Cleaning Agents

The entire class of cleaning compounds may be divided into two groups: a) the alkaline cleaners and b) the acid cleaners in addition to wetting, sequestering agents and surfactants.

 

i. Alkaline Cleaners

This group comprises of the basic alkalis, polyphosphates and the wetting agents.As none of these groups alone can fulfill all the functions of a cleaning agent,blends of their mixtures are generally used.

Basic Alkalis : Basic alkalis, such as soda ash, caustic soda, tri-sodium phosphate and sodium metasilicate are the ingredients in most of the common dairy cleaners.Two or more of them are used in combination as a rule to give the needed properties to the blended product. In addition to providing alkalinity for the cleaning process, they have other properties that affect the cleaning process in various ways. Some of these are detailed below.

a) Caustic soda (Sodium hydroxide, NaOH)

•  High germicidal action
•  Dissolves milk proteins
•  Lacks deflocculating & emulsifying power
•  Most corrosive on hands & metals

b) Soda ash (Sodium carbonate, Na2CO3)

•  Most inexpensive
• Good buffering capacity. The good buffering capacity of soda ash makes it useful in solutions that are used over extended periods, as in hand bottle washing.
•  Poor water softener
•  Only fair deflocculating & emulsifying action
•  Not suitable for hard water. When soda ash is used in hard water, calcium carbonate is precipitated and this pre-cipitate causes hard water spotting and helps develop milk stone deposits on dairy equipment. This may be prevented by using along with soda ash, higher phosphates in quantities large enough to sequester or tie up the water hardness.

c) Trisodium phosphate (Na3PO4)

•  High solubility, deflocculating & emulsifying powers
•  Fairly expensive
•  Fair water softening capacity owing to the flocculent character and insolubility of the calcium and magnesium phosphates formed.
•  Relatively corrosive on tin. Corrosive action can be reduced by adding meta-silicate as a protective agent in the mixture.
•  Limited levels permitted. Concentrations are limited to 0.5 – 1.5% today to minimize phosphate levels in wastewater.

d) Sodium metasilicate (Na2SiO3. 5H2O)

•  High active alkalinity
•  Excellent deflocculating & emulsifying properties
•  Relatively non-corrosive despite strong alkalinity, protects metals from other corroding alkalis
•  Good suspending abilities. Very effective in holding the soil in suspension during the washing operation so that complete cleaning is possible.
• Only a fair water softener. Fair water softening capacity because the calcium and magnesium silicates formed in hard water are floccu-lent and insoluble in solutions.

e) Modified sodas

• These are mixtures of soda ash and sodium bicarbonate. They are useful for manual washing operations, as they do not cause skin irritation.

ii. Acid Cleaners

Acid cleaners are used in dairy plants mostly to remove milk stones. They are also vastly employed in the cleaning of high-temperature processing machines. Equipment such as plate heat exchangers (pasteurizers), tubular heaters etc. are normally cleaned in two phases, the first phase with alkali and in the second phase, with acids. Acid type cleaners are also used in can washing.The acids used in the dairy industry are blends of organic acids, inorganic acids,or acid salts usually with the addition of a suitable wetting agent. To be effective,an acid type detergent at the point of use should be at a pH of 2.5 or below. To be effective, it should work well in hard as well as soft water and should show a minimum of corrosion on dairy metals. The characteristics of acids normally used are listed below.

(i) Inorganic (mineral): muriatic acid, sulfuric acid, nitric acid, phosphoric acid)

•  Corrosive, dangerous to metals
•  High concentrations dangerous to handle
•  Injurious to clothing
•  Irritating to skin
•  Low pH due to high degree of ionization
•  Strong
•  Under certain conditions some inorganic acids will precipitate insoluble salts

(a) Nitric acid (HNO3): This inorganic acid is very good for removing milk stones and hard water scale. Although it attacks tin readily, it is suitable for aluminium and stainless steel (SS). Nitric acid is hazardous on the skin. It is widely used at strengths of 60% in automatic cleaning of plants (CIP – Cleaning-in-Place).

(b) Phosphoric acid (H3PO4): This is a mildly strong acid that replaces nitric acid in many dairy cleaning operations.

(ii) Organic (generally vegetable acids): acetic acid, lactic acid, hydroxyacetic acid, citric acid, levulinic acid, tartaric acid)

• Acid reaction tends to prevent and remove deposits of calcium and magnesium salts derived from either milk or water
•  Can be combined with wetting agents, hence penetration
•  Mild, stable, less corrosive
•  Safe, gentle, harmless to hands in use-dilutions

  iii. Wetting Agents

Water and most other aqueous solutions wet metal surfaces with difficulty unless these surfaces are free from fats and oils. Wetting or surface acting agents thus help to improve the wetting of surfaces. They also aid in penetration of the solution into capillary pores and minute spaces between the equipment surface and soil particles. The three groups of surfactant solutions are anionic (e.g. sulphosoaps,sulphated alcohols, alkyl aryl sulphonates), non-ionic (e.g. condensation products between ethylene oxide and an alkyl phenol) and cationic (e.g. quaternary ammonium compounds - QACs). Even at concentrations as low as 0.15% they reduce the surface tension of water to half. Increasing the concentration does not affect the degree of lowering of surface tension, and therefore, the amounts used in cleaners are usually small.

 

iv. Sequestering Agents

Sequestering and chelating agents prevent precipitation of salts formed due to hardness of water. There are three main classes of such agents.

a) Ethylene diamine tetra-acetic acid (EDTA) or its sodium salts

•  Heat stable
•  Compatible with Quarternary Ammonium Compounds (QACs)
•  Bacteriostatic property
•  Prevents redeposition

b) Sodium salts of gluconic and heptonic acids

•  Stronger than EDTA in chelating action of Ca and Mg
•  Requires high concentration of NaOH (~ 2.5%) for effectiveness

c) Polyphosphates (sodium tripolyphosphate, sodium pyrophosphate)

• Not heat stable
•  Limited levels permitted. Environmental regulations limiting the levels of phosphates in waste waters, many cleaning compounds have removed or reduced phosphates, using chelating agents to eliminate the effects of water hardness. Concentrations may be limited to 0.5 to 1.5%.

  v. Enzymes

Proteolytic enzymes are utilized, generally in combination with alkali and surfactants to increase the cleaning efficiency of equipment heavily soiled with protein.They have been especially useful in the cleaning of membrane processing plants.Lipases have been used also in a few cases to improve the removal of fat from surfaces.

 

vi. Chlorine

Chlorine increases the effectiveness of alkaline components tremendously (50-200/ml chlorine increases the peptizing efficiency). As removal of protein films lessens the development of mineral milk stone deposits, it also reduces the build--up of mineral deposits. Chlorinated trisodium phosphate, hypochlorides and chloro-isocuranic are the commonly utilized chlorine compounds. The chlorine compound has to be compatible with the alkaline reagent, or else, it will result in the development of white deposits upon the equipment. Chlorinated alkalis do not function as bactericidal agents because of their high pH. The high pH also minimizes the corrosive activity of the chlorine component.

 

vii. Inhibitors and Antifoaming Agents

Inhibitors such as sodium sulphite are used to minimize the effect of acids and alkalis on metals. Sodium sulphite protects tinned surfaces, whereas sodium silicates protect aluminium and its alloys from mild alkalis. Antifoaming agents reduce the  foam in detergent solutions. This, in turn, decreases the need for water.