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Chapter 4

FOOD 2010 Chapter Notes - Chapter 4: Glass Transition, Water Activity, Miscibility

Food Science
Course Code
FOOD 2010
Massimo Marcone

of 3
Chapter 4: Food Chemistry 1, Functional Groups and Properties, Water,
and Acids
4.1 The Nature of Matter
-its a review of Chem
4.2 Chemical Reactions in Food
-review of Chem
4.3 Functional Groups
-review of Chem
4.4 The Chemical and Functional Properties of Water
-solvation and dispersing agent
-food molecules can form H-bonds with water meaning that they can be dispersed or dissolved
-this means that they are soluble
-hydrophilic compounds (can easily H-bond)
-Hydration is process by which water molecules surround and interact with solutes by acting as a
-can disperce amphiphilic agents (part hydroscopic, part hydrophobic)
-micelles are formed
-water activity and moisture
-moisture: amount of water present in a food relative to all the solid constituents and non- water
-free water: lightly entrapped, so easily pressed from food matter
-absorbed water: associates by layers via intermolecular H-bonds around hydrophilic food
-bound water: (water of hydration) tight chemically bound situations [ in crystalline structure]
-aw: measure of the availability of water molecules to enter into microbial, enzymatic, or chemical
-water as a component of emulsions
-immiscible with fat
-thus emulsifier is needed if need to have 1 continuous phase
-water and heat treatment
-important vehicle for heat transfer in foods during processing and preparation
-water acts as a conductor of thermal energy to food molecules, process = heat transfer
-water as an ingredient
-can have repercussions as it can
-act as solvent
-change state with temperature changes
-exhibit motion within a food system
-in frozen foods, stabilizing movement of water is desirable for better quality
-water as plasticizer
-lowers glass transition temperature (To @ which change in physiochemical state and the mobility of
the water and polymer molecule constituents of a food occurs)
Chapter 4: Food Chemistry 1, Functional Groups and Properties, Water,
and Acids
-plasticizer acts as a food system softener, increasing food polymer molecular volume as well as
4.5 Chemical and Functional Properties of Food Acids
-typical food acid : carboxlic/organic acid. (COOH group) attached to molecule
-some have low hygroscopity (low attraction to water) and will be added to foods that need to remain
-functions are related to molecular size and structure
-# COOH (carbox acids) creates difference in functional properties
-acid strength
-food acids generally donate protons
-weak acid: COOH exists more than COO- and H+
-strong acid: more COO- and H+ than COOH
-fumaric acid and dough softening
-the proteins in wheat flour contain cysteine (contain -SH). Under regular baking conditions of mixing
etc the -SH become oxidising and form disulfide bonds. These bonds or linkages represent a
tightening of the dough structure. If fumaric acid is added the disulfide bonds are broken and a softer
more easily manipulated dough results.
-salts of organic acids
-formed when the H in COOH is replaced with a metal ion
-solution of a weak acid and its salt at a pH where the solution has the ability to maintain that pH
when quantities of base are added
-buffering action of any acid/salt system limited to a pH range extending 1/2 a pH unit on either side
of the pKa.
-refers to the production of gas by yeast fermentation by reaction of acid with baking soda, or by
heating of salts
-leavening gases = carbon dioxide, water vapour, air, ammonia, ethanol
-leavening acids = generate H ions that facilitate the release of carbon dioxide from baking soda. The
gas release causes the expansion of a baking dough, due to the increased pressure inside the gas
-baking powder is double-acting (see food 2700 notes)
4.6 Food Acidity
-pH and pH scale
-pH = -log [H+]
-7> acidic
-7= neutral
-7< basic
-titratable acidity
-measure of the total acidity in a sample. Both as free hydrogen and still bound
-ie fermentation in milk, ripeness in fruit
-pH and acid foods
Chapter 4: Food Chemistry 1, Functional Groups and Properties, Water,
and Acids
-acid food : natural food 4.6 or below
-natural pH: pH prior to processing
-acidified foods: low-acid foods to which acids are added and water activity exceeding 0.85 and pH
4.6 or below
-low-acid foods: have an equilibrium pH greater than 4.6 and water activity greater than 0.85
-fermented foods: low-acid foods subjected to the action of certain microorganisms. The
microorganisms produce acid during their growth and reduce the pH of the food to 4.6 or below.
Partially fermented foods require addition of acid to reduce the pH to 4.6 or less.