Enhanced production of individual phenolic compounds by subcritical water hydrolysis (SWH) of pumpkin leaves was investigated at various temperatures ranging from 100 to 220°C at 20 min and at various reaction times ranging from 10 to 50 min at 160°C. Caffeic acid, p-coumaric acid, ferulic acid, and gentisic acid were the major phenolic compounds in the hydrolysate of pumpkin leaves. All phenolic compounds except gentisic acid showed the highest yield at 160°C, but gentisic acid showed the highest yield at 180°C. The cumulative amount of individual phenolic compounds gradually increased by 48.1, 52.2, and 78.4 μg/g dry matter at 100°C, 120°C, and 140°C, respectively, and then greatly increased by 1,477.1 μg/g dry matter at 160°C. The yields of caffeic acid and ferulic acid showed peaks at 20 min, while those of cinnamic acid, p-coumaric acid, p-hydroxybenzoic acid, and procatechuic acid showed peaks at 30 min. Antioxidant activities such as 2,2-diphenyl-1-picrylhydrazyl and ferric reducing antioxidant power values gradually increased with hydrolysis temperature and ranged from 6.77 to 12.42 mg ascorbic acid equivalents/g dry matter and from 4.25 to 8.92 mmol Fe2+/100 g dry matter, respectively. Color L* and b* values gradually decreased as hydrolysis temperature increased from 100°C to 140°C. At high temperatures (160°C to 220°C), L* and b* values decreased suddenly. The a* value peaked at 160°C and then decreased as temperature increased from 160°C to 220°C. These results suggest that SWH of pumpkin leaves was strongly influenced by hydrolysis temperature and may enhanced the production of phenolic compounds and antioxidant activities.

To enhance the production of phenolic compounds with high antioxidant activity and reduce the level of phototoxic fagopyrin, buckwheat leaves were extracted with subcritical water (SW) at 100~220°C for 10~50 min. The major phenolic compounds were quercetin, gallic acid, and protocatechuic acid. The cumulative amount of individual phenolic compounds increased with increasing extraction temperature from 100°C to 180°C and did not change significantly at 200°C and 220°C. The highest yield of individual phenolic compounds was 1,632.2 μg/g dry sample at 180°C, which was 4.7-fold higher than that (348.4 μg/g dry sample) at 100°C. Total phenolic content and total flavonoid content increased with increasing extraction temperature and decreased with increasing extraction time, and peaked at 41.1 mg gallic acid equivalents/g and 26.9 mg quercetin equivalents/g at 180°C/10 min, respectively. 2,2-Diphenyl-1-picrylhydrazyl free radical scavenging activity and ferric reducing ability of plasma reached 46.4 mg ascorbic acid equivalents/g and 72.3 mmol Fe2+/100 g at 180°C/10 min, respectively. The fagopyrin contents were reduced by 92.5~95.7%. Color values L* and b* decreased, and a* increased with increasing extraction temperature. SW extraction enhanced the yield of phenolic compounds with high antioxidant activity and reduced the fagopyrin content from buckwheat leaves.