Thermal Processing Flashcards
types of thermal processing?
cooking, blanching, pasteurization, sterilization
most widely applied unit op in food processing?
thermal processing
three basic mechs of heat transfer?
conduction, convection, radiation
conduction is heating of ___, convection is heating of ___
solids; fluids
examples of radiation?
infrared, microwave, dielectric
primary objective of cooking?
increase palatability
baking and roasting happen at _____degrees, frying happen at ____ degrees
150-200; 175-225
cooking inactivates ____ factors like ___ in pulses
anti-nutritional factors; lectins
___ bioavailability reduced by ___ browning
lysine; Maillard (non enzymatic)
these vitamins decrease in bioavailability but not concentration with cooking
vitamin A and D
these vits decreases in both [ ] and availability
thiamine, niacin, folate
primary purpose of blanching?
inactivate deteriorative enzymes, kill spoilage bacteria
blanching usually done on __ foods, prior to ____
solid; freezing/canning
blanching reduces ___ by removing tissue gases
volume
blanching of fruits before ___ allows surface ___
drying; pasteurization
blanching inactivates these deteriorative enzymes
LOX (lipoxygenase), polyphenol oxidase (PPO), pectinase
pectinase ___ plant tissues
softens
blanching is referred to as :
hot break process
loss of nutrients during blanching is mainly due to;
leaching (loss of ascorbic), thermal destruction, oxidation
what is observed as indicator of severity of blanching?
loss of ascorbic acid
A heat treatment which kills part of the microbial population present in food
pasteurization
target pathogens in pasteurization in milk?
tuberculosis (old), coxiella burnetti (new)
What are the two processes in pasteurization?
LTH, HTST
LTH is at __ degrees for ___ minutes; HTST is at ___ degrees for ___ seconds
63; 30; 72; 15
Is LTH or HTST more detrimental to nutritional/sensory properties?
LTH
2 processes in pasteurization?
batch (small), continuous (large)
equipment used in continuous process?
PHE (plate heat exchanger)–>high production rate, no overheating
why is PHE corrugated?
for more surface area–>more points of contact
foods that are pasteurized?
milk, beer, juices, eggs
process used in canning, retorting, and ultra high temp processing
sterilization (appertization)
how is sterilization diff from pasteurization?
much higher temp used in sterilization
4 types of microorg destruction processes?
sanitation, pasteurization, commercial sterilization, sterilization
how is sterilization diff from commercial sterilization?
sterilization means no living orgs present–>only possible with autoclaving; commercial uses heat sufficient destroy all microorg able grow under conditions of storage
low acid food is pH ___, acid is ____, high acid is ___
> 4.5; 3.7-4.5;
most severe process is needed for canning ____ acid foods; need to process at ____ degrees C for ___ min.
low; 121; 15
how to get water boil at 121 degrees instead of 100?
high pressure boiling
food processing industry uses ____ chamber to create temp >100 degrees inside cans for low acid foods
retort
examples of acid foods?
fruit jams, fruit cocktail, tomatoes, peaches, veg juice
primary target when canning acid foods?
facultative anaerobes (bacillus sp.)
temp for canning acid foods?
100 degrees C
examples of high acid foods?
apple juice, cider, berries, citric juices, picles, sauerkraut
targets for high acid foods?
yeasts, molds
for high acid foods, can ____ containers at ___ degrees C
hot fill; 90
milk sterilized this way is a shelf-stable product that needs no fridge
UHT (140 degrees C for 2 seconds)
UHT products are ____ packaged
aseptically
severity of thermal process required to produce commercial sterility depends on:
nature/heat resistance of microbes, initial microbe load, nature of food, heat transfer characteristics of food/container, conditions of storage, characteristic of canning equipment
what is conductivity?
conduction through can wall and solid foods
what is specific heat?
convection through liquid foods
cold point in conduction is ___, convection is ___
centre; below centre
units used in thermal conductivity
Watt/m/K
most foods have conductivity ____
copper has ___ conductivity, glass has ___ conductivity
high; low
Units used in specific heat capacity (Cp)
J/kg/K
If heat food containing oil and water (like milk), which part of food will be more hot?
oil
survivor curve of microbes becomes ____ with time
asymptotic
time needed to achieve 90% kill at given temp
D value (decimal reduction time)
Calculation of D value?
D= (T1-T2)/logD2-logD1
often assume there are _____ microorganisms present
10^12
temperature increase needed to cause a 1 log reduction in D value
Z value
number of min required kill known population of specific microorganism in given food under specific condition
F value
how to calculate F value?
=D value * (log starting pop-log ending pop)
factors affecting D value before processing?
types of microorg, growth temp, medium and phase
factors affect D val during processing?
type of food, pH, water activity, salt [ ], [ ] of microorg, rate of heating
factors affect D val after processing?
recovery medium, temp, presence of O2, background microflora
where does cooked flavour come from?
reaction of S from amino acid “cysteine”
which is more heat resistant: bacteria or vitamins?
vitamins
4 thermal process techniques?
batch process, continuous process, indirect heating, direct heating
example of indirect heating?
can, pouch, pot on stove
example of direct heating?
steam injection in UHT
