Pratice exams - Closed questions
43 important questions on Pratice exams - Closed questions
In a phase diagram, the eutectic point is the point indicating the theoretical chemical composition and temperature corresponding to the lowest melting point of a mixture of components. T/F
When freezing a product, if the dimensions of the product are large, the time of freezing scales with the square of the typical dimension of the product. T/F
Planck’s equation shows that when the dimensions of the product are small (L>> L2), heat transfer from the air towards the product is limiting and the time of freezing is linearly dependent on the size of the product. When the product is large (L<< L2), the heat conduction in the product is rate limiting, and then the freezing time mostly depends on the square of the size of the product
Lipids are a suitable material to make coatings against moisture migration. T/F
Lipids are hydrophobic and are thus suitable to prevent moisture migration.
There are two main categories of food emulsifiers: low molecular weight emulsifiers and amphiphilic biopolymers. T/F
A food product can have a heat capacity of 3 kJ/(kg K). T/F
The heat capacity of water is 4.2 kJ/(kg K), that of protein and fat 2.0 kJ/(kg K), and of carbohydrate 1.6 kJ/(kg K). Thus, a food product that is a mixture of these components can very well have a heat capacity of 3 kJ/(kg K).
Encapsulation by spray-drying generally leads to high loading of the encapsulated component. T/F
The typical loading of spray-dried encapsulates is 40 wt. % while the loading with fluid bed drying or drum
coating can be 60-90 wt. %.
The structure of a food product can be used to contribute to a healthy diet. T/F
True, think for example of W/O/W emulsions. In these emulsions part of the oil is replaced by water and
thus such a structure leads to a lower caloric intake while maintaining the desired mouth feel.
Membrane emulsification is more energy-efficient than conventional agitation techniques for emulsification. T/F
Membrane emulsification is a much milder technique than conventional emulsification methods based on agitation and thus is more energy efficient.
If you want to make a particle-stabilised water-in-oil emulsion, the particles should be preferentially
wetted by water. T/F
To form a water-in-oil emulsions the particles should preferentially be wetted by oil as stated by Bancroft’s
rule. To form an oil-in-water emulsion the particles should preferentially be wetted by water.
An elastomer does not contain crosslinks between (bio)-polymer chains. T/F
Elastomers are polymer chains that are slightly crosslinked and elastic.
A mixture of oil and water is suitable for making structured products because the oil and water are not miscible. T/F
A mixture of oil and water can be used to create an emulsion because they are not miscible and can thus be used to structure products.
In food products, homogeneous nucleation is often encountered. T/F
Homogeneous nucleation is only encountered in very pure systems. Food products are generally not such
The addition of a rigid dispersed phase makes the resulting material more brittle, compared to the same non-filled material. T/F
When the filler does not act as an active filler (i.e., with attractive interactions between the dispersed phase and the continuous phase), the filler will behave as voids and will weaken the material and is thus more brittle.
The state in which a product in practice is, is always an equilibrium state. T/F
Biopolymers can be divided in two categories: Proteins and phospholipids. T/F
The two biopolymer categories are proteins and carbohydrates.
See phase diagram below. A mixture indicated with arrow 1 will phase separate into two other mixtures indicated with arrows 2 and 3. The phase indicated with arrow 2 will become the phase with the largest volume (i.e., the volume fraction of phase 2 is larger than that of phase 3). T/F
The dotted line indicates when the volume fraction of the two phases was equal. Arrow 1 is left of this line, closer to arrow 3 which is therefore the phase with the largest volume.
In laminar flow conditions, the critical Weber number is independent of the viscosity ratio between the continuous and dispersed phases. T/F
The figure in the formularium shows the dependency of the critical Weber number on the viscosity ratio for the laminar flow conditions (i.e., simple shear flow and extensional flow).
The migration of permeant molecules through a barrier depends on the balance between the driving force for migration, and the friction force exerted by the barrier components. T/F
During transfer, molecules experience a force balance: on the one hand, they experience the driving force pulling towards the region with lower chemical potential or activity, and on the other hand they are slowed down by friction with the environment. This friction is dependent on the difference in velocity between the molecule and its environment, and on the density of the environment.
In an oil-in-water emulsion, the larger the emulsion droplets, the faster creaming will occur. T/F
According to Stokes law, gravitational separation is faster when the droplet radius is larger.
In most foods, the water activity increases linearly with the moisture content of a product. T/F
At low and intermediate moisture contents, a large variation in water activity is accompanied by a limited change in moisture content. For very wet products, the opposite is valid.
If a saturated salt solution with a water activity of 0.76 is placed in an environment with relative humidity of 85%, some water from the solution will evaporate. T/F
The water activity of the saturated salt solution is 0.76 and that of the environment 0.85. Thus, water will migrate from the environment to the salt solution until an equilibrium is reached.
In a mixture of two monomers, polymerisation of one monomer favours phase separation. T/F
According to the Flory-Huggins theory an increase in chain length will favour phase separation, so a
polymer with a large i value will be less likely to completely mix than a monomeric solution with i = 1.
Application of multiple layers of the same coating material is generally efficient to avoid defects in
coating films. T/F
When a layer has defects these defects can be closed by applying multiple layers, even though each
layer has defects.
Fermented sausages (which can be represented as cylinders with 3 cm diameter and 30 cm length) are stored in dry environment chambers for ripening, which leads to loss of moisture. Which of the following options could NOT substantially help to decrease the moisture loss during the ripening process?
- (a) Increasing the diameter of the sausages
- (b) Increasing the length of the sausages
- (c) Increasing the relative humidity of the chamber
- (d) Applying a lipid-based coating on the sausages
Moisture loss can be prevented by applying a lipid-based coating because this hydrophobic coating will prevent migration of hydrophilic compounds.
The chamber now has a low relative humidity and thus there is a high driving force for water migration. Increasing the relative humidity of the chamber will help to reduce the moisture loss during ripening.
The smallest dimension of this product is the diameter (diameter = 3 cm, length = 30 cm) and thus moisture loss can only be prevented by increasing the sausage diameter and not by increasing the length of the sausage.
A product in the glassy state:
- (a) May taste smooth and chewy
- (b) Is in thermodynamic equilibrium
- (c) Has some molecular mobility
- (d) May evolve to a crystalline phase if a plasticiser is added
A crystalline material is characterized by the fact that:
- (a) Molecules are regularly packed and have freedom to move
- (b) Molecules are immobile and regularly packed
- (c) Molecules are randomly oriented and have freedom to move
- (d) Molecules are immobile and randomly oriented
Crystallization is the formation of crystals: regions where molecules are arranged in a regular pattern, usually in three dimensions, and because of this arrangement the molecules are immobilized.
What is the main reason that SPC (soy protein concentrate) is a suitable raw material to make a meat analogue?
- (a) SPC contains two separate phases naturally, being a protein-rich phase and a fat phase
- (b) SPC contains two separate phases naturally, being a protein-rich phase and a carbohydrate-rich phase
- (c) SPC contains two different types of proteins that form two phases in the product
- (d) SPC can be considered as a homogeneous material
To make a layered fibrous structure that is suitable as a meat analogue a two component system is needed which can be protein-protein or protein-polysaccharide. Soy protein concentrate consists of soy protein isolate (proteins) and pectin (polysaccharides).
Micronutrient availability in vegetables and legumes is often increased by cooking. What is the main reason for this?
- (a) Cooking leads to crystallisation of pectin, which reduces the interaction between pectin and nutrients
- (b) Cooking denatures the proteins, thereby reducing the binding between proteins and nutrients
- (c) Cooking makes the product softer and therefore easier to digest
- (d) Cooking leads to opening of the cells, which leads to extraction of nutrients
Our body does not have the possibility to break down cell walls of vegetables and legumes effectively and without cooking much of the nutritional value remains undigested. When they are slowly heated under water, the pectin swells and is extracted by the water. The cell opens and becomes softer. As a result the vegetable becomes soft and may rupture and with that also nutrients become available during consumption.
Why is it difficult to replace sugar in food products?
- (a) Sugar has a more pronounced sweet taste compare with artificial sweeteners
- (b) Sugar forms a network in food products
- (c) Sugar addition leads to a reduced viscosity of the product
- (d) Sugar is less sweet than artificial sweeteners
The Smucker’s Uncrustables are a popular snack in the US: these are soft bread bites filled with peanut butter and grape jelly. You are asked to expand the Smucker’s Uncrustables portfolio by developing new recipes. Which of the following changes could compromise the product quality, due to undesirable transfer of components during storage?
- (a) Replacing peanut butter by low-fat pectin-based paste
- (b) Replacing grape jelly by concentrated apple puree
- (c) Replacing soft bread by soy-based genoise (i.e., sort of sponge cake)
- (d) Replacing peanut butter by chocolate
The peanut butter now acts as a barrier against moisture transfer from the grape jelly to the bread because of the high lipid content of peanut butter. If you would replace peanut butter by a low-fat alternative you will lose this moisture barrier and the bread will become moist.
In oil-in-water emulsions, droplet coalescence is associated with:
- (a) A decrease in the creaming/sedimentation rate
- (b) A decrease in droplet size
- (c) A sharp increase in the emulsion’s viscosity
- (d) A merging of the lipid material of two droplets
You have to develop an ice cream flavoured with an alcoholic beverage:
- (a) It may result in a grainy texture of the ice cream, because ice crystal growth will be favoured
- (b) The potential effect on texture could be counteracted by replacing sucrose with the same
- mass of a sugar with lower molecular weight
- (c) It may result in a too hard ice cream, because alcohol crystals will be formed
- (d) It may result in a too soft ice cream, because alcohol will depress the freezing point of water
Addition of alcohol to the ice cream mix will lead to freezing point depression because the freeze point of alcohol is much lower than that of the mix without alcohol. So, at the same temperature as before you will have less ice crystals and thus a softer ice cream.
Bread baking is a very old process. Which of the following statements is correct?
- (a) Dough consistency is determined by gluten, while consistency of bread is determined by starch
- (b) Both dough and bread consistencies are determined by gluten
- (c) Both dough and bread consistencies are determined by starch
- (d) Dough consistency is determined by starch, while consistency of bread is determined by
Consistency of dough originates from the gluten network that is very flexible and forms nice closed films around the air bubbles created by the yeasts. Upon heating, starch gelatinizes and retrogrades during and after baking by which a strong gel or rubber is formed and which determines the consistency of the bread.
The microstructure is defined as the structure with a typical length scale smaller than 1 μm. The mesostructure is defined as the structure with a length ranging from 1 μm to 1 mm. The macrostructure relates to structures larger than 1 mm. Which of the following statements is true?
- (a) Self-assembly is not important when considering microstructures
- (b) The macrostructure cannot be altered by deformation
- (c) Through deformation, structures can be altered at all length scales
- (d) Mesostructures are influenced by both deformation and ingredient properties
Ingredient properties and self-assembly occur especially in microstructures, but also in mesostructures. Deformation cannot change microstructures, however it can affect meso- and macrostructures.
If we freeze a sugar solution below the liquidus, at a given temperature:
- (a) The concentration of the sugar solution that remains liquid is lower compared to the initial concentration
- (b) The higher the initial sugar concentration, the smaller the ice crystals will be
- (c) The amount of ice that will form is independent of the molecular weight of the sugar
- (d) The higher the initial sugar concentration, the lower the amount of ice that will form
When a solution is frozen below the liquidus, the water will change to ice and the sugar to glass. Thus, the higher the initial sugar concentration, the less water that will be present and thus also less ice will form upon freezing
Which of the following devices would you recommend to homogenise milk (i.e., disrupting the native fat globules, which are a few micron large, into sub-micron droplets)?
- (a) Premix emulsification column
- (b) High pressure homogeniser
- (c) Colloid mill
- (d) Batch mixer
The smallest droplets can be obtained with the high pressure homogeniser and is thus the preferred device to homogenise milk.
The main difference between a phase and state diagram is:
- (a) Phase diagrams contains more information than a state diagram
- (b) A state diagram includes all information given in a phase diagram plus extra information about kinetic effects
- (c) A state diagram can only be used for a limited number of ingredients
- (d) The behavior of fat can be included in the phase diagram, but not in the state diagram
Phase diagrams describe the phase behaviour expected at thermodynamic equilibrium. State diagrams contain also non-equilibrium conditions and can be used for multiple ingredients.
Structuring can be used to alter the properties of a food product. Which properties are NOT influenced by structure?
(a) The viscosity
(b) The diffusivity of a component in water
(c) The heat capacity
(d) The heat conductivity
Viscosity, heat conductivity, and diffusivity are influenced by structure. The heat capacity of a product is not influenced by structure.
Skin creams are usually oil-in-water emulsions that behave as soft solids. Body milk is also an oil-in- water emulsion, but it is liquid. How could you convert a body milk into a skin cream?
(a) By reducing the concentration of thickening agents in the continuous phase
(b) By increasing the continuous phase fraction of the product
(c) By increasing the amount of oil in the product
(d) By using a surfactant that induces stronger electrostatic repulsion between the oil droplets, such as sodium dodecylsulfate
According to Einstein’s equation (η=η0(1+2.5φ)), the viscosity of a dispersion depends on the viscosity of the continuous phase and the dispersed phase volume fraction. Body milk will convert to a skin cream when the dispersed phase volume fraction is increased sufficiently, resulting in an increased total product viscosity until it reaches skin cream viscosity.
When making a composite film with two materials of very different permeabilities, the structure that will be the most efficient to prevent permeant migration is:
(a) A structure in series: layers of both materials are aligned perpendicular to the direction of permeation
(b) A parallel structure: layers of both materials are aligned parallel to the direction of permeation
(c) A dispersion: one of the phases is dispersed in the other one
(d) No difference will be seen depending on the structure: what matters is only the volume
fraction of both materials in the composite film
A layered structure (series model) is most effective to suppress permeation/diffusion of water. The figure below indicates the effect of the structure on the permeability of a coating
When freezing vegetables with high water content (e.g., green beans):
(a) Ice crystals can damage the cell walls, leading to loss of turgor upon thawing
(b) Slow freezing should be applied, such that small ice crystals are formed
(c) Freezing too fast can lead to undesirable serum loss upon thawing
(d) Ice crystals should preferably form between the fibrillar cells
Ice crystals can damage the cell walls and lead to a loss of turgor upon thawing. Cell wall damage can be limited when small crystals are formed instead of large ones. These small crystals can be obtained by fast freezing.
Which components can be used to soften a product that consists of a starch-based matrix?
(a) protein, glycerol and oil
(b) oil, glucose and glycerol
(c) water, glucose and oil
(d) water, glycerol and glucose
Plasticizers are low molecular weight components such as water, glycerol, and glucose.
In the process of making a cheese analogue, the product is made using a twin screw extruder to which a long slit-shaped, cooling die is attached. What is the main purpose of the cooling die in case of making a cheese analogue? You may assume that the product structure is isotropic.
(a) To make oil droplets smaller due to the shear flow in the die
(b) To create a fibrous structure
(c) To increase the viscosity of the protein phase to entrap already formed oil droplets
(d) To get a homogeneous product
Upon cooling in the die the structure that was formed inside the extruder will set, resulting in a set protein matrix that encloses oil droplets.
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