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What are some food deteriorative factors?
- Various forms of microbial growth
- Enzymatic reactions
- Lipid oxidation
- Hydrolytic Reactions
- Non-enzymatic browning
What relation do most reactions have with watr activity?
Most reactions are exponential functions of water activity- implies that even a slight reduction of water activity will ahve a significant effect in reducint the rate of a reaction
What is the break point for many reactions?
What are intermediate moisture foods considered?
What is the water activity of dried/dehydrated products?
Aw of <0.6
What does the water activity have to be in order to obtain a minimum for most deteriorative reactions?
The Aw has to be reduced to about 0.3-0.4 to obtain a minimum for most deteriorative reactions
Is there a value/region where all reactions are stopped?
No, however the optimum apears to be aruond 0.3-0.4
What is the hurdle concept?
The use of miltiple hurdles or barriers (water activity, pH, ionic strength, modification of atmosphere) which can be bundled to produce synergistic effects
What are the 2 general categories of food in terms of gross structure?
- Intact edible tissues (complex/natural)
- Food Dispersions (usually man-made)
What are intace edible tissues?
This classification refers to natural biological systems- plant and animal tissues that are stucturally very complex
What are food dispersions?
- Still complex systems
- A system consisting of one or more discontinuous phases (dispersed phase) in a continuous phase
What is an example of a food dispersion?
Emulsion is a man-made dispersion
What is the most common man made food dispersion?
What is a complex dispersion?
Tomato juice- a disrupted tissues system
What is an example of a biphasic dispersion?
What is an example of a multiphase dispersion?
Can macromolecules produce tru solutions?
Macromolecules ca produce true solutions, however, under certain conditions (ie small change in pH or higher concentrations) they can become colloidal
What are the three classifications of solutions?
- True solutions
- Colloidal dispersions
What are the characteristics of a true solution?
- The molecules and ions are present in their lowest subdivision
- The particles are <0.1 microm in diameter
- The solution formed is transparent
- Solution has high osmotic pressure
- Solution passes through parchment membranes withouth separation
What are the characteristics of colloidal dispersions?
If the material does not pass through a parchment membrane but also does not settle under the force of gravity
What is the particle size in colloidal dispersions?
How does the osmotic pressure of a colloidal solution related to that of a true solution?
Colloidal solutions have significantly reduced osmotic pressure than true solutions
Do colloids settle out of solution?
True colloids do not settle out of solution but may aggregate or cross0link to form gels- a common charactersitic of proteins and polysaccharides or their complexes
What is a suspension?
The suspended material can be filtered out and/or will settle out of solution by gravity given enough time
What is the particle size of suspensions?
Particles >1 microM
What color are suspensions?
Describe the osmotic pressure of suspensions?
Suspensions show negligible or have no measurable osmotic pressure
What is an example of a suspesion?
Ungelatinized starch granules will form a suspension when stirred, but will soon settle out
What kind of system is a colloids or suspensions considered?
Colloids and suspensions are considered to be discontinuous biphasic systems
How does the conversion of a true molecular solution to a colloidal solution occur?
The conversion of a true molecular solution to a colloidal solution often occurs when macromolecules are dispersed in water
What are the sequential steps in changing from a true molecular solution to a suspension?
- Initially macromolecules repel because of similar charge- thus a molecular solution
- Change pH- supress charge--> aggregation- charge re-accumulates --> colloidal
- Change pH- further suppress charge- associate- molecular weight of aggregate too high to staty in solution --> suspension- precipitation
In the case of starch and proteins, which is a common mechanism for aggregation?
How can hydrophobic attraction affect solutions?
Hydophobic attraction can also be a menas of large polymers associating to form colloids (casein micelles) and/or gels- or a combination of multiple forces
How can the associations in solution result in problems?
- These associating fores can result in major practical problems, especially in terms of organic waste strems from food processing operations
- A classic example is waste water from potato peeling operations
- Here, the waste stream will contain some protein, soluble starch, pectin, pigments, sugars and cellular debris- molecular associations take place which result in a colloidal dispersion which makes water treatment very diccigult as the dispersion will not settle out
How does one control biological oxygen demand (BOD)?
- A common method of control is to convert these colloidal solutions into suspensions
- This is usually done by addint coagulating salts to modify the charge of the colloids to facilitate
- The formation of larger groupings of molecules (Flocs) to produce a suspension which can settle out
What does flocculation do?
Flocculation alows organic material to be separated from the waste stream- reducing BOD and pollution
What is another way of forming colloidal solutions?
Another means of forming colloidal solutions is through the forced interaction of molecular systems having strong hydrophilic and hydrophobic character
What happens at the interface of water and air?
- At the interface, hydrophilic water comes into forced contact with hydrophobic air
- This forces water into a structured state in such a way as to minimize the free energy associated with this forced interaction
What results from the surface of water having a different arrangement than the bulk solution?
Why are oil in water dispersion so unstable?
- Hydrophilic-hydrophobic repulsion (most important)
- Density differences between the phases
How does one stabilize oil-water dispersion?
One needs to minimize or mediate the hydrphobic-hydrophilic repulsive forces when such molecules find themselves in a 'hostile' environement
What happens when emulsifiers are dissolved in water?
- They initally appear to 'dissolve' or go into solution, but are in fact not uniformly distributed as sguar dissolved in water would be
- If one could analyze their molecular distribution in solution, one would find that initially, most of the molecules are found near the solution surface
Why are most emulsifiers found near the solution surface when added to water?
- This is due to the fact that the air-water itnerface is the location of the lowest free energy for the surface active compounds to locate themselves
- The reason for this is that the hydrophobic portion of these molecules are 'unhappy' in a strongly hydrophilic environment such as water
- hence, they orient themselves toward any less hydrophilic environment, usually hdyrophobic air, while the hydrophilic ends will orient themseloves toward the bulk of water
What is the net effect of the orientation of emulsifiers at the surface of solution?
The net effect of this orientation is a reduction in surface tension of the water- iself a structured form of water that is quite different than bulk water
What happens once the surface is completely saturated with surfactant and more is added?
Once the surface is completely saturated with surfactant and more is added, new strctures termed micelles are formed in the bulk of the solution
What are micelles?
These are colloidal particles produced by itner-molecular associations between the hydrophobic tails as well as the hydophilic heads of the molcules
Why do micelles form spontaneously?
Micelles orm spontaneously to reduce the free energy in solution after the air/water interface has been saturated
What are the types of dispersions?
- Liquid in liquid
- Gas in liquid
- Liquid in a (plastic) solid
- Gas in a solid- solid foam
What is an example of a liquid in a liquid dispersion?
Emulsions- salad dressing
What is an example of a gas in liquid dispersion?
Foam- Meringue, cake, bread
What is an example of a liquid in solid dispersion?
Solid emulsion- butter/margarine
What is an example of a gas in solid dispersion?
Solid foam- Aero chocolate bar
What are the most common food dispersions?
Emulsions and foams
What type of tension is present in an emulsion?
What is the different between interfacial tension and surface tension?
Interfacial tension can seperate, surface tension cannot
What is coalescence?
Attraction of the dispersed phases
What is the key seperation factor of an emulsion?
The key speration factor is the interfacial tension even though the interfacial tension between oil and water is quite a bit lower than that between air and water
How are emulsions stabilized?
Emulsions can be stabilized if the interfacial tension between the dispersed phases is <10 Dynes/cm2
How is a reduction in interfacial tension achieved?
Reduction in interfacial tension can be achieved using surface active molecules
What happens to the surface tension after micelle formation?
After micelle formation, the surface tension stabilizes and does not change much
Why make emulsions?
- It is a method for incorporating oil into a food system without impartin an oil sensation
- Allows the enhancement of viscosity as well as deelopment of a unique texture (usually plastic-like properties)
- It changes the optical characteristics of the product
What affects the opacity of an emulsion?
The opacity of an emulsion is a function of droplet size
What affects the droplet size of an emulsion?
The droplet size formed is a function of the energy put into the system
How is engine oil emulsified?
Contains a base additive
What are emulsifiers?
Characterized by the amphipathic nature- having both hydrophobic and hydrophilic groups
What are the two basic categories of emulsifiers?
What are the three groups of ionic emulsifiers?
- Anionic (-)
- Amphoteric (+/-)
- Cationic (+)
What are non ionic emulsifiers?
- These do not carry a charge- independent of pH
- They are predominant emulsifiers used in food systems
- Their practical use is assisted by the use of the HLB system
What is the HLB system?
- Hydrophile-Lipophile balance
- The HLB system is a systematic approach to aid one in deasling with non-ionic emulsifiers- although the system can be applicable to some ionic emulsifiers
What does the HLB value represent?
The HLB value represents the weight percentages of hydrophilic groups in an emulsifier molecule divided by 5
What does a low HLB signify?
What does a high HLB signify?
What does an HLB of 0-3 represent?
Antifoaming agent (mineral oil)
What does an HLB of 4-6 represent?
Hydrophobic emulsifier- promotes water in oil emulsions
What does an HLB of 7-9 represent?
Intermediate- can produce either W/O or O/W emulsions- also a goof wetting agent
What does an HLB of 8-18 represent?
Hydrophilic emulsifiers- promote oil in water emulsions (O/W)
Why are two or more emulsifiers often blended together?
To produce a more stable emulsion
Based on a target HLB, how can the respective amounts of any two emulsifiers required be calculated?
- Where X=target HLB
What is a stability assessement?
Testing the solution under stress conditions such as high temperature, freezing, agitation, etc
What are some common non-ionic emulsifiers?
- Those based on glycerol esters and their derivatives
- Highly lipophilic with HLB values range from 3-10
- Mono, Di-glycerides and non charged derivatives such as acetylated monoglycerides
What is our extimated monoglyceride consumption?
Monoglyceride consumption is estimated to be ~250 million pounds/annum
How are monoglycerides/diglycerides produced?
Production of monogycerides/diglycerides by interesterification and their purifacation by fractional distillation
How are acetylated monoglycerides formed?
Acetylated monoglycerides are formed by reacting with monoglyceride hydrosyls with acetic acid
How are polyoxyethylene monoglycerides produced?
Polyoxyethylene monoglycerides are another group produced by treating monoglycerides with ethylene oxide
How are sorbitan derivatives made?
Made up of a sugar alcohol esterified to fatty acid
How are polyglycerols formed?
Glycerol itself can be polymerized to form polyglygerol by the reaction of glycerol with an alkaline catalyst
What are sugar esters?
- Esterification of sucrose is also possible to produce emulsifiers
- Can produce Mono-, Di-, and Tri- esters of sucrose with fatty acids
- Usually obtain emulsifiers with HLB values randing from 7-13
What was a by-product of sugar ester research?
What is olestra?
A non-caloric fat substitute
Why is olestra not suitable as an emulsifier?
What is the most important category of emulsifiers for food applications and why?
The non-ionic emulsifiers are the most important emulsifier category for food applications because they are insensitive to pH and ionic strength
What is an example of anionic emulsifiers?
- Monoglyceride derivatives
- Most important- succinyl monoglyceride (SMG)
How is stabilization achieved in the case of all anionic emulsifiers?
- Stabilization in the case of all anionic emulsifiers is achieved by electrostatic repulsion
- Hence all anionic emulsifiers are sensitive to anything that can affect the charge (pH and ionic strength)
What is an example of a non-glycerol based anionic emulsifier?
What is an advantage of stearoyl lactates as an anionic emulsifier?
Forms very stable oil in water emulsions which are very resistant to freeze thaw cycles and therefor good for frozen foods
When is sodium lauryl sulfate used as an emulsifier?
Used as an anionic emulsifier- its chief use is as a whipping aid for egg white
How is sodium lauryl sulfate produced?
Produced by the reduction of coconut oil fatty acids (~C12) to their alcohols and sulfonating the alcohol produced
Why are cationic emulsifiers not used in food emulsions?
Because they are toxic
How does the food industry use cationic emulsifiers?
Use as cleaning agents as they are excellent surfactants and have strong antibacterial activity
What is a typical industrial cationic emulsifier?
Quaternary ammonium compounds
What is an example of an amphoteric emulsifier?
How is lecithin produced?
Lecithin is commonly produced as a by-product from soybean, corn, safflower oil processing
What other compounds are often mixed in with the lecithin?
Usually a complex mixture which may contains ome phosphatidyl inositol which is an anionic emulsifier
How are lecithins bleached?
Often treated with hydrogen peroxide and/or benzoyl peroxide to bleach the product
Why is lecithin bleached?
Bleaching (oxidation) introduces hydroxyl groups at the sites of fatty acid unsaturation to produce hydrosylated lecithin
Why is hydrosylated lecithin better than lecithin?
It is more dispersible in cold water and a more effective emulsifier
When are proteins used as emulsifiers?
Forming sausage emulsions- forming a protein film around the oil droplets and preventing the coalescence of the fat
Why are proteins also used as surfactants?
Have good foam forming and setting properties (egg albumin)
What are hydrocolloids?
Hydrocolloids are often used in conjunction with emulsifiers- generally polysaccharide such as starch and gums
What is the major contribution of hydrocolloids?
The major contribution lies in the enhancement of the viscosity of the hydrophilic phase (usually the continuous phase)
Why is increasing the viscosity of the hydrophilic phase important?
Increasing the viscosity of the continuous phase makes it more difficult for the oil droplets in an emulsion to coalesce
How are gums used as stabilizing agents?
- Gums can also form films around oil emulsion droplets- a role played by gyms suhc as gum arabic and gum ghatti
- This role is especially important in encapsulating essential oils
Why are conditioning agents used in bread?
- In bread- conditioners can have the ability to interact with proteins such as gluten to improve the cohesive and film forming strength
- Can improve tollerance to mixing and allow incorporation of non-whate proteins
- Result in improved loaf volume, crumb texture and greater resistance to staling
How do emulsifiers act as ani-staling agents?
- Emulsifiers (especially saturated monoglycerides) will complex with starch to slow retrogradation
- Fits into the core of the amylose helix (somewhat hydrophobic)
- Emulsifier-helix complex starch retarde retrogradation by interfereing with hydrogen bonding