Food Chemistry Flashcards
What is water activity
Aw is the water activity is a term that relates to the ability of a microbe to grow in a particular environment
Moisture sorption isotherm
Moisture sorption isotherm is used to determine relationship between water content & water activity
Water-holding capacity
Water-holding capacity (WHC) results from the physical entrapment of water within a food matrix that restrict flow but no other physical properties of water
How are carbohydrates bonded
Glycosylic bonds
Retrogradation
Retrogradation is the crystallization of starch molecules such that they begin to separate from other molecules present in the product
How are digestible and non-digestible carbohydrates differentiated
Recognition
Is glucose an aldehyde or ketone
aldehyde
What are reducing sugars
Carbohydrates that are aldehydes are reducing sugars and can react with amino group of protein / amino acids i.e. Maillard reaction
Why are carbohydrates soluble
Prescence of oh group
What is tollens reagent used for
to identify reducing sugars/ aldehydes
What are lipids
Soluble in organic solvents but not water
3 main groups of lipids
triglycerides, sterols, phospholipids
Triglycerides
3 fatty acids side chain
Phospholipids
1 polar head with 2 fatty acid chains
Sterols
ring structure but does not contain fatty acids
What are Saturated fatty acids
They contain no c-c double bonds
What can lipids act as
antioxidants & pro-vitamins
What are trans fatty acids at room temperature
Solid
Saturated fatty acids are _ are room temperature
solid
Lipid hydrolysis
Lipid hydrolysis involves separation of a fatty acid from the glycerol backbone or phospholipid
I produces a free fatty acid & glycerol
If the free fatty acid is short-chained, it will be volatile and contribute to the odor of the food (Hydrolytic rancidity)
Lipid oxidation
Lipid oxidation is a reaction of lipids with oxygen that proceeds through a free radical mechanism
Free radical consist of carbon atom with an extra electron resulting from removal of hydrogen atom allowing oxygen to attach to the free electron resulting in lipid hydroperoxide
It can generate volatile compounds that have an off-flavor
Saturated fatty acids are unable to undergo lipid peroxidation due to lack of double bonds and they tend to be more stable
What do antioxidants do
Antioxidants inhibit or retard oxidation through one or more mechanisms
Why does trans fatty acids have better van der Waals interactions
Saturated fatty acids tend to have stronger van der Waals interactions with other saturated fatty acids because they can stack together and form a repeating structure, very similar to a crystalline structure
Why dies cis fatty acids have weaker van der waals interactions
Cis double bonds form a kink in fatty acids which interfere with stacking & interactions causing weaker Van Der Walls interactions causing it to be liquid at room temperature
What can phospholipids be used as
emulsifiers in food and water
What are proteins
sequence of amino acids linked by peptide bonds
Where does the hydrophilic side chain fold to
Hydrophilic side chain tend to be on the surface exposed to aqueous environment
Where does the hydrophobic side chain fold to
Hydrophobic side chain fold towards the core of the protein
What are enzymes
Proteins which catalyze chemical reactions
What does blanching do to enzymes
Blanching can denature enzymes to prevent enzymatic reactions in fruits & vegetables
What does heating do to enzymes
Heating will cause the enzyme to unfold and disrupt its structure (denaturation)
Cellular compartmentation
Cellular compartmentation is to control enzyme reaction in plant & animal tissue
What are enzymes affected by
It is affected by pH, moisture content of food, storage temperature, presence of oxygen & carbon dioxide & light
What are alkaloids
Alkaloids are naturally occurring alkaline organic compounds which contain nitrogen atom(s) in their structures
What do sequestrants or chelating agent do
Sequestrants or chelating agents bind metal ions preventing them from oxidizing fats
To participate in crosslinking what is needed
Multivalent cations
What are the properties of whey protein
Whey proteins are sensitive to heat and will unfold to expose their hydrophobic surfaces which will interact with each other to form a gel
What are Cassin proteins
Cassin proteins are heat stable but will coagulate in acidic pH as casein proteins are negatively charged. In acidic pH, the proteins will become neutral & coagulate due to hydrophobic interaction
How is a gel formed
A gel is formed when polymers interact and form cross link
What is a sol
a sol is when a solid is dispersed in liquid
what is a gel
a gel is when a solid is dispersed in liquid
What is a emulsion
an emulsion is when liquid is dispersed in liquid
What is a foam
a foam is when air is dispersed in liquid
What is a colloidal system
Particles dispersed in a medium that are suspended that is large enough to scatter light.
What do carbohydrates do in a colloidal system
They are hydrolysed and interact with water. When cooled it will form a gel or a vicious paste
What does high HLB indicate
The emulsifier is more soluble in water in oil emulsion
What does cartorenoid do
It will bound to protein to give food its pigment
What happens in the Maillard reaction
pyrazine compounds is formed, It contributes to the roasted flavor & aroma of foods
what is enzymatic browning catalysed by the enzyme polyphenol oxidase
This enzyme catalyses the oxidation and polymerisation of polyphenols present in fruits and vegetables
Are naturally occurring pigments more or less shelf stable
Less shelf stable
How is spoilage prevented
Antioxidants are added to oil to prevent spoilage
Oxidation is catalyzed by transition metals, adding sequestrants can retard oxidation
Additives that slow down or prevent growth of microorganisms are preservative
What are natural additives
Additives derived from natural food sources
