J. Sci. & Devel., Vol. 10, No. 5: 805-811

Tp ch Khoa hc v Pht trin 2012 Tp 10, s 5: 805-811www.hua.edu.vn

NGHIN CU S BIN I HM LNG VITAMIN C, POLYPHENOL V HOT TNH KHNG OXI HO CA QU I TRONG QU TRNH CHN

Nguyn Th Huyn Trang1, L Thu Thy1*, Nguyn Vn Lm2, Nguyn Hng Thy2 1 Lp BQCBA K54, Khoa Cng ngh thc Phm, Trng i hc Nng nghip H Ni

2 Khoa Cng ngh thc phm, Trng i hc Nng nghip H Ni Email*: thuycntp@hua.edu.vn

Ngy gi bi: 29.05.2012 Ngy chp nhn: 12.08.2012

TM TT Nghin cu ny nhm theo di ng thi bin i ca hm lng vitamin C, hm lng polyphenol ca qu i

lin quan n hot tnh khng oxi ha ti cc giai on chn khc nhau ca qu i c trng ti x ng D, Gia Lm, H Ni. i c chia lm 4 chn: xanh gi ( chn 1), chuyn mu ( chn 2), chn ( chn 3) v chn mm ( chn 4). Kt qu nghin cu cho thy hm lng vitamin C tng dn qua cc giai on chn v t gi tr cao nht chn 3, hm lng polyphenol v hot tnh khng oxi ha gim dn trong qu trnh chn v th hin mi tng quan tuyn tnh cht ch.

T kho: chn, hot tnh khng oxi ho, polyphenol, qu i.

Changes in Vitamin C, Polyphenol Content and Antioxidant Activity of Guava Fruit During Ripening

ABSTRACT

Changes in chemical composition (vitamin C, polyphenol) and antioxidant activity of guava fruits collected in Dong Du, Gia Lam, Hano at different maturity stages were examined. The maturity stages were mature green, color turning, ripe and overripe. The results showed that vitamin C content sharply increased during ripening and reached the maximum value at ripe stage. Both polyphenol content and antioxidant activity decreased during ripening. Changes in polyphenol content was significantly correlated with changes in antioxidant activity.

Keywords: Antioxidant activity, guava fruit, polyphenol, ripening stage

1. T VN Vitamin C cn gi l ascorbic acid, l mt cht dinh dng khng oxy ha rt quan trng c trong rau, qu. N tn ti trong c th di hai dng D v L, tham gia vo cc hot ng khc nhau ca c th. Vitamin C m nhim nhiu chc nng nh: chc nng min dch, thc y s hnh thnh collagen - mt protein chnh ca c th, tham gia vo qu trnh chuyn ha cholesterol v bi tit cht c khi c th.(L Th Hp v Nguyn Th Hong Lan, 2010).

Khi x hi ngy mt pht trin, con ngi ang phi i mt vi nguy c mc nhng cn bnh mn tnh nguy him do tnh trng nhim mi trng, stress, tip xc vi ha cht c hi. Nhiu nghin cu dch t hc ch ra rng vic s dng thng xuyn cc cht khng oxi ha t nhin c kh nng ngn nga cc cn bnh nguy him nh tim mch hay ung th (Renaud v cs.,1998; Temple, 2000). Con ngi ngy mt nhn thc r c tm quan trng ca thc phm t nhin trong vic phng trnh bnh tt. V vy, nhng cht khng oxi ha t nhin c trong rau, qu ngy cng thu ht c s quan tm ca ngi tiu dng cng nh cc nh khoa hc.

Polyphenol l nhng hp cht thm c nhm hydroxyl nh trc tip vi nhn benzene (L Ngc T, 2003). Chng c nhiu trong thc vt nh rau, qu, hoa. Polyphenol to mu sc c trng cho thc vt. Ngoi ra, polyphenol cn

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Nghin cu s bin i hm lng vitamin c, polyphenol v hot tnh khng oxi ho ca qu i trong qu trnh chn

bo v thc vt khi vi sinh vt hi, s oxi ha v tc hi ca tia cc tm. V y hc, polyphenol l mt trong nhng hot cht t nhin c nhiu tc dng nh chng oxy ha, khng vim, khng khun, chng d ng v chng lo ha cho con ngi (Scalbert v cs., 2005).

i l mt loi cy ph bin nc ta c tn khoa hc l Psidium guajava, l mt trong nhng loi cy c ngun gc nhit i giu cht khng oxi ha. Tri i khng ch l loi tri cy c nhiu ngi a thch m cn l loi tri cy tt cho sc khe. i c cha hm lng cao ascorbic acid (vitamin C), ln ti 113mg/100g khi lng ti (Bulk v cs., 1996). Ngoi ra trong i cn cha hm lng cao cc hp cht phenol v y l nhng hp cht khng oxi ha t nhin rt c li cho sc khe con ngi (Thaipong v cs., 2006). Tuy nhin, nhng nghin cu v kh nng khng oxi ha ca qu i trong qu trnh chn cn hn ch. V vy, nghin cu ny tp trung vo vic xc nh hm lng vitamin C, polyphenol v hot tnh khng oxi ho ca qu i trong qu trnh chn, t gip hiu r hn v gi tr ca qu i i vi sc kho con ngi.

2. I TNG V PHNG PHP 2.1. i tng nghin cu

Qu i c thu hi ti x ng D, Gia Lm, H Ni, s lng 7 kg (khong 100 qu) trn 20 cy. Qu i sau khi c thu hi c vn chuyn v phng th nghim Khoa Cng ngh thc phm, Trng i hc Nng nghip H Ni.

Tin hnh phn loi s b qu i thnh 4 chn khc nhau da vo mu sc v qu (Jain v cs., 2003) (Bng 1).

2.2. Phng php nghin cu 2.2.1. Xc nh cc ch tiu v chn

- Ch tiu mu sc v qu: c o bng my o mu CR-400 (Nht), t xc nh cc ch s L, a v b. Mu ca v qu c o 3 v tr khc nhau trn qu v ly gi tr trung bnh.

- Ch tiu ng knh qu: c o bng thc kp (o 10 qu/1 chn v ly gi tr trung bnh).

- Ch tiu t trng ring: ca qu l t l gia khi lng qu trong khng kh v s chnh lch gia khi lng qu trong khng kh v khi lng qu khi nhng trong nc (Mercado-Silva v cs., 1998).

- Phng php bo qun mu: Sau khi xc nh cc ch tiu v chn, qu i c ra sch, ro v ct thnh cc phn nh. Sau , i c cho cc ti nha ng kn ( chia theo chn) v bo qun -530C dng cho phn tch. 2.2.2. Xc nh hm lng vitamin C (ascorbic acid)

- Phng php chit vitamin C: Ly 5 g mu i mi chn v nghin nh. Sau thm vo 20 mL dung dch m (HPO 3 2% v CH3COOH 8%) v nghin tip ng nht mu. Ln th tch 50 mL bng dung dch m. Tin hnh ly tm mu v thu ly phn dch trong (dch chit vitamin C). phn dch ny trong bng ti t 10-15 pht trc khi phn tch. Th nghim c tin hnh lp li 3 ln.

- Hm lng vitamin C c xc nh theo phng php chun bng KIO3 (Science Outreach, Unive rsity of Canterbury). ng chun vitamin C c xy dng bng cch chun b cc im chun vitamin C (0; 0,5; 1; 1,5; 2 mg/mL).

Bng 1. Phn loi qu i theo chn Mc chn c im K hiu

Xanh gi 100% xanh chn 1 Chuyn mu 80% xanh, 20% vng chn 2 Chn 50% xanh, 50% vng chn 3 Chn mm 100% vng chn 4

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Nguyn Th Huyn Trang, L Thu Thy, Nguyn Vn Lm, Nguyn Hng Thy

Sau ly 20 mL dch chit vitamin C, thm vo 10 mL nc ct, 1 mL dung dch KI 0,066M v 1 mL dung dch HCl 1M v tin hnh chun bng dung dch KIO3 0,002M. Hm lng vitamin C c biu th bng mg/100 g cht ti. Th nghim c tin hnh lp li 3 ln. 2.2.3. Xc nh hm lng polyphenol

- Phng php chit polyphenol: Phng php chit polyphenol (Alothman v cs., 2009) c iu chnh nh sau: Ly 5 g mu mi chn v tin hnh nghin trong dung dch acetone 90%. Sau , tng ln th tch 25 mL bng dung dch acetone. Tin hnh ly tm dch nghin trong 20 pht vi tc 6,000 vng/pht. Thu ly phn dch trong (dch chit i) v bo qun -200C phn tch. Th nghim c tin hnh lp li 3 ln.

- Xc nh hm lng polyphenol: Hm lng polyphenol c xc nh theo phng php Folin-Ciocalteu (Fu v cs., 2011). ng chun gallic acid c xy dng bng cch chun b cc dung dch chun gallic acid (0, 20, 40, 60, 80, 100 g/L). Hm lng polyphenol c xc nh da trn ng chun gallic acid v c biu th bng mg gallic acid tng ng (GAE)/100 g cht ti. Th nghim c tin hnh lp li 3 ln. 2.2.4. Xc nh hot tnh khng oxi ha

Phng php DPPH (Thaipong v cs., 2006) dng xc nh hot tnh khng oxi ho c iu chnh nh sau: Xy dng ng chun Trolox bng cch chun b cc dung dch chun

Trolox (1000, 750, 500, 250, 100 v 25 M). Dung dch gc DPPH c chun b bng cch ho tan 24 mg DPPH trong 100 mL methanol v bo qun -200C. Dung dch DPPH th nghim c chun b bng cch ly 10 mL dung dch gc cho vo 45 mL methanol ( c hp th l 1,1 0.02 n v khi so mu bc sng 515 nm). Sau ly 150 L dch chit i v cho vo 2850 L dung dch DPPH ri trong bng ti 30 pht. Tin hnh so mu 515 nm (cng ng i chng ch cha methanol). Kt qu c biu th bng % km hm DPPH theo cng thc:

AA = (ODcontrol - ODmu) / ODcontrol

Trong : ODcontrol: hp th quang ca mu control ODmu: hp th quang ca mu cn xc nh AA : % km hm DPPH

Th nghim c tin hnh lp li 3 ln. 2.2.5. X l thng k

Gi tr trung bnh ca cc kt qu c so snh bng phn mm SPSS 16.0. H s tng quan c phn tch bng cch s dng h s Pearson (r).

3. KT QU V THO LUN 3.1. Xc nh cc ch tiu v chn 3.1.1. Ch tiu ng knh qu

ng knh trung bnh ca qu i ng D cc chn khc nhau c th hin hnh 1.

chn 1 chn 2 chn 3 chn 4

n

g k

nh q

u (c

m)

Hnh 1. S bin i ng knh trung bnh theo chn (cm)

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Nghin cu s bin i hm lng vitamin c, polyphenol v hot tnh khng oxi ho ca qu i trong qu trnh chn

Trong sut qu trnh chn ca qu, ng knh qu tng do c s phn bo trong t bo ca qu. iu ny ph hp vi quy lut chung ca qu: trong qu trnh chn, qu tch ly c nhiu cht dinh dng t cy, v vy qu tng c v kch thc v khi lng, v do vy th tch cng tng. Tuy nhin, qu i ng D, s tng kch thc qu l khng ng k gia cc chn (Hnh 1). S khc bit ln nht c th hin gia chn 1 v chn 4, khi qu tng kch thc tng ng t 4,70cm n 6,21cm. 3.1.2. Ch tiu t trng ring ca qu

T trng ring ca qu i ng D cc chn khc nhau c th hin hnh 2.

T hnh 2 nhn thy, t trng ring ca qu i ng D gim dn t chn 1 (1,01) ti

chn 4 (0,92). Theo Yusof and Suhaila (1987), s gim t trng ring ca qu c th c coi l cn c phn loi qu theo chn. Tuy nhin trong nghin cu ny, s khc bit v t trng ring ca qu i ng D cc giai on chn l khng ng k. V vy, cn kt hp ch tiu ny vi cc ch tiu v chn khc c th phn bit r hn cc giai on chn ca qu i thu hi ti ng D. 3.1.3. Ch tiu cng mu qu

mu ca qu i ng D cc chn khc nhau c th hin hnh 3.

Ch s L (Light) phn nh sng ca v qu c gi tr t 0-100, ch s a l di mu t xanh l cy ti c gi tr t -60 n +60 , ch s b l di mu t xanh nc bin ti vng c

chn 1 chn 2 chn 3 chn 4

T trn

g ri

ng

Hnh 2. S bin i ca t trng ring theo chn

Hnh 3. S bin i ca ch s L, a, b theo chn

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Nguyn Th Huyn Trang, L Thu Thy, Nguyn Vn Lm, Nguyn Hng Thy

gi tr t -60 n +60. Kt qu nghin cu cho thy trong qu trnh chn ca qu i ng D, ch s L tng dn v chn nh hng c ngha n ch s L (P < 0,05), trong khi ch s b cng tng nhng mc tng chm v khng ng k, v ch s a gim dn (Hnh 3). iu ny ng ngha vi vic mu v qu ngy cng sng hn, vng hn, mu xanh nht dn. Nghin cu ca Jain v cs. (2003) ch ra rng s thay i v sc t l mt trong nhng du hiu phn bit qu cc giai on chn khc nhau. Trong , h thy rng trong qu trnh chn ca qu i, hm lng chlorophyll gim dn do hot ng ca cc enzyme nh chlorophyllase, chlorophyll oxidase v peroxidase, cn hm lng carotenoid tng dn. Do vy, cng chn, v qu cng vng, mu xanh gim dn. 3.2. S bin i hm lng Vitamin C trong qu trnh chn

Hm lng vitamin C ca qu i ng D trong qu trnh chn c th hin hnh 4.

T th hnh 4 c th thy hm lng vitamin C tng dn t chn 1 (39,92 mg/100g cht ti (CT)) v t gi tr cao nht chn 3 (296,79 mg/100g CT), sau gim chn 4 (258,38 mg/100g CT). Hm lng vitamin C t gi tr cao nht ti giai on chn ca qu ( chn 3), gi tr ny cng tng t nh kt qu ca nhng nghin cu trc y. Mercado-Silva v cs. (1998) khi nghin cu xc nh hm lng vitamin C ging i trng ti Mexico cng thy rng hm lng vitamin C t gi tr thp nht chn 1 v 2 v c s tng t bin v t gi tr ln nht chn 3. Tng t, Bulk v cs. (1996) cng ch rng hm lng vitamin C t gi tr ln nht giai on chn (ripe) ca qu i. 3.3. S bin i hm lng polyphenol trong qu trnh chn

Hnh 4. S bin i hm lng vitamin C theo chn (mg/100g cht ti)

Hnh 5. S bin i hm lng polyphenol theo chn (mg GAE/100g cht ti)

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Nghin cu s bin i hm lng vitamin c, polyphenol v hot tnh khng oxi ho ca qu i trong qu trnh chn

Hm lng polyphenol ca qu i ng D trong qu trnh chn c th hin hnh 5.

Theo kt qu nghin cu (Hnh 5) cho thy, hm lng polyphenol gim trong sut qu trnh chn ca i, chn 1, hm lng polyphenol l 545,61 mg GAE/100g CT, sau gim mnh ti chn 2 (P < 0,05). T chn 2 n chn 3 th s bin i hm lng polyphenol l khng ng k. Sau hm lng polyphenol tip tc gim chm cho ti chn 4 (254,46 mg GAE/100g CT). iu ny c th gii thch l do polyphenol b oxi ha bi enzyme nh polyphenol oxidase (PPO) trong qu trnh chn. Kt qu nghin cu ny cng tng t nh kt qu ca mt s nghin cu trc y: theo Bulk v cs. (1996), hm lng polyphenol gim trong sut qu trnh chn ca 4 ging i trng ti Sudan. Ngoi ra, theo Sancho v cs. (2010), u , trong qu trnh chn, hm lng polyphenol trong v qu v tht qu gim dn, ln lt t 471,97 mg GAE/100g CT n 358,67 mg GAE/100g CT v t 1,91 n 0,88 mg GAE/100g CT.

3.4. S bin i hot tnh khng oxi ha trong qu trnh chn

Hot tnh khng oxi ho ca qu i ng D trong qu trnh chn c th hin hnh 6.

T th hnh 6 nhn thy hot tnh khng oxi ha gim dn t chn 1 n chn 4, tng t nh xu hng bin i hm lng polyphenol (Hnh 5). Kt qu x l thng k cho thy cc chn khc nhau nh hng c ngha n hot tnh khng oxy ha (P < 0,05). Mi tng quan gia hm lng polyphenol v hot tnh khng oxy ha ca qu i thu hi ti ng D c xc nh thng qua h s tng quan Pearson. Kt qu cho thy mi tng quan ny l quan h tuyn tnh cht ch (r = 0,936). Nghin cu ca Gruz v cs. (2011) trn qu sn tr cng cho thy rng hm lng polyphenol v hot tnh khng oxi ha c mi lin quan n nhau trong kh nng khng oxi ha ca qu sn tr ph thuc vo hm lng polyphenol.

Hnh 6. S bin i hot tnh khng oxi ha theo chn (M TE/100g cht ti)

4. KT LUN Trong qu trnh chn ca qu i thu hi ti

ng D, hm lng vitamin C t gi tr cao nht khi i giai on chn ( chn 3). Trong khi , hm lng polyphenol gim dn t chn 1 n chn 4. Hot tnh khng oxi ha

cng th hin xu hng bin i tng t nh hm lng polyphenol. Gia hm lng polyphenol v hot tnh khng oxi ho c mi tng quan tuyn tnh cht ch. iu ny cho thy rng cc hp cht phenol c th ng vai tr chnh i vi hot tnh khng oxi ho ca qu i ng D.

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TI LIU THAM KHO Alothman M., Rajeev Bhat, A. A. Karim (2009).

Antioxidant capacity and phenolic content of selected tropical fruits from Malaysia, extracted with different solvents. Food Chemistry 115(3), pp. 785-788.

Bulk R., E. Babiker & A. Tinay (1996). Changes in chemical composition of guava fruits during development and ripening. Food Chemistry 59(3), 395-399.

Fu L., X.-R. Xu, R.-Y. Gan, Y. Zhang, E.-Q. Xia & H.-B. Li (2011). Antioxidant capacities and total phenolic contents of 62 fruits. Food Chemistry 129(2): 345-350.

Gruz J., F.A. Ayaz, H.Torun M. Strnad (2011). Phenolic acid content and radical scavenging activity of extracts from medlar (Mespilus germanica L.) fruit at different stages of ripening. Food Chemistry 124:271-277.

Jain N., K. Dhawan, S. Malhotra & R. Singh (2003). Biochemistry of fruit ripening of guava (Psidium guajava L.): Compositional and enzymatic changes. Plant Foods for Human Nutrition 58: 309-315.

L Th Hp v Nguyn Th Hong Lan (2010). Gio trnh Dinh dng. NXB Khoa hc T nhin v Cng ngh.

L Ngc T (2003). Ha hc thc phm. NXB Khoa hc v k thut H Ni.

Mercado-Silva E., P. Benito-Bautista, M. de los Angeles Garcia-Velasco (1998). Fruit development, harvest index and ripening changes

of guavas produced in central Mexico. Post harvest Biology and Technology 13, 143-150.

Renaud SC, R. Guenguen, J. Schenker, A. d'Houtand (1998). Alcohol and mortality in middle-aged men from Eastern France. Epidemiology 9:184-8.

Sancho L., E. Yahia, G. Gonzlez-Aguilar (2010). Identification and quantification of phenols, carotenoids, and vitamin C from papaya (Carica papaya L., cv. Maradol) fruit determined by HPLC-DAD-MS/MS-ESI. Food Research International, 44 (5), 1284-1291.

Scalbert A., C. Manach, C. Morand and C. Remesy (2005). Dietary Polyphenols and the Prevention of Diseases. Critical Reviews in Food Science and Nutrition, 45:287-306.

Science Outreach, University of Canterbury, New Zealand. Determination of vitamin C concentration by a redox titration using iodate. http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodate.pdf, truy cp thng 02/2012.

Temple NJ. (2000). Antioxidants and disease: more questions than answers. Nutr Res 2:449-459.

Thaipong K., U. Boonprakob, K. Crosby, L. Cisneros-Zevallo, DH. Byrne (2006). Comparison of ABTS, DPPH, FRAP, and ORAC assays for estimating antioxidant activity from guava fruit extracts. Journal of Food Composition and Analysis 19, 669-675.

Yusof S., M. Suhaila (1987). Physicochemical changes in guava during development and maturation. J.Sci. Food Agric. 38, 31-59.

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