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Week 4: Proteins- Gelation & Emulsification - Coggle Diagram
Week 4: Proteins-
Gelation & Emulsification
Primary Sources Of PROTEIN :check:
Milk
2 types
Whey proteins
Properties
Native form stable at isoelectric point (pH 4.6)
Heat-sensitive
Exists in 4 major forms
Native: 10% protein
Concentrate: 34 – 89% protein
Isolate: 90 – 92% protein
Hydrolysate – partially hydrolysed
Caseins
Exists as:
Acid casein – the form obtained directly from extraction from milk
Calcium/Sodium caseinate – water soluble casein and of the lowest quality
Rennet casein – obtained when milk is treated with Rennet enzyme
Micellar casein – the purest form of casein
Properties
Good emulsifiers
Relatively heat stable
Insoluble at their isoelectric point (~pH 4.6)
Sensitive to calcium, so it needs to be stabilized by κ-carrageenan (stabiliser)
Exists in 2 major forms:
Concentrate: 40 – 90% protein
Isolate: min 90% protein
Egg
a. Albumin (white)
gels at lower temperatures than other proteins
b. Lipoproteins (Yolk)
serve as good emulsifiers (used in salad dressings)
Soy protein
Functionality can be modified by different processing conditions
Properties
Good/fair emulsifiers
Insoluble at their isoelectric point (~pH 4.6)
Sensitive to calcium, so it needs to be stabilized by κ-carrageenan
Unstable to heat
Used in structured meat analogs and extruded product
Wheat gluten
Gelatin
Functions :check:
Gelation: A gel is a continuous network in which polymeric molecules cross-link each other within liquid medium/solvent.
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In food system:
the liquid medium/solvent is water.
the polymeric molecules are the solute eg. protein
Stages in heat-induced gelation
Protein unfolding
Water binding
Protein-protein interactions
Water immobilization
During Heating, the 3D protein network unfolds.
During Cooling, the proteins start to form 3D network, will eventually will form a gel.
Factors Affecting Gel Formation
Protein concentration: Higher Protein → Higher gel strength
Temperature: required to unfold Protein, which allows interaction of water and Protein and gel to be formed
Too high temperature may denature Protein, which may cause Gel not to formed.
pH: affects the strength and nature of the gel
In alkaline condition (↑ pH values), gels formed are more elastic, transparent & greater gel strengths.
In acidic condition (↓ pH values), gels formed are rather soft, opaque & appear like coagulated milk.
Calcium concentration
When low amount of Calcium is present, weak gel is formed.
When high amount of Calcium is present, heating causes protein aggregation to occur before protein unfolding and a 3D network could not be formed.
Chelating Calcium ion with Phosphate or other chelating agent prevents protein aggregation, hence allowing proteins to unfold, binding water and so on, which eventually will actually produce stronger gel.
Free sulfhydryl concentration
Cystine, an amino acid in protein, contains Sulfhydryl group (or thiol) ie. Sulfur bonded to Hydrogen atom
When thiol groups come together, they will form disulfide bond, serving as effective crosslinks in protein gels.
In WPC, increases in sulfhydryl groups increase gel strength.
WPC = Whey Protein Concentrate
Emulsions: form and stabilize an emulsion, a protein must:
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Diffuse to the interface
Rate of diffusion affected by
Salts – it reduces the rate due to osmotic pressure
Viscosity - higher viscosity, slower the rate
Unfold
Expose hydrophobic groups
Interact with lipid
Effect of Temperature on Emulsions
Emulsion formation is favoured around 60oC due to lower viscosity
Freezing can cause physical damage to the interface, eg. dried surface will hinder diffusion, thus preventing the interaction of protein and lipid.
Lower temperature decreases energy barrier to lipid-water interactions
Applications Of Proteins Functions :check:
For Cakes: Final structure is due to heat gelation of proteins (from egg white & gluten)
Presence of sugar in cakes increases the gelation temperature of gluten, therefore higher baking temperature may be required.
Egg white is used in cakes because of its lower gelation temperature than gluten, which helps to build/retain the structure of the cake during baking process preventing it to collapse before the proteins in gluten gels in the higher temperature.
For Imitation Dairy Products (Coffee Whitener): Usually use sodium caseinate
possess the following properties:
A good emulsifier
Low flavor impact
Heat stable protein
Able to minimize effect of Calcium as weak gel is required to be formed to mimic creaminess. Phosphate is added in this product to chelate calcium, so that gel can be formed.
for Reformed & Water Added Ham;Soya protein or other plant protein (eg.pea) is best choice
Gives equal nutritional quality to meat proteins by increasing the protein content
Gives good gelling properties which provides the texture of the meat products
Improves water binding, hence increasing moistness especially when lean meat is used.
Gives a final product with good sliceability (elastic)
Requirements For High Protein Beverages: Whey protein isolate/concentrate or soy protein
High protein
Need to be acid and heat stable
Low flavour impact
Meet nutritional requirements for good muscle rebuilding for sports beverages
Requirements For Nutrition Bars: generally soy protein isolate, whey protein and caseinate are used in various combinations.
Produce shelf life is usually 1 year, therefore must have good flavour stability and ability to retain softness over 1 year too.
Good nutrition/source of protein.
Functional Requirements Of Food Protein Ingredients :green_cross:
Functionality Of Common Food Proteins :green_cross:
Protein Requirements For Application In Different Food Products
Choosing A Protein :check:
Functions required or to avoid in the product?
Cost to meet budget of the product.
Flavor: contribute flavour / NO flavor to the product
Calcium content - too much calcium prevent gel forming.
pH - select one that is stable under the desired product’s pH.
Amount of heat - Processing temperature affects protein’s functionality or stability
Allergenic - Protein is a common source of allergenic material; hence choose a suitable one for the target market and regulatory requirement.
