Unit 1- Fining, Ion ex, tartrates Flashcards
(32 cards)
Define a colloidal state
When a substance is dispersed in another in such a degree of subdivision as to possess properties different from those of the substances in true solution.
Most beverages we consume are colloids. e.g chocolate milk has a liquid continuous phase and a solid dispersed phase.
What is the size range of particles in colloids and what is the significance of size to the Brownian motion of the colloid?
-10-10 000 angstroms (1 nm to 1 μm). -
- Particles are big enough to prevent the formation of a true solution and small enough to be kept in Brownian motion.
- Brownian motion is the random motion of particles in a solution that stops them from settling out due to gravity.
What is a basic property of colloids relating to turbidity and particle size?
-Ability to scatter light and look turbid is proportional to the particle size.
With colloidal products, what are the 2 options available for producing a stable product?
- Keep the dispersed phase suspended for long enough for it to be consumed, e.g. whole milk homogenisation.
- Remove the suspended dispersion quickly through filtration, clarification or fining.
What are 4 properties of Colloids?
- Scatter light
- Turbidity is measured in NTU.
- Particle size 1 nm to 1 μm
- Particles do not readily settle out of solution.
What is the major cause of hazes that occur after clarification in beverages?
interactions between proteins and polyphenols that form a colloidal suspension.
What are the forces that can lead to aggregation of colloidal species?
What is the result of aggregation?
- Electrostatic interactions
- Hydrogen bonding
- Hydrophobic interactions
- Van der Waals attraction
Aggregation leads to destabilisation in most cases as particles become big enough to settle out of the continuous phase.
What are the two mechanisms of destabilisation of a colloidal substance?
- Flocculation
- Coalescence
Describe flocculation.
Individual particles touch and associate to form clusters or stringy extended forms.
Can be reversible depending on the cause of flocculation. e.g. pH reversal for ionic interactions, change of solution polarity for hydrophobic interactions/
Describe Coalescence.
Emulsified oil droplets encounter each other and lose their identity to form bigger droplets. Not reversible. aggregate at a rate controlled by 1st order kinetics (constant proportion formed with time).
What is the cause of haze in wine?
- aggregation of components in the beverage that form a colloid.
- Often result of a protein-polyphenol interaction. hydrogen bonding or hydrophobic interactions, Therefore are reversible.
- can be the result of microbial activity that causes precipitation of carbohydrates or salts.
What makes a protein likely to be haze active?
-Proline-rich polypeptides. Gives an open fibrous structure due to the lack of H (partially positive) bonded to the amino group Nitrogen. This partially positive Hydrogen can hydrogen bond with the slightly negative carbonyl group of phenolics.
What makes a Polyphenol likely to be haze active?
-Dimers and higher polymers. e.g. catechin-epicatechin dimer. Monomers and simple phenols have no haze forming activity.
Do all haze active constituents have to be removed to make the beverage stable?
No. There is an optimum ratio in every system, as long as the active components are at a higher or lower level then no haze forms. Therefore adequate reductions suffice.
What processing conditions affect the onset and extent of haze?
pH, temperature, ethanol concentration.
Why is the proline rich nature of gelatin and isinglass significant to its ability to bind phenolics?
Does not have a carbonyl group so cannot hydrogen bond with other sites on the peptide chain. This leads to an open and fibrous structure that has many sites that are open to phenol binding.
What is the interaction that is responsible for the effectiveness of protein fining?
Hydrogen bonding
Between hydrogen atom of the phenolic group and the oxygen of the amide group in protein.
What are 3 possible benefits of protein fining?
- wine clarification
- colour and flavour improvement by the removal of unwanted phenolics.
- prevention of wine deterioration by removal of phenolics that may contribute to browning or interact with proteins to cause hazes.
Explain why the phenolic hydrogen is an effective participant in hydrogen bonding
The negative charge on oxygen can delocalise. this leaves the Hydrogen slightly positive. The oxygen is already very electronegative but this delocalisation further increases the electron deficiency of hydrogen.
Why would we add tartaric acid to a gelatin solution before adding to wine?
At a low pH below the isoelectric point, the protein will be as protonated as possible, making it positive in charge and more able to interact with the negatively charged phenolic Oxygen.
Why is the proline-rich nature of gelatin and isinglass relevant to its ability to bind phenolics?
In proline, the amide nitrogen lacks a hydrogen, so will not be involved in hydrogen bonding and therefore will not bind to other parts of the polypeptide chain, giving an open filamentous structure that has many exposed sites for hydrogen bonding with phenolic compounds.
What are the 2 processes that are important for the removal of phenolic material with proteinaceous fining agents?
- hydrogen-bonded complex between polypeptide and phenolic compounds.
- flocculation and precipitation of the polypeptide-phenolic complex.
Why might tannin be added to a white wine of low tannin before fining with gelatin?
To ensure complete precipitation of any added protein that may cause haze further down the track.
What fining agents are soluble, semi-soluble and insoluble?
Soluble- gelatin, isisglass, albumin/egg white.
Semi-soluble- skim milk
Innsoluble- casein. PVPP
