Food processing Flashcards
At what AW does a) microbe growth and b) deterioration stop?
a) ≤ 0.65 (RH=65%)
b) ≤ 0.3
4 factors affect heat/liquid transfer in food, and therefore the rate of drying:
Surface area (+)
Temperature (+)
Humidity (-)
Atmospheric pressure (-)
3 phases of the drying curve
Lag phase - Fast; water lost from surface
Constant (fast) rate - Dry layer on outside forms– insulation barrier; solute conc. increases
Falling rate - Reaching a normal equilibrium in RH
Nutritive changes due to drying
Vitamin C
Thiamine (B1)
Protein quality
» all decreased
Pre-hydration steps (e.g. cooking, blanching); high temp; slow drying
Sensory changes due to drying
Colour – browning reactions (enzymatic* & non-enzymatic)
Flavour – loss of volatile compounds
Taste – mostly intensified
Texture – altered in rehydrated products
*inactivate enzymes 1st by pasteurising/blanching
Safety changes due to drying
Improved (linked to preservation)
But good hygiene is needed
Sun-drying – slower process & can risk of bacterial spoilage
> Use of smoke/salt as further preservative agents evolved
What humidity control is needed in fridges to avoid mould growth?
80-90%
Conduction
Transfer by contact & molecules vibrating against one another
Reduces with density (solids>liquids>gases)
Thermal conductivity depends on type of material
Convection
Transfer by movement of a heated fluid
Natural vs. forced (uses fan)
Radiation
Occurs through empty space or via electromagnetic energy
Energy absorbed at particular wavelengths (e.g. microwave cooking)
3 types of Thermal preservation
Blanching and pasteurisation (mild)
Sterilisation (severe)
Blanching
Inactivated endogenous enzymes to avoid spoilage, e.g. Polyphenol oxidase (PPO) catalyses browning in peeled apples/potatoes
Useful before canning/freezing
Applied to: fruits & veg | Temp-time: 95oC, 5 min
Pasteurisation
Destruction of pathogenic bacteria to remove health hazard; 3 temp-time combinations:
-Low temp 63oC, 30 min
-High temp-short time (HTST) 75oC, 15s
-Ultra-high temperature (UHT) 150oC, 1-3s
Applied to: liquid foods e.g. milk, beer, juices, sauces, liquid egg, marinades, soups
Sterilisation
Complete destruction of microorganisms – objective to eliminate C botulinum spores
Applied to: canned/bottled foods
Temp-time: 121oC, 15-30 min
D-Value
decimal reduction time (time to reduce bacteria by 10-fold) at specified temp
12D process = food safety
D-value @ 63°C 2.5 min (12*2.5) = 30 min
Z-Value
temp requires to increase the D-Value by 10-fold
4 types of non-thermal processing
- Modified Atmosphere Packaging (MAP)
- High Pressure Processing (HPP)
- Food Irradiation
- Chemical Preservatives
Modified Atmosphere Packaging (MAP)
Definition: a one-time change in the atmosphere within a food package or storage area in order to extend shelf life
Uses gas mixtures for food preservation
MAP vs CAP = one time vs continual attempts
(Controlled Atmosphere Packaging)
Extends product shelf-life (x2-5 fold @ 1°C storage)
Preserve SNSS characteristics
Improve food supply chain distribution (↓ losses at POS)
Improves manufacturing efficiency by enabling longer production runs (↓ # deliveries)
Effect of gas composition
Normal air = 78% N2, 21% O2, 0.035% CO2)
>30% CO2 for meat, poultry & seafood
~10% CO2 for fruits & vegetables
CO2 is antimicrobial agent:
Alters cell membrane & nutrient uptake
Inhibits food enzymes
Denatures protein
Changes pH inside cells
N2 is a passive filler (avoids package collapse)
Food irradiation
Kills all pathogens, e.g. Lysteria monocytogenes, E. coli,
Leaves no residues
Low cost (~ 1-pence) / lb of food
Endorsed by WHO, IFT and American Medical Association
Moderate or no loss of nutrients at < 3kGray
1 gray (Gy) = 1J/ per kg of food material
Low dose applications (up to 1 kGy)
Sprout inhibition, delay fruit ripening, destroy insects
Medium dose applications (1 – 10 kGy)
Kill spoilage microbes in meat
Kill pathogenic microbes in fresh and frozen meat
High Pressure Processing
Food is subjected to very high pressures
(liquid/solid foods)
100-200 MPa
Kills pathogens
Colours and nutrients retained
Mild SNSS changes
Additives definiton
GENERAL STANDARD FOR FOOD ADDITIVES CODEX STAN 192-1995
any substance not normally consumed as a food by itself and not normally used as a typical ingredient of the food – whether or not it has nutritive value*
intentional addition to food for a technological (including organoleptic) purpose
Additives labelling requirements
Food additives REGULATION (EU) No. 1333/2008Food labelling REGULATION (EU) No. 1169/2011
Must be named in list of ingredients
(main) functional class and specific name or E number
e.g. ‘Preservative: Sodium Nitrite’ or ‘Preservative: E250’
Additives for same function in a food can be grouped together
No requirement to label some additives not considered an ingredient
Carry-over from an ingredient (e.g. preservatives in fruit puree > yoghurt)
Processing aids (e.g. ascorbic acid to prevent discolouration of fruit > pie making, but has no effect in fruit pie - cooked off)
Other substances used in the quantities strictly necessary as solvents or media for additives or flavouring
Antimicrobials - Weak Acids
Mostly weak acids that “short circuit” membrane H+ gradient, e.g.
Poly(3-hydroxybutyrate (PHB)
Sorbic Acid, Benzoic acids
Propionic, acetic acid
Sulphite, sulphur dioxide
Anitmicrobials - Oxidising Agents
Disrupt redox balance of cells:
Chlorine water
Hydrogen peroxide
Hypochlorite
Antioxidants - Chain Breaking
Free radical quenching/stabilisation:
Butylated hydroxytoluene (BHT)
Butylated hydroxyanisole (BHA)
Vitamin E
Antioxidants - secondary antioxidants
Metal chelators (EDTA, citric acid, vit C)
Oxygen scrubbers (glucose oxidase)
Brink et al
1964 - Events leading up to the legislation of pasteurization of all milk sold in Ontario… story marks a milestone in Canadian public health… great opportunities
Monteiro et al
2010 - A new classification of foods based on the extent and purpose of their processing (NOVA)
Dwyer et al
2012 - Ongoing efforts/challenges at the nutrition–food science–public health interface… processed F&V make important contributions to diet/nutr intake… addresses misinformation
Snowdon et al
2013 - To develop a dataset (Pacific Islands) on nutrient composition of processed foods sold & their sources… labelling difficulties & consumer interpretation challenge
Weaver et al
ASN Statement: nutritional impacts of processed foods… processed foods are nutritionally important to American diets (food & nutr security)… new tech & more education
Gibney
2019 - UPF: Definitions and Policy Issues…debate – improving diet pattern from food processing rather than nutr intake
