Better Material for food handling and processing
Worries
in human health have become important in developing countries,
for this reason the food purity in handling and processing has
been made increasingly stringent. It is world wide recognized
that Stainless Steel is the material of construction for plant
equipment in the food processing industry to achieve sanitation
and corrosion resistance. With these basis it becomes necessary
to establish a market development program for these countries
that consider all the great variety of problems in the food
industry and hope that stainless steel satisfy them.
Introduction:
There are two main concepts responsible for food fitness for
human consumption.
Sanitation - Bacteriological contamination during handling,
production, processing and serving.
Contamination - Foodstuff, like other chemical substance is
responsible in all phases of processing for corrosive effects.
These effects are in addition influenced by environmental condition
of processing, that is, by the temperatures involved, by the
rates of flow and by stresses in component parts of process
machinery. The corrosive effects will result in harmful substances
include in foodstuffs.
Material Selection:
When the technicians face the question
what material will be satisfactory for the fabrication of the
equipment they want a material which will most nearly fulfil
all the requirements. The questions have been generalized and
are listed in the following order of importance as we see them.
Which material does not contaminate
the product?
This is a general requirement that should
be broken down into branches related among themselves. First,
the direct or chemical contamination by metals or metallic ions.
The
Nickel Development Institute developed an interesting study
about nickel pick up in pots made in stainless steel The food
samples were selected to obtain their acidity and chloride content,
representing a typical pickling medil (lemon, marmalade, green
tomato, chutney, potatoes, rhubarb and apricots). There used
twelve new pots from fc different manufacturers. All pots were
stainless steel.
The
level of nickel pick up on cooling with the most aggressive
food "rhubarb" mean. 10- .15 pg. This amount smaller
than the normal daily intake by human of 150-200 pg of nickel
per day even more the facts show that the is no evidence about
people will be sensitized by nickel ingested in food.
A
second study, developed by Acerinax, S. A. about metal transfer
into food under acidic conditions, in which were test Stainless
steel AISI 403, stainless steel AISI 304, commercial aluminum
and carbon steel and the medium was 2 Acetic acid by weight
at 40C in contact for 10,20 and 30 days. The results are summarized
as below.
Time Fe Cr Al Ni
Stainless 304 10 Days 4.2 022 0.19 < 0.12
20 Days 2.7 0.22 0.19 < 0.12
30 Days 2.3 0.28 0.19 < 0.12
Stainless 130 10 Days 7.3 0.4 0.19 < 0.12
20 Days 8.6 0.71 0.19 < 0.12
30 Days 6.6 0.87 0.19 < 0.12
Aluminum 10 Days 18.2 3.41 5,300 < 0.12
20 Days 17.9 5.58 7,160 < 0.12
30 Days 31.3 12.4 15,350 0.22
Carbon steel 10 Days 57,770 7.44 26.7 < 0.12
20 Days 62,990 6.82 25.0 < 0.12
30 Days 112,000 14 39.9 < 0.12
Metal
Pick up at 400C under 3% Acetic Acid (pg/cm2)
We also know that the high ductility, tensile strength and wear
resistance of the stainless steel prevent the possibility of
mechanical contamination. Second, The indirect, bacteriological
or biological contamination resulting from the material selected.
The
best we can do on this matter is the design for the "Clean
up" process. The fabrication of equipment will meet the
most exact requirements for the easy maintenance and cleaning.
Which material is easy to clean?
The surface finish of material should
be smooth, free of pits or scratches and present minimum opportunity
for the adhesion of food particles or bacteria. Food technologists
and fabricators concerned with the prevention of bacteriological
contamination developed this "Sanitary finish" produced
by grinding with 480 mesh abrasive and then butting to remove
grind lines. The finish highly polished on all surface which
came in contact with the food product give a thorough cleaning
an disinfecting surface.
The
Nickel Development Institute developed an interesting research
on bacterial cleanability. Using the latest technology to quantify
bacterial contamination the research compares stainless steel
with polycarbonate plastic and mineral-resistant enameled steel.
Under standardized condition, specimens were contaminated with
acinetobacter calcoaceti, a bacterium associated with foods
spoilage. After a period of bacterial inculcation they were
spray washed tor up to 40 seconds with water with domestic detergent.
The bacteria remaining were stained and viewed under a microscope
with UV source.
When specimens were tested in spray washed conditions, all showed
a similar level of the retained bacteria then, specimens had
been subjected to controlled rubbing with a 40 grit abrasive
cloth showed significant difference Stainless steel retained
10 times lower bacteria than the other materials.
Latest works on this matter have shown that addition of wiping
action to the washing treatment enhances the bacterial cleanability
of stainless steel as illustrated as below.
Which material does not corrode
in operation conditions?
The driving force of the corrosive reaction
between metal and environment is electrochemical. The resultant
electrochemical potential varies with the corroding media and
the metal and determines the tendency of the reaction. The protective
oxide film formed in stainless steel is very thin, almost of
molecular thickness, invisible and it is formed instantaneously
when exposed to oxidizing condition. This film can be destroyed
by reducing conditions such as those present in halogen acid
solutions, fortunately, we seldom encounter these conditions
in the food industry. This is substantiated by literally thousands
of laboratories.
Which material has the proper
physical properties?
Stainless steel has high tensile strength
and yield point and relatively high hardness, withstands the
mechanical attacking of high-pressure water, scouring, brushing
and abusive handling. For any material of equipment construction,
this strength - weight ratio is most important. We can consider
the yield point as a measurement of strength.
Interpretation to the above table can be summarized as below:
Stainless steel has a higher strength - weight ratio than any
of the other materials used for food processing equipment. We
can consider hardness as a measure that indicates the resistance
to abrasive wear. If we combine hardness with Strength - weight
ratio, it indicates that stainless steel is having an excellent
resistance to both abrasion and mechanical deformation.
Which material has the low maintenance
cost?
When specifiers analyzed initial cost
they should consider the best life span costing of stainless
steel.
It does not require protective coating. Very little weight reduction.
Wide time interval between maintenance / replacement. It does
not present for a short time of loss of production for maintenance
replacement event.
Even
more, when we consider the superior characteristics of stainless
steel in this applications. Food technologist know the cost
of one production day ruined by metal iron contamination.
Which material is available in
required forms?
Stainless steels are produced in practically
every form required, include wrought or cast pieces, hot and
cold rolled plate, bar and wire, seamless and welded tube, fittings,
welding electrodes, fasteners, etc.; also are available in different
chemical compositions and with different surface finishing.
Which material has an attractive "hygienic
appearance" ?
The public in general and the housewives
in specific associate stainless steel with culinary cleanliness.
Many companies want to show to the public the cleanability of
the stainless steel equipment.
This hygienic appearance has a psychological effect on consumers,
inspectors and plant personal.
All these above discussion accentuates the utility of Stainless
steel over other conventional materials in food handling and
processing industry.
