CHEMICAL QUALITY ASSURANCE

Module 5. Water, detergents and sanitizers for dairy plant operations

Lesson 18
DETERGENTS AND SANITIZERS

18.1 Introduction

Milk is a good source of many nutrients like proteins, salts, lactose and vitamins, which are responsible for the fast growth of micro-organisms and scaling of heat exchangers etc. In dairy operations main processing treatment given to milk is heating which causes the scaling on the surfaces of heat exchangers and tubings. Milk traces, if left in the pipes and valves lead to the deterioration in the quality of milk. Therefore, the cleaning and sanitation of the dairy equipment is of utmost importance to meet the sanitary and phyto-sanitary requirements of the industry. The efficiency of cleaning and sanitization is directly related to the strength of the detergents and sanitizers used in the cleaning and sanitization purpose.

18.2 Detergents

A detergent is a substance which is (i) used to enhance the cleansing action of water

(ii) an emulsifier, which penetrates and breaks up the oil film that binds dirt particles,

(iii) capable of wetting surface(s) to allow it to penetrate the soil deposits and break

the soil into fine particles (deflocculation) and to hold them in suspension so that they do not redeposit on the cleaned surface(emulsification) (iv) must have good sequestering power to keep calcium and magnesium salts in solution.

There are two types of cleaning detergents: alkaline or acid that are often formulated with surfactants, chelating agents, and emulsifiers to enhance the effectiveness of the detergents. The most effective detergents in the dairy today are formulated with alkaline solutions that have chelators and surfactants. a wetting agent, which helps them to float off.

18.2.1 Alkaline detergents

The alkaline detergents are generally comprised of basic alkali, polyphosphates and wetting agents. None of the basic alkalis, higher phosphates or wetting agents can meet all the requirements of a good cleaner when used alone.

Basic Alkalis: The basic alkalis, such as soda ash, caustic soda, trisodium phosphate and sodium metasilicate form the bulk of most of the common dairy cleaners. Two or more of them are used in combination to overcome the weaknesses of a single compound and to give certain desirable properties to the blended product. For instance, Caustic soda is high in germicidal action and dissolving action on milk proteins, but it lacks deflocculating and emulsifying power as compared with other alkalis. In addition, caustic soda is objectionable in jobs requiring cleaning by hand because of hand burning as it is the most corrosive alkali.

Soda ash, is the most common constituent of dairy detergents today, and is the most inexpensive form of alkali. It is a poor water softener and has only fair deflocculating and emulsifying action. It has the advantage of being a good buffer. This makes it useful in solutions that are used over extended periods, as in hand bottle washing. When soda ash is used in hard water, calcium carbonate is precipitated and this precipitate causes hard water spotting and helps develop milk-stone deposits on dairy equipment. This may be prevented in products containing soda ash by the addition of the higher phosphates in quantities large enough to sequester or tie up the water hardness. It is obvious that soda-ash cannot be used in large proportions in cleaners to be used in extremely hard water.

Trisodium phosphate, have become a very popular constituent in dairy cleaners because of its ready solubility and high deflocculating and emulsifying powers. It is a fair water softener because of the flocculent character and insolubility of the calcium and magnesium phosphates formed. When compared with metasilicate or soda ash, trisodium phosphate is also relatively corrosive on tin unless metasilicate is present as a protective agent in the mixture. Concentrations are sometimes limited to 0.5–1.5% to minimize phosphate levels in wastewater.

Sodium metasilicate, has high active alkalinity and excellent deflocculating and emulsifying properties. It, like trisodium phosphate, is only a fair water softener. The calcium and magnesium silicates formed in hard water are flocculent and insoluble in solutions. Although it is the strongest alkali next to caustic soda, it is relatively non-corrosive and has the property of protecting metals against corrosion by other alkalis. Metasilicate is very effective in holding the soil in suspension during the washing operation so that complete cleaning is possible.

18.2.2 Acid detergents

The use of acid detergents is commonly restricted to the removal of milkstone, water scale (calcium and magnesium carbonates). Acid detergents are more effective against bacteria than are alkaline detergents. The two most common types of acid detergents used are:-

18.2.2.1 Nitric acid

Nitric acid not only is used to remove milk-stone and other inorganic deposits, it also has biocidal properties when used either as a pure acid or in more stable, less hazardous mixtures with phosphoric acid. In addition, nitric acid attacks proteins. Nitric acid offers the added benefit of forming a protective layer of chromium oxide on the surface of food processing equipments made up of stainless steel which contains chromium, thus preventing the leaching of iron ions into the milk. Commercially available aqueous blends of 5-30% nitric acid and 15-40% phosphoric acid are commonly used for cleaning food and dairy equipment primarily to remove precipitated calcium and magnesium compounds (either deposited from the process stream or resulting from the use of hard water during production and cleaning). It should not be used in >1% concentration for stainless steel surfaces.

18.2.2.2 Phosphoric acid

Phosphoric acid is used widely as the basis of acid cleaning materials and finds greatest application in the removal of milk-stone and similar deposits on surfaces such as protein deposits. Its performance is greatly enhanced by adding an acid-stable surfactant, which promotes penetration of surface deposits and also assists in the process of rinsing at the end of the cleaning process. It often is used at a concentration between 2 and 3% w/v phosphoric acid for cleaning. Small quantities of complex organic acids are often added to enhance its effectiveness.

18.3 Sanitizers

According to United States Environmental Protection Agency (EPA) specifications, these are the compounds or type of antimicrobial that kills or irreversibly inactivates at least 99.9 percent of all bacteria, fungi, and viruses (called microbials, microbiologicals, microorganisms) present on a surface. Most sanitizers are based on toxic chemicals such as chlorine, iodine, phenol, or quaternary ammonium compounds, and which (unlike some antiseptics) may never be taken internally. Sanitizers used in the dairies should have the following properties- i) non toxic ii) quick acting iii) non corrosive to hands and equipments iv) can be quickly applied and v) inexpensive.

The most commonly used sanitizers are the compounds of chlorine and iodine.

18.3.1 Chlorine compounds

These compounds include liquid chlorine, hypochlorites, inorganic chloramines, and organic chloramines. Chlorine-based sanitizers form hypochlorous acid (HOCl, the most active form) in solution. Chlorine compounds are broad spectrum germicides which act on microbial membranes, inhibit cellular enzymes involved in glucose metabolism, have a lethal effect on DNA, and oxidize cellular protein. Chlorine has activity at low temperature, is relatively cheap, and leaves minimal residue or film on surfaces.

18.3.1.1 Disadvantages

Chlorine compound is corrosive to many metal surfaces (especially at higher temperatures). Health and safety concerns can occur due to skin irritation and mucous membrane damage in confined areas. At low pH (below 4.0), chlorine (Cl₂) may interact with residual food components containing sulfur and form deadly mustard gas {bis(2-chloroethyl) sulfide}.

18.3.2 Iodine compounds

This sanitizer exists in many forms and usually exists with a surfactant as a carrier. These mixtures are termed as iodophors. The most active agent is the dissociated free iodine (also less stable). This form is most prevalent at low pH. Iodophors, like chlorine compounds, have a broad spectrum effect. These compounds are active against bacteria, viruses, yeasts, molds, fungi, and protozoans. These compounds are more specific against non- spore forming bacteria.

18.3.2.1 Disadvantage

Iodine is highly temperature-dependent and vaporizes at 120°F. Thus, it is limited to lower temperature applications.

18.3.3 Quaternary ammonium compounds (QACs)

Quaternary ammonium compounds (QACs) are a class of compounds which have the general structure as follows .

Fig. 18.1 General structure of quaternary ammonium compounds

These compounds are generally positively charged cations, hence their mode of action is related to their attraction to negatively charged materials such as bacterial proteins. QACs are active and stable over a broad temperature range. Because they are surfactants, they possess some detergency. Thus, they are less affected by light soil than are other sanitizers.

18.3.3.1 Peroxyacetic acid (PAA)

This compound is known for its germicidal action, which remains for a long period. Peroxy acetic acid is relatively stable when used with a strength of 100 to 200ppm. This compound is free from phosphates and do not form foam when used. Another advantage of this compound is that it has low corrosiveness, tolerance to hard water, and favorable biodegradability. Peroxy acetic acid solutions are found to be useful in removing biofilms.

18.4 Determination of Sodium Hydroxide in Lye

Take 10 ml of concentrated lye solution in 100 ml volumetric flask. Dilute to 100 ml with distilled water. Take 10 ml dilute lye solution in conical flask. Add a few drops of phenolphthalein indicator. Titrate against 2.5 N hydrochloric acid till pink color disappears.
% NaOH in concentrated lye solution = Burette reading x 10

18.5 Analysis of Detergents and Sanitizers

18.5.1 Determination of nitric acid

Take 10 ml of concentrated sample of nitric acid in 100 ml volumetric flask. Dilute it to 100 ml with distilled water. Take 10 ml of the dilute sample in conical flask. Add a few drops of phenolphthalein indicator. Titrate against 0.1N sodium hydroxide solution till permanent light pink color appears.

% nitric acid in concentrated solution = Burette reading x 6.3

Derivation:

(Acid) = (Base)
N₁V₁ = N₂V₂
N₁ X 10 = 0.1 X V₂
N₁ (Dilute acid) = (0.1 x V₂)/10
N₁ (Undiluted) = (0.1* V₂ * dilution factor)/10
Where dilution factor = 10
Therefore,
N₁ = (0.1* V₂ * 10)/10
Strength of undiluted acid = (0.1* V₂ * 10 * Eq. wt. of acid )/10
Where eq. wt. of acid = 63
Therefore,
Strength of undiluted acid = (0.1* V₂* 10 * 63 )/10
Strength of undiluted acid = V₂ x 6.3

18.5.2 Determination of available chlorine in sanitizer (Sodium Hypochlorite and Calcium Hypochlorite) solution

The method of determination of available chlorine is based upon the reaction between available chlorine from hypochlorite solution and acidified potassium iodide solution in which iodine is liberated. The liberated iodine is then titrated against 0.1 N Sodium thiosulfate using starch as indicator. From the volume of sodium thiosulfate used, the quantity of available chlorine can be found out based on standard equation:
One ml of 0.1N Sodium thiosulfate = 0.003546 gm available chlorine.

Reaction:

Take 5.0 ml of stock solution of sanitizer into a 250 ml volumetric flask. Make up the volume to the mark with distilled water and mix well. Pipette 50 ml of diluted solution in a 100 ml conical flask. Add 2 g of potassium iodide followed by 10 ml acetic acid. Titrate the solution against 0.1N sodium thiosulphate solution till the brown red color changes to straw yellow. At this stage add 1 ml of starch indicator and continue the titration till the blue color disappears. Note the titre value.

Available chlorine in sanitizer (ppm) = 3546 x burette reading.

18.5.3 Determination of available iodine in sanitizer solution

The method of determination of available iodine in iodophore is based on the reaction of liberated iodine with sodium thiosulfate, forming sodium iodide and sodium tetrathionate. The end point of the reaction is indicated by the disappearance of the blue color produced by the solution with the starch indicator.

Take 5 ml of concentrated iodophor solution into 500 ml volumetric flask. Dilute it to 500 ml with distilled water. Take 10 ml of the dilute solution into conical flask. Add 30 ml chloroform and shake well, so that the pink color appears. Titrate against 0.01N sodium thiosulphate solution till pink color disappears.
% available iodine in iodophor = Burette reading x 1.27
ppm of available iodine in iodophor = % available iodine x 104