Food Preservation Lecture - PDF

MARK KEY JOHN V. SABIO, RMicro Food preservation encompasses the careful handling and processing of food to deter spoilage by impeding the proliferation of foodborne pathogens, averting fat oxidation (rancidity), and maintaining the nutritional quality, texture, an...

MARK KEY JOHN V. SABIO, RMicro Food preservation encompasses the careful handling and processing of food to deter spoilage by impeding the proliferation of foodborne pathogens, averting fat oxidation (rancidity), and maintaining the nutritional quality, texture, and flavor of the food. A practice with a longstanding history, food preservation has enabled sustained food availability beyond harvest periods while mitigating the risk of foodborne illnesses. microbial activities self-decomposition (enzymatic, chemical reactions) physical damages (insects, animals, mechanical processes) removal of microorganisms keeping out microorganisms killing microorganisms inhibiting growth of microorganisms lengthen lag phase lower growth rate  destructive effect to microorganisms inactivates enzymes level of heat treatment depends on: kinds of microorganisms effect on nutritional and organoleptic properties of food other preservation method(s) employed Pasteurization mild heat treatment kills all pathogens reduce microorganisms e.g. milk Sterilization/Appertization destruction of all viable organisms commercial sterile e.g. canned foods  63°C for 30 min. - low temperature, long time 72°C for 15 sec. - high temperature short time 140°C to 150°C for 1 to 2 sec. - ultra high temperature vegetative cells - 100°C for 10 min. viruses - 100°C for 10 min. spores - 100°C for 30 min.  time and temperature number of initial population of microorganisms temperature of incubation nature of the medium water fat salt sugar protein pH  The heat resistance of microbial cells increases with decreasing humidity, moisture, or Aw. spores of B. cereus at Aw of 1.00 and pH 6.5, D95 was 2.386 mins while at Aw of 0.86, D95 was 13.842 mins. the presence of water allows for thermal breaking of peptide bonds a process that requires more E the absence of water  In the presence of fats, there is a general increase in the heat resistance of some microorganisms. fat protection presumed to increase heat resistance by directly affecting cell moisture Clostridium botulinum long-chain fatty acids are better protectors than short-chain acids.  Some salts have a protective effect on microorganisms, and others tend to make cells more heat sensitive. supplementation of the growth medium of B. megaterium spores with CaCl2 yields spores with increased heat resistance, whereas the addition of I-glutamate, I-proline, or increased phosphate content decreases heat resistance  The presence of sugars in the suspending menstruum causes an increase in the heat resistance of microorganisms suspended sucrose increased the heat resistance of Salmonella senftenberg compared to the 4 tested substances: sucrose > glucose > sorbitol > fructose > glycerol  Proteins in the heating menstrum have a protective effect on microorganisms. High protein-content foods must be heat processed to a greater degree than low-protein-content foods in order to achieve the same end results.  Microorganisms are most resistant to heat at their optimum pH of growth. As the pH is lowered or raised from this optimum value, there is a consequent increase in heat sensitivity. in the heat processing of high-acid foods, less heat is applied to achieve sterilization compared to foods at or near neutrality Survival Curve D-value Thermal Death Time (TDT) Curve Phantom TDT Curve Z-value F-value  number of survivors vs. heating time Food sample with known number of microorganisms Heated at specific temperature Sample food each time interval Determine number of microorganisms of each sample  time (min) required to reduce microbial population by 90% at a specified temperature time that it would take for the survivor curve to traverse 1 log cycle reflects the resistance of one specific organism temp specific substrate specific t t D = log a - log b  time required to kill a given number of organisms at a specified temperature Food sample with known number of microorganisms Heated at specific temperature time Sample food each time interval Determine time where in no growth is seen  TDT Curve Killing time vs temperature Z value temperature needed for TDT curve to traverse 1 log cycle relative resistance of mcg to different destructive temperatures temp increment needed to reduce heating time 10x. Z=10 C. botulinum in canned food  D values vs. temperature 90% killing only parallel with TDT curve time to destroy a specific number of viable cells having a specific Z value at a specific temperature 1. spore-formers of public health significance (C. botulinum) low acid, pH 4.6 and above 12D heat treatment 12D Concept enough heat treatment to reduce 1012 spores to 1 spore per unit volume botulinum cook Given Dr = 0.21, then Fo= Dr (log a - log b) Fo= 0.21 (log 1 x 102-log 1) = 2.52 2. mesophilic spore-formers more resistant than C. botulinum economic considerations, reduce from 105 to 1 spore per unit volume e.g. B. coagulans Given Dr = 1.0, then Fo = 1 (log 1 x 105 - log 1) = 5 3. spore-forming thermophile most heat-resistant, intense heat treatment cause spoilage when storage temp is high e.g. G. stearothermophilus Given Dr = 4.0, then Fo = 4 (log 5 x 104 - log 1) ~19  slows down microbial activities lower enzymatic activities = slow growth stops microbial activities no enzymatic activities = no growth death or injury to microbial cells (cryo-injured) can also damage food tissues Type of microorganism and state of growth Rate of freezing Time of storage at frozen state Type of food  Viruses inactivated Protozoan parasites killed Spores more resistant than vegetative cells. Vegetative cells: G (+) more resistant than G (-) In log phase more easily killed Psychrophiles more resistant Adaptations of Psychrotroph Slower metabolic rates Cold-active enzymes Active transport system More unsaturated fatty acids in cytoplasmic membrane Retain semi-fluidity at low temp Types of Freezing 1. Quick freezing 20°C within 30 min Smaller intracellular ice crystals 2. Slow freezing within 3 to 72 hours large extracellular ice crystals Solutes become more concentrated Plant/animal cells (food) are dehydrated irreversible changes in texture, taste and appearance Death/injury of microorganism by freezing increased solute concentration ice crystal formation - dehydration intracellular freezing Slow freezing more harmful to microorganisms (-1°C to -5°C) allow time for microbial growth  Rapid initial death Gradual death during storage ↑ length of storage, ↑survivors cryoprotective agents: glycerol, tween 80, milk, egg white sugars, salts, proteins, fats Reduce amount of ice formed Lower viscosity hasten killing of mcg High water content Low pH  Initial number of mcg is low No signs of spoilage Properly wrapped to lessen freezer bums Freezer burns - browning of light colored foods - loss of moisture at the surface, irreversible Organoleptic and nutritional quality Freezer life each frozen food is assigned. freezer life based on factors such as texture flavor, tenderness, color, and overall nutritional quality upon thawing, and subsequent cooking  Slower than freezing Can kill microorganisms Lethal temp of -1 to -5 C Ice recrystallization ↑ Rate of thawing, ↑survivors No to re-freezing of thawed food Freeze-thaw cycle 1. Ice nucleation 2. Dehydration 3. Oxidative damage  lower moisture content limits microbial growth and activities limits activity of food enzymes some microorganisms are killed room temperature storage easier product transport Solar/Sun-drying slow 3 to 4 days subject to weather change pollution insects Cabinet dryer controlled heat and air circulation - 6 hours Spray dryer Drum dryer Affected by: size and shape of food temperature relative humidity air velocity Early Phase/Warming-up (20-40C) possible microbial growth Later Phase (50-70C) not much growth not very lethal unless held for long time RH in air > ERH of food absorption microbial growth hysteresis effect RH in air < ERH of food no take up of moisture no microbial growth ‘Alarm Water’ - threshold moisture content of dried foods, beyond which mold growth will be possible Chemical reactions oxidative rancidity non-enzymatic browning/Maillard reaction loss of vitamin C Control/minimize chemical changes Less moisture Less reducing sugar (involved in non-enzymatic browning) Pre-treatment with SO2 PROPER STORAGE (low RH of environment)  moisture content: 15 to 50% Aw: 0.6 to 0.85 dehydrated fruits Syrups/honey sweetened condensed milk Jams fruit juice concentrates some bakery products (pies, brownies) some dehydrated meat (peperoni)  additives - glycerol, glycols, sorbitol, sucrose Fungistats - sorbate, benzoate Moist infusion (desorption) Dry infusion (adsorption) Osmotic drying Component blending  Low Aw inhibit microbial growth Aw=0.6 - no microbial growth Above Aw of 0.6, tolerant mcgs can grow (molds) Aw~0.86 - S. aureus Heat during processing kills some mcg Length of storage lessen survivors Drying + solutes/ chemical preservatives Vacuum-packed/ gas-impermeable Low RH storage environment RH of environment < %ERH of food (Aw x 100)  Lyophilization, cryophilization dehydrates frozen food vacuum sublimation Quick Less movement More expensive of solutes during freezing Freeze-drying of Microbial Cultures Mild treatment Adding cryoprotectants (glycerol) Vacuum-packed Freeze-dried Foods Very low Aw = no microbial growth No. of survivors Enhanced by CHO, proteins in food Decreases over time of storage Storage Room ambient temp Gas-impermeable containers Prevents spontaneous lipid oxidation Rehydration Less microbial cells die  altering gaseous environment of foods ↑ CO2 (against aerobes/facultative anaerobes) ↓02 (against aerobes) low temp storage packaging materials are gas impermeable 1. Modified atmosphere Packaging (MAP) 2. Controlled-Atmosphere Packaging or Storage (CAP/CAS) 3. Vacuum packaging  hyperbaric process flushing varying mixtures of CO2, N2, 02 Low-02 system 02: 10% CO2: 20-30% N2: as necessary High 02 system 02: up to 70% CO2: 20-30% N2:0-20% For red meats (oxymyoglobin)  Controlled air in chamber More gas-impermeable packaging material Aluminum foil laminates, metal or glass containers agents to bind 02 gas-generating kit air is removed before sealing heat shrinking air squeezed out before sealing gas-impermeable containers Pressure: 1 bar to 0.3-0.4 bar  retard lag and log phases of microbial growth 10% competitive (inhibition of ethylene (senescence factor in fruits) enzymatic decarboxylation affects permeability Accumulates in lipid more fluid CM) Lowers intracellular pH inhibits enzyme functions  Kills microorganisms With sufficient energy to eject electrons from an atom shorter wavelength, ↑ energy, ↑ damage  Absorbed by protein and nucleic acids thymine dimers of nucleic acid, (mutation) poor penetrating power Bottled water Surface treatment of baked products (fruitcake) Tables/equipment surface sterilization  rapid changes in electric currents 915 million times per second Food molecules align with alternating current. Intermolecular friction heat bombarding heavy metal targets with Cathode rays high-velocity electrons)  ionizing radiation Breaks phospho-diester backbone of DNA Produce free radicals from excited nucleus 50Co or 126Cs atomic fission waste excellent penetrating power Application rate: 1-100 grays (Gy) per mín 1 Gy absorption of 1 joule per kg Radiation chamber concrete-lead walls) Element source, emission in all directions  Accelerated e Beta rays (from radioactive source) Cathode rays (from cathode like linear accelerators) poor penetrating power Application rate: 103-106 Gy per sec Directed beams Amount of energy is controlled x-rays generation Turn on/off Radappertization Radicidation Radurization  radiation sterilization commercially sterile products For pre-packaged foods (enzymes are inactivated) destroy pathogenic microorganisms 12D concept Typical dosage level: 30-40 kGy Low salt, non-acid foods: 45-50 kGy Meats at subfreezing temp (-30C) minimum radiation doses (MRD) in kGy  reduce numbers of viable non-spore-forming pathogens to undetectable levels using standard methods Typical doses: 2.5-10 kGy substantial reduction in number of spoilage microorganisms Typical doses: 0.75-2.5 kGy  Addition free radical acceptors reducing temperature during treatment treatment under anaerobic conditions reduction of moisture in food prior to irradiation  type of organisms number of organisms composition of food presence or absence of O2 moisture content temperature age of organisms  chemicals added or naturally present retard microbial growth or kills cells preservatives  added intentionally in small amounts antimicrobial agents antioxidants (B-hydroxytoluene, BHT) Emulsifiers flavors stabilizer and thickener (pectin or gelatin) Color bleaching agents sequesterants or clarifying agents anti-caking agents humectants (glycerols) foam inhibitors  maintain or improve nutritional quality enhance keeping quality make food more attractive aid in food processing Based on success of chemical of treatment diseases Only GRAS can be used in food generally recognized as safe List by US FDA ineffective chemotherapeutic agent Host toxicity  disguise faulty/processing and handling methods lessen nutritive value not safe for human consumption  static agents (inhibit) cidal agents (kill) can be relative: high concentration low concentration diluted interference with genetic system damage to cell wall and cell membrane inhibition of enzymes binding to essential nutrients  type of chemical and its concentration- higher conc, more cells are affected Acceptable level type of organisms and its physiological state Spores vegetative cells Yeasts < molds Stationary < log no of organisms ↑ microbial load, ↑ conc of chemical  composition of food and its pH In solid food < in liquid food ↓pH, ↑ activity of preservative Temperature ↑ temp, ↑ effective (away from opt T) Time ↑ Time of contact, ↑ effective  maximum level: 0.1% antifungal agent antibacterial (50 to 500 ppm) used in: tomato catsup, salad dressings, soft drinks, fruit juices pH 4: 60% undissociated - most active blocks oxidation of glucose and pyruvate (inactivates enzymes) Inhibits nutrient uptake Prevents endospore outgrowth  esters of p-hydroxybenzoic acid methyl-, propyl-, heptyl- maximum level: 0.1% Anti-fungal (~100 ppm) Anti-bacterial (10-4000 ppm) G+ > G- less sensitive to pH Undissociated at pH 8.3 Foods with pH 3 to 8 (acidic, beer, bakery products) Inhibits nutrient uptake Inactivates enzymes  Ca, Na, K salts maximum level: 0.2% anti-fungal (molds) antibacterial (aerobics) LAB are resistant Clostridia and S. aureus can be inhibited used in cheeses, cakes, cured meats (+ nitrite) membrane disruption inhibits enzymes impairs nutrient uptake  Ca or Na salts fungistatic (molds) used in bakery products membrane disruption inhibits enzymes impairs nutrient uptake  K or Na salts maximum level: 120 ppm inhibit microbial growth stabilize red color of meat flavor development interfere with iron-sulfur enzymes (ferredoxin) Perigo factor (antibotulinal): nitrite + heat  Gas/liquid SO2, Na or K salts of SO3, HSO3, S205 Maximum level: 300 ppm Used in: dried fruits, lemon juice, molasses, wines, fruit juices Antimicrobial (against LAB, yeasts and molds) Antioxidant, protection against free radicals Not allowed in meat and other thiamine sources Strong reducing agent SO2 and sulfurous acid: reacts with enzymes in cell  4.8% Na lactate in pre-cooked meats Effective against: spore-formers, S. aureus. Y. enterocolitica, L. monocytogenes, Salmonella Na diacetate against-yeasts and molds in breads and cakes lower pH microbial growth enzyme activity  lactic antagonism (LAB) inhibition due to: decrease in pH due to acid produced by introduced microorganisms diacetyl, H2O2, or other antimicrobials (bacteriocin) e.g. Microgard cottage cheese with skim milk culture of Propionibacterium freudenreichii subsp. Shermanii acetate, propionic acid and proteins against G-and molds Bacon produced by 'Wisconsin' process With Pediococcus acidilactici and other preservatives  Anti-microbial proteins from LAB first use: prevent spoilage of C. batyricum in Swiss cheese e.g. Nisin By Lactococcus lactis Lantibiotic (meso- and 3-methyl-lanthionine) Against G+(spore-formers) As food preservative: milk and dairy products, canned foods, mayonnaise, baby foods, meat (replace NO2) MOA: form spores in CM, inhibits amino acid transport  viruses that infect bacteria Host-specific some studies in: beef to control Pseudomonas poultry to control C. jejuni and Salmonella cheese to control L. monocytogenes and E. coli Factors to consider: Lysis of host Replicating host Food constituents effect on attachment and lysis  High Hydrostatic Pressures (HHP) or Pascalization non-thermal 100 to 1000 MPa for few min Against vegetative cells organoleptic properties not affected meats, seafoods jams and fruit juices  high electric fields in short pulses non-thermal 5-55 kV per cm 2 microseconds Electroporation of cell membrane fruit juices and liquid eggs  Spores are exposed to: Ultrasonic waves: release Ca and other components in spores Heat: kills cells MTS has been shown to be effective in reducing the thermal resistance of the enzymes peroxidase, lipoxygenase, and polyphenol oxidase. Control of Microbial Growth disruption of homeostasis pH, temp, water content etc. metabolic exhaustion Autosterilization during storage overcoming stress response Shock proteins Hurdle Concept combination of various food preservation methods temperature (high or low) Aw pH Eh chemical preservatives competitive organisms (LAB) Multi-target preservation