Bioaccessibility of Polyphenols from Wheat (Triticum aestivum

Oct 23, 2014 - (iii) Microwave heating: Powdered grain samples were microwave heated in triple-distilled water (10 g in 50 mL) for 4 min in a househol...
4 downloads 11 Views 500KB Size
Subscriber access provided by BOSTON COLLEGE

Article

Bioaccessibility of polyphenols from wheat (Triticum aestivum), sorghum (Sorghum bicolor), green gram (Vigna radiata) and chickpea (Cicer arietinum) as influenced by domestic food processing Gavirangappa Hithamani, and Krishnapura Srinivasan J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/jf503450u • Publication Date (Web): 23 Oct 2014 Downloaded from http://pubs.acs.org on November 4, 2014

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 38

Journal of Agricultural and Food Chemistry



Bioaccessibility of polyphenols from wheat (Triticum aestivum), sorghum (Sorghum bicolor), green gram (Vigna radiata) and chickpea (Cicer arietinum) as influenced by domestic food processing



Gavirangappa Hithamani and Krishnapura Srinivasan*



Department of Biochemistry and Nutrition, CSIR – Central Food Technological Research Institute, Mysore – 570 020, India

1  2 

6  7  8  9 

Running Title: Bioaccessibility of polyphenols from cereals and legumes

10  11  12  13  14  15 

-----------------------------*Corresponding author E-mail: [email protected]; Fax # +91-821-2517233; Tel # +91-821-2514876

16 

1   

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 2 of 38

17  18 

--------------------------------------------------------------------------------------------------------------------ABSTRACT

19 

Cereals (wheat and sorghum) and legumes (green gram and chickpea) commonly consumed in

20 

Asia and Africa were evaluated for the polyphenolic content. Bioaccessibility of polyphenols

21 

from these grains as influenced by domestic processing was also estimated. Total polyphenol

22 

content of wheat and sorghum was 1.20 and 1.12 mg/g respectively, which was increased by

23 

49% and 20% respectively, on roasting. In contrary, a significant reduction of the same was

24 

observed in both the cereals after pressure-cooking, open-pan boiling and microwave heating.

25 

Total flavonoids that was 0.89 mg/g in native sorghum, reduced drastically after processing.

26 

Tannin content of both the cereals significantly increased on sprouting as well as roasting. Total

27 

polyphenol content reduced by 31% on sprouting but increased to 24% on roasting in green

28 

gram. Pressure-cooking (53%), open-pan boiling (64%) and microwave heating (>2-fold

29 

increase) significantly increased total polyphenol content in chickpea, while drastic reduction

30 

was observed in the total flavonoid content. Bioaccessible total polyphenols from these grains

31 

were in the order: green gram > chickpea > wheat > sorghum. Domestic processing of these

32 

grains had minimal/ no effect on the bioaccessible total flavonoid content. Not all the phenolic

33 

compounds present in them were bioaccessible. Concentration of bioaccessible phenolic

34 

compounds increased especially on sprouting and roasting of these grains, except chickpea,

35 

where sprouting significantly reduced the same (476 to 264 µg/g). Microwave heating

36 

significantly enhanced the concentration of bioaccessible polyphenols especially from chickpea.

37 

Thus, sprouting and roasting provided more bioaccessible polyphenols from the cereals and

38 

legumes studied.

39  40 

KEYWORDS: Bioaccessibility, Polyphenols, Domestic processing, Wheat, Sorghum, Green

41 

gram, Chickpea 2   

ACS Paragon Plus Environment

Page 3 of 38

42 

Journal of Agricultural and Food Chemistry

INTRODUCTION

43 

Phenolic compounds are popular phytochemicals found in plants known for their potential

44 

health effects. Indeed, polyphenols are the most abundant antioxidants in diet. Challenges for

45 

research on polyphenols from food with respect to bioavailability, metabolism, and cellular and

46 

molecular mechanisms have been recently reviewed.1

47 

Cereals and legumes, which form staple foods for the majority of Asian and African

48 

population, contain these phenolic compounds and have found immense applications in

49 

functional foods.2,3 Wheat (Triticum aestivum) being the most widely cultivated cereal in the

50 

world contributing to 27% of total cereal production,4 serve as one of the important protein

51 

source for human population. Wheat flour and wheat bran are extensively used as ingredients in

52 

dietary fiber rich ready-to-eat breakfast cereals. Phytochemical content and antioxidant activity

53 

of different varieties of wheat have been reported.5 Some varieties of sorghum (Sorghum

54 

bicolor), which are drought-resistant staple food crop of semi-arid regions of Africa and Asia are

55 

found to contain high amounts of phenolic compounds compared to other cereals.6,7 Many

56 

epidemiological studies have correlated consumption of whole-grain cereals with a reduced risk

57 

of developing colonic and breast cancer, type-2 diabetes and coronary heart disease.8-10

58  59 

Legumes, though secondary to cereals in terms of consumption, are important as protein

60 

supplements to cereals, play an important role in human nutrition. Chickpea (Bengal gram, Cicer

61 

arietinum) is the second most important legume in the world.4 Green gram (Mung bean; Vigna

62 

radiata), is reported to be a good source of carbohydrates, proteins and minerals.

63 

Antiproliferative effects of legumes have been associated with the presence of phenolic

64 

compounds.11-13

65  3   

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 4 of 38

66 

In order to exert their health beneficiary effects, the polyphenols from these cereals and

67 

legumes should be bioavailable. The bioavailability depends on the release of these compounds

68 

from the food matrix which is referred as bioaccessibility. It is suggested that the gastro-

69 

intestinal tract may act as an extractor where polyphenols are progressively released from the

70 

solid matrix and made available for the absorption or to exert their biological effects in the

71 

gastro-intestinal tract.14 Cereal grains and legumes generally undergo different types of

72 

processing during food preparation, depending on the food culture and taste preferences.

73 

Information on the effect of food processing on the polyphenol content as well as their

74 

bioaccessibility is very scarce. We have recently reported the effect of domestic processing on

75 

the polyphenol content and bioaccessibility in finger millet (Eleusine coracana) and pearl millet

76 

(Pennisetum glaucum).15 Most common forms of domestic processing are sprouting, roasting,

77 

pressure-cooking, open-pan boiling and microwave heating, which may bring about several

78 

changes in the nutritional quality of food. Hence, the present investigation was carried out to

79 

determine the extent to which domestic processing influence phenolic profile and

80 

bioaccessibility of polyphenols from commonly consumed cereals – wheat and sorghum and

81 

legumes – green gram and chickpea.

82  83 

MATERIALS AND METHODS

84 

Materials.

85 

Sorghum (Sorghum bicolor L. Moench), wheat (Triticum aestivum L.), green gram (Vigna

86 

radiata L.), and chickpea (Cicer arietinum L.) were procured from the National Seeds

87 

Corporation (Mysore, Karnataka, India). Standard phenolic compounds, pepsin, pancreatin and

88 

bile extract (porcine origin), were procured from Sigma-Aldrich Chemical Co. (St. Louis, MO,

4   

ACS Paragon Plus Environment

Page 5 of 38

Journal of Agricultural and Food Chemistry

89 

USA). HPLC grade solvents were from Qualigens Chem. Co. (Mumbai, India). All other

90 

chemicals and reagents used were of analytical grade.

91  92 

Processing of grain samples. A known amount of grain samples was subjected to various types of domestic processing in

93  94 

triplicates as described below:

95 

Sprouting: After soaking the grains overnight (30 g in 90 mL), water was decanted; samples

96 

were allowed to germinate for a period of 48 h under ambient conditions (25 ºC), while keeping

97 

them wet by intermittently spraying water. The sprouted grains were dried under shade,

98 

powdered and used for extraction.

99 

Heat processing:

100 

(i) Pressure cooking: Powdered grain samples were pressure-cooked (15 p.s.i.) in triple distilled water (10 g in 30 mL) for 15 min.

101  102  103 

(ii) Open-pan boiling: Powdered grain samples were boiled in triple distilled water (10 g in 50 mL) on a hot plate for 10 min.

104  105  106 

(iii) Microwave heating: Powdered grain samples were microwave heated in triple distilled water

107 

(10 g in 50 mL) for 4 min in a household microwave system (SAMSUNG Trio, Combi-

108 

CE1031LAT; Samsung Electronics Co. Ltd., Suwon, Korea) at 450 W. Cooked samples

109 

were used for further studies.

110  111 

(iv) Roasting: Known quantity of each sample (30 g) was roasted on preheated acid washed sand

112 

at 150 ºC ± 2 ºC for 5 min (until the sample gave a characteristic aroma and color). Roasted

5   

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 6 of 38

113 

sample was cooled to room temperature, powdered and stored in air-tight pouches in dark at

114 

4 ºC until future studies.

115  116 

Analysis of Polyphenols.

117 

Extraction of polyphenols

118 

Extraction of polyphenols was carried out by refluxing the grain samples (2 g) in acidified

119 

methanol for 2 h.16 Total polyphenols, total flavonoids and tannins were analyzed in the filtered

120 

extracts as described below.

121  122  123  124 

Total polyphenols Total polyphenol content was estimated by Folin-Ciocalteu method as described by Singleton

125 

et al.,17 with slight modifications. Briefly, an aliquot of acidified methanolic extract was

126 

appropriately diluted with water to 3.0 mL, mixed with 1 mL each of 1N Folin–Ciocalteu reagent

127 

and 20% sodium carbonate and incubated for 30 min at room temperature. The absorbance was

128 

recorded in a spectrophotometer (Model UV-1800, Shimadzu Corporation, Kyoto, Japan) and

129 

compared with those of known standard gallic acid concentrations (R2 = 0.999). The total

130 

polyphenol content was computed as mg equivalent gallic acid per g of sample.

131  132  133  134 

Total flavonoids Total flavonoid content was determined according to the method of Zhishen et al.18 Acidified

135 

methanolic extract (0.1 mL) was diluted with 4.9 mL of distilled water and mixed with 0.3 mL of

136 

(5% w/v) NaNO2. After 5 min, 0.3 mL of (10% w/v) AlCl3 and 2 mL of 1 M NaOH were added,

137 

and diluted with distilled water to a total volume of 10 mL. The mixture was vortexed and the

138 

absorbance was read at 510 nm. Standard catechin was used to prepare a calibration curve (R2 =

139 

0.999). The flavonoid concentration was expressed as mg catechin equivalents per g of sample. 6   

ACS Paragon Plus Environment

Page 7 of 38

140  141  142  143 

Journal of Agricultural and Food Chemistry

Tannins Tannin content was determined by the modified vanillin–HCl method.19 An aliquot of

144 

acidified methanolic extract was appropriately diluted to 1 mL with distilled water and was

145 

mixed with 5 mL of vanillin–HCl reagent. The samples were allowed to stand at room

146 

temperature for 20 min and the colour developed was recorded at 500 nm. The absorbance was

147 

also recorded for standard catechin solution (R2 = 0.998) and the tannin concentration was

148 

expressed as mg catechin equivalents per g of sample.

149  150 

HPLC analysis

151 

Phenolic extract of native and processed samples were analyzed by HPLC to obtain a profile

152 

of individual phenolic compounds.20 Analysis was carried out in a HPLC system (Agilent 1200

153 

Series; Agilent Technologies Inc., Santa Clara, CA, USA) equipped with a Diode Array detector.

154 

Filtered samples (20 µL) were analyzed for polyphenols using C18 analytical column (250 × 4.6

155 

mm; 5 µm; Agilent Technologies Inc., USA) with the mobile phase consisting of 0.1%

156 

trifluoroacetic acid as solvent A and 100% methanol as solvent B. The total run time was 60 min

157 

with a flow rate of 1.0 mL/min with the gradient programme as follows: initial B concentration

158 

of 20% to 40% in 40 min which was maintained for 10 min and then again to 20% B in the next

159 

five min and 5 min of post-run for reconditioning. Peaks were recorded simultaneously at 280

160 

and 320 nm.

161  162 

Bioaccessibility of polyphenols.

163 

Bioaccessibility of polyphenols was determined by an in vitro method as described by Luten

164 

et al.,21 involving simulated gastrointestinal digestion with suitable modifications. Initially,

165 

simulated gastric digestion was carried out by incubating the powdered samples (10 g) with 7   

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 8 of 38

166 

pepsin at pH 2.0 and a temperature of 37 °C for 2 h. At the end of gastric digestion, titratable

167 

acidity was determined in an aliquot of gastric digest as the amount of 0.2M sodium hydroxide

168 

required to attain a pH of 7.5 in the presence of a mixture of pancreatin and bile extract dissolved

169 

in 0.1 M sodium bicarbonate (4 g pancreatin and 25 g bile extract per liter).

170  171 

Subsequently, intestinal digestion was simulated by suspending segments of dialysis tubing

172 

(molecular mass cut-off: 10 kDa) containing 25 mL aliquots of sodium bicarbonate solution,

173 

being equivalent in moles to the titratable acidity (sodium hydroxide needed to neutralize the

174 

gastric digest) in Erlenmeyer flasks containing the gastric digest and incubated at 37 °C with

175 

shaking until the pH of the digest reached 5.0. Pancreatin–bile extract mixture (5 mL) was then

176 

added and incubation was continued for 2 h or longer until the pH of the digest reached 7.0. At

177 

the end of this simulated gastrointestinal digestion, the dialyzate was analyzed for polyphenols

178 

by both spectrophotometry and HPLC as described in previous paragraphs. The bioaccessible

179 

polyphenol present in the grain sample is the dialyzable portion of the total polyphenol which is

180 

expressed as percent bioaccessibility.

181  182 

Statistical analysis.

183 

All determinations were made in three replicate, and the average values are reported.

184 

Statistical analysis was carried out using Graphpad INSTAT, Version 3.06, Graphpad software.

185 

Data was analyzed by applying one-way analysis of variance (ANOVA) and the differences

186 

between means were assessed by Dunnet’s test and considered significant when P < 0.05.

187  188  189  190  191  192  8   

ACS Paragon Plus Environment

Page 9 of 38

193 

Journal of Agricultural and Food Chemistry

RESULTS

194 

Phenolic extracts of native and variously processed cereals and legumes as well as of

195 

dialysates obtained after simulated gastric digestion of these samples were analyzed for total

196 

polyphenols, flavonoids, tannins and individual polyphenol profile.

197  198 

Total polyphenol, flavonoid and tannin content of cereal grains.

199 

Total polyphenol content, total flavonoid content and tannin content of wheat are given in

200 

Table 1. Total polyphenol content of unprocessed wheat was 1.20 mg/g, which significantly

201 

increased on sprouting (by 19%) and roasting (by 20%) (P