Lecture 3 - Part 1 Flashcards
it is the presence of a liquid, especially water, often in trace amounts. It is defined as the water in adsorbed or absorbed phase
Moisture
amount of moisture in the grain expressed as percentage of the total weight of the sample,
Moisture content
amount of water per unit mass of moist (or wet) sample
Moisture content, wet basis (MCwb)
amount of water per unit of dry solids (bone dry) present in the sample
Moisture content, dry basis (MCdb)
Most water in foods. It is lightly entrapped and therefore easily pressed or squeezed from food
Free water
it acts as a dispersing agent and solvent and can be removed by drying foods
Free water
can promote the growth of microoragnisms
Examples are citrus fruits, tomato, pineapple
Free water
this water associates in layer through intermolecular hydrogen bonds around hydrophilic food molecules
Absorbed water (Capillary Water)
Water is held tightly to proteins, or cell walls or protoplasm. It is not readily squeezed out of food
Absorbed water (Capillary Water)
it refers to the hydration proteins such as starch. Examples are carrots, camote, radish, kamote
Absorbed water (Capillary Water)
cannot be boiled or the water remains unfrozen below 0 degrees Celsius, usually -20 C
Bound Water
water in food that is unavailable as solvent. Examples are egg white, egg yolk, meat and fish, cheese
Bound Water
it is most easily removed from foods by evaporation, whereas more severe conditions are needed to remove chemically or physically bound water
Free Water
What are methods of removing water or moisture??
Distillation Method
Oven drying method
Vacuum drying
Freeze-drying
are based on direct measurement of the amount of water removed from a food simply by evaporation
Distillation Method
what are the major uses of distillation in the food industry?
for concentrating essential oils, flavours and alcoholic beverages and in the deodorization of fats and oils
it is a thermogravimetric method (water losses on drying) in which the sample is dried for a defined period of time at constant temperature.
Oven Drying Method
allows dehydration to be carried out at low temperatures in a closed system. The heat transfer mode in vacuum drying is by radiation
Vacuum drying
To increase the drying rate, it may be installed to allow conductive heat transfer
heating plates/ trays or heating chamber
it can usually heat up foods up to 98-102 degrees celsius with low pressure of 25-100 mm of Hg.
Vacuum drying
Lower temperatures (60-70 degrees celsius) are used for what? to prevent decomposition
high sugar food products
it suited for drying high value liquid foods such as coffee and juices, as well as high value solid foods strawberries, shrimp, diced chicken, sliced mushrooms, and even steaks and chops
Freeze-drying or lyophilization
method of grain moisture determination based on actual extraction of water either by convection heating (oven method) or distillation.
Primary Method
method of grain moisture determination based on some characteristics of the grain sample such as electrical resistance and capacitance which are related to moisture content and must be periodically calibrated against and official primary method
Secondary Method
