Quantitative Changes of Flavonol Glycosides from Pine Needles by Cultivar, Harvest Season, and Thermal Process

Five flavonol glycosides including quercetin 3-O-beta-D-glucoside (QG), kaempferol 3-O-beta-D-glucoside (KG), quercetin 3-O-(6 ''-O-acetyl)-beta-D-glucoside (QAG), kaempferol 3-O-(6 ''-O-acetyl)-beta-D-glucoside (KAG), and quercetin 3-O-(3 ''-O-p-coumaroyl)-beta-D-glucoside (QCG) were isolated and purified from red pine (Pinus densiflora Sieb. et Zucc.) needles, and identified by nuclear magnetic resonance and mass spectrometer spectral analyses. In addition, the quantification of the five flavonol glycosides in pine needles was performed by high-performance liquid chromatography analysis according to cultivar, growing district, harvest season, and thermal processing. The red pine needles had higher amounts of the five flavonol glycosides than the black pine needles except for QCG. There were no large differences in flavonoid composition and content among pine needles grown in three different areas. Levels of the five flavonol glycosides in red pine needles harvested during Spring ranged from 6.13 to 27.03 mg/100 g dry weight. Levels of two flavonol glycosides, QG and KG, gradually decreased with increasing harvest time, whereas the acylated flavonol glycoside, QCG, a predominant flavonoid in pine needles, increased gradually with increasing harvest time. Two acetyl flavonol glycosides, QAG and KAG, increased steadily through Spring to Autumn, and then decreased gradually by Winter. Meanwhile heat treatments, such as roasting and steaming, increased the five flavonol glycosides during heating for 3 min, but then slowly decreased these when heating for 10 min. Microwave processing increased to some extent the five flavonol glycosides when heating for 3 min, and remained unchanged during the 10 min heating. These results suggest that the pretreated red pine needles with enhanced flavonoid content may be useful as potential sources for nutraceuticals and cosmeceuticals.