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. In this thread, we will discuss both, starting with the indices of butterfat quality and then we'll look at the quantitative analysis methods in the thread replies.
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.
The two common fat indices include:
Several methods of analysis exist to determine the quantity and the quality of butterfat. In this thread, we will discuss both, starting with the indices of butterfat quality and then we'll look at the quantitative analysis methods in the thread replies.
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:- Synthesized by the mammary gland from acetate and B-hydroxybutyrate that are produced by the rumen bacteria. These are majorly 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.
- 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.
- 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.
- 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.
Fat Indices Used to Score and Categorize Butterfat
Butter fat indices indicate the type and quantity of fatty acids in the butterfat of any given dairy product, which helps in scoring the quality of the product. See the thread replies for several methods for determining the butterfat content. The indices covered here 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.
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 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 cake, produces fats with low iodine value.
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.