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.