Quality control of the ketchup. Acidity and pH

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Greetings dear friends of Hive.

The tomato-based sauce known as ketchup is one of the most consumed dressings, it is the perfect companion to the mayonnaise we prepare hamburgers and other fast food, and who does not enjoy its rich flavor bathing some delicious fries.

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Evaluation of acidity in ketchup. Source: image designed by @yusvelasquez, the background image is public domain.

This popular sauce is obtained by the concentration of the juice and pulp of fresh, healthy and ripe red tomatoes, with the addition of salt, spices and edible vinegar[1]. And for this sauce, many technical standards specify that it must not contain colorants, thickeners or artificial preservatives, which makes evident the need to establish quality controls that guarantee the production of optimal products for human consumption, and the analysis of the physicochemical properties of this type of food is the main way to ensure its quality.

And among the controls established for this type of sauce, acidity and pH are of special importance, as they are the main regulatory parameters of organoleptic properties such as taste and smell, as well as setting the conditions for the stability and control of microorganisms in the product. That is why in this post I want to address how the determination of pH and acidity is performed in this type of sauce.

Let's talk about the sauce

Very different from what we may think, the origin of this sauce goes back to the middle of the first century A.D. and has as its ancestor a hot sauce that became popular among fishermen in southern China used to accompany meat and fish, in their dialect they named it "kôe-chiap", kôe means fish and Chiap brine; and it is pronounced ketsiap[2], the particular thing is that this sauce did not contain tomatoes.

The modern ketchup we know was devised by the American Henry J. Heinz, who in 1876 incorporated the tomato into the sauce recipe. Initially prepared with fresh tomatoes, they were later substituted by tomatoes preserved in vinegar to improve preservation[1], so acidity is a determining factor in the product.

Heinz.jpg
Today we associate this brand with the image of ketchup. Source: @yusvelasquez..

The red color of the sauce responds to a pigment called lycopene, which according to some studies has antioxidant characteristics. It differs from other tomato sauces in that it does not use fried tomatoes, so its fat content is practically zero, but it contains more salt and sugar, it also has a higher caloric content due to its carbohydrate content[3].

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Nutritional information about the sauce. Source: @yusvelasquez.

Principles of the analysis

The acidity in foods is due to the content of free acids, and can be determined by a simple titration with a basic agent, such as sodium hydroxide, reporting the result as the % of predominant acid in the sample.

The acidity of tomato juice should be between 1 and 2%[3], and controlling this value is very important, much higher will bring problems for the sterility of the product, being necessary to acidify the sauce.

The pH value can be measured by means of a potentiometer or pH-meter, an instrument that measures the potential difference between two electrodes, and is a determining factor in controlling bacterial growth. For example, a decrease in pH may be due to an increase in the lactic acid content resulting from bacterial activity.

Methods

pH evaluation

The pH is determined by taking different samples of tomato sauce, taking aliquots of diluted product and measured using a previously calibrated potentiometer.

Procedure:

  • Weigh 5 g of the tomato sauce sample.
  • 10 mL of distilled water is added.
  • Introduce the electrode in the solution and make a measurement.
  • Shake the sample after taking the reading and make another measurement; repeat this step until you get two readings that match.

Imagen2.jpg
Measurement of pH in the sample. Source: @yusvelasquez.

Acidity evaluation

Acidity is determined by volumetry from diluted samples, using a NaOH solution, taking into consideration that it is a strongly colored solution.

Procedure:

Preparation of the sample

  • A solution is prepared by weighing 150 g of the sample and transferred to a 1000 mL volumetric balloon. Distilled water is added and heated to 70 °C in a water bath.
  • It is allowed to cool, then it is completed with distilled water up to the gauging and it is mixed by agitation.

Acidity determination

  • 25 mL are taken from the prepared sample.
  • The measured sample is transferred to a 250 mL Erlenmeyer and diluted to a volume of 100 mL with previously boiled distilled water.
  • A pH meter is introduced and titrated with the 0.1 N sodium hydroxide solution to a pH of 8.3.
  • Write down the volume of NaOH used.

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Titration of the sample. Source: @yusvelasquez.

Results

The titratable acidity of this product is expressed in grams or % of the predominant acid, depending on the expression:

ecuac.png

Where,
Ac: titratable acidity in g/100g
V1: spent volume of NaOH in the titration, in mL
N: Normalization of NaOH solution
me: acid miliquivalents.

Physicochemical characteristics

The following table shows some average values measured in three tomato sauces available in the market.

Table n°1. Average acidity and pH of ketchup

ParameterSample 1Sample 2Sample 3Standard Value
pH3,883,673,724
Acetic acidity (%)1,621,681,682

Conclusion and contribution

As mentioned above, acidity and pH are very important quality control parameters in the food sector, since they represent a measure of the stability and degree of conservation of products; and since, according to the respective standard, ketchup cannot contain added artificial preservatives, this control parameter is very important for preserving the product during storage.

The set of techniques shown are very important for the knowledge of analytical chemistry students, since they constitute the basic tools of any chemical analysis laboratory. Therefore, the article serves as a guide for their study and to associate the principles with a practical application.


Well friends, until here the present post, I hope that the information presented will be very useful to you, until a next post!


References

  1. Wikipedia.com. Ketchup.
  2. Ramírez-Rosas, J. y col. Evaluación Fisicoquímica de la calidad en salsas de tomate (Cátsup). Electronic article..
  3. Martínez, I., Blanco, R. Determinación y comparación de parámetros físico-químicos de salsas de tomate obtenidas en centros de abastecimiento de la ciudad de León. Universidad Nacional Autónoma de Nicaragua-León. Document online


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