation during roasting to the oxidative stability of sesame oil.

ß-carbolines norharman and harman in vegetable oils in China.

The beta-carbolines norharman and harman, two heterocyclic aromatic amines with potential mutagenicity, have been determined in vegetable oils. Identification and analysis were carried out by ultra-performance liquid chromatography-triple quadrupole tandem mass spectrometry (UPLC-MS/MS). In 88 samples analysed, the concentrations of norharman and harman were < LOD to 336.22 ng/g and < LOD to 505.14 ng/g, respectively. A high variability of norharman and harman levels among different oil types was observed. Sesame-, flaxseed-, sunflower seed-, peanut- and rapeseed oils were most contaminated. Both ß-carbolines were most likely formed during roasting of the oilseeds. Oil consumption, especially of oils obtained after roasting of the seeds, was a major dietary source of the ß-carbolines norharman and harman. Under existing oil risk factors, this investigation contributes to the unprecedented and essential information for dietary assessments associated with oil consumption.