Thermal and Non thermal food processing technology

8/10/2019 Thermal and Non thermal food processing technology

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Thermal and Non-Thermal Technique in Food Technology

Non-thermal technique Thermal technique

1. High Hydrostatic Pressure (HHP)

2. Pulsed Electric Field (PEF)

3. Ultrasound

4. Pulsed Light (PL)

5. Irradiation

6. Electron Beam

7.

Oscillating Magnetic Field (OMF)

8. Ozone

9. Gas, cold plasma

1. Thermal processing

2. Aseptic packaging

3. Baking

4. Frying

5. Ohmic heating

6. Microwave

7.

Radio frequency

8. Infrared

9. Drying

10.Extrusion

11.Chilling

12.Freezing

13.Freeze drying

NON-THERMAL PROCESSING TECHNIQUE:

Objectives: Render foods free ofpathogenic & spoilage organisms


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Retain color, flavor

Improve shelf life

Improve texture

Methods:

Non-thermal Processing

1. High Hydrostatic Pressure (HHP)

2. Pulsed Electric Field (PEF)

3. Ultrasound

4. Pulsed Light (PL)

5. Irradiation

6. Electron Beam

7. Oscillating Magnetic Field (OMF)

8. Ozone

9. Gas, plasma

Mind map:

High Pressure Processing:

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).

Pasteurization using 400 -600 MPa,

-at room temperature for a few minutes

Fresh-like quality attributes,

-Pasteurized shelf stable high acid foods

-Pasteurized low acid food products

Non-thermal

Processing

Field

PEF, PL, OMF,Irradiation,

Ultrasound

Mechanical Mixing,

Emulsifying,

GasOzone, CO2, Cold

Plasma


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What is high pressure? (Three African elephants (~5 tons each) standing on a 18 mm (dia.)

disk)

High pressure processing model:

Hite (1899) reported treatment and prevention of souring of milk treated by HHP Hite (1914) reported

results from studies, which were mainly growth or no growth (no kinetics) on non-spore forming

Bacillus prodigiosus (now called as Serratia marcescens), and vegetative cells of Bacillus subtilis,

yeasts, as well as pathogens Bacillus typhosus (Salmonella

typhimurium), Bacillus diphtheriae, anthrax, tuberculosis,

bubonic plague Cruess predicted in 1924 that HHP would be

used to preserve fruit juices.

High pressure as a sterilization process

Combination of pressures (600-800 MPa) and

temperatures (60-90C)

-Vegetative cell inactivation

-Bacterial spore inactivation

-Minimal thermal degradation

Foods with superior quality attributes

Temperature profile:


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Effects of High Pressure

For orange juice processed at 483 MPa, 60 s, 7 log reduction of pathogens (E. coli, Salmonella) HHP

treated OJ was very close to freshly squeezed For RTE meats, processed at 600 MPa, 3-4 log

reduction of L. Monocytogenes HHP acts instantaneously and uniformly throughout a mass of food

independent of size, shape and food composition.

Rutgers HHP Facility


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HHP Processed Current and Potential Products in the Market

Apple cider,

fruit smoothies,

Ham,

chicken,

turkey,

sausages

Oysters,

High Intensity Pulsed Electric Field (PEF) Processing

Applications of high voltage pulses to foods placed between two electrodes.

10 to 80 kV/cm

10 to 10000 s

Novel food preservation technology recognized for its ability to inactivate bacteria present in liquid

food products at low temperatures.

Yeast cells visualized under PEF

by Optical Camera (Howard Zhang,

OSU)

Clams,

other shell fish

Hummus,

Guacamole,

Salsa,

wet salads

Meat joints

Breakfast items (eggs)

Pot roasts/stewsPot

High quality fruit/vegetables

High quality soups

RTD Teas/coffee Dairy desserts/smoothiesdesserts

Cheese/cream /sauces

Low acid pastas

Liquid flavors/herbs


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Examples of PEF Processed

Apple juice

Orange juice

Milk Beaten eggs

Green pea soup

Brine solution

Electromagnetic Radiation

PEF processed products

Phosphate buffer

Milk

Saline solution

Yogurt

Deionizedwater

Sodium alginate

Orange juice

Potato dextrose agar

Apple juice

Simulated milk ultrafiltrate

Pea soup

High Intensity Pulsed Light Processing

Intense, short duration, broad-spectrum light is exposed to a food or package

Very effective on product surfaces

Marginally effective at penetrating to depths in foods

Reduces the need for chemical disinfectants and preservatives

Sucrose and xanthan solution

Liquid egg

Cranberry juice

Dry spices

Wheat flour Rice wine

Rice pudding

Apple cider

Cheese sauce

Beef burgers

Horchata


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Food Applications of Pulsed Light FDA

( approved Pulsed Light Technology for food)

Use of high intensity PL as am irradiation processing method

Safe use of a source of high intensity light to control microorganisms on the surface offoods.

Irradiation source: Xenon flash lamps 200-1100 nm wavelength

Pulse durations no longer than 2 ms

Total cumulative treatment not to exceed 12 J/cm2

Pulsed Light Processing

Treatment of packaged products by pulsed light minimizes risk of further recontamination.

Many plastics can be used to efficiently transmit light to the product. Ex.: polyethylene,

polypropylene, nylon

Radiation vs. Irradiation

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

Radiation Nature of rays Typical energy in

MeV (1 eV = 10-19 J)

Penetration

x rays Man made photons 0.01-10 20-150

rays Photons from

pisotopes

0.1several 30-100

rays Electrons from

isotopes

0.01- 1 0.1-0.5

Cathode rays Electrons from

accelerators

0.10 110 0.1015

Protons Protons from

accelerators

MeV range 0.003

Neutrons Neutrons from

fission or isotopes

MeV range 10


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rays He nuclei from

isotopes

1-10 0.005

Ref: Physical Principles of Food Preservation, 2nd ed., M. Karel and D.B. Lund, Chapter 11

Ionizing Radiation

The energy is at such high levels that electrons leave their orbits forming ions

The ions cause destruction of microorganisms, insects and other pests

Radiation Source:

Cobalt-60

Cesium-137

Linear acceleration Electron beam technology uses electricity. Beam penetrates 2-3 cm. Good for thin

products. Gamma rays from radioactive material penetrate more deeply .

Current Food Products Processed by Ionizing Radiation

Potatoes,

Spices,

Dry vegetable seasoning,

Ground beef,

pork,

poultry,

Some fruits and

vegetables

More than 150 food irradiation facilities in 40 countries Food irradiation is one of the most

extensively and thoroughly studied methods of food preservationThakur and Singh (1994)

Labeling Requirements

Irradiated foods are required to have either treatedwith irradiation or treated by

irradiationdisplayed prominently on the label.

Radura must be displayed.

Ingredients (e.g. spices) are not required to have any labeling.

Restaurant foods do not require labeling

Consumer Acceptance

The greatest disadvantage of food irradiation is its nameevokes unpleasant associations of

radioactivity, nuclear threats, high technology, genetic mutation, and cancer

Ozone Processing

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 solublein water, but more so than oxygen.

Effect on Meat


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Ozone treatment: up to 97% reduction of E. coli

Sensory Evaluation (after cooked): No significant Difference

Appearance (color and texture): No Significant Difference

High-Intensity Oscillating Magnetic Field (OMF) Processing

Superconducting coils

Coils which produces DC fields

Coils energized by the discharge of energy stored in a capacitor.

Coil-Capacitor System for OMF Generation

Examples of

Foods

Preserved with OMF Milk (with Streptococcus thermophilus)

Yogurt or Curd (with Saccharomyces)

Orange juice (with Saccharomyces)

Brown N Serve rolls dough (with bacterial spores)

Power Ultrasound Processing

Ultrasound processing: principle

Energy generated from waves of 20,000 or more

vibrations per second

-high frequency or diagnostic ( 2-10 MHz)

-low frequency or power (20-100 kHz)

Lyses and inactivates cells

-Intracelullar cavitation

Variables to control:

-Temperature

-Amplitude of the ultrasonic wave

-Time of treatment

-Cycles

Modes of sonication

Sonication(US)

-Ultrasound


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Thermo-sonication (TS)

-Ultrasound plus heat

Mano-thermo -sonication (MTS)

-Ultrasound plus heat and pressure

Ultrasound treatment of milk

Cavitation:

1. High-speed microjets of liquid, 400 km/h2. High spot temperature, 5000C

3. High pressure, several hundreds of atmospheres.

Shock waves produced by cavitation have been shown sufficient to

cleave polymers by mechanical breakage of the chains

Ultrasound Application in Food Processing

Mechanical Effects Chemical/Biochemical Effects

Crystallization of fats, sugars, etc.sugarsetc

Microbial inactivation Effluent treatment


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Degassing

Destruction of foams

Extraction of flavorings

Filtration and drying

Freezingg

Mixing and homogenization

Precipitation of airborne powder

Tenderization of meat

Modification of growth

of living cells

Alteration of enzyme

activity

Oxidation

Sterilization of equipment

Plasma Processing

Temp. 20-60 C

Partially ionized or activatedgas (ppm)

Non-chemical low temperature decontamination of heat sensitive surfaces (plastics, vegetables,

fruits, meat)

Cold plasma


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Concluding Remarks

Non-thermal food processing is still an evolving field

Some non-thermal processes seem to have better potential than others

Equipment cost (though coming down) still is a major limiting step

Process documentation, verification procedures need to be worked out for

government approval to assure safety (adequate processing)

Thermal processing

Thermal Processing is the application of heat treatment for the production of consumer safe and shelf

stable ready to consume food products in sealed containers

Definition:Thermal Processing is the application of sufficient heat treatment to cause destruction of

all pathogenic microorganisms and inactivate or destroy those

microorganisms and enzymes that deteriorate the food under ordinary conditions of storage

and distribution

Primary objective:

Destroy the most heat resistant pathogenic spore -forming organism ---- Clostridium

botulinum

Secondary objective:

Destroy vegetative and spore-forming microorganisms that cause spoilage. Spoilage spore-

formers are usually more heat resistant than pathogenic spore formers.

Thermal Death Time:

It is the shortest time necessary to kill a given number of organisms at a specified temperature. By

this method, the temperature is kept constant and the time necessary to kill all cells is determined.

Thermal death point:It is the lowest temperature necessary to kill a given number of organisms in a fixed time, usually 10

minutes.

D value:

This is the decimal reduction time, or the time required to destroy 90% of the organisms.

The destruction of vegetative bacteria by heat is logarithmic and follows a first order reaction.

Z value

This is refers to the temperature change (C) which results in a tenfold (1 log) decrease or increase in

the D value. The z value provides information on the relative resistance of an organism to different

destructive temperatures and can be used to determine the equivalent D values at different

temperatures.Fvalue / Farenheit value:

F-value is the time in minutes required to destroy the spores / vegetative cells of a particular

organisms at 121C. F Value represents, a measure of the ability of the heat process to reduce the

number of spores or vegetative cells of a given organisms in a container.

The 12D concept

the widely accepted minimum lethality for a heat process applied to low acid canned foods is that it

should produce 12 decimal reductions in the number of surviving Cl. botulinum spores at 121C. This

is known as the 12D concept or botulinum cook or commercially sterile. If D121 of Cl. botulinum

is 0.21 minutes


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Aseptic Packaging

Aseptic packaging can be defined as the filling of a

commercially sterile product into a sterile container under aseptic

conditions and hermetically sealing the containers so that infection is

prevented. This results in a product, which is shelf-stable at ambient

conditions.

Aseptic packaging technology is fundamentally different from

that of conventional food processing by canning. In canning, the

process begins with treating the food prior to filling. Initial operations

inactivate enzymes so that these will not degrade the product during

processing. The package is cleaned, and the product is introduced into

the package, usually hot. Generally, air that can cause oxidative

damage is removed from the interior. The package is hermetically

sealed and then subjected to heating. The package must be able to

withstand heat up to about 100C for high acid products and up to127C for low acid products, which must receive added heat to

destroy heat-resistant microbial spores. Packages containing low-acid

(above pH 4.5) food must withstand pressure as well. Although conventional canning renders food

products commercially sterile, the nutritional contents and the organoleptic properties of the food

generally suffer in the processing. Moreover, tinplate containers are heavy in weight, prone to rusting

and are of high cost.

Aseptic ProcessingMethodology

Aseptic processing comprises the following:

Sterilisation of the products before filling

Sterilisation of packaging materials or containers and closures before filling Sterilisation of aseptic installations before operation (UHT unit, lines for products, sterile air and

gases, filler and relevant machine zones) Conventional Process Flow Aseptic Process Flow

Maintaining sterility in this total system during operation; sterilization of all media entering the

system, like air, gases, sterile water

Production of hermetic packages

Retort pouches:

Retort pouches which are containers made either of laminates of synthetic materials or laminates of

aluminium foil with synthetic materials, are of growing importance in thermal food preservation.


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Thermo-stabilized laminated food pouches, have a seal layer which is usually PP (polypropylene) or

PP-PE (polyethylene) polymer, and the outside layers are usually made of polyester or nylon. From

certain laminated films, for instance, polyester / polyethylene (PETP/PE) or polyamide/polyethylene

(PA/PE), relatively rigid containers can be made. The advantage of the retortable pouches/laminated

containers is their good thermal conductivity which can considerably reduce the required heat

treatment time and hence is beneficial for the sensory product quality.

Canning:

Various steps involved in the canning process are

1. Selection and preparation of raw materials

2. Blanching

3. Filling of cans

4. Exhausting/vacuumization

5. Sealing of the container/closure

6. Processing/sterilization/retorting

7. Chilling

8. Washing of cans9. External lacquering

10. Labeling

11. Storage/maturity

UHT PROCESSING

Definition:UHT milk can be defined as a product obtained by heating food material (especially milk)

in a continuous flow to a temperature in excess of 125C for not less than two seconds and

immediately packaging in sterile packages under aseptic conditions. In India, UHTmilk is generally

processed at 140oC for 2 seconds.

Direct Heating Plant: There are two types of direct heating plants

(a) Injection type(b) Infusion type.

Injection type:Processing is through steam-into-milk arrangement. Steam injector is the heart of this

plant. Preheated milk at 80-90 C enters the injector nozzles from one side. Steam at slightly higher

pressure enters the injector from the other side. As the steam mixes with milk, steam condenses and

the product is rapidly heated. Rapid condensation of steam prevents entry of air in holding tube. Air in

holding tubes results in improper heating. Backpressure is maintained on the discharge side.

Backpressure ensures that product does not boil in holding tube. Boiling may result in fouling and

improper heating of milk. Several designs of injector are available.

Infusion type:In this system, milk is heated by milk-into steam arrangement. The processing unit

consists of a chamber filled with pressurized steam. Milk enters the chamber from the top. There are

two alternative arrangements for distribution of milk. In the first type, milk flows to a hemispherical

bowl with loose circular disc closing the top. When the bowl is full, milk overflows and falls in

droplets through the steam environment. In an alternative arrangement, milk flows through a series of

parallel and horizontal distribution tubes. These tubes have slits along the bottom and milk flows like

a thin film through the chamber. As milk reaches the bottom of the chamber, it is heated to desired

temperature. This system is particularly suitable for thicker liquids and for liquids suspended with

smaller chunks.

Indirect Type Heating System:There are three types of indirect heating systems:

(a) Plate heat exchangers

(b) Tubular heat exchanger

(c) Scraped surface heat exchanger.


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Plate heat exchanger: This resembles plate heat exchanger of HTST plants. Several rectangular

stainless steel plates with corrugations are arranged in sequence. These plates are then mechanically

tightened to hold together. Corrugations on the plates induce turbulence and therefore result in high

heat transfer. High temperature processing generates high internal pressure. The gaskets are therefore

made of heat resistant materials such as medium nitrile rubber or resin cured butyl rubber. A major

advantage of this plant is therefore simple design and comparatively less cost. If deposit formation is

more, plates can be removed and manually cleaned.

Tubular heat exchanger:There are two types of tubular heat exchangers (a) concentric tube, (b)

shell and tube type. Concentric tube type heat exchangers comprise two or three stainless steel tube

lengths put one inside another. Spacer is placed in each inner tube space to maintain them concentric.

Several such multiple tubes are bound together and placed into an outer cylindrical housing. Two tube

heat exchangers are used for simple cooling and heating. In triple tube heat exchanger, available heat

transfer area is doubled. It is generally used in final cooling section. It is also suitable for processing

of thick liquids, which generally reduces heat transfer rate. Product flows through the middle annular

space. Heating or cooling medium passes through inner tube and outer annular space. In shell and

tube type heat exchangers, 5-7 straight lengths of smaller tubes (10-15 mm internal diameter) areassembled in an outer tube. The smaller tubes are connected to large outer tube at both ends by a

manifold. Product passes through the smaller tubes. Heating or cooling medium passes through the

space around them in a counter current flow. Tubular heat exchangers are mechanically very strong

and can withstand even very high internal pressure generated during homogenization (200- 300 bar).

Therefore the need for acquiring an aseptic homogenizer to be placed after heating section is totally

eliminated. Instead, the high pressure reciprocating pump of an ordinary homogenizer can be placed

before the sterile section. The homogenizing valve can be put at any point on the downstream side

(even after final heating section). The problem of product contamination arises from the

homogenization pump and not the valve. Therefore, with tubular heat exchangers, the product can be

homogenized before sterilization, after sterilization or on both the occasions. Fat rich products likecream require homogenization after final heating to prevent re-association of fat globules due to high

temperature processing after homogenization.

Scraped Surface Heat Exchanger (SSWE): It is a very specialized type of heat exchanger. It

consists of a jacketed cylinder. A shaft passes along the axis of the cylinder. The shaft is supported by

bearings at both ends of the cylinder. The shaft also carries several scrapper blades. As shaft rotates,

scrapper blades provide turbulence and physically remove the product from the surface of the wall.

The colder product subsequently replaces the heated product and the cycle continues. SSHE is used

only for heating very thick liquids. SSHE units are very expensive and have poor energy conversion

efficiency. The cost of processing is therefore very high.

Extrusion

Adiabatic Isothermal Polytropic

ExtrudersSingle

screw

extruders

Intermeshed Non

intermeshined

Counter rotating

Self-wiping Partially

self-wiping

Intermeshed non

Intermeshed

Co-rotating

Twin

screw

extruders

Continuous screw extruders


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Extrusion is the process by which a block/billet of

metal is reduced in cross section by forcing it to flow

through a die orifice under high pressure.

In general, extrusion is used to produce cylindrical

bars or hollow tubes or for the starting stock for drawn

rod, cold extrusion or forged products.

Most metals are hot extruded due to large amount of

forces required in extrusion. Complex shape can be

extruded from the more readily extrudable metals such as aluminium. The products obtained are alsocalled extrusion.

The reaction of the extrusion billet with the container and die results in high compressive stresses

which are effective in reducing cracking of materials during primary breakdown from the ingot.

This helps to increase the utilisation of extrusion in the working of metals that are difficult to form

like stainless steels, nickel-based alloys, and other high-temperature materials.

Similar to forging, lower ram force and a fine grained recrystallised structure are possible in hot

extrusion.

However, better surface finish and higher strengths (strain hardened metals) are provided by cold

extrusion.

Hot extrusionHot extrusion is done at fairly high temperatures, approximately 50 to 75 % of the melting point of the

metal. The pressures can range from 35-700 MPa (5076 - 101,525 psi).

The most commonly used extrusion process is the hot direct process. The cross-sectional shape of

the extrusion is defined by the shape of the die.

Due to the high temperatures and pressures and its detrimental effect on the die life as well as other

components, good lubrication is necessary. Oil and graphite work at lower temperatures, whereas at

higher temperatures glass powder is used.

Thermal and Non thermal food processing technology

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