Sunday, May 15, 2011

A Comparative Study of the Romanian Milk Brands

About a month ago, I participated in a national chemistry contest, ChimeXpert for which I had to make a scientific poster based on my personal observations regarding a certain area of applied chemistry. As a consequence, I tried to find a subject close to my chemical study at school at that given moment, proteins, which is why I have chosen milk as a subject of study.

Purpose

The poster aimed to create an accurate comparative analysis of different Romanian milk brands' quality. The analysis was bound to answer to the need of information amongst the ordinary buyers. The analytical methods consisted in checking the compliance to quality standards of each dairy product selected.

Milk Facts

Milk is a complex liquid used as a food source by young mammals. Chemically speaking, the exact composition of milk varies from species to species, but it generally consists of water, fat, proteins and minerals.

Proteins

Cow milk contains numerous types of proteins (~3.4%), classically divided into two groups:

Globular Proteins: albumins, lyzozime, lactoferin, all playing vital roles in providing immunity for the newly born.
Heteroproteins - Caseins (proteins containing phosphorylated groups)
Caseins are proteins which are made of up to almost 200 amino-acid residues. H2PO3- groups are attached to the serine residues, thus enhancing the reactivity of caseins towards calcium salts.

Caseins from milk come in many different sorts (αS1 - casein, αS2 - casein, k - casein, β - casein or λ - casein), all of which present coagulation properties at a pH = 4.6, except k - casein (due to a small number of phosphorylated serine residues in k - casein).

Fats

Raw milk has about 3.5% fats of which butyric acid is the most predominant fatty acid. It has been proved that butyric acid has anticarcinogenic properties, mechanism yet to be understood. Apart from butyric acid, milk also contains linoleic acids, octadecanoic acids and others as well.

Analytical Methods

For doing the study, I used six different brands: Milli, Zuzu, Rarăul, Covalact, Brenac and Tnuva. Two analytical methods have been used. The first one, is a quick but quite unaccurate method for analysing dairy products. It uses a device called LactoScan, based on the interpreting of ultrasonic resonance patterns of the milk being scanned.


Image: Lactoscan.com

The following charasteristics were measured: acidity, fat content, total dry substance (TDS), ash content (SOL), lactose content, proteic content, freezing point (crioscopic point) and density of the samples.

 The coulours indicate the quality of the product:
bad, unsatisfactory, medium, satifactory, optimum

It can be easily noticed that the 6 brands generally comply to the ISO 22000 standard, except Brenac, which has a potential value of 17% added water (so as to reduce acidity of old milk), which is illegal. Moreover, almost all values for Brenac are out of standards.

The second approach to this analysis was the classical method. Through this method, I determined the pH and the acidity (in Torner degrees), the calcium content, and the eventual counterfeiting with NaHCO3.

Acidity

Acid milk, generally old, is not proper for general consumption due to the excessive lactic acid formed by the Lactobacillus acidophilus in the milk.

CH3CH(OH)COOH + NaOH → CH3CH(OH)COO-Na+ + H2O
Therefore the pH of the samples was tested (3 weeks before the expiry date). Normal milk pH is around 6.5. The six samples had a pH varying between 6.17 and 6.58, both values of which are within standards.

Counterfeiting

Generally, milk forgery is done in order to trick the acidity tests. Although illegal, the producers sometimes add NaHCO3 or starch.

Testing for forgery with baking soda can be done by adding bromthymol blue. A normal milk would stay yellow-orange while a counterfeited one would turn green. All the samples have proven to be counterfeited with NaHCO3.

When testing for starch, after boiling for two minutes and adding vinegar (to enhance coagulation) and iodine (starch detectiong purpose), the counterfeited tubes should have turned blue (as in the M tube used for demonstration purpose only), all the test-tubes turning out not to have been counterfeited with starch.


Calcium ions detection

Calcium is determined through a rather complex method. First, we have to reduce milk to ashes by heating in an oven at 600oC for three hours.


The ashes are then incorporated into 50 ml solutions further brought to a pH af about 11.

Then EDTA (Ethylenediaminetetraacetic acid) is titrated into the milk ash solution in the presence of a few drops of murexide. The pink solution will turn purple.


The reaction involved in this mechanism is the following:


The calcium levels measured were at normal levels 800-1300 mg/L.

Conclusions

All the brands were more or less within standards, except Brenac, where severe disconcordances have been noticed. The best quality milk has turned out to be Covalact, respecting virtually all issues stipulated in standard with the exception of baking soda counterfeiting.

Outcome

At the contest, I have won the best poster award and a special award from the Romanian Inventors Forum.

Finally, you can find the poster here, in the version presented by me at the contest.

1 comment:

  1. UPDATE: The subject of study was chosen by me at my chemistry teacher's advice, occasion with with which I would like to thank Miss Lidia Mînză, who gave me this great idea.

    Nonetheless, I would also like to thank my classmate and good friend, Daniel Moisescu, who designed the visual format of the poster.

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