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Literature Review

The Centers for Disease Control estimates that two thirds of American adults are obese or overweight (1). A definition of obesity is based on Body Mass Index, calculated as kg/m2, with overweight defined as 25 to 29 and obese as more than 30 (2). The American Dietetic Association (ADA) includes waist circumference in the assessment (2). There is some controversy about recommendations for weight loss per different levels of overweight. The National Heart Lung and Blood Institute guidelines recommend weight loss for overweight plus two or more risk factors, while the Dietary Guidelines for Americans recommend it for even borderline overweight (2). The American Heart Association (AHA) calls the situation a “pandemic of obesity” (3), which describes a constant underlying rate of disease. This is more accurate than the usual moniker, epidemic, which suggests a sudden disastrous rise in illness. Obesity rates have risen gradually over the last thirty years and may take just as long to decrease. There is consensus among public health organizations regarding implications of obesity. Extra pounds, lack of physical activity, and suboptimal diet increase risks of chronic disease such as hypertension, Type 2 diabetes, hyperlipidemia, as well as depression, social stigma, and workplace discrimination (4). The attendant health care costs are becoming apparent as the baby boomers retire and live longer with chronic disease.

The current literature discusses many causes of obesity: lack of physical activity, related medical conditions, psychological factors, lack of access to nutritious foods, and socio-economic status (2). A key concept in the literature is the energy gap, described as a deficit between calories consumed and calories expended (2). Increases in sedentary professions, car centric versus pedestrian based civic planning, longer work hours, and cuts in physical education and recess for children contribute to decreases in physical activity and energy expenditure. On the intake side of the equation, many authors mention readily available overabundance of calories (4). Between 1970 and 2008, Americans had access to 600 additional calories for sale and consumption (6). Our wealth may have sabotaged our health. The market is flooded with food choices, but many lack nutrient density. Larger portions, more meals eaten out of the home, and ubiquitous sugar, salt, and fat laden processed and fast foods contribute to the “obesogenic” environment (4,6).

Researchers are targeting added sugars as a culprit equal to or greater than dietary fat (5). Sucrose, fructose, high fructose corn syrup, agave syrup, honey, and others are added to seemingly every food on the supermarket shelf: cereals, soups, yogurt, juice drinks, and baked goods. The AHA found that between 2001 and 2004, Americans consumed 22.2 teaspoons (355 calories) of added sugar per day (3). AHA guidelines recommendations are for nine teaspoons per day for men and six teaspoons for women (5). According to National Health and Nutrition Examination Survey (NHANES) data analyzed by the ADA, the #1 source of energy for 2-18 year olds was grain-based desserts, defined as cakes, cookies, donuts, pies, and granola bars totaling 138 kcal/day. The #1 source of added sugars was soda, totaling 173 kcal/day. Of total energy consumed, 40% was empty calories: 433 kcals solid fats and 365 kcals added sugar (4).

Energy dense foods combined with a lack of appetite regulation leads to rampant over consumption of calories. The homeostatic system governing food intake relies on interactions between macronutrient and fluid intake and hormones such as leptin, insulin, and ghrelin to signal hunger and satiety (2). This is the food as sustenance scenario. The hedonic pathway relies on interactions between cognitive and emotional aspects with serotonin and dopamine (3). This pathway seems to be influenced by genetics, physiology, culture, and socio-economic status. Both systems are regulated centrally, but they appear to lack integration. There is a discrepancy between intake and satiety and between taste preferences and food choices (7). The role of the hedonic system from the initial sensory impressions to food selection and consumption needs more research (7). The “inappropriate sensitization” of the hedonic network, or taste gone wild, combined with hyper calorie and sugar products always available, may lead to weight gain (2). The phrase “sweet tooth” may have some truth to it because sweet foods enable opoids and dopamine in the brain, engendering positive feelings. However, some studies show that predilection for sweets do not contribute substantially to obesity (3). Individuals do not become obese simply because they love to eat sweets, but those that do have seemingly unlimited access to sugar. The 2010 Dietary Guidelines for Americans include specific parameters about added sugars (6). The recommended amounts are substantially less than typical American consumption. The ADA suggests short-term reduction of all carbohydrates as means for weight loss for some individuals, but downplays the low-glycemic index strategy. The AHA warns about the connection between added sugars and abnormal lipids, blood pressure, and inflammation (3). Lustig and colleagues believe that sugar, be it sucrose, agave, or fructose that is not naturally occurring is responsible for a host of health problems (4). Nutrition education may focus on nutrients and calories, energy in and energy out, but their needs to be appreciation of innate preferences for sugar (7). Interventions and products must highlight taste and palatability as well as nutritional quality.

Energy consumption and satiety should be directly correlated, but this is not always the case. Research conducted at the Pennington Biomedical Center by Anton, et al, examined the effects of stevia, aspartame, and sugar on satiety, glucose, and insulin levels (8). Nineteen healthy, lean adults and twelve obese adults were fed “pre-load” snacks before lunch and dinner. Two variations provided 290 calories with stevia or aspartame and one variation provided 493 calories with sucrose. The authors found that subjects did not reduce their consumption at subsequent meals. Subjects with the stevia and aspartame preloads reported similar satiety levels as the sucrose groups, despite having consumed fewer calories. Energy intake was lower in the alternative sweetener groups solely due to the lesser amount of calories in the pre-load meal. Subjects preferred the taste of aspartame to stevia and sugar, but there was no difference in the ratings for appearance, aroma, sweetness, or texture of the cream cheese used in the experiments (8).

The overabundance of sugar in the diet is a twentieth century phenomenon and animal research helps determine the effect on humans. A group of scientists from university, hospital, and research organizations in Seattle experimented on rats with two alternative sweeteners (9). They were looking at metabolic changes that would lead to development of metabolic syndrome from consumption of fructose. Agave was chosen as a “natural” source of fructose with a low glycemic index. Stevia was chosen because it is from a natural source as well; the authors think that these products are more desirable to consumers for that quality. They found that moderate intake of fructose may result in changes in lipid and liver metabolism, independent of weight gain (9). This corresponds to Lustig’s ideas on fructose and added sugar as a major player in obesity and attendant chronic conditions (5).

Registered Dietitians for the United States Department of Agriculture (USDA) reported in the Journal of the American Dietetic Association about putting research into practice (10). Their study investigated palatability ratings of muffins. Nine variations of muffins were baked to test different combinations of fat and sugar. The muffins made with “moderate fat and moderate sugar” were closest to the control for acceptability, tenderness, flavor, and texture. Based on their results, they recommend ¼ cup vegetable oil and 3 tablespoons of sugar for two cups of flour in a muffin recipe. This represents a substantial reduction of sugar from the usual ¾ or 1 cup per two cups of flour (10).

This review of literature reveals consensus among nearly all health professionals that obesity is a public health crisis that should be addressed through nutrition education and dietary and physical activity interventions. There are parties that name added sugar in the food supply as a major factor to be addressed. The relationship between taste, satiety, preference, and intake is complex and not always intuitive. One strategy may be to present lower calorie versions of products that are perceived as “natural”, palatable, and commensurate with typical reference foods.

The purpose of this experiment was to determine the effect on caloric intake, color, flavor, aroma, tenderness, weight, and height when sugar was replaced with agave nectar or Stevia (Truvia) in a basic blueberry muffin recipe.

The Centers for Disease Control present statistics showing a dramatic rise in obesity across age groups over the last two decades (1). Nutrition professionals should develop products lower in calories that maintain palatability and acceptability. Since muffins are a popular and accessible source of grain, they are an appropriate product to adjust. Stevia and agave are naturally sourced alternative sweeteners that may appeal to consumers. Stevia does not contribute calories to a recipe. Agave is considered a source of added sugar, but it may be possible to use less and reduce calories.

Materials and Methods

Basic Blueberry Muffins Recipe

Blueberry basic muffins = 12 cupcakes

All-purpose flour – 250.0 grams

Baking powder – 13.8 grams

Salt- 3.0 grams

White Sugar – 150.0 grams

Large Egg- 50.0 grams

Whole Milk- 244.0 grams

Vegetable oil – 44.0 grams

Blueberries – 148.0 grams

• Variation 1: Stevia (Truvia) – Substitute 63 grams of stevia for sugar.

Sweetness equivalent: 18 packets = ¾ cups of sugar.

• Variation 2: Agave Nectar – Omit sugar; add 68 grams of agave nectar

Sweetness equivalent: 1/4 cup Agave Nectar = 1 cup sugar.

Preparation

1. Preheated oven to 375°F.

2. Lined the cups of 12-cup muffin pans with paper muffin cups.

3. In a large bowl, added flour and stirred in baking powder, salt, and sugar.

4. Added blueberries to dry mixture and made sure they were completely coated. Made a well in the center for the dry mixture and set aside.

5. In a small bowl, beat egg with a fork. Stirred in milk and oil.

6. Poured all at once into the well in the flour mixture. Mixed quickly and lightly about 20 times with a wooden spoon until moistened.

7. Poured 72 grams of batter into 12 paper-lined baking cups.

8. Baked for 15-20 minutes until a toothpick inserted in the center of a muffin came out clean.

9. Cooled muffins for five minutes in muffin pan, then removed and cooled completely on rack.

*In step three, omitted sugar and added Stevia.

**In step three, omitted sugar and in step five, added agave nectar to liquid ingredients.

Evaluations

Objective:

Blueberry muffin variation cooled. Heights of three muffins from each variation were measured in centimeters with a ruler. Three new muffins from each variation were weighed in grams using a digital food scale and were individually measured for tenderness using the penetrometer. When using the penetrometer, we held it for 20 seconds to get the tenderness value in millimeters.

Subjective:

Fifteen sensory panelists were recruited from student and faculty population from Ranger Hall and the University Quad. Panelists were presented with plates labeled with three random evaluation numbers and three correlated muffin variations. Each sample was ¼ of a whole muffin. A small cup of water was provided to cleanse their palate in between tasting each variation. The scorecard, measuring crust color, interior color, aroma, flavor, tenderness, moistness, and aftertaste, was placed by each plate so the panelist could evaluate the muffins as they tasted. To measure crust color, a whole muffin from each variation was placed in the center of the table for evaluation (the panelist did not eat these variations).

|Blueberry Muffin Scorecard |

|Instructions: |

|1. From the labeled plate in front of you, please evaluate each muffin sample based on the assigned values from 1 to 5 (though not |

|listed, this includes numbers 2 and 4). 2. There will be a whole muffin of each variation placed |

|in the center of table for you to evaluate the crust color. |

|3. Water is available to cleanse the palate between samples. |

|4. Thank you for your participation! |

|Characteristics |Sample |

| |713 |682 |549 |

|Crust Color |  |  |  |

|1=Pale ; 3= Golden Brown ; 5= Very Brown | | | |

|Tenderness |  |  |  |

|1=Crumbly ; 3=Pleasingly Tender ; 5= Tough | | | |

|Flavor |  |  |  |

|1=Bland ; 3=Sweet ; 5=Too Sweet | | | |

|Moistness |  |  |  |

| | | | |

|1=Dry ; 3=Moist ; 5= Too Moist | | | |

|Aftertaste |  |  |  |

|1=None ; 3=Somewhat Distinct ; 5=Extremely Distinct | | | |

|Which Variation Would Be Your Preference?_________________ |

Nutritional Analysis

The nutritional analysis software used to analyze data was Food Works.

Statistical Analysis

Data was analyzed to determine mean values for the evaluated characteristics.

Control Variation

1. Preheated oven to 375oF.

2. Assembled baking equipment including:

• 3 muffin pans

• Muffin paper cups

• 3toothpicks

• Digital scale

3. Assembled ingredients including:

• 3 bags with pre-weighed and mixed dry ingredients (stevia and agave variations did not include sugar in pre-weighed dry ingredients)

4. Placed pre-weighed and mixed dry ingredients in a large bowl.

• 250g flour

• 13.8g baking powder

• 3.0g salt

• 150g sugar

5. Weighed 148g blueberries, add to dry ingredients.

• Stirred around the edge of bowl and underneath, and coated blueberries well.

6. Cracked 1 egg in ramekin – 50grams.

• Beat with a fork until homogenized.

7. Measured and weighed liquid ingredients.

• 1 cup whole milk

• 44 grams vegetable oil

8. Combined liquid ingredients; egg, whole milk and vegetable oil.

9. Made a well in the center of the bowl.

• Poured all wet ingredients into bowl at once.

• Mixed with rubber spatula 20 times until all dry ingredients were wet.

10. Put on scale and weighed 72 grams of batter in the muffin paper lining.

• Put muffin into muffin pan and repeated 11times.

11. Baked for 20 minutes until golden brown.

12. Removed pan from oven once toothpick was inserted and no residue was remaining.

13. Cooled slightly on wire rack.

14. Weighed three muffins with the paper lining from variation on a digital scale in grams.

• Subtracted paper-lining (0.4 grams) from weight.

15. Measured tenderness on the penetrometer for same three muffins from step 14.

• Held pin for 20 seconds then pressed down on the piston until reached resistance.

16. Measured height of three new muffins from variation.

• Cut in half and measured highest point of muffin with a ruler in centimeters.

Stevia Variation

• Repeated steps 1-3.

• Step 4 – Weighed 63grams of stevia (Truvia) and replaced for sugar.

• Continued with step 5-16.

Agave Variation

• Repeated steps 1-3.

• Step 4 – Sugar not included.

• Repeated steps 5 & 6.

• Step 7 – Measured 68g agave nectar.

• Step 8 – Added 68 grams of agave nectar to the liquid ingredients.

• Continued with steps 9 -16.

Results

Chart 1: Comparison of Subjective and Objective Measures of Tenderness in Muffins Made with Sugar, Stevia, and Agave

1=Crumbly

5=Tough

Chart 2: Subjective Flavor and Aftertaste Ratings for Muffins Made with Sugar, Stevia, and Agave

Chart 3: Preference of 15 Member Tasting Panel for Muffins Made with Sugar, Stevia, or Agave

Table 1: Energy and Sugar Content of Muffins Made with Sugar, Stevia, and Agave

| |Control |Stevia |Agave |

|Energy (kilocalories) |182.4 |139.3 |163.5 |

|Sweetener (kilocalories) |48.4 |5.3 |20 |

|Sugar (grams) |12.5 |0 |5 |

|Added sugar (tsp) |3 tsp |0 |1tsp |

**NOTE: the AHA recommendations for total added sugar per day are 6 tsp for women and 9 tsp for men

Discussion

As seen in Chart One the agave variation had the highest penetrometer reading and was voted the best in tenderness by the evaluators. It was interesting to see that the evaluators predicted the tenderness of the agave variation without knowing the penetrometer reading. The agave variation had the highest penetrometer reading and was the most tender, since it contains 92% fructose and 8% glucose. Fructose has hygroscopic capabilities to pull the water away from the flour in the muffins therefore resulting in a tender product. Sugar delays the formation of structure and it tenderizes. Fructose being the more hygroscopic sugar provides more moistness. Since agave nectar contains mostly fructose it provides more moistness than granulated sugars. Agave is a liquid so it may have helped to hydrate some of the dry ingredients which can also result in a tender product.

According to Chart Two, the evaluators felt that the control did not have a significantly different aftertaste. This was interesting to see since sugar alcohols are usually known to have a strong aftertaste. The aftertaste may have been diminished due to the blueberries, which may have helped to hide the aftertaste of the stevia and agave variations that would normally be detected in a plain muffin. Baking the variations may have also helped to hide the strong aftertaste by making the flavor milder. Even though not much of an aftertaste was detected, the evaluators enjoyed the flavor of the control the best. As for preference, the stevia and control tied as shown in Chart Three. This may be because the control and the stevia variation have very similar textures.

Since each variation had different traits, it was not surprising that they would all have different appearances. After stirring each variation exactly twenty times, the control variation had a thinner batter when compared to both the stevia and the agave variation. The erythritol, which is in Truvia, is non-hygroscopic and insoluble which may have made the batter more viscous. Agave, which is more hygroscopic and therefore competes with the starch for water, increased the viscosity of the batter. Since both stevia and agave had a viscous batter it was hard to place exactly 72 grams of batter into each paper muffin lining.

The color of each variation also differed. The agave variation was darker in color due to the high fructose content. Since agave is 92% fructose it participated in the maillard reaction. The control, which was sucrose, needed to be inverted into fructose and glucose in order for the maillard reaction to occur which resulted in a slightly brown muffin. As for the stevia, it was the lightest of the three variations since stevia does not caramelize like granulated sugar. Stevia is made up of erythritol, rebiana and natural flavors so it does not brown like sugar does.

When looking at Table One, the stevia variation had the least amount of kilocalories, providing only 5.3 grams of sugar, and had zero teaspoon of added sugar. This variation also had almost the same penetrometer reading as the control and was tied with the control for preference by the evaluators. Surprisingly, the stevia variation was appealing to the evaluators and confirmed our propose statement.

Conclusion

If the experiment were performed again it may have been beneficial to increase the amount of agave in the muffin. This would have helped to give the agave variation more flavors. This can be done by decreasing the amount of flour and adding more agave in order to keep a low caloric intake and may contribute to an increase in the palatability of the agave variation. Another way to help make the muffin more palatable and hide the aftertaste would have been to add cinnamon, nutmeg, or vanilla.

Due to the high levels of added sugar consumption, people are looking for ways to eat what they love but reduce the amount of calories and added sugar they consume each day. After evaluating the three variations, the experiment revealed stevia to be the best alternative sweetener to use when wanting to make a product that is low in calories, palatable, and a way to decrease the amount of added sugar. The results of the stevia variation helped to conclude that there are alternative ways to create a muffin that is lower in calories, has less added sugar, and is still appetizing to consumers.

References

1. Centers for Disease Control and Prevention. Overweight and Obesity section. Available at: . Accessed April 17, 2011

2. Position of the American Dietetic Association: Weight Management. Journal of the American Dietetic Association. 2009; 109, 2: 330-346.

3. Johnson R., Appel L, Brands M, Goward B, Lefevre M, Lustig R, Sacks F, Steffen L, Wylie- Rosett J, Steffen L. Dietary Sugars Intake and Cardiovascular Health. Circulation: Journal of the American Heart Association. 2009; 120; 1011-1020.

4. Reedy J, Krebs-Smith S. Dietary Sources of Energy, Solid Fats, and Added Sugars among Children and Adolescents in the United States. Journal of the American Dietetic Association. 2010; 110, 10: 1477-1484.

5. Johnson R, Yon B. Weighing in on Added Sugars and Health. Journal of the American Dietetic Association. 2010; 110, 9: 1296-1299.

6.Dietary Guidelines for Americans. Chapter 2, Balancing Calories to Manage Weight: 8-12. Chapter 3, Foods and Food Components to Reduce: 27-28. Available at:

. Accessed February 15,2010.

7. Drewnowski, A. Taste Preferences and Food Intake. Annual Review Nutrition. 1997; 17: 237- 53.

8. Anton S, Martin C, Han H, Coulon S, Cefalu W, Geiselman P, Williamson D. Effects of Stevia, Aspartame, and Sucrose on Food Intake, Satiety, ands Postprandial Glucose and Insulin Levels. Appetite. 2010; 55: 37-43.

9. Figlewicz DP, Ioannou G, Bennet Jay J, Kittleson S, Lavard C, Roth CL. Effect of Moderate Intake of Sweeteners on Metabolic Health in the Rat. Physiology and Behavior. 2009; 98: 618-624.

10. Fulton L, Hogbin M. Eating Quality of Muffins, Cake, and Cookies Prepared with Reduced Fat or Sugar. Journal of the American Dietetic Association. 1993; 93, 11: 1313-1316.

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