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Introtofoodsci_exam1
Water in foods
| Question | Answer |
|---|---|
| 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
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