Korean Journal of Food Science and Technology (한국식품과학회지)

Korean Society of Food Science and Technology (한국식품과학회)
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Physicochemical and antioxidant properties of garlic (A. sativum) prepared by different heat treatment conditions

  • Kim, Il-Doo (International Institute of Research & Development, Kyungpook National University) ;
  • Park, Yong-Sung (School of Applied Biosciences, Kyungpook National University) ;
  • Park, Jae-Jeong (School of Applied Biosciences, Kyungpook National University) ;
  • Dhungana, Sanjeev Kumar (National Institute of Crop Science, Rural Development Administration) ;
  • Shin, Dong-Hyun (School of Applied Biosciences, Kyungpook National University)
  • Received : 2019.08.17
  • Accepted : 2019.10.10
  • Published : 2019.10.31
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Abstract

The objective of this study was to investigate the physicochemical characteristics and antioxidant potential of garlic processed using different heat treatments conditions, which is an effective method for removing the unpleasant odor and taste of raw garlic. The pH and soluble solid content of raw garlic (pH 6.07, $7.7^{\circ}Bx$) were almost equal or slightly higher than that of processed garlic samples (pH 5.06-6.09, $7.1-7.4^{\circ}Bx$). The color of processed garlic was also significantly affected. The amounts of amino acids such as ${\gamma}$-amino-n-butyric acid and few essential amino acids also increased after the thermal treatment of garlic. The antioxidant potentials of red and black garlic were higher than that of raw garlic. The polyphenol content of processed garlic ($38.51-81.51{\mu}g$ gallic acid equivalent/g sample) was significantly higher than that of raw garlic ($30.66{\mu}g$ gallic acid equivalent/g sample). These results indicated that heat treatment for different durations under a controlled environment enhanced the nutritional and functional properties of garlic.

Keywords

Introduction

Garlic (Allium sativum) has been used as a culinary seasoning and a medicinal herb for a long time (Butt et al., 2009). It contains various nutrients and functional materials like anthocyanin, glycosides, essential oil, flavonoids, lectins, fructan, adenosine, pectin, vitamins B1, B2, B6, C and E, prostaglandins, biotin, essential amino acids, nicotinic acid, glycolipids, fatty acids and phospholipids (Bozin et al., 2008). Allicin, one of the major phytochemicals of garlic, is well known for its pharmacological properties, including antibacterial, antihyperlipidaemia, antitumour, and immunoregulatory activity (Ye and Zhang, 2003).

Unpleasant odor and taste are main reasons for the limited consumption of raw garlic in many countries in spite of its high food and medicinal values. The unpleasant odor and taste of raw garlic could be eliminated by heat treatment. Thermal treatment could also improve the palatability of garlic (Capuano and Fogliano, 2011). Thus, heat treatment has been considered as an effective technique to process the raw garlic and to improve the flavor and quality, and further enrich the processed garlic with new functions (Corzo-Martinez et al., 2007). When garlic is subjected to heat treatment, its bioactive aspects are greatly influenced (Corzo-Martinez et al., 2007). Heat treatment changes alliin and deoxidised alliin to allyl sulfurcontaining compounds, and some of which in thermal degradation have a fragrant smell (Lanzotti, 2006). The heat treatment also causes many unstable and unpleasant compounds in raw garlic to get converted into stable and tasteless compounds.

Black garlic, a processed product of raw garlic, is prepared by exposing the whole raw garlic to high temperature (70~80°C) environment under controlled humidity conditions for 1~3 months without additives (Kim et al., 2012). This processed black garlic has a fruity taste and is edible in uncooked form. In addition, the black garlic does not cause abdominal pain or other gastrointestinal problems (Bae et al., 2012). Black garlic has higher antioxidant potential than fresh garlic (Corzo-Martinez et al., 2007) and are more effective in preventing metabolic diseases and alcoholic hepatotoxicity (Ide and Lau, 1999).

The heat treatment may lead to nonenzymatic browning reactions, such as the Maillard reaction, caramelisation and the chemical oxidation of phenols. The nonenzymatic browning reactions can provide the black garlic a typical dark brown color, and lead to the formation of some antioxidant compounds (Osada and Shibamoto, 2006). Considering the non-enzymatic reactions during thermal treatments as well as nutritional and functional value of heat treated garlic, the objective of this study was to investigate the quality characteristics and antioxidant potentials of heat treated garlic for different aging periods.

Materials and Methods

Chemical and Materials

Folin-Ciocalteu phenol reagent and 1,1-diphenly-2-picrylhydrazyl (DPPH) were purchased from Sigma-Aldrich (St. Louis, MO, USA). All the chemical and reagents were analytical grade. Fresh garlics (Allium sativum L.) from the 2018 harvest season were obtained from a local market in Namhae-gun, Korea.

Preparation of garlic sample

Garlic cloves were separated from the bulbs and peeled off for treatment. Three different samples were prepared from the raw/ fresh garlic cloves. The samples were named by their color developed with different aging durations as W-G: raw garlic without any treatment, Y-G: yellow garlic prepared by heating the fresh garlic under controlled condition of 60 and 60% relative humidity for 3 days, R-G: Red garlic prepared by heating the fresh garlic under controlled condition of 60 and 60% relative humidity for 4.5 days, and B-G: Black garlic prepared by heating the fresh garlic under controlled condition of 60 and 60% relative humidity for 10 days.

All garlic samples were freeze-dried and ground into powder using a commercial grinder (HIL-G-501, Hanil Co., Seoul, Korea). The pulverized samples were stored at 4 until analyses.

Determination of pH and total soluble solid

Five grams of sample powder was mixed with 45 mL of distilled water. The pH value of the sample mixture was determined using a pH meter (Model 210; Hanna, Seoul, Korea). The total soluble solid (TSS) content of the sample powder was measured by following the method described in the Official Methods of the National Tax Service (2006).

Color measurement

The International Commission on Illumination (CIE) Lab color scale was used to determine Hunter L* (lightness), a* (redness, + or greenness, ), and b* (yellowness, + or blueness, ) values of the garlic powders. Color values were determined using a Chroma Meter (CR-300; Minolta Corporation, Osaka, Japan). A Minolta calibration plate (YCIE=94.5, XCIE=0.3160, YCIE=0.3330) and a Hunter lab standard plate (L*=97.51, a*=0.18, b*= +1.67) were used to standardize the instrument with D65 illuminant as described earlier (Kim et al., 2014).

Determination of free amino acid

Amino acid composition of the garlic powder was determined using an amino acid analyzer (Biochrom-20, Pharacia Biotech Co., Stockholm, Sweden) by following the method described earlier (Je et al., 2005). Sample powder (1 g) was hydrolyzed with 6 N hydrochloric acid (10 mL) in a sealed-vacuum ampoule at 110°C for 24 h. The hydrochloric acid was eliminated by evaporating using a rotary evaporator, and then the extract was mixed with 5 mL 0.2 M sodium citrate buffer (pH 2.2).

For the determination of free amino acid content in the garlic powders, the sample (1.5 g) was homogenized (12,000 rpm, 2 min) with ice-cold 6% (v/v) perchloric acid (10 mL) in an ice bath using an ACE homogenizer (Nissei AM-7, Nihonseikei Kaisha Ltd., Tokyo, Japan) and then incubated in ice for 30 min. Two milliliters of the reaction mixture was mixed with 1 mL lithium citrate buffer (pH 2.2) and the mixture was used to determine the free amino acids using the amino acid analyzer.

Determination of mineral composition

The sample powder (0.5 g) was digested in a mixture of 15 mL nitric acid (65%) and 2 mL H2O2 (35%). The sample mixture was diluted with an equal volume of distilled water. The mineral elements in the garlic powders were determined using an inductively coupled plasma atomic emission spectrometer (ICP AES; Varian Inc., Victoria, Australia) by following the method described by Skujins (1998). The instrument was calibrated using known standards for each mineral.

DPPH radical scavenging activity

The DPPH radical scavenging potential of garlic powders was determined by following the method described by Blois (1958). One gram of sample powder was extracted with 10 mL absolute methanol at room temperature for 3 h. The mixture was centrifuged at 1,660×g for 10 min, and the supernatant was filtered through a syringe filter (0.22 µm). An equal volume (100 µL) of sample extract and freshly prepared DPPH solution (0.1%, w/v in methanol) was mixed in microplate wells and left in dark for 30 min. The optical densities of reaction mixtures were measured at 517 nm using a microplate spectrophotometer (Multiskan GO, ThermoFischer Scientific, Vantaa, Finland). The DPPH radical scavenging activity was calculated using the following equation.

DPPH radical scavenging potential (%)=[1−(AAb)/Ao]×100

where A is the absorbance of sample and DPPH mixture, and Ab is the absorbance of sample and methanol mixture, and Ao is the absorbance of DPPH and methanol mixture.

ABTS radical scavenging activity

The ABTS radical scavenging activity of garlic powder was determined following the method described by Re et al. (1999). The radical cation of ABTS (ABTS+) was produced by mixing an equal volume of potassium persulfate (2.5 mM) and ABTS (7 mM) and incubating in the dark for 16 h. The solution was diluted with distilled water to get the absorbance value near to 0.7. Twenty microliters of sample extracts (as prepared for DPPH assay) were mixed with 180 μL of ABTS solution and the absorbance of reaction mixture was measured at 734 nm using a spectrophotometer (Multiskan GO, Thermo Fischer Scientific). The ABTS radical scavenging activity was calculated using the following equation.

ABTS radical scavenging activity (%)=[(ACtrl–ASample)/ACtrl)]×100

where ACtrl is the absorbance of ABTS radical cation and ASample is the absorbance of a mixture of ABTS radical solution and sample extract.

Polyphenol content

The polyphenol content in garlic samples was determined following the Folin-Ciocalteau method (Singleton, 1999). Sample extracts of garlic powders were prepared as in the DPPH assay. The sample extracts (50 μL) was mixed with 2% (w/v) aqueous Na2CO3 (1000 μL) and allowed to react for 3 min. After 3 min, 50 μL of 1 N Folin-Ciocalteau reagent was added to the mixture and incubated in dark for 30 min at room temperature. The absorbance value of reaction mixtures was measured at 750 nm using a microplate spectrophotometer (Multiskan GO, Thermo Fischer Scientific). Gallic acid was used as standard to make calibration curve. Polyphenol content was determined as gallic acid equivalents (μg GAE/g dry weight).

Statistical analysis

Data were subjected to analysis of variance using SAS 9.4 (SAS Institute, Cary, NC, USA) and significant differences among the samples were determined using Tukey test at 5% probability. The mean values of triplicate measurements were considered for statistical analysis unless otherwise mentioned in any specific analysis.

Results and Discussion

General chemical properties

The pH and soluble solid contents of garlic samples were significantly different with heat treatments and/or aging time (Table 1). The pH values of R-G (5.18) and B-G (5.06) were significantly lower than those of W-G (6.07) and Y-G (6.09). The soluble solid contents of processed garlic samples were significantly reduced as compared to the raw garlic. The highest value of soluble solid content was found in R-G (7.4°Bx) followed by B-G (7.3°Bx) and Y-G (7.1°Bx).

Similar results of decreased pH in the aged garlic were also found in a previous study (Kang, 2016). The reduction in pH values of heat-treated garlic samples was, in part, resulted due to the production of browning compounds, including carboxylic acid, and decreased basic amino acids by combining with sugar upon heat treatment (Bae et al., 2014). In the present study, the soluble solid content of processed garlic was lower than that of raw garlic. This reduced soluble solid content in the processed garlic was in opposite to a previous report (Ríos-Ríos et al., 2016) which might be due to the variation in treatment conditions including temperature and relative humidity.

Table 1. General chemical properties of heat-treated garlic for different aging times

Color

The color of processed garlic is an important factor from the viewpoint of consumers’ preference. The color values of processed garlic were significantly affected by the heat treatments, as expected. The highest lightness, redness, and yellowness values were found in Y-G (L value: 54.26), R-G (a value: 5.30), and Y-G (b value: 24.32), respectively (Table 2).

Color of foods plays a big role in buying behavior of consumers. The change in color of different garlic samples might be due to an extended drying and high temperature (Cui et al., 2003). Similar results of color variations found in the present study of heat-treated garlic were found in a previous study (Choi et al., 2014). The color variations in heat-treated garlics might have resulted due to the Maillard reaction, known as non-enzymatic browning reaction.

Table 2. Hunter color values of heat-treated garlic for different aging times

Free amino acid

A total of 8 and 23 essential and non-essential amino acids were detected in at least one garlic sample (Table 4). All 8 essential amino acids were detected in all samples but not all 23 non- essential amino acids were detected in all garlic samples. The highest amount of essential amino acid was found in B-G (9.43 mg/g sample powder) followed by W-G (7.85 mg/g sample powder) and R-G (7.74 mg/g sample powder). However, total amino acid content of raw garlic, W-G (57.66 mg/g sample powder) was higher than those of the processed garlic samples, Y-G (1.37 mg/g sample powder), R-G (38.38 mg/g sample powder), and B-G (44.01 mg/g sample powder). The amino acid content of Y-G was much lower than the other samples. The ratio of essential to non-essential amino acids was the highest for B-G (0.27 mg/g sample powder) followed by R-G (0.25 mg/g sample powder), Y- G (0.23 mg/g sample powder), and W-G (0.16 mg/g sample powder). The content of γ-amino-n-butyric acid (GABA) was 1.13, 0.01, 1.53, and 2.77 µg/g in W-G, Y-G, R-G, and B-G, respectively. The heat treatment significantly increased the GABA contents of R-G and B-G.

The variation in amino acid content was probably due to the degradation of proteins or peptides, which may result from enzymatic hydrolysis or non-enzymatic hydrolysis, such as pyrolysis (Liang et al., 2015). Thermal processing, perhaps caused by reactions with reducing sugars, such as the Maillard reaction might also have played roles in causing variations in amino acid contents of raw and processed garlic samples (Ichikawa et al., 2006). Foods containing higher ratios of essential to non-essential amino acids are considered good from the protein deposition viewpoint (Reeds, 2000). Glutamic acid is a precursor for the synthesis of GABA in plant tissues (Nikmaram et al., 2017). GABA is thought to be related to learning and memory; against stroke and neurodegenerative diseases; relieving anxiety, sedation, anticonvulsant; and muscle relaxation functions (Oh and Oh, 2004). The foods containing high GABA are known as brain foods and believed to play roles in different bioactive functions, including regulating blood cholesterol and pressure, decreasing insomnia and depression, and relieving pain (Dhakal et al., 2012). GABA is also reported to have function against diabetes (Reeds, 2000). The increased GABA contents in red and black garlics shows that heat treatment technology could be adopted to enhance the nutritional value of raw garlic.

Table 4. Free amino acid composition (mg/g sample powder) of heat-treated garlic for different aging times

Mineral content

The amount of mineral elements in raw and processed garlics was significantly different according to aging time (Table 5). The most abundant mineral found in the raw and processed garlic samples was K. Garlic samples R-G (15,294 mg/kg) had the highest and Y-G (575.25 mg/kg) had the lowest amounts of K among the samples. Na contents of processed garlic samples (192.12-303.98 mg/kg) were significantly reduced as compared to the raw garlic (1,254 mg/kg). Samples R-G and B-G had significantly higher amounts of Mn and Zn than in W-G. The total mineral contents of garlic samples were in the order of R-G>W-G>B-G>Y-G.

The amounts of several mineral elements found in the heat- treated garlic samples were increased compared to the raw garlic. The increased mineral contents in the processed garlics than in the raw garlic might be due to the physiological changes occurred during heat treatment (Kang, 2016). High Na and low K intake are reported to have association with hypertension and cardiovascular disease risk (Luta, 2018). Thus the elevated K and reduced Na in the processed garlic could be an ideal food to improve health. Zn is associated with growth, development, differentiation, DNA synthesis, RNA transcription, and cellular apoptosis (MacDiarmid et al., 2000). Thus, heat treatment could be an effective technique to reduce the amount of undesirable element like Na and to increase the amount of others like K and Zn, making the processed garlic more beneficial to human health.

Table 5. Mineral content (mg/kg dry powder) of heat-treated garlic for different aging times

DPPH and ABTS radical scavenging activities and polyphenol contents

The DPPH and ABTS radical scavenging activities and polyphenol content of processed garlic were higher than those of raw garlic (Table 3). The ABTS radical scavenging activity and polyphenol content of R-G (83.83% and 81.51 µg GAE/g sample powder) were more than three- and two-time higher as compared to W-G (24.26% and 30.66 µg GAE/g sample powder).

The result of higher polyphenol content in aged garlic as compared to the raw was in agreement with that of Jastrzebski et al. (2007). This increased phenolic content might be due to heat treatment (Xu et al., 2007). The aging treatment did not have constantly increased the antioxidant potential and polyphenol contents of processed garlic samples. Gorinstein et al. (2008) also found that the garlic processing conditions affect the contents of bioactive compounds of the processed garlic, such as polyphenols, and that this is influenced by the type and duration of treatment. The change in total phenols content affects the total antioxidant capacity of heat-processed garlic (Jastrzebski et al., 2007). Although significant, the heat treatment was not found to effectively improve the DPPH scavenging potentials of the processed garlics. However, ABTS radical scavenging activities and polyphenol contents of the processed garlics were remarkably increased by the heat treatments. One of the reasons for this discrepancies might be due to the complex nature of the antioxidant potential of foods as an outcome of various factors, including the partitioning properties of particular antioxidants, the oxidation conditions, and the physical state of the oxidizable substrate (Frankel and Meyer, 2000). Thus, an increment in a particular antioxidant, including total polyphenol content, might not always contribute to an enhanced antioxidant potentials as found in W-G and Y-G. Consumption of antioxidant-rich foods is considered as a preventive way to control various diseases (Serafini, 2006).

Table 3. DPPH and ABTS radical scavenging activities and polyphenol contents of heat-treated garlic for different aging times

Conclusion

Garlic cloves were subjected to heat treatment at controlled conditions of 60°C and 60% relative humidity for 3, 4.5, and 10 days. The physicochemical characteristics and antioxidant potentials of garlic processed at the different aging time were investigated. The pH and soluble solid content of processed garlic samples were significantly reduced as compared to unprocessed raw garlic. The color of processed garlic was also varied by heat treatments. The amounts of amino acids like γ-amino-n-butyric acid and few essential amino acid contents of the processed garlic were also increased. Minerals like K, Mn, and Zn were increased in some of the heat-treated garlic samples. The antioxidant potentials and polyphenol content of processed garlic samples were enhanced by the heat treatments. Overall results of this study showed that heat treatments under controlled humidity conditions could be carried out to enhance the nutritional and functional values of garlic.

Conflict of interest

The authors declare no conflict of interest.

Acknowledgments

This work was financially supported by Kyungpook National University Research Fund, 2018, Daegu, Korea

References

  1. Bae SE, Cho SY, Won YD, Lee SH, Park HJ. A comparative study of the different analytical methods for analysis of S-allyl cysteine in black garlic by HPLC. LWT-Food Sci. Technol. 46: 532-535 (2012) https://doi.org/10.1016/j.lwt.2011.11.013
  2. Bae SE, Cho SY, Won YD, Lee SH, Park HJ. Changes in S-allyl cysteine contents and physicochemical properties of black garlic during heat treatment. LWT-Food Sci. Technol. 55: 397-402 (2014) https://doi.org/10.1016/j.lwt.2013.05.006
  3. Blois MS. Antioxidant determinations by the use of a stable free radical. Nature 181: 1199-1200 (1958) https://doi.org/10.1038/1811199a0
  4. Bozin B, Mimica-Dukic N, Samojlik I, Goran A, Igic R. Phenolics as antioxidants in garlic (Allium sativum L., Alliaceae). Food Chem. 111: 925-929 (2008) https://doi.org/10.1016/j.foodchem.2008.04.071
  5. Butt MS, Sultan MT, Butt MS, Iqbal J. Garlic: nature's protection against physiological threats. Crit. Rev. Food Sci. Nutri. 49: 538-551 (2009) https://doi.org/10.1080/10408390802145344
  6. Capuano E, Fogliano V. Acrylamide and 5-hydroxymethylfurfural (HMF): A review on metabolism, toxicity, occurrence in food and mitigation strategies. LWT-Food Sci. Technol. 44: 793-810 (2011) https://doi.org/10.1016/j.lwt.2010.11.002
  7. Choi I, Cha H, Lee Y. Physicochemical and antioxidant properties of black garlic. Molecules 19: 16811-16823 (2014) https://doi.org/10.3390/molecules191016811
  8. Corzo-Martinez M, Corzo N, Villamiel M. Biological properties of onions and garlic. Trends Food Sci. Technol. 18: 609-625 (2007) https://doi.org/10.1016/j.tifs.2007.07.011
  9. Cui ZW, Xu SY, Sun DW. Dehydration of garlic slices by combined microwave-vacuum and air drying. Drying Technol. 21: 1173-1184 (2003) https://doi.org/10.1081/DRT-120023174
  10. Dhakal R, Bajpai VK, Baek KH. Production of GABA (${\gamma}$-aminobutyric acid) by microorganisms: a review. Braz. J. Microbiol. 43: 1230-1241 (2012) https://doi.org/10.1590/S1517-83822012000400001
  11. Frankel EN, Meyer AS. The problems of using onedimensional methods to evaluate multifunctional food and biological antioxidants. J. Sci. Food Agric. 80: 1925-1941 (2000) https://doi.org/10.1002/1097-0010(200010)80:13<1925::AID-JSFA714>3.0.CO;2-4
  12. Gorinstein S, Leontowicz H, Leontowicz M, Namiesnik J, Najman K, Drzewiecki J, Cvikrova M, Martincova O, Katrich E, Trakhtenberg S. Comparison of the main bioactive compounds and antioxidant activities in garlic and white and red onions after treatment protocols. J. Agric. Food Chem. 56: 4418-4426 (2008) https://doi.org/10.1021/jf800038h
  13. Ichikawa M, Yoshida J, Ide N, Sasaoka T, Yamaguchi H, Ono K. Tetrahydro-${\beta}$-carboline derivatives in aged garlic extract show antioxidant properties. J. Nutr. 136: 726S-731S (2006) https://doi.org/10.1093/jn/136.3.726S
  14. Ide N, Lau BHS. Aged garlic extract attenuates intracellular oxidative stress. Phytomedicine 6: 125-131 (1999) https://doi.org/10.1016/S0944-7113(99)80047-6
  15. Jastrzebski Z, Leontowicz H, Leontowicz M, Namiesnik J, Zachwieja Z, Barton H, Pawelzik E, Arancibia-Avila P, Toledo F, Gorinstein S. The bioactivity of processed garlic (Allium sativum L.) as shown in vitro and in vivo studies on rats. Food Chem. Toxicol. 45: 1626-1633 (2007) https://doi.org/10.1016/j.fct.2007.02.028
  16. Je JY, Park PJ, Jung WK, Kim SK. Amino acid changes in fermented oyster (Crassostrea gigas) sauce with different fermentation periods. Food Chem. 91: 15-18 (2005) https://doi.org/10.1016/j.foodchem.2004.05.061
  17. Kang OJ. Physicochemical characteristics of black garlic after different thermal processing steps. Prev. Nutr. Food Sci. 21: 348-354 (2016) https://doi.org/10.3746/pnf.2016.21.4.348
  18. Kim ID, Lee JW, Kim SJ, Cho JW, Dhungana SK, Lim YS, Shin DH. Exogenous application of natural extracts of persimmon (Diospyros kaki Thunb.) can help in maintaining nutritional and mineral composition of dried persimmon. Afr. J. Biotechnol. 13: 2231-2239 (2014) https://doi.org/10.5897/AJB2013.13503
  19. Kim JH, Nam SH, Rico CW, Kang MY. A comparative study on the antioxidative and antiallergic activities of fresh and aged black garlic extracts. Int. J. Food Sci. Technol. 47: 1176-1182 (2012) https://doi.org/10.1111/j.1365-2621.2012.02957.x
  20. Lanzotti V. The analysis of onion and garlic. J. Chromatogr. A 1112: 3-22 (2006) https://doi.org/10.1016/j.chroma.2005.12.016
  21. Liang T, Wei F, Lu Y, Kodani Y, Nakada M, Miyakawa T, Tanokura M. Comprehensive NMR analysis of compositional changes of black garlic during thermal processing. J. Agric. Food Chem. 63: 683-691 (2015) https://doi.org/10.1021/jf504836d
  22. Luta X, Hayoz S, Krause CG, Sommerhalder K, Roos E, Strazzullo P, Beer-Borst S. The relationship of health/food literacy and salt awareness to daily sodium and potassium intake among a workplace population in Switzerland. Nutr. Metab. Cardiovasc. Dis. 28: 270-277 (2018) https://doi.org/10.1016/j.numecd.2017.10.028
  23. MacDiarmid CW, Gaither LA, Eide D. Zinc transporters that regulate vacuolar zinc storage in Saccharomyces cerevisiae. EMBO J. 19: 2845-2855 (2000) https://doi.org/10.1093/emboj/19.12.2845
  24. Nikmaram N, Dar BN, Roohinejad S, Koubaa M, Barba FJ, Greiner R, Johnson SK. Recent advances in aaminobutyric acid (GABA) properties in pulses: An overview. J. Sci. Food Agric. 97: 2681-2689 (2017) https://doi.org/10.1002/jsfa.8283
  25. Official Methods of the National Tax Service. National Rural Resources Development Institute. Food composition table. Rural Development Administration, Seoul, Korea. pp. 353-370 (2006)
  26. Oh CH, Oh SH. Effect of germinated brown rice extracts with enhanced levels of GABA on cancer cell proliferation and apoptosis. J. Med. Food 7: 19-23 (2004) https://doi.org/10.1089/109662004322984653
  27. Osada Y, Shibamoto T. Antioxidative activity of volatile extracts from Maillard model system. Food Chem. 98: 522-528 (2006) https://doi.org/10.1016/j.foodchem.2005.05.084
  28. Re R, Pellegrini N, Proteggente A, Pannala A, Yang M, Rice-Evans C. Antioxidant activity applying an improved ABTS radical cation decolorization assay. Free Radical Biol. Med. 26: 1231-1237 (1999) https://doi.org/10.1016/S0891-5849(98)00315-3
  29. Reeds PJ. Dispensable and indispensable amino acids for humans. J. Nutr. 130: 1835S-1840S (2000) https://doi.org/10.1093/jn/130.7.1835S
  30. Rios-Rios KL, Gaytan-Martinez M, Mercado-Silva E, Rivera-Pastrana DM, Moreno-Mayorga S, Vazquez-Barrios ME. Effect of convective drying pretreatment on the physicochemical properties of black garlic pp. 845-852. In: VIII International Postharvest Symposium: Enhancing Supply Chain and Consumer Benefits-Ethical and Technological Issues, June 21-24, Cartagena, Region of Murcia, Spain (2016)
  31. Serafini M. The role of antioxidants in disease prevention. Medicine 34: 533-535 (2006) https://doi.org/10.1053/j.mpmed.2006.09.007
  32. Singleton VL, Orthofer R, Lamuela-Raventos RM. Analysis of total phenols and other oxidation substrates and antioxidants by means of folin-ciocalteu reagent. Methods Enzymol. 299: 152-178 (1999) https://doi.org/10.1016/S0076-6879(99)99017-1
  33. Skujins S. Handbook for ICP-AES (Varian-Vista). A Short Guide to Vista Series ICP-AES operation. Varian Int. AG, Zug. Version 1.0. Switzerland (1998)
  34. Xu G, Ye X, Chen J, Liu D. Effect of heat treatment on the phenolic compounds and antioxidant capacity of citrus peel extract. J. Agric. Food Chem. 55: 330-335 (2007) https://doi.org/10.1021/jf062517l
  35. Ye HY, Zhang ZY. Study progress on immune regulation effect of garlic. J. Chin. Med. Pharmacol. 3: 54-56 (2003)