Glycemic Index and Chemical Composition of Traditional Omani Breads

Abstract

This study evaluated the chemical composition and glycemic index (GI) of eight different types of traditional Omani breads made from wheat flour. Significant (P < 0.05) differences were observed in the proximate chemical composition, dietary fibre content, and gross energy value of these breads. The moisture, crude protein, total fat, ash, crude fibre and nitrogen free extract (NFE) contents ranged between 21.6–51.6, 4.3–10.5, 0.8–13.8, 1.2–2.3, 1.0–2.0, and 34.5–61.8 g/100 g of sample respectively. The values for dietary fibre were between 5.6, 9.6 g/100g, and the gross energy contents ranged between 897 and 1468 kJ/100 g. The GI value of these breads also differed significantly (P < 0.05). No significant differences were however observed among the GI values for White Toast Bread (local commercial bread), Brown Toast Bread (local commercial bread), White Khubz Lebanani (local commercial bread), Brown Khubz Lebanani (local commercial bread), and Chapati (local homemade bread), which were 63 ± 12, 58 ± 15, 63 ± 10, 57 ± 20, and 58 ± 10, respectively. Paratha (local restaurant made bread with fat), Goleh (local homemade soft bread), and Rekhal (local homemade thin bread) showed significantly (P < 0.05) lower GI values as compared to other breads, and these were 32 ± 13, 43 ± 13 and 39 ± 7, respectively. No specific correlation was observed in the chemical composition and glycemic index of these breads. These breads fall within low to medium GI category of foods.

Keywords:

• Glycemic index
• Chemical composition
• Omani breads

INTRODUCTION

Cereal grains and cereal products constitute most of the calories and protein in the diet of Middle Eastern countries.[1] Wheat and rice are the two staple foods in Oman.[2] Wheat is mainly consumed in the form of bread. Bread is a type of food, which is made from cereal grains (mainly wheat) that have been ground into flour or meal, moistened with water, kneaded into dough, and then backed. The other ingredients, which may be added to bread include milk, fat, eggs, salt and sugars.[3] Bread has always been considered not only as the core component of diet of both rich and poor, but also for its versatile role in health and disease.[4] Together with various modern types of breads, some traditionally baked breads are also present in the local Omani markets. In Oman, the breads are commonly consumed in a variety of ways and are served almost at all three mealtimes, breakfast, lunch, and dinner, whereas the rice is mainly served at lunchtime. Based on family purchases, Lebanese bread (Khubz Lebanani) is the most commonly consumed bread as compared to other types found in Oman.[2] No exact quantification is however available on the consumption of these breads by Omani population. The average per capita per day consumption of breads in different Arab Gulf and Mediterranean countries has been reported to be 355 g in Saudi Arabia,[5] 277g in Kuwait,[6] 548, 444, 438, 419 and 350g in Libya, Egypt, Algeria, Morocco and Greece respectively.[7] Only a few studies have reported the nutritional quality and chemical composition of breads consumed in various parts of the Arab Gulf region like wheat breads consumed in Saudi Arabia,[8] fortified wheat bread in Kuwait,[9] different types of breads consumed in Bahrain[11] and the Arabic bread used in various Middle Eastern countries.[11] The quality and nutritive value of various breads can differ due to variety of wheat, flour extraction rate and the recipe used for their preparation.[8,12,13]

The glycemic Index (GI) of foods has shown its significance as a useful nutrition concept/tool for classifying the carbohydrate rich foods based on their postprandial blood glucose responses. According to this system, the individual foods are assigned numeric values how fast they are digested, absorbed and produce the glycemic responses during the postprandial period as compared to a standard reference food, which is either glucose or white bread.[14] A number of variables however affect the glycemic index of foods by changing their digestion rate, gastric emptying time and/or starch amylolysis.[15,16] These factors include the physical form of food molecules, nature of monosaccharide components, nature of starch, processing of foods, the amount and type of other food components as well as the nutrient interactions.[17–19] The particle size of wheat can affect the digestion rate and metabolic response in healthy subjects.[20] With the increasing proportion of whole grain bulgur (cracked wheat) in place of miller flour in bread, the GI value of breads decreased in patients with Type 2 Diabetes.[21] Mesci et al.[22] however did not observe any significant differences in the glycemic or insulinemic responses among four different types of breads (white, whole wheat, wheat bran and rye breads) in type 2 diabetic patients. Reducing the volume of white bread (loaf structure) has been shown to favourably alter its metabolic and appetite responses.[23]

Low glycemic index foods have been shown to lower the risk of Type 2 Diabetes, reduce the rate of cardiovascular diseases, and certain types of cancers as well as can promote weight loss and help in controlling obesity.[24–28] Identification of low glycemic index foods is therefore important as relatively small differences in the GI value of regularly consumed cereal products, such as breads, can have long term beneficial effects on health. Data bank of local/regional foods for their chemical composition and glycemic index (GI) is important to make dietary recommendations for both the people with physiologic abnormalities as well as for the general population who wish to control and prevent the development of non-communicable chronic diseases. No such data is currently available for various types of commonly consumed breads in the Sultanate of Oman. The present study was therefore conducted to determine the chemical composition and glycemic index of some of the commonly consumed traditional Omani breads.

MATERIALS AND METHODS

Materials

Eight different types of breads (White toast bread, Brown toast bread, Khubz Lebanani white (local commercial bread), Khubz Lebanani brown (local commercial bread), Chapati (local homemade bread), Paratha (local homemade bread with fat), Goleh (local homemade soft bread), Rekhal (local homemade thin bread), made from wheat flour and commonly consumed in Oman, were used for this study. Representative samples of these breads were either purchased from the local market or were prepared according to the traditional homemade recipes published by the Ministry of Health, Sultanate of Oman.[29]

Proximate Chemical Analysis

Representative samples of these breads were analyzed to determine their proximate chemical composition (moisture, protein, fat, ash, and carbohydrate contents) according to the methods of Association of Official Analytical Chemists (AOAC).[30] The energy value was calculated from the protein, fat and nitrogen free extract (NFE) contents using the factors of 17, 37, and 17 kJ/g respectively.

Glycemic Index Testing

Nine normal healthy human volunteers, free from any clinical signs or symptoms of chronic diseases and not using any medications with normal fasting blood glucose values (96 ± 4 mg/dL) and oral glucose tolerance test, to rule out the diabetes,[31] were recruited for this study. The average age, weight, height and body mass index (BMI) of volunteers were 22.4 ± 1.5 years, 50.8 ± 9.1 kg, 1.57 ± 0.06 m, and 20.6 ± 2.7 kg/m², respectively. The volunteers were briefed about the study protocol and also signed a written informed consent. The study was approved by the Research in Ethics Committee of Sultan Qaboos University, Muscat, Oman.

The glycemic index testing started at 8:00 am. Portions of test foods and standard reference food (glucose) containing 50 g of available carbohydrates were given to the subjects in random order on separate occasions after an overnight fast of ≥ 10 hours. A standard drink of pure water (250 ml) was given with each test food. The volunteers were asked to eat the test foods within 5–6 minutes. The glycemic index of more than one test food was determined in one series of tests. The test for the reference standard food (glucose) was repeated thrice and the average values were used to calculate the GI of the test foods. The blood samples were taken by capillary finger prick method at 0 (fasting), 15, 30, 45, 60, 90, and 120 minutes after the intake of test foods. A drop of blood was applied to the SureStep Hospital Test Strip, which was immediately inserted into the SureStep Brand Professional Blood Glucose Meter, and the blood glucose level was measured. The test employs a dry reagent technology based on the glucose oxidase method, which is specific for D-glucose.[32] The area under the glycemic response curve for each food is expressed as a percent of the mean response to the standard reference food taken by the same subject, ignoring the area beneath the fasting concentration. The calculations, for the incremental area under the curve (IAUC), were carried out according to the methods as described by Wolever et al.[33] and FAO/WHO[34] The GI values were calculated as:

Statistical Analysis

The data collected was subjected to statistical analysis using one way analysis of variance (ANOVA) and the means were compared by least significant difference (LSD) test as described by Snedecor and Cochran.[35] Significant differences were defined at P < 0.05.

RESULTS AND DISCUSSIONS

Chemical Composition

The results on the chemical composition of breads are presented in Table 1. Significant (P < 0.05) differences were observed in the proximate chemical composition of these breads. Paratha showed the highest fat content (13.8%) whereas both the White and Brown Khubz Lebanani had the lowest fat contents (i.e., 0.9 and 0.8%, respectively). The dietary fibre and the energy contents of breads also differed significantly (P < 0.05). The highest energy value was observed for Paratha (1468 kJ/100 g) whereas the Goleh showed the lowest energy value (897 kJ/100 g). The differences in the chemical composition of these breads could partly be attributed to the recipes used for the preparation of these breads as well as due to variability in the processing/cooking methods. The highest fat content found in Paratha is because; it is mostly cooked/fried with a lot of fat. Both white and brown Khubz Lebanani, as well as the white and brown toast breads showed the lowest fat levels. The variability in the chemical composition of these breads also contributed to the differences in their energy contents. Our results are with in the similar ranges of selected earlier findings, which have reported the nutritional quality and chemical composition of breads consumed in various parts of the Arab Gulf region such as wheat breads consumed in Saudi Arabia,[8] fortified wheat bread in Kuwait,[9] different types of breads consumed in Bahrain,[10] and the Arabic bread used in various Middle Eastern countries.[11] The quality and nutritive value of various breads can differ due to variety of wheat, flour extraction rate and the recipe used for their preparation.[8,12,13] The results of this study provide the basic data on the chemical composition and energy value of traditional Omani breads.

Table 1 Proximate chemical composition (%), dietary fibre content (%) and energy values of breads (kJ/100g) (on as such basis)

Type of bread/ Parameter	Moisture (%)	Crude protein	Total fat (%)	Ash (%)	Crude fibre (%)	NFE (%)	Energy (kJ/100 g)	Dietary fibre (%)
White toast bread	30.3 ± 3.7 ^c	8.0 ± 0.4 ^b	1.1 ± 0.8 ^e	1.5 ± 0.1 ^ab	1.2 ± 0.1 ^b	57.8 ± 1.0 ^b	1145 ± 24 ^d	7.9 ± 1.1 ^b
Brown toast bread	36.9 ± 3.6 ^b	9.0 ± 0.4 ^b	1.2 ± 0.4 ^e	1.8 ± 0.2 ^a	1.5 ± 0.1 ^ab	49.6 ± 1.9 ^c	1024 ± 22 ^e	9.6 ± 1.1 ^a
White Khubz Lebanani	26.1 ± 1.3 ^d	8.9 ± 0.1 ^b	0.9 ± 0.3 ^e	1.2 ± 0.2 ^b	1.0 ± 0.1 ^b	61.8 ± 1.4 ^a	1216 ± 10 ^c	8.4 ± 1.0 ^b
Brown Khubz Lebanani	29.4 ± 0.4 ^e	10.3 ± 0.2 ^a	0.8 ± 0.3 ^e	1.8 ± 0.6 ^a	2.0 ± 0.2 ^a	55.6 ± 1.3 ^b	1134 ± 10 ^d	7.5 ± 1.2 ^b
Chapati	27.3 ± 0.4 ^d	10.5 ± 0.1 ^a	3.9 ± 0.3 ^d	2.3 ± 0.6 ^a	1.5 ± 0.2 ^ab	54.5 ± 1.2 ^b	1084 ± 6 ^c	8.1 ± 1.2 ^b
Rekhal	21.6 ± 0.5 ^e	10.1 ± 0.1 ^a	4.9 ± 0.4 ^c	2.3 ± 0.4 ^a	1.7 ± 0.2 ^a	59.4 ± 1.3 ^ab	1348 ± 8 ^b	6.2 ± 1.2 ^c
Goleh	51.4 ± 2.1 ^a	4.3 ± 1.8 ^c	6.6 ± 2.1 ^b	1.9 ± 0.6 ^a	1.2 ± 0.1 ^b	34.5 ± 1.3 ^d	897 ± 33 ^f	7.4 ± 1.1 ^b
Paratha	25.7 ± 0.2 ^d	8.1 ± 0.1 ^b	13.8 ± 0.4 ^a	1.9 ± 0.1 ^a	1.9 ± 0.1 ^a	48.6 ± 1.2 ^c	1468 ± 6 ^a	5.6 ± 1.1 ^c
^a, b, c, d, e, f = Different alphabets in the same column means significantly different at 5%.

Glycemic Index of Breads

The average blood glucose responses for standard reference food (glucose) and different test breads at 0 (fasting), 15, 30, 45, 60, 90, and 120 minutes after the ingestion of foods are shown in Fig. 1. The average fasting blood glucose values (96 ± 4 mg/dL) for all the volunteers were within the normal range. The volunteers also did not show any impaired fasting blood glucose (IGF) values. The oral blood glucose tolerance test for all the volunteers was also within the normal range as judged by the criteria of American Diabetic Association (ADA).[31] The results indicated that different types of traditional Omani breads produced significantly (P < 0.05) different effects on the blood glucose responses in normal healthy subjects. The blood glucose responses at various time intervals as a result of intake of Paratha were the lowest as compared to all other breads. All other breads showed almost the same pattern in producing the glucose responses. All the test breads however produced lower blood glucose responses two hours postprandial as compared to blood glucose responses to a 50 g glucose load for the same volunteer.

Figure 1 Average blood glucose responses of volunteers on standard reference food (glucose) and eight test breads.

The results for the glycemic index of breads are given in Table 2. The glycemic index of these breads differed significantly (P < 0.05). The White Toast bread and White Khubz Lebanani showed almost similar GI values of 62.8 and 62.5, respectively. Although the Brown Toast bread, Khubz Lebanani brown and Chapati showed slightly lower GI values (57.8, 56.6, and 58.2 respectively) as compared to White Toast bread and White Khubz Lebanani, the difference were non-significant (P < 0.05). The GI values of Paratha, Rekhal, and Goleh were significantly (P < 0.05) lower as compared to other breads. The lowest GI value (31.8) was observed for Paratha followed by Rekhal (39.1) and Goleh (42.9). However, no significant (P < 0.05) differences were observed among the GI values of Paratha, Rekhal, and Goleh. No specific pattern of correlation was found between the chemical composition and the GI values of these breads. The fat content of Paratha however did show a significant (P < 0.05) correlation with its GI value. The differences in the GI values may be attributed to a number of factors mainly because of different processing/cooking methods as well as the recipe used in the preparation of these breads. The particle size of wheat can affect the digestion rate and metabolic response in healthy subjects.[20] Our results for the GI value of Chapati (58.2 ± 11.0) are somewhat lower than the GI value (65 ± 9.0) of Sadha Roti (a very similar type of bread), as reported by Ramdath et al.[36] These differences may partly be explained due to some variability in the type of flour or the processing methods used in the preparation of these breads, which otherwise appear to be very similar to each other. The reasons for the relative differences in the GI value of these breads cannot however be exactly explained. It may be hypothesized that the variability in cooking/baking processes of these breads might have contributed to these differences. The chemical composition, use of leavening agent, dough making, and baking processes may be considered as the main factors. It was suggested that the rate of starch accessibility to enzyme activity is reduced due to a combination of compact form and the need for protein digestion to free the starch granules.[37] During the process of dough making, the neighbouring network of proteins in wheat flour interacts with water and the gluten protein fills up the space between starch granules, producing viscoelastic dough.[38] This physical barrier created by the wheat gluten protein network with starch may influence the relative accessibility of starch to amylase.[39] The wheat germ of the whole grain acts as a natural amylase inhibitor, which can be destroyed during the milling of wheat into whole meal flour.[40] In the leavened foods, the high porosity caused by the entrapment of gas bubbles, which expand during cooking, greatly increase the surface area exposed to enzyme activity. The lower GI values shown by the unleavened types of breads like Chapati, Goleh, Paratha, and Rekhal as compared to other types of breads (White and Brown toast breads and White and Brown Khubz Lebnani), which are leavened up to some extent, can be explained because of these differences. Substituting the increasing proportion of whole grain bulgur (cracked wheat) with miller flour in bread, decreased the GI value of breads in patients with Type 2 Diabetes.[21] Mesci et al.[22] however did not observe any significant differences in the glycemic or insulinemic responses among four different types of breads (white, whole wheat, wheat bran and rye breads) in type 2 diabetic patients. As a result of modern bread making processes relatively much softer, easily digestible breads with higher glycemic index and low satiety index values are being currently produced and are being made available in the market.[23]

Table 2 Glycemic index of different types of Omani breads

Types of bread	Glycemic index x ± SD
Khubz Lebnani White	62.5 ± 10.5 ^a
Khubz Lebnani Brown	56.6 ± 20.4 ^a
White Toast Bread	62.8 ± 12.2 ^a
Brown Toast Bread	57.8 ± 15.3 ^a
Chapatti	58.2 ± 9.9 ^a
Rekhal	39.1 ± 7.5 ^b
Paratha	31.8 ± 13.5 ^b
Goleh	42.9 ± 13.1 ^b
^a,b = Different alphabets in the same column means significantly different at 5%.

No specific pattern of correlation was found between the chemical composition and the GI values of these breads. The fat content of Paratha however did show a significant (P < 0.05) correlation with its GI value. It has been shown that a high amount of fat in the food may alter the gastric emptying time and might tend to lower the postprandial blood glucose responses due to an altered hepatic extraction of blood glucose.[41–44] Henry et al.[45] suggested that the glycemic response of bread can be lowered using any type of fat. Paratha, which contained significantly higher amounts of fat as compared to other breads, showed lower GI values, which may be because of its higher fat content. In addition to this, the preparation method of Paratha might have resulted in the production of more compact and dense starch granules, with a reduced access of amylase for starch hydrolysis. Chan et al.[46] suggested that fat alone does not alter the glycemic response of rice or porridge. Porridge produced higher glycemic response than rice and noodles despite similar carbohydrate contents. Different noodles lead to differences in glycemic responses, suggesting that the GI of common Chinese foods is impacted by cooking methods and food processing. Starchy foods release their glucose at very different rates. This emphasizes the importance of porosity and structural characteristics of a food. The digestibility of foods also affects the GI values; the higher the digestibility, higher is the GI. However, still little is known about the effects of food processing, cooking methods and other dietary constituents on the GI of foods. Since fat has other effects in health it is not recommended that the consumers should use a low GI food, whose lower GI value is achieved based on its high fat content and must consider the overall nutritional composition.

It has been suggested that dietary fibre may reduce the postprandial blood glucose responses, simply by reducing the rate of absorption of carbohydrates due to the formation of a viscous gel in the small intestine. However, the dietary fibre content of these breads did not show any specific correlation with their GI values. Total dietary fibre has been shown to be significantly related to glycemic index.[47] Out of all the 10 sugar components, the dietary fibre however explained only 54.4% of the variability in glycemic index. In determining the potential metabolic effects of diet, the physiologic assessment of foods is a useful supplement to the chemical analysis of their dietary fibre content and composition.[47] The quantity and quality of fibre in the food plays a pivotal role to its GI value. Therefore, sometimes it becomes hard to conclude whether the positive changes, in relation to health and disease, were simply due to low GI-food intakes, to fibre, or to both. Fibre can slow the digestion of associated carbohydrates but only if the fibre remains an intact part of the original food. Milling of grains crushes the fibre into small shards, which separates them from the carbohydrates (starches) they had been protecting.

According to the published criteria,[48] the commonly consumed Omani breads tested in this study fall within the medium (White Toast bread Brown Toast bread, White Khubz Lebanani, Brown Khubz Lebanani and Chapati) and low (Paratha, Rekhal and Goleh) GI category of foods. The range of GI values between different types of breads however is significantly large, and if carefully selected with respect to their GI values can positively affect in reducing the risk of chronic diseases. This is particularly important since a relatively small difference in the GI value of regularly consumed foods and small change in overall lowering of dietary glycemic loads have been shown to be associated with a significant reduction in the risk of CVD,[49,50] diabetes,[51] and cancer[28] as well as towards an improvement in insulin sensitivity and glycemic control.[52] Further studies are required to determine the GI values of other traditional Omani foods and to categorize them into low, medium and high GI foods so that they can be incorporated in healthy meal planning, not only to reduce the risk of chronic diseases but also to have a better understanding of dietary management strategies, to control the chronic disease conditions.

CONCLUSION

Significant variability exists in the proximate chemical composition and glycemic index of different types of Omani breads. No specific correlation was however observed between the chemical composition and glycemic index of these breads. The glycemic index of commonly consumed Omani breads tested in this study ranged between 32 and 63 and falls within the medium to low GI category of foods. The results of this study could be useful for health professionals in developing the appropriate dietary management strategies in meal planning utilizing the concept of GI of foods for reducing the risk of chronic diseases.

ACKNOWLEDGMENTS

The authors would like to thank the volunteers for their sincere cooperation towards the successful completion of this study. The financial support provided by Sultan Qaboos University under internal research grant (IG/AGR/FOOD/04/01) is greatly acknowledged. Thanks are also due to Prof. Thomas S. Wolever of University of Toronto, Canada, for providing us the software to calculate the IAUC and GI values of foods.