**2. General corrosion considerations**

FI is a complex network conformed by primary producers and the industries linked to them. The plants involved in the processes of products and packaging must preserve the capital invested and minimize operation costs. The physicochemical characteristics of processed foods permit them to achieve different corrosivity grades depending on the type of content (Valdez et. al., 2004, Jellesen**,** et. al., 2006).

Three types of foods are recognized according to their corrosivity:


Acetic acid, used as an acidifying agent for the production of pickles and canned vegetables is mildly corrosive to SS. Three types of cleaning and sanitation agents are applied in the FI:

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

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

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

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

FI is a complex network conformed by primary producers and the industries linked to them. The plants involved in the processes of products and packaging must preserve the capital invested and minimize operation costs. The physicochemical characteristics of processed foods permit them to achieve different corrosivity grades depending on the type of content

Mild corrosivity, foods with pH 6 – 7 and less than 1% of salt: dairy products, fruit

 High corrosivity, foods with pH 3 – 5, such as citric fruit juices, jams and acidic canned fruits or hot gravies, sauces and dressings, vegetables and fish pickled in brines with 1 –

 Many cleaning, disinfection 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. Acetic acid, used as an acidifying agent for the production of pickles and canned vegetables is mildly corrosive to SS. Three types of cleaning and sanitation agents are

security organizations to prevent these hazards events.

useful service in food plants.

on food corrosivity.

and food contamination.

3 % salt.

applied in the FI:

**2. General corrosion considerations** 

(Valdez et. al., 2004, Jellesen**,** et. al., 2006).

Non corrosive: milk, meat, fish, oil, fat, cereals

Three types of foods are recognized according to their corrosivity:

syrups, wine, carbonated sweet drinks, beer, soups, canned meat.


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 prevent equipment damage and food contamination.

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

**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, alcohols, etc. Water is dissociate into ions: H2O → H+ + OH forming the hydronium ion 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 equipment.

Acidic metallic salts undergo hydrolysis in water:

$$2\text{FeCl}\_3 + 3\text{H}\_2\text{O} \rightarrow 6\text{HCl} + \text{Fe}\_2\text{O}\_3\tag{1}$$

forming an acidic and corrosive environment.

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 and water: the solvent.

**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,

total U.S. manufacturing output. The total food sales including the supermarket and traditional food store, restaurant food and drinks, non-traditional food store and convenience stores sales were 1,638 billion US dollars in 2010 (Plunkett Research, 2010). Assuming that SS consumption and cost in the FI is entirely attributed to corrosion, total annual direct cost corrosion was \$ 2.1 billion, according to National Association of Corrosion Engineers report for corrosion costs in 1999. This cost includes SS usage for beverage production, food machinery, cutlery and utensils, commercial and restaurant equipment

361

Food can be an important source of disease-causing organisms, the investigations on risk management in food handling, diet and health (Buchanan et. al., 2001, and Oddy et. al., 1985), revealed an association between human diseases and food contaminated by flies. Food can contain beneficial bacteria, but contamination with harmful microorganisms from external reservoirs must be prevented not only by removal of food residues and disinfection but also by the modification of surfaces specially designed to avoid sites for the development of bacterial colonies, such as accumulated corrosion products or degraded protective coatings. These surfaces must not introduce toxic substances or influence flavour. Materials that fulfil these requirements are glass, earthenware, some plastics, and metals like SS and aluminium alloys. Glass is sensitive to shock and fragments are sharp, while inexpensive plastics are not heat resistant and, in thin gage, they are permeable to gases. Metals do not have these

The modern FI combines the application of the latest production processes, the use of cleanable corrosion resistant SS equipment and computerized information with an efficient, environmentally sound approach to meet the needs of food products consumers everywhere. Cleanability is important in relation to taste, colour, odour and contamination of edible products such as milk, processed and canned foods and alcoholic beverages. This is of particular hygienic importance in food handling. Food processing involves operations by which raw foodstuff are suitable for human consumption, it includes the basic preparation of food, preservation and packaging techniques. Many innovations have resulted in new

Sterilization is one of the most important aspects of hygiene and sodium hypochlorite is a disinfectant widely used to kill microorganisms through an oxidizing reaction that yields

 NaClO NaCl + O\* (2) Where O\* represents oxygen species capable to kill biological material by oxidation. Both sodium chloride and sodium hypochlorite can be easily removed from surfaces used in the FI by rinsing with water, but it is not permissible to leave any residue because residual chlorides and hypochlorites can be concentrated by evaporation and induce localized pitting

Microorganisms are primitive unicellular organisms capable to live in colonies at aqueous media. They are diverse and for the interest of this chapter it is appropriate to mention;

disadvantages, but they must be corrosion resistance in food environments.

products such as concentrated fruit juice, freeze-dried coffee and instant food.

**4. Microbiological induced corrosion in the food industry** 

and appliances.

**3. Public health and hygiene** 

sodium chloride as final product.

corrosion

salad, salutary, salud (Spanish for health) . The Bible describes hospitable reception of visitors and travellers offering water, salt and bread (M. Schorr et al., 2011).

**Acids.**- Acids in water solution impart a sharp sour taste to food but also a corrosive action on steel. Therefore steel for food containers should be protected with corrosion-resistant material or fabricate from stainless steels or plastic materials. The word acid derives from ancient European language meaning sour. Acids and bases play a large part in industrial chemistry and particularly in chemical cleaning in food processing equipment. Water, the "universal" solvent, dissolves acids and bases. The acidity of foodstuffs is determined by measuring their pH. The majority of the vegetables and fruits consumed by human beings are acidic, with a pH between 5 and 2; in particular citrus fruits displaying pH values between 2 and 4. Two acids: acetic acid (vinegar CH3-COOH) and phosphoric acid (H3PO4) are widely applied in the FI, the first for the conservation of vegetables and the second for acidifying beverages, drinks and juices.

**Sugar.**- Sugar is a sweet substance obtained from the juices of various plants, chiefly the sugarcane and the sugar beet but also from date palm and the maple tree. It is an article for human nutrition and a sweetener for other foods, especially beverages, confectionaries and canned fruits. It is a carbohydrate, called sucrose and the prime source of energy in the human diet, needed to maintain body temperature and activity. Most of the sugar is consumed in the form of white, granulated sugar, produced in refineries processing sugar cane or beets. Liquid concentrated sugar syrup is used for sweet food manufacture purposes, such as confectionary and candies. Sugar dissolves easily in water forming a molecular solution without electrical conductivity and therefore slightly corrosive since there is some amount of dissolved oxygen.

**Environments in FI**.- The pH values associated with foods ranges from 3 to 8 that corresponds to a mildly acidic water and has an acceptable corrosive behaviour for aluminium, stainless steel and tin. Table 1 shows the pH ranges for different foodstuffs branch in the FI. Nevertheless, the aggressive ions hypochlorite and chloride could be concentrated by evaporation of the cleaning solutions on specific localized areas of the metal surface, inducing pitting corrosion. The combination of both anions chloride and hypochlorite can lead to a more positive redox potential (E0 = +0.9 V vs Satured Hydrogen Electrode (SHE)) and to synergize the pitting corrosion process of stainless steel.


Table 1. Ranges of pH values for different foodstuffs

The cost of corrosion.- The food processing industry is one of the largest manufacturing industry in the United States of America, accounting for approximately 14 percent of the

salad, salutary, salud (Spanish for health) . The Bible describes hospitable reception of

**Acids.**- Acids in water solution impart a sharp sour taste to food but also a corrosive action on steel. Therefore steel for food containers should be protected with corrosion-resistant material or fabricate from stainless steels or plastic materials. The word acid derives from ancient European language meaning sour. Acids and bases play a large part in industrial chemistry and particularly in chemical cleaning in food processing equipment. Water, the "universal" solvent, dissolves acids and bases. The acidity of foodstuffs is determined by measuring their pH. The majority of the vegetables and fruits consumed by human beings are acidic, with a pH between 5 and 2; in particular citrus fruits displaying pH values between 2 and 4. Two acids: acetic acid (vinegar CH3-COOH) and phosphoric acid (H3PO4) are widely applied in the FI, the first for the conservation of vegetables and the second for

**Sugar.**- Sugar is a sweet substance obtained from the juices of various plants, chiefly the sugarcane and the sugar beet but also from date palm and the maple tree. It is an article for human nutrition and a sweetener for other foods, especially beverages, confectionaries and canned fruits. It is a carbohydrate, called sucrose and the prime source of energy in the human diet, needed to maintain body temperature and activity. Most of the sugar is consumed in the form of white, granulated sugar, produced in refineries processing sugar cane or beets. Liquid concentrated sugar syrup is used for sweet food manufacture purposes, such as confectionary and candies. Sugar dissolves easily in water forming a molecular solution without electrical conductivity and therefore slightly corrosive since

**Environments in FI**.- The pH values associated with foods ranges from 3 to 8 that corresponds to a mildly acidic water and has an acceptable corrosive behaviour for aluminium, stainless steel and tin. Table 1 shows the pH ranges for different foodstuffs branch in the FI. Nevertheless, the aggressive ions hypochlorite and chloride could be concentrated by evaporation of the cleaning solutions on specific localized areas of the metal surface, inducing pitting corrosion. The combination of both anions chloride and hypochlorite can lead to a more positive redox potential (E0 = +0.9 V vs Satured Hydrogen

Electrode (SHE)) and to synergize the pitting corrosion process of stainless steel.

Foodstuff pH range Vegetables 3.0 to 6.0 Fruits 2.0 to 5.0 Bakery 5.0 to 6.5 Meat 6.0 to 7.0 Fish 5.5 to 6.0 Dairy 5.0 to 6.5 Beverages 2.0 to 5.5

The cost of corrosion.- The food processing industry is one of the largest manufacturing industry in the United States of America, accounting for approximately 14 percent of the

visitors and travellers offering water, salt and bread (M. Schorr et al., 2011).

acidifying beverages, drinks and juices.

there is some amount of dissolved oxygen.

Table 1. Ranges of pH values for different foodstuffs

total U.S. manufacturing output. The total food sales including the supermarket and traditional food store, restaurant food and drinks, non-traditional food store and convenience stores sales were 1,638 billion US dollars in 2010 (Plunkett Research, 2010). Assuming that SS consumption and cost in the FI is entirely attributed to corrosion, total annual direct cost corrosion was \$ 2.1 billion, according to National Association of Corrosion Engineers report for corrosion costs in 1999. This cost includes SS usage for beverage production, food machinery, cutlery and utensils, commercial and restaurant equipment and appliances.
