C2. Dehydration, browning rxns, caramelization, sweetness
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Dehydration reactions are significant to food industry bc they are the basis of (2) reactions
• Caramelization (color and flavor) • Maillard reaction
best conditions (temp + pH) for dehydration reactions? but can still happen at ?
• concentrated sugar solutions are heated at temps above 130°C and under very acidic conditions (pH < 2.2), dehydration reactions become prevalent • can still happen, but very slowly at temps below 100°C and in dilute solutions
as water evaporates from solution (dehydration reaction), 2 things take place, leading to breakdown of what into what?
• molecular (internal) dehydration and oxidative fission take place • leading to breakdown of carbon chain into smaller units (flavor compounds)
2 ways that water can be eliminated from sugar molecules? - which one is more predominant?
• loss of water from 2 sugar molecules by reaction of their hydroxyl groups (R-OH + OH-R –> ROR (polymer) + H2O) –> results in random polymerization (generally not predominant reaction) • elimination of water from within a sugar molecule, leading to formation of highly unsaturated ring structures
common intermediate formed during caramelization reactions by dehydration is ?
hydroxymethylfurfural (HMF)
fragmentation reactions of highly unsaturated ring structures produce various compounds (3 characteristics) - 3 examples
• low-molecular weight • unsaturated • reactive • acetol, diacetyl, acetoin
many of highly unsaturated ring structures and their breakdown products (3) can _____________
breakdown products like short-chain aldehydes, ketones, carboxylic acids) - can polymerize
extensive dehydration reactions eventually lead to formation of an amorphous, _________ ________ pigment called _________
• charged brown pigment • caramel
browning reactions can be classified into 2 categories:
• enzymatic (oxidative) browning: when fruits/veggies turn brown when left on table • non-oxidative browning/non-enzymatic browning
enzymatic/oxidative browning: - related to carbohydrates? - associated with browning of ________ tissues - what enzymes oxidizes what into what?
• not related to carbs! • plant tissues • most commonly polyphenol oxidase (PPO) oxidizes mono or dihydroxy phenols into quinones
quinones are quite reactive/unreactive and can react ___-_________ to _________ into a ________ pigment
• reactive • non-enzymatically to polymerize into a brown pigment
what other enzymes (apart from polyphenol oxidase) are indirectly associated with browning? (2) - these can produce/supply reactive _______ compounds that can undergo ___-_________ _________
• ascorbic acid oxidase and lipoxygenase • carbonyl compounds –> non-enzymatic browning
2 types of non-oxidative browning - caramelization vs Maillard?
• sugar-sugar reactions (caramelization) • sugar-amine reactions (Maillard reactions)
caramelization reactions occurs when any concentrated sugar solution is ________
heated
caramelization is used commercially to produce (2) - each is generally made from what?
• caramel flavor/syrup –> made from concentrated sucrose solutions • caramel color –> generally made from glucose syrup (more reducing)
which 2 reactions produce what type of polymers that are very dark in color? (high tinctorial power)
• dehydration and polymerization • produce high-molecular weight water-soluble polymers
caramel colors produced in what foods (5)
baking, beer, soft drinks, whiskey, soy sauce…
Maillard reaction involves reaction of what with what (generally (2))
• of reducing sugars with primary amines (generally amino acids and proteins: free amino groups on side chains (ie: e-amino group of lysine))
which aromas are associated with Maillard reactions? (4 ish)
• coffee flavor, color and aroma (formed during roasting) • popcorn aroma/flavor • roasted peanuts, cashews • baked bread aroma
condensation of primary amine and reducing sugar form a _______ ______ –> followed by formation of an _________ compound
• Schiff base • Amadori compound
what is a key intermediate in Maillard reaction, comparable to _____ in caramelization
Amadori compound! - comparable to HMF
converting Schiff base to amadori compound is termed what?
amadori rearrangement
can the amadori compound lose water from within the molecule?
yes
at higher temps, what are the major reactions following amadori rearrangement? - key difference with caramelization?
dehydration and fragmentation (much like caramelization) - key difference: there is an amine group attached to sugar –> end products tend to contain nitrogen in their structure