Antioxidative Activity of Bound-Form Phenolics in Potato Peel Kazuhiro N ARA,y Takayuki M IYOSHI,Tamaki H ONMA,and Hidenori K OGA Calbee Foods Co.,Ltd.,2-11-4Yoshino-cho,Kita-ku,Saitama331-0811,Japan
Received October11,2005;Accepted February4,2006;Online Publication,June23,2006
[doi:10.1271/bbb.50552]
明清铜器Free and bound-form phenolics were isolated from potato(cv.Toyoshiro)flesh and peel.The free and bound-form phenolics in the peel showed high DPPH radical scavenging activity,while tho in theflesh showed low activity.The total amount of chlorogenic acid and caffeic acid in the free-form phenolics from the peel was highly correlated with the DPPH radical scavenging activity.Ferulic acid was identified as the active radical scavenging compound in the bound-form phenolics from the peel.The potato peel may therefore offer an effective source of an antioxidative.
Key words:potato;peel;DPPH radical scavenging
activity;bound-form phenolics;ferulic acid The phenolic compounds commonly found in many plants are involved in many biological activities, including the chelation of metals,scavenging active oxygen speci
我喜欢英文怎么写es,and antioxidative activity.1,2)Phenolic compounds are generally either in the free-form or bound-form.Most rearch has determined free soluble phenols by using aqueous methanol,ethanol,and acetone,either parately or mixed together.3,4)
The prence of free-form phenolic compounds(such as chlorogenic acid and caffeic acid)has been reported in potato,and recent studies have been conducted on the antioxidative activity of a potato extract.5,6)However, detailed information about the bound-form of phenolics has not yet become available.
Such bound-form phenolics as ferulic acid and p-coumaric acid are ester-linked to the cell wall polysac-charides in veral plants.7)Ferulic esters are a subject of great interest,given their functional role in cell adhesion and thermal stability of the texture in food plants.8,9)Ferulic acid and its sugar ester have high antioxidative potential.Moreover,ferulic acid has less of a suppressive effect on LDL oxidation than its sugar ester.10)We described here the phenolic content and antioxidative activity in the free-and bound-form phenolics extracted from potato.We also analyze the compounds related to radical scavenging activity. Potatoes(Solanum tuberosum cv.Toyoshiro)of similar size and appearance were obtained for the experiment from afield in Hokkaido,Japan.The potatoes were cleaned with tap water and then peeled in strips about1-mm thick with a common vegetable peeler.T
he remaining tissue is designated asflesh.The peel andflesh were immediately freeze dried,and each then ground to afine powder(flesh=21.34g/100g of fresh weight;peel=13.76g/100g of fresh weight). The powder(2g)was homogenizedfive times with 80%(v/v)ethanol(20ml)at room temperature(20Æ3 C),and the homogenate centrifuged.The precipitate was washed in acetone and then dried.The dried material is designated as the alcohol-insoluble solid (AIS).The supernatant thus obtained was combined and is designated as the alcohol-soluble fraction(free-form phenolics).The yields of AIS from theflesh and peel were1.95g and1.76g,respectively.
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To extract the bound-form phenolics,AIS(200mg) was treated with20ml of4M NaOH for one hour at room temperature(20Æ3 C),and the solution centri-fuged.The supernatant was acidified with HCl and extracted three times with ethyl acetate.The ethyl acetate pha was evaporated to dryness at40 C under a vacuum.The bound-form phenolics were dissolved in 50%methanol for subquent determination.The free-and bound-form phenolics were then determined by the Folin-Ciocalteu method.11)Table1shows the total phenolic content of free-and bound-forms in potato. The content of free and bound-form phenolics in the peel was more than that in theflesh.In respect of the distribution of free and bound-form phenolics,the bound-form in the peel was more widely distributed (26%)than that in theflesh(1%).Chu et al.have reported that the bound-form accounted for40%of the
total phenolic content in the edible part of potatoes.1) The total amount of phenolics in potato also varies Table1.Total Contents of Free-and Bound-Form Phenolics in Potato
Sample
Total phenolics
(mg of ferulic acid equiv/g of dry matter)
Free Bound Flesh 1.680.02
Peel 3.66 1.26
y To whom correspondence should be addresd.Tel:+81-48-653-3631;Fax:+81-48-653-3033;E-mail:k
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Biosci.Biotechnol.Biochem.,70(6),1489–1491,2006 Note
significantly among different varieties of potato.12)It is conceivable that there would be a difference in the amount of bound-form phenolics.
In order to obtain uful information about the components of the free-form phenolics,on HPLC analysis was conducted in an Inertsil ODS-3column (4:6Â250mm;GL Science,Tokyo,Japan)with photo-diode array detection.Elution was done at 40 C by using a linear gradient of 10%to 25%acetonitrile containing a 20m M sodium phosphate buffer (pH 3.3)at a flow rate of 1.0ml/min.Two major peaks were identified in the peel as chlorogenic acid and caffeic acid by co-chromatography with a standard (data not shown).The chlorogenic acid and caffeic acid contents of the free-form phenolics in the peel were 6.75m mol/g of dry matter and 3.00m mol/g of dry matter,respectively.The amount of chlorogenic acid found in potato has been reported to vary among different varieties of potato.12)In addition,chlorogenic acid has 1,1-diphenyl-2-picrylhydrazyl (DPPH)radical-scavenging activity.Therefore,the radical-scavenging activity was deter-mined by using the DPPH stable radical.Briefly,150m l of a 50%ethanol solution was added to 50m l of a sample solution in a 96-well microplate.The reaction was initiated by adding 100m l of 20m M DPPH to the ethanol solution.After the solution had been left standing for 15minutes,a microplate reader (Bio-Rad,CA,USA)was ud to measure the absorbance at 540nm.The DPPH radical-scavenging ac
tivity was estimated from the decrea in absorbance at 540nm and is expresd as the trolox equivalent per g of dry matter,using a standard curve for trolox.The antioxidative activity in the peel extract (20.72m mol of trolox equiv/g of dry matter)was higher than that in the flesh (7.03m mol of trolox equiv/g of dry matter).
The DPPH radical-scavenging activities of chloro-genic acid and caffeic acid of the free-form phenolics in the peel were respectively calculated as 7.87and 3.95m mol of trolox equiv/g of dry matter.The totals from the chlorogenic acid and caffeic acid are equivalent to about 57%of total activity (20.72m mol of trolox equiv/g of dry matter).The findings suggest that the level of antioxidative activity and the amount of
phenolics were cloly related.Therefore,chlorogenic acid and caffeic acid are important components of the free-form phenolics in potato peel.
The bound-form phenolics (extracted with NaOH)were diluted,and a UV–vis spectrophotometer (Shimadzu,Kyoto,Japan)was ud to determine the UV–vis spectrum in the range of 200nm to 500nm.The bound-form phenolics in the peel exhibited a spectrum near 325nm (data not shown).Such phenolic acids as chlorogenic acid,caffeic acid and ferulic acid are generally found in a
typical UV–vis spectrum,with a maximum absorption peak at 325nm.Therefore,the peel exhibited a spectrum with maximum absorption near 325nm due to the prence of cinnamic acid.The components of the bound-form phenolics were then subjected to an HPLC analysis.The chromatogram shows veral peaks (Fig.1),including a particularly large one at Rt ¼26:62(peak 1).Peak 1corresponded to cinnamic acid-related compounds with a maximum absorption near 325nm.The MS/MS data showed the peak 1ion at m =z 134,149,178and 193,as well as ferulic acid.Finally,peak 1was identified as ferulic acid by co-chromatography with an authentic standard (data not shown).The total amount of ferulic acid in the peel was estimated to be 0.37m mol/g of dry matter.
Ferulic acid is a major phenolic acid that is ester-linked in the cell wall polysaccharides of veral plants.8)Ferulic acid has recently been reported to be a good antioxidative,the oxidation of human plasma LDL induced by CuSO 4being inhibited by the ferulic sugar ester.10)Figure 2shows the total antioxidative activity in the bound-form phenolics as determined by a DPPH radical-scavenging assay.The bound-form phenolics in the peel showed much stronger activity (5.70m mol of ferulic acid equiv/g of dry matter)than tho in the flesh (0.28m mol of ferulic acid equiv/g of dry matter).The results indicate that the bound-form phenolics in the peel had strong activity as judged from the estimated amount of ferulic acid in the peel.
In conclusion,we have clearly demonstrated DPPH radical-scavenging activity in potato peel.Given the large quantity of potato peel waste generated by potato processing,the results obtained in the prent study
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Fig.1.HPLC Chromatograms of the Bound-Form Phenolics in Potato Peel.
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读书笔记800字suggest that potato peel can be effectively ud as a new source of a natural antioxidative.Moreover,ferulic acid (ester-linked to the cell wall polysaccharides)oxidizes to form diferulic acid.Such oxidative coupling of wall matrix polysaccharides has been considered to drasti-cally affect cell wall extensibility and its growth rate.7–9)Bad on the findings,the ferulic acid found in potato is expected to play an important role in such growth.It is therefore necessary to examine the detailed structure of cell wall polysaccharides in the future.
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246810Flesh
Peel
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T o t a l a n i t i o x i d a t i v e a c t i v i t y ( m o l o f f e r u l i c a c i d e q u i v /g o f d r y m a t t e r )
µFig.2.DPPH Radical-Scavenging Activity of Bound-Form Phenol-ics in Potato Flesh and Peel.金丝熊吃什么
Vertical bars indicate the standard deviation.
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Bound-Form Phenolics in Potato Peel 1491
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