Effect of microwave pretreatment of sunflower kernels on the aroma-active composition, sensory quality, lipid oxidation, tocopherols, heterocyclic amines and polycyclic aromatic hydrocarbons of sunflower oil

The application of microwaves on sunflower kernels, as a new flavour generation technique, to produce sunflower oil was investigated. Using solvent-assisted flavour evaporation (SAFE), HS-SPME and GC-O-MS, 75 odourants were identified in sunflower oils, where 44 were newly found. With the increasing microwave time, aroma-active terpenes decreased from 74 to 33 mg/kg, aroma-active heterocyclics increased from 0 to 196 mg/kg, and aroma-active carbonyls increased from 2 to 28 mg/kg in sunflower oils (p < 0.05). Meanwhile, the perceived intensities of roasted and smoky aromas enhanced, while the intensities of raw sunflower seed and woody aromas decreased in sunflower oils (p < 0.05). Microwaves did not cause surface rupture but increased the interior porosity of sunflower kernel. The tocopherol loss in sunflower oils was less than 7.2% and the oil yield increased from 19.45% to 35.10% after microwaves. The temperature rise by microwaves was responsible for the gradually decreased protein solubility and increased HCAs (7.3–820.6 ng/g) and PAHs (7.78–109.76 ng/g) in oils. Microwave technology, when being applied at appropriate power and duration, is promising for producing sunflower oil, however, process temperature needs to be controlled to balance between sufficient flavour formation and denaturation of protein as the by-product.