Analysis of milk and milk products?

Answer 1

I work as a Lab Tech in the milk industry in Australia. The milk industry is heavily regulated, as is most industries involving food.

We test Farm vats, milk tankers, our own milk vats, every step of production, and of course the end product.

The most common analysis on milk and milk products are:

Fat % T.A% (Titratable Acidity)

Protein % p.H

Lactose % S.P.C (Standard Plate Count aka Total plate count)

TS % (Total solids)

SNF % (solids non fat)

We test the fat, protein, Lactose, TS, and SNF using an FT120 which is made by a company called Foss. This machine is widely used in milk production factory's due to its accuracy in such a small time (about 30seconds for results). However it would be rare to find this machine at a Dairy due to its expense (a few million $$)

It is also to be noted that the Australian Standards allow for us to use the FT120. However it cannot process all milk based samples. Things that are dense, or have high fat content we test using 'Mojonnier' method. This method is long and complex so i wont go into that.

T.A is tested using Sodium hydroxide (NaOH) and an indicator called phenolphthalein. To understand this test properly you need to know a bit about chemistry. Basic tho, we add the phenolphthalein to 9mls of milk (or milk product) and then slowly add sodium hydroxide. When the milk starts to turn pink, it indicates that the milk is now turning to the Alkalize side. Therfore by measuring how much sodium hydroxide it took to turn the milk, we can determine how much Titratable acidity is in it.

p.H is measured using a p.H probe. p.H of milk should be slightly acidic. around 6.7 is good.

SPC is a basic Microbiological test to count the amount of bacteria. Again this subject is quite complex. Firstly it should be noted that milk directly from a cow is actually sterile (provided the cow is healthy). But during the milking stage it picks up alot of bacteria.

There are different methods for testing SPC, but we use 'pour-plates' which we make a agar with bacteria pleasing nutrients, and pour it in one 1ml of milk. (Often milk and milk products are actually diluted down during micro analysis due to high levels of bacteria). IF you tested 1ml of Raw milk from a Dairy it would not be uncommon to have 1000's of bacteria. A pour plate is only about 90mm wide so its very hard to count so much bacteria in a small area. Therefore the milk is often diluted down. If we dilute the milk to 1 in 10, for every 1 bacteria colony that's counted on the plate, there is 10 colonys actually in the 1ml of milk.

Milk products are often tested for mould, yest, E.coli, and coliforms. Again testing methods vary, but we test using 'pour-plates'. We make an agar specifically for these sort of bacteria and test them.

I hope that gives you a general over-view of milk analysis. There are ofcourse many other tests that are done on milk and milk products. Keep in mind that testing regulations are different from country to country and even from state to state.

any questions about any of the info here, email me at aussie_jaffa@hotmail.com