Oats (Avena satica L.) are an important source of dietary fiber mainly composed of β-glucans, which is reported to be effective in lowering of cholesterol and decreasing the risk of heart attack. Subcritical water extraction (SWE) is a new and promising method for the extraction of β-glucan due to its polarity-selectivity, efficiency of recovery, time-efficiency, and lower cost. In this study, efficiencies of the SWE were investigated for the extraction of β-glucan from oat flour. The conditions for maximizing the extraction efficiency were determined by varying temperature (110-190°C), pH of solvent (pH 3.0-10.6), static time (5-20 min) and particle size of oat flour. The amount of β-glucan was determined with a ‘Mixed-linkage β-glucan’ assay kit (Megazyme International Ltd.), according to McCleary and Codd (1991). The overall results showed that the concentration of β-glucan was highest under the following conditions: extraction temperature of 200°C, pH value of 4.0, static time of 10 min, and particle size of 425-850 μm. The extraction yield under the optimum condition was 6.98±1.17 g/100 g oat flour, which was over two-fold higher than that obtained using hot water extraction method (60°C, 3 h). Therefore, SWE is a feasible alternative for extracting soluble dietary fiber (β-glucan) from oat flour.

Citrus fruit is important source of flavonoids, mainly flavanones which are narirutin and hesperidin. Those citrus flavonoids have been found to have health-related properties including antioxidant, anticancer, and anti-inflammatory. The main purpose of this study was to verify that the extraction of narirutin and hesperidin from Citrus peel can be more effective by combining pulsed electric field (PEF) pre-treatment and subcritical water extraction (SWE). Citrus unshiu peels were treated with PEF under conditions of electric field strength (3 kV/cm) and times (1 and 2 min). Subsequent SWE was conducted by using a Dionex Accelerated Solvent Extractor (ASE, Model 350) at extraction temperature 170°C for 10 min. The total flavonoids content was measured by using the aluminum chloride colorimetric method and the antioxidant capacity was analyzed by the Ferric reducing antioxidant power (FRAP) assay using spectrophotometer. The concentrations of narirutin and hesperidin were increased as PEF pre-treatment time increased. The highest concentrations of narirutin and hesperidin were 13.41 mg narirutin/g dry citrus peel and 141.16 mg hesperidin/g dry citrus peel at PEF pre-treatment condition of 3 kV/cm and 2 min. The total flavonoids contents of the extracts increased 105.2% and 123.1% for citrus peel PEF treated at 1 and 2 min, respectively. In addition, compared to the untreated sample, PEF pre-treatments of 1 and 2 min increased the antioxidant capacity of the extracts 109.2% and 160.8%, respectively. Therefore, the results demonstrate the potential of PEF pre-treatment to improve the SWE of flavonoids from citrus unshiu peel.

Angelica gigas Nakai has been used for traditional Korean medicine which acts anti-inflammatories, protects the liver, and enhances the immune system. Subcritical water extraction (SWE) is an eco-friendly extraction method in which the pressure is applied between the boiling point and critical temperature of water that maintains the liquid state. The aim of study was to determine the optimal extraction conditions for subcritical water extraction of the decursin and nodakenin from Angelica gigas Nakai, comparing two scales, laboratory-scale (22 mL) and pilot-scale (8 L) devices to assess the feasibility of industrial applications. Extraction efficiencies were evaluated by measuring total polyphenol contents and DPPH radical scavenging activity with a spectrophotometer, extraction yields of decursin and nodakenin with a high-performance liquid chromatography. The subcritical water extraction conditions of pilot-scale were as follows: extraction temperature of 150, 170, 190 and 210°C; extraction times of 5, 10, 15, and 20 min. The highest yields of decursin and nodakenin were at 190°C/15 min (17.65 mg/g Angelica gigas) and 170°C/20 min (4.35 mg/g Angelica gigas), respectively. These were not significantly different from the maximum contents of decursin (13.49 mg/g Angelica gigas), and nodakenin (4.66 mg/g Angelica gigas) for lab-scale subcritical water extraction. The maximum values for total polyphenol content and DPPH scavenging activity of subcritical water extraction were 64.32 mg/g Angelica gigas and 74.4%, respectively. On the other hand, those of conventional extraction method using methanol (60°C/120 min) were obtained as 14.31 mg/g Angelica gigas and 41.9%. Therefore, the subcritical water extraction is a rapid and efficient method for extracting polyphenols and anti-oxidative compounds.