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The control factors for commercial applications are:
flow rate, temperature, heating rate and holding time of the process.
In practise the ohmic method heats particulates faster than the carrier liquid (heating inversion), which is not possible by traditional, conductive heating.
Although the heating rate may be uniform, the temperature distribution across the food material can vary significantly. Therefore design of effective ohmic heaters depends on the electrical conductivity of the food.
In general e.g. fruits are less conductive than e.g. meat samples and lean meat is more conductive than fat.
The transfer of microwave energy to food is done by contactless wave transmission.
frequencies used : 2450 MHz or 915 MHz
In microwave heating less water is needed so that less extraction of valuable nutrients including minerals occur.
One major limitation for industrial application of microwave heating for sterilization is the difficulty in controlling heating uniformity caused by the limited penetration depth of microwaves.
The parameters important for the heating uniformity are:
food composition , geometry, packaging, applicator design (microwave energy feed system).
The effect of high pressure sterilization on colour is product dependen.
The quality of the high pressure sterilised products is usually superior to conventionally heat sterilised products, particularly to texture, flavour, and retention of nutrients.
Pressure alone is in general not enough to inactivate food deteriorative enzymes.
However when pressure is used in combination with other factors, such as mild heat treatment, enzyme inactivation can be attained.
Ultrasound is a form of energy
generated by sound waves of
frequencies that are too high
to be detected by human ear,
i.e. above 20 kHz .
• Irradiation source: Xenon flash lamps 200-1100 nm wavelength
• Pulse durations no longer than 2 ms
PEF is suitable for liquid or semi-solid product .
Mechanisms of Microbial Inactivation
1. Electrical Breakdown
2. Electroporation
The susceptibility of a microorganism to PEF inactivation is highly related to the intrinsic parameters of the microorganism such as size, shape, species or growth state .
Ozone (O3)
• A gas - triatomic form of oxygen.
• Most powerful oxidizing agent available
for conventional water treatment - highly
reactive.
• Unstable - must be generated onsite
and used.
• Slightly soluble in water, but more so
than oxygen.
RADURIZATION - Reduce number of common spoilage organisms - extends shelf life.
RADICIDATION - Elimination of non-spore forming pathogenic bacteria.
RADAPPERTIZATION - Commercial sterilization of foods.
pears get mushy
milk becomes rancid
.
Use of high temperatures to destroy enzymes and microorganisms that could reduce quality and/or safety of food
EGG PASTEURIZATION: Based upon killing and preventing growth of salmonella (food-borne illness microorganism).
Liquid eggs heated to 140-144° F (60-62° C) and held for 3.5-4.0 minutes. Often sugar or salts are added. 275-284° F (135 to 140° C) for a few seconds
Thermal sterilization of canned foods is such a mature technology that it might be supposed that there is little potential for further development.
Optimum thermal sterilization of food always requires a compromise between the beneficial and destructive influences of heat on the food.
On the positive side,
heat destroys microbial pathogens, spoilage organisms and endogenous and introduced enzymes that would otherwise render the food inedible or unsafe.
negative side :
Covers almost all food product groups
1. PROTEIN : Quality of the protein can be improved or impaired.
2. FATS : Oxidative rancidity can be increased if oxygen not properly removed from cans.
3. CARBOHYDRATES - Nonenzymatic browning increases.
4. VITAMINS - Some water soluble vitamins lost: Thiamin, vitamin C. High temperature short time .
º Fat soluble vitamin A and D lost at high temperatures in presence of oxygen
Loss of original flavor, taste appearance, color
Direct energy transport to the product (steam)
Well established technology
High food safety
High heat load for the product causing structural
and nutritional defects
Energy consuming
Ohmic (electrical resistance) heating is a heat treatment process in which an electric current is passed through the food to achieve sterilization and desired degree of cooking.
Ohmic heating is a high temperature short-time method (HTST) that can heat an 80 % solids food product from room temperature to 129oC in ca. 90 seconds allowing the possibility to decrease of high temperature over processing.
1. Dipolar Interaction
Once microwave energy is absorbed, polar molecules such as water molecules inside the food will rotate according to the alternating electromagnetic field. The water molecule is a “dipole” with one positively charged end and one negatively charged end. Similar to the action of magnet, these “dipoles” will orient themselves when they are subject to electromagnetic field. The rotation of water molecules would generate heat for cooking .
2. Ionic Interaction
In addition to the dipole water molecules, ionic compounds (i.e. dissolved salts) in food can also be accelerated by the electromagnetic field and collided with other molecules to produce heat.
Generates the heat in the food itself, delivering thermal energy
where it is needed.
Ease of process control with instant switch-on shut-down.
Faster than conventional heat processing.
Minimal mechanical damage to the product and better nutrients and vitamin retention.
High energy efficiency because 90 % of the electrical energy is converted into heat.
Lack of temperature monitoring techniques in continuous system.
Differences on electrical conductivity between solids and liquid.
Particulate temperatures similar or higher than liquid temperatures
Foods are heated by transmitting electromagnetic energy through the food placed between 2 electorods.
The advantage is increased power penetration. The longer wavelength at radio frequencies compared to microwave frequencies mean that RF power will penetrate further in the most products than microwave power.
This can be advantage especially when thawing frozen products.
Direct energy transfer into the food
No structural damages to food
Improved food quality: more uniform
heating
increased throughput
Shorter processing lines
Maillard reactions may be reduced
Technology is in a early stage
of the development
High energy consumption
Not compatible with organic
High pressure processing (HPP),
or
high hydrostatic pressure (HHP),
or
ultra high pressure (UHP) processing,
subjects liquid or solid foods, with or without packaging, to pressures between 40 and 1000 MPa ( 1-20 min).
When high pressures up to 1000MPa are applied to packages of food that are submerged in a liquid, the pressure is distributed instantly and uniformly throughout the food (isostatic).
Pulsed light (PL) is a technique to decontaminate surfaces by killing microorganisms using pulses of an intense broad spectrum, rich in UV-C light.
UV-C as the most important part of the spectrum Xenon flash lamps have an emission spectrum ranging from ultraviolet to infrared light.
The UV-C part of the spectrumis the most important for microbial inactivation.
Industrial
Advantage
Disadvantage
Not yet commercial application for shelf-stable low-acid products
Energy consuming
Expensive equipment
Food should have ca. 40% of free water for antimicrobial effect
Limited packaging options
Texture, taste and retention of nutrients are better than for conventional retort.
Shorter treatment times
Lower maximum temperature
Faster heating and cooling
More uniform temperature rise within the product
In principal independent of the size, shape and composition of the food product
No evidence of toxity
Any food that is heated
Disadvantage
Advantage
Cavitation is the formation of vapour cavities in a liquid that are the consequence of forces acting upon the liquid.
It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low. When subjected to higher pressure, the voids implode and can generate an intense shockwave.
Can denaturate proteins and produce free radicals which can affect the flavour (high fat foods)
Effective against vegetative cells, spores
and enzymes
Reduction of process times and temperatures
Most PEF studies have focused on PEF treatments effects on the microbial inactivation in
milk,
milk products,
egg products,
juice
and other liquid foods.
Not accepted in EU at all for
food
Not compatible with organic
foods
Only for specific foods useful
Expensive
Ultrafiltration (UF) is a variety of membrane filtration in which forces like pressure or concentration gradients leads to a separation through a semipermeable membrane.
Suspended solids and solutes of high molecular weight are retained in the so-called retentate, while water and low molecular weight solutes pass through the membrane in the permeate.
The typical particle size used for microfiltration ranges from about 0.1 to 10 µm.[1] In terms of approximate molecular weight these membranes can separate macromolecules generally less than 100,000 g/mol
The filters used in the microfiltration process are specially designed to prevent particles such as, sediment, algae, protozoa or large bacteria from passing through a specially designed filter.
More microscopic, atomic or ionic materials such as water (H2O), monovalent species such as Sodium (Na+) or Chloride (Cl-) ions, dissolved or natural organic matter, and small colloids and viruses will still be able to pass through the filter.
Microfiltration (commonly abbreviated to MF) is a type of physical filtration process where a contaminated fluid is passed through a special pore-sized membrane to separate microorganisms and suspended particles from process liquid.
increase in the membrane potential leads to reduction in the cell membrane thickness.
The plasma membranes of cells become permeable to small molecules after being exposed to an electric field, and permeation then causes swelling and eventual rupture of the cell membrane.
MF membranes are employed in food industry as a method to remove bacteria and other undesired suspensions from liquids, a procedure termed as cold sterilization , which negate the use of heat.
PEF technology is considered superior to traditional thermal processing methods because it avoids or greatly reduces detrimental changes in the sensory and physical properties of foods.
Kills vegetative cells
Colours, flavours and nutrients are preserved
No evidence of toxity
Relative short treatment time
Difficult to use with conductive materials
Only suitable with liquids or
particles in liquids
Energy efficiency not yet certain
No effect on enzymes and spores
Combining nonthermal processes with conventional processing methods enhances their antimicrobial effect so that lower process intensities can be used.
Combining two or more nonthermal processes can also enhance microbial inactivation and allow the use of lower individual treatment intensities. For conventional preservation treatments, optimal microbial control is achieved through the hurdle concept, with synergistic effects resulting from different components of the microbial cell being targeted simultaneously.
The energy is at such high levels that electrons leave their orbits forming ions.
The ions cause destruction of microorganisms, insects and other pests
GAMMA RADIATION - Cobalt 60 or cesium 137 (radioactive isotopes).
Food does not become radioactive
Gamma rays from radioactive material penetrate more deeply .
• Radiation: Mode of heat transfer in vacuum
Non-Ionizing Radiation: RF, microwaves, IR
Ionizing Radiation: X-rays, gamma rays, and energy from radioactive isotopes.
Irradiation: Ionizing radiation
electrons, positive and negative ions, free radicals, and gas atoms, molecules in the ground or excited state and quanta of electromagnetic radiation (photons).
forth state of matter
Low pressure glow discharge plasmas are of great interest in microelectronic industries but their vacuum equipment limits their application.
Therefore one of the recent challenges was developing new plasma sources that can operate at or near 1 atmospheric pressure.
Power sources of atmospheric pressure plasma generation can be microwave, RF (radio frequency), pulsed, AC (alternating current) or DC (direct current).
It can be generated in the large range of temperature and pressure
Low temperature plasma
High temperature plasma
Depends on :
Irradiated foods are required to have either “treated
with irradiation” or “treated by irradiation” displayed
prominently on the label.
“Radura” must be displayed.
The greatest disadvantage of food irradiation is
its name…
evokes unpleasant associations of radioactivity,
nuclear threats, high technology, genetic mutation, and
cancer
Covers almost all food product groups
Pre-packed products can be processed
Not accepted in EU at all for
food
Not compatible with organic
food
Several mechanisms are considered to be responsible for microbial inactivation.
1. direct contact to antimicrobial active spices.
2. Accumulation of charged particles at the surface of the cell membrane can rupture the cell membrane.
3. Oxidation of the lipids, amino acids and nucleic acids with reactive oxygen and nitrogen spices cause changes that lead to microbial death
or injury.
In addition to reactive spices, UV photons can modify DNA of microorganisms and as a result disturb cell replication.
Contribution of mentioned mechanisms depends on:
plasma characteristics and to the type of microorganisms.
The main problem with the thermal processing of food is loss of volatile compounds, nutrients, and flavour. To overcome these problems non thermal methods came into food industries to increase the production rate and profit. The non thermal processing is used for all foods for its better quality, acceptance, and for its shelf life. The new processing techniques are mostly employed to the liquid packed foods when compared to solid foods. Since the non thermal methods are used for bulk quantities of foods, these methods of food preservation are mainly used in the large scale production. The cost of equipments used in the non thermal processing is high when compared to equipments used in thermal processing. After minimising the investment costs of non thermal processing methods, it can also be employed in small scale industries.