Preservation and processing Flashcards
thermisation heat, time, and goal
65C, 15 seconds, kill heat-sensitive spoilage
goal of pastuerisation
killing spoilage and pathogenic bacteria
types of pastuerisation and what it involves
low temp: 65C for 30 min
high temp: 72C for 15 secs
goal of sterilisation and what it involves
kill all bacteria including spores
-UHT: 140C for 5 secs
-container: 112C for 15 mins
if milk has greater than 10% fat why does the temperature need to increase
fat is not a good conductor of heat
what is the most heat-stable bacterium in milk
mycobacterium tuberculosis
which enzyme is used as an indicator of pasteurisation sufficiency
alkaline phosphotase
what are the negative impacts of pasteurisation
development of cooked/flat flavour
maillard reaction
affects heat sensitive nutrients
what can happen to milk proteins during pastuerisation
denaturation
what can happen to milk if pasteruisation is done under basic conditions
degradation of lactose to lactulose and acids
what is lactulose
non-fermentable and non-absorbable sugar
what can severe heat treatment during pasteurisation of milk cause
heat induced coagulation
dephosphorylation and hydrolysis of caseins
alternative to pastuerisation
native antimicrobials in milk
microfiltration
bactofugation
UV pasteurisation
microwave or pulsed electric feilds
how can native antimicrobials in milk be used to treat it
use of enzymes, lactoferrin, lactenins to kill or control bacteria growth
how can microfiltration be used to treat milk
ceramic filter removes (99.9%) bacteria
-it removes fat globules so can alter flavour
how can bactofugation be used to treat milk
removes microbes using centrifugal force
how can UV be used to treat milk
UV ligh frequencies affect the DNA of bacteria
why is UV treatment difficult
the opacity of milk makes it difficult to penetrate further than the surface
how can microwave/electric feilds be used to treat milk
microwave energy/electric feilda destroy bacteria
how can microwave/electric feilds be used to treat milk
microwave energy/electric field destroys bacteria
why is milk prone to creaming
fat is less dense than water so it floats to the top
how does homogenisation affect the sensory properties of milk
creamier, white colour, blander
why must pasturisation occur before homogenisation
inactivate lipases making it less prone to rancidity
how can the coagulation of milk occur
acid addition
acid/heat addition
enzyme action
age gelation
how can the coagulation of milk occur
acid addition
acid/heat addition
enzyme action
age gelation
how does acid coagulation occur
micelle have a negative charge under normal pH but when it reaches the isoelectric point (around 4.6) the micelles aggregate
how does acid/heat coagulation occur
whey proteins are denatured by heat then in the presecne of acid of acid begin to aggregate to other whey and/or caseins
how does enzyme coagulation occur
chymosin (enzyme in rennet) cuts off the k-casein which reduced the intra-micelles repulsion which leads to coagulation
how does age gelation cause coagulation
actual cause is unknown, possible
-breakdown of casein by heat stable enzymes (plasmin)
-polymerisatoin of casein and whey through maillard reaction
-formation of kappa-casein-beta-lactoglobulin
why is evaporated milk thicker and creamier than normal milk
more concentrated milk solids
what concentrated is milk concentrated to before drying
50%
key features, advantages, and disadvantages to spray drying
uses hot air
retains nutrients
moderate cost
key features, advantages, and disadvantages to drum drying
uses hot surfaces
very low cost
dried milk has cooked flavour
key features, advantages, and disadvantages to freeze drying
uses sublimation
retains nutrients
high costs
what is membrane processing techology
separation that uses semi-permeable membrane filters to concentrate/fractionate the liquid
what is the permeate
liquid passing through the membrane
what is the retentate
the concentrate (retained liquid)
four types of membrane processes
reverse osmosis
nanofiltration
ultrafiltration
microfiltration
what becomes the permeate during reverse osmosis
water
what becomes the permeate in nanofiltration
water and minerals
what is fouling
blockage of pores
what are the limitations of membrane processing
creates a bacteria biofilm and fouling cna occur
