Risk
Assessment Studies
Report
No. 7
MICROBIOLOGICAL
RISK ASSESSMENT OF ICE-CREAM
SEPTEMBER
2001
Food
and Environmental Hygiene Department
HKSAR
This is a publication of the Food and Public Health Branch of
the Food and Environmental Hygiene Department of HKSAR Government. Under no circumstances should the
research data contained herein be reproduced, reviewed, or
abstracted in part or in whole, or in conjunction with other
publications or research work unless a written permission
is obtained from the Department. Acknowledgement is required if other
parts of this publication are used.
|
Correspondence:
Risk Assessment Section
Food and Environmental Hygiene Department
43/F, Queensway Government Offices,
66 Queensway, Hong Kong.
Email: enquiries@fehd.gov.hk
Table
of Contents:
Abstract
Production
of Ice-cream
Mixing of
Ingredients
Pasteurization
Homogenization
Aging
Freezing
Packaging
Hardening
Storage
Potential
Microbiological Hazards
Regulatory
Framework
Local Manufacture
and Sale
Microbiological
Quality of Ice-cream
Hygienic
Quality
Presence
of Specific Pathogens
Discussion
Conclusion
& Recommendations
Advice
to trade
Advice
to public
Reference
Figure
1: Flow Chart of Ice-cream Production
Figure
2: Trend Analysis of Hygienic Quality of Ice-cream
(1998
– 2000)
Table 1:
Hazards and Typical Control in the Production of
Ice-cream
Table 2:
Microbiological Surveillance Results of Ice-cream
(1998
– 2000)
Risk
Assessment Studies
Report
No. 7
MICROBIOLOGICAL
RISK ASSESSMENT OF ICE-CREAM
An
Evaluation of Microbiological Surveillance
of
Ice-cream
1998
– 2000
Abstract
Ice-cream is a frozen dairy
product. It is sold in
soft or hard status. The
production of ice-cream includes totally eight steps.
Pasteurization, freezing and hardening are the main steps to
eliminate the microbiological hazards.
In Hong Kong, sale of ice-cream is governed
by the Public Health and Municipal Services Ordinance and its subsidiary
legislations, especially the Food and Drugs (Composition and Labelling)
Regulations and the Frozen Confections Regulation. Reviewing the microbiological
surveillance findings on 16,379 ice-cream samples collected from 1998
through 2000, 543 samples (3.3%) were found unsatisfactory in either
total bacterial count or coliform count.
Trend analysis showed that the unsatisfactory rates of all ice-cream
decreased from 4.7% in 1998 to 3.2% in 1999, and then, to 2.2% in 2000. Comparing the unsatisfactory rates of
both types of ice-cream, the relatively high unsatisfactory rates of
soft ice-cream were observed.
In addition, 198 additional samples were taken for Listeria monocytogenes examination in
the past three years. No
sample was found to contain L.
monocytogenes. A gradual
improvement in the hygienic quality of ice-cream was observed in the
period of 1998-2000. To
ensure food safety, the trade and the public are advised to pay attention
on some key areas from the preparation to consumption of ice-cream.
INTRODUCTION
Ice-cream represents a congealed dairy
product produced by freezing a pasteurized mixture of milk, cream, milk solids other than fat, sugars, emulsifier and stabilizers.
Products of dairy origin are the main ingredients of ice-cream. These include whole milk, skimmed milk,
cream, frozen cream, condensed milk products and milk solid. Other ingredients include flavouring matters
and water. Fruits, nuts,
candies and syrups are optionally added into ice-cream for flavour enrichment.
Two types of ice-cream, soft and hard, are available on the market.
OBJECTIVE
2.
This paper describes the manufacturing procedures, identifies
the potential microbiological hazards and outlines the local regulatory framework of ice-cream products. The food surveillance findings in the
period of 1998-2000 are reviewed and analyzed to evaluate the actual microbiological hazards in ice-cream.
PRODUCTION OF ICE-CREAM
3.
The production of ice-cream includes
many steps classified under the following three main parts (Figure
1) –
1.
Ice-cream mix making (mixing of ingredients,
pasteurization and homogenization);
2.
Soft ice-cream production (aging and
freezing); and
3.
Hard ice-cream production (packaging,
hardening and storage).
4.
The manufacturing of ice-cream mix involves
mixing of ingredients, pasteurization and homogenization. For soft ice-cream, pre-made ice-cream mix is supplied to the retail
outlets under refrigeration (< 7°C). Aging and freezing at around -5°C are performed in the vending machines
at the retail level. Other
ingredients, such as fruits and nuts, may be added to the soft ice-cream
at the time of sale for flavour enrichment.
In frozen confection factories, the soft ice-cream will be packed
and hardened to produce the hard ice-cream.
The following paragraphs describe the technological details
of each processing step.
Mixing of ingredients
5.
The first step of preparing ice-cream
mix is to combine the liquid ingredients and heat them to around 43°C. Then, sugar and other dry ingredients,
except nuts and fruits, are added to the lukewarm mix.
Pasteurization
6.
The mixture is then pasteurized by a heating process, either
in batch or continuous modes, depending on the production size. Pasteurization temperatures for ice-cream
mix, around 70°C for 10 – 30 minutes (1),
are higher than that for plain milk because high fat and sugar contents tend to protect bacteria from heat
treatment.
Homogenization
7.
The pasteurized mix is then homogenized.
High pressures of 4.1 x 106 Pa (600 psi) to 1.7 x 107 Pa (2500 psi) are used to break down
fat globules(2). This pressure can clump fat globules and, together with the added
emulsifiers, can prevent churning of fat into butter
granules (milk fat) during freezing step. Homogenization also improves the texture
of ice-cream. In other
words, the ice-cream becomes smoother.
After that, the homogenized mix is cooled down to 4°C for further processing. For production of soft ice-cream using
vending machines, it is packed and delivered to the retail outlets.
Aging
8.
Aging is the first step in soft ice-cream
production. The mix is
held in sterilized vats from 3-24 hours at temperature
of around 4°C or lower. It allows some physical changes, such
as fat crystallization, adsorption of protein onto fat globules, and
incensement of the mix’s viscosity. These changes lead to quicker whipping
to the desired overrun in freezing process, smoother ice-cream
body and texture, and slower ice-cream melt-down.
Freezing
9.
During freezing, air is incorporated
in the mix and cooled down to around -5°C. Freezing must be performed as quickly as possible to prevent the formation of large
ice crystals. The air cells
in ice-cream should be small and evenly distributed in order to maintain
a stable frozen foam. At
this low temperature, -5°C, not all water particles are crystallized and, therefore, ice-cream is only in semisolid state. The semisolid ice-cream emerging from
the freezer is similar to the constituency of soft ice-cream produced at the retail
level. Other ingredients,
like fruits, nuts, or syrup, may then be added to enrich the flavour
of ice-cream.
Packaging
10.
To produce hard ice-cream, the semisolid
ice-cream is packed into cartons or drums for hardening process to form
specific shape of ice-cream products and to have longer shelf-life (more
than one year).
Hardening
11.
The pre-packed semisolid ice-cream is then
placed in a hardening room where the temperature of about -34°C is maintained. This low temperature keeps the core temperature
of ice-cream at around -18°C. Hardening should be performed quickly
to prevent the formation of large ice crystal and to maintain
better quality of ice-cream.
Storage
12.
After hardening, the hard ice-cream
will then be placed back in the cold store rooms with temperature of
around -18°C. From this stage, the hard ice-cream must
be kept at -18°C or below throughout storage, transportation
and display.
POTENTIAL MICROBIOLOGICAL HAZARDS
13.
Ice-cream, a milk-based product, is
a good media for microbial growth due to high nutrient value, almost
neutral pH value (pH ~6-7) and long storage duration of ice-cream (3). However, pasteurization, freezing and
hardening steps in the production can eliminate most of the microbiological hazards.
According to the Frozen Confections Regulation under Chapter 132, ice-cream must be heat-treated during the production process. Pasteurization is most commonly applied
heat treatment in the dairy industry. This can destroy almost all pathogenic bacteria in milk. The subsequent process that subjects the
mixtures to freezing temperature can also inhibit the growth of any
remaining flora. Hardening
is also the important control point that further reduces the hazards (4). Furthermore, as automatic machines are
commonly used for ice-cream making in dairy industry, the chance of
contamination through direct hand manipulation can be reduced.
14.
Nevertheless, there are some steps in the production of ice-cream
that (Figure
1) can lead to the microbiological hazards.
Table 1
summarizes the possible hazards associated with different stages of
ice-cream production (5). Heat treatment by pasteurization can destroy
most of the specific pathogens that pose risk to public health. However, the potential microbiological
hazards found in the final products can still be introduced after pasteurization
through adding contaminated ingredients and improper handling
procedures (6). This is especially important in the preparation
of soft ice-cream as its final stage of the production is carried out
at point of sale. Some
pathogens that can survive in food even at low temperature include Salmonella spp., Listeria monocytogenes, Campylobacter spp. and Yersinia spp. (7).
15.
For ice-cream products, L. monocytogenes is of significant food safety concern
worldwide (3). In Hong Kong, regular surveillance to
monitor L. monocytogenes in ice-cream has been in place. In 1997, L. monocytogenes was found in 4 imported ice-cream samples.
Consequently, the importer had voluntarily recalled all incriminated ice-cream
products on sale. No report
of any persons being affected was received in that case.
REGULATORY FRAMEWORK
Local manufacture and sale
16.
The composition of ice-cream is defined
in Part II of Schedule 1 of the Food and Drugs (Composition and Labelling)
Regulations (Chapter 132, sub. leg. W). Ice-cream shall contain not less than 5% fat, 10% sugar and 7.5%
milk solids other than fat: Provided
that ice-cream containing any fruit, fruit pulp or fruit puree shall
either conform to the aforesaid standard or, alternatively, the total
content of fat, sugar and milk solids other than fat shall not be less than
25% of the ice-cream including the fruit, fruit pulp or fruit puree,
as the case may be, and such total content of fat, sugar and milk solids
other than fat shall include not less than 7.5% fat, 10% sugar and 2%
milk solids other than fat. For the purpose of the aforesaid standard
relating to ice-cream, "sugar" means sucrose, sugar or solids of any
sweetening material derived from starch, provided that no ice-cream
shall contain less than 7.5% sucrose.
17.
For control of ice-cream, premises manufacturing
ice-cream must be covered by valid Frozen Confection Factory licence
under the Frozen Confection Regulation.
Frozen Confection permits are also required for retail outlets selling
ice-cream in bulk or cone in original wrappers. All these premises are also required to
comply and observe relevant licencing requirements and conditions.
18.
The Frozen Confection Regulation stipulates the requirement
for the manufacturing of frozen confections including ice-cream and the microbiological standards of the
finished products. In addition,
the microbiological limits for Listeria monocytogenes in the guidelines of ready-to-eat food
are used for the monitoring.
