Far infrared irradiation alters total polyphenol, total flavonoid, antioxidant property and quercetin production in tartary buckwheat sprout powder

https://doi.org/10.1016/j.jcs.2013.12.007Get rights and content

Highlights

  • Far infrared irradiation (FIR) increases scavenging activity on DPPH radicals of tartary buckwheat sprouts (TBS) powder.

  • FIR increases total polyphenol and total flavonoid content in TBS powder.

  • FIR decreases metal chelating activity and total antioxidant capacity of TBS powder.

  • FIR enhances quercetin production and decreases rutin content in TBS powder.

Abstract

The effects of far infrared irradiation (FIR) on total polyphenol (TP), total flavonoid (TF) content, antioxidant properties and aglycone quercetin production in tartary buckwheat sprout (TBS) were investigated. The study showed that FIR treatment decreased the total antioxidant capacity and metal chelating property in TBS in a temperature dependent manner, however, 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity increased with the temperature. Similarly, TP and TF content also increased with temperature. The HPLC result revealed that quercetin production was directly proportional to the temperature, and the maximum production (average 14.8 mg/g dw) of quercetin was at 120 °C which was 13.5 times higher than the untreated control sample of TBS. Overall, this research is expected to be helpful to improve the nutritional value of tartary buckwheat by optimizing the FIR conditions.

Introduction

Buckwheat (Fagopyrum spp.) is an annual crop belonging to the Polygonaceae family and cultivated in most Asian and European countries. Among the different varieties, common (Fagopyrum esculentum) and tartary (Fagopyrum tartaricum) buckwheat are the most popular varieties, which are recognized as healthy foods because of high rutin content (Mukoda et al., 2001). Nowadays, many people take interest in the utilization of buckwheat seed because of its high nutritional and pharmaceutical values. Especially, tartary buckwheat has been drawing attention for its high rutin content, which is beneficial to health. Similarly, quercetin is a flavonoid present in a glycoside or an aglycone form in most fruits and vegetables including buckwheat. It has been reported that the quercetin exhibits more potent biological activity than its corresponding glycosides (Kwon et al., 2004, Hou et al., 2004, Williamson et al., 1996). Therefore, due to the greater biological activity, safe and efficient production of quercetin, without using hazardous chemicals or expensive enzymes is crucial from a health and economic point of view.

Since a decade ago, the buckwheat sprout has been considered as a new vegetable. The sprout has mild flavor and attractive odor, so is used as fresh vegetable, salad, cooking ingredient, etc. (Kim and Kim, 2001). The sprouts are rich in flavonoid compounds (rutin and quercetin), phenolic acids, amino acids, minerals, vitamins and crude fibers (Kim et al., 2004). The powdered form of dried buckwheat sprout is used to make bread, snacks, and also added to make rice cake (Kim et al.; Kim and Kim, 2001).

Thermal processing changes the physical, chemical and biological properties of fruits and vegetables by altering carbohydrates, fats, vitamins, proteins, etc. to different extents (Hoyem and Kvale, 1977). Nowadays, several reports have shown that the far infrared (FIR) drying method is more advantageous over the conventional oven drying method (Eom et al., 2009, Niwa et al., 1988). The high penetration power (wave length 3–1000 nm) of FIR helps the exudation of chemical components without destroying the plant cells and thereby altering biological activity. Recently, some studies have been done on how buckwheat phenolics or antioxidant activity are affected by different processing methods (Sensoy et al., 2006, Sun and Ho, 2005, Zielinski et al., 2006). However, the use of FIR as a thermal treatment on buckwheat has not been studied yet.

The objective of this research was to study the alteration of total polyphenol, total flavonoid content and antioxidant properties of tartary buckwheat sprout (TBS), and also to monitor the maximum quercetin production in TBS resulting from FIR thermal treatment.

Section snippets

Chemicals

Analytical grade organic solvents (methanol, acetonitrile, ethanol) used for the extraction of TBS and detection in HPLC were purchased from Merck KGaA Darmstadt, Germany. Gallic acid (GA), and 1,1-diphenyl-2-picrylhydrazyl (DPPH) were purchased from Sigma Chemical Co. (St. Louis, Mo). Folin-Ciocalteu’s reagent was purchased from Wako Pure Chemicals, Japan. Rutin and quercetin were purchased from Sigma Chemical Co. (St. Louis, MO). All other chemicals and reagents used were of the highest

Effects of FIR on total polyphenol (TP) and total flavonoid (TF) content in TBS

The TP and TF content of FIR treated and untreated (control) samples of TBS are shown in Figs. 1 and 2, respectively. According to the mean values calculated, a gradual increase in TP content was observed after 80 °C and a significant (P < 0.05) increase was obtained at 100 °C with 41.2 mg GAE/g dw compared to the untreated control (37.0 mg GAE/g dw) sample. At 120 °C, maximum increase in TP content was observed with 49.2 mg/g dw, which was nearly 1.33 times higher than the control. At a higher

Conclusion

Our results highlighted that FIR thermal treatment increased the TP and TF content in a temperature-dependent manner. Likewise, scavenging activity on DPPH also increased; however, the metal chelating activity and total antioxidant capacity decreased. The FIR irradiation enhanced aglycone quercetin production in TBS due to the breakage of glycoside bonds of rutin in a temperature-dependent manner with the maximum production at 120 °C. This study suggests that the nutritional value of buckwheat

Conflict of interest

None.

Acknowledgments

Authors appreciate the Institute of Bioscience & Biotechnology of Kangwon National University for supporting research fund.

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