Green Tea Catechins Reduced the Glycaemic Potential of Bread: An In Vitro Digestibility Study - Unika Repository

(1)

92.38%

Originality

7.62%

Similarity

149

Sources

Doc vs Internet + Library

Web sources: 72 sources found

1. https://docplayer.es/72639994-Universidad-complutense-de-madrid.html

1%

2. https://nacchocommunique.com/category/diabetes/page/3

0.3%

3. https://nacchocommunique.com/tag/diabetes-australia

0.3%

4. https://link.springer.com/article/10.1007%2Fs10989-017-9641-1

0.15%

5. http://www.besjournal.com/Articles/Archive/2015/No8/201509/t20150910_120237.html

0.15%

6. http://onlinelibrary.wiley.com/doi/10.1111/j.1747-0285.2009.00899.x/full

0.15%

7. http://europepmc.org/articles/PMC3722045

0.15%

8. http://www.mdpi.com/2072-6643/10/1/6/htm

0.15%

9. http://www.candybaskets.com/Home/SweetNewsNewsletterMarsProducts/tabid/245/Default.aspx

0.15%

11. http://www.moonofalabama.org/2018/03/governments-decree-truth-about-skripal-dissenters-will-be…

0.15%

12. http://onlinelibrary.wiley.com/doi/10.1111/jnc.12711/full

0.15%

13. https://docplayer.es/82526054-Estudio-de-la-funcion-de-annexina-a6-en-el-higado.html

0.15%

14. https://docplayer.es/14439569-Desarrollo-de-estrategias-analiticas-para-la-identificacion-de-conta…

0.15%

15. http://docplayer.es/54772329-Aplicaciones-de-la-electroforesis-capilar-a-la-determinacion-de-feno…

0.15%

16. https://annals-csis.org/proceedings/2012/pliks/69.pdf

0.15%

17. https://2012books.lardbucket.org/books/an-introduction-to-nutrition/s06-04-national-goals-for-nutrit…

0.14%

18. http://joliverwellness.com/blog

0.14%

19. https://2012books.lardbucket.org/books/an-introduction-to-nutrition/s06-achieving-a-healthy-diet.h…

0.14%

20. http://onlinelibrary.wiley.com/doi/10.1111/1541-4337.12081/full

0.14%

21. http://onlinelibrary.wiley.com/doi/10.1111/xen.12205/full

0.14%

22. http://stopobesityalliance.org/wp-content/themes/stopobesityalliance/pdfs/Fast%20Facts%20Chr…

0.14%

23. http://diabetes-bloedsuiker.pilliewillie.nl/diabetes/studies.diabetes.1.php

0.14%

24. https://molecularautism.biomedcentral.com/articles/10.1186/s13229-016-0109-5

0.14%

25. http://www.texilajournal.com/clinical-research/edition/45-volume3-issue2

0.14%

26. http://www.orthop.washington.edu/?q=patient-care/articles/arthritis/diabetes-basics.html

0.14%

27. http://centaur.reading.ac.uk/view/year/2010.default.html

0.14%

28. http://drrajivdesaimd.com/2012/09/04/electricity

0.14%

29. https://courses.lumenlearning.com/boundless-accounting/chapter/introduction-to-intangible-assets

0.14%

30. https://en.wikipedia.org/wiki/Health_effects_of_wine

0.14%

31. http://jddonline.com/articles/search_result?txtSearch=Aging

0.14%

32. https://transition.fcc.gov/Bureaus/Common_Carrier/Notices/1999/fcc99204.doc

0.14%

33. https://www.unicef.org/publications/files/State_of_Food_Security_and_Nutrition_in_the_World_20…

0.14%

(2)

35. https://www.healthline.com/nutrition/9-weight-loss-diets-reviewed

0.14%

36. https://gailraegarwood.wordpress.com/tag/hormone

0.14%

37. http://thechart.blogs.cnn.com/2011/02/09/late-nights-early-mornings-a-ticking-time-bomb-for-healt…

0.14%

38. http://uir.ulster.ac.uk/view/year/2010.default.html

0.14%

39. https://gailraegarwood.wordpress.com/category/hormones

0.14%

40. http://jddonline.com/articles/search_result?txtSearch=Melanoma+and+Non-Melanoma+Cancers

0.14%

41. https://bmcmedinformdecismak.biomedcentral.com/articles/10.1186/s12911-017-0508-3

0.14%

42. http://pubs.acs.org/doi/10.1021/pr3007705

0.14%

43. https://www.readkong.com/page/polyphenolic-chemistry-of-tea-and-coffee-a-century-of-1690976

0.14%

44. http://europepmc.org/articles/PMC2928966

0.14%

45. http://www.bloggen.be/diabetescheck/archief.php?ID=706919

0.14%

46. http://onlinelibrary.wiley.com/doi/10.1002/bio.2341/abstract

0.14%

47. https://www.webmd.com/vitamins/ai/ingredientmono-960/green-tea

0.14%

48. https://www.bettycjung.net/Blog2011.htm

0.14%

49. http://isindexing.com/isi/searchedpapers.php?page=19800&limit=50

0.14%

50. http://rongmawlin.blogspot.com/2017/11/glyphosate.html

0.14%

51. http://www.isindexing.com/isi/searchedpapers.php?page=8080&limit=5

0.14%

52. http://www.isindexing.com/isi/searchedpapers.php?page=1040&limit=10

0.14%

53. https://www.ijeart.com/page/search

0.14%

54. https://link.springer.com/article/10.2165%2F11595870-000000000-00000

0.14%

55. http://isindexing.com/isi/searchedpapers.php?page=15650&limit=50

0.14%

56. https://bibliometria.ucm.es/fichaDepartamento/234/NUTRICION,%20BROMATOLOGIA,%20HIGI…

0.14%

57. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/fi…

0.14%

58. https://docplayer.es/68416290-Editores-jose-felix-meco-y-vicente-pascual.html

0.14%

59. http://www.phcogres.com/article.asp?issn=0974-8490;year=2009;volume=1;issue=4;spage=166;e…

0.14%

60. https://www.science.gov/topicpages/q/quality+cassava+flour

0.14%

61. https://docplayer.es/25057152-Tesis-doctoral-determinacion-de-contaminantes-en-lugares-remoto…

0.14%

63. https://www.sciencedirect.com/science/article/pii/S0308814613018037

0.14%

64. https://www.healthyfoodguide.com.au/references

0.14%

66. http://dspace.thapar.edu:8080/jspui/bitstream/10266/1358/3/1358.pdf

0.14%

67. https://docs.wfp.org/api/documents/WFP-0000022419/download/?_ga=2.111532740.1172316052.…

0.14%

68. https://eprints.ucm.es/38812/1/T37648.pdf

0.14%

70. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4020750

0.14%

71. http://rusplant.ru/index.php?page=Posts.ViewPost&id=956

0.14%

72. https://patents.google.com/patent/EP1883413A2/en

0.14%

Web omitted sources: 67 sources found

1. http://expertscape.com/ar/tea/a/Gao%2C+Jing

3.9%

2. https://www.sciencedirect.com/science/article/pii/S0308814615002253

2.75%

3. http://www.fst.nus.edu.sg/OurPeople/ZhouW.html

2.62%

4. http://expertscape.com/au/tea/Zhou%2C+Weibiao

1.86%

(3)

6. http://pubs.acs.org/doi/abs/10.1021/jf048655x

1.55%

7. https://link.springer.com/chapter/10.1007%2F978-981-10-2612-6_7

1.55%

8. http://pubs.acs.org/doi/abs/10.1021/jf000877h

1.49%

9. https://link.springer.com/article/10.1007%2Fs11947-012-0986-3

1.06%

10. https://link.springer.com/content/pdf/10.1007%2Fs11947-015-1544-6.pdf

1.03%

0.9%

12. http://pubs.acs.org/doi/abs/10.1021/jf9706080

0.84%

13. http://www.tandfonline.com/doi/ref/10.1080/10408398.2014.922043

0.83%

14. http://onlinelibrary.wiley.com/doi/10.1002/jsfa.2423/abstract

0.79%

0.78%

16. https://pubs.acs.org/doi/abs/10.1021/jf200203n

0.74%

17. http://www.cochemist.com/author_A095809992.html

0.68%

18. https://link.springer.com/article/10.1007/s13197-012-0833-6

0.66%

19. http://www.pfigueiredo.org/TA33.pdf

0.66%

20. https://link.springer.com/chapter/10.1007%2F978-81-322-1683-4_4

0.66%

21. http://stablemicrosystems.com.cn/papersnew.htm

0.59%

22. http://www.textureanalyser.co.uk/PublishedPapers.htm

0.59%

0.56%

24. http://www.garfield.library.upenn.edu/histcomp/jenkins_am-j-clin-nutr_1981/index-ncr.html

0.46%

25. http://repository.unika.ac.id/702/7/10.70.0097%20Selly%20Gesilia%20Santiana%20DAFTAR%20…

0.44%

26. http://repository.unika.ac.id/1102/8/09.70.0061%20Yosua%20Handoko%20DAFTAR%20PUSTAK…

0.44%

27. https://www.deepdyve.com/lp/elsevier/digestibility-of-starch-fractions-in-wholegrain-rolled-oats-piu…

0.42%

28. https://pubs.acs.org/doi/abs/10.1021/nn505554y

0.42%

29. https://rd.springer.com/content/pdf/10.1007%2F978-1-4614-3804-5_5.pdf

0.42%

30. http://downloads.hindawi.com/journals/jamc/2008/502953.xml

0.42%

31. https://www.european-mrs.com/2014-spring-symposium-f-european-materials-research-society

0.42%

32. http://onlinelibrary.wiley.com/doi/10.1111/j.1541-4337.2008.00043.x/full

0.41%

33. https://www.pubfacts.com/search/zirconium%20tetratert-butoxide/2

0.35%

34. https://www.nap.edu/read/13153/chapter/2

0.35%

35. https://www.deepdyve.com/lp/elsevier/starch-digestibility-in-food-matrix-a-review-iyI2cVkLkl

0.32%

36. http://onlinelibrary.wiley.com/doi/10.1111/1541-4337.12064/full

0.32%

37. https://www.seedo.es/images/site/documentacionConsenso/Documento-Consenso-FESNAD-SEE…

0.3%

38. https://docplayer.es/49942667-Efecto-en-el-perfil-aromatico-del-vino-por-la-presencia-de-fungicida…

0.3%

39. http://scholar.google.com/citations?user=sYy3NCYAAAAJ&hl=en

0.3%

40. https://link.springer.com/article/10.1007/s13197-014-1487-3

0.3%

41. http://www.nutricion.org/publicaciones/pdf/Documento-Consenso-FESNAD-SEEDO-Oct2011.pdf

0.3%

42. http://scielo.isciii.es/scielo.php?script=sci_arttext&pid=S0212-16112012000300017&lng=en&tlng…

0.3%

0.27%

0.25%

45. https://academic.oup.com/ajcn/CrossRef-CitedBy/4596677

0.25%

46. http://repository.unika.ac.id/view/year/2015.type.html

0.24%

47. http://repository.unika.ac.id/view/year/2015.html

0.24%

48. https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/tea-fact-sheet

0.24%

49. http://helvia.uco.es/xmlui/bitstream/handle/10396/7632/573.pdf.txt;sequence=3

0.24%

50. https://www.jstage.jst.go.jp/browse/bbb/57/6/_contents

0.24%

(4)

52. http://www.ctns.cat/public/docs/06_2014_caimari-et-al-fiberox-food-chemistry.pdf

0.24%

53. http://www.doc88.com/p-9522116447822.html

0.24%

54. http://www.journaltocs.ac.uk/index.php?action=browse&subAction=pub&publisherID=317&journal…

0.2%

55. https://www.chemweb.com/articles/SV11947/0000600012

0.19%

56. http://repository.unika.ac.id/view/year/2013.html

0.19%

57. https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-10-24

0.17%

59. http://ucce.ucdavis.edu/files/datastore/234-2408.pdf

0.17%

60. https://link.springer.com/chapter/10.1007/978-1-4614-5441-0_28

0.17%

61. https://www.ncbi.nlm.nih.gov/books/NBK83190

0.17%

62. https://www.slideshare.net/raffaavill/medical-students-knowledge-and-attitude-towards-compleme…

0.15%

63. https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-014-0174-6

0.15%

64. http://onlinelibrary.wiley.com/doi/10.1038/oby.2006.128/full

0.14%

65. http://www.greenlocal175.com/unewsL11.html

0.14%

66. https://greatist.com/grow/what-you-can-control-for-happiness-success

0.14%

67. https://en.wikipedia.org/wiki/Glyphosate

0.14%

Library sources: 9 sources found

Green Tea Catechins During Food Processing and Storage.pdf

2.45%

Food Bioprocess Technology Impact of Green Tea Extract.pdf

1.39%

Heat Transfer during Steaming of Bread.pdf

1.23%

Heat Transfer during Steaming of Bread.pdf

1.23%

11 ICEF (Hal 647).pdf

0.81%

A Study on Bifidobacterium lactis Bb12 Viability in Bread du.pdf

0.59%

A Study on Bifidobacterium lactis Bb12 Viability in Bread du (1).pdf

0.59%

SKRIPSI EUNIKE 13.70.0128-6 Nov.docx

0.41%

14.I1.0001-Marcellina-26 FEB.docx

0.37%

Library omitted sources: 1 source found

(5)

Green tea catechins reduced the glycaemic potential of bread: An

in vitro

digestibility study

Royston Goh

a

, Jing Gao

a

, Victoria K. Ananingsih

a,b

, Viren Ranawana

c

, Christiani Jeyakumar Henry

c

,

Weibiao Zhou

a,d,⇑

aFood Science and Technology Programme, c/o Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore

b_{Department of Food Technology, Soegijapranata Catholic University, Jalan Pawiyatan Luhur IV/1, Semarang 50234, Indonesia} c_{Clinical Nutrition Research Centre, Singapore Institute for Clinical Sciences, 14 Medical Drive, #07-02, Singapore 117599, Singapore}

d_{National University of Singapore (Suzhou) Research Institute, 377 Linquan Street, Suzhou Industrial Park, Jiangsu 215123, People’s Republic of China}

a r t i c l e i n f o

Article history:

Received 15 November 2014

Received in revised form 10 February 2015 Accepted 11 February 2015

Available online 16 February 2015

Keywords: Green tea catechins Bread

In vitro digestibility Glycaemic potential

a b s t r a c t

Green tea catechins are potent inhibitors of enzymes for carbohydrate digestion. However, the potential of developing low glycaemic index bakery food using green tea extract has not been investigated. Results of this study showed that addition of green tea extract (GTE) at 0.45%, 1%, and 2% concentration levels significantly reduced the glycaemic potential of baked and steamed bread. The average retention levels of catechins in the baked and steamed bread were 75.3–89.5% and 81.4–99.3%, respectively. Bread forti-fied with 2% GTE showed a significantly lower level of glucose release during the first 90 min of pancre-atic digestion as well as a lower content of rapidly digested starch (RDS) content. A significantly negative correlation was found between the catechin retention level and the RDS content of bread. The potential of transforming bread into a low GI food using GTE fortification was proven to be promising.

1. Introduction

Baked bread has a history dating back to the Neolithic era and is currently the staple food of Europe, European-derived cultures such as the Americas, Middle East and North Africa. Steamed bread, a type of bread that originates from China, is made from fermented wheat ﬂour dough and processed by steaming. Steamed bread is getting popular in Hong Kong, Taiwan and countries of Southeast Asia. Studies have shown that with the appropriate formulation and processing conditions, bread of acceptable qualities can be produced with the fortiﬁcation of phytochemical based ingredients such as green tea extract (GTE) (Ananingsih, Gao, & Zhou, 2012;

Wang, Zhou, & Isabelle, 2007).

GTE is derived from dried green tea leaves and contains mainly natural tea polyphenol antioxidants. One major component of the polyphenol antioxidants is known as tea catechins. Due to its increasingly evident health beneﬁts such as being anti-oxidative and anti-mutagenic which contribute to lowered risk of chronic

diseases, green tea and GTE enriched food are highly sought after among people who pursue healthier lifestyles (Basu & Lucas,

2007). The effects of GTE fortiﬁcation on the physical and sensory characteristics of baked and steamed bread have been studied pre-viously (Lee, 2012; Wang et al., 2007).

Studies conducted by Liu, Wang, Peng, and Zhang (2011),

Yilmazer-Musa, Grifﬁth, Michels, Schneider, and Frei (2012), Koh, Wong, Loo, Kasapis, and Huang (2010), showed that tea polyphe-nols such as tea catechins inhibited the activity of

a

-amylase and

a

-glucosidase which are two key enzymes for starch digestion in human. Another study showed that among 4 types of digestive enzymes (

a

-amylase, pepsin, trypsin and lipase) investigated, tea

polyphenols inhibited the activity of

a

-amylase the most (He, Lv,

& Yao, 2007). These findings suggested the potential role of tea catechins in influencing the digestibility of starch in GTE-fortified bread which has not yet been addressed in literature. The retarded starch digestion is favorable in developing low glycaemic index (GI) food (Robyt, 2009). The consumption of low GI foods results in relatively small fluctuations in blood glucose level (Englyst &

Hudson, 1996) which can reduce the risk of developing type 2 dia-betes mellitus over a prolonged period of time (Simmons, Unwin, &

Grifﬁn, 2010). Hence, fortiﬁcation with green tea catechins might be able to reduce the glycaemic potential of bread.

Although it has been argued that food values intended as guide-lines for glycaemic control must be validated based on clinical

Abbreviations: GTE, green tea extract; ECG, ()-epigallocatechin; EGCG, ( )- epigallocatechin-3-gallate; CG, catechin-3-gallate; GCG, ( )-gallocatechin-3-gal- late; RDS, rapidly digested starch; SDS, slowly digested starch.

⇑ Corresponding author at: Food Science and Technology Programme, c/o Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore. Tel.: +65 6516 3501.

E-mail address: chmzwb@nus.edu.sg (W. Zhou).

Food Chemistry 180 (2015) 203–210

Contents lists available at ScienceDirect

Food Chemistry

(6)

trials, in vivo digestibility analysis has been reported to be intrinsi-cally poor in precision even in well-controlled experiments (Monro, Mishra, & Venn, 2010). This is largely due to inherent vari-ability in human blood glucose responses (Monro & Mishra, 2010). Therefore, many authors have used in vitro digestibility analysis to study the digestion of carbohydrate food (Chung, Liu, Peter Pauls,

Fan, & Yada, 2008; Monro & Mishra, 2010; Monro et al., 2010; Woolnough, Monro, Brennan, & Bird, 2008). In vitro digestibility model described by Monro and Mishra (2010) has been used to determine important starch fractions such as rapidly digested starch (RDS), slowly digested starch (SDS), and resistant starch (RS) in foods. Since the in vitro approach was demonstrated to be a viable, rapid and cost effective alternative toin vivo studies for the preliminary screening of the GI of foods (Woolnough et al., 2008), it can be used to investigate the effects of GTE fortiﬁcation on the digestibility of bread which has yet to be reported in the literature.

In this study, the digestibility of baked and steamed bread con-taining various concentrations of GTE was investigated using an

in vitro digestibility test. The amount of catechins in the bread after baking and steaming was quantiﬁed using high performance liquid chromatograph (HPLC) analysis (Wang & Zhou, 2004; Wang, Zhou,

& Jiang, 2008). Correlations between the amount of green tea cate-chins retained and the digestibility of bread were analyzed and compared between baked and steamed bread. Results of this study would provide insights on the nutritional beneﬁts of green tea catechins on the glycaemic potential of bread.

2. Materials and methods

2.1. Materials

Baked bread flour (13.1% protein, Prima, Singapore), steamed bread flour (7.9% protein, Gim Hin Lee, Singapore), shortening (Phoon Huat, Singapore), instant dry yeast (Saccharomyces cerevisi-ae) (Algict Bruggeman N.V., Belgium), fine salt and sugar were pur-chased from local supermarket. Green tea extract (GTE) was procured from Pure Herbal Remedies Pte Ltd. (Singapore), which was made from green tea (Camellia sinensis) leaves harvested in Guangxi, China. The GTE was specified by the manufacturer to con-tain total polyphenols (P95%), total catechins (P65%) and total ()-epigallocatechin gallate (EGCG) (P30%) as a quality marker of GTE.

Four catechin standards ()-epigallocatechin gallate (EGCG),

()-epigallocatechin (ECG), ()-gallocatechin-3-gallate (GCG),

and catechin-3-gallate (CG) were purchased from Sigma–Aldrich (St Louis, MO, USA). Pancreatin (P7545; 8XUSP speciﬁcations; amylase activity 200 units/mg), pepsin (800–2500 units/mg),

a

-amylase (P10 units/mg solid) and amyloglucosidase (P300 units/mL) used in thein vitro digestion study were pur-chased from Sigma–Aldrich (St Louis, MO, USA). Amyloglucosidase (E-AMGDF; 3260 units/mL) used in the reducing sugar assay was purchased from Megazyme International (Wicklow, Ireland). For-mic acid (ACS grade) was purchased from Merck (Germany). Methanol (HPLC grade) and absolute ethanol (HPLC grade) were purchased from Tedia Company Inc (USA). Chemicals used for 3,5-dinitrosalicylic acid (DNS) analysis were described in previous work (Ranawana & Henry, 2013).

2.2. Preparation of GTE fortiﬁed baked and steamed bread

Baked and steamed bread fortified with 0% (control), 0.45%, 1% and 2% GTE were prepared using a no-time bread-making process described by Wang and Zhou (2004), Ananingsih et al. (2012) with slight modifications, respectively. The ingredients of baked bread included 1 kg flour, 620 mL water, 40 g sugar, 30 g shortening,

20 g salt and 10 g dry instant yeast. The formulation of steamed bread was 1 kg ﬂour, 550 mL water, 10 g of shortening, dry instant yeast, salt and sugar for each. GTE powder was added at levels of 0, 4.5, 10 and 20 g per 1000 g of ﬂour for both types of bread. All ingredients were slowly mixed (44 rpm) for 1 min followed by an intense mixing (100 rpm) of 7 min or a mild mixing (66 rpm) of 5 min for baked and steamed bread, respectively. After mixing, the dough was rested for 10 min at 22 °C and then divided into spherical shape using an automated moulder (DR. ROBOT2, Daub Bakery Machinery B.V., Goirle, Netherlands). The dough pieces (57 ± 2 g each for baked bread and 53 ± 2 g each for steamed bread) were then proofed at 40 °C and 85% relative humidity for 75 and 45 min for baked and steamed bread, respectively. Finally, the dough pieces were baked at 185°C for 15 min or steamed for 20 min. After cooling in room temperature for 1 h, crumb sample was taken from the center of the bread. The crust of baked bread was taken as the layer of 1.5–2 mm thickness from the surface while the skin of steamed bread was peeled off from the surface by hand. Samples of crumb and crust/skin were used for in vitro

digestibility and HPLC analysis.

2.3. HPLC analysis of tea catechins

To determine the retention level of tea catechins in bread after baking or steaming, bread samples were lyophilized, ground and sieved (diameter 250

l

m, Mesh 60) to ensure particle size consis-tency. Ground samples were weighed accurately (0.5 g) into a 50 mL centrifuge tube and homogenized with 50 mL of solvent mixture (70% methanol, 29.7% distilled water and 0.3% formic acid, pH3.4) using vortex. Next, the centrifuge tubes were shaken

mechanically in a water bath maintained at 70 °C for 45 min. The supernatant was collected using vacuum ﬁltration (Vacuubrand MDIC, Germany). In order to determine the amount of tea cate-chins in bread digesta, solvent mixtures were prepared by mixing 14.85 mL of digesta aliquot with 35 mL of methanol and 0.15 mL of formic acid. The percentage composition of this mixture was simi-lar to the extraction solvent mixture used for the analysis of ground bread samples since the main bulk of the digesta was made up of distilled water. A syringe ﬁlter of 0.45

l

m was used to

trans-fer 3 mL of the supernatant or mixture into HPLC vials for analysis. The HPLC method used for catechin quantiﬁcation was described previously (Wang & Zhou, 2004).

2.4. In vitro digestibility study

The protocol of in vitro digestion study was adapted from the study of Ranawana and Henry (2013). Bread skin/crust and crumb samples were cut into pieces (0.5 cm0.5 cm) and weighed

(2.5 ± 0.1 g) into biopsy pots containing 30 mL distilled water and a magnetic stirring rod that continuous stirring at 130 rpm. The biopsy pots were placed in an aluminum block seated a circulating water bath (Model GD-120, Grant instruments, Shepreth, UK). The temperature of the biopsy pots was kept at 37 °C. In vitro digestion consisted of simulated oral, gastric and pancreatic digestion phas-es. The oral phase was initiated by adding 0.1 mL of 10%

a

-amylase

solution dissolved in distilled water. After 1 min, 0.8 mL of 1 M aqueous HCl was added to stop oral digestion. Oral phase samples were collected by transferring 0.5 mL aliquot samples into tubes containing 2 mL ethanol. The gastric phase of digestion was initiat-ed by adding in 1 mL of a 10% pepsin solution dissolvinitiat-ed in 0.05 M HCl. After 30 min, the gastric digestion phase was halted by adding 2 mL of 1 M sodium bicarbonate and 5 mL of 0.2 M Na maleate buffer, pH 6. Gastric phase samples were collected by transferring 0.5 mL aliquot samples into tubes containing 2 mL ethanol. Final digesta volume for each pot was then topped up to 55 mL with distilled water. The pancreatic phase of digestion was

(7)

initiated by adding 0.1 mL of amyloglucosidase and 1 mL of 5% pancreatin in 0.2 M maleate buffer. Timed aliquots of 0.5 mL were withdrawn at 20th, 60th, 90th, 120th and 180th min and trans-ferred to test tubes containing 2 mL absolute ethanol for reducing sugar analysis following the protocol described byRanawana and

Henry (2013). At the end of 180 min of digestion, the digesta con-tents in each pot were collected and stored at _20 °C for HPLC analysis.

Total reducing sugar concentration at each time point (baseline, oral, gastric and pancreatic phases at 20th, 60th, 90th, 120th and 180th min) was calculated (Woolnough, Bird, Monro, & Brennan,

2010). RDS was calculated as the amount of glucose present in the sample aliquot that was taken at 20 min from the start of pan-creatic digestion while SDS was calculated as the difference between the amount of glucose measured at 120 and 20min (Mishra, Monro, & Hedderley, 2008).

In order to understand the matrix effect of bread on the efﬁcacy of green tea catechins, green tea extract was spiked into control sample at three concentration levels, (i) the amount of GTE left in 2% fortiﬁed bread (2% Matched); (ii) 2% GTE (2% spiked); and (iii) 5% GTE (5% spiked), during digestion study. Hence, total 6 dif-ferent types of samples were studied for their digestibility.

2.5. Statistical analysis

All experiments were conducted at least in triplicates. One-way ANOVA analysis and Pearson correlation analysis were carried out using SPSS 17.0 software (IBM Corporation, Chicago, IL, USA).

3. Results and discussion

3.1. Retention of catechins after bread-making and digestion

The retention levels of catechins in baked and steamed bread are shown in Fig. 1(A) and (B), respectively. For baked bread, the

average retention levels of GCG and CG were higher (88.6% and 89.5% respectively) as compared to EGCG and ECG (75.3% and 80.2% respectively) after baking. Similarly, the average retention levels of GCG and CG (99.3% and 94.8% respectively) were higher as compared to EGCG and ECG (81.4% and 84.5% respectively) after steaming. The lower retention level of EGCG and ECG could be due to epimerization of EGCG and ECG to GCG and CG, respectively, during the baking and steaming process. The epimerization of epi-catechins induced by heating was also observed in the thermal processing of longjing tea (Chen, Zhu, Tsang, & Huang, 2001) and the roasting of cocoa ingredients (Payne, Hurst, Miller, Rank, &

Stuart, 2010).

The average retention level of catechins was lower in the baked crust (78.7%) as compared to the baked crumb (83.5%). This could be attributed to the higher temperature experienced by the crust (165 °C) compared to the crumb (100–105 °C) during baking, which could have increased the occurrence of epimerization, oxidation and degradation of catechins (Wang et al., 2008). The average retention level of catechins in baked crumb was similar to that of steamed bread (88%). It further suggested that tem-perature is the determinant factor of the degradation and epimer-ization of catechins, which was also claimed in other system such as green tea infusion (Komatsu et al., 1993) and powder (Li, Taylor,

& Mauer, 2011).

Furthermore, the retention levels of all catechins were higher in 1% and 2% fortified baked bread than that of 0.45% fortified baked bread. This observation suggested that the degradation of catechins was greater at lower initial concentrations of GTE. It was proven by Wang, Zhou, and Wen (2006) that the degradation and epimerization of tea catechins in an aqueous system followed first order kinetics which means the retention levels should be independent of the initial concentration. One possible explanation for this discrepancy could be the matrix effect of bread. As com-pared to a simple aqueous system, bread contains starch–gluten matrix as the major component, binding with lipids, water, and

Fig. 1.Retention levels of catechins in (A) baked bread and (B) steamed bread. Different letters indicate signiﬁcant differences among four types of catechins at the same level of fortiﬁcation in the same part of the bread (p< 0.05).

(8)

sugar, to form a multiphase and multicomponent food system. This observation is in agreement with the study of Sharma and

Zhou (2011) about the stability of catechins during the biscuit making process, in which the retention level of EGCG and ECG increased when the initial concentration of GTE in the biscuit increased.

The retention levels of catechins after in vitro digestion process are shown in Fig. 2. In general, retention rates of all catechins in the digesta samples were much lower than those in the bread samples, particularly EGCG. This could reﬂect the catechin’s participation or degradation in the digestion process. Moreover, the fact that there were still catechins left in the digesta samples could indicate that the amount of GTE fortiﬁed was adequate from the digestion viewpoint.

3.2. Digestion proﬁle of bread

Fig. 3 illustrates the pancreatic digestion profile of baked bread and steamed bread. Oral and gastric phase were not shown due to the minimal amount of glucose release compared to pancreatic phase. In general, all the bread samples demonstrated a similar digestion profile in which the amount of glucose release increased markedly in the first 20 min of the pancreatic digestion phase and then reached a plateau between 90 and 120 min. This indicated a relatively rapid digestion rate of bread with complete hydrolysis within 90 min of pancreatic digestion. A similar digestion profile was observed in a previous study of the digestibility of commercial bread (Ranawana & Henry, 2013).

It was observed that with the increase in GTE concentration, the digestibility of GTE fortified and spiked bread decreased during the first 90 min of pancreatic digestion. A significant decrease in glu-cose release was observed at 20th, 60th, and 90th min sampling time points for all bread samples containing or being spiked with

2% or more GTE. The slower release of glucose at these time points might be explained by the inhibitory effect of tea catechins, espe-cially EGCG, against the activity of

a

-amylase. The inhibitory effect

of tea catechins on

a

-amylase was characterized as

non-com-petitive inhibition (He et al., 2007). However, the mechanism of the formation of catechin and

a

-amylase complex has not been elucidated yet. Some studies suggested the primary interaction between catechins and protein is hydrogen bonding or hydropho-bic interaction (Bandyopadhyay, Ghosh, & Ghosh, 2012; Siebert,

Troukhanova, & Lynn, 1996) while others suggested hydrogen bonding is not (Li et al., 2009; Miao et al., 2014). Nevertheless, the hydroxyl group on the 3-position or 5-position of A–C rings as well as the number of hydroxyl groups on the B-rings played an important role in inhibiting the activity of catechins (Wang,

Du, & Song, 2010; Miao et al., 2014).

Moreover, due to the high pH conditions in the pancreatic digestion phase, the gallate groups of catechins might have disso-ciated more completely into its anionic form, resulting in an increase in ionic interactions between the catechin and enzyme (Koh et al., 2010). Catechins are also susceptible to oxidation at high pH and the oxidation products are able to react with nucle-ophiles available in the food system such as amino or sulfhydryl groups of proteins via covalent bonding (Beart, Lilley, & Haslam,

1985). All the possible interactions between proteins and catechins might result in a signiﬁcant alteration on the quaternary structure of enzymes and thus modify its active site conﬁguration resulting in a loss of enzyme activity.

3.3. Glycaemic potential of GTE fortiﬁed bread

The quantity of starch that was digested in the ﬁrst 20 min of pancreatic digestion phase is deﬁned as RDS whereas the starch that gets digested between 20 and 120 min of pancreatic digestion

Fig. 2.Retention levels of catechins in (A) baked bread sample and (B) steamed bread sample after in vitro digestion study. Different letters indicate signiﬁcant differences among four types of catechins at the same level of fortiﬁcation in the same part of the bread (p< 0.05).

(9)

is deﬁned as SDS (Monro et al., 2010). The amounts of RDS and SDS were calculated and expressed in amount of glucose released (mg/ g of sample) as shown in Fig. 4. The amounts of RDS in steamed and baked bread were signiﬁcantly more than that of SDS, which is consistent with previous studies of commercial bread (Ranawana

& Henry, 2013).

The amounts of SDS were not significantly different among most of the bread samples except for steamed bread with 1% and 2% GTE. Baked bread and steamed bread fortified more than 2% GTE were found to contain significantly lower amounts of RDS. For baked bread containing 2% GTE or more, the decrease in RDS ranged from 8.3% to 14.9% for crust and 5.4% to 14.8% for crumb. For steamed bread containing 2% GTE or more, the decrease in RDS ranged from 7.6% to 25.2% for skin and 10.2% to 17.7% for crumb. The amount of RDS in a particular food product reflects the amount of readily digestible starch and plays an important role in predicting the acute in vivo post-prandial glycaemic response (Englyst & Hudson, 1996). The significant decrease in RDS indicat-ed that a lower amplitude of glycaemic response might be observed after ingestion of GTE fortified bread, which was favor-able for the controlling of acute increase in postprandial blood glu-cose level.

Furthermore, the percentage of RDS in total amount of digesti-ble starch (i.e. RDS + SDS) is shown inFig. 4C. The addition of GTE did not affect the percentage of RDS in the baked bread but sig-niﬁcantly reduced the RDS percentage in both the skin and crumb portions of the steamed bread. This was due to that the fortiﬁca-tion of GTE not only decreased the RDS content but also increased the SDS content in the steamed bread while it only reduced the RDS content in the baked bread. Therefore, the reduction of gly-caemic potential was more profound in the steamed bread.

The correlation between the amount of RDS and the amount of GTE retained in bread was shown in (Fig. 5). Signiﬁcantly linear correlations were found for baked crust (r=_0.578, p< 0.05), baked crumb (r=0.636, p< 0.05), steamed skin (r=0.836,

p< 0.01), and steamed crumb (r=0.847, p< 0.01). The RDS

con-tent was well predicted by GTE amount in baked crumb, steamed skin, and steamed crumb samples. The negative correlation between RDS content and GTE amount indicated that the presence of GTE might contribute to a lower short-term postprandial gly-caemic response. Hence, the presence of GTE could result in reduced digestibility of bread. It further suggested the promising effect of GTE fortiﬁcation of bread on reducing the glycaemic response after ingestion of bread. Such bread may be beneﬁcial to manage type 2 diabetes and reducing the risks of developing chronic diseases that are associated with high GI foods (Jenkins

et al., 2002).

Different from steamed bread, the crust and crumb portions of baked bread contained signiﬁcantly different amount of moisture (average 24.7% in crust and 74.6% in crumb). The amounts of RDS and SDS were corrected for moisture content and evaluated on dry solid basis (Fig. 6). Results showed that the digestibility of bread crust was signiﬁcantly lower than that of crumb, as indicated by its lower RDS and higher SDS content. This observation was expected since approximately 40% of the starches present in crust are not gelatinized after baking (Primo-Martín, van

Nieuwenhuijzen, Hamer, & van Vliet, 2007). Gelatinization of starch, which is the swelling of starch granules in the presence of heat and water, increases its susceptibility to enzymatic hydrolysis (Ross, Brand, Thorburn, & Truswell, 1987). The limited extent of gelatinization in baked bread crust would retard the in vitro enzy-matic digestion process as observed in this study.

Fig. 3.In vitro digestion proﬁle for (A) baked bread crust; (B) baked bread crumb; (C) steamed bread skin, and (D) steamed bread crumb. Zoomed in imaged shoed the glucose release proﬁle during the 20–120 min of pancreatic digestion.

(10)

3.4. Matrix effect of bread on efﬁcacy of catechins

In order to investigate the matrix effect of bread on catechins, control bread sample was spiked with the same amount of GTE

that was determined in the bread fortiﬁed with 2% GTE after baking/steaming but prior to the digestion process (denoted as sample GTE 2% (Matched)). As shown in Fig. 3, slightly lower amount of glucose release was observed in the spiked sample as compared to their respective GTE incorporated bread samples, especially during the 120–180 min period of pancreatic diges-tion. This observation suggested a possible interaction between tea catechins and the bread matrix, most probably with the glu-ten network.

The active component of GTE, EGCG, can form covalent adduct with the cysteinyl thiol residues in protein through autoxidation (Ishii et al., 2008). Catechins could also interact with wheat pro-teins via hydrogen bonding and hydrophobic interaction during dough preparation (Wang & Zhou, 2004). The hydroxyl groups of catechins could form hydrogen bond with the carbonyl group of the proteins while the hydrophobic ring structure of catechins could form hydrophobic interaction with hydrophobic amino acid residues such as proline which has a high content in the glutenin fraction (Hagerman & Butler, 1989). Therefore, catechins incorpo-rated in bread could be less assessable to the digestive enzymes as compared with free catechins in the spiked samples. Higher level of fortiﬁcation of tea catechins is required to achieve the same level of anti-glycaemic effect determined in aqueous system.

Fig. 4.(A) RDS and SDS contents in the baked bread, (B) RDS and SDS contents in the steamed bread, and (C) the percentage of RDS in total digestible starch of the baked bread and the steamed bread. Different letters indicate signiﬁcant differences among four types of catechins at the same level of fortiﬁcation in the same part of the bread (p< 0.05).

Fig. 5.Correlation between retained GTE amount and RDS content in bread. Baked bread crumb and steamed bread skin showed strongly linear correlations. Dashed line represents the linear regression line.

(11)

4. Conclusion

The average retention levels of GCG (99.3–88.6%) and CG (94.8– 89.5%) were higher as compared to EGCG (81.4–75.3%) and ECG (84.5–80.2%) in both the baked and steamed bread. This study demonstrated the effects of GTE on the in vitro digestibility of GTE-fortified baked and steamed bread. There was a significant reduction in glucose release from the GTE-fortified steamed and baked bread during the first 90 min of pancreatic digestion phase, particularly at concentrations of 2% GTE. Similarly, the baked and steamed bread containing 2% GTE exhibited a significantly lower RSD content. These results suggest a possible inhibitory effect of tea catechins on the enzymatic activity of pancreatic

a

-amylase

and glucosidase during bread digestion. A significant correlation was found between the estimated amounts of GTE retained in bread and the RDS content determined fromin vitro digestion. This indicates that the fortification of GTE into bread products may con-tribute a significant impact on reducing the glycaemic response. The potential of transforming bread into a low glycaemic index food was proven to be promising. However, further evidence from animal studies or clinical trials is needed.

Acknowledgements

The authors gratefully acknowledge the research funding from A⁄STAR Grant SERC 112 117 0033 and the National University of

Singapore (Suzhou) Research Institute under the grant number NUSRI2011-007.

References

Ananingsih, V., Gao, J., & Zhou, W. (2012). Impact of green tea extract and fungal alpha-amylase on dough prooﬁng and steaming. Food and Bioprocess Technology, 6(12), 1–12.

Bandyopadhyay, P., Ghosh, A. K., & Ghosh, C. (2012). Recent developments on polyphenol-protein interactions: Effects on tea and coffee taste, antioxidant properties and the digestive system. Food & Function, 3(6), 592–605. Basu, A., & Lucas, E. A. (2007). Mechanisms and effects of green tea on

cardiovascular health.Nutrition Reviews, 65(8 Pt 1), 361–375.

Beart, J. E., Lilley, T. H., & Haslam, E. (1985). Plant polyphenols—secondary metabolism and chemical defence: Some observations. Phytochemistry, 24(1), 33–38.

Chen, Z., Zhu, Q. Y., Tsang, D., & Huang, Y. (2001). Degradation of green tea catechins in tea drinks.Journal of Agriculture and Food Chemistry, 49(1), 477–482. Chung, H.-J., Liu, Q., Peter Pauls, K., Fan, M. Z., & Yada, R. (2008). In vitro starch

digestibility, expected glycemic index and some physicochemical properties of starch and ﬂour from common bean (Phaseolus vulgaris L.) varieties grown in Canada. Food Research International, 41(9), 869–875.

Englyst, H. N., & Hudson, G. J. (1996). The classiﬁcation and measurement of dietary carbohydrates. Food Chemistry, 57(1), 15–21.

Hagerman, A., & Butler, L. (1989). Choosing appropriate methods and standards for assaying tannin. Journal of Chemical Ecology, 15(6), 1795–1810.

He, Q., Lv, Y., & Yao, K. (2007). Effects of tea polyphenols on the activities of a-amylase, pepsin, trypsin and lipase. Food Chemistry, 101(3), 1178–1182. Ishii, T., Mori, T., Tanaka, T., Mizuno, D., Yamaji, R., Kumazawa, S., etal. (2008).

Covalent modiﬁcation of proteins by green tea polyphenol ( )-

epigallocatechin-3-gallate through autoxidation. Free Radical Biology and Medicine, 45(10), 1384–1394.

Jenkins, D. J., Kendall, C. W., Augustin, L. S., Franceschi, S., Hamidi, M., Marchie, A., et al. (2002). Glycemic index: overview of implications in health and disease. American Journal of Clinical Nutrition, 76(1), 266S–273S.

Koh, L. W., Wong, L. L., Loo, Y. Y., Kasapis, S., & Huang, D. (2010). Evaluation of different teas against starch digestibility by mammalian glycosidases.Journal of Agriculture and Food Chemistry, 58(1), 148–154.

Komatsu, Y., Suematsu, S., Hisanobu, Y., Saigo, H., Matsuda, R., & Hara, K. (1993). Effects of pH and temperature on reaction kinetics of catechins in green tea infusion. Bioscience, Biotechnology, and Biochemistry, 57(6), 907–910.

Lee, J. L. (2012). Sensory and Physicochemical Analysis of Green Tea Extract Fortiﬁed Steamed Bread during Storage [Unpublished B. Appl. Sc. Hons Thesis]. Singapore: National University of Singapore.

Li, Y., Gao, F., Gao, F., Shan, F., Bian, J., & Zhao, C. (2009). Study on the interaction between 3 ﬂavonoid compounds and alpha-amylase by ﬂuorescence spectroscopy and enzymatic kinetics. Journal of Food Science, 74(3), C199–C 203.

Li, N., Taylor, L. S., & Mauer, L. J. (2011). Degradation kinetics of catechins in green tea powder: Effects of temperature and relative humidity. Journal of Agricultural and Food Chemistry, 59(11), 6082–6090.

Liu, J., Wang, M., Peng, S., & Zhang, G. (2011). Effect of green tea catechins on the postprandial glycemic response to starches differing in amylose content. Journal of Agriculture and Food Chemistry, 59(9), 4582–4588.

Miao, M., Jiang, H., Jiang, B., Li, Y., Cui, S. W., & Zhang, T. (2014). Structure elucidation of catechins for modulation of starch digestion. LWT - Food Science and Technology, 57(1), 188–193.

Mishra, S., Monro, J., & Hedderley, D. (2008). Effect of processing on slowly digestible starch and resistant starch in potato. Starch - Stärke, 60(9), 500–507. Monro, J. A., & Mishra, S. (2010). Database values for food-based dietary control of

glycaemia. Journal of Food Composition and Analysis, 23(5), 406–410. Monro, J. A., Mishra, S., & Venn, B. (2010). Baselines representing blood glucose

clearance improve in vitro prediction of the glycaemic impact of customarily consumed food quantities.British Journal of Nutrition, 103(2), 295–305. Payne, M. J., Hurst, W. J., Miller, K. B., Rank, C., & Stuart, D. A. (2010). Impact of

fermentation, drying, roasting, and dutch processing on epicatechin and catechin content of cacao beans and cocoa ingredients.Journal of Agricultural and Food Chemistry, 58(19), 10518–10527.

Primo-Martín, C., van Nieuwenhuijzen, N. H., Hamer, R. J., & van Vliet, T. (2007). Crystallinity changes in wheat starch during the bread-making process: Starch crystallinity in the bread crust. Journal of Cereal Science, 45(2), 219–226.

Ranawana, V., & Henry, C. J. (2013). A comparative evaluation of the glycaemic potential of commercial breads consumed in South East Asia. International Journal of Food Sciences and Nutrition, 64(2), 223–229.

Robyt, J. F. (2009). Enzymes and their action on starch. In J. BeMiller & R. L. Whistler (Eds.), Starch chemistry and technology (3rd ed., pp. 237–292). London: Academic Press/Elsevier.

Ross, S. W., Brand, J. C., Thorburn, A. W., & Truswell, A. S. (1987). Glycemic index of processed wheat products. American Journal of Clinical Nutrition, 46(4), 631–635.

Sharma, A., & Zhou, W. (2011). A stability study of green tea catechins during the biscuit making process. Food Chemistry, 126(2), 568–573.

Siebert, K. J., Troukhanova, N. V., & Lynn, P. Y. (1996). Nature of polyphenol protein interactions. Journal of Agricultural and Food Chemistry, 44(1), 80–85. Simmons, R. K., Unwin, N., & Grifﬁn, S. J. (2010). International Diabetes Federation:

An update of the evidence concerning the prevention of type 2 diabetes. Diabetes Research and Clinical Practice, 87(2), 143–149.

Wang, H., Du, Y.-J., & Song, H.-C. (2010).a-Glucosidase anda-amylase inhibitory activities of guava leaves. Food Chemistry, 123(1), 6–13.

Wang, R., & Zhou, W. (2004). Stability of tea catechins in thebread making process. Journal of Agricultural and Food Chemistry, 52(26), 8224–8229.

Wang, R., Zhou, W., & Isabelle, M. (2007). Comparison study of the effect of green tea extract (GTE) on the quality of bread by instrumental analysis and sensory evaluation.Food Research International, 40(4), 470–479.

Fig. 6.RDS and SDS contents in baked bread after moisture correction. Different letters indicate signiﬁcant difference among four types of catechins for the same level of fortiﬁcation at the same part of the bread (p< 0.05).

(12)

Wang, R., Zhou, W., & Jiang, X. (2008). Mathematical modeling of the stability of green tea catechin epigallocatechin gallate (EGCG) during bread baking.Journal of Food Engineering, 87(4), 505–513.

Wang, R., Zhou, W., & Wen, R. A. (2006). Kinetic study of the thermal stability of tea catechins in aqueous systems using a microwave reactor.Agricultural and Food Chemistry, 54(16), 5924–5932.

Woolnough, J. W., Bird, A. R., Monro, J. A., & Brennan, C. S. (2010). The effect of a brief salivary alpha-amylase exposure during chewing on subsequent in vitro starch digestion curve proﬁle. International Journal of Molecular Sciences, 11(8), 2780–2790.

Woolnough, J. W., Monro, J. A., Brennan, C. S., & Bird, A. R. (2008). Simulating human carbohydrate digestion in vitro: A review of methods and the need for standardisation.International Journal of Food Science & Technology, 43(12), 2245–2256.

Yilmazer-Musa, M., Grifﬁth, A. M., Michels, A. J., Schneider, E., & Frei, B. (2012). Grape seed and tea extracts and catechin 3-gallates are potent inhibitors of a-amylase anda-glucosidase activity. Journal of Agricultural and Food Chemistry, 60(36), 8924–8929.