Fundamentals of food enzymes Flashcards
what are enzymes
complex globular protein catalysts
-accelerate the chemical reaction rate
-exist in almost all living systems, needed for metabolism
activity of an enzyme depends on
the species/source
-different foods have a different matrix resulting in a different function
why is knowledge of enzyme activity important
shelf life
behaviour of a product
what is the active site of a protein
location or portion of enzymes consisting of a binding site at which a chemical reaction occurs
who proposed the lock and key theory and explain it
fischer 1894
substrates fits like a key to binding site on protein
who proposed induced fit and explain it
Koshland 1965
dissimilar molecules can also be a substrate for the same protein, less rigid
active site is more flexible
what is a cofactor
participate directly in reactions or serve as an activator
why are enzyme in food different to regular chemistry
enzymes are not in isolation
-they are found with the substrate
what is found in the food matrix
enzymes
enzyme inhibitors
enzyme-substrate interactions
reaction products
co-factor/coenzymes
substrate
enzyme inhibitor interactions
what is an enzyme inhibitor
compound that decreases rate of enzyme-catalysed reactions
what can enzyme inihibitors react with
enzyme
enzyme-substrate complex
both
two classes of inhibitors
reversible
irreversible
what is enzyme activity dependant on
purity
location
environmental properties
Prescence of other factors
stability of enzyme
what effects enzyme specificity
bond
group
absolute specificity
name three types of inhibitors
competitive
uncompetitive
non-competitive
what are competitive inhibitors
react with the enzyme
what are uncompetitive inhibitors
react with enzyme-substrate complex
what are non-competitive inhibitors
react with both the enzyme and ES complex
what influences enzyme activity
intrinsic: pH, substrate, cofactors, inhibitors, activators, buffer concentrations, ionic strength, water activity
extrinsic: temp, pressure, time exposure
what is enzyme stability dependant on
sources
varieties
purification steps
denaturation vs inactivation
denaturation: protein structure alteration
inactivation: loss of enzyme activity not necessarily due to denaturation
temp range for most enzymes
30-40C
when do most enzyme begin to denature
45C
how can ice inactivate
ice changes structure
-may still be active before freezing so need to think how fast a thick product might freeze
factors that affect enzyme behaviours in partially frozen systems
composition of medium
freezing rate
viscosity
sample complexity
phase changes
how does viscosity in frozen systems impact enzyme activity
viscosity is high, diffusion rate is decreased
enzymes that can be damaged by cold denaturation
catalase
lactate dehydrogenase
effect of pH on enzymes
extreme pH may = denaturation
velocity of reaction
affinity of substrate to enzyme
stability of enzyme
optimal pH of most enzymes
4.5-8
optimal pH of pepsin
1.8
optimal pH of arginase
10
effect of water activity
water serves as a medium for reaction and vehicle for substrate
-still active at dry conditions but rate of reaction is limited by rate of diffusion
effect of ionic strength
changes solubility of protein
-salting in/out, protein participation
what is the michaelis-menten reaction used for
time course of enzyme-catalysed reactions
y axis of MM reaction graph
intial velocity
x axis of MM reaction graph
substrate concentration
when can maximum velocity be acheived
when there is a saturated substrate solution
what happens to the velocity during the reaction and why
it decreases as substrate is depleted
