Food Science

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Food Science is a Division B event for the 2020 and 2021 seasons that focuses on fermentation and pickles. The competition includes a test portion on the chemistry of food, with a focus on pickles and fermentation, and a lab portion where competitors must use a pre-constructed salinometer to measure the salinity content of a sample. Food Science was originally a trial event in states including Texas and North Carolina. When it was run in Texas as a Trial, it differed from many other states.

The event was named Calorimeter as a Division C event in 1988.

Contents

The Event

The event (2017-2018) consisted of a written test and a lab portion where students must use a homemade calorimeter. The competition often required competitors to run chemical detection tests such as Benedict's test or a Biuret test. The event (2019-2020) is focused on fermentation and pickling. It consists of a lab portion, where you can have anywhere from 1 to all of the following labs: using a student-made salinometer to find the salt content (0-10%) of an unknown solution, find the pH of a pickle, and find the water content of a pickle. To be allowed to participate, you must bring:

  • ANSI Z87 goggles (eye protection #4)
  • Lab coats or lab aprons that reach the knees. If aprons are used, then sleeves must reach the wrists.
  • Closed-toe shoes (no sandals)
  • Pants or skirts that cover the legs to the ankles (leggings don't count)
  • 1 page (front and back) per competitor, containing notes in any form from any source
  • Plastic bags,cups, and spoons
  • Graduated cylinders and beakers
  • pH paper
  • A homemade salinometer

Types of Fermented Foods

There are many types of fermented foods. Below are some of examples of types of fermented foods.

  • Beer is made from cereal grains (brewed) through alcoholic fermentation.
  • Bread is made from flour through alcoholic fermentation.
  • Cheese is made from milk through alcoholic fermentation.
  • Chocolate is made from cocoa beans through alcohol and acetic fermentation.
  • Kefir is made from a mixture of kefir grains and milk through lactic acid fermentation.
  • Kimichi is made from Korean cabbage through lactic acid fermentation.
  • Kombucha is made from tea through alcoholic fermentation.
  • Sauerkraut is made from cabbage through lactic acid fermentation.
  • Yogurt is made from milk through lactic acid fermentation.

Types of Metabolic Pathways

Anabolic Pathway

Catabolic Pathway

Amphibolic Pathway

Types of Cellular Respiration

Aerobic Respiration

Aerobic means "involving oxygen." Therefore, it can be concluded that aerobic respiration is a process involving oxygen, consisting of three metabolic processes to create ATP from glucose. In order, these processes are glycolysis, the Krebs cycle (also known as the tricarboxylic acid cycle (TCA) or the citric acid cycle), and the electron transport chain with chemiosmosis, better known as oxidative phosphorylation.

Aerobic respiration occurs in the mitochondria of eukaryotic cells (our human cells!). Its final electron acceptor is oxygen and produces water and carbon dioxide as byproducts. Theoretically, 36-38 ATP is produced in this process, a lot more than in anaerobic respiration, the reason that this process is the preferred pathway when oxygen is available for aerobic and some anaerobic organisms.

It is represented by the following chemical equation.

Glycolysis

Glycolysis is a metabolic pathway of both aerobic and anaerobic respiration. There are multiple types of glycolysis, but the Embden–Meyerhof–Parnas (EMP) pathway is the one most focused on in Food Science. It can occur in conditions with or without oxygen and occurs in the cytosol of both prokaryotic and eukaryotic cells.

Its purpose is to extract energy from glucose by converting it into pyruvate, a three-carbon molecule. Technically, this process produces 4 ATP, but because two are needed for the preparatory phase, one of the two phases of this process, only 2 net ATP is produced. During this process, NAD+ is also reduced (gains electrons) and converted into NADH. Mg2+ is used as a cofactor in steps involving glucose and substrate-level phosphorylation, but Mn2+ can also be used.

This metabolic pathway can be represented by the following chemical equation.

This process can be separated into ten steps. Each step is described below.

Phase I

Step 1: Glucose is converted into glucose 6-phosphate through the addition of a phosphate group taken from ATP and is catalyzed by the enzyme hexokinase. To keep the glucose concentration from getting too high and leaving the transport, 1 molecule of ATP is utilized for this step and converted into ADP. This step is also known as the phosphorylation of glucose.

Step 2: Glucose 6-phosphate can then be converted into fructose 6-phosphate, an isomer of glucose-6-phosphate through the rearrangement of its atoms. The enzyme phosphoglucose isomerase is used and required to carry this reaction out. This reaction is also reversible under the condition that there is a high concentration of fructose 6-phosphate, which is often not the case, so therefore most of the time this reaction is in the forward direction.

Step 3: The end product of step 2, fructose 6-phosphate is converted into fructose 1, 6-biphosphate, also known as the phosphorylation of fructose 6-phosphate. Once again, a phosphate group used from an ATP molecule is added to fructose 6-phosphate to make this reaction occur, converting ATP to ADP also once again. The enzyme used to catalyze this reaction is phosphofructokinase, an enzyme which is limited where ADP concentrations are low, and vice versa.

Step 4: Fructose 1, 6-biphosphate further continues in this pathway and is split into two isomers, glyceraldehyde-3-phosphate, an aldose, and dihydroxyacetone phosphate, a ketose. The enzyme fructose diphosphate aldolase is used for this step.

Step 5: After step 4, only dihydroxyacetone phosphate continues to step 5, which is then converted into the same molecule as the other molecule product of step 4, glyceraldehyde-3-phosphate, catalyzed by the enzyme triosephosphate isomerase, and thus concluding the first phase of glycolysis.

Phase II

Step 6: Unlike ATP, where something was taken away from it, NAD+ is converted to two molecules of NADH through the addition of electrons, which used from glyceraldehyde-3-phosphate, converting glyceraldehyde-3-phosphate to producing 1,3-bisphosphoglycerate after the addition of another phosphate group included, but not from an ATP molecule. This reaction is catalyzed by the enzyme glyceraldehyde 3-phosphate dehydrogenase. However, NADH must be oxidized and converted back into NAD+ again and again for glycolysis to continue, which can be done in conditions with oxygen. Fermentation can be used as a pathway to do so if oxygen is not available. The end product of this pathway is NADH though, and not NAD+.

Step 7: A high-energy phosphate group is transferred from 1,3-bisphosphoglycerate to ADP, catalyzed by the enzyme phosphoglycerate kinase and forming 3-phosphoglycerate and ATP, respectively. This process of a transfer of a phosphate group to ADP from another molecule is also known as substrate-level phosphorylation, which also occurs in the last step.

Step 8: This reaction is catalyzed by the enzyme phosphoglycerate mutase. It occurs during the movement of the phosphate group in 3-phosphoglycerate from the third carbon atom to the second carbon atom, forming 2-phosphoglycerate, which is an isomer of 3-phosphoglycerate.

Step 9: 2-phosphoglycerate is dehydrated in this second to the last step, losing two moles of water in the process and is converted into phosphoenolpyruvate. The enzyme enolase (aka phosphopyruvate hydratase) helps by catalyzing this reaction.

Step 10: Once again, as stated in step 7, a phosphate group is transferred from phosphoenolpyruvate (aka PEP) to an ADP molecule, forming another ATP molecule and converting PEP to pyruvate, marking the last step of glycolysis. The enzyme pyruvate kinase is used to catalyze this reaction and is required for cellular respiration to continue.

Aftermath

Since we're talking about aerobic cellular respiration here, pyruvate is first converted to Acetyl-CoA and then continues with the Krebs cycle and the rest of the cellular respiration. If a cell fails to reach the aftermath of glycolysis, it will die. However, in anaerobic cellular respiration, fermentation can be used as an alternate pathway since there isn't any oxygen involved in the process of anaerobic respiration.

Pyruvate Decarboxylation

Before continuing with carrying out cellular respiration, as stated in the aftermath section of glycolysis, pyruvate must be first converted to Acetyl-CoA in a process called pyruvate decarboxylation. This happens in a three-step process where pyruvate is broken down to do as said above.

The chemical equation of this process is shown below:

These steps are shown and explained as follows.

Step 1: A pyruvate molecule with a hydroxyethyl group with two carbon atoms after the removal of a carboxyl group, where one molecule of CO2 is released into the medium surrounding it. This hydroxyethyl group binds to the enzyme pyruvate dehydrogenase. Since two pyruvate molecules are produced from glycolysis, this step occurs twice.

Step 2: This hydroxyethyl group can then be oxidized to an acetyl group through the removal of electrons that are given to a NAD+ molecule and reduces it to NADH. These high-energy electrons in NADH are used to produce more ATP later on.

Step 3: A coenzyme A is transferred to the acetyl group, forming acetyl-CoA, where it is now finally ready to continue in the Krebs cycle and the rest of cellular respiration.

Krebs Cycle

The Krebs cycle, also known as the citric acid cycle (and TCA cycle), is a metabolic pathway that makes up the second part of aerobic cellular respiration, after glycolysis. However, unlike glycolysis, the Krebs cycle can only occur in conditions with oxygen, the reason that it cannot be part of anaerobic respiration. The cycle occurs in the mitochondria matrix of eukaryotic cells and the cytosol of prokaryotic cells. It can be used in synthesizing amino acids, so this process is known as both catabolic and anabolic (amphibolic).

The cycle can also be represented by a chemical equation, just like glycolysis, see below. In the case of some cells, ADP can be used in the place of GDP and ATP can be used in the place of GTP.

The steps that make up this pathway are explained and shown below.

Step 1: This step is a condensation reaction where a four-carbon oxaloacetate molecule is combined with the two-carbon acetyl group from the acetyl-CoA produced in an earlier process, and a sulfhydryl group (-SH) is bounded with the remaining CoA, which diffuses away and becomes acetyl-CoA after binding with another acetyl group. This reaction is irreversible due to this process being highly exergonic. The rate of this process is directly proportional to the amount of ATP available. The enzyme catalyzing this reaction is citrate synthase.

Step 2: Citrate in this step loses and gains an H2O molecule, and is, as a result, converted to isocitrate, an isomer of citrate. The enzyme catalyzing this reaction is aconitase.

Step 3: α-ketoglutarate, a five-carbon molecule, also known as alpha-ketoglutarate is then formed through oxidation of the product of the previous step, isocitrate. Isocitrate loses two electrons here, and these electrons are handed over to NAD+, converting it into NADH and also forming a CO2 molecule as part of the process. Through negative feedback from both NADH and ATP plus a positive effect of ADP, this step is regulated. The enzyme catalyzing this reaction is isocitrate dehydrogenase.

Step 4: Alpha-ketoglutarate is then oxidized to form a succinyl group, and the reactions are once given to a NAD+ molecule, and converting it into NADH, thus marking the second NADH molecule formed as a product of the citric acid cycle. This succinyl group is combined with CoA, forming an unstable molecule, succinyl CoA. The enzyme catalyzing this reaction is α-ketoglutarate dehydrogenase. This step is very similar and often compared to the third step.

Step 5: The CoA in succinyl CoA is substituted for a single phosphate group and converted to succinate, where a single high-energy bond is formed, and depending on the type of cell, forms GTP from GDP or ATP from ADP through substrate-level phosphorylation. The enzyme used to catalyze this reaction is the succinyl-CoA synthetase.

Step 6: Succinate is dehydrated to form fumarate, where two hydrogen atoms are released and transferred to FAD, where its electrons reduce it to FADH2. The FADH2 molecule is attached to these electrons and therefore becomes an electron carrier in the ETC, along with NADH. NAD+ however cannot be converted to NADH because there isn't enough energy in these electrons. The enzyme catalyzing this reaction is succinate dehydrogenase.

Step 7: Water is now added to fumarate in this step, where it forms malate through hydrolysis, another four-carbon molecule like fumarate. The enzyme catalyzing this reaction is fumarase.

Step 8: This last step is the reason why this pathway is considered a cycle. The product in this step, oxaloacetate can be used in step one once again after another molecule of acetyl-CoA. Now, to the last step. Malate is oxidized to form oxaloacetate and these high-energy electrons are transferred to a NAD+ molecule, converting it into NADH and marks the third and final NADH molecule formed as a product.

Aftermath

After the citric acid cycle, the NADH and FADH2 molecules formed as products and continue to the ETC, where they are used as electron carriers to generate more ATP. Since 2 molecules of acetyl-CoA are produced from one molecule of pyruvate that enters the citric acid cycle, we multiply all the products of the citric acid cycle by two. Also, carbon dioxide does not contain the carbons from acetyl-CoA, even though carbon dioxide is released as part of the singular turn of the citric acid cycle. These two acetyl carbon molecules will be later released in later turns of the cycle and fully incorporated into carbon dioxide.

Oxidative Phosphorylation

Oxidative phosphorylation is simply the combination of the electron transport chain, also sometimes called the electron transport system, and chemiosmosis, the utilization of ATP synthase to generate ATP from ADP. This process can occur in both eukaryotic and prokaryotic cells, but unlike eukaryotic cells, prokaryotic cells do not have mitochondria, so the plasma membrane is used as a location for this process to occur instead.

The chemical reaction of this pathway is as follows. Keep in mind that this equation only includes the ATP synthesized from the utilization of the NADH and FADH2 molecules produced from the citric acid cycle.

Electron Transport Chain

The electron transport chain, ETC, is a chain of enzymes that transport electrons across the inner mitochondrial membrane, hence the name electron transport chain. Also known as the respiratory chain, it is the last part of aerobic respiration and requires oxygen. The components that are part of the ETC are located in the inner mitochondrial membrane, where the different multi-protein complexes are located, named I to IV. The coenzyme Q and cytochrome C are electron carriers that help to connect these complexes. When the complexes are supercharged enough by the electrons they receive, they pump hydrogen ions across the intermembrane space, the area between the outer mitochondrial membrane and the inner mitochondrial membrane, specifically complexes I, III, and IV. The generation of ATP from the hydrogen ions produced is not part of the ETC, but instead part of chemiosmosis, also known as ATP synthase.

Complex I

Also known as the NADH dehydrogenase complex or NADH-CoQ oxidoreductase, the complex I consists of an L-shaped flavoprotein (fP), where the vertical leg of the protein is in the mitochondrial matrix and the horizontal leg in the inner mitochondrial membrane, that consists of FMN as a prosthetic group, and an iron-sulfur protein, also called Fe-S. NADH first transfers two electrons to FMN, which transfers it to the iron-sulfur protein Fe-S, which transfers it to CoQ. NADH is oxidized to NAD+, FMN is reduced to FMNH2, and Fe-S can be reduced to Fe (ii) or Fe (iii) depending on the energy of the electrons. There is enough energy in the electrons that the complex becomes supercharged and pumps 4 hydrogen ions into the intermembrane space.

Complex II

In Complex II, also known as succinate-CoQ reductase or succinate dehydrogenase, succinate is first oxidized to fumarate and passes on two electrons to FAD, reducing it to FADH2, passing it on to the iron-sulfur proteins, Fe-S (it is not reduced to a lack of energy), which passes it on to CoQ. There is not enough energy in these electrons to supercharge this complex and therefore it cannot pump hydrogen ions (protons) into the intermembrane space.

Coenzyme Q

Coenzyme Q or ubiquinone serves as an electron carrier in the ETC that connects complexes II and II, receives the electrons from complex I and II, is reduced to QH2, and passes these electrons on to complex III.

Complex III

Complex III is also recognized by other names such as cytochrome C reductase or Q-cytochrome C oxidoreductase. The complex starts with two molecules of cytochrome B, receiving the electrons from CoQ and passing them on to the iron-sulfur proteins (once again can be reduced to Fe (ii) or Fe (iii) depending on the energy of the electrons), which pass them on to cytochrome C1, and finally onto cytochrome C. The complex is supercharged like complex I and pumps 4 hydrogen ions from the matrix of the mitochondria into the intermembrane space.

Cytochrome C

Like CoQ, cytochrome C is also an electron carrier that receives the electrons from complex III that connects complexes III and IV and passes them on to complex IV.

Complex IV

At the start of complex IV (aka cytochrome c oxidase), the last complex of the ETC, copper ions of the A-type (CuA) receives the electrons from cytochrome C and transfers them to cytochrome A. Cytochrome A transfers the electrons to copper ions of the B-type (CuB), which then transports them to cytochrome A3, leading to the final step of complex IV and the ETC, where the electrons are transferred to the final electron acceptor, oxygen, which splits into two half oxygen ions. These ions bond with two hydrogen ions each to form two H2O molecules.

Aftermath

From proton pumps from the energy that supercharges complexes I, III, and IV, a proton gradient is formed in the intermembrane space. There is a high proton concentration in the intermembrane space in comparison to the mitochondrial matrix, where there is a low proton concentration. These protons cannot cross the inner mitochondrial membrane to the matrix because the membrane is non-permeable to these hydrogen ions, basically meaning they will not let them pass through and thus forming an electrochemical gradient.

Chemiosmosis

The proton gradient of hydrogen ions "want" to cross the inner mitochondrial membrane to the matrix, but cannot as said before, because of the non-permeability of the IMM that disallows this. This is what the enzyme ATP synthase is for. Chemiosmosis is also called ATP synthase, after the enzyme used in this process and in some cases referred to as the "fifth complex" of the ETC since it uses the energy from the redox reactions of the ETC to use phosphorylation to convert ADP and inorganic phosphate (Pi) to ATP. The type of phosphorylation that is used in this process is called oxidative phosphorylation.

Overview of ATP Synthase

ATP synthase is an enzyme shaped like a lollipop, is sometimes called F1-Fo ATPase and used for ATP synthesis, which is regulated by concentrations of ADP and ATP, The two units that make up this enzyme are named F1 and Fo. These units are connected by a protein stalk. The following sections will be talking about these units, the different subunits, and their roles in the unit.

F1 unit

The F1 unit is located in the matrix of the mitochondria and is made up of 9 subunits (polypeptide chains): 3 alpha (α), 3 beta (β), 1 gamma (γ), 1 delta (δ), and 1 epsilon (ε). It is water-soluble and is therefore responsible for the hydrolysis of ATP molecules. The alpha and beta subunits make a hexamer that has 6 binding sites, 3 (the beta subunits) of which catalyze the reaction of synthesis of ATP and the other 3 (the alpha subunits) bind ADP and ATP molecules. The gamma, delta, and epsilon subunits make a central stalk (axle), part of a rotating mechanism, acting as a rotor used in the ATP synthesis process. The gamma subunit penetrates the beta subunits, engaging them and allowing them to go through their three conformational changes, loose, tight, and open while synthesizing and releasing ATP.

The conformational changes occur in the order from left to right in the previous paragraph: loose, tight, and then the open conformational change. During the loose conformational change, ADP and inorganic phosphate (Pi) substrates are allowed to bind together loosely, but the reaction that synthesizes ATP is not catalyzed until the tight change. In the tight conformational change, ATP is now produced because the reaction is now catalyzed, binding ADP and Pi more tightly together. Finally, in the open conformational change, the ATP molecules are released and can be used for normal cell activity. A change in conformational change occurs each time the gamma subunit of the central stalk rotates by 120°.

Fo unit

The Fo unit is located in the inner mitochondrial membrane, is not water-soluble, unlike the F1 unit, and is composed of a varying number of subunits depending on the cell. These subunits include a, b, and c for most cells. In human cells, there are six additional types of subunits, including d, e, f, g, F6, and 8 (also called A6L). There is 1 a subunit, 2 b subunits, and 10-15 subunits. The "o" in Fo stands for oligomycin, the inhibitor of the Fo unit. This protein unit allows the protons from the proton gradient created by the electron transport chain to enter through a pore. The c subunits make a c-ring that acts as a rotor which is embedded in the inner membrane of the mitochondria and turns when protons to translocate through the membrane through two half-channels: an entry and exit half-channel.

Aftermath

We see that after the process of the glycolysis and the citric acid cycle, along with the decarboxylation of pyruvate, there are 10 NADH molecules and 2 FADH2 molecules that are used as electron acceptors in the ETC to pump protons and utilize them to convert ADP to ATP. 112 total hydrogen ions are pumped into the intermembrane space, and for every 4 hydrogen ions, one ATP molecule is formed, forming a total of 32 ATP molecules from the NADH and FADH2 molecules and the 4 ATPs (or 2 ATPs and 2 GTPs, which is energy equivalent to 4 ATPs) produced from glycolysis and the citric acid cycle. While it is said that 38 ATP molecules are produced in aerobic respiration and the total number of ATP molecules total to 38 using the chemical equations, this is only based on theory and does not account for the energy required to move molecules to the mitochondria. Therefore, only 32 ATP molecules are produced from aerobic respiration. This is also only if the malate-aspartate shuttle is used as well and not the less-efficient glycerol-phosphate shuttle is used, which only produces 30 ATP molecules. The following paragraphs will briefly explain what these two are and why they produce the number of ATP molecules that they do.

Anaerobic Respiration

Unlike aerobic respiration, which uses oxygen as its final electron acceptor, anaerobic respiration does not require oxygen. There are two methods of anaerobic respiration, one which uses an organic molecule as its final electron acceptor, and one that uses an inorganic molecule as its final electron acceptor.

Method I

Glycolysis
Fermentation

Method II

Glycolysis
Krebs Cycle
Oxidative Phosphorylation
Electron Transport Chain
Chemiosmosis

Fermentation

Fermentation is a metabolic process where organic molecules, such as carbohydrates, are broken down chemically by a microorganism such as yeast, and in some cases converting it to an acid or alcohol through enzyme action anaerobically. One of its goals is to regenerate NAD+ from NADH so glycolysis again. Microbiologist Louis Pasteur discovered that fermentation can be carried out by yeasts and other organisms. The science of fermentation is also known as zymology, studied by scientists called zymologists. According to the rules, the three types of fermentation processes that must be studied for this event is alcohol (ethanol) fermentation, heterolatic fermentation, and homolactic fermentation. The mechanic of how each one works is explained in the following sections.

Health Benefits

Types of Fermentation

Alcohol Fermentation

Alcohol fermentation also called ethanol fermentation is used in many alcoholic beverages such as beer and wine, where ethanol is the intoxicating agent used and is also used to make bread dough rise through the carbon dioxide produced from the reaction. As you may have guessed, yeast cells also undergo this pathway, since yeast is part of the bread dough rising process. Feedstocks such as corn are also fermented through ethanol fermentation, and the ethanol produced is used in gasoline.

In the context of the anaerobic respiration process, we start with two molecules of pyruvate that are produced via glycolysis. These pyruvates are broken down into acetaldehyde molecules, releasing two carbon dioxide molecules. The acetaldehyde molecules are then converted into ethanol, oxidizing NADH back to NAD+ for glycolysis to continue again and the cycle repeats. The enzymes pyruvate decarboxylase and alcohol dehydrogenase catalyze this reaction.

The reaction of this fermentation pathway is summarized by the following equation.

Lactic Acid Fermentation

Heterolactic and homolactic fermentation are two types of lactic acid fermentation studied for this event, with the bifidium pathway being the third. This type of fermentation is used by mammal red blood cells and our muscle cells when there is a lack of oxygen, the reason for our cramps. This causes a build-up of lactic acid, used by our liver to produce pyruvic acid for metabolism processes. 2 molecules of pyruvate is converted into 2 molecules of lactate and NADH is oxidized back to NAD+.

The following equation represents the reaction of lactic acid fermentation. The reaction is reversible, but the forward reaction is inhibited by acidic conditions.

Heterolactic Fermentation

A variation of lactic acid fermentation is the one mentioned in this section, heterolactic fermentation, also known as the heterofermentive process. Heterofermentative bacteria use this process, in which one molecule of glucose is concerted into lactate, with the addition of the byproducts ethanol and carbon dioxide, along with one molecule of ATP through substrate-level phosphorylation with the use of the energy of the reaction.

The chemical reaction of this pathway is represented by the following equation.

Homolactic Fermentation

Similar to heterolactic fermentation, homolactic fermentation is another variation of lactic acid fermentation and is also known as the homofermentative process. Performed by homofermentative bacteria, glucose is converted to 2 molecules of lactate. Using the energy from this reaction, substrate-level phosphorylation is used to bind ADP to Pi to produce 2 molecules of ATP.

The chemical equation representing this reaction is shown below.

Food Preservation

The purpose of food preservation processes are to keep bacteria and molds from reproducing on or fermenting foodstuff before it is consumed. It prevents contamination with molds and pathogens and slows down enzymes that cause rancidity.

Low Temperature Preservation

Maintaining a low temperature in low-temperature preservation slows down the growth rates of microorganisms and any chemical or physical reactions (ex: oxidation). By converting water inside the food into ice, it is effectively lowering the aw (water activity) value of the food, preventing microbial growth.

Refrigeration

Refrigeration is the process of removing heat. This causes the life of foods to increase when refrigerated. It does not stop decay but slows it down. Refrigeration usually occurs at temperatures of 4°C and under. Refrigeration is used to preserve foods such as fruits, vegetables, meat, dairy, etc. Microbial growth slows down starting from 50°F. However, pathogenic bacteria cannot reproduce in temperatures less than 40°F.

Freezing

Freezing is the removal of all heat from foods and slows down decay more extremely than refrigeration. It converts the water in food into ice. Freezing occurs at 0°C and under. Freezing is used to preserve fish and meat.

Flash Freezing

Flash freezing is food being frozen within a few hours by subjecting them to cryogenic temperatures or through direct contact with liquid nitrogen at −196°C (−320.8°F). Flash freezing is also called lyophilization or cryodessication.

Thermal Processing

Thermal processing is the combination of heat and time to eliminate unwanted microorganisms or to destroy microorganisms that can cause spoilage or enzymes that can affect different characteristics of the food.

Canning

In canning, foods are canned once they reach a high temperature so that all microorganisms are gone & no more can enter again.

First, the food is cleaned. Then, it is canned and vacuumed airtight so that no oxygen-requiring organisms can survive (exhausting). Any remaining organisms are destroyed during the heating process. The food is then cooked, labeled, cased, and stored.

However, the downside of canning includes a loss of nutrients from heat processing and overheating of closer areas of the food from the heat source. Canning is used to preserve fruits, vegetables, soups, etc.

Sterilization

Types of Microorganisms

Macromolecules

Macromolecules are very large molecules. There are conventionally four different biopolymers: lipids, carbohydrates, proteins, and nucleic acids. The last does not apply to Food Science; therefore, the first three should be focused on. In each of these categories of macromolecules, some subcategories exist.

Lipids

Lipids have many subcategories including fats, waxes, and sterols. The main ones you need to worry about are the triglycerides: fats and oils.

Fats

Fats are a good source of energy, giving 9 kcal/g of fat.

  • The daily recommended amount of fat intake is limited to 65g. These contribute to a large amount of the obesity problem in the U.S.

Fats are most commonly found as triglycerides. Triglycerides are made up of a glycerol "backbone" with three fatty acids attached. Fatty acids are long chains of carbon molecules with an ester group on the end.

A triglyceride

The fatty acids may be saturated, unsaturated, or trans. Triglycerides can use any combination of these different fatty acids.

Saturated Fatty Acids

Saturated fatty acids are one long chain of carbon atoms meaning no double bonds and no fancy stuff. Saturated fats are generally unhealthy since they clog arteries, increasing the risk of heart attack and stroke. Since the carbon atoms in a saturated fatty acid are packed closely together, saturated fats are usually solid at room temperature. Saturated fats are generally found in animals.

Unsaturated Fatty Acids

Unsaturated fatty acids are also a long chain of carbon atoms, this time with one or more double bonds. Unsaturated fatty acids with one double bond are monounsaturated, and those with two or more double bonds are polyunsaturated. Unsaturated fats are generally healthier when not overeaten because they may help lower blood cholesterol level. Since double bonds exist, these fatty acids are much more wobbly and, therefore, are usually liquid at room temperature. Unsaturated fats are generally found in plants such as nuts and seeds. They are also found in fish as omega-3 unsaturated fatty acids.

Omega-3 Essential Fatty Acids

Omega-3 essential fatty acids are found in fish and plants. The name means there exists a double bond three carbon atoms from the non-ester end of the chain. Omega is the last letter in the Greek alphabet (lowercase omega is used). These fatty acids are "essential" because the body cannot produce them on its own, and they are vital for normal metabolism.

Trans Fats

Trans fats are not found in nature, although recent studies suggest that there may be small amounts. Trans fats are unsaturated fatty acids heated up then made so "dizzy" that it changes from cis to trans configuration.

CisvsTrans.jpg

Trans fats are unhealthy since they lower high-density lipoproteins (HDLs or "good" cholesterol) and raise low-density lipoproteins (LDLs or "bad" cholesterol). The recommended daily intake should be limited to 2g per day.

Esters

Esters are found on the end of all fatty acids.

Esters are a group of organic molecules that contain -C=O-O- as part of the molecule. More specifically, esters are only one part of the molecules in this group, but any molecule that contains an ester is classified as an "ester".

Esters are derived from carboxylic acids. When a carboxylic acid reacts with alcohol, an ester will form. For example, acetic acid will react with ethanol to make ethyl acetate.

Common esters include ethyl acetate and ethyl ethanoate.

Sterols

The one sterol you'll want to know about is cholesterol. Cholesterol, like all sterols, come in this form:

Sterol.png (picture credit Wikipedia)

Cholesterol comes in high-density lipoproteins (HDLs or "good" cholesterol) and low-density lipoproteins (LDLs or "bad" cholesterol. HDLs are made by your liver, while LDLs are generally consumed. Some types of foods, such as trans fats, are thought to raise LDL levels and lower HDL ones.

If a body has too much LDL, arteries will clog and result in a heart attack. This is cardiovascular disease, the leading cause of death in America.

Carbohydrates

Carbohydrates are, as suggested by the name, hydrates of carbon. They consist of carbon, oxygen, and hydrogen atoms. The formula for a carbohydrate can be expressed as [math]C_m(H_2 O)_n[/math], where, most commonly, [math]m[/math] and [math]n[/math] are the same.

Carbohydrates include simple sugars (carbohydrates made of one or two molecules of sugar), monosaccharides (any of the class of sugars, e.g., glucose, that cannot be hydrolyzed to give a simpler sugar) and disaccharides (a sugar [i.e. carbohydrate] composed of two monosaccharides), complex sugars (carbohydrates made of three or more molecules of sugar attached), and polysaccharides (a carbohydrate (e.g., starch, cellulose, or glycogen) whose molecules consist of several sugar molecules bonded together).

Simple Sugars

Simple sugars consist of single sugar units (monosaccharides) and disaccharides (which are made up of two monosaccharides). The names of sugars often end in the suffix -ose. Hexose sugars are 6 carbon monosaccharides while pentose sugars are 5 carbon monosaccharides. Some monosaccharides include:

  • Glucose/Dextrose (hexose)
  • Fructose/Levulose (hexose)
  • Galactose (hexose)
  • Mannose (hexose)
  • Ribose (pentose)
  • Xylose (pentose)
  • Arabinose (pentose)

Some disaccharides include:

  • Sucrose (glucose+fructose)
  • Lactose (glucose+galactose)
  • Maltose (only found as a byproduct of hydrolysis of starch; glucose+glucose)
  • Trehalose (also found as a byproduct of hydrolysis of starch; glucose+glucose)
  • Melibiose (formed when there is an alpha-1,6-glycosidic linkage between glucose+galactose)

Simple sugars are small, easy to break down, and, therefore, give energy quite soon after consumption. However, they run out quickly, leaving one tired. Think about crashing after a sugar high.

The "Sugars" on food labels consist of mono- and disaccharides. That's why you see sugar in milk; that's lactose, not added by the manufacturer.

Complex Sugars

Complex sugars are mainly polysaccharides. Polysaccharides are chains of many monosaccharides, most commonly glucose.

Polysaccharides are divided into two main groups, storage polysaccharides and structure polysaccharides.

Storage Polysaccharides

Storage polysaccharides are our main source of energy. There are two main storage polysaccharides: glycogen and starch.

  • Glycogen is the storage polysaccharide found in animals. Its purpose is to maintain blood glucose levels and serve as a readily mobilized energy source.
  • Starch is the storage polysaccharide found in plants. We, humans, consume a lot of it from foods like pasta or potatoes.

Starch comes in two forms: amylose and amylopectin. Amylose is a straight chain of glucose molecules that coils up. Amylopectin is branched. Since there are more ends to be broken down in amylopectin, it is more quickly digested.

When looking at a food label, the Dietary Fiber and Sugars don't quite add up to the Total Carbohydrate; the remainder is starch.

Structure Polysaccharides

Structure polysaccharides are polysaccharides meant to give structure. Two common structure polysaccharides are cellulose and chitin.

  • Cellulose is the structural polysaccharide found in plant cell walls. Cellulose is better known as (dietary) fiber. It is insoluble, which means it is indigestible by our bodies, so it cleans out our insides and comes out as feces.
  • Chitin is the structural polysaccharide found in the cell walls in fungi, the exoskeletons of arthropods (think crustaceans and insects), the radula (teeth) of molluscs (think snails and clams), the beaks of cephalopods (think octopus and squids), and the scales of fish & lissamphibians (modern amphibians). Chitin is composed of long chains of N-acetylglucosamine, a derivative of glucose.

Proteins

Proteins are polymers of amino acids. Proteins are essential to human life because they carry out orders from the genes in cells.

Proteins can be converted to energy by the liver when there is a lack of carbohydrate or fat; therefore, they provide 4 kcal/g.

Protein Denaturation and Coagulation

Protein denaturation is the undoing of the natural structure by chemical or physical means. Denaturation doesn’t change the composition of the protein, only the structure. Protein denaturation can happen because of heat (140-180 degrees Fahrenheit/ 60-80 degrees Celsius), high acidity, air bubbles, or any combination of the three. Since denaturation changes the folds of the proteins, there are more open bonds, so they form new bonds. This creates a thickness or density. Coagulation is the process when these new bonds are formed.

Enzymes

Enzymes are a type of special proteins that catalyze chemical reactions. The names of enzymes often end in the suffix -ase. Examples are maltase (breaks down maltose), amylase (breaks down amylose and amylopectin), and lactase (breaks down lactose).

Some enzymes cause disease because some people do not contain them or possess distorted, non-functional forms. The most common disease is phenylketonuria (PKU), which is a lack of functional phenylalanine hydroxylase, an enzyme. When functional, phenylalanine hydroxylase is supposed to break down phenylalanine, an amino acid found in the artificial sugar aspartame.

Amino Acids

Amino acids are the building blocks of proteins. Amino acids consist of 10-40 atoms each, mainly carbon, hydrogen, sometimes sulfur, and at least one nitrogen in the amino group, -NH2. Proteins are formed by linking the amine nitrogen with a carbon atom on another amino acid, forming a peptide bond.

Complete and Incomplete Proteins

All amino acids are needed to live. There are 9 essential amino acids and 11 non-essential ones. The body does not make the essential ones, therefore they need to be consumed. The body makes the other 12 itself, therefore it is not essential to eat them. For a person with a normal diet, all 9 essential amino acids are normally found in most meats.

This poses a problem for vegetarians, who cannot eat proteins with all the essential amino acids. So they must eat complementary proteins, or two different food ingredients, when, eaten together, make complete protein sets that contain all the proteins that you need to eat. An example of a pair of complementary proteins is rice and beans.

Emulsification

An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable). Emulsions are part of colloids. In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). The word "emulsion" comes from the Latin word for "to milk", as milk is an emulsion of fat and water, among other components. Emulsions, being liquids, do not exhibit a static internal structure. The droplets dispersed in the liquid matrix (called the “dispersion medium”) are usually statistically distributed.

Hydrogenation

The chemical reaction between hydrogen (H2) and another compound or element, usually in the presence of a catalyst (nickel, palladium, or platinum). Reduces or saturates organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, generally an alkene. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogenation reduces double and triple bonds in hydrocarbons, hydrogenation of unsaturated fats produces saturated fats. Partial hydrogenation can produce trans fats.

Food Testing

At the competition, teams are expected to be prepared to perform certain experiments on the Approved List of Ingredients. Most tests will include instructions for performing the experiments, but it is good to be familiar with them beforehand.

Calorimetry

Calorimetry is the required testing subject of Food Science. Teams need to make their own homemade calorimeters.

Making a Calorimeter

To make a calorimeter, you will need a small metal can and a large metal can. Puncture four small holes in the small can and slide two thin rods (paperclips also work) between the holes. Fill the small can with water. Place the small can inside the large can, with a space for a sample of food. To use the new calorimeter:

  1. Measure the water in the small can and record.
  2. Measure the mass of the food sample you will be using.
  3. Measure the temperature of the water and record.
  4. Using a match or a lighter, set the food on fire. Note - Do this near an open window. It will exude smoke.
  5. Quickly, put the food in the slot or cover it with the calorimeter. Note - The water temperature will rise.
  6. When the temperature of the water is done rising, then record the final temperature. You can take the food sample out; it should be done burning.
  7. Using these measurements, fill out the equation.

Calorimeter Equation

This equation is [math]Q=m \times c \times \Delta T[/math]

  • Q is total heat generated by food (calories)
  • m is mass of the water in grams (1 mL=1 gram)
  • c is the specific heat of water (1 calorie/gramxdegree Celsius)
  • ΔT is the difference in temperature between the start and the end (e.g. if T1 = 32 and T2 = 40, then ΔT = 40-32 = 8). Note that the temperature can be in either units of Celsius or Kelvin when you are taking the difference (since Kelvin is just Celsius + 273.15), as long as your specific heat is given with units of Celsius or Kelvin.
  • Substitute all of the measurements that you took before.
    • Make sure to have all of the units!
  • The units of gram from m and gram from c cancel each other out, as well as degree Celsius from c and T.
    • This leaves calories as the unit for Q.
  • Now solve the equation! At the end, divide by 100.

Note - The event uses joules/gram as the energy unit. To transfer calories to joules/gram:

  • Divide the total calories by the mass of the food from before. Then, convert the units using the conversion below.
    • 1 calorie/gram = 4.1868 joules/gram.

Molecule Detection Tests

There are certain tests used to detect macromolecules and other molecules in food. Teams may have to perform some of these at the competition. The most common tests are Benedict's, Biuret's, Iodine, and the Brown Bag test.

Benedict's

Benedict's solution is also known as Fehling's solution. It tests for reducing sugars, or a sugar with a free aldehyde. The reaction between a reducing sugar and Benedict's is between the reducing sugar's aldehyde and the copper sulfate in Benedict's.

To use Benedict's:

  1. Put a small sample of the food into a test tube.
  2. Liquefy the food by adding enough water to make it a liquid, if the food is not already a liquid.
  3. Add 5-10 drops of Benedict's Solution.
  4. Carefully heat the test tubes in a hot water bath at 40-50 degrees Celsius (104-122 degrees Fahrenheit) for five minutes.

To deduce the results:
The liquid will turn green, yellow, or brick red depending on the amount of sugar present. Green is the least sugar, yellow is more, and red is the most. If negative, it will be blue.

Note that Benedict's will only work with reducing sugars, which are sugars with free aldehydes. (An aldehyde group is of the form R-CH=O where R is something organic). Here's a rule of thumb: all monosaccharides are reducing sugars but not all reducing sugars are monosaccharides. Lactose, for example, is reducing; however, sucrose is not. Make sure to know the reducing sugars, because trick questions often arise on tests on this subject.

Remember that Benedict's needs heating to work when answering test questions about it!

Biuret's

Biuret's Reagent is for detecting the presence of proteins. The active agent in Biuret's is also copper sulfate. The reaction is due to the formation of complex between the cupric ions in copper sulfate and the lone pair of electrons present on the nitrogen and oxygen atoms of peptide bonds of proteins.

To use Biuret's:

  1. Put a small sample of the food into a test tube.
  2. Liquefy the food by adding enough water to make it a liquid, if the food is not already a liquid.
  3. Add 2-5 drops of Biuret's Solution.
  4. Swirl gently to mix.
  5. Let sit for five minutes.

To deduce the results:
Biuret's will turn a pink/purple in the presence of proteins. If negative, the solution will have no color.

Iodine

Iodine solution, also Lugol's Iodine, is used to detect starch. It is a mix of the element iodine and potassium iodide. The reaction is the result of the formation of polyiodide chains from the reactive starch and iodine.

To use Iodine:

  1. Put a small sample of the food into a test tube.
  2. Liquefy the food by adding enough water to make it a liquid, if the food is not already a liquid.
  3. Add 2-5 drops of Iodine.
  4. Swirl gently to mix.

To deduce results:
The solution will turn dark blue, almost black, in the presence of starch. It will be brownish-yellow if negative.

Note that amylose (straight chain form of starch) will stain less than amylopectin (a branched form of starch).

Brown Bag

The brown bag is the easiest and least formal test. It tests for lipids (fats).

To perform this test, spread, rub or pour some of the food on a brown bag. Wipe away the excess, and hold the bag to the light. Foods containing more lipids will stain the bag more transparently than ones that have fewer lipids.

This test can also be done with plain paper, though the paper has to dry before it can be analyzed.

Density

Teams may have to find the density of certain baked foods made from ingredients on the Approved List of Ingredients such as bread. To do this, you will have to first cut it into a uniform cuboid (a 3-D rectangle). Next, use a ruler to measure the height, length, and breadth (AKA width) of the object. Record these measurements. Now, weigh the object. The event supervisor must provide a scale. Use the density formula to find the density of the food. Make sure to answer the units wanted. The most common units wanted is [math]\frac{g}{cm^3}[/math].

The density formula is [math]\text{Density}=\frac{\text{weight}}{\text{height}\cdot\text{length}\cdot \text{breadth}}[/math]

Competition Tips

  1. Study a lot. This event is one of the heaviest in terms of what teams need to know, therefore retention is crucial.
  2. Ask the event supervisor if tests can be unstapled and then later re-stapled. This strategy may help teams divide work to save valuable time.
  3. Get a lot of rest before the competition! Self-explanatory. Also, eat a big breakfast.
  4. Make sure to be able to recognize the structures of basic molecules very quickly (mono and disaccharides, triglycerides, etc)