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Module 8. Cleaning and sanitization

Lesson 39
DETERGENTS AND SANITIZERS

39.1 Introduction

Detergents and sanitizers are used in the cleaning and maintenance of safety levels in a dairy plant. It is important to monitor the strength of these solutions that are used in the dairy so as to ensure the efficacy of the cleaning programme.

39.2 Determination of Strength of Washing Solution (Alkalinity Test)

The strength of washing solution is generally expressed in terms of NaOH as it is often used as such or in combination with other chemicals. Repeated usage of washing solutions in automatic machines generally gets diluted. It is important to maintain the proper alkalinity of detergent solution for efficient cleaning and germicidal effects. An alkali equivalent to 1.5% NaOH is generally used for glass bottles and 0.5% for can washing.

39.2.1 Qualitative test

To 10 ml of detergent solution in conical flask, add 12.5 ml of 0.1 N hydrochloric acid and 5 drops of 0.5% phenolphthalein indicator. If the mixture turns red, it indicates alkalinity greater than 0.5% as caustic soda, which is sufficient.

39.2.2 Quantitative test

39.2.2.1 Direct reading method

This is a quick method that can be used daily. Take 10 ml of detergent solution in a 100 ml conical flask and add 5 drops of phenolphthalein indicator. Titrate with 2.5 N sulphuric acid until solution becomes colourless. The quantity in ml of acid used for titration is a direct indicator of percent alkali as NaOH.

39.2.2.2 Laboratory method

Take 5 ml of washing solution in 250 ml volumetric flask and makeup the volume with distilled water. After mixing well, transfer 50 ml of this solution in a 100 ml conical flask, add few drops of phenolphthalein indicator and titrate against 0.1 N sulphuric acid to colourless solution. Record ml of acid used as X. Add few drops of methyl orange indicator and continue titration till appearance of slight pink colour. Note ml of acid used as Y.

% free caustic = (X-Y)*0.4
% total alkali = (X+Y)*0.4

39.3 Determination of Strength of Sanitizer

The strength of sodium hypochlorite, which is widely used as a sanitizer in the dairy industry, is expressed in terms of the available chlorine in it. The strength of stock solution of chlorine is about 35% in terms of available chlorine. As the strength of chlorine solution decreases on storage, it is necessary to check its strength regularly. The method to determine available chlorine in solution is based on reaction between available chlorine from hypochlorite solution and acidified potassium iodide solution, as a result of which iodine is librated. Available chlorine which is librated by the addition of acid liberates an equivalent amount of iodine from potassium iodide which produces yellowish brown colour upon titration with sodium thiosulphate solution using starch as indicator.

Stock solution of sanitizer: Weigh 10 g of bleaching powder, convert into paste with small quantity of water and transfer the contents quantitatively to 250 ml volumetric flask using distilled water. Make up the volume and mix well.

Take 10 ml of stock sanitizer solution in a 250 ml volumetric flask and makeup the volume with distilled water. To 25 ml of diluted solution in a 250 ml conical flask, add 2 g potassium iodide crystal followed by 10 ml glacial acetic acid. Titrate the contents with 0.1 N sodium thiosulphate until brown colour changes to light straw yellow (Reading X). Add 1 ml of 1% starch solution and continue titration till colour disappears (Reading Y). Record volume of thiosulphate used as V ml (X+Y). Make a blank determination using same reagents and deduct the titre value from V.