FOOD 2010 Chapter Notes -Buffer Solution, Adsorption, Earthbound

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Published on 17 Apr 2013
School
University of Guelph
Department
Food Science
Course
FOOD 2010
CHAPTER 4: Food Chemistry
Functional Properties Physical and chemical properties of food molecules that affect
behaviour in foods during formulation, processing and storage. Include sensory and mechanical
properties (flavour)
- The dipole nature of water affects its physical characteristics like boiling point. Results in
hydrogen bonding.
Solubility Food molecules can form hydrogen bonds with water so they can dissolve or
disperse.
Hydrophilic Compounds Compound’s that hydrogen bond easily to water to form solutions
or colloidal dispersions. Generally charged or polar.
Hydration Water molecules surround and interact with solutes by acting as a solvent
Amphiphilic molecules contain both hydrophilic and hydrophobic regions in their structures. In
water form micelles Clusters of molecules in which the hydrophobic groups are directed away
from the water, while the polar (charged) groups are exposed on external surfaced. The non-polar
hydrophobic groups form a stable inner core due to hydrophobic interactions. Micelles are
stabilized structures of amphiphilic molecules.
Known as noncovalent interaction and include hydrogen bonding, ionic interactions and
hydrophobic interactions.
Presence of water in foods, is known as moisture content or as the water activity of food.
Moisture refers to absolute amount of water present in a food, while water activity has to do
with the form the water exists in.
Moisture Amount of water present in a food, as a component, relative to all the solid
constituents.
Most water in foods is called free water. Free water is lightly entrapped, thus easily pressed
from food matter. Acts as a dispersing agents and solvent and can be removed by drying foods.
Absorbed Water Associates in layers vi intermolecular hydrogen bonds around hydrophilic
food molecules.
Bound Water (Water of hydration) is a third form of water in food. Exists in a tight
chemically bound situation, such as within crystalline structure, via water-ion and water-dipole
interactions. Does not show typical water properties, failing to freeze at 0 and fail to act as
solvent.
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Water Activity (Aw) Measure of the availability of water molecules to enter into microbial,
enzymatic or chemical reactions. Determines shelf life of food. Bound water is inversely related
to water activity, as % of bound water increases, water activity decreases.
Aw= P/P0 P is the vapour pressure P0 is vapour pressure of pure water at same temp
Relative humidity: RH%= 100 x Aw
Water sorption isotherms (MSI, moisture sorption isotherms) are graphs of data that interrelate
the water (moisture) of a food with its water activity at a constant temp. A sorption isotherm
indicates water activity at which a food is stable and allows predictions of the effect of changes
in moisture content on Aw and storage stability.
Water activity will increase an increase in temperature. WSI plots are used to determine rate of
drying, frozen storage temp and moisture barrier properties required in food packaging materials.
Water as Component of Emulsion:
- Emulsion is a type of colloidal dispersion, system containing two liquids or phases that
normally do not mix: a dispersed phase and a continuous phase.
- Water as aq component can function in either a dispersed or continuous phase. Water
phase is hydrophilic while fat phase is lipophilic.
Water and Heat Transfer:
- Water molecules always possess kinetic energy as long as temp is above 0 Kelvin. With
the addition of heat energy, kinetic energy of water molecules increase. Water acts as a
conductor of thermal energy to food molecules, process called heat transfer.
Water as a Plasticizer:
- Water acts as a plasticizer, especially in low moisture and frozen foods. A plasticizer
when added to polymer food system, lowers the glass transition temperature (Tg). The
glass transition temp refers to temp at which a change in the physciochemical state and
mobility of water and polymer of molecule constituent of a food occurs. A decrease in Tg
with an increase in water activity being linear.
- A plasticizer acts as a food system softener, increasing food polymer molecular volume
and mobility.
Food Acid Structure:
- A typical food acid is a carboxylic/organic acid, containing the carboxylic acid group
(COOH). Acids lacking carboxylic group are inorganic.
- Some foods that remain free-flowing have acids added to them because acids exhibit low
hygroscopicity, which means a low attraction for moisture. Without benefit of acid,
clumping of ingredients due to moisture would occur.
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Document Summary

Functional properties physical and chemical properties of food molecules that affect behaviour in foods during formulation, processing and storage. The dipole nature of water affects its physical characteristics like boiling point. Solubility food molecules can form hydrogen bonds with water so they can dissolve or disperse. Hydrophilic compounds compound"s that hydrogen bond easily to water to form solutions or colloidal dispersions. Hydration water molecules surround and interact with solutes by acting as a solvent. Amphiphilic molecules contain both hydrophilic and hydrophobic regions in their structures. In water form micelles clusters of molecules in which the hydrophobic groups are directed away from the water, while the polar (charged) groups are exposed on external surfaced. The non-polar hydrophobic groups form a stable inner core due to hydrophobic interactions. Known as noncovalent interaction and include hydrogen bonding, ionic interactions and hydrophobic interactions. Presence of water in foods, is known as moisture content or as the water activity of food.

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