XNB250 Caramelen - Sugar Browning and Caramelisation Week 5
XNB250 Food Science
Topic: Sugar, Browning, and Caramelisation
SUGAR
Overview
• main
... [Show More] sugars of interest are monosaccharides and disaccharides
• sucrose (table sugar) = glucose + fructose; key sources are sugar cane and sugar beets
ENZYMATIC BROWNING
Overview
• results in brown discolouration of fruits, vegetables, and seafood; bitter taste and astringent feel
• cell disruption must occur to liberate membrane-bound enzyme, polyphenoloxidase
• two-stage process
o presence of oxygen, pH between 5 and 8, and polyphenoloxidase
o first stage is enzymatic; monophenol ® diphenol ® quinone
o second stage is nonenzymatic; quinone ® melanin (insoluble, dark compound)
• melanin seen in food as brown pigmentation
• desirable in tea, coffee bean, cacao, dried fruit e.g. plum as prunes, grapes as raisins and sultanas, dried fig
• undesirable in fresh fruits and vegetables e.g. pear, apple, banana, avocado, eggplant, potato, mushroom,
and seafood e.g. prawns and lobsters
Inhibition
• denaturing/ deactivating enzymes
o heat treatment (e.g. blanching) or high pressure processing
o addition of acid to lower pH
o addition of compounds to chelate copper in polyphenoloxidase
• lowering storage temperature
• blocking exposure to oxygen through coatings e.g. sugar syrup
• addition of ascorbic acid and sulfites
NONENZYMATIC BROWNING
Maillard Reaction
• series of reactions between a reducing sugar and amino acid, resulting in formation of brown complex
o reducing sugar = sugar with free carbonyl (aldehyde or ketone) group
• brown pigments known as melanoidins produced, along with potent volatile aroma compounds, and
bitter-tasting flavour compounds
• desirable results include aroma and colour of browned baked goods and cooked meat, chocolate flavour,
roasted coffee, and production of compounds that can stabilise food
• undesirable results include off-odours and browning that occurs with long storage of certain foods (e.g.
powdered/ dried egg whites, milk powder, instant mashed potatoes), reduction in availability of digestible
essential AAs arising from glycosylation (glycosylated AAs are unavailable to human metabolism), and
formation of compounds with potential mutagenic properties
Factors Influencing Maillard Reaction
• sugar must be reducing sugar e.g. glucose, fructose, galactose, lactose, maltose, but not sucrose
• presence of amino acid: sugar reacts with nitrogen in amino group in side chain e.g. lysine, arginine;
different AAs result in different end products, with free AAs being more reactive than peptide chains
• reactions peak at water activity (Aw) of about 0.6
o Aw > 0.6 results in dilution of reactants; temperature may not exceed 100°C
o Aw < 0.6 results in reactants being less mobile
• reactions accelerated at pH ≥ 6
o alkaline pH results in conversion of sugars to open chains, and AAs more active (H+ ions removed)
• reactions proceed more quickly at about 140 to 160°C, but can occur slowly at room temperature
Caramelisation
• breakdown of sugars due to heat or high/ low pH
• involves dry sugar or sugar syrup, with most water evaporated (thus highly concentrated)
• no single compound identified as ‘caramel’
• steps in caramelisation
o sucrose (if used) broken down by heat to glucose and fructose
o monosaccharides are isomerised to enediol
o enediol undergo dehydration or b-elimination to form a-dicarbonyl compounds
o further degradation to form range of products e.g. caramelan, caramelen, caramelin groups;
product formed depends on type of sugar, pH, and temperature
• caramel flavours include diacetyl (butterscotch), esters and lactones (sweet rum-like), furans (nutty), and
maltol (toasted)
Practical Considerations for Caramelisation
• occurs at about 170°C for sucrose or glucose, and about 110°C for fructose
• slow increase in temperature allows breakdown and melting to occur simultaneously
• timing is crucial – caramel becomes less sweet as it becomes darker
o too little time results in too little sugar converted; too long results in too many caramel
compounds produced, and thus bitter
• using white sugar enables easier identification of readiness
• use high sugar content fruits and vegetables for caramelisation e.g. onions, pineapple
o maximise surface area by cooking in one layer; cook for sufficient duration, and at appropriate
temperature
Dextrinisation
• breakdown of starch to dextrins (lengths vary) due to exposure to dry heat (no water added) e.g. toasting
bread, browning flour for use in gravy
• temperature rises rapidly, and beyond that possible in presence of water
• dextrins taste sweeter than starch
o chemical degradation of starch by reacting with water in starch when high energy applied
o starch molecule (both amylose and amylopectin) split between glucose units, forming dextrins
CONFECTIONARY PREPARATION
Overview
• sugar confectionary = sugar with added flavour
o crystalline e.g. fondant, fudge; non-crystalline e.g. toffee, peanut brittle, butterscotch
• four basic steps
o creating syrup (supersaturated) solution
o concentrating contents of mixture by heating and evaporation
o cooling
o beating/ stirring for crystalline; no beating for non-crystalline
Description of Steps
• supersaturated solution = solution that contains more than the maximum amount of solute that can be
dissolved at that particular temperature
o increasing temperature allows more sugar to be dissolved in a given amount of water
o evaporation of water and cooling of the solution (without disturbance) leads to mixture
becoming supersaturated (solution is unstable, thus precipitates to form hard candies)
• confectionary production highly sensitive to timing and temperature
o rapid cooling for crystalline; slow cooling for non-crystalline
o heat to lower temperature for crystalline; higher temperature for non-crystalline
• important aspect of production is controlling crystallisation (= precipitation of crystals from a solution into
a solid, geometric network; crystal = orderly arrangement of molecules)
o avoid vigorous boiling/ stirring when heating solution at its final temperature
o avoid syrup splashing onto sides of pan
3
Crystalline Confectionary
• goal is to develop numerous, very fine nuclei in syrup solution, which serves as basis of sugar crystals
o nuclei = small aggregates of molecules serving as starting point of crystal formation
Non-crystalline Confectionary
• goal is to ensure sugar does not crystallise
• two major methods used to inhibit crystalline
o creation of very concentrated (supersaturated) sugar solutions
o addition of large amounts of interfering agents (any molecule different in shape/ size from
sucrose e.g. corn syrup, cream of tartar) that block sugar molecules from clustering together to
form large crystals, resulting in candies with waxy, chewy texture [Show Less]
