Comparing Hyperspectral Imaging and Near IR spectroscopy for detection of Salmonella and other bacteria in Milk, Juice and Poultry

Milk is rich in its ingredients and contains fat, protein minerals, vitamins, carbohydrates and tens of thousands of other ingredients. It is a perfect environment for bacterial cultures such as Salmonella to develop due its rich nutritional nature. Unprocessed milk that has not been heat treated or pasteurized can host a variety of bacterial cultures that could cause Gastroenteritis and other intestinal diseases (Reference 1). Figure 1 shows the variety of bacterial cultures that could exist in milk.

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Figure 1: Different bacteria present in Milk

Another source of bacterial infection is poultry. The number of cases due to Salmonella sickness in the United States exceeds one million per year and out of this, 200,000 cases are originated from poultry alone (Reference 2). The bacterial infection can also occur in commercial fruit pulp such as pine-apple. In addition, orange juice and mango juice could also get infected by bacteria (Reference 3).

The analytical methods of detection of Salmonella such as Polymerase Chain Reaction (PCR) require sample preparation, colony isolation and confirmation. Considerable amount of liquid and solid media need to be consumed and reagents are required. Not to mention, the turn-around time of the test approximating 5 to 7 days.

A faster, non-destructive, non-invasive method of testing which does not require chemical reactions are required for testing and identification of Salmonella. There are two candidates for this kind of fast testing. These two methods are hyperspectral imaging and near IR Spectroscopy (NIRS). Hyperspectral Microscopic Imaging (HMI) which uses an Acousto-Optic Tunable Filter (AOTF) and a microscope to look at individual bacterial cells from micro-colony on agar plates and the use of Principle Component Analysis (PCA) to detect and identify different types of bacteria (Reference 2). A picture of the setup is shown in figure 2.

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