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Introtofoodsci_exam1

Water in foods

QuestionAnswer
Water content of fruits&vege 80-90%
Water content of muscle foods 50-70%
Water content of processed foods less than 40% in order to improve shelf life
Importance of water in foods controls growth of microbes, affects chemical and enzymic reactions, affects physical properties - texture, affects stability and function of food chemicals (esp proteins and polysaccharides)
Water also acts as a trasport medium and enables chemical and biochemical change
Structure of Water hydrogen bonds continuously made and broken rapidly which makes it a non-permanent liquid structure
Each water molecule hydrogen bonds to as many as four other water molecules at max
In liquid water, molecules have lots of energy rotational energy, vibrational energy, kinetic energy
When temperature is lowered all energies slow down and water molecules come together to form nuclei
Water molecules attach themselves to the nuclei to form ice crystals
In ice each water molecule is bonded to four other water molecules
freezing pt is below 0 degrees fahrenheit
Water content of fruits&vege 80-90%
Water content of muscle foods 50-70%
Water content of processed foods less than 40% in order to improve shelf life
Importance of water in foods controls growth of microbes, affects chemical and enzymic reactions, affects physical properties - texture, affects stability and function of food chemicals (esp proteins and polysaccharides)
Water also acts as a trasport medium and enables chemical and biochemical change
Structure of Water hydrogen bonds continuously made and broken rapidly which makes it a non-permanent liquid structure
Each water molecule hydrogen bonds to as many as four other water molecules at max
In liquid water, molecules have lots of energy rotational energy, vibrational energy, kinetic energy
When temperature is lowered all energies slow down and water molecules come together to form nuclei
Water molecules attach themselves to the nuclei to form ice crystals
In ice each water molecule is bonded to four other water molecules
Freezing pt is below 0 degrees fahrenheit
What are the roles of water in food chem? 1) to interact/bind with food components, 2) to transport molecules/reactants to facilitate chemical rxns, 3) to take part in reactions as a reactant
Gels are formed when protein or polysaccharides interact and entrap water
Water interacts with itself, micromolecules, macromolecules
Water activity (Aw) is a measure of the extent to which the water in a substance has the properties of pure, unbound water. Its value is expressed in the range 0-1
Aw of 0 when molecules are completely bound to each other like ice
Aw of 1 when water is absolutely pure
Normal bacteria growth Aw = 0.91
Normal yeasts Aw = 0.88
Normal molds Aw = 0.80
Halophilic bacteria (salt loving) Aw = 0.75
Xerophilic molds Aw = 0.65
Osmophilic yeasts (sugar loving) Aw = 0.60
Microbiologically Stable Aw example sugar syrup with 80% sugar, 20% water and Aw of 0.60
Microbiologically Unstable Aw example sugar syrup with 60% sugar, 40% water and Aw of 0.95
High sugar activity reduces water activity
Low Aw lipid oxidation during food storage
High Aw chemical rxn and microbial growth during food storage
To control water activity we can use drying, freezing, adding salts and sugars
Created by: lindarim