Methods of Quality Control Testing

Microorganisms are cosmopolitan, and they are important to carry out fermentation during food production. As per the FSSAI 2006, every food product must be tested before approval and introduction in the market. The exponential increase in food production has also increased the chances of food due to microbes. Microorganisms such as moulds, fungi, yeast, and other bacteria can lead to food spoilage.

Sample Collection and Sampling is a tedious job to analyze the entire batch for quality by the food inspector or Quality analyst. Therefore random sampling is done, and a fraction of the product is analyzed and assumed that the entire batch of products has the same characteristics. Hence it is a crucial step, and the sampling should be completely random because this can lead to error and poor yield.


1. Total Viable Count (TVC)

Bakery products like bread, biscuits, and cakes are prone to microbial contamination because they are a rich source of sugars and nutrients which support microbial growth. It is a quantitative estimation of the concentration of microorganisms and bacteria present in a sample that is being tested. The total viable count represents the total number of colony-forming units per gram of the test sample. The bioburden test is usually performed along with TVC.


  • Add 1 g of the test sample in 10 ml of distilled water and label it as 10-1 dilution.
  • Invert and thoroughly mix the sample several times
  • Prepare serial dilution by transferring 1 ml of the sample from 10-1 to the next test tube with 10-3 dilution.
  • Set up a blank and mix all the test tube well
  • Repeat the dilution up to 7 test tubes using a sterile pipette.
  • Now plate the dilution using an L-shaped rod on a nutrient agar plate.
  • Incubate for 37 degrees for 24-48 hours
  • Examine microbial growth after incubation and check for contamination.

2. Most Probable Number (MPN)

 It is one of the best techniques that is used to determine the coliform bacteria indicating fecal contamination. Coliform bacteria are aerobic or facultative anaerobes. They are gram-negative, rod-shaped bacteria capable of fermenting lactose sugar followed by gas production.

Presumptive Test:

The test enables estimating the number of coliform bacteria present in the sample.


  •  Positive results:-After incubation for 24 hours, 10% or more gas production in the Durham’s tube.
  • Doubtful:-Production of gas after 48 hours of incubation.
  • Negative result:-No gas production even after 48 hours of incubation.

Determination of Composition

Determines the major constituent of the baked product. The method divides the nutrients present in food into total proteins, carbohydrates, fats, ash, moisture, etc.



The moisture content of a food product is the loss in a sample’s weight when it is subjected to heat in a hot air oven or any other condition.

Scope and objective: –

This method can be used for estimating the moisture content of the flour, semolina, and bread and wheat grain. The moisture content of the flour is influenced by environmental or storage conditions such as humidity and storage temperature. Such conditions affect the overall quality of the flour. High moisture content can lead to spoilage and the formation of lumps. On the other hand, lower moisture content causes loss to the baker in low dry matter. Many different methods are available to estimate the moisture, e.g., air oven method, direct distillation, chemical, and electrical methods. The electrical method could also be used satisfactorily, provided they are accurately calibrated.


  • Homogenize the test sample
  • Weigh approximately 5 g of sample in a clean Petri plate and place it in a hot air oven at 100 degrees temperature for 1 hour.
  • Cool in a desiccator and then measure its weight.
  •  The percentage of moisture can be calculated by subtracting the initial sample weight and final sample weight.



It is separated gluten content from other constituents; the wheat flour is mixed with water. The protein content of flour interacts to form a sticky substance of wet mass called wet gluten. The wet gluten is washed using potable water using an automatic gluten washer. Then this wet gluten is dried to form a light-coloured powder. Depending upon the quality, wide variation is seen in gluten content.

Scope and objectives:

The procedure applies to whole-wheat meal and refined flour. The dough was developed by mixing wheat flour with water. The viscoelastic nature of dough is attributed to gluten proteins, namely gliadins and glutenin. The gliadins impart extensibility to the dough, whereas glutenin is held responsible for gluten and dough’s strength and elastic character.


  1. The quantity of wet gluten is estimated using an automatic gluten washer.
  2. A 10g flour sample is used to make the dough using 5.2 ml of 2% sodium chloride solution, and the dough is introduced into the plastic chamber of the gluten washer.
  3. Washing is started, and after 10 min of washing cycle with 2% sodium chloride solution, the washing cycle completes.
  4. The wet gluten so obtained is weighed, and it is flattened between twin hot plates of the drier, where it is heated for 4 min.
  5. The dried, thin sheet of gluten is then weighed and recorded as dry gluten.
  6. The wet gluten can also be dried in the oven at 100°C for 24 hours to get dry gluten value.


 Principle: –

The protein content is measured using the Kjeldahl method. The method estimates the total nitrogen content in the test sample and assumes a constant relationship between total nitrogen and wheat’s protein content. The results are obtained by multiplying the total nitrogen content by 5.7 factor, and therefore, this method is used to determine the crude protein.’ Recently, many other methods have been developed to determine the sample’s total protein content by using the near-infrared reflectance (NIR) technique.

Estimation of wheat flour protein is difficult and tedious because there is no standard method available. Some methods such as sodium dodecyl sulfate sedimentation test, Pelshenke test, and Lowrys reagent test are used to determine wheat flour quality.


Principle: Wheat flour contains approximately 70-80% of starch. It is one of the major components of flour. Damaged starch is one, which has been physically damaged during the milling process. Starch damage also influences water absorption capacity and dough handling of flour. Damaged starch is readily susceptible to action by amylolytic enzymes compared to undamaged starch, resulting in dextrin formation. The desired level of damaged starch in bread flour should be 7-9%. Higher damaged starch is not advisable.

5. Determination of Crude Fat by Soxhlet Method

This method is used to estimate the total fat content of the sample. The process starts with weighing approximately 10 g of dry sample into a thimble. The thimble is then placed in a Soxhlet apparatus and ½ ml of Ether into a pre-weighed flat-bottom flask (W2) and distilled for 16 hours (Cool the apparatus and filter the solvent into a pre-weighed conical flask (W2). Rinse the flask with some ether. The Ether is removed by evaporation, .and the flask with fat is dried at 100°C, followed by cooling in a desiccator.

6. Determination of glucose content 

The glucose content of the samples is estimated by enzymatic oxidation using sa glucose oxidase reagent. 

  • Add 20 µl of the sample with 2.0 ml of oxidase reagent.
  • Mix it well and incubate the mixture for 10 minutes at 37°C. 
  • Take the absorbance of the sample and the standard against a reagent blank using spectrophotometric analysis.

Once the product sample undergoes all the chemical, biochemical, and microbiological testing to ensure its good quality, the sample that fulfills the quality standards then proceeds towards the packaging department to fill and packaging the product into the final container boxes.


Nielsen SS, editor. Food analysis. New York: Springer; 2010 Jun 25.

Van Der Spiegel M, Luning PA, De Boer WJ, Ziggers GW, Jongen WM. How to improve food quality management in the food sector. NJAS-Wageningen Journal of Life Sciences. 2005 Jan 1;53(2):131-50.

Van der Spiegel M, Luning PA, Ziggers GW, Jongen WM. Evaluation of performance measurement instruments on their use for food quality systems. Critical Reviews in Food Science and Nutrition. 2005 Feb 10;44(7-8):501-12.

Van der Spiegel M. Measuring effectiveness of food quality management. 2004.