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Food 2130

Molecules controlling sensory properties

What's the common name applied to the group of reactions that occur when sugars are exposed to high temperatures? Caramelisation
Why does caramelisation differ from other browning reactions? No amino groups are used
What do the reactions of caramelisation form? Volatiles (caramel aroma) and Brown - coloured products
An example of caramelisation in foods is... When food surfaces are heated strongly Processing of food with high sugar content In wine production In the preparation of sucrose syrups
At what temperature does caramelisation occur? >120 degrees for prolonged periods in the presence or absence of a catalyst
What are the 4 stages of caramelisation? Enolisation, Dehydration, Fragmentation and Polymerisation
What occurs during Enolisation? A reversible isomerisation of the aldose/ketose sugar (via the open chain forms) to a 1,2-enediol intermediate (Initiates the chain of events)
What occurs during Dehydration? (Caramelisation) The high temperature dehydrates the intermediate, causing it to loose a water molecule. Further dehydration is responsible for the formation of compounds such as 5-hydroxymethylfurfural (HMF)
What occurs during Fragmentation? (Caramelisation) Products such as HMF can be degraded to molecules such as furfural via fragmentation
What occurs during Polymerisation? (Caramelisation) The typical brown colour is produced, and is attributed to polymeric products such as HMF and furfal
What effects the rate of colour development in the sugar? The structural stability of the sugars
Alongside the production of HMF in caramelisation, what other products are produced? Dicarbonyl compounds give rise to some flavours (aldeydes and pyrazines), 'Burnt sugar smell' is produced by large variety of intermediates
Define Ascorbic Acid browning. The thermal decomposition of ascorbic acid under both aerobic and anaerobic conditions, thus losing the nutritional value of the ascorbic acid
Does Ascorbic Acid browning always occur following ascorbic acid degradation? No.
What is the first step of ascorbic acid browning? The degradation of A.A. to dehydroascorbic acid in the presence of Oxygen
What reactions follow the initial stage of ascorbic acid browning? DHA isn't stable, and spontaneously converts to 2,3-diketo-L-gulonic acid. If there's no Oxygen to start with, DHA isnt formed (instead, A.A. is converted to the above molecule via its keto tautomer)
Depending on the conditions, different intermediates are formed in A.A. degradation. What do/could the reduction products form/do next? Enter into reactions with other reactants to form brown prodcuts
What are the conditions for A.A. browning? Temperature dependent, but can occur at low temps. Occurs at low pH levels in the presence of amino acids or proteins
Name two molecules that could be effective at suppressing A.A. browning Sulphites, L-cysteine, Sugars, Sorbitol
The interaction of ________ with _______ causes lipid browning Oxidised fatty acids and amino groups
Unsaturated fatty acids are very susceptible to oxidation. This leads to the formation of _____ and ______ Free Radicals and Lipid Hydroperoxides
Created by: runwindmc