Determination of lactic acid content in commercial milks: whole milk Alqueria and skim milk Colanta

  RESEARCH ARTICLE                        [pic 2][pic 1]

Determination of lactic acid content in commercial milks: whole milk Alqueria and skim milk Colanta

González Juan David[a], Puche María José[a], Rincón Iris Mariana[a] and Roa Juan Sebastian[a] 

[a]        González,J, Puche. M, Rincón i and Roa. J, Department of pharmacy, National University of Colombia, 45 Street, Bogotá, Colombia.

           E-mail: jgonzalezald@unal.edu.co

           E-mail: mpuche@unal.edu.co

           E-mail: irrinconr@unal.edu.co

           E-mail: jroag@unal.edu.co

Abstract: In order to obtain lactic acid of whole milk Alqueria and skim milk Colanta a titration was performed through the method of the indicator, which in this case was used phenolphthalein. As a consequence of the difficulty of seeing the subtle change to a faint colour pink, due to the colour and consistency of the milk it was necessary to have a control sample, an untreated sample of milk. Therefore, it was easier to identify the end-point of the titration. For the whole milk Alqueria, 10 mL aliquot was used. The average volume of NaOH used  was 2.05 mL, with this result through stoichiometry the percentage mass over volume of lactic acid was determined, the result obtained was 0.17%. On the other hand, for skim milk Colanta, 20 ml aliquot was used. The average volume obtained of NaOH used for the Colanta skim milk was 4.25 mL; the percentage of acid lactic was determined with equation (1).  Due to the difference in volume of the aliquots, skim milk colanta´s aliquot is double whole milk Alqueria´s aliquot, it is expected that the result of the spent volume of hydroxide in the skim colanta milk will be double that of the whole milk Alqueria.

Introduction

Milk acidity is a fundamental parameter in the production of a safe milk product. The titratable acidity contains both natural and developed acidity. Natural acidity is a consequence of casein, mineral substances, organic acids, dissolved carbon dioxide and secondary reaction products derived from phosphate. On the other hand, the developed acidity is due to lactic acid. Lactic acid belongs to the group of hydroxy acids, noting that its structure contains a carboxyl and a hydroxyl group.[1][pic 3]

Scheme 2. structural form of lactic acid [2]

Lactic acid titration is an extremely important procedure in the food industry, particularly in the dairy sector. Lactic acid, an organic compound naturally present in various dairy products, plays a crucial role in the taste, texture, and overall quality of these products[3]. Moreover, lactic acid also influences the shelf life and microbial stability of dairy items, making its quantification vital for ensuring product safety and maintaining high standards of quality.

In this study, we aim to investigate and develop effective analytical methods for the titration of lactic acid in skim milk and whole milk. Skim milk, obtained by removing the cream from whole milk, is a commonly consumed dairy product known for its lower fat content. Whole milk is a type of milk that has not undergone a process of reduction in the original fat content[4].By focusing on the analysis of lactic acid in skim and whole milk, we can gain valuable insights into the composition and properties of this specific dairy product.

To achieve our objectives, the acid-base titration technique will be used using colorimetric indicators, using phenolphthalein as the indicator. Since the pH of whole and skim milk must be in the range 6.50-6.85 [5], it is not possible to use the potentiometric titration method. Therefore, adding a base, NaOH, will only increase the pH and no abrupt change will be evident. Acid-base titration method has been widely employed in the titration of acids and bases, and its suitability for determining lactic acid content in skim milk makes it an ideal choice for our research. Due to the chemical structure of lactic acid, exposed in scheme 1,  it is classified as a monoprotic acid. Therefore, in aqueous solution it will only donate one proton per molecule, therefore only one equilibrium point is expected to be obtained during the titration.[6a]

Scheme 2 illustrates the chemical reaction during the titration process, resulting in the formation of salt and water, a neutralization reaction. By comprehensively studying this chemical reaction and its characteristics, we can establish a solid foundation for the accurate determination of lactic acid content in skim milk and facilitate further advancements in the field of dairy analysis.

[pic 4]

Scheme 2. Equation of chemical changes in milk titration with sodium hydroxide[7]

By comparing the lactic acid content in these two types of milk, we can explore any potential variations and gain a deeper understanding of how processing and fat content may affect the lactic acid composition in dairy products. It is expected that the results obtained in this study are within the regulations governing dairy products in Colombia. Decree 616 of 2006 establishes that the %w/v of lactic acid in whole and semi-skimmed milk should be within the range of 0.13%-0.17%[8]

In addition a low percentage of lactic acid could imply cows with mastitis or a watery process in the milk. Whereas milks with high percentages of lactic acid have lost thermal equilibrium, consequently these milks could not be pasteurised and sterilised, since they would coagulate [9].

Apart from the importance of the milk in the food industry, the titration of lactic acid is also important due to its relevance in human health. Lactic acid, moreover of being an essential component in the lactic fermentation and dairy products, has a crucial role in the physiology of exercise and the human metabolism.

...