Demystifying cooking in a black box

New technology allows continuous sampling of food in a can during sterilisation


Pet food is commonly available as a dry kibble or a wet product. Both types, when described as ‘complete and balanced’, provide the essential nutrients in the right ratios for dogs or cats. Wet pet food is made by carefully blending ingredients, which are sealed in cans or pouches. These are then sterilised to ensure they are safe to feed during their shelf life. However, understanding how the food components interact during this essential process has been a puzzle, until recently.

Food is complicated

Our diets, along with our pets, are comprised of carbohydrates, proteins and fats. The building blocks of these are a variety of sugars, amino acids and lipids. However, the combination and individual structure of these vary between, and also within, food types. Is one carrot the same as another? Some carrots taste sweeter than others and, therefore, may have a different sugar content. There is natural variation in all raw materials through variety, seasons and suppliers. How does this change the cooked food?

Each simple ingredient is actually very complex to a chemist. Individually containing different types of amino acids, sugars and lipids are arranged in a plethora of ways. Mixing these foodstuffs during cooking causes their components to interact through millions of chemical reactions. And this is exactly what happens when every can or pouch of pet food is sterilised. Yet, despite the complexity of the science, it is important for food manufacturers to generate consistent quality products regardless of the variation in the raw materials and processing.

The chemistry of cuisine

Sampling ingredients as they are cooked in a pan is easy to do. Although understanding the chemical reactions that are occurring between the sugars and amino acids are not. Find out how Daniel Hemmler is exploring the complex chemical reactions in cooking for his PhD. Tracking changes when food is cooked in a sealed, pressurised container has proved far more troublesome.
To produce food that is free from germs and safe to eat, it is sterilised after it has been sealed into its package. For this, the can or pouch is heated up to 130˚C for 30 to 60 minutes at high pressure. This process also allows packaged food to have a much longer shelf life compared to fresh products.

Peaking inside the black box

Until now, to explore the changes that occur during sterilisation involved a laborious process. Many repeated experiments were carried out in numerous small vials. Each small container was filled with food and sealed. All of these were then subject to the same heat and pressure used in factories for sterilisation. At different time points during the cooking, the vials were removed one by one to test the contents. However, this method has limitations. Glass vials in a lab are not good representations of cans in a factory. The results from experiments set up in the same way were not comparable. And, to further restrict the findings, each vial would only contain enough food to carry out a single analytical test. For example, to examine the amino acids, sugars and flavour compounds three separate vials were required. This ultimately means that the efficiency of the experiments was very low.

Scientists from Waltham, Helmholtz Zentrum Muenchen and the Technical University of Munich have recently published a new way in which to monitor the changes that occur during sterilisation. To better understand all the chemical interactions that may occur, the team created a laboratory based model to simulate the factory sterilisation process. The apparatus allowed five samples to be taken during the continuous heating and whilst maintaining the pressure. The samples were then analysed using a type of mass spectrometry. This means that all the compounds are sorted and recorded based on their size and electrical charge.

With the new method, different types of compounds can be measured in a single analysis. These include fatty acids, amino acids, sugars, flavour compounds amongst others. This allows each sample to reveal more of its chemical secrets. In addition to this, the new technique is much more robust and repeatable than the traditional multiple vial approach. The chemical changes during sterilisation can be monitored by comparing different time points, shedding insight on how the compounds from the ingredients interact together under heat and pressure.
To check whether the repeated sampling during the pressurised sterilisation procedure impacted the final product, the team compared results from the lab system to the actual factory. The same starting mixture of meat chunks in gravy was processed in a factory and in the lab. Many of the compounds responsible for the odour of the product are produced during the sterilisation, and are very good indicators of consistency. The smell of the product was similar between both methods, demonstrating that the laboratory system was representative of the factory environment.

Lifting the lid

“This new method is more accurate and efficient than existing techniques” explained Dr James Marshall, lead author and Chemistry Research Manager at Waltham. “For pets, this means we will have a better understanding as to how the flavours develop and nutritional composition/value changes during sterilisation. Ultimately allowing us to improve the quality of our products on the shelf”.

This new technique provides the tools for food chemists to understand the impact and timing of the interactions of ingredients during the sterilisation process. The laboratory based system improves the efficiency, accuracy and cost of monitoring these changes. By using a broad ranging, untargeted analysis like mass spectrometry, a greater number of compounds and changes can be tracked. The new method allows a greater potential for discovery compared to targeted approaches, which carries an element of knowledge bias. Due to this, you will only ever find what you are looking for. By understanding what happens to the food in a can, scientists can continue to provide optimum nutrition whilst potentially improving the flavour and other attributes. We can, therefore, advance formulations so that pets will benefit from the best of both worlds in the final product that sits on your cupboard shelf.

Marshall, Schmitt-Kopplin, Schuetz, Moritz, Roullier-Gall, Uhl, Colyer, Jones, Rychlik, Taylor. 2018. Monitoring chemical changes during food sterilisation using ultrahigh resolution mass spectrometry. Food chemistry, 242, 316-322.