chapter5-energy Flashcards
when does scientist start to understand energy?
1800
what is internal energy?
result of forces between the atoms and molecules of a system.
example for internal potential energy?
body fat and glycogen.
example for mechanical energy
water wheel
what is metabolism?
use body to convert stored chemical energy in food
how electrons moves?
from - to +
examples of radiant energy?
radio waves , ultraviolet waves and microwaves.
example of electrical energy?
lamps–>light.
toaster–>heat.
lamp and toaster属于radiant energy
blender–>mechanical energy
example of radiant energy?
electric coils, charcoal grills and gas flames–>cook food.
what does magnetron do?
electrical energy–>microwaves.
how does microwave travel? how they reflected?
straight lines, reflected by metals
what does microwave cause?
polar compound(water) to vibrate–> friction–>heat
more water in food, faster the food will cook
also quick if food are high in sugar and fats
what are low frequency long wavelength?
radio wave
microwave–>cook
infrared wave–>heat, only absorb in the surface
what are high frequency short wavelength?
UV–>kill bacteria, food preservation, produce VD
X ray
gamma ray–>food preservation: irradiation, destroy living organisms could cause spoilage
what is the frequency of rapid electrical pulse? what does it do?
10000per second.
kill microorganisms and inactive enzymes that present in food.
what does induction cooktops use?
electromagnetic waves to generate heat in food.–>special pan need–> current crate magnetic field–>produce low electric current–>heat时间更短
microwave safety. 5 points
vent plastic wrap used to cover food container
pierce whole fruit and veges have tough, unbroken skins
never hard-cook or soft-cook eggs in their shell
no aluminum foil–>cause sparks to jump from foil to walls.
no metals
what is the cancer causing substance name?
how to prevent?
- carcinogens–>when meat grilled. not vege and fruits
- no more than 1-2 per week, use gas to grill
- clean grill before use
- bone-side down
- add vinegar or lemon juice speed cooking
- reduce grill time-precook,use marinades 10%soy sauce and 1%sugar decrease 60% carcinogens.
- turn by tongs , not folk reduce dripping, which cause flame flare-ups
what are factors influence individual’s calorie?
hormones activity level type of food mineral level age sex sleep level genetics stress illness
what is basal metabolism?
body need calories to support basic functions such as breathing, blood circulation and cell growth and repair.
突然降低或升高10%体重会降低新陈代谢
what are 2 factors make up the balance of your daily calorie need?
physical activity and energy used to process the food you eat
why food scientist measure food energy?
know capacity to produce heat
what is heat capacity?
how is water’s heat capacity?
ability to absorb heat
greatest
what cause a convection current?
fluid heat–>molecules push farther apart–>density of fluid decrease
what does convection use?
boil water
baking
what cooking method use radiation?
broiling and rotisserie cooking
when is sublimation use?
in food industry to freeze and dry food at same time
sublimation?
solid to gas
deposition?
gas to solid
what is dry ice?
solid carbon dioxide
if a substance is being cooled, what happen to latent heat? when does it occur?
being release
during condensation, deposition, freezing
if a substance is being heated, what happen to latent heat? when does it occur?
absorbed
melt, sublimation, vaporization
what affect rate of reaction in food preparation?
enzyme
SA
thickness
temp
what you do if you want to speed up cook?
increase SA, temp and decrease the distance to the center
If too thick, use lower power level to avoid overcooking the surface
