Introducing 

Prezi AI.

Your new presentation assistant.

Refine, enhance, and tailor your content, source relevant images, and edit visuals quicker than ever before.

Loading…
Transcript

The classical approach to overcome or

minimise undesirable quality changes in thermal processing is the high temperature short time (HTST)

concept.

The problem in applying the HTST principle to solid and high viscosity foods is that the parts

of the food in contact with the hot surfaces will be overheated and quality losses will occur. One way

to overcome this problem is by heat processing unpacked foods followed by aseptic packaging.

On the whole improvements in conventional heating processes can come about only two routes;

higher rates of heat transfer to critical locations in the food, or more homogenous heat distribution within the food.

The control factors for commercial applications are:

flow rate, temperature, heating rate and holding time of the process.

The factors influencing the heating in the food are:

the size, shape, orientation, specific heat capacity, density, thermal and electrical conductivity.

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.

  • Both high and low acid products can be processed by this method.

  • In this process simultaneous and uniform heating of solid and liquid phases can be achieved, thus reducing the danger of under processing as well as nutritional loss.

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).

To minimise temperature variation and also for process economy reasons, microwaves should be used in combination with conventional heating.

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.

Microbial inactivation achieved depends on :

  • Type and number of micro-organisms
  • The magnitude and duration of HHP treatment
  • Temperature
  • Composition of the suspention media or food.

  • In general, yeast and molds are more easily inactivated by pressure than bacteria.

  • Among bacteria, vegetative forms are more susceptible than spores.

  • Gram positive bacteria are more resistant than gram-negative-negative bacteria.

  • However, bacterial spores are difficult to inactivate by HPP alone and HPP must be used with other preservation methods.

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.

The structure of food protein and polysaccharides can be changed with hight pressure to bring about modification in rheology and mouthfeel.

Gels ontained by HHP processing have lighter color and lower strength than gel obtained with traditional heat processing.

However, the nutritional value of HHP obtained gels is better retained and their novel texture could potentially be used in food product development areas.

Gels obtained from HHP gelatinized starches have a weaker matrix than heat-induced types.

Generally, an increase in pressure increases microbial inactivation.

However, increasing the treatment time does not necessarily increase microbial death rates.

When combined with other preservation factors, such as water activity, pH, temperature or antimicrobials, pressure action can have an antagonistic, additive, or synergistic effect.

Food with low water activity achieved by high sugar concentration decrease the sensibility of micro-organisms to pressure (antagonistic effect).

Low pH and the use of combined moderate temperature promote pressure efficacy (synergistic effect) on microbial inactivation.

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 .

  • The effects of localized heating, free radical production causing DNA damage, and microstreaming, which causes thinning of cell membranes, are crucial in the inactivation.

  • large cells, such as yeast (520 mm), are more susceptible to the effects of cavitation, due to having a larger surface area than smaller sized cells.

  • In general, spores of bacteria (e.g. Bacillus and Clostridium spp.) are more resistant to cavitational effects than vegetative cells, which are in growth phase.

  • Fungi are generally more resistant than vegetative microorganisms,
  • aerobes more resistant than anaerobes,
  • cocci typically more resistant than bacilli, due to the relationship of cell surface and volume.

  • The bactericidal efficiency of ultrasound on Gram-positive versus Gram-negative bacteria is controversial.

Some studies report Gram-positive bacteria to be more resistant to cavitation than Gram-negative bacteria while others found no significant differences in their resistance to inactivation by ultrasound

• Irradiation source: Xenon flash lamps 200-1100 nm wavelength

• Pulse durations no longer than 2 ms

Gram-negative bacteria, Gram-positive bacteria and fungal spores.

The colour of the spores can play a significant role in fungal spore susceptibility.

Aspergillus niger spores are more resistant than Fusarium culmorum spores, which could be because the pigment of the A. niger spores absorbs more in the UV-C region than that of F. culmorum spores.

The antimicrobial effects of UV light on bacteria are attributed to structural changes in the DNA, increased cell membrane permeability and depolarization of the cell membrane.

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 .

Generally,

Gram-positive vegetative cells are more resistant to PEF than Gram-negative bacteria, while yeasts show a higher sensitivity than bacteria.

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.

  • Grains - kill insects (no fumigation gases)
  • Tubers - inhibits sprouting
  • Spices – kills bacteria and insects
  • Vegetables and fruits - kill pests
  • Pork - control Trichinae Poultry - kill salmonella
  • Beef - kill E. Coli 0157:H7
  • Hospital meals - persons with low immunological resistance
  • NASA meals

pears get mushy

milk becomes rancid

  • Plasma

.

Because of the limit information about the nutritional and chemical changes in food products treated with this technology, specially, sensitive food which has high amount of lipid and vitamins additional issues concerning food quality and safety must be considered.

Food Processing

Is needed to

•Ensure safety (kill microorganisms)

•Increase digestibility

•Increase shelf life

(destruction of enzymes, toxins)

•Add value (texture, flavor, color)

•Make new products

•Meet the needs of specific section of

population (allergic to food proteins)

Thermal Processing

Use of high temperatures to destroy enzymes and microorganisms that could reduce quality and/or safety of food

PASTEURIZATION

A mild heat treatment used primarily to destroy pathogenic organisms but it also destroys enzymes and reduces microbial load. Requires an addition preservation method to extend shelf life (example: refrigeration, drying)

Conventional thermal sterilization

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

Used for milk, liquid eggs, fruit juices and beer.

NUTRITIVE AND OVERALL QUALITY OF CANNED FOOD

CANNING -

COMMERCIALLY STERILE PRODUCT

THEORY - Commercial sterilization is the process where all spoilage and pathogenic micro organisms that could be present in packaged food under normal temperatures are destroyed.

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

Comparison of thermal and non-thermal sterilization in food industry

Electric heating methods

Ohmic Heating

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.

MICROWAVE HEATING

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.

Covers almost all food product groups

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

High frequency/radio frequency heating

Foods are heated by transmitting electromagnetic energy through the food placed between 2 electorods.

The main disadvantages are equipment and operating costs: RF heating equipment is more expensive than conventional convection, radiation, steam heating or ohmic heating systems.

In particular, RF used for:

post-baking of biscuits and cereals and

RF drying of foods are well-established applications.

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

Non- Thermal processing

High Pressure Processing

Pulsed Light

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).

Effects on micro-organism

Ultra sound Processing

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.

Effect on micro-organism

Industrial

Applications of High Intensity Light Technology

  • High-acid products like juices, jams, jellies and yoghurts
  • Pasteurization of meats and vegetables

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

  • Decontamination of vegetables, dairy products.
  • Microbial inactivation of water.
  • Sanitation of packaging
  • materials Disinfection of equipment surfaces

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

Pulsed electric field

Membrane Processing

Ozone Processing

PEF is a non-thermal food preservation technology that involves the discharge of high voltage electric pulses (up to 70 kV/cm) into the food product, which is placed between two electrodes for a few microseconds.

Most PEF studies have focused on PEF treatments effects on the microbial inactivation in

milk,

milk products,

egg products,

juice

and other liquid foods.

Disadvantage

Not accepted in EU at all for

food

​​ Not compatible with organic

foods

​​ Only for specific foods useful

​​ Expensive

Ultrafiltration

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.

Ultrafiltration

Microfiltration

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.

Combined technologies

increase in the membrane potential leads to reduction in the cell membrane thickness.

Cold Sterilization

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.

  • Liquid foods fruits juices,soups liquid egg and milk
  • Accelerated thawing

​​ 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

Irradiation

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.

Radiation vs. Irradiation

Plasma Processing

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

Atmospheric pressure plasmas

plasma definition, generation and classification

electrons, positive and negative ions, free radicals, and gas atoms, molecules in the ground or excited state and quanta of electromagnetic radiation (photons).

Depending on the type of energy supply and amount of energy transferred to the plasma, density and temperature of the electrons are changed.

forth state of matter

TYPES OF RADIATION PROCESSES

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

Potential application in food

Depends on :

Labeling Requirements

  • RH ( higher RH lead to higher effectiveness of treatment),
  • the type of food which is being reated

Irradiated foods are required to have either “treated

with irradiation” or “treated by irradiation” displayed

prominently on the label.

“Radura” must be displayed.

The Limitations of APP process for food sterilization

The greatest disadvantage of food irradiation is

its name…

evokes unpleasant associations of radioactivity,

nuclear threats, high technology, genetic mutation, and

cancer

Microbial inactivation mechanism of plasma

  • In treatment of bulky and irregularly shaped food, restricted volume and size of the food should be considered.

  • microbial inactivation occur on the surface of the food being treated since plasma reactive species are limited to penetrate into foods.

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.

Supervisor: Dr. Z. Piravi

Presented by : Sona Rasoulian

CONCLUSION

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.

Learn more about creating dynamic, engaging presentations with Prezi