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The highly branched fraction of starch, with α-1,4 chains joined by α-1,6 branch points roughly every 20–25 units.
The branched starch that makes rice sticky and gives bread its soft crumb; waxy rice varieties are almost pure amylopectin.
See also: Amylose, Starch gelatinisation
The essentially linear fraction of starch, made of α-1,4-linked glucose units. Typically 20–30% of common starches.
The straight-chain starch behind the firm, separate grains in basmati rice and the hard set of cooled boiled potatoes.
See also: Amylopectin, Retrogradation
A substance that delays oxidative rancidity. Primary antioxidants (BHA, BHT, TBHQ, tocopherols) donate hydrogen to break the radical chain; secondary antioxidants (citric acid, EDTA) chelate pro-oxidant metals.
Added to potato chips, cooking oils and butter — as BHA, BHT or vitamin E — to stop them turning rancid on the shelf.
See also: Rancidity, Peroxide value
Thermal degradation of sugars in the absence of amino groups, producing colour and flavour compounds. It requires much higher temperatures than the Maillard reaction.
What gives roasted onions, seared steak crust and toffee their brown colour and flavour — distinct from the browning caused by a Maillard reaction.
See also: Maillard reaction
The main phosphoprotein of milk, about 80% of milk protein, existing as micelles stabilised by κ-casein. Precipitates at pH 4.6 or on rennet action.
The protein that curdles when lemon juice is added to hot milk to make paneer or cheese; also why milk clots when it reaches an acidic stomach.
See also: Isoelectric point, Whey protein
The percentage of galacturonic acid carboxyl groups in pectin that are methyl-esterified.
Determines whether a fruit jam needs added sugar and acid to set (high-ester pectin) or can be made as a low-sugar spread (low-ester pectin).
See also: Pectin
Loss of a protein's secondary, tertiary and quaternary structure without breaking peptide bonds, caused by heat, pH change, salts, solvents or shear.
Why an egg turns solid when fried or boiled, and why milk proteins clump together if boiled with lemon juice.
See also: Isoelectric point, Protein coagulation
A surface-active molecule with hydrophilic and lipophilic regions that lowers interfacial tension and stabilises an emulsion.
What keeps mayonnaise, ice cream and chocolate from separating into oil and water layers while sitting on a shelf.
A dispersion of one immiscible liquid in another, stabilised by an emulsifier. Oil-in-water as in milk and mayonnaise, or water-in-oil as in butter and margarine.
Milk, mayonnaise, butter and salad dressings are everyday examples — mixtures of oil and water that would otherwise separate.
See also: Emulsifier, HLB, Homogenisation
Browning catalysed by polyphenol oxidase, which oxidises phenolic compounds to quinones that polymerise into brown melanins. It requires oxygen, the enzyme, and a phenolic substrate.
Why a cut apple or potato turns brown within minutes, and why a squeeze of lemon juice slows it down.
See also: Polyphenol oxidase, Blanching, Maillard reaction
A number from 0 to 20 describing an emulsifier's relative affinity for water and oil.
Used by food formulators to pick the right emulsifier for a product — a low-HLB emulsifier suits butter-type spreads, a high-HLB one suits salad dressings.
See also: Emulsifier, Emulsion
Addition of hydrogen across double bonds of unsaturated fatty acids using a nickel catalyst, raising melting point and oxidative stability.
What turns liquid vegetable oil into solid vanaspati or margarine — and why health advisories now warn about the trans fat it can create.
See also: Trans fat, Iodine value
The equimolar mixture of glucose and fructose produced by hydrolysing sucrose, so called because the optical rotation inverts from positive to negative.
Used in commercial baking and sweet-making, including Indian mithai syrups, to stop sugar crystals forming and keep the product moist.
See also: Reducing sugar
The pH at which a protein carries no net electrical charge, so electrostatic repulsion between molecules is minimal.
Why paneer and cheese are made by adjusting milk's acidity — the proteins clump together and separate from the whey at this exact pH.
See also: Denaturation, Casein
A non-enzymatic browning reaction between a reducing sugar's carbonyl group and a free amino group of an amino acid or protein, producing melanoidin pigments and a wide range of flavour compounds.
What gives bread crust, roasted coffee, fried onions and a seared tandoori chicken their brown colour and flavour — distinct from sugar caramelising on its own.
See also: Caramelisation, Enzymatic browning, Reducing sugar, Acrylamide
The total amount of water in a food, expressed on a wet basis (mass of water per mass of wet sample) or dry basis (mass of water per mass of dry solids).
What determines whether a bag of wheat, rice or spice powder is safe to store long-term or will spoil and grow mould.
See also: Water activity
A structural polysaccharide of plant cell walls based on galacturonic acid. High-methoxyl pectin (DE > 50%) gels with sugar and acid; low-methoxyl pectin gels with calcium.
The setting agent in homemade jam — naturally present in fruits like apple and citrus peel, or added as a powder when a fruit's own pectin is too low.
See also: Degree of esterification, Syneresis
A copper-containing enzyme responsible for enzymatic browning in cut fruit and vegetables. Optimum pH is around 6–7 and it is largely inactivated above about 80 °C.
The enzyme responsible for cut apples, bananas and potatoes turning brown — the same reaction as enzymatic browning, named for the enzyme that drives it.
See also: Enzymatic browning, Blanching
The aggregation of denatured protein molecules into an insoluble network, following denaturation and driven by newly exposed hydrophobic groups.
Why beating and heating egg whites turns a runny liquid into a firm meringue or omelette.
See also: Denaturation, Isoelectric point, Casein
Deterioration of fats producing off-flavours. Hydrolytic rancidity releases free fatty acids by lipase or water; oxidative rancidity is a free-radical chain reaction with oxygen at unsaturated bonds.
The “off” smell and taste in old cooking oil, stale namkeen or biscuits made with old ghee — caused by fat breaking down over time.
See also: Peroxide value, Antioxidant, Free fatty acid
A sugar with a free aldehyde or ketone group that can act as a reducing agent — glucose, fructose, lactose and maltose are reducing sugars. Sucrose is not, because both anomeric carbons are involved in the glycosidic bond.
Involved in the Maillard browning of bread crust and biscuits, and the basis of the test strips used to check sugar levels in some quality labs.
See also: Maillard reaction, Invert sugar
The re-association of gelatinised starch chains, mainly amylose, into an ordered crystalline structure during cooling and storage, expelling water (syneresis).
Why rice and bread go hard and stale in the fridge faster than at room temperature — the starch re-crystallises as it cools.
See also: Starch gelatinisation, Syneresis, Amylose
The irreversible swelling of starch granules when heated in water above a characteristic temperature, in which the crystalline structure is lost, amylose leaches out and viscosity rises sharply.
Why raw rice and raw atta dough have to be cooked with water and heat before becoming soft rice or roti — the starch granules swell and burst.
See also: Retrogradation, Amylose, Amylopectin
The ratio of the vapour pressure of water in a food to the vapour pressure of pure water at the same temperature. It measures how much water is available for microbial growth and chemical reactions — not how much water is present.
Why honey and jam don't need refrigeration despite containing a lot of water, while fresh bread does — bacteria and mould need “available” water, not just any water.
See also: Moisture content, Hurdle technology, Water sorption isotherm
The soluble milk proteins remaining after casein removal — chiefly β-lactoglobulin and α-lactalbumin. Heat-labile but acid-stable.
The liquid left over from making paneer or cheese, now sold separately as a popular protein supplement powder in gyms and nutrition stores.
See also: Casein, Denaturation
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