Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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Roll

Forming collar

Tube former

Belts or roller

which transport

the film

Transversal

jaws

Knife

Front-view

Side-view

Roll of

corrugated

material

Roll of film

Tear-tape

Cut

Side

folders

Block sealers

Roll of

corrugated

material

Sealing rollers

Folding former

1 Pair of sealing rollers

Product

(a) (b)

(d)(c)

Heating plates

Teflon band

Sealing block

Lateral folders

Bottom folder Folding tucker

Gripper

Knife

Top folder

Heater block for

the tear-tape

Roll

Tear-tape

Wax bath

Infeed

Sealing jaws

Figure 1 (a) Horizontal form–fill–seal machine; (b) vertical machine (‘pillow bag’); (c) overwrapping machine; (d) overwrapping machine (with adjustment to the circumference of the

product).

fig0001

intermediate bulk container of 1 tonne capacity. This

supersack is made of woven polypropylene and it is

able to stand unsupported on the pallet.

Packaging Machines

0038 A good packaging solution for solid foods should not

ignore packaging machines and the complex inter-

actions between the machine and the packaging

material. (Figure 1) shows an example of a horizontal

form–fill–seal machine, a vertical pouch form–fill–

seal machine, and two overwrapping machines.

0039 The suitability of a packaging machine for a certain

packaging material and product can be summarized

in the following key points:

0040 The angle at which the wrapping material comes

into contact with the folding former is important,

as it may cause a mark or even a cut in the material.

The tightness of the packaging film depends on the

shape of the former.

0041 The quality of heat sealing of the packaging mater-

ial depends on the temperature control, pressure,

and dwell time. Optimal results are obtained when

the dwell time at the melting temperature of the

coating or copolymer is long enough to ensure

tightness without damage to the basic material.

0042 The wrapping material should slip easily after

sealing at high temperature. In some cases, it is

even necessary to cool the plate fixed above the

sealing rollers.

0043 The quality of cutting depends on the knife, cut

angle, position of the knife in relation to the sealing

jaws, etc.

Overwrapping also requires compatibility between

the machine and the wrapping material, and preven-

tion of static electricity, poor slip under hot condi-

tions, temperature control disruption, and rolling of

the film. The packaging material should be sealable

on both sides, the sealing area should be sufficient,

and the structure (soft or rigid) of the solid food

should not affect the shape and sealing surface if a

good gas tightness is desired.

0044 Packaging machines for food powders, and espe-

cially sugar, cover a large range of sizes of packages,

starting with small flat pouches containing between 4

and 10 g of sugar. These are produced using simple

machines that assemble sachets by bringing together

two webs of polyethylene-coated paper, heat sealing

three sides, filling with sugar, and sealing the top.

There are also carton packing machines, especially

designed for sugar cubes. For ease of handling, ‘brick-

packs’ are preferred. These are produced by forming a

polyethylene pack and dropping it into a horizontal

solid upstanding pack with similar characteristics to

the paper packet.

0045The quality of packaged food powders should

comply with the necessary regulations. Any foreign

matter should be eliminated. All packages go through

metal detectors to control metal contamination. Like-

wise, traceability of packets and even full pallets is

needed for identification of the product according to

EU regulations. A printed code showing the date and

line of production, factory of origin, etc. is required.

The spread of use of scanning at the shop point of sale

imposes the printing of a bar code on each domestic

package.

See also: Browning: Nonenzymatic; Chilled Storage: Use

of Modified-atmosphere Packaging; Packaging Under

Vacuum; Chill Foods: Effect of Modified-atmosphere

Packaging on Food Quality; Oxidation of Food

Components; Spoilage: Chemical and Enzymatic

Spoilage; Bacterial Spoilage; Storage Stability: Shelf-life

Testing; Water Activity: Effect on Food Stability

Further Reading

Gary JI, Harte BR and Miltz J (eds) (1987) Food–Product

Package Compatibility, Lancaster, PA: Technomic.

Hotchkiss JH (ed.) (1988) Food and Packaging Inter-

actions, American Chemical Society Series. Washington,

DC: American Chemical Society.

Mathlouthi M (ed.) (1986) Food Packaging and Preserva-

tion, Theory and Practice. London: Elsevier.

Rockland LB and Beuchat LR (eds) (1987) Water Activity.

Theory and Application to Food. New York: Marcel

Dekker.

Roge

B and Mathlouthi M (2000) Caking of sucrose crys-

tals: effect of water content and crystal size. Zuckerin-

dustrie 125: 5.

Van der Poel PW, Schiveck H and Schwartz T (eds) (1998)

Sugar Technology, Beet and Cane Sugar Manufacture.

Berlin: Dr Albert Bartens Verlag.

Versanyi I (1985) Food Packaging Technique [H]. Buda-

pest: Mezo

gazdasagi Kiado.

Aseptic Filling

L Mauer, Purdue University, West Lafayette, IN, USA

Background

0001Aseptic processing is a high-temperature–short-time

thermal process to commercially sterilize a product

and fill the cooled sterile product into a presterilized

package in a sterile environment. Purposes for aseptic

4316 PACKAGING/Aseptic Filling

processing include extending the storage life of food

products, optimizing product quality, and reducing

cost. A diagram of an aseptic processing system for

consumer products is shown in Figure 1. In the aseptic

process, the aseptic filler is designed to sterilize the

package material, fill the sterile product into the pack-

age in a sterile environment, and then hermetically

seal the package. Aseptic filling differs from other

traditional methods of food packaging in that the

food product and the package are continuously steril-

ized separately and then meet in the sterile environ-

ment provided by the aseptic filler. Important factors

in the aseptic filling process are the type of product,

type of package, obtaining and maintaining a sterile

environment for filling, and the sealing process.

Types of Product

0002 A variety of food products are aseptically packaged.

Examples include milk and dairy products, fruit and

vegetable juices, fruit juice concentrates, sport and

dietetic beverages, tomato products, edible oils, pud-

dings, soups, cheese and soy sauces, and products

containing small or large particles of fruits, vegetables,

or potatoes. The aseptic process must be designed so

that the product is sterilized, the package is compat-

ible with the product composition and storage needs,

and the type of filler treats the product gently while

maintaining sterility to achieve optimum quality.

Products are usually sterilized by high-temperature

heat treatments for short periods of time, cooled, and

conveyed to the filler via aseptic pumps or nitrogen.

Packaging and filling considerations for different

product types include the following:

Low-acid Products (pH > 4.5)

0003 The concept of aseptic heat treatments for low vs.

high acid foods is similar to the canning principles

for these food types. In low-acid foods, such as many

milk and vegetable products, pH is not a barrier to

pathogenic microbial growth. Therefore, aseptic pro-

cessing conditions must be designed with stringent

controls to achieve a 10-decimal reduction value for

Clostridium botulinum, the most heat-resistant

pathogen able to grow in low-acid foods, both in the

food product and in the package materials. Targeting

the most resistant pathogen ensures safety because all

other pathogens are killed faster than it. The package

must attain the same level of sterility as the product;

therefore, package materials for low-acid foods may

have stricter sterility controls than those for high acid

foods. Bacillus subtilis is the most resistant organism

to hydrogen peroxide sterilization of packages, and a

four-decimal requirement for it exists to achieve the

required reduction for C. botulinum in low acid foods.

Acid and High-acid Products (pH < 4.5)

0004In acid and high-acid foods, such as fruit juices and

many tomato products, pH is a barrier to pathogenic

microbial growth, most notably for C. botulinum. For

these foods, spoilage microorganisms may cause more

problems than pathogens. Processing temperatures

and holding times may be lower than for low acid

foods. Spoilage organisms are much more sensitive to

hydrogen peroxide sterilization of packages than

B. subtilis. Aspergillus niger is usually the target organ-

ism for dry and moist heat sterilization of packaging

materials for use with acid and high-acid products.

Homogeneous vs. Heterogeneous Products

0005Knowledge of heat-transfer characteristics of a food,

quality parameters, flow characteristics, mean resi-

dence time, type of heat exchanger or sterilizing

system, and heat resistance and required death values

for target microorganisms are important factors in

designing an effective aseptic process. Homogeneous

products contain no particles that disrupt heat trans-

fer. Heterogeneous products contain particles with

sufficient size to create a thermal gradient during

processing. Therefore, heat treatments for homo-

geneous liquids may be less damaging than those

required to insure commercial sterility of particulates

in similar liquids. Pumps used to convey aseptically

processed products must be able to maintain both

product sterility and integrity; therefore, pumps

used for heterogeneous products must limit shear

forces so as not to damage particulate structures.

Homogeneous liquids are often conveyed to a filler

with either a centrifugal pump or sterile nitrogen;

however, highly viscous liquids may require use of a

positive displacement pump. Heterogeneous products

are conveyed to the filler using a positive displace-

ment pump that limits pressure and shear placed on

Aseptic zone

Raw material

Continuous

heating

Package

material

Hold tube

Aseptic filler Hold tank

Continuous cooling

Finished product

fig0001 Figure 1 Aseptic process diagram.

PACKAGING/Aseptic Filling 4317

the particulates. Opening sizes in an aseptic system

designed for heterogeneous products must be suffi-

cient to allow passage of the particulates without

creating pinch points. In the filler, contamination of

the seal area, especially with particulates, must be

avoided.

Types of Packages

0006 The type of aseptic package used must be suitable

for a product’s requirements, package surfaces must

withstand sterilization by heat, irradiation, and/or

chemicals prior to filling, and the package must con-

tain, protect, and preserve the food product through-

out its distribution and shelf-life. Properly aseptically

processed products remain microbiologically stable

as long as the package remains intact. Often, shelf-life

and product quality are limited more by package

performance than any other factor. Needs to consider

for an aseptic packaging system include:

0007 Compatibility of product and package – product

composition, needs for maintaining quality (barrier,

mechanical), and shelf-life requirements.

0008 Packaging material – type (plastic, metal, glass,

laminate, etc.), barrier and mechanical properties,

machineability, recyclability, and cost.

0009 Package form – size, shape, compatible machinery,

sealing properties, appeal to consumer, communi-

cation of information, and cost.

0010 Sterilization method (heat, irradiation, chemicals,

combination of methods) – efficiency, throughput,

residues, compatibility with product/package/

environment, worker safety, regulations, and cost.

0011 Filling equipment – reliability, efficiency, capacity,

and cost of installation/operation/maintenance.

Aseptic Package Materials

0012 A significant drive in the conversion from traditional

to aseptic processing is the reduction in packaging

costs for both materials and transportation. Trad-

itional thermal processes require packages to with-

stand high temperatures, whether for in-package

sterilization or for hot-filled products, as well as

vacuum forces created on cooling. Packages that

meet these structural requirements include metal,

glass, and plastics (rigid, semirigid, some with vacuum

panels incorporated into the design, and pouches).

The cold aseptic filling allows for a lighter container

with a greater design flexibility (squeezable, ergo-

nomic, etc.). By weight, most plastic materials cost

significantly less than glass and metals, and less plas-

tic is needed for a cold-filled product than a hot-filled

product. Plastics are the most common material used

for aseptic packaging; however, plastics are more

permeable to oxygen and moisture than either glass

or metals. The quality of products may suffer after

extended storage in permeable packages. An example

of this is oxidation of dairy products in packages

permeable to oxygen. To limit permeability, plastics

with different barrier characteristics are often com-

bined using lamination or coextrusion methods to

optimize barrier properties. This can maximize prod-

uct quality and package function while maintaining

low package costs.

0013The variety of plastic materials used in aseptic

packaging is continuously increasing, along with

the use of laminates, coextrusions, and copolymers.

Adhesive and thermal lamination methods are used

to create multilayer packages, often with a structure

based on the diagram in Figure 2. More than one

barrier layer may be incorporated into a package

design. Commonly used plastics include polyolefins

(polyethylene, polypropylene, polystyrene), polyes-

ters (polyethylene terephthalate), vinyl plastics (poly-

vinyl chloride, polyvinylidene chloride, polyvinyl

alcohol), polyamides (nylon), ionomers, acrylics,

fluorocarbons, and polycarbonates. Polyethylene

(PE) is the most widely used polymer in packages

and is available in a variety of densities: low density

(LDPE), linear low density (LLDPE), medium density

(MDPE), and high density (HDPE). LDPE is used in

flexible bags and pouches and is a good heat-sealing

material. HDPE used in blow-molded bottles is more

rigid and has better barrier properties than LDPE.

Polypropylene (PP) provides clarity, stiffness, and

heat resistance. Polyethylene terephthalate (PET) has

good barrier and clarity properties and a high tensile

strength, and is resistant to high temperatures. PET is

often used to meet consumer demand for round and

recloseable plastic bottles. Ethylene vinyl alcohol

Outer structural

layer (barrier)

Inner structural

layer (barrier)

Environment

Adhesive

Barrier

Food

fig0002Figure 2 General structure of a laminate aseptic package.

4318 PACKAGING/Aseptic Filling

(EVOH) and polyvinylidene chloride (PVDC) are

generally the best plastic barriers to moisture and

oxygen migration. Metal and glass are used for

barrier properties either alone or within a laminate

package. A paperboard layer in a laminate package is

used for printing and light-barrier purposes.

Package Formation

0014 Packages formed for the aseptic process require min-

imum levels of contaminating microorganisms prior

to the sterilization process, and the packages must

pass leak-testing procedures. Packages may be pre-

formed or formed in the filler just prior to filling.

Metals are formed into cans, and metal films may be

incorporated into laminate structures. Glass is blow-

molded into bottles and jars. Plastics and laminated

materials are blow-molded or thermoformed into

various package shapes. The blow-molding process

involves the melting of a glass or plastic, forming a

parison (tube), and then blowing the parison into the

package shape (designated by the mold) using sterile

air or nitrogen. Extrusion, injection, and stretch

blow-molding methods are used for different package

applications. A sheet of plastic is heat-softened then

molded to shape via vacuum, pressure, or matched

mold forming in the thermoforming process. Cups

and trays are thermoformed packages.

Aseptic Package Systems

0015 Package forms and filler types are interwoven to the

extent that discussion of one is not complete without

discussion of the other, as the aseptic process hinges

on the placing of a sterile product into a sterile pack-

age in the sterile filler environment. Common aseptic

package forms are discussed in this section, leaving

classification of filler types for a later section.

0016 Cartons The brick-style, paperboard packaging

used for cartons is recognized as the traditional

aseptic package used for juice boxes. The laminate

material used for carton formation generally consists

of multiple polyethylene, paper, and aluminum foil

layers. Outer and inner polyethylene layers provide

protection and sealing properties, the paperboard is

printed with product information and provides stiff-

ness, and the aluminum foil contributes gas- and

light-barrier functions. Cartons are prefabricated, or

rolls of the laminate material are sterilized and formed

in the filler just prior to filling and sealing. Cartons are

sterilized using hydrogen peroxide and hot air.

0017 Bottles The convenience of plastic bottles that are

clear, round, resealable, recyclable, and able to be

formed in a variety of shapes and sizes is a driving

force in the beverage industry. Aseptic milk, creamer,

sports, and nutritional beverages in PET, PE, and PP

bottles are currently available to consumers. Bottles

for use with high-acid products are generally steril-

ized using steam, a combination of heated air and

steam, or heat of formation (extrusion and blow

molding). Bottles for low-acid products are sterilized

with hydrogen peroxide.

0018Cups The thermoformed cup is a common aseptic

package for puddings, particulates, fruits, purees, and

baby food. Package materials for cups include PS, PP,

and laminates of PS, PVDC/EVOH, and LDPE mater-

ials. Cup lids are often aluminum foil coated with

LDPE or other heat-sealant plastic. Cups are gener-

ally sterilized using hydrogen peroxide or saturated

steam under pressure.

0019Pouches Pouches for institutional and fast food

chain use are easier to open, take up less space for

transportation, storage, and waste, and decrease

product loss when compared with traditional metal

cans. Form-fill-seal systems are used for converting a

sheet film of plastic (LDPE, laminate) into a pouch.

Plastics formed as lay-flat tubes require fewer seals to

form pouches than the sheet films. Aseptic products

available in pouches include tomato-based sauces, ice

cream mixes, cheese sauces, and puddings. Pouches

are often sterilized using hydrogen peroxide.

0020Bag-in-box The bag-in-box aseptic packaging

system is used for bulk packaging (1–10 000 or more

liters). The product is filled into a presterilized plastic

bag. The bag is placed into a protective container,

such as a corrugated box or metal drum, either before

or after filling. A laminate of barrier (PVDC, EVOH)

and heat sealant (LDPE) plastics is commonly used

for bag formation. Tomato, fruit juice, and dairy

products are packaged using the bag-in-box system.

Preformed bags are sterilized by ionizing gamma

irradiation. The exterior of bags for low-acid prod-

ucts is also sterilized with steam or hydrogen peroxide

vapor.

0021Metal cans The metal can traditionally used in ther-

mal processes also has advantages for use with aseptic

products despite the added weight over plastic mater-

ials. The durability, consumer acceptance, barrier

properties, and recyclability of metal cans combined

with the ability to sterilize the cans with superheated

steam instead of chemicals make the metal can

attractive for some applications. Aseptic dietetic bev-

erages, pudding, and cheese sauces are available in

metal cans. Superheated steam is used to sterilize

metal cans prior to filling.

PACKAGING/Aseptic Filling 4319

The Sterile Environment

Obtaining a Sterile Environment

0022 Establishing, maintaining, and validating sterility in

an aseptic system are essential. Processes used for

obtaining a sterile environment for products, equip-

ment, and packages include thermal, chemical,

irradiation, and mechanical treatments along with

combinations of these. Thermal processes include

saturated steam, superheated steam, hot air, mixtures

of hot air and steam, and extrusion/heat of forma-

tion (although extrusion may not be acceptable for

sterilization purposes). Heat is the most common

method for product sterilization and is often used

for equipment sterilization as well. The most

common chemical used for sterilization is hydrogen

peroxide (20–35% concentration), and a combin-

ation of hydrogen peroxide treatment followed by

hot air is often used to reduce the level of hydrogen

peroxide to less than 0.5 p.p.m. on packages and

equipment. Peracetic acid and ethylene oxide also

have applications; however, regulations for accept-

able chemicals, uses, and residue limits must be

checked. Chemicals are applied by dipping, spraying,

or rinsing, or in vapor form. Irradiation treatments

may include ultraviolet radiation, infrared radiation,

and ionizing gamma radiation. Mechanical processes

are generally designed to reduce initial microbial load

to a level the aseptic system is designed to handle. If

an initial microbial load is too high, sterility might

not be achieved during aseptic processing. Therefore,

water rinsing or flushing, air blasting, brushing, and

ultrasound methods are used to reduce the initial load

on equipment and packaging prior to other steriliza-

tion processes.

0023 Equipment and packages must attain the same

level of sterility as the products they will come into

contact with. Therefore, equipment is sterilized with

hydrogen peroxide or a time/temperature steam

sterilization at least equivalent to what the product

will receive. Thermal processes for equipment used

with low-acid foods will be higher, both time and

temperature, than for high-acid products. Packages,

other than metal cans, may not withstand high

temperature treatments; therefore, chemical and

irradiation sterilization procedures are commonly

used.

Maintaining a Sterile Environment

0024 Once equipment, packages, and products are steril-

ized, the challenge is to maintain sterility during

the filling and sealing operation. This is accom-

plished using either an overpressure of sterile air

or continuous flow of superheated steam, the latter

generally being used for the metal can aseptic pro-

cess. Air is sterilized by filtration, usually using a

series of high-efficiency particulate air (HEPA)

filters. Since all equipment must attain commercial

sterility, the HEPA air filters also must be sterilized.

The positive pressure maintained by a continuous

sterile air flow prevents contamination during the

filling process when the product may be exposed

to air. If the integrity of an aseptic zone is com-

promised because of line stoppages or other

occurrence, it is necessary to repeat the initial ster-

ilization process.

Validating Sterility

0025Validating sterility is a combination of implementing

an appropriate hazard analysis critical control point

program, documenting product and filler sterilization

procedures, filing the process with the appropriate

agency, maintaining accurate temperature, time,

pressure recording devices, and testing all aseptically

processed foods for sterility using appropriate micro-

biological sampling techniques. Challenge testing

with inoculated foods is part of validating a thermal

process.

The Sealing Process

0026At the end of the filling process, packages are often

sealed using heated sealing bars, jaws, and plates. The

temperature, pressure, and time of sealing must be

strictly controlled for each sealing compound to

maximize package integrity. Common heat sealant

polymers include polyethylene, polypropylene, ethyl-

ene vinyl acetate, and polyvinyl chloride. These com-

pounds have demonstrated a desirable mechanical

strength of the seal (impact strength, tensile strength,

tear strength, seal strength, puncture resistance)

and product holding properties (chemical resistance,

product compatibility, oxygen and moisture barrier

properties). Problems occur when particulates, fibers,

or other food contaminants are caught in the seal area

and prevent a completely fused seal. To avoid seal

contamination, especially with particulate foods, the

filler must be designed to avoid or remove product

from the seal area prior to fusion.

Types of Fillers

0027The filling method depends on both the type of prod-

uct (high or low acid, homogeneous liquid, viscous

product, size of particulates, etc.) and type of package

(retail, institutional, cup, pouch, bottle, etc.) desired

for the end product. Common filler classifications are

named for the processes that occur in the filler and

are outlined below.

4320 PACKAGING/Aseptic Filling

Fill and Seal

0028 In the fill and seal process, a preformed sterile con-

tainer (bottles, cups, irradiated pouches, bag-in-box)

is aseptically filled and sealed. The fill and seal pro-

cess for cups is shown in Figure 3. In bulk packaging

systems (500-liter bins, large totes, million gallon

storage tanks), product is filled directly into a steril-

ized large storage container. This system is often used

for seasonal food products to extend the supply

throughout the year.

Form, Fill, and Seal

0029 Brick pack juice boxes and pouches (LDPE, laminate)

enter the filler as a roll of packaging material and are

sterilized, aseptically formed into the box or pouch

shape, filled, and thermally sealed in the form, fill,

and seal process.

Thermoform, Fill, and Seal

0030 In the thermoform, fill, and seal process, the pack-

aging material (PS, PP, laminates) enters the filler as

roll stock and is sterilized, heated, thermoformed

(usually into cups), filled, and thermally sealed with

presterilized lid material (aluminum foil coated with

LDPE).

Blow Mold, Fill, and Seal

0031 Plastic bottles are formed, filled, and sealed in the

blow mold, fill, and seal filling process. An extrud-

able material (PET, PP, PE) is blow-molded into a

container that is filled and sealed in place before the

mold opens. For low-acid products, a chemical steril-

ization after the bottles are formed is used to insure

sterility prior to filling.

Advantages and Disadvantages of Aseptic

Filling

0032Advantages of aseptic filling include a high product

quality, decreased storage space for packaging mater-

ials, decreased weight of packaging materials, de-

creased package costs, decreased shipping costs for

packaging materials, reduced energy consumption,

increased flexibility for package options, increased

convenience for easy open containers, feasibility of

long-term bulk storage, and increased shelf-life and

storage time for products. Disadvantages include the

high cost of aseptic fillers, potential for product con-

tamination in the aseptic filler owing to the complex-

ity of the system, decreased recyclability of pouch and

laminate package materials compared with metal and

glass packages, and slower line speeds than trad-

itional process methods. For many, the advantages

far outweigh the disadvantages.

See also: Canning: Principles; Heat Treatment: Ultra-

high Temperature (UHT) Treatments; Packaging:

Packaging of Liquids; Pasteurization: Principles;

Storage Stability: Mechanisms of Degradation;

Parameters Affecting Storage Stability; Shelf-life Testing

Further Reading

Chambers JV and Nelson PE (ed.) (1993) Principles of

Aseptic Processing and Packaging. Washington, DC:

The Food Processors Institute.

David JRD, Graves RH and Carlson VR (eds) (1996)

Aseptic Processing and Packaging of Food: A Food

Industry Perspective. New York: CRC Press.

Floros JD (1993) Aseptic packaging technology. Chambers

JV and Nelson PE (eds). In: Principles of Aseptic Pro-

cessing and Packaging, pp. 115–148. Washington, DC:

The Food Processors Institute.

Sterile chamber

Dryers

Cup

feed

Indexing

conveyor

Filter heads

spray

lid tank

Lid dryer

Cut and

seal

Lid feed

Coder

Shred

Discharge

fig0003 Figure 3 Aseptic filler design.

PACKAGING/Aseptic Filling 4321

Holdsworth SD (ed.) (1992) Aseptic Processing and Pack-

aging of Food Products. London: Elsevier Applied

Science.

Moruzzi G, Garthright WE and Floros JD (2000) Aseptic

packaging machine pre-sterilisation and package steril-

ization: statistical aspects of microbiological validation.

Food Control 11(1): 57–66.

Reuter H (ed.) (1993) Aseptic Processing of Foods. Lancas-

ter, PA: Technomic.

Robertson GL (ed.) (1993) Food Packaging Principles and

Practice. New York: Marcel Dekker.

Sommers CH, Thayer DW, Pauli G et al. (2000) New Pro-

cessing and Packaging Technologies. Washington, DC:

National Food Processors Association.

Willhoft EMA (ed.) (1993) Aseptic Processing and Pack-

aging of Particulate Foods. London: Blackie Academic

& Professional.

Packaging Materials See Chill Foods: Effect of Modified-atmosphere Packaging on Food Quality;

Chilled Storage: Use of Modified-atmosphere Packaging; Packaging Under Vacuum; Packaging: Packaging of

Liquids; Packaging of Solids; Aseptic Filling

PALM KERNEL OIL

K G Berger, Chiswick, London, UK

Introduction

0001 Palm kernel oil is obtained from the oil-rich seed of

the oil palm (Elaeis guineensis Jackqu). A description

of the oil palm and its development into a major crop

is given in the entry on Palm Oil. The production

process of the kernels in the oil mill is also described

there.

0002 The quantity of palm kernel oil produced is on

average 12% that of palm oil. World production in

1998 was 2.9 million tons.

Production of the Oil

0003 The palm kernels leave the oil mill at about 50% oil

content and up to 8% moisture. Further processing

typically consists of:

0004 Comminution in hammer mills to approximately

2-mm pieces.

0005 Cooking to 110–120



C in a continuous cooker.

This breaks the oil cells and reduces moisture to

2.5%.

0006 Pressing in a screw press at high pressure to yield

crude palm kernel oil and a meal containing 7–9%

oil. The meal is used for animal feed.

An alternative process is to submit the broken nuts

after step (1) to a cold pressing at low pressure,

leaving a meal containing 10–12% oil. This may be

further treated by solvent extraction, depending on

the market prices of oil and meal.

Refining

0007Palm kernel oil may be refined either by an alkali or

by the physical process, as described in the entry on

Palm Oil. However, because most of the fatty acids

present are of 12 carbon atoms or less, the deodoriza-

tion temperatures used are lower – typically 220



Cin

the alkali process and 230–235



C in the physical

process.

Further Processing

0008Palm kernel oil is treated by fractionation or hydro-

genation and/or interesterification to obtain products

with closely defined functionality. These processes are

described in the entry on Palm Oil.)

Chemical Composition and Physical

Properties

0009The fatty acid composition of palm kernel products is

given in Table 1, while Table 2 gives the glyceride

composition by carbon number. Typical values for the

minor components of palm kernel oil are given in

Table 3.

0010Palm kernel oil has a high content of lauric and

shorter-chain fatty acids and a low content of unsat-

urated acids. Coconut oil has a somewhat similar

4322 PALM KERNEL OIL

composition. They contrast strongly with the other

common vegetable oils, which contain no shorter-

chain fatty acids. In consequence the physical proper-

ties are unusual, as will be seen from Tables 4 and 5.

Palm kernel oil has a relatively high solid fat content

and a rather hard structure at 20



C, but melts sharply

at 28



C – well below mouth temperature. These

properties are accentuated in palm kernel stearin. As

is clear from the last two columns of Table 5, hydro-

genation raises the solids content further, but the

products are still substantially molten at mouth

temperature. Hydrogenated palm kernel olein, on

the other hand, having a higher content of long-

chain saturated acids, has a higher melting point.

The products shown in Table 5 are examples of the

properties that can be obtained by further processing.

A wide range of proprietary products based on palm

kernel oil is available, giving variations in physical

properties required for specific food applications.

0011 The data shown in Tables 1–4 are average figures

taken from an extensive survey of Malaysian palm

oil. The figures are not significantly different from

those recently obtained for oils from other sources

in other producing regions.

Food Uses of Palm Kernel Products

0012The most important applications of palm kernel oil

products are in the confectionery industry, where its

high solid fat content and sharp melting characteris-

tics are important. However, palm kernel oil itself

melts at too low a temperature for some applications.

It is therefore hydrogenated to give a variety of prod-

ucts, one of which is indicated in Table 5. Hydrogen-

ated palm kernel oil is suitable for chocolate-type

couvertures for biscuits and sugar confectionery, and

for biscuit cream fillings. Hydrogenated palm kernel

oil is also used to replace butterfat in filled milk,

coffee creamers, and imitation cream. The higher-

melting-point grades tend to leave a waxy residue

on the palate. They can be improved by fractionat-

ing to remove the highest melting point compon-

ents. A superior and more expensive product is

obtained by the direct fractionation of palm kernel

oil. The stearin has good contraction when it solidi-

fies and is therefore suitable for molded chocolate.

(See Cocoa: Production, Products, and Use.)

0013The palm kernel olein produced is the lower-value

fraction. It may be hydrogenated (Table 5)togive

a range of confectionery fats of somewhat lower

quality. Alternatively, palm kernel olein is used

in margarine blends. It is a useful component of

tbl0001 Table 1 Fatty acid composition % of palm kernel oil products

Fatty acid Palmkernel oil Palm kernel olein Palm kernel stearin

6:0 0.3 0.4 0.2

8:0 4.2 5.4 1.2–3.5

10:0 3.7 3.9 2.4–3.6

12:0 48.7 41.5 55.6–58.6

14:0 15.6 11.8 18.1–24.7

16:0 7.5 8.4 7.1–7.9

18:0 1.8 2.4 1.5–1.8

18:1 15.0 22.8 2.6–8.8

18:2 2.6 3.3 0.2–1.5

Data from Palm Oil Research Institute of Malaysia, with permission.

tbl0002 Table 2 Triglyceride composition of palm kernel oil products:

carbon number by gas–liquid chromatography

Carbon

number

Palm kernel

oil (%)

Palm kernel

olein (%)

Palm kernel

stearin (%)

28 0.5 0.3 0.1

30 1.3 1.6 0.5

32 6.4 7.8 3.3

34 8.4 9.3 6.5

36 21.0 18.3 27.5

38 15.6 12.5 24.8

40 9.5 7.6 15.2

42 9.0 9.3 9.2

44 6.8 7.8 5.2

46 5.3 6.5 3.0

48 6.2 8.3 2.4

50 2.5 3.1 0.9

52 2.7 3.4 0.7

54 3.3 4.2 0.8

Data from Palm Oil Research Institute of Malaysia, with permission.

tbl0003Table 3 Minor components of palm kernel oil typical values

Refined palm kernel oil (mg kg

1

)

Carotenoids Less than 8

Tocopherols and tocotrienols Less than 33

Sterols

875

Triterpene alcohols 470

Main components b-sitosterol (68%), stigmasterol (14%), and

campesterol (9%).

tbl0004Table 4 Physical properties of refined palm kernel oils

Solid fat content % by

NMR at:

Palm

kernel oil

Palm

kernelolein

Palm

kernel stearin



C 72.8 65.6 93.2



C 67.6 56.9 91.6



C 55.7 40.4 90.1



C 40.1 20.9 82.8



C 17.1 1.4 68.2



C 34.6

Slip melting point



C 27.3 23.6 32.2

NMR, nuclear magnetic resonance.

Data from Palm Oil Research Institute of Malaysia, with permission.

PALM KERNEL OIL 4323

interesterified mixtures for various applications

(Table 6).

0014 Palm kernel oil without modification is used for

chocolate coatings for icecream bars, usually in a

blend with liquid oil or palm oil to give the right

consistency without excessive brittleness.

Palm Kernel Products in Margarine

1.0015 Palm kernel oil forms a eutectic with palm oil in a

mixture containing about 30% palm kernel oil.

This feature is used to improve the mouth feel

(rapid melting) in the following formula:

Palm oil 63%

Palm stearin 7%

Palm kernel oil 30%

0016 Palm kernel olein (30 parts) interesterified with

palm stearin (70 parts) forms a margarine stock.

To make margarine, 60 parts are blended with 40

parts liquid oil.

0017 Equal quantities of fully hydrogenated palm

kernel oil and fully hydrogenated palm oil are

interesterified. A margarine high in polyunsatur-

ated fatty acids is made by blending 12% of this

hard stock with 88% of a liquid oil such as

sunflower oil.

See also: Cocoa: Production, Products, and Use; Palm Oil