Course:FNH200/2012w Team24 GlutenFree

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Introduction

A current topic of controversy in food science and nutrition concerns gluten and gluten-free (GF) products. Specifically, this paper focuses on the effect of elimination of gluten on structural and functional properties of food, as well as their effect on human health. The key issue regarding food science for replacing gluten is whether or not finding a universal substitute is achievable for all GF products. In terms of health and nutrition, the components and process of digestion and absorption of gluten and GF products are discussed, with the focus on individuals with Celiac Disease (CD). It is important to research this topic because the production of nutritious and palatable GF foods will help provide safe options to those that are affected by CD or gluten sensitivity. By identifying the key components of gluten, its digestion process in non-CD individuals is also studied.

What is Gluten? What are Some Properties of Gluten?

As the main protein in wheat, spelt and rye, most breads and traditionally baked goods depend on gluten for structure, elasticity, appearance and flakiness.[1]Gluten is a glutinous component in food products which gives food the chewy texture.[2] It is formed by the combination of several proteins, carbohydrates, and lipids and is usually found in wheat, barley, and other grain containing food products.[2] Gluten has been found to decrease the rate of starch retrogradation.[3] It has the ability to bind more water than starch does when it is cold, thus there would be less water available for starch granules to absorb while being heated.[3] Other than that, gluten is beneficial in bread making. The proteins in gluten harden after being exposed to heat. [4] , thus giving baked goods their firm texture. Besides the ability to provide structural stability for food products after being heated, gluten can also be used as a carbon dioxide capturing agent, a flavour enhancing agent, as well as a stabilizer.[2] [5]

Functions of Gluten in Bread Products

Proteins, apart from their role as important macronutrients, affect bread quality by their various functional properties such as incorporation and stabilization of air in the dough, coagulation (resulting in loss of protein solubility) and the formation of sponge structure from the foam in the dough. Various proteins display different functional properties depending on their structure (amino acid composition) and functional (enzymatic) activities, as well as their interactions with other components of the matrix; therefore substituting gluten with other proteins results in different product properties. [6]

Why are There Gluten-free Food? What is the Standard for a Gluten-free Claim?

Because of gluten’s multi-functional characteristics, it is widely used in processed food products which can be easily seen in a regular supermarket. However, some consumers are not able to digest gluten or are allergic to gluten. Gluten-free(GF) foods are designed for individuals who suffer from Celiac disease or gluten intolerance.[7] A GF product either does not contain gluten or the level of gluten in it is not significant. A specific GF claim can be made and shown on a food product if the gluten level in the food product does not exceed 20 ppm.[7]

Gluten Free Muffins

Comparing Gluten and Gluten-free Foods

Since gluten has several desirable characteristics in wheat or grain products, it is important to understand the differences between gluten and GF food products. Several studies have been conducted to compare the structure, property, flavour, palatability, and consumer acceptance of gluten and GF foods.

The structural and functional differences between gluten-containing and GF products are remarkable. In comparison to gluten, GF foods have a weaker hardening feature because they generally contain fewer proteins. Therefore, GF flours are usually used for soft baked goods like cake.[4] Another important functional difference is that gluten has the ability to make heated food products fluffy by capturing carbon dioxide.[5] Baked GF goods may have a denser structure without any additional ingredients. The flavour and palatability are also different. According to Rehman et al., the flavour of bread and other grain products is generated by breaking peptide bonds.[8] Because of gluten’s protein-rich property, there are more breakable peptide bonds between amino acids in gluten-containing products than GF ones. In terms of palatability, gluten gives food chewiness. GF foods are, therefore, less chewy. Although GF foods are essential for people with Celiac disease, most GF foods lack several proteins, carbohydrates, and fibers that are nutritionally important for the general population.[9] In most cases, consumers prefer gluten foods that taste and look better, and contain higher nutrient levels. Therefore, gluten foods are more accepted by the public.

How are Gluten-free Products Formulated?

The major challenge of GF baking is mimicking the structure, flavour, texture and mouthfeel of gluten without the use of this protein. Since there is no perfect substitute for gluten, much research has been done to develop a ratio of alternative grains, gums, thickeners, and starches that creates a product similar to conventional wheat products. While white rice flour is suitable to bread making because it is bland and colourless[10], it requires a gum such as hydroxypropylmethylcellulose (HPMC), locust bean gum, guar gum, carrageenan, xanthan gum or agar, which are used in relatively small quantities. HPMC is successful when used at a ratio of 1.7% while guar gum is used at approximately 0.7%.[1] Starches are also very important in GF products as they may act as an “inert filler in the continuous matrix of the dough or be part of a bicontinuous network of protein and starch,” and may be derived from corn, cassava, sweet potato, potato, sorghum, barley, and rice.[10] Several researchers found that 72.4% cornstarch 17.2% rice flour, 8.6% cassava starch, and 0.5% soy flour formed bread with adequate crumb structure and volume.[11] Since on a “dry matter basis, gluten contains 75–86% protein”[1], it is only natural that gluten can be partially replaced by other proteins such as those derived from dairy, eggs, soy or corn. These proteins improve water retention, viscoelastic properties essential for foam creation, and storage life.[10]

Improving Protein Content of Gluten-free Products

Addition of soybean flour is a common method to achieve high-protein GF bread.[6] Researchers suggest that adding 125-150 g kg−1 of full-fat enzyme-active (non-heated) soybean flour to a mixture of rice and cassava enhances the quality (volume and structure) of GF bread more than semi-active and inactive flours, in which enzymatic activity is lost due to protein denaturation caused by industrial heating.[6] Another factor influencing product quality is flour particle size, with an optimum range of 90-120 μm.[6]

The dairy component of the gluten replacement combination discussed above, contributes to elastic and strain hardening properties.[12] A study indicates the use of whey protein particles of intermediate size (mesoscopically structured), combined with starch to a certain extent, and evaluated the effects of disulfide bonds (crosslinks) on the mechanical properties of the particle network.[12] Results of this study suggest that it is necessary for the protein components of the batter to form disulfide bonds; however, too many bonds can make the dough too stiff, leading to low bread quality in terms of mechanical stability, phase volume and formation of a viscoelastic network.

Processing Techniques

There is also evidence that enzymatic processing, High Hydrostatic Pressure Technology, and fermentation can have excellent influences on texture and structural properties of GF baked goods. For example lactic acid fermentation among other fermentation processes has shown in several studies to enhance [10]:

(a) gas retention

(b) textural quality

(c) flavour

(d) nutritional value in terms of mineral bioavailability, starch digestibility, and concentration of bioactive compounds

(e) shelf life by retarding staling and by protecting bread from spoilage

Shelf Life and Preservation

One of the most important quality indicators of bread is its staling pattern. Researchers suggest that addition of sourdough results in improved quality (softness) and a delay in staling of GF bread, in addition to preserving the product from spoilage.[13] Also, results of a quantitative descriptive analysis (QDA) and mechanical compression testing of different types of bread showed that after a 120-hour staling period, high-protein GF rice bread had superior moistness, freshness and mechanical stability over low-protein starchy counterparts and conventional wheat bread.[14] Therefore, staling can be delayed by achieving a gluten-like bicontinuous matrix with specific formulation of rice, egg and milk proteins, xanthan gum, HPMC and starch fragments.[14] Another study on the 6 most consumed GF breads of the Italian market that were evaluated for their sensory profiles by ten trained celiac assessors suggests that this matrix is created by polymeric substances with viscoelastic properties of gluten and can be obtained by incorporation of starch (normal and pre-gelatinized form) and hydrocolloids, as well as the aforementioned protein-based ingredients such as dairy or soy.[15] These results were based on evaluation of texture (porosity, crust, softness, adhesion and rubbery texture), aroma, appearance (color) and taste (sweetness and saltiness) descriptors.[15]

Nutrition

Prior to its recent popularity, the gluten-free (GF) diet was used mainly as a proven medical treatment for Celiac Disease (CD).[16] Sensitivity to gluten can range from very mild to severe, and is diagnosed as a gluten sensitivity or gluten intolerance (Celiac Disease, CD), respectively. A common misconception is that a GF diet is healthier than a diet containing gluten. In fact, going GF can create nutritional inadequacies if not properly executed.

How is Gluten Digested and Absorbed in Normal Individuals?

Gluten is a polypeptide protein composite of gliadin, glutenin and starch that displays elastic properties originating in foods such as wheat, barley and rye.[17] Gluten is digested in the stomach by enzymes called proteases and is absorbed as small peptides and single amino acids by intestinal absorptive cells found on the villi in the small intestine.[18] The carbohydrate component of gluten starts breaking down initially in the mouth by action of salivary amylase, and finally in the small intestine with pancreatic amylase and disaccharidases.[18] Absorption of macronutrients is greatly improved with the increased surface area of the villi; a component of the GI tract essential to absorption.

How Do Individuals with CD React to Gluten?

An experiment conducted by Gass et al. investigates the effect of addition of a combination enzyme product comprised of a “glutamine-specific endoprotease and a prolyl endopeptidase” on the digestibility of gluten under gastric conditions, to study the increase in the safe threshold of ingested gluten in individuals with CD.[19] The results show that a 1:1 ratio of the enzymes will work synergistically by proteolyzing the gluten proteins and detoxifying the residual polypeptide products of digestion. While this experiment displays an endeavor towards a cure for CD, its method is unsound in that it is conducted in vitro by a system designed to imitate human gastric digestion, and in vivo in rats. Although preliminary testing on animals and in simulated environments is crucial before subjecting humans to new technologies, the experiment conducted by Gass et al. would gain greater concrete evidence towards their hypothesis by commencing testing on patients with CD.

Are GF Options Healthier for Individuals with CD?

Contrary to popular belief, there are some GF alternatives that are lower in nutrient content than gluten containing products. For example, the use of white rice flour in many GF products results in a “low contribution to the recommended daily protein intake, [but, contributes highly] to the carbohydrate dietary reference intake”.[20] With the incorporation of unrefined GF options like brown rice, quinoa, buckwheat, and soy, the risk of malnutrition is decreased due to higher levels of fibre, protein, calcium and iron.[10]
Dietary fibres play a significant role in our digestive tract. Insoluble fibre works by directly influencing the stool quality and therefore allowing easier excretion.[18] Furthermore, soluble fiber balances the cholesterol level [21], and slows glucose absorption, which maintains blood sugar levels and prolongs the feeling of fullness.[18]

Due to the fact that gluten-containing products hinder absorption in people with CD, going GF will, in most cases, allow their microvilli to repair and resume proper absorption of macro and micronutrients. This improves overall health and greater uptake of nutrients for individuals with CD and gluten sensitivity.

Despite the removal of gluten, many GF flours contain trace amounts of gluten and may cause a response in individuals with CD or gluten sensitivity.[22] Although this response will do less damage than consuming gluten-containing food, it is still an area of concern.

Is a GF Diet Beneficial to Individuals Who are not Sensitive to Gluten?

Although a GF diet is usually utilized as treatment for celiac disease (CD), research shows that it may be an adequate option for other medical conditions.[23] These conditions include, but are not limited to, neurological disorders, diabetes mellitus (DM), as well as HIV enteropathy.[23] With respect to neurological disorders, associations between gluten consumption and symptoms distant from the GI tract have been observed. Although, the direct mechanism by which this occurs is ambiguous, a GF diet (GFD) has shown improvement in patients on multiple accounts.[23] Furthermore, a GFD has shown improvements in DM patients as well. A beneficial effect on the preservation of B-cell function in beings at risk for type I DM was noticed simply after six months of gluten exclusion from daily diets.[23] Lastly, a GFD has shown to decrease the frequency of diarrhea in patients with HIV enteropathy, which essentially allows for beneficial weight gain.[23]

5 Minute Video


Gluten-free Banana Blueberry Muffins

Conclusion

In conclusion, studies suggest that there is no universal substitute for gluten. In order to achieve high quality GF products that are comparable to gluten-containing foods in terms of nutrient content and consumer acceptability, each GF product must be researched individually to determine the specific ingredients and proportions that work for that product. GF products are beneficial to individuals with CD by not damaging microvilli. They can also positively affect non-celiac individuals suffering from health issues such as DM, HIV enteropathy and neurological conditions, given that the right ingredients are used to replace gluten so that the overall nutritional value of the food is maintained. Overall, using appropriate gluten substitutes can alleviate symptoms of gluten sensitivity and/or intolerance.

Future Research

Although the effects of a GF diet on CD individuals are evident, future research is needed to solidify the effects of this diet on non-celiac individuals because the available body of knowledge is limited. There is still ambiguity regarding this topic, so a general consensus has not been reached in the studies. Another suggestion is that individuals suffering from mild to chronic conditions or malnutrition be tested early for gluten sensitivity. Developing easily accessible tests to identify this condition as well as raising awareness about the extent of occurrences are recommended future research topics. Perhaps a future study could consist of a class offered at UBC in which enrollment entails student participation in a study focusing on GF diet adherence and health benefits. Students will benefit from this study by determining whether or not they are gluten sensitive or intolerant. Lectures could include analyzing past research as well as the study that they are a part of. The study could consist of a diet analysis for each student, as well as blood tests and BMI measurements that indicate any fluctuations in overall health over the course of the semester. Sample size will be a representative of student population in terms of age, ethnicity and health levels.

Potential Exam Question

What is the function of Xanthan gum in GF baking?

a. Makes bubbles to create a solid foam

b. Creates a crunchy crust

c. Is an egg replacer, contributing to moistness

d. Mimics the matrix usually created by glutinous protein


Answer:d

References

  1. ↑ 1.0 1.1 1.2 Gallagher E, Gormley T. R., Arendt E. K. (2004). Recent advances in the formulation of GF cereal-based products. Trends Food Sci. Tech. 15, 143–52.
  2. ↑ 2.0 2.1 2.2 Kietzman, Shannon. (2013) What is gluten. wiseGEEK. Conjecture Corporation. Retrieved from http://www.wisegeek.com/what-is-gluten.htm
  3. ↑ 3.0 3.1 Wang, Xin, Choi, Sung-Gil, Kerr, William L. (2004). Effect of gluten content on recrystallisation kinetics and water mobility in wheat starch gels. J. Sci. Food & Agric. 84, 371-379.
  4. ↑ 4.0 4.1 Alfaro, Danilo. (n.d.). What is gluten. About.com. N.p. Retrieved from http://culinaryarts.about.com/od/bakingdesserts/p/gluten.htm
  5. ↑ 5.0 5.1 Ohlson, Kristin. (n.d.). Can baked goods taste good without gluten. EatingWell. Meredith Corporation. Retrieved from http://www.eatingwell.com/nutrition_health/gluten_free_diet/can_baked_goods_taste_good_without_gluten
  6. ↑ 6.0 6.1 6.2 6.3 Ribotta, Pablo D., et al. (2004). Production of gluten‐free bread using soybean flour. J. Sci. Food & Agric. 84 (14), 1969-1974.
  7. ↑ 7.0 7.1 Health Canada’s position on GF claims. (2012). Health Canada. N.p. Retrieved from http://www.hc-sc.gc.ca/fn-an/securit/allerg/cel-coe/gluten-position-eng.php
  8. ↑ Rehman, Salim, Paterson, Alistair ,and Piggott, John R. (2006). Flavour in sourdough breads: a review. Trends in Food Sci. & Tech. 17, 557-66.
  9. ↑ Barry, Denise. (2011, Oct. 17). The pros and cons of a gluten-free diet. [Web log post] Retrieved from http://www.coreperformance.com/daily/nutrition/the-pros-and-cons-of-a- gluten-free-diet.html
  10. ↑ 10.0 10.1 10.2 10.3 10.4 Zannini E, Jones JM, Renzetti S, Arendt EK. (2012). Functional replacements for gluten. Annual Review of Food Sci. and Tech. 3, 227-245.
  11. ↑ Sanchez HD, Osella CA, de la Torre MA. (2002). Optimisation of gluten-free bread prepared from cornstarch,rice flour and cassava starch. J. Food Sci. 67, 416-419.
  12. ↑ 12.0 12.1 Van Riemsdijk, Lieke E., Atze J. Van der Goot, and Rob J. Hamer. (2011). The use of whey protein particles in gluten-free bread production, the effect of particle stability. Food Hydrocolloids 25 (7), 1744-1750.
  13. ↑ Moore, M. M., et al. (2007). Effect of lactic acid bacteria on properties of gluten-free sourdoughs, batters, and quality and ultrastructure of gluten-free bread. Cereal Chemistry 84 (4), 357-364.
  14. ↑ 14.0 14.1 Ahlborn, Gene J., et al. (2005). Sensory, mechanical, and microscopic evaluation of staling in low-protein and gluten-free breads. Cereal Chemistry 82 (3), 328-335.
  15. ↑ 15.0 15.1 Pagliarini, E., M. Laureati, and V. Lavelli. (2010). Sensory evaluation of gluten-free breads assessed by a trained panel of celiac assessors. European Food Research and Tech. 231 (1), 37-46.
  16. ↑ Kam, K. (2013). Going Gluten-Free: What to know about celiac disease, gluten sensitivity, and gluten-free diets. Retrieved from http://www.webmd.com/digestive-disorders/celiac-disease/features/gluten-intolerance-against-grain
  17. ↑ Fasano, A., Berti, I., Gerarduzzi, T., et al. (2003). Prevalence of Celiac Disease in At-Risk and Not-At-Risk Groups in the United States: A Large Multicenter Study. Arch Intern Med.163(3):286-292. doi:10.1001/archinte.163.3.286.
  18. ↑ 18.0 18.1 18.2 18.3 Hammond, G., Piche, L. A., Rolfes, S. R., Whitney, E., (2013). Understanding Nutrition, First Canadian Edition. Nelson Education Ltd. (pp. 86-87, 175-176). USA.
  19. ↑ Gass, J., Bethune, M. T., Siegel, M., Spencer, A., Khosla, C. (2007). Combination Enzyme Therapy for Gastric Digestion of Dietary Gluten in Patients With Celiac Sprue. Retrieved from http://www.gastrojournal.org/article/S0016-5085(07)01010-4/fulltext
  20. ↑ "Segura, M. E. M., & Rosell, C. M. (2011). Chemical composition and starch digestibility of different gluten-free breads. Plant Foods for Human Nutrition (Dordrecht, Netherlands), 66(3), 224-230. doi: 10.1007/s11130-011-0244-2
  21. ↑ Cohan, W. (2008, October 2). Nutritional Content of Alternative Gluten-Free Grains and Flours. Retrieved from http://www.celiac.com/articles/21652/1/Nutritional-Content-of-Alternative-Gluten-Free-Grains-and-Flours/Page1.html
  22. ↑ EnzymeStuff. (2007, January 15). Gluten. Retrieved from http://www.enzymestuff.com/rtgluten.htm
  23. ↑ 23.0 23.1 23.2 23.3 23.4 El-Chammas K. et al. (2011). Gluten-Free Diet in Nonceliac Disease. Nutrition in Clinical Practice 26.3 (2011): 294-9. Print.
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