Butter Fat Testing Using Gerber Method

Methods of Butterfat Testing & Indices Used to Score Fats

In the early days, it was not possible to determine the quantity of butterfat in milk. Unscrupulous farmers watered down their milk and scooped off cream to increase their volumes. They ended up with more money while honest farmers earned less since they did not adulterate their milk.

Compositional analysis of milk is a basic quality assurance procedure to ascertain the quality of the product. Milk fat is a crucial content of the product that determines the value of milk.

Several methods of analysis exist to determine the quantity and the quality of butterfat. Here we will discuss both starting with the quantitative analysis methods the later we will look at the indices of butterfat quality. The quantitative methods of determining butterfat content in milk include the following:

1. Gerber Butterfat Content Determination Method

Butter fat testing using Gerber method is one of the many quality assurance test procedures carried out in milk. It is a simpler modification of the Babcock method with special butyrometers for various dairy products.

Butter fat determination is necessary to determine the amount of butter fat present in milk and milk based products.

One can be able to conduct a butter fat test on fresh milk, fermented milk, cream, etc.

The Gerber method is the most widespread and direct method of butter fat content analysis in milk Click To Tweet

Advantages of butterfat testing using Gerber method

  • Simple/easy to use
  • Very fast
  • You read the results directly

Disadvantages of the Gerber method

  • Needs expertise
  • Required equipment are costly.

The principle of butter fat testing using Gerber method

The centrifugal force exerted in the mixture separates the lighter fat portion from the heavier non-fat portion of the milk. Sulfuric acid dissolves the protein that encapsulates the butterfat (fat globule membranes). Amyl alcohol provides a clear distinction between the fat and non-fat portions.

Before we go into the technical aspects of butterfat testing, let’s establish some facts about fatty acids since they are the basic units of fats.

Sources of fatty acids that constitute butterfat

The milk butterfat comes from three major sources/pathways, namely:

  1. Synthesized by the mammary gland from acetate and B-hydroxybutyrate that are produced by the rumen bacteria. These are majory composed of short chained fatty acids and some medium chained fatty acids. The chain length differs among species and is controlled by the specificity of the enzymes involved in the removal of fatty acids from the synthetase complex. This is the major source of fatty acids in butterfat synthesis.
  2. Fatty acids synthesized from glucose via glycolysis, citric acid cycle, and cleavage of citrate leading to formation of acetyl coenzyme A and oxaloacetate. This pathway leads to formation of only minimal amounts of fatty acids in milk.
  3. Fatty acids can also come from pre-formed fats that are transferred to the mammary gland via blood and lymph. This pathway leads to formation of long-chained fatty acids of 16 carbons or more.

What is “low-fat-syndrome” and how do you deal with it?

Animals fed on low-roughage diet have diminished acetate and increased propionate production in the rumen. As a result, they produce milk whose butterfat content is nearly half the content of butterfat from cows fed on high-roughage diets.

Due to low acetate, the former can only produce minimal proportions of short and medium-chained saturated fatty acids hence low butterfat content in the milk they produce.

Low fat syndrome is when a cow produces milk with low #butterfat content. #lowfatsyndrome Click To Tweet

To address this problem, cows should be fed on high roughage diet to promote synthesis of acetate, which is responsible for synthesizing short and medium chained fatty acids.

Equipment and materials needed for Gerber method:

  1. Sulphuric acid (density 1.807 – 1.812 g/ml at 270C, colourless).
  2. Amyl alcohol (specific gravity 0.815-0.818).
  3. Butyrometers: 6%, 8% and 10% scales depending on the sample fat content. (Ensure they have proper stoppers).
  4. Automatic acid dispenser (use 10 ml acid pipette in the absence of an automatic dispenser) for sulphuric acid.
  5. 10.75 ml pipette for milk sample.
  6. 1 ml pipette for amyl alcohol.
  7. Gerber centrifuge (you can also use a hand driven centrifuge in the absence of an electric one). Gerber centrifuge are the best (like the one in the anchor image) because they are self heated hence will eliminate the need for a water bath.
  8. Water bath at 650C (in the absence of a Gerber centrifuge)

Gerber butterfat test procedure

The most reliable, straightforward method is the Gerber butterfat test method, and it is conducted as follows:

  • Add 10 ml of Gerber acid into the butyrometer followed by 10.75 ml of the milk sample and then 1 ml of amyl alcohol.
  • Cork the butyrometer tightly and mix the contents. This helps to dissolve all the Milk solid Non Fat (MSNF) and separate the fat.
  • Balance the butyrometers in the Gerber centrifuge and run it for 5 minutes. (Gerber centrifuge is self heating; the fat remains liquid)
  • After centrifuging the butyrometer, read the butterfat content directly on the stem.

Why do we use 10.75 ml of milk for the Gerber method?

The principle relies on the weight of fat in the sample. For each 1% callibration of the butyrometer, there will be 0.125ml of fat.

This means that the weight of the fat content is equivalent to the volume X density; 0.125 x 093 = 0.1125.

Now, if 1 % graduation represents 0.1125g then 100 % will give us 11.25g of the fat content.

Milk has an average specific gravity of 1.032, you should use 11.25 / 1.032 = 10.9 ml of milk. There are impurities introduced by the isoamyl alcohol (about 2.5%) into the sample that will affect the reading.

#Butterfattesting Why do we use 10.75 ml of milk for the #Gerber method? Learn more... Click To Tweet

Again, there is also some residual volume of milk left in the pipette, hence the pipette calibration to 10.75 ml.

Functions of Gerber’s acid (conc sulphuric acid) :

  • Digests casein and organic matter in milk to facilitate fat separation. The differences in density between the acid and fat will make the distinction clearer during and after centrifuging.
  • Adding milk into the acid produces an exothermic reaction. The heat produced melts the fat and reduces its viscosity. This makes its quantity easy to determine on the butyrometer stem.
#Gerber #acid dissolves #casein & #milk proteins to facilitate easy #fat separation Click To Tweet

Gerber determination of butterfat content in a cheese sample

When determining the butterfat content of cheese, add the 10 ml Gerber acid and follow with cold distilled water.

Ensure that, while topping up with water, the level reaches the 6 mm mark.

After that, weigh 3 g of the cheese sample and add into the butyrometer followed by addition of 1 ml of amyl alcohol.

Shake to dissolve all the contents after securely corking it.

Finally, centrifuge using the procedure outlined above to determine the butter fat content.

Modern centrifuges are self-heated, so you don’t need to put the butyrometer into the water bath after centrifuging.

The video below illustrates how you should carry out the butter fat testing using Gerber method (video by Weber Scientific Inc).

Problems/Defects of butterfat testing

a) Charring

The most common defect you can encounter while testing for butterfat content is charring. This is when you observe black specs at the lower fat/non-fat interface of the butyrometer contents.

Possible causes and how to avoid charring:

Possible cause of charringHow to avoid
The acid is either too strong or too muchReduce the volume of acid used or use an equivalent quantity of weaker acid
Pouring milk directly into the acidHold the butyrometer at an angle to allow the milk to flow on the side of the bottle
Failure to mix the acid and the milk evenlyEnsure all the mix thoroughly mixes (use a rotary motion to achieve this). Take caution because the reaction is exothermic
Too warm milk or acidTemper to between 15°C and 20°C.

b) Light colored fat column and/or specs

The other defect of butter testing that is closely related to the first one is the presence of a light colored fat column. You may also observe light colored specs at the bottom of the fat column. This may affect your reading of the butyrometer column when performing butter fat testing using Gerber method.

Here are the causes and remedies

Possible causesHow to avoid
The acid is either too weak or too littleIncrease the volume of acid used or use an equivalent quantity of a stronger acid
Failure of the curd to dissolve completely before you start centrifugingEnsure all the curd thoroughly dissolves (Thoroughly mix it up in a rotary motion).
Too cold milk or acidTemper to between 15°C and 20°C.

While working in the lab, you must abide by the laboratory safety rules. Wash off any acid spills on skin with plenty of water.

Always practice safe disposal of the acid contents after the experiment. The acid may corrode the plumbing works.

Reasons for butterfat content variations in milk from cows of the same breed

Ideally, cows of the same breed should produce milk with a consistent butterfat content. However, that is not the case. You will notice that the butterfat content varies widely and these are some of the possible causes of this variation:

a) Individual variation

Butterfat content varies from cow to cow based on some individual traits and other prevailing conditions. It is a natural occurrence.

b) Stage of lactation

Healthy cows hit their peak in butterfat production immediately after parturition. The content reduces regularly until it hits its lowest after 60 days. From that point, the butterfat content begins to increase again until it hits the peak at the end of the lactation period.

c) Age of the cow

As the cows advance in age, they experience a slight uniform decline in butterfat production. It is perfectly normal.

d) Heat period (oestrus)

The hormonal imbalance that comes with estrus affects milk production. While there is an observed drop in milk production, the milk has a slightly higher butterfat content.

e) Season of the year

Butterfat is highest during dry seasons when the animal has plenty of roughage than during rainy/cold seasons when the amount of dry matter intake drops.

f) Time/frequency of milking

When milking regularly, e.g. twice a day, the morning milk will have a lower volume but higher butterfat content than the evening milk. The cow’s system has adequate time at night to create more butterfat due to reduced activity.

g) Prevailing weather conditions

Cool weather favors production of more milk with higher butterfat content than hot humid weather.

h) Feeding and nutrition regimen

Cows that feed on balanced diet will produce more milk that is rich in butterfat content than those that lack crucial nutrients in their diet.

Other contributors to butterfat variation that can affect Gerber butter fat testing

  • Frequency of milking and complete emptying of the udders
  • Health of the animal
  • Milking methods used
  • Disturbances/excitement level of the animal

2. Rose Gotlieb Method of Butterfat Determination

Rose Gotlieb method of butterfat determination is useful in determining butterfat content of milk, especially if the product has other additives like sugar in it.

Rose Gotlieb method is suitable for samples with added sugars #butterfat #foodsafety #qualityassurance Click To Tweet

The principle of Rose Gotlieb method

  1. Treat the sample with ammonia and ethyl alcohol. The ammonia will dissolve the protein in milk while ethyl alcohol will precipitate the proteins.
  2. Fat extraction is done by di-ethyl ether and petroleum ether. Evaporate the mixed ethers and weigh the residue.
  3. To obtain reliable results, you should strictly adhere to the details. The results obtained through this method is suitable for reference purposes.

Apparatus for Rose Gotlieb method

  • Mojonnier fat extraction flask or any other suitable extraction tube (ISO certified)
  • Cork or an inert stopper (should not be affected by the usual fat solvents)
  • 100 ml flat-bottomed flask with G/G joint or stainless steel (you can also use glass/aluminum dishes – 5.5cm high and 9cm in diameter)

Required reagents

  • Ammonia (S.G. 0.8974 at 16°C)
  • Ethyl alcohol (95%)
  • Diethyl ether (should be peroxide-free)
  • Petroleum ether (boiling at 40-60°C)

The Rose Gotlieb procedure

  1. Accurately weigh 10g of the sample and transfer to the extraction tube.
  2. Add 1.25ml of the ammonia at 0.8974 S.G. and mix thoroughly by shaking.
  3. Add 10ml of diethyl alcohol into the flask containing the mixture and mix again. Immediately add 25ml of diethyl ether (peroxide-free) then stopper the flask and shake vigorously for about a minute.
  4. Add 25ml of petroleum ether and shake vigorously for about half a minute.
  5. Let the flask stand until there is a clear distinction between the upper and the lower layers. Otherwise you could use a low r.p.m Mojonnier centrifuge for the separation purpose.
  6. If you notice that the mix has an emulsion that prevents the formation of a clear boundary, use a little alcohol to break the emulsion.
  7. Decant the clear upper ethereal layer into a suitable receptacle (bowl/flask/dish). Make sure you wash off the delivery channel of the extraction tube with a little ether. Add these to the receptacle.
  8. Repeat the extraction of the remaining liquid in the extraction tube two more rounds. Use 15 ml of each solvent for every round and add the clear upper ethereal layer into the receptacle.
  9. Evaporate the contents of the receptacle completely.
  10. Dry and weigh the receptacle in the oven at 102°C for two hours, cool it in the desiccator and weigh.
  11. Heat the flask again in the oven for 30 minutes, cool and weigh. Repeat the process until the difference between two successive weights does not exceed 1mg.
  12. After reaching that point, carefully wash the receptacle with petroleum ether. Leave any insoluble residue in the flask.
  13. Dry the flask in the oven and re-weigh it. The difference in weights indicate the fat content of the milk.
  14. Make sure you correct the weight by the blanks used in the determination process. Any variance more than 0.5mg indicates that the reagents have an impurity. You should purify or replace the reagents and repeat the process.

A reliable result should not have a variance of more than 0.03mg of fat per 100g of the product.

Calculation

Percentage fat w/w = {Weight of fat / Weight of milk}*100

Source: AOAC Official Methods.

3. Werner Schmidt Method – (Acid Digestion)

This is a rapid fat determination method that relies in acid extraction. It is a great alternative for the Rose Gotlieb method due to the speed with which it yields results.

The principle of Werner Schmidt method

Concentrated hydrochloric acid dissolves milk proteins. The remaining fat is extracted by alcohol, ethyl ether, and petroleum ether. After evaporating the ethers, the remaining residue is weighed to determine the fat content.

Reagents

  • Ammonium hydroxide (S.G. 0.8974 at 16°C)
  • Concentrated hydrochloric acid (S.G. 1.16)
  • Ethyl alcohol at 96% by volume
  • Diethyl ether (peroxide-free)
  • Petroleum ether (Boiling range 46-60°C)

Procedure

  1. Weigh 10g of the material in a small beaker and add 10ml of the concentrated hydrochloric acid.
  2. Heat the mixture on a Bunsen burner while stirring continuously with a glass rod until all the contents turn dark brown. Cool the mixture to room temperature.
  3. Add 10ml of ethyl alcohol first to the beaker and mix thoroughly.
  4. Add 25ml of ethyl ether into the mixture in the beaker and then transfer the contents into a Mojonnier fat extraction flask. Stopper the flask with a cork or a stopper that is resistant to usual solvents. Shake vigorously for one minute.
  5. Add 25ml of petroleum ether and shake the mixture vigorously.
  6. Centriguge the Mojonnier flask at 600 r.p.m. If you happen to have used Rohrig tube, let it stand until there is a clear separation of layers.
  7. Decant the ether solution into a suitable receptacle. Wash the decanting tip with a mixture of the solvents in equal parts into the receptacle.
  8. Repeat the extraction of the remaining liquid in the flask by using 15ml of each solvent. If the level of the liquid goes down (as in the case of milk powder), you can adjust it to the mark with water.
  9. Evaporate the solvent in a water bath. Make sure the temperature is not very high to cause sputtering of the contents.
  10. Dry the resultant fat in the oven at 100°C to a constant weight and cool the flask and its contents.
  11. Weigh the cooled flask/receptacle then remove all the fat using warm petroleum ether. Re-weigh the receptacle.

Calculation

Percentage fat w/w = {(W1 – W2)/W3}*100

Where:

W1 = Weight of the flask contents before removal of fat in grams

W2 = Weight of the flask contents after removal of fat in grams

W3 = Weight of the test sample in grams

NOTE: \\

If the sample has added sugar, acid extraction procedure is not suitable to determine its fat content. Please use Rose Gotlieb method.

Source: Pearson’s Composition and Analysis of Foods, 9th Ed.

4. Babcock Method of Butterfat Determination

Following the challenges facing honest farmers who were facing undue competition from dishonest farmers (those who were adulterating their milk to get more volumes), Professor Stephen Babcock of the University of Wisconsin developed a non-solvent wet extraction method, which became known as the Babcock method of butterfat determination.

While conducting experiments, he had found that when he added concentrated sulphuric acid (92% or S.G 1.82) to 18 g/17.6 ml of milk, the butterfat would separate out.

It would then be easy to determine the volume of the butterfat by subtracting it from the initial volume of milk used.

The Babcock rapidly became popular, as farmers could easily determine the quality of their milk. They were even able to select animals that produced high quality milk for breeding.

The Principle of the Babcock Method

It uses the same principle as the Gerber method. Sulphuric acid dissolves all the milk solid non-fat (MSNF), which facilitates separation of fat.

Centrifuging at 50°C improves the separation and maintains the butterfat in a liquid state for easy reading of the volume.

Determination of butterfat content is done in a specially graduated Babcock test tube. The volume is expressed as %w/w milk.

The whole test takes about 45 minutes to finish.

Apparatus and Materials for the Babcock Method

  1. Babcock sulphuric acid (92% or S.G. 1.82-1.83)
  2. Glassware (17.6 ml pipette, 8% milk bottles, 50% cream bottles, 50% Paley bottles, 17.5 ml cylinders).
  3. Babcock shaker.
  4. Torsion balance, 9 and 18 g weights.
  5. Water bath at 50°C.
  6. Babcock centrifuge.
  7. N-butyl alcohol
  8. Glymol.

The Babcock Procedure for Determining Butterfat Content

  1. Temper milk sample to 20°C and mix thoroughly to obtain a homogeneous sample.
  2. Pipette 17.6 ml of milk into the 8% bottle. Blow out the last drop into the bottle.
  3. Add 17.5 ml Babcock acid incrementally into the milk sample and mix thoroughly to obtain a chocolate brown color.
  4. Put the sample into the centrifuge and run for 5 minutes.
  5. Adjust the volume of the mix to three quarters of the bulb (below the neck) by adding distilled water at 60°C. Ensure you do not mix it.
  6. Put the adjusted mix into the centrifuge and run for 2 minutes.
  7. Add more water at 60°C until the fat floats in the neck of the bottle. Ensure the meniscus is within the graduated section. Again, do not mix.
  8. Run the adjusted mix in a centrifuge for a further 1 minute.
  9. After centrifuging, temper the bottle in a water bath at 50°C for about 5 minutes.
  10. Read the butterfat content off the graduated section.

Determining Butterfat Content of Cream and Cheese by Babcock Method

  1. Grind cheese into fine particles. Temper both cream and cheese to about 20°C and mix.
  2. Weigh 9 g of cream (or cheese) into 50% cream bottle (Paley bottle for cheese sample) and add 9 ml of distilled water at 20°C (10 ml of distilled water at 60°C for cheese sample).
  3. Add 17.5 ml Babcock acid incrementally and mix after each addition until all the contents dissolve resulting into a chocolate brown solution in case of cream and all the cheese dissolve.
  4. Centrifuge the resultant mix for 5 min.
  5. Add distilled water at 60°C to bring the volume of the bulb to about three quarters. Unmixed, send to the centrifuge and run for 2 minutes.
  6. Add more water at 60°C to bring the fat into the neck of the bottle. Again, unmixed, send to the centrifuge and run for 1 minute.
  7. Temper the bottle in a water bathe at 50°C for 5 minutes.
  8. Add 4-5 drops glymol on the fat column and let the drops run down the side of the bottle. They will demarcate the length of the fat column.
  9. Read the fat content from the graduated section of the bottle. Express as percent weight.

Determining the Butterfat Content of Skim milk, Buttermilk, and Whey by Babcock Method

  1. Temper the sample to 20°C and mix gently.
  2. Transfer 2 ml N-butyl alcohol into the 18 g double neck bottle followed by 9 ml of the sample. Swirl the mix gently to obtain a homogeneous mix.
  3. Once you have the homogeneous mix, add 9 ml of Babcock acid into the sample of skim milk or buttermilk (add 7 ml in case of whey sample whey).
  4. Place the sample bottles into the Babcock centrifuge with the small neck facing outside. Run the centrifuge for 6 minutes.
  5. Adjust the contents of the bottle to just 1 cm below the neck by adding water at 60°C. Unmixed, centrifuge the mix for 2 minutes.
  6. After centrifuging, temper the sample bottles in water bath at 50°C for 5 minutes.
  7. Place your finger over the neck and press down until you can read the lower meniscus on a major division. Read the butterfat content of the graduated section.

Advantages of the Babcock method

  1. The Babcock method is very rapid.
  2. Its accuracy is undisputed
  3. It is a cheaper method of butterfat determination.

Limitations of the Babcock method

  1. It is not possible to determine the quantity of phospholipids
  2. Due to the high acid concentration, this method is unsuitable for products with sugar or chocolate (such as ice cream). The acid has an adverse effect on the sugars or chocolate. Here’s the modified method for the determination of ice cream butterfat content.

Determination of Ice Cream Butterfat Content Using Modified Babcock Method

Determination of ice cream butterfat content can be quite a daunting task due to the presence of sugar in the product. Butterfat content determination procedures (e.g. Babcock method) rely on the use of a strong acid. This reagent presents a special challenge when sugar is present in the sample.

#Icecream contains sugar, which makes its #butterfat content determination via #Babcock method impossible. Here's how to do it right. Click To Tweet

Strong acids cause charring of sugar, which interferes with reading of the results. The analysis of butterfat content in ice cream, therefore, requires a modification of the current methods to circumvent the challenge.

The Babcock method has been widely adopted as a standard method for butterfat content analysis. It would be a perfect analytical procedure for this test but for its utilization of a strong acid. Sulfuric acid used in the procedure causes charring of sugar in ice cream, which interferes with the results.

Research has shown that sugar dissolves in 72% perchloric acid without charring. This presents a unique opportunity to modify the Babcock procedure by utilizing this reagent to avoid charring of sugar. One does not need any additional modification of the procedure or equipment, and the results will be very accurate. In addition, the centrifuge will only need to run for two minutes for complete separation.

Butterfat tends to darken in the presence of perchloric acid when heated to 100°C, which makes reading the levels quite difficult. To overcome this challenge, a mixture of 72% perchloric acid and 95% glacial acetic acid is used (in equal parts).

This can drive up the cost of testing but it offsets the negatives by improved speed, accuracy, consistency, and simplicity. Other ingredients in the ice cream such as stabilizers, flavors, and even chocolate do not interfere with the test.

Apparatus and reagents for the determination of ice cream butterfat content

All the apparatus used in the Babcock method applies here, except for the Babcock sulfuric acid.

  1. Perchloric acid (72%) and 95% glacial acetic acid (1:1 mix)
  2. Glassware (17.6 ml pipette, 20% Babcock ice cream bottles, 50% Paley bottles, 50 ml graduated cylinder).
  3. Torsion balance, 9 and 18 g weights.
  4. Water bath at 50°C.
  5. Babcock centrifuge.
  6. Glymol.

Procedure for determination of ice cream butterfat content

  • Weigh nine grams sample of ice cream mix (or melted ice cream) into a 20% Babcock ice cream test bottle.
  • Add approximately 30 ml. of the acid reagent (equal parts by volume of 72% perchloric acid and 95% glacial acetic acid) to the test bottle, rinsing the adherent mix off the graduated stem of the test bottle into the body of the bottle while adding the acid. Ensure all the ingredients are at room temperature.
  • Immerse the ice cream and acid mixture in water for 5 minutes. Agitate the mixture two to three times during the process to completely digest it. You will observe no color formation at first, but upon digestion there is color progression to tan, brown and finally deep chocolate color. The curd completely dissolves in 1 to 2 minutes. After 5 minutes, the fat will form an immiscible supernatant layer.
  • Add enough of the acid mixture to bring the fat into the calibrated stem of the bottle.
  • Place the test bottles in balanced pairs in a standard Babcock test centrifuge and run for 2 minutes. If the centrifuge is heated to 60°C., you can read the fat content immediately after removing the sample from the centrifuge. However, if you use an unheated centrifuge, temporarily immerse the test bottles in a water bath ( 50°C – 60°C / 130°F – 140°F) for 5 minutes before reading. You can add glymol for a distinct separation between the supernatant and the digested mass.
  • After the test, pour the contents of the test bottle into a reservoir of water before disposing in a sink drain. Rinse the bottle with hot water for the next test. The acid mix dissolves all calcium salts in the sample hence no deposition in the inner walls of the test bottle expected.

Important notes:

  • You are dealing with acids; precautions taken when dealing with mineral acids for the unmodified Babcock method applies.
  • The mixture of perchloric acid and acetic acid is not hazardous and does not deteriorate under storage.
  • Butterfat is as insoluble in aqueous perchloric acid as it is in aqueous sulfuric acid.
  • You don’t need to add water to the mix since centrifugation takes only two minutes.

Reference

The Determination of Butterfat in Ice Cream Employing Mixed Perchloric and Acetic Acids.

Fat Indices Used To Score and Categorize Butterfat

Butter fat indices indicate the type and amount of fatty acids in the butterfat of any given dairy product, which helps in scoring the quality of the product.

We have already discussed several methods for determining the butterfat content. However, the indices we shall be looking at not only reveal the content, but also the type of fatty acids present in the butterfat sample.

The two common fat indices include:

1. Saponification Value

It is a base catalyzed hydrolysis of an ester into its constituent elements of alcohol and acid.

Saponification number is the amount (in mg) of a base/alkali (KOH) that completely hydrolyzes one gram of fat.

The higher the saponification value, the higher the amount of short-chained volatile fatty acids present in the fat sample.

Saponification value is the amount of an alkali needed to completely hydrolyze 1 g of fat. Click To Tweet

Example

Stearin + Potassium hydroxide —> Potassium stearate + Water

If the fat contains low molecular weight fatty acids, the number of molecules in one-gram fat sample will be greater than of the fat of high molecular weight fatty acids. Thus, the fat with low molecular weight fatty acids will have a higher saponification number.

Fats with high saponification value are prone to hydrolytic rancidity.

CH3(CH2)16 + 3KOH —> 3KOOCC17H35 + C3H5(OH)3

2. Iodine Value

This is the most important and widely used of the indices. It states the ideal value/percentage of the iodine (or any other hydrogen) required to bind a 100 g fat. As such, it is an addition reaction.

This is significant because, in fat with double bonds, iodine reacts readily with the fat’s double bonds to form an additional compound.

Iodine value gives a picture of the degree of saturation of fatty acids present in a given fat. Click To Tweet

Iodine number, therefore, gives a picture of the degree of saturation of fatty acids present in a given fat. Research shows that oleic acid is the most predominant of the unsaturated fatty acids present in the milk fat.

Consequently, iodine value has been taken to indicate the measure of oleic acid content in milk, hence, the softness of the fat.

The normal level of iodine value in milk ranges between 24 to 46. It depends on the feeding regime of the animal. Certain fodder concentrates promote high iodine value, e.g. sunflower cakes make animals produce fat with high iodine number.

On the other hand, palm oil cake and coconut cakes, produces fats with low iodine value.

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    1. Thank you Edward for catching that gas proton. Just reminded me of William Shakespeare’s line in Act 3 of A Comedy of Errors (1594) where he states: “A man may break a word with you, sir; and words are but wind; Ay, and break it in your face, so he break it not behind.”

  1. why only garber acid is use for fat estimation???
    can we use different acid for fat estimation??? like HCL, 98%H2SO4????

    1. The preference for Gerber acid is due to is high efficiency in digesting milk proteins to release fat. The concentration is optimized at 90% to avoid some of the defects listed in this article.

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