**Corrosion in the Food Industry and Its Control**

Benjamín Valdez Salas, Michael Schorr Wiener, Margarita Stoytcheva, Roumen Zlatev and Monica Carrillo Beltran *Universidad Autonoma de Baja California. Instituto de Ingeniería, Mexicali, Baja California, Mexico* 

### **1. Introduction**

362 Food Industrial Processes – Methods and Equipment

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Wium; H.; Pedersen, P.S. & Qvist, K.B. (2003). Effect of coagulation conditions on the

from ultrafiltered milk. Food Hydrocolloids, Vol.17, No.3, pp. 287-296

microstructure and the large deformation properties of fat-free Feta cheese made

From ancient times human beings have survived on a diet consisting on a relatively few species of plants and animals, domesticated and then cultivated and grown. Three cereals, wheat, rice and corn, supply the need of human energy, protein and vitamins requirements for the network of metabolic processes to maintain normal body function and temperature. In a prehistoric era, indigenous peoples all over the world were moving in inhospitable grounds obtaining their daily sustenance by hunting and gathering fruits, seeds and roots.

Actually, the three largest markets worldwide, according to their production extent, the number of consumers and their economic and social significance are the food, energy and water markets. Furthermore, their increasing scarcity and soaring prices lead to a global critical situation. The demand for increased food supply is related both, to population increase and personal and family income. Consequently, the food market is the largest one, including all the inhabitants of this planet, about seven billion, since everyone eats!

The organized food production and supply starts with the agricultural revolution, developed and implemented in the fertile valleys of the rivers Tigris-Euphrates in Mesopotamia and the Nile in ancient Egypt. Afterwards the food industry expanded, avoided widespread famine and ensured that sufficient food is supplied for all people to stay healthy. Current food research had been largely stimulated by rapidly growing world demand but technological advances in food processing, equipment and production plants have also contributed. A most significant aspect in the search of new nutritional food is the requirement for adequate protein in regions where meat and fish are not available. Additionally, advances in the food industry (FI) such as preservation, packaging and storage facilitate food delivery and minimized health hazards. Space flight conditions have stimulated the creation of space food which meets highly demanding standards for conservation and to be ready for easy digestion e.g. solid dehydrated food easily converted into liquid or paste food.

Techniques for preserving food from natural deterioration following harvest or slaughter dated to prehistoric times applying drying, salting, fermentation of milk and fruits and pickling of vegetables. Modern techniques include canning, freezing, dehydration, cooking under vacuum and addition of chemicals. The principal causes of food spoilage are growth

1. Alkaline: such as caustic soda (NaOH), alkali phosphates (Na3PO4), sodium carbonate

This great variety of corrosive environments and aggressive chemical agents require the use of Corrosion Resistant Alloys (CRAs). SS are the obvious choice of the food industry to

Food main constituents.- Foods are constituted by two essential groups of substances: those with nutritional values: proteins, carbohydrates and fats and the components imparting particular tastes: salt (NaCl) for saltiness, acids for sourness or acidity and sugars for sweetness. Few peculiars foods have a bitter taste e.g. almonds. A central component of food

**Water.-** The vegetables and ripe fruits contain a considerable amount of water between 70% and 90%. Since water is used as a medium for food preparation e.g. cooking , confectionery, hot and cold beverages, even cooked foods contain water. The water behaviour and its interaction with food depends on its physicochemical properties, its molecular and ionized structure and its chemical bonding. Water is considered as the universal solvent since all chemical substances have a finite solubility in water ranging from acids, bases, salts, sugars,

H3O+ a bonding between an hydrogen ion H+ and a water molecule, these are the ions involved in corrosion of metallic materials used for the construction of food processing

2FeCl3 + 3H2O → 6HCl + Fe2O3, (1)

Water is the medium for countless chemical and biological reactions. With the exception of petrochemical and combustion reaction, most chemical processes occur in aqueous systems, including vegetal and animal respiratory and metabolic functions. Food preparation involving dehydration, softening, takes places in water. The operation requires some energy to break hydrogen bond and form new bonds between the solute: food components

**Salt.-** Table salt (NaCl) is encountered in many natural environments: seawater, natural brines, enclosed seas, e.g The Dead Sea, Israel and the Salt Lake, Utah, USA, with a salt concentration of about 300 g/L; in aboveground and underground mines found as rock salt. An aqueous salt solution is decomposed by electrolysis into several useful products: metallic sodium, hydrogen, sodium hydroxide and chlorine, all important raw materials for the chemical processing industry (CPI). The meat packing, sausage making, fish curing and food conservation employ salt as a preservative or seasoning or for both purposes. Up to the 19th Century, during the invention of industrial food freezing and cannery; commercial and navy ships conserved meat in wood barrels full of solid, granular salt for their long voyages since putrefaction bacteria cannot live in salt. Salt is a hygroscopic substance, absorbing atmospheric moisture, forming a concentrated salt solution or slurry, corroding steels and deteriorating ceramic materials such a masonry bricks. Salt is part of mankind history and tradition. Modern and ancient words, in many languages, are derived from salt: salary,

forming the hydronium ion

359

3. Oxidizers: chlorine, nitric acid, ozone, hypochlorite, hydrogen peroxide (H2O2)

and bicarbonate (Na2CO3, NaHCO3). 2. Acidic: phosphoric, citric and sulphamic acids.

prevent equipment damage and food contamination.

is water as in fruits, vegetables, meat, eggs, milk, etc.

Acidic metallic salts undergo hydrolysis in water:

forming an acidic and corrosive environment.

equipment.

and water: the solvent.

alcohols, etc. Water is dissociate into ions: H2O → H+ + OH-

of microorganism, enzyme action, oxidation and dehydration. The economic and social relevance of the FI is evident by the diverse international and national professional associations, R & D institutions, regulation and standards agencies and potent multinational industrial enterprises involved in all aspects of food science, engineering and technology (S.O. Jekayinfa et al, 2005). It includes authorities from government, industry and academia that address progress crucial for national and global prosperity. Lately, the threats of bioterrorism by poisoning food have pushed the FI to the front of efforts by safety and security organizations to prevent these hazards events.

Among others, aluminium, tin, cooper, titanium and mainly stainless steel (SS) are widely used in FI for the manufacture of processing, production, storage and transportation equipment and machinery. Modern science and technology have developed an extended range of materials with increased corrosion resistance, improved mechanical strength, easier forming and fabrication, weldability and health friendly features. The workhorses of food processing industry are UNS S30400 and S31600, but other austenitic and duplex SS are in useful service in food plants.

Food consists mainly of proteins, carbohydrates and fats. Processed foods contain diverse aqueous solutions, syrups and additives, used to improve food appearance, quality and preservation. They have a wide pH range and salt, water and vinegar content, that impact on food corrosivity.

Many cleaning and sanitation agents are employed to remove bacteria, scale, fouling and corrosive biological and mineral deposits. They include alkaline, acidic, strong or weak oxidizing and reducing chemicals to ensure a high hygiene level. This great variety of corrosive environments and aggressive chemical agents require the use of Corrosion Resistant Alloys (CRAs). SS are the obvious choice of the FI to prevent equipment damage and food contamination.
