FOOD PRESERVATION

Food Preservation Methods Inhibition Inactivation Avoid contamination

Inhibition low T storage reduction of aw decrease O2, increase CO2, vacuum acidification fermentation freezing surface coating structural modification

Inactivation sterilization pasteurization radiation electrifying high pressure blanching cooking frying

Avoid recontamination packaging hygienic processing hygienic storage aseptic processing

Thermal processing pasteurization

inactivation of vegetative cells and/or enzymes sterilization

inactivation of spores blanching

inactivate enzymes fruits and vegetables ohmic heating

electrical conductivity for foods with 30-40% water dissolved ionic components uniform heating short processing time

Cold storage Chilling

slowing microbical growth reduce enzymatic and chemical reactions slow postharvest metabolism reduce moisture loss

Freezing slowing microbial and chemical reactions water immobilization reducing molecular mobility some microbial destruction

Reducing aw drying freeze-drying humectants freezing

slowing microbial and chemical reactions

water immobilization reducing molecular mobility

Fermentation inhibition of spoilage/pathogenic

flora by beneficial microbial flora consumption of substrate for

biochemical/chemical reactions production of antimicrobials acidification

Preservatives acidification

pH change antimicrobial property

other preservatives antimicrobial antioxidant enzyme inhibitor control redox potential

Control of redox potential CA/MAP

prevent postharvest ripening reduce microbial activity

Nonthermal processing Irradiation

free radical species hydrogen, H2O2, OOH

High pressure 3500-10000 atm protein damage

Pulsed electric field dielectric cell membrane destruction

Oscillating magnetic fields Microwave

thermal effect (?)

Irradiation- nonthermal - process in package, minimize contamination- form of food is not a factor- can replace preservatives, insecticides- can be used in fresh foods

Canada1960 – sprout control in potatoes and onions1961 – insect control in wheat1983 - spices

Irradiation

Doses of irradiationsprout inhibition: 0.15-0.2 kGyflour disinfestations: <= 1kGyspice cleaning: 5 kGyparasite elimination: <=6 kGypathogen destruction: <=10 kGybacterial destruction: <=5 kGy

Irradiation <= 10 kGy harmless to human health

(UN) pasteurization effect need to be used in combination with

refrigeration and CA/MAP

currently used forspices, disinfestations of cereal grains, pathogen control in poultry, trichinosis control in fresh pork, tropical fruits

Chilling

storage at T > Tfp (-1) - (+10 C)

chilling injury near Tfp

texture degradation in vegetables cold shortening of muscle foods,

staling of bread

Freezing

small many crystals desired, fast freezing entrapment of solutes, less than max concentration in the unfrozen phase

large crystals, slow freezing max concentration of solutes, tissue damage, partial dehydration,

local freeze concentration freezer burn, sublimation of ice, dry brown spots

on poultry, beef antimicrobial effect due to concentration,

intracellular freezing destabilization of proteins, vitamin and pigment

degradation, oxidation of lipids

Concentration and dehydration

concentration > 20% moisturedehydration < 20% moistureevaporation, crystallization,

sublimation, membrane separations

microorganisms survive, can recover, grow depending on aw

Controlled atmosphere

control of atmosphere composition during storage

in packaging, gas impermeable films with absorbers

Modified atmosphere closed storage rooms, allow

respiratory activity in packaging, remove air, replace

with other gases, N2, CO2

vacuum packaging vacuum, nitrogen: cheese, meat CO2 : fruits and vegetables, meat

Ohmic heating short processing times < 90 s, then

transfer into holding tube, aseptic packaging, commercial sterilization

no heat transfer surfaces, food heats inside, more efficient and uniform heating, reduces thermal quality defects

suitable for solid pieces containing liquid foods, like stews

Microwave heating

rapidcan be used in sterilizationapplicable to packaged productsprevent contaminationthermal inactivation

High pressure processing

better quality foodsready-to-serve foods, vegetablesjams, preserves, meat, seafoodpulsed high pressure applicationpressure environment, glycerol, edible

oils, water/edible oil emulsions700-900 MPa

Preservatives Legally allowed1. toxicity 2. soluble in food 3. food pH

- inhibition of chemical/biochemical reactions

- antimicrobial effect

Organic acids acidity, antimicrobial effect benzoic acid, Na- or Ca-benzoateparabens (p-OH-methyl or propylbenzoate)mold and yeast inhibitorat low pH antibacterial, 0.1%

jams, preserves, bakery products, salad dressingfruit juices

Organic acidssorbate (2,4-hexadienoic acid), K/Ca/Na

saltsmold and yeast inhibitorcheese, fruit juices, salads, bakery products

 propionic acid, Ca/Na saltsrope inhibitors in bread, cheese, spreadsmold inhibitor at high pH

Organic acidsacetic acidrope inhibitor, mold inhibitorbakery products 

lactic acid antimicrobial

citric acid acidulantion chelatorreduce oxidation

Nitrites and nitrates (NO2/NO3)

color stabilization C. botulinum inhibitor

Sulfur compounds (SO2, HSO3

-, SO32-, S2O5

2-)

antioxidant browning inhibitorantibacterial limited use due to allergic

reactions in some people wines, dried fruits, vegetables

Salt (NaCl) control of water antimicrobial

Antioxidants

rancidity inhibitorsBHA, BHT, tocopherolsascorbic acidEDTA (ion chelator)

Smoke (phenols, formaldehyde, ketones, alcohols, acids)

antioxidantantibacterial, C. botulinum

Carbon dioxide

antimicrobialcarbonated beverages

Antibiotics

nisin antibotulinal, antibacterialprocessed cheese

natamycinmold inhibitorsalami, cured cheese

Ethylene oxide

antimicrobialspices, nuts aseptic packaging

Other antimicrobials

chlorine (Na, Ca hypochlorite)ozonehydrogen peroxide

fresh fruits, vegetables

Packaging glass, metal, plastics, paper transport of gases, water vapor, low

MW components resistance (mechanical, heat,

chemical) oxygen, carbon dioxide, moisture

permeability light transmission inertness

Active packaging

interact with food or package environment responding to changesincorporation of different materials into the film or package

headspace to improve package performance- antimicrobial films

sulfur dioxide releaserethanol releaser

- oxygen scavengersiron scavengerphotosensitive dye scavengersenzyme scavengers

- moisture absorbersdessicant packages, clay, minerals, silica

- ethylene absorbers

KMnO4

Smart packaging

interact with food or package environment and give signals

indicate time/T historyindicate spoilage, remaining shelf

life, end of shelf life

Aseptic packaging

1. product sterilization2. package sterilization3. Aseptic filling and sealingLonger shelf life, better quality (?)

Hurdle technology

developed for limiting the growth of microorganisms in nonsterile foods (Leistner, 1978)

combined effects of preservation methods > sum of effects individually or large amounts of a single factor

Hurdle technology

has been used unintentionally

pickles pH + preservative (acid) + salt

sausage

aw + smoke + salt + spices + preservativesIMF (dried fruit, soft cookies)

aw + heating + preservatives pastırma

salt + spices + aw

Hurdle technology

HurdlesTpHsaltredox potentialmodified atmospherepackaginghigh pressureradiation, other physical processescompetitive flora (lactic acid bacteria)preservatives

all hurdles at the same intensity

all hurdles at different intensity

low initial microbial loadgood hygienic practice

high initial microbial load

low initial microbial loadmore nutrients

substerilizing treatmentdamaged cells

t : chillingF : heatingRVP : relative vapor pressure, awpH Eh : redox potentialpres : chemical preservativeN : nutrients