Food fire and physics exam 2

From a food safety perspective, what is the relationship between cooking time and temperature?

- Foods that are cooked at lower temperatures often require longer times to make them safe to eat. For example, cooking a steak at 140 F versus 155 F. If a steak is cooked at 140 F, it should be cooked for a longer time as compared to 155 F. - If you are cooking at a lower temp then recommended then you should hold the cooking temp for longer.

What is the main role of the main three categories of food molecules

Proteins: Structure and texture. Proteins are needed to reproduce the texture of muscle fibers. Lipids: flavor and mouthfeel (mouth being coated with fats). Carbohydrates: Helps with water binding and used as a space filler.

What temperature range represents the 'danger zone' for food? Why is it considered the danger zone? and What temp leads to the fastest rate of microbe growth

- 41 F to 135 °F is the "danger zone" from a food safety perspective. Sometime, 40 F to 140 F is used. Zone you are trying to keep your food out of (either too hot or too cold) - What temp leads to the fastest rate of microbe growth = 100 --> you do not want to leave it at 100 because the microbes will start multiplying. - too hot= denature proteins killing the organism

Explain how a pressure cooker works and why it cooks faster than boiling water at atmospheric pressure

- Boiling point of water depends on pressure: increase pressure= increase temp - In the pressure cooker the water is boiling at a higher temp (compared to a regular pot) --> as you increase the pressure you are increasing the number of molecules that are moving --> cooking time decreases the higher pressure

Explain how a candy thermometer works and how it can be used to tune the sugar concentration in a water- sugar solution

- Use it to tune sugar concentration because the sugar concentration changes the texture - The different stages (dif temps) change the texture of the candy --> You care about measuring the temp because the temp tells you how much sugar is in the water - The more sugar in the water the higher the boiling temp - You can Increase sugar or decrease water molecules (by letting it sit and boil) to change the stages if you are not happy about the temp -> for example, if you want to make soft- crack and you got higher then 290 then let some water molecules out

Explain lactose intolerance in terms of the lactase enzyme

- if you are missing the lactase enzyme then you are lactose and tolerance --> the lactase enzyme needed to digest lactose (milk sugar). The lactase enzyme breaks down the sugar, so it is digestible. Without this enzyme, the milk sugar cannot be broken down into smaller monosaccharides and digested.

What are three examples of bacteria to be concerns about in food? What foods can they be found in?

1. E. cole (undercooked ground beef, raw (unpasturized) milk, juice 2. Salmonella (milk, eggs, meat, vedgetables) 3. listeria (deli meats, seafood, raw sprouts )

What would an ideal viscous look like? shear- thinning? shear thickening?

1. Ideal viscous (newtonian fluid) viscosity doesn't change the amount of shear = water -- straight line on graph. This is an example of an ideal fluid 2. Shear-thinning (try to make the viscosity go down) = xanthin gum 3. Shear-thickening - viscosity is increasing with shear = Oobleck ( cornstarch + water)

State five common gelling agents and what type of molecule (protein, carbohysrate, lipid, water) each one is

1. Sartch - carbohydrate 2. Pectin- carbohydrate 3. Genlatin - protein 4. Agar agar - carbohydrate 5. Guar gum - carbohydrate

What are some meat alternatives

1. Tofu (soy is the main source of protein) 2. Tempeh (soy is the main source of protein) 3. Seitan (wheat is the main source of protein)

What are the three microorganisms that are more relevant for food

1. mold: penicillium difiatum, phizophus stolonifeer 2. bacteria (we hear about this more in the news) 3. Yeast

What is a hydrogel

A hydrogel is a gel (liquid dispersed in a solid) where the liquid is water

Gels often form through a sol-gel transition

A sol is solid particles suspended in a liquid. Raw egg white is composed of solid particles (globular proteins) suspended water. When eggs are cooked, the sol (raw eggs) become a gel (cooked eggs).

If the doubling time of bacteria is 10 minutes and there are initially 2 bacteria, how many are there after 10 minutes? One hour? Two hours?

After 10 minutes, there are 4. After one hour, there are 128. After two hours, there are 8,192.

What is the difference between an oil-in-water emulsion and a water-in-oil emulsion? Which one is mayonnaise

An oil-in-water emulsion is oil droplets dispersed in water. --> nice and thick --> mayonnaise is an oil-in-water emulsion A water-in-oil emulsion is water droplets dispersed in an oil --> greasy mess and is liquid Note: This is why emulsifier is so importantn You could fix water-in-oil by adding more of an emulsifier (egg, lecithin, polysorbate 60)

Distinguish between a physical gel and a chemical gel

Answer: A physical gel is reversible with temperature. The bonds that form in the gel are weak, often involving the entanglement of molecules. A chemical gel is not reversible with temperature. The bonds that form are strong and do not break if the temperature changes.

What are the two main lipids used in Beyond Meat and Impossible Burger? Why are two used?

Answer: Coconut oil and sunflower oil. 1. Coconut oil is a saturated fat (more fatty acids) 2. Sunflower oil is an unsaturated fat (more kinks) --> Meat burgers have a mix of both. Therefore, to create a similar mouthfeel and cooking experience, plant-based burgers use two as well.

Describe the technique called spherificiation (or reverse spherificiation) using the example of sodium alginate and calcium ions. Clearly explain how a gel is formed.

Answer: Spheriification is the encapsulation of a liquid using a gel. An example is when a water bath is prepared with sodium alginate molecules. The sodium alginate molecules form bonds with each other in the presence of positively charged ions (typically calcium). Thus, a large droplet of a liquid with calcium ions is placed in the sodium alginate water bath. The calcium ions in the liquid diffuse into the water bath can create bonds between the sodium alginate molecules. This leads to a gel forming and encasing the liquid.

What does pH represent

Answer: pH is a measure of the acidity of a substance. The lower the value of pH, the more acidic the substance. A pH of 7 is neutral. It represents the concentration of H+ ions in the substance as compared to OH- ions.

At the molecular level, explain why a xanthan gum solution is shear-thinning

As a fluid with xanthan gum is sheared (add force or pressure) the molecules start banging into each other and they don't flow every well and because of this the viscosity is very high--> the rod-like molecules align with each other. This alignment makes it easier for the molecules to slide by each other and reduces the viscosity.

At higher elevations, the temperature at which water boils is lowered. Explain why.

As elevation increases, there is less pressure. As the pressure is reduced, the boiling point of water also decreases. Thus, at higher elevations, water boils at a lower temperatures --> increase pressure is going to take more energy (temp) for water molecules to jiggle free

How does the stiffness of a gel depend on the concentration of the gelling agent? Explain the relationship

As the concentration of the gelling agent increases, so does the stiffness. This occurs because an increase in concentration of the gelling agent leads to an increase in the bonds formed in the gel network. The more bonds that form, the stiffer the network

At the molecular level, explain why cornstarch is shear-thickening at high shear rate.

At high shear rate, corn starch granules can not rearrange fast enough for the fluid to flow smoothly. They form a jammed network which dramatically increases the viscosity

Microorganisms are often used to prepare food. What are examples of food prepared with bacteria, yeast, and mold?

Bacteria= yogurt yeast= bread mold= soy

If no air is being added to the sealed bag, explain how it can expand and look inflated --> airplane

Because the pressure on the outside of the bag is being reduced. Since there is less pressure on the outside, the pressure on the inside pushes on the walls of the bags and increases it size

Describe the difference between the continuous phase and the dispersed phase

Continuous: outside of a dot/ the base - Is the overall structure of it, if it is a liquid it is hard to hold the structure Disperse: dispersed in the continuous= inside of a dot - Globular proteins = solid (disperse) are in water =liquid (continuous)

For the following, explain by microbes do not grow on or in the food. 1. dried fruit 2. canned vegetables 3. a bottle of water 4. refrigerated milk 5. cheesecake eaten after being prepared

Dried Fruit: Lack of moisture ... low water activity. Canned vegetables: Lack of oxygen. Often sterilized prior to sealing. A bottle of water: Lack of food. Refrigerated milk: Temperature is below the danger zone. A cheesesteak eaten soon after being prepared: Not enough time for microbes to grow. (FAT TOM)

Explain why low acidity leads to low microbial growth. Also, state how low the pH value needs to be to be considered low

If a food is acidic (low pH), the acid can prevent microbial growth. This is because acids can disrupt the digestive system of microbes and prevent them from growing. A pH value of 4.6 or lower is considered acidic enough to prevent microbial growth

Explain how mixing two liquids together (water and oil) can result in a solid-like substance (mayonnaise).

In the case of mayonnaise, the oils droplets are packed so densely that they are touching each other. This dense packing of oil droplets begins to behave as a solid, so it is difficult for the oil droplets to move around

Does it take longer or shorter amount of time to cook pasta at the top of a tall mountain compared to see level

Its not heating up faster but it gets to a boiling point faster at tall mountain, this doesnt mean that it cooks faster though --> tall mountain takes longer for pasta to cook then at see level

Explain the meaning of a shear-thinning fluid

Ketchup is an example of a shear-thinning fluid. As ketchup is sheared, its viscosity decreases because when it is shaked it increased the force which decreases the viscosity

Describe each of these dispersions and provide an example of each one: 1. Liquid aerosol 2. Solid aerosol 3. Foams 4. Emulsions 5. Sols and suspensions: 6. Solid foams 7. Gels 8. Solid sols

Liquid aerosol: Liquid particle dispersed in a gas. Example: steam. Solid aerosol: Solid particle dispersed in a gas. Example: smoke. Foams: Gas bubbles dispersed in a liquid. Example: whipped cream. Emulsions: Liquid droplets dispersed in a liquid. Example: mayonnaise. Sols and suspensions: Solid particle dispersed in a liquid. Example: steam. Solid foams: Gas bubbles dispersed in a solid. Example: bead. Gels: Liquid droplets dispersed in solid. Example: Jello. Solid sols: Solid particles dispersed in a solid. Example: chocolate (cocoa solids dispersed in cocoa butter).

What is an emulsion

Liquid dispersed inside another liquid. --> If you pack enough oil droplets that they are touching each other that it begins to act like a solid 64% of the mayonnaise needs to be oil for it to act like a solid

Describe the structure of mayonnaise when viewed with a high-powered microscope

Mayonnaise looks like droplets of fat dispersed in water. The droplets are packed tightly together.

Emulsifiers can form micelles. What is a micelle? Describe its structure.

Micelles are surfactants - wen surfactants form a structure where the non polar tails are in the inside and the polar is on the outside

Do the USDA guidelines for cooking eliminate all microorganisms from the food?

No, only the amount they need to in order not to get you sick. The recommended cooking temperatures drastically reduce the number of microorganisms

The extrusion process to make PBMA often involves heat. What type of molecules are particularly sensitive to heat? What role might heat play in the extrusion process?

Proteins are particularly sensitive to heat. Extrusion involves heating so that the proteins in the plant-based mixture denature and they can then coagulate

Briefly describe the process of making tofu. In your description, explain the role of the coagulant

Puree soybeans with water, bring to a boil to denature proteins, add a coagulant (like lemon) to facilitate coagulation, press to remove excess liquid. types of tofu coagulations 1. gypsum 2. nigiri 3. lemons

Many foods contain both stabilizers and emulsifiers. Discuss the different role each plays in a food product

Stabilizers reduce the rate that a mixture separates. --> thickening agent (xanthan Gum) the stabilizer will help get in the way of the oil droplets—making the oil stay dispersed For example, if a sauce contains droplets of fat, a stabilizer would prevent the droplets from 'creaming' and floating to the top of the sauce. Emulsifier wants to live on the boundary of the oil and the water= have to be both hydrophilic and phydophobic - They coat the oil droplets so they do not combined --> does not stop oil from rising to the top of the substance. Both of these things will help condiments shelf stable and be able to sell longer

What is the difference between sterilization and pasteurization?

Sterilization: kill off all microorganisms—for bread it will be burnt in order to get rid of all microorganisms Pasteurization: get rid of enough that you won't get sick

Describe the physical difference between super firm tofu and medium firm tofu at the molecular level

Super firm tofu has more crosslinking (bonds) in the soy protein network. The increased number of bonds (add more coagulate) increases the stiffness of the network - more coagulant --> more bonds = stuffer it will get

What is a surfactant? Why are surfactants found in detergents?

Surfactants are molecules with polar (head) and nonpolar parts (tail). --> non polar tails want to be in the air --> Because the non-polar tails go into the dirt on your hands, the surfactant coat the dirt, so it helps lift the dirt of your hand and clean it off They are used in detergents because they coat dirt, which is oily and nonpolar, and allow it to be washed away in water

What is the extrusion process

The extrusion process is a method used to create a texture like muscle fibers but with plant proteins. The process pushed the plant-based mixture through a screw-like system. --> Heat the proteins (denature) and add water (hydrated proteins)àheat and shear proteins (stretches and allgnes the proteins) by aligning the proteins they are creating the texture of meat

Why is the extrusion process used to make plant-based meat alternatives?

The process pushed the plant-based mixture through a screw-like system. The shear forces on the mixture align the denatured proteins and create a protein structure that is similar to meat-based proteins.

Explain why a lack of food (particularly protein) leads to low microbial growth

To grow, microbes need food. Thus, if a food (like a bottle of water) doesn't contain the nutrients for microbial growth, the microbes can't grow and multiple.

Some gels are reversible with temperature. For the case of gelatin, at what temperature does the gel transition to a sol upon heating? At what temperature does the sol transition to a gel upon cooling?

Upon cooling, a gelatin gel is formed at 20 C. Upon heating, the gelatin gel becomes a sol at 30 C.

List the following fluids in order of increasing viscosity: honey, ketchup, peanut Butter, and water

Water, honey, ketchup, peanut putter

Seitan is often used as a meat alternative. what proteins are used to create the texture

Wheat portions -- the glutenin and gliadin proteins --> The gluten network in dough can resemble muscle fibers

For the case of gelatin, describe how a gel is formed when the gelatin solution (gelatin mixed with water) cools.

When it cools the gelatin will become more of a solid (gel texture) and if it is melted again it will come back to a liquid - Think of chicken in the fridge and it gets hard and gel like and looks gross but when you heat it up it comes back to a liquid juice

Describe how starch granules can be used to thicken a sauce

When the starch granules in flour are heated, they swell with water. This swelling is called gelation The swollen starch granules increase the viscosity of the Sauce since they prevent the liquid in the sauce from moving around easily. In addition, starch molecules (amylose) begin leaking out of the starch granules. These molecules can further thicken the sauce. At high enough concentration, the amylose molecules can from a network that forms a gel --> Starch granules absorb water and swell (gelation). Starch molecules (amylose) leak out

Describe the molecular structure of xanthan gum. Also, explain why xanthan gum can be used as a thickening agent. Briefly explain the relationship between the concentration of xanthan gum and the viscosity.

Xanthan gum molecules are rod-like in shape and very stiff. - backbone is composed of glucose They are hydrophilic and bind well with water. Because of these properties, xanthan gum is an excellent thickening agent ... it really gets in the way of the water and even binds to it. As the concentration of xanthan gum increases, so does the viscosity of the liquid.

In food, microorganisms grow exponentially. What does that mean?

means that it keeps doubling - starts slow but it gets out of hand fast

The main three categories of food molecules are?

proteins, carbohydrates, and lipids

From a texture point of view, what element of real meat is challenging to duplicate in plant-based meat alternatives?

the texture of muscle fibers

Explain why the oil droplets in mayonnaise don't coalesce. In your explanation, use the words emulsifier, lecithin, hydrophobic and hydrophilic

Emulsifier wants to live on the boundary of the oil and the water= have to be both hydrophilic and phydophobic - The emulsifier has a part of that needs to be hydrophobic (wants to be in the oil) and the emulsifier also has a part that is hydrophilic (which wants to be in the water) ----- A typical emulsifier for mayonnaise is lecithin. Lecithin is composed of molecules that have both a hydrophobic section (the tail) and a hydrophilic section (the head). Thus, the lecithin molecules coat the surface of the oil droplets. The hydrophobic heads embed in the oil and the hydrophilic heads remain on the outside of the droplet in the water. This coating makes the oil droplets stable and prevents them from coalescingwithout these things the substance will end up coalescing which will make it liquidy and not have a nice thick consistancy (look at pic -- mod 7 question 3)

What is an enzyme? What role does it play in foods prepared with microorganisms?

Enzymes are a protein, that is used to break up molecules in the food that you are eating --> they take larger molecules (carbohydrates, proteins, lipids) and make them into smaller molecules (gas, ethanol, acids, etc.).

FAT TOM and why is it useful

Food, Acidity, Temperature, Time, Oxygen, Moisture - By varying these elements, one can slow the growth of microbes in food.

? Explain why scrambled eggs can be considered a hydrogel

For scrambled eggs, the continuous phase is the protein network, and the dispersed phase is water.

What are the main plant proteins used in Beyond Meat and Impossible Burger?

For the Impossible burger, it is soy protein. For beyond meats, it is pea protein