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

Подождите немного. Документ загружается.

Dietary Diversification

0037 Dietary diversification, including vitamin A-rich

foods, is the most effective long-term sustainable

solution. Since animal foods containing preformed

vitamin A are expensive, attention is focused on

plant sources of provitamin A carotenoids. Green

leafy vegetables, yellow/orange vegetables and fruits

like papaya and mango are common sources of vita-

min A. Green leafy vegetables are abundant in most

countries where VAD exists, but their consumption is

low due to lack of knowledge. Dietary intake can be

improved through nutrition education and social

marketing strategies. In areas with limited availabil-

ity, horticulture programs should be undertaken

to increase the production of vegetables and fruits.

Large-scale home gardening programs have been

successfully implemented in some countries like

Bangladesh and Thailand. Evaluation studies have

shown that the consumption of vegetables was higher

in families with home gardens.

0038 Bioavailability of plant carotenoids is relatively

low and it is difficult to meet vitamin A requirements

of young children through vegetable foods alone.

Programs to improve vitamin A status must

encourage consumption of a variety of foods, includ-

ing animal foods like milk and eggs, at least in small

amounts to improve the quality of diet. Bioavailabilty

varies not only with the food source but also the way

it is prepared. Intervention programs should focus on

high-carotene varieties of vegetables and promote

appropriate methods of processing/cooking to min-

imize carotene losses. Fat content of diet should be

increased to promote carotene absorption. However,

effective dietary changes require a thorough under-

standing of the local sociocultural and behavioral

factors that predispose to hypovitaminosis A.

0039 Apart from dietary interventions, improvement in

environmental conditions and control of parasitic

infection are important to improve the vitamin A

status of the population. VAD must be seen in the

broader context of malnutrition that afflicts the poor.

Greater emphasis should be laid on integrated

multisectoral comprehensive strategies, taking into

account the community’s overall needs.

See also: Carotenoids: Occurrence, Properties, and

Determination; Physiology; Food Fortification; HIV

Disease and Nutrition; Malnutrition: Malnutrition in

Developed Countries

Further Reading

ACC/SCN Consultative Group (1994) Controlling Vitamin

A Deficiency. ACC/SCN State-of-the-art series, nutrition

policy discussion paper no. 14. Geneva: United Nations.

Beaton GH, Martorell R, Aronson KJ et al. (1993) Effect-

iveness of vitamin A supplementation in the control of

young child mortality in developing countries. ACC/

SCN State of the art series, nutrition policy discussion

paper no. 13. Geneva: United Nations.

FAO/WHO Expert Consultation (1998) Requirements of

Vitamin A, Iron, Folate and Vitamin B

, pp. 16–31.

Rome: FAO.

McLaren DS and Frigg M (1997) Sight and Life Manual on

Vitamin A Deficiency Disorders. Basel, Switzerland:

Sight and Life.

Reddy V (1986) Vitamin A deficiency control in India. In:

Bauernfeind JC (ed.) Vitamin A Deficiency and its Con-

trol, pp. 389–404. Orlando, FL: Academic Press.

Reddy V (1994) Strategies to control vitamin A deficiency –

Indian experience. In: Puri RK (ed.) Current Concepts in

Pediatrics, pp. 211–216. New Delhi, India: Jaybee

Brothers.

Sommer A and West KP (1996) Vitamin A Deficiency,

Health, Survival and Vision. New York: Oxford Univer-

sity Press.

Villamor E and Fawzi WW (2000) Vitamin A supplemen-

tation: implications for morbidity and mortality in

children. Journal of Infectious Diseases 182(suppl. 1):

S122–S123.

West CE (2000) Meeting requirements for vitamin A.

Nutrition Reviews 58: 341–345.

WHO (1995) Global Prevalence of Vitamin A Deficiency.

Micronutrient Deficiency Information System. Working

Paper #2. WHO/NUT/95.3. Geneva: WHO.

WHO (1996) Indicators for Assessing Vitamin A Defi-

ciency and Their Application in Monitoring and

Evaluating Intervention Programmes. Micronutrient

series, WHO/NUT/96. 10. Geneva: WHO.

WHO (1997) Vitamin A Supplements: A Guide to their Use

in the Treatment and Prevention of Vitamin A Defi-

ciency and Xeropthalmia, 2nd edn. WHO/UNICEF/

IVACG Task Force. Geneva: WHO.

WHO/CHD Immunization-linked Vitamin A Supple-

mentation Group (1998) Randomized trial to assess

benefits and safety of vitamin A supplementation

linked to immunization in early infancy. Lancet 352:

1257–1263.

HYPOVITAMINOSIS A 3219

ICE CREAM

Contents

Methods of Manufacture

Properties and Analysis

Dietary Importance

Microbiology

Methods of Manufacture

R T Marshall, University of Missouri, Columbia, MO,

USA

Introduction

0001 Ice cream is a frozen emulsion. The continuous phase

consists of unfrozen syrup containing the dissolved sub-

stances, mostly sugars and minerals. The disperse phase

consists of air cells, globules of milk fat (and in some

countries other sources of fat), ice crystals, and insoluble

substances including proteins and hydrocolloids.

0002 Steps in the manufacture of ice cream are as

follows: decide on composition; determine the avail-

ability and characteristics of ingredients needed to

make the mix; calculate amounts of each ingredient

needed; combine the ingredients of the mix; process

the mix; store the mix cold until certain components

have hydrated; add liquid flavorings; freeze the mix to

a soft consistency while stirring and introducing air;

to the soft-frozen product add desired syrups or solid

types of flavorings; package; and harden and store the

packaged product.

0003 A product called Dippin Dots

is made from ice

cream mix but is not stirred while being frozen. In-

stead, droplets of ice cream mix are caused to fall into

a bath of liquid nitrogen where they are frozen rapidly

into small spheres. The frozen bead-like particles are

removed, packaged, and stored at a very low tempera-

ture to prevent them sticking together. The beads can

be dipped into containers for serving. These beads

contain little or no air, and the ice crystals within

them are very small compared with those in ice cream.

Deciding on Mix Composition

0004Ice cream is composed of milk fat, nonfat milk solids,

sweetener, flavoring, stabilizer, and emulsifier. In a

simple formulation cream provides the milk fat and

some nonfat milk solids, the remainder of which is

supplied by concentrated or dried skim milk. Sugar

and corn syrup are the major sweeteners, vegetable

gums are the stabilizer and mono- and diacylglycerols

are the emulsifiers. There are many other sources

of these basic ingredients (See Ice Cream: Properties

and Analysis). Costs, availability, quality, stability

and ease of handling are considered in deciding

which ingredients to use. Once the ingredients have

been chosen, amounts of each component must be

calculated.

Calculating Ice Cream Mixes

0005As long as the sources of the major components of ice

cream are few, mix calculation is relatively easy.

However, multiple sources of components make the

process complex. The illustration provided below is

for a simple mix.

0006Let us assume a mix composition of 12% milk fat,

10% nonfat milk solids, 15% sugar, 0.2% stabilizer,

and 0.1% emulsifier. Further assume that ingredients

used are cream containing 30% fat and 6.3% nonfat

solids, nonfat dry milk containing 96% solids (4%

moisture), sugar, gum stabilizer and mono- and di-

acylglycerol emulsifier. To make 100 units of the mix

we need 40 units of cream (12/0.3) and it provides

2.52 units of nonfat milk solids (40 0.063). We

subtract 2.52 from the 10 units of nonfat milk solids

needed and find we need to add 7.79 units of nonfat

dry milk [(10  2.52)/0.96] to supply the remainder

of the nonfat milk solids. We add 15 units of sugar,

0.2 unit of stabilizer, and 0.1 unit of emulsifier. The

latter two contain insignificant amounts of moisture.

On addition (40 þ 7.79 þ 15 þ 0.2 þ 0.1) we find we

have only 63.09 units of mix. Therefore, we make

up to 100 units with 36.91 units of water. Had the

combination of cream of lower fat content and

concentrated skim milk been used, little or no water

would have been required.

Compounding the Ice Cream Mix

0007 In making the mix, liquid ingredients are combined in

a vessel and solid ingredients are added while stirring.

Because gums are in the form of particles that adsorb

water but do not dissolve, they tend to clump when

added to mix in the dry form. To overcome this they

can be suspended in sugar syrup by blending for a

short time. The suspension is then stirred into the mix

and particles of stabilizer disperse well. Similarly,

nonfat dry milk tends to form lumps when added in

large amounts to a liquid. Instantizing of nonfat dry

milk overcomes this problem, making it a desirable

form of concentrated nonfat milk solids for use in the

home. However, the cost of instantization and the

high bulk of the product, compared to regular nonfat

dry milk, restrict its use in industry. Instead, a device

called a powder funnel delivers the dried milk into a

rapidly flowing stream of water or of liquid ingredi-

ents of the mix where it disperses well and dissolves

quickly. In the home or small industry, nonfat dry

milk or stabilizers can be mixed with sugar before

adding them to the liquid portion of the mix. When

dry ingredients that tend to lump are added slowly to

liquid that is being rapidly agitated, they usually dis-

perse adequately. Therefore, some processors use this

approach to combining the dry ingredients. Usually

the mix is being heated as the ingredients are being

combined.

Processing the Mix

0008 Two processes are normally used in preparing the mix

for freezing, namely, pasteurization and homogeniza-

tion. Pasteurization destroys undesirable bacteria and

enzymes while homogenization reduces the sizes of

fat globules and particles of stabilizer, thus improving

smoothness of the finished product. These processes

necessitate heating and cooling. The minimal tem-

perature for pasteurization depends on the amount

of time the mix is to be held at pasteurization

temperature.

0009 When the process is done by the ‘batch’ method,

the entire mix is heated in a vessel to at least 69



(155



F) and held at that temperature for 30 min.

Following this treatment, the mix is pumped through

a homogenizer, then to a cooling device to lower the

temperature to 4



C or lower. Small batches of mix

often do not receive the homogenization treatment.

0010The most common method of pasteurization in-

volves pumping the mix through a high-temperature,

short-time (HTST) pasteurizer (Figure 1). This device,

called a platetype heat exchanger, employs hot and

cold water to heat and cool the mix, respectively. In

addition, a section of plates called the ‘regenerator’ is

used to transfer heat from the outgoing pasteurized

mix flowing on one side of thin stainless-steel plates

to the incoming cooler mix flowing in an opposite

direction on the opposite side of the same plates. This

device can save up to 90% of the heat and refrigerant

that would otherwise be needed. Minimal time and

temperature requirements for this process are 25 s at



C (175



F). Higher temperatures with shorter

times are also permitted in many countries.

0011Mixes must be heated before homogenization

because fat must be in the melted rather than the

crystalline state to be broken into smaller globules.

Diameters of the fat globules of cows’ milk range

from about 1 to 10 mm. Homogenization reduces

diameters to 2 mm and less. One globule 10 mmin

diameter yields eight new globules 5 mm in diameter,

and they have a combined surface area twice that of

the original globule. Thus, homogenization increases

the creaminess attribute of the product. The process is

accomplished by pumping the mix through exceed-

ingly small space (the homogenizer valve) at pressures

of about 14 MPa.

Storing the Mix

0012The purpose of cooling the mix to lower than 5



and holding it for a few hours is to permit the added

hydrocolloids, the gum-type stabilizers, to become

hydrated and to permit some crystallization of the

fat so it will partially churn in the freezer. The min-

imal time for this treatment is usually 2 h. Cooling at

this stage of production decreases the amount of heat

that will need to be removed in the freezer, thus

increasing the capacity of the freezer by permitting a

shorter time to reach the desired exit temperature.

Freezing the Mix

The Batch Process

0013Batch freezing involves introducing ice cream mix,

often by gravity, into a cylinder containing a ‘dasher’

with scraper blades (Figure 2). The cylinder is open to

the atmosphere and is surrounded by refrigerant. The

dasher is caused to rotate within the cylinder so that

3222 ICE CREAM/Methods of Manufacture

air will be incorporated into the mix, fat globules will

be partially churned, and ice crystals that form on the

inside wall of the cylinder will be scraped off by the

sharp edges of the dasher blades. As the water is

frozen into ice, the viscosity of the mix increases.

Air bubbles are trapped in the viscous mix, increasing

its volume and producing overrun. The maximal

overrun permitted in ice cream is about 100%, but

that amount of overrun is difficult to obtain in the

batch-freezing process.

0014 Capacities of batch freezers vary from less than 1 l

(home freezers) to about 40 l (commercial oper-

ations). Those freezer buckets that are refrigerated

with ice and salt, mostly home freezers, must be

completely closed to avoid entry of the salt brine

into the ice cream. Therefore, any additives such as

fruit must be placed in the mix prior to freezing or

must be mixed into the soft-frozen product postfreez-

ing. Batch freezers that are cooled with liquid refriger-

ant, such as the freons, usually have openings above

the cylinder through which flavorings, such as fruits,

nuts, and bakery products, can be added near the

Recorder

controller

Flow

diversion

valve

Sight

glass

Raw

product in

Balance tank

Booster pump

Bypass valve

Homogenizer

Differential

pressure

controller

Vacuum breaker

Modulating

valve

Bypass

valve

Pasteurized

product out

Cold product

recorder

80 ⬚C

4 ⬚C

72 ⬚C

12 ⬚C

4 ⬚C

Check valve

Bypass cycle

Timing pump

Thermometer

Recycle

Holding tube

Plate heat exchanger

Heat

Reg.

Cool

fig0001 Figure 1 System for high-temperature, short-time pasteurization and homogenization of ice cream mix. The rippled surface of the

heat exchanger plates is shown in the lower center. Temperatures (



C) appear near critical locations.

fig0002Figure 2 Batch-type ice cream freezer barrel containing beater

and blades. The door has an opening through which particulate-

type flavorings can be added near the end of the freezing cycle.

Frozen product exits through a hatch in the door.

ICE CREAM/Methods of Manufacture 3223

end of the freezing process. This allows the particles

of additives to maintain their shape and reduces the

adverse effect on incorporation of air bubbles. The

refrigeration units are mostly contained within

the freezer cabinet. These units pump liquid refriger-

ant into a chamber surrounding the freezing cylinder

where a drop in pressure and migration of heat into

the refrigerant change it to a gas. The gas is then

mechanically compressed and cooled. On cooling,

the refrigerant changes back to a liquid and begins

another cycle through the freezer.

The Continuous Process

0015 Most of the ice cream produced commercially is

frozen in continuous freezers (Figure 3). They range

in capacities from about 100 to 3000 l h

1

per freezer

barrel. These freezers, except for small ones, are com-

monly refrigerated with ammonia supplied from a

remote compressor unit. The refrigeration cycle starts

with liquid ammonia being released into the barrel

surrounding the freezing cylinder that contains the

mix. The mix, being warmer than the ammonia,

gives up heat to the liquid ammonia, transforming it

into a gas. This gaseous ammonia is pulled into a

compressor that compresses it and forces it through

condensing coils where sufficient heat is removed to

change the gas into a liquid. This liquid is then ready

to be circulated into the freezer to take on more heat

from the ice cream mix. At atmospheric pressure

ammonia boils at a temperature of 15.6



C. Redu-

cing the pressure enables it to boil at much lower

temperatures. Ice cream is frozen to 5to7



Cin

the continuous freezer. The internal structure of the

ice cream never improves after the ice cream leaves

the freezer. All of the air cells and ice crystals that can

be formed are formed within the freezing cylinder.

Subsequent treatments only reduce the numbers of

these inclusions by forcing air cells to collapse or

merge and ice crystals to grow in size while being

reduced in number.

0016The design of the dasher of the continuous freezer

affects the throughput and physical properties of the

ice cream. Dashers with a solid core on to which

scraper blades are attached may displace as much as

80% of the freezer cylinder volume. Rates of rotation

of these dashers tend to be high. They churn the fat

quickly, producing stiff ice cream that melts slowly

and is favored by producers of extruded novelty prod-

ucts. However, the small annular space between the

dasher and freezer cylinder limits the amount of mix

that can be contained and increases the probability of

freeze-up within the cylinder. Open dashers (Figure 4)

that displace 15–50% of the freezer volume are com-

monly placed into freezing cylinders of comparatively

large diameter. The large volume of mix within the

fig0003 Figure 3 (see color plate 97) Continuous-type freezer with front

removed revealing the freezing cylinder and dasher. To regulate

the flow of mix and the extent of freezing, pressure is exerted on

the freezing chamber by turning the handle located at the outlet

for the frozen product in the cylinder cover.

fig0004Figure 4 (see color plate 98) Open-type dasher with sharp

scraper blades. The dasher is partially inserted into the freezing

cylinder of the continuous freezer.

3224 ICE CREAM/Methods of Manufacture

chamber limits the effects of variations in refrigerant

supply. Output is more uniform in temperature and

overrun than the output from cylinders that have

solid dashers, but the ice cream tends to appear wet

and to melt rapidly. To prevent freeze-up of cylinders,

most modern freezers provide for hot refrigerant gas

to be turned into the space surrounding the freezing

cylinder when current flow through an ammeter to

the dasher motor gets excessively high, indicating

very high mix viscosity. This procedure can also be

done manually.

0017 Quality of the finished ice cream can be improved

by decreasing the sizes while increasing the numbers

of ice crystals and air cells during freezing. Two ap-

proaches are taken to achieve these conditions. The

first method is to use two freezing cylinders. The first

is essentially the same as the usual chamber while the

second cylinder has a dasher designed to agitate the

mix vigorously and to cool it to about 3



C lower than

does a conventional freezer. Pressure within the freez-

ing chamber is kept 4–6 times higher than in a con-

ventional cylinder. The second method is to preaerate

the mix by passing it through an emulsifier prior to

entry into the freezing cylinder. The device adds air

and breaks it into fine bubbles.

0018 All continuous freezers have a variable-speed pump

that supplies mix to the freezer chamber. Some also

have a pump that operates at a higher speed to

remove frozen mix from the freezer. A single pump

must force the mix all the way to the filler, whereas

placement of a pump at the outlet of the cylinder

permits the mix pump to work against only the pres-

sure in the cylinder. The outlet pump then works

against the pressure within the cylinder and the

downstream line pressures.

0019Programmable freezers are in wide use. Sensors

feed data to the microprocessor that controls the

system. Air input is set in proportion to the amount

of mix entering the chamber. Some programmable

freezers can be linked to filler machines so they

sense the appropriate flow rate of the mix into the

freezer.

0020Compared with batch freezers, the advantages of

continuous freezers are: (1) volume frozen per freezer

is much higher; (2) the product is usually much

smoother in texture; (3) overrun can be more closely

controlled and higher; (4) ingredient feeders and

variegating equipment can be placed downstream

from the freezer to introduce additives; and (5) ice

cream can be more easily formed into special shapes

and packaged with multiple flavors per package.

Some continuous freezers have multiple cylinders,

making it possible to extrude two or more flavors

simultaneously (Figure 5).

Packaging the Ice Cream

0021Once the ice cream exits the freezer it can be eaten in

the soft-frozen form or packaged and hardened. In

the USA about 75% of frozen desserts are consumed

fig0005 Figure 5 Twin-barrel ice cream freezer: 1, hoppers for mixes; 2, dasher (beater) assembly; 3, front bearing; 4, front cover with two

outlet valves; 5, one of four scraper blades; 6, clip to attach scraper blade; 7, cabinet containing refrigeration unit. Adapted from Taylor

drawing of Model H84.

ICE CREAM/Methods of Manufacture 3225

in the hard-frozen form. It is imperative that pack-

aging be done immediately after freezing to prevent

melting of the frozen product and that the packages

be transferred to the hardening facility quickly.

0022 Container sizes vary from 90 ml to 11.36 l (3 to 384

fl. oz.), with most packages of the 1–2-l capacity

(more than 80% of the ice cream sold in retail stores

in the USA is of the 1.89-l (1/2 US gallon) capacity).

Rectangular containers dominate the market. How-

ever, higher-priced premium and superpremium

frozen desserts are commonly packaged in straight-

wall cylindrical or nested cylindrical containers,

because these containers connote high quality. A

relatively new package is a tapered rectangle with

rounded corners. The most popular packaging mater-

ial is paperboard coated with plastic, but all-plastic

containers hold a share of the market.

0023 The package should be convenient to use; attract-

ive; appropriately labeled, including the lot number;

and capable of protecting the product from

tampering, contamination, and chemical changes,

especially oxidation.

0024 Filling is done by volume, but weight per unit

volume is controlled to prevent fraud. In the USA

the minimal weight is 540 g l

1

(4.5 lb gal

1

) for

regular ice cream, whereas ice creams with lowered

fat content (reduced-fat, light, low-fat, and nonfat)

may weigh as little as 480 g l

1

(4.0 lb gal

1

). Volume

usually varies as little as 1% within a filling oper-

ation. In most commercial operations the container

is formed on the premises from preprinted stock.

Small operations may receive and fill preformed

nested containers.

Hardening Frozen Desserts

0025It is essential to reduce the temperature of packaged ice

cream to not more than 18



C(0



F) within a few

hours of packaging. Otherwise, ice crystals grow

excessively in size and the product becomes coarse in

texture. Lower temperatures of approximately 30



(22



F) are needed if the product is to be held for

more than a few days. To achieve the optimal rate of

hardening, the environmental temperature is 40



(40



F) or lower. Speed of hardening depends on the

environmental temperature, rate of heat conductivity,

distance the heat must travel, and speed of removal of

heat from the surface of the container. Therefore, large

volumes cool slowly because heat must travel far to get

to surfaces and there is a low surface area per unit

volume with large packages. Rate of removal of heat

can be increased by placing packages in contact with

cold surfaces. This is done effectively with rectangular

packages that are placed between cold steel plates.

Another way to remove heat quickly from package

surfaces is to force cold air over the surfaces rapidly.

This is best done with conical-shaped packages that

allow passage of air between stacked packages.

Stacking of packages reduces air movement, especially

when package surfaces fit well together and when mul-

tiple packages are overwrapped with films to facilitate

handling. Therefore, stacking and overwrapping

should await completion of the hardening process. To

maximize heat transfer in minimal space, manufactur-

ers use hardening chambers through which packages

are conveyed on trays, shelves, or belts as cold air is

blown on to them (Figure 6). Since the environment of a

fig0006 Figure 6 Hardening freezer equipped with a belt-type conveyor that spirals upward toward the storage freezer. Courtesy of

Frigoscandia, Northfield, MN.

3226 ICE CREAM/Methods of Manufacture

hardening facility is unfavorable to humans, it is desir-

able that the frozen product be unloaded mechanically

so it can be stacked either mechanically or by hand on

to pallets for transfer to the storage facility.

Storage of Frozen Desserts

0026 The temperature of the storage facility need not be as

low as that of the hardening facility, but the longer the

product is to be held, the lower the temperature needs

to be. Usually, 30



C(22



F) is satisfactory. Since

the environment within a storage facility is unfavor-

able to humans, storage retrieval systems have been

developed that allow workers to move product in and

out of storage using computer-controlled mechanical

devices. The system keeps a current inventory of

numbers and locations of each flavor, package size,

lot number, and time of production. Proper quality

control and risk management procedures make it

necessary that records be kept of ingredients and

their sources, results of tests of composition and

bacterial counts, and the net weight per unit volume.

Temperatures of the storage facility should be moni-

tored continuously, and alarm should be sounded

when the temperature exceeds a specified maximum.

See also: Freezing: Operations; Storage of Frozen Foods;

Ice Cream: Properties and Analysis; Dietary Importance;

Microbiology

Further Reading

Andreasen TG and Nielsen H, revised by Christensen ES

(1998) Ice cream and aerated desserts. In: Early R (ed.)

The Technology of Dairy Products, 2nd edn, pp. 301–

324. Gaithersburg, MD: Aspen Publishers.

International Dairy Federation (1998) Ice cream. In:

Buchheim W (ed.) Proceedings of the International

Symposium, Athens, Greece, Sep. 18–19, 1997. Brussels:

International Dairy Federation.

Koxholt MMR, Eisenmann B and Hinrichs J (2001) Effect

of fat globule size on the meltdown of ice cream. Journal

of Dairy Science 84: 31–37.

Li Z, Marshall RT, Heymann H and Fernando L (1997)

Effect of milk fat on flavor perception of vanilla ice

cream. Journal of Dairy Science 80: 3133–3141.

Marshall RT (1998) Ice cream and frozen yogurt. In: Marth

EH, Steele JL (eds) Applied Dairy Microbiology, pp.

81–108. New York: Marcel Dekker.

Marshall RT and Arbuckle WS (1996) Ice Cream, 5th edn.

Gaithersburg, MD: Aspen Publishers.

Pappas CP (1988) Comparative laws and regulations on

compositional requirements for ice-cream in the EEC.

British Food Journal 90: 250–254.

Prindiville EA, Marshall RT and Heymann H (1999) Effect

of milk fat on the sensory properties of chocolate ice

cream. Journal of Dairy Science 82: 1425–1432.

Properties and Analysis

R T Marshall, University of Missouri, Columbia, MO,

USA

Introduction

0001Ice cream (glaces a

la cre

me in French; Eiskrem

in German; helado in Spanish; morozhenoe in

Russian; roomijs in Dutch; flødeis in Danish) is a

frozen emulsion. The continuous phase consists of

unfrozen syrup containing the dissolved substances,

mostly sugars and minerals. The disperse phase con-

sists of air cells, globules of milk fat (and in some

countries, other sources of fat), ice crystals, and

insoluble substances, including proteins and hydro-

colloids.

0002This article discusses the unique chemical, nutri-

tional, physical, microbiological, and sensory proper-

ties of frozen desserts. Both objective and subjective

methods are used to measure these properties.

Definition of Ice Cream

0003According to the US standard for frozen desserts,

plain ice cream must contain at least 10% milk fat

and 20% total milk solids. Manufacturers are permit-

ted to substitute up to 25% of the nonfat milk solids

content by the solids of cheese whey. Furthermore,

milk fat may be substituted for nonfat milk solids in

1% increments up to 14% milk fat. For example, a

product containing 12% fat need contain only 8%

nonfat milk solids and 2% of this amount may be

whey solids. Ice cream must weigh at least 540 g l

1

(4.5 lb gal

1

) and contain at least 192 g l

1

of food

solids (1.6 lb gal

1

). This limits the maximum amount

of air that can be whipped into the mix during freez-

ing to approximately 100% or the same volume as

the volume of the mix that goes into the package.

Standards for ice cream having lowered fat content,

namely reduced fat, light, lowfat and nonfat ice

creams, permit the weight to be as low as 480 g l

1

(4.0 lb gal

1

0004The following are the US Food and Drug Adminis-

tration requirements for labeling of foods with a

lower fat content:

0005Reduced fat: at least 25% less fat than the reference

product.

0006Light: 50% reduction in total fat from the reference

product, or one-third reduction in calories if less

than 50% of the calories are from fat.

0007Lowfat: not more than 3 g of total fat per serving.

0008Nonfat or fat free: less than 0.5 g of fat per serving.

ICE CREAM/Properties and Analysis 3227

0009 When large amounts of flavoring ingredients, such

as chocolate, nuts, and fruits, are added to plain ice

cream mix, the requirements for percentages of milk

fat and total milk solids are reduced in proportion to

the weight of the ‘bulky flavoring.’ In no case, how-

ever, may there be less than 8% milk fat or 16% total

milk solids.

0010 Canadian standards differ somewhat from those of

the USA. Whereas plain ice cream must contain at

least 10% milk fat, Canada has no minimum for

total milk solids. The minimum amount of solids

permitted is essentially the same in the two countries.

Canada requires a minimum of 36% of total solids in

the ice cream and a solids weight of 180 g l

1

in the

finished product. The US standard calls for minimal

foods solids of 1.6 lb gal

1

(192 g l

1

). As in the USA,

Canada permits cocoa or chocolate, fruit, nuts, and

confections to displace up to 2% of the milk fat.

0011 Canadian standards permit sales of light ice cream

with 5–7.5% milk fat and ice milk with 3–5% milk

fat. Total solids in each must be at least 33% and

comprise at least 160 g l

1

. The maximal fat permit-

ted when bulky flavors are added to light ice cream is

6%. No reduction is permitted in fat content when

bulky flavors are added to ice milk.

0012 Although countries in the European Union (EU) are

attempting to agree on common compositional stand-

ards, the current minimum fat content of ice cream

ranges from 5% in the UK to 10% in Germany. Italy,

where ice cream is called gelato, has no requirement.

Most EU countries permit the sale of milk ice (ice

milk) containing, variously, at least 2.5–5% fat.

Some countries permit vegetable fat to replace milk

fat, provided disclosure is by obvious labeling. How-

ever, products labeled with dairy or milk as part of the

name must contain milk fat only. Most of the EU

countries have a minimum total solids (dry-matter)

requirement of 29 or 30% for ice cream. European

standards generally do not specify minimum weights

per unit of volume. Most do specify which nondairy

ingredients are permitted, including fruits, nuts, fla-

vorings, sweeteners, color additives, stabilizers, and

emulsifiers.

0013 In India, ice cream can be made from cows’ or

buffalo milk. The minima for content of fat, protein,

and total solids are 10%, 3.5%, and 36%, respect-

ively. Fat content may be reduced in proportion to the

amount of bulky flavorings added but not below 8%.

The limit for added stabilizers and emulsifiers is 0.5%

and for added starch is 5%.

Chemical Properties

0014 Since ice cream is composed primarily of cream, non-

fat milk solids, sweeteners, and flavorings, the major

components are milk fat, lactose, milk protein, sugar,

and corn syrup solids. Minor ingredients are vege-

table gums and mono- and diacylglycerols. Tests com-

monly used to determine the chemical composition of

ice cream and to determine whether it meets regula-

tory standards include ether extraction for fat and the

hot air oven for total solids.

0015The fat content of ice cream is measured by ex-

tracting the lipids from a weighed sample with or-

ganic solvents, evaporating the solvents, weighing the

extracted fat, and calculating the percentage. Protein

is measured with the Kjeldahl test, involving digestion

of the sample with strong sulfuric acid, a catalyst, and

heating then distilling and measuring the nitrogen in

the sample. Nitrogen content is then multiplied by a

factor of 6.38 to calculate the protein value. Calories

are assayed by burning a sample in a bomb calorim-

eter to determine how much heat is produced per unit

sample. Minerals are quantified using flame photom-

etry or atomic adsorption spectroscopy. Biometric

or spectrophotometric assays are used for several

vitamins.

0016To analyze for total solids, about 3 g of melted

ice cream is weighed into a dried and weighed pan.

Moisture is evaporated on a steam bath and then in

an oven at 100



C for 3.5 h. On cooling, the pan with

its dry contents is weighed and the percentage of total

solids is calculated.

0017Tests for total milk solids are not performed

by regulatory agencies because of the complexity of

ice cream formulae. Rather, control agencies have

the option to check records of production and

of dairy ingredient utilization to ascertain whether,

on a general basis, a firm has met the ice cream

standard.

Nutritional Properties

0018Ice cream products vary widely in nutrient content,

primarily because of the differences in content of

water, fat, nonfat milk solids, and air per unit of

serving. Water content varies from about 70% in

soft-serve low-fat or light ice creams to 57% in super-

premium ice creams. Fat content varies from 0.5 to

16%, and air displaces ice cream mix on a volume

basis from 10% in some superpremium ice creams to

over 50% in fat-free ice creams. Based on nutrition

labels, a serving of 120 ml (4 fl. oz. and a minimum of

about 70 g) of vanilla ice cream varies in caloric con-

tent from 90 in the nonfat to 240 in the premium full-

fat type.

0019Ice cream mix contains 3–4.5% protein so that a

70-g serving furnishes 2–3 g. Ranges of other com-

ponents per 120-ml serving of nonfat through pre-

mium plain ice creams, excluding the sugar-free types,

3228 ICE CREAM/Properties and Analysis

are: carbohydrate 13–19 g; sugar 13–15 g; fat 0–10 g;

and calcium 58–135 mg. Because milk fat is a good

source of vitamin A, manufacturers are required to

add this nutrient to lowfat and nonfat ice creams.

Additionally, a serving of ice cream provides about

10% of the daily value of riboflavin plus significant

amounts of thiamin, pyridoxine, and pantothenic

acid. (See Vitamins: Overview.)

0020 A serving of regular ice cream contains about 3.5 g

of lactose, enough to cause intestinal discomfort in

some persons who digest lactose poorly. Such persons

produce insufficient lactase (b-galactosidase) in the

small intestine. Lactose can be removed from nonfat

milk by ultrafiltration and diafiltration or can be

hydrolyzed to glucose and galactose by the addition

of lactase enzyme. By using a combination of the two

treatments, the freezing point of a mix can be main-

tained while reducing the amount of lactose below

biologically significant levels.

0021 Analyses for lactose in milk can be done by both

chemical and instrumental methods. However, the

presence of significant amounts of other sugars in

ice cream precludes using the polarimetric method

for it. In milk and milk products to be used in ice

cream the concentration of lactose can be determined

by removing the fat and protein by precipitation and

filtration followed by measuring the degree of rota-

tion of polarized light, which is proportional to the

concentration of lactose. The 9.610-nm wavelength

of infrared light is highly absorbed by the hydrogen

bonds that are abundant in lactose, and this is the

principle of a widely used instrumental method of

analyzing for lactose in milk. For ice cream itself,

high-pressure liquid chromatography is the method

of choice for determining the concentration of

lactose. (See Lactose.)

Physical Properties

0022 The major physical characteristic of frozen desserts

that concerns regulatory agencies is weight per unit

volume of product, and this is affected by the overrun

developed in the product. When enough air is

whipped into a mix during freezing to cause doubling

of the volume, 100% overrun has been obtained.

Thus, a mix weighing 1.1 kg l

1

would produce 2 l

of ice cream weighing 0.55 kg each. Ice creams are

classified by industry as superpremium, premium,

regular or trade-brand, and economy. The overrun

of superpremium ice creams may be as low as 20%,

whereas that of economy ice creams is usually at the

maximum limit.

0023 Overrun can be calculated for individual contain-

ers by determining the portion of mix displaced by air

in the specific package as follows:

%Package overrun ¼½ðmix weight 

product weightÞ=product weight100

‘Plant overrun’ is an expression of the increase in

volume of an entire lot of ice cream mix. For example,

if 5000 l of mix is frozen into 9000 l of ice cream, the

overrun is 80%.

%Plant overrun ¼½ðvolume of product 

volume of mixÞ = volume mix100

0024Hardness of the product at the temperature at

which it has the optimum consistency for dipping is

an important consideration. Hardness is affected by

several factors: principally, melting point, total solids,

overrun, and amount and type of stabilizer. When

an ice cream store keeps several containers of product

in a single cabinet from which each is to be dipped or

scooped, only one temperature setting is available.

Therefore, it is desirable to have the melting points

and overruns of all flavors of ice cream nearly the

same. This is not easy to accomplish, because formu-

lae involve several variables that affect the concen-

tration of dissolved substances and, therefore, the

melting point. The higher the concentration of

water-soluble substances, the lower the freezing and

melting points. The ice cream formulator must care-

fully choose amounts of monosaccharide sweeteners,

such as glucose, to use. On an equal-weight basis,

glucose lowers the freezing point twice as much as

does the disaccharide sucrose while providing only

three-fourths as much sweetness.

0025Choice of the amount and type of stabilizer depends

on factors other than hardness, and especially on the

need to bind water to increase shelf-life. Hardness can

be determined with a puncture probe placed on a

texture analyzer. The resistance to penetration of the

probe is measured repeatedly in ice cream that is

adjusted to a precise temperature. Comparisons to a

reference curve enable decisions to be made regarding

needs for changes in formulation.

0026When fat globules are very large, the melting rate

of ice cream becomes quite slow because of excess

churning of the fat during freezing. The critical mean

fat globule diameter is slightly more than 1 mm.

Single-stage homogenization at a pressure of 10

MPa is sufficient to produce a favorable size

distribution.

0027Characteristics of the emulsified components of

ice cream are not easily determined in tests. Sizes of

ice crystals, air cells, and fat globules can be measured

by examining a thin film of product using a light

microscope equipped with a ‘cold stage.’ Application

of image analysis enables large data sets to be ana-

lyzed, thus increasing accuracy in determinations of

sizes of emulsified components. Electron microscopy

ICE CREAM/Properties and Analysis 3229