Using Food Science Demonstrations to Engage Students of All Ages in Science, Technology, Engineering, and Mathematics (STEM)

Authors

  • Shelly J. Schmidt,

    1. Authors Schmidt, Bohn, and Sutherland are with Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana-Champaign, 367 Bevier Hall, 905 South Goodwin Ave, Urbana, IL 61801, U.S.A. Author Rasmussen is with Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana-Champaign, 105 Agricultural Bioprocess Laboratory, 1302 W Pennsylvania, Urbana, IL 61801, U.S.A. Direct inquiries to author Schmidt (E-mail: sjs@illinois.edu)
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  • Dawn M. Bohn,

    1. Authors Schmidt, Bohn, and Sutherland are with Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana-Champaign, 367 Bevier Hall, 905 South Goodwin Ave, Urbana, IL 61801, U.S.A. Author Rasmussen is with Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana-Champaign, 105 Agricultural Bioprocess Laboratory, 1302 W Pennsylvania, Urbana, IL 61801, U.S.A. Direct inquiries to author Schmidt (E-mail: sjs@illinois.edu)
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  • Aaron J. Rasmussen,

    1. Authors Schmidt, Bohn, and Sutherland are with Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana-Champaign, 367 Bevier Hall, 905 South Goodwin Ave, Urbana, IL 61801, U.S.A. Author Rasmussen is with Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana-Champaign, 105 Agricultural Bioprocess Laboratory, 1302 W Pennsylvania, Urbana, IL 61801, U.S.A. Direct inquiries to author Schmidt (E-mail: sjs@illinois.edu)
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  • Elizabeth A. Sutherland

    1. Authors Schmidt, Bohn, and Sutherland are with Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana-Champaign, 367 Bevier Hall, 905 South Goodwin Ave, Urbana, IL 61801, U.S.A. Author Rasmussen is with Dept. of Food Science and Human Nutrition, Univ. of Illinois at Urbana-Champaign, 105 Agricultural Bioprocess Laboratory, 1302 W Pennsylvania, Urbana, IL 61801, U.S.A. Direct inquiries to author Schmidt (E-mail: sjs@illinois.edu)
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Direct inquiries to author Schmidt (E-mail: sjs@illinois.edu)

Abstract

Abstract:  The overarching goal of the Science, Technology, Engineering, and Mathematics (STEM) Education Initiative is to foster effective STEM teaching and learning throughout the educational system at the local, state, and national levels, thereby producing science literate citizens and a capable STEM workforce. To contribute to achieving this goal, we have assembled six food science demonstrations for use at all educational levels and have presented these lessons to students at the elementary through higher education levels. The focus of this article is to share these food science demonstrations and our experiences using them so that others can use them for engaging students in STEM disciplines, through food science, at any educational level. Featured demonstrations include: (1) liquid nitrogen ice cream: a matter of changing phases, (2) seeing our senses work together, (3) whipping up the cream, (4) milk versus dark: what is the difference?, (5) counting calories by burning them, and (6) culinary spherification: the wonders of cross-linking. Overall, our experience with using these demonstrations has been very positive. Students appear engaged in the learning process and love to consume the demonstration end products. Downloadable handouts containing demonstration details for each demonstration are available as supporting information.

Introduction

The overarching goal of the Science, Technology, Engineering, and Mathematics (STEM) Education Initiative is to foster effective STEM teaching and learning throughout the educational system at the local, state, and national levels, thereby producing science literate citizens and a capable STEM workforce. To contribute to achieving this goal, we have assembled six food science demonstrations for use at all educational levels and have presented these lessons to students at the elementary through higher education levels.

Demonstrations are an excellent means of transforming students from passive to active learners (Taylor 1988). Instead of just hearing a lecture on a topic, students are given the opportunity to participate in what is being talked about. Although there are many factors that contribute to successful student learning, transforming students from being passive to active learners is considered one of the primary factors (Chickering and Gamson 1987; Hutchings 1993; Farmer 1999; Handelsman and others 2004).

Using food science based demonstrations to teach about STEM disciplines is advantageous for a number of reasons. First, students are familiar with food materials. This familiarity helps instructors begin with what the students already know (prior knowledge about food items, e.g., appearance, taste, and unit operation used to produce the food) to what they need to know/learn (e.g., new knowledge about STEM). Brain science research strongly emphasizes the importance of starting with prior student knowledge when attempting to add new knowledge (Zull 2002). This is not a new idea, as stated by David Ausubel in 1968 (p. vi)“If I had to reduce all of educational psychology to just one principle, I would say this: The most important single factor influencing learning is what the learner already knows. Ascertain this and teach him accordingly.” Second, there is currently a strong public interest and awareness of food and health. Young and old alike are being exposed to food and health information and issues through a wide array of media sources everyday. For example, when reading or listening to the daily news it is common to come across one or more stories about food and/or health (e.g., “Deadly E. coli outbreak linked to german sprouts,”Dempsey and Neuman 2011). Food science based demonstrations take advantage of this current abounding inquisitiveness about food and health, making food science based demonstrations not only useful and engaging, but also extremely relevant. Third, by its very nature, food science allows for an interdisciplinary approach to learning, because food science itself is a union of several disciplines, including chemistry, microbiology, engineering, nutrition, and sensory sciences (Calder and others 2003; Duffrin and others 2010). Finally, students can often consume the demonstration end products. People like to eat and what better teaching and learning tool than allowing students, when and where possible, to sample the very items that they have just learned about! Perhaps we could even consider consuming the demonstration end products as a form of kinesthetic learning.1

In addition to the advantages food science demonstrations offer as a means to foster STEM teaching and learning initiatives, using these demonstrations to expose students to STEM disciplines is advantageous for both the food industry and the food science discipline, because the envisioned results are increased student science literacy, a more capable STEM workforce, and more students who know what food science is and can make a knowledgeable selection of food science as a college major and/or future career option. The focus of this article is to share six food science demonstrations and our experiences using them so that others can engage students in STEM-based disciplines at any educational level through the wonders of food science. Handouts are available via downloadable supporting information, which contain the “how to” details of the demonstrations described herein.

Demonstration 1: Liquid Nitrogen Ice Cream: A Matter of Exchanging Phases

Student centered learning objectives

Students will be able to: (1) examine the interconnection between phase transitions and heat transfer and (2) explain the effect of fast freezing on frozen food quality.

Demonstration overview

Students are introduced to phases of matter and phase transitions quite early in their science education (Figures 1a and b). This demonstration provides an excellent opportunity to help learners of all ages visualize phases and phase transitions and experience the fun of learning science. In this demonstration students are able to visualize the effects of the heat transfer process, as they observe the phases of both the ice cream mix (liquid to solid) and the liquid nitrogen (liquid to gas) change before their very eyes. After the ice cream mix is frozen, the students are also able to taste the liquid nitrogen ice cream and feel how smooth it is in their mouth. They learn that fast freezing produces small ice crystals and yields high quality frozen food products. This demonstration can be extended to include calculating the amount of heat energy that needs to be removed to freeze the ice cream mix from room temperature (e.g., 23°C) to typical freezer temperature (–18°C). Heat balance equations can be found in a basic food engineering text, such as “Physical Principles of Food Preservation” by Karel and Lund (2003).

Figure 1.

–(a) Making liquid nitrogen ice cream for a fifth grade science class. (b) Ice cream mix ingredients and phase exchange map generated by the students via class discussion.

Discussion questions

(1) What phase transitions take place during the making of liquid nitrogen ice cream? (2) Where does the heat come from to cause the liquid nitrogen to change phases? and (3) Why does liquid nitrogen ice cream feel so smooth in the mouth?

Instructor observations

Students seemed genuinely excited learning about phases and phase transitions. The fog generated by the liquid nitrogen is always exciting to the students. Voting on the different flavors of ice cream is very popular. While doing the demonstration, students tended to ask a good number of questions about ice cream mix ingredients, ice cream, liquid nitrogen, and about food science in general. Students often comment that it is the best ice cream that they have ever tasted! It never hurts to bring a few extra items to this demonstration (e.g., balloons, racquetballs, bananas, and fresh flowers),2 so if there is any liquid nitrogen left over, other liquid nitrogen demonstrations can be included. One of the students’ favorites is submerging a blown up balloon in a bowl of liquid nitrogen. The liquid nitrogen causes the balloon to shrink completely (gas molecules slow down and take up less volume); however when the balloon is removed from the liquid nitrogen it “magically“ returns to its original size and shape.

Demonstration 2: Seeing Our Senses Work Together

Student centered learning objectives

Students will be able to: (1) list and describe the six senses and (2) experience how the senses of sight and taste influence each other when making sensory judgments.

Demonstration overview

Students are introduced to the six human senses and how they are used to probe the five major sensory properties of food materials (Figure 2). Students also learn how the senses influence each other when making sensory judgments. Students are divided into three groups and asked to taste a series of sample beverages. The three beverage groups are: clear beverages with flavor, colored beverages with flavor where the color matches the flavor, and colored beverages with flavor where the color does not match the flavor. After tasting the beverages the students are asked to identify the flavor of each beverage. The group where the color and flavor match has the easiest time and is the most accurate at correctly identifying the flavor; whereas the group where the color and flavor do not matched has the hardest time and is the least accurate at correctly identifying the flavor. The clear beverage group falls in the middle, because there is no sensory interference, but there is also no sensory cue either.

Figure 2.

–Illustration of how the five major sensory properties of food materials are probed by the six primary human senses (excerpted in part with permission fromLee and others 2006).

Discussion questions

(1) Which group had the easiest time deciphering the flavor? Which the hardest? Explain why? (2) Can you think of any other combination of senses that influence each other when making sensory judgments? (3) Do you think a food or beverage where the flavor and color did not match would be successful in the marketplace? Why or why not?

Instructor observations

This demonstration effectively illustrates that our senses influence each other when making sensory judgments. Students enjoy trying to guess the flavor of the beverage and compete with fellow students. Students are surprised at how difficult it is to correctly identify the flavor of a beverage when the flavor and color do not match.

Demonstration 3: Whipping Up the Cream

Student centered learning objectives

Students will be able to: (1) explain the structural changes taking place in the conversion of liquid heavy cream to aerated whipped cream and (2) visualize and describe the key role mechanical shear plays to bring about these changes.

Demonstration overview

The two main changes that occur during the mechanical shear of heavy cream are partial coalescence of fat and denaturation of protein (Figure 3). Partial coalescence is an irreversible clustering of fat globules, held together by a combination of fat crystals and liquid fat, and the retention of identity of individual globules as long as the crystal structure is maintained (Goff 2011a). Denaturation is the process during which a protein unfolds, losing its tertiary (long distance interactions) and secondary (short distance interactions) structure, while maintaining only its primary structure (linear sequence of amino acids). The main components of heavy cream are water, fat (approximately 35%–40%), proteins, and lactose. When a bowl of heavy cream is whipped, mechanical shear and the air bubbles that are incorporated cause the fat globules to begin to partially coalesce in chains and clusters and get adsorbed to and spread around the air bubbles (Goff 2011b). At the same time, the mechanical shear causes the proteins to denature and adhere to the surface of the air bubbles. With students gathered around, the liquid heavy whipping cream is poured into a chilled mixing bowl.3 The students are asked to record their observations about the cream's appearance, color, viscosity, aroma, and mouth-feel in a provided table. They are also asked to share with the group their general observations of the heavy whipping cream, such as what phase it is in, how thick it is, and does it adhere to the mixing beaters. Once the whipping, or mechanical shear, begins, the students are asked to observe and record the physical changes in the heavy whipping cream. It does not take long before the whipped cream starts to become stiff and dry, taking on a smooth texture. This new texture results from the formation of the partially coalesced fat structure, which stabilizes the air bubbles and traps the water, lactose, and denatured proteins in the spaces around the fat-stabilized air bubbles. While whipping, the group continues to discuss how these structural changes alter the functionality of both the fat and proteins in the cream, allowing for the production of a deliciously light and airy whipped topping. An extension of this demonstration is to continue to whip the cream so that the fat begins to churn and butter particles form (Goff 2011b).

Figure 3.

–Helping students begin to visualize, at both the macroscopic (image on left-hand side) and molecular (image on right-hand side) levels, the processes of fat coalescence and protein denaturation caused by mechanical shear, and the impact these structural changes can have on fat and protein functionality (molecular level image adapted fromGoff 2011b).

Discussion questions

(1) What is fat coalescence? (2) What is protein denaturation? (3) Draw a picture of whipped cream at the molecular level showing the air bubbles, the denatured proteins, and the partially coalesced fat molecules.

Instructor observations

Students can watch as the beaters whip the heavy whipping cream, physically forcing the cream near each beater to move in opposite directions. They can also see how the sheared cream can “trap” air, allowing it to grow in volume and change in phase (to a semisolid), texture, and appearance. By demonstrating how to make a simple whipped topping from heavy cream, students can begin to visualize, at both the macroscopic and molecular levels, the processes of fat coalescence and protein denaturation caused by mechanical shear and the impact these structural changes can have on fat and protein functionality.

Demonstration 4: Milk versus Dark: What is the Difference?

Student centered learning objectives

Students will be able to: (1) define key chocolate terms, (2) describe the concept of “Standard of Identity” for food products, and (3) differentiate between the main types of chocolate (white, milk, dark semisweet, dark bittersweet, and unsweetened).

Demonstration overview

Chocolate is well liked by many different populations, particularly children, but it is often difficult to understand what makes one chocolate type different than another (Figure 4). In this demonstration, students are introduced to key chocolate terms (e.g., cacao, cocoa butter, etc.) and the federally regulated Standards of Identity (SOI) related to chocolate that are specified in 21 Code of Federal Regulations Part 163. Students then explore the different ingredient standards and processes associated with making white, milk, dark semisweet, dark bittersweet, and unsweetened chocolates, while at the same time evaluate the sensory properties of the different chocolate types (except for unsweetened chocolate, which is typically used only as an ingredient in other chocolate-based products). During the demonstration, students are asked to record their perceptions of appearance, color, aroma, mouth-feel, and melt-time for each of the chocolates. For an extended version of this demonstration, students could be introduced to the world of food processing by discussing the processing steps necessary to transform the cacao beans, from the Theobroma cacao tree, to the components (e.g., liquor, butter, and solids) used in the making of chocolate.

Figure 4.

–An example chocolate presentation and samples for junior high and high school students visiting the Illinois campus.

Discussion questions

(1) Which was your favorite type of chocolate? Explain what you liked about the product, try and be specific. (2) Which of the chocolate products melted in your mouth the fastest? The slowest? Considering the standards of identity for these products, what ingredient do you think the melting time is related to?

Instructor observations

Students are often unaware of the strict standards associated with chocolate production and that the changes in raw materials and processing methods, no matter how small, can produce products that are sensorially unique. In this demonstration, students learn to use all of their senses when evaluating a food material, as well as gain a greater understanding for the quality measures associated with food products. Of course the students enjoy consuming the chocolate samples, but this demonstration allows them to truly begin their “appreciation” for chocolate and other foods.

Demonstration 5: Counting Calories by Burning Them

Student centered learning objectives

Students will be able to: (1) calculate the amount of heat energy released in joules per gram when burning a Cheetos® using the data collected in the demonstration and then convert this value to kcals per gram, and (2) compare the calculated kcals per gram value to the kcals per serving value given on the Nutrition Facts Label on the Cheetos® (Frito-Lay, Inc., Plano, Tex.) bag.

Demonstration overview

In this demonstration students learn how to determine the energy content of foods by burning a Cheetos® (Figure 5). The burning Cheetos® heats a known quantity of water contained in a homemade bomb calorimeter. The increase in the temperature of the water and the initial and final weights of the Cheetos® are used to calculate the joules per gram content of the Cheetos®, which is then converted to kcal per gram (for comparison to the kcals per gram provided on the Nutrition Facts Label.

Figure 5.

–Burning Cheetos® demonstration setup using a homemade bomb calorimeter.

Discussion questions

(1) What is the definition of a calorie? (2) How is energy measured in a bomb calorimeter? (3) Compare the calculated kcal per gram value to the value given on the nutrition label on the package. Discuss possible reasons for any differences between the two values.

Instructor observations

An important aspect of this demonstration is to get as much of the heat from the burning Cheetos® directed toward heating the water in the homemade bomb calorimeter. Loss of heat results in the calculated kcal per gram being much less than the value on the Nutrition Facts Label. An additional beneficial aspect of this demonstration is that the students observe energy being directly derived from a food material.

Demonstration 6: Culinary Spherification: The Wonders of Cross-Linking

Student centered learning objectives

Students will be able to: (1) explain the chemical interaction between sodium alginate and calcium ions, (2) differentiate between spherification and reverse spherification processes, and (3) identify the by-product produced during the spherification processes.

Demonstration overview

Culinary spherification (referred to herein as spherification) is a process of shaping liquid drops into spheres (Figures 6a and b). The resultant spheres can either have a solid, gel-like texture throughout or have a solid, gel-like outer shell, and a liquid center. Spherification was originally developed as a technique to create a matrix type encapsulation of lipid-based flavors or ingredients and was patented in 1946 by W.J.S Peschardt (United States Patent Number 2403547) for the manufacture of artificial cherries (Anonymous 2009a). The culinary adaptation of this process is often credited to Ferran Adrià and his culinary team at elBulli around 2003. Since then, spherification has gained acceptance and is used in restaurant kitchens around the world to create small spheres (termed caviar or faux caviar) or large spheres (termed “ravioli”; Harris 2009). The spheres are created when calcium ions replace sodium ions and form cross-links between the alginate molecules, creating a thermally irreversible solid gel. This initially forms as a gel shell, leaving a liquid center; as the reaction continues, the center becomes a solid gel as well. Traditional ingredients used to carry out this reaction, are sodium alginate4 and calcium chloride, although other forms of calcium, as well as other divalent ions, can be used. In order for the cross-linking reaction to occur, a high enough concentration of calcium ions must be present. As shown later, the reaction between calcium chloride and sodium alginate requires one free calcium ion for every two alginate molecules and yields two sodium chloride (table salt) molecules, per reaction. The formation of NaCl from the reaction is one of the key reasons you need to rinse the spheres before consuming them.

image
Figure 6.

–(a) In the spherification process, spheres (cola-flavored soda spheres, bottom right-hand side) are created when drops of a soda–sodium alginate mixture (sodium alginate building blocks, bottom left-hand side) are placed into a calcium chloride solution (top). The calcium ions replace the sodium ions, forming cross-links between the alginate polymer molecules, creating a thermally irreversible solid gel. The calcium replaced sodium ions can form NaCl (table salt), a cross-linking reaction by-product. (b) In the reverse spherification process, yogurt ravioli (bottom right-hand side) are created when the calcium-containing yogurt (top left) is dropped into a sodium alginate solution (top right-hand side). As with spherification (Figure 6a), cross-linking occurs between the calcium ions and the alginate polymer molecules, however, the center of the yogurt ravioli does not become solid because the matrix formed by the alginate is not porous enough to allow the larger alginate molecules through. The calcium replaced sodium ions can form NaCl (table salt), a cross-linking reaction by-product.

In the original spherification method developed by Ferran Adrià, sodium alginate is dispersed in the desired food liquid and dropped into a calcium chloride solution. In the spherification demonstration herein, sodium alginate is added to cola-flavored soda and, in turn, the soda-alginate mixture is dropped into a calcium chloride solution, where spheres are immediately formed. Adrià developed the reverse spherification process to combat the solidification of the spheres after creation, that is, the continuation of the cross-linking process resulting in a solid, gel-like texture throughout the sphere, rather than just on the surface (Anonymous 2009b). Reverse spherification uses a high calcium food or calcium-fortified5 food and places it into a sodium alginate bath. By reversing the process, the alginate can be washed off and the reaction is stopped, leaving a liquid-filled thermally stable sphere. In the reverse spherification process demonstrated herein, yogurt, a high calcium containing food, is dropped into a sodium alginate bath.

Discussion questions

(1) What type of bonding is involved in the cross linking reaction? (2) Why can a calcium ion attach to two strands of the alginate polymer, but a sodium ion to only one? (3) Why can the liquid center solidify in spherification, but not in reverse spherification? (4) What is the by-product of the spherification reaction?

Instructor observations

Both spherification and reverse spherification demonstrations were preformed for graduate students in a graduate level food science and human nutrition course. Students were able to sample the soda spheres over time and experience the hardening described in the demonstration overview; whereas, the yogurt spheres, made using the reverse spherification process, retained their liquid center. Student commented that when the center remains a liquid, the burst of the spheres in the mouth is a delightful, flavor-filled surprise. To enrich this demonstration, students can be treated to a YouTube video of Ferran Adrià producing a liquid olive (one of Adrià's famous appetizers) employing the reverse spherification process (Ferran Adrià Demonstrates Alginates 2008).

Adapting the Demonstrations to Learners of All Ages Using the National Science Education Standards

The demonstrations presented herein can be adapted to learners of all ages by using age appropriate language and explanations. This can be achieved by employing the age appropriate science content standards from the National Science Education Standards (National Science Education Standards 1996; in the example, selected Physical Science Standards are given in italics later) for audiences at difference grade levels. For example, in the case of the liquid nitrogen ice cream demonstration, for K to 4th grade audiences the instructor can focus the explanation on the properties of the materials (e.g., the liquid nitrogen is very cold, whereas, the ice cream mix is at room temperature). For 4th to 8th grade audiences, the instructor can focus the explanation on the properties and changes of properties in matter (e.g., the liquid nitrogen transitions to the gas state [heat is required], while the liquid water in the ice cream mix transitions to the solid or ice state [heat is released]). For the 9th to 12th grade audiences, the instructor can focus the explanation on the structure and properties of matter at the atomic or molecular level (e.g., discuss the molecular level events occurring during the simultaneous phase transitions). The adjustments employed to adapt the level of the liquid nitrogen ice cream demonstrations earlier can be applied to the other demonstrations.

Footnotes

  • 1

    Kinesthetic learning is where learning takes place by the student actually carrying out a physical activity, rather than just listening to a lecture (Lengel and Kuczala 2010). It is also referred to as tactile learning. Usually kinesthetic learning involves physical movement (e.g., children physical acting out the role of molecules in processes such as network formation and enzymatic breakdown, Rowat and others 2010), but perhaps we could include the physical act of eating as a form of kinesthetic learning. If not, as advocated by Zull (2002), we could at least relate the involvement of the human senses to the enhancement of learning.

  • 2

    Racquetballs are bouncy and rubbery (amorphous rubbery state) at room temperature, but hard and brittle (amorphous glassy state) after being submerged in liquid nitrogen. A liquid nitrogen frozen racquetball will shatter when thrown against the floor or wall, to the pleasant surprise and amazement of the students. A liquid nitrogen frozen banana can be used as a hammer to pound a nail in a board. Students can crush into small bits fresh flowers frozen in liquid nitrogen with their bare hands.

  • 3

    To obtain the largest volume of whipped cream, the cream, bowl, and beaters should be chilled before use, because if the fat in the cream is too warm, it softens and is ineffective in stabilizing the air bubbles. If the cream is too warm, it is difficult to whip.

  • 4

    Sodium alginate is the sodium salt of alginic acid. Alginic acid, also called algin or alginate, is an anionic polysaccharide obtained from the cell walls of brown algae. It is a linear copolymer composed of (1-4)-β-D-mannuronate (M) and its C-5 epimer α-L-guluronate (G). The monomers are covalently linked together and can appear in homopolymeric blocks of consecutive G-residues (G-blocks), consecutive M-residues (M-blocks), or alternating M and G-residues (MG-blocks; FMC BioPolymer 2010; Alginic acid 2011).

  • 5

    Calcium gluconolactate, which has a mild taste, can be used instead of calcium chloride, as calcium chloride has an unpleasant bitter–salty taste (Anonymous 2009b).

Ancillary