We investigated the effect of various cooking methods (boiling, steaming, stir-frying, and roasting) and three cooking times (5, 10, and 15 min) on the antioxidant properties of red pepper. Raw and cooked peppers were measured for proximate composition, ascorbic acid (AsA) content, total carotenoid content (TCC), total polyphenol content (TP), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging activities. Results showed that the proximate composition, AsA content, TCC, TP, and antioxidant activities were significantly (p<0.05) affected by the cooking procedure; the loss rate varied among individual compounds. Boiling and steaming significantly reduced AsA content (24.3~66.5%), TP (13.9~ 54.9%), and antioxidant activity (21.7~60.5%) in red pepper, while stir-frying and roasting slightly reduced AsA content (2.7~25.9%), TP (1.8~4.9%), and antioxidant activity (4.9~17.9%). The highest loss was observed after boiling, followed by steaming, roasting, and stir-frying. Stir-frying and roasting better preserved AsA content, TCC, TP, and antioxidant activity. In conclusion, dry-heat cooking methods such as stir-frying and roasting may be preferred to retain the nutrient compositions and antioxidant properties of red pepper.

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Zingiberaceae is the large diverse family comprised of rhizomatous plants with a higher concentration of phenolic compounds. The normal ginger (Zingiber officinale Rosc.) and black ginger (Kaempferia parviflora Wall.) belongs to this family and have similar morphological characteristics of rhizome, but their phenolic composition revealed differently. On this study, the phenolic composition of normal ginger (from Ethiopia and Korea) and black gingers (from Korea and Thailand) were profiled using ultra performance liquid chromatography coupled with diode array detector, quadrupole time-of-flight mass spectrometry (UPLC-DAD-QToF-MS). The result revealed that gingerol-related phenolic acid was detected only in normal gingers while, the methoxyflavones were identified exclusively in black gingers. 6-gingerol, 8-gingerol, 10-gingerol, 1-dehydro-6-gingerdione, and diacetoxy-8-gingerdiol were the major constituents among 18 phenolic acids detected from normal gingers, and 3,5,7,3′,4′-pentamethoxyflavone and 5,7,4′-trimethoxyflavone were confirmed as predominant constituents among 13 methoxyflavones from black gingers. The total phenolic content was 434.7 and 698.1 mg/100 g dry weight (DW) in Korean and Ethiopian sample, respectively. The total methoxyflavone concentration was 4388.0 mg/100 g DW and 3940.2 mg/100 g DW in Korean and Thai black ginger sample, respectively. The higher concentration of methoxyflavones is from advanced biosynthetic pathway related to accumulated color of black ginger. In addition, new possible structural fragmentation was proposed for gingerol homologous series as additional pathway under the positive ionization mode, and further rationalized that ferulic acid moiety is the biosynthetic precursor. The result suggested that despite the morphological similarity, normal and black ginger showed distinct biosynthetic difference to synthesis their major secondary metabolites.Electronic supplementary material The online version of this article (https ://doi.org/10.1007/s0021 7-018-3188-z) contains supplementary material, which is available to authorized users. Graphical AbstractKeywords Kaempferia parviflora Wall. · Phenolic compounds · UPLC-DAD-QToF-MS · Zingiberaceae · Zingiber officinale Rosc.

Most previous studies have been focused on the variation of tea chemical composition by fermentative processes as well as different cultivars and regions. The detailed changes of flavonoid profiles were described for the first time by each processing step of green and black tea leaves in this study. A total of 24 flavonoid derivatives including catechins, theaflavins, and flavonols were separated and identified from the tea samples based on UPLC-DAD-QToF/MS data and constructed library. Among these, the fragmentation pathway of theaflavins was proposed specifically in positive ionization mode for structural interpretation. During leaf processing, the individual flavonols were changed as diverse patterns according to their aglycone types and glycosylated forms, but their total content showed a slight difference. EGCG and ECG were increased after roasting approximately twofold higher than that of fresh leaves (EGCG, 2709.5 →6085.6; ECG, 1548.0 →2318.2 mg/100 g dry weight, respectively) in green tea while considerably decreased their contents due to oxidation and conversion to theaflavins after fermentation during black tea processing. Especially, the drying steps also found to be factor to influence positively to increase the flavonoid contents in both tea processing. Therefore, this result indicated that detailed conditions of each processing step played important roles in changing the flavonoid profiles from tea leaves.

Graphical abstract