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Food 2130
Molecules controlling sensory properties
| Question | Answer |
|---|---|
| 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
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