Milk test: Cheminformatics past your eyes
- Published: Aug 15, 2015
- Author: David Bradley
- Channels: Chemometrics & Informatics
Researchers describe a non-destructive method for the analysis of the freshness or otherwise of raw cow's milk using cheminformatics techniques applied to data from Fourier transform near infrared (FT-NIR) spectroscopy.
Supermarket price wars and the apparent financial crippling of British dairy farmers are headline news in the UK at the time of writing, but one issue is universal - quality control. Yanwen Wang, Wu Ding, Liping Kou, Liang Li, and Chen Wang of the College of Food Science and Engineering, at Northwest A&F University, in Yangling, Shaanxi, China, and Wayne M. Jurick II of the Food Quality Laboratory, at the USDA-ARS, in Beltsville, Maryland, USA, have developed a non-destructive freshness test for raw milk.
"The degree of change in a given sample during storage depends primarily on the variables time and temperature. Raw milk stored under different conditions can be qualitatively different to the consumer, in terms of freshness and taste," the team writes in the August issue of the Journal of Food Science and Technology.
Fresh in the fridge?
Raw milk is commonly refrigerated across the dairy industry, but keeping unpasteurised milk cool is not sufficient to prevent it going off because enzymes in the milk remain active even at refrigerator temperatures (about 4 degrees Celsius). For instance, plasmin and EC 188.8.131.52 from the cow are present in milk while others produced by psychrotrophic bacteria growing in the milk (those enzymes might include lipoprotein lipase, LPL, EC 184.108.40.206). These enzymes break down milk proteins and fats spoiling the flavour and generating unpleasant odours. Some enzymes also ferment the milk sugar, lactose, to lactic acid, turning milk sour as acidity increases and pH drops. The shelf life of "green top", as it is sometimes known, becomes a significant problem for suppliers offering this unprocessed form of milk to their customers.
Testing but not to destruction
The FT-NIR approach developed by the researchers uses a fibre-optic probe to acquire diffuse transmittance spectra in the spectral range 833 to 2500 nanometres. This data is coupled with other measurable quality parameters such as acidity (obtained by traditional titration techniques) and lactose content obtained by conventional detection methods; lactose concentration is determined using potassium permanganate titration, for instance. These methods. The team was then able to use PLS (partial least squares regression), MLR (multiple linear regression), and ANN (artificial neural networks) analyses to help them develop a model for predicting freshness for a new sample based on the FT-NIR spectra alone recorded at different ages (from one to eight days, in their experiments) and under a hierarchical cluster analysis approach.
The team explains that their spectral analysis can reveal the factors associated with freshness falling below the threshold for when milk becomes unfit for human consumption, namely when acidity is greater than 20.7 degrees T, pH is below 6.71 and lactose content is less than 3.42%, without having to determine those three characteristics using conventional analyses. They add that their approach could thus replace the raft of methods currently used to test the freshness of raw milk, which are both time consuming and labour intensive. The spectroscopic probing method offers a much simpler approach for the quality control laboratory in a dairy. Moreover, the technique even lends itself to online testing, rather than the removal of samples to the lab. The team describes their technique as being able to determine raw milk freshness "quickly and conveniently".
J Food Sci Technol 2015, 52, 5305-5310: "Researchers describe a non-destructive method for the analysis of the freshness or otherwise of raw cow's milk using cheminformatics techniques applied to data from Fourier transform near infrared (FT-NIR) spectroscopy."
Article by David Bradley
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
Follow us on Twitter!