Volume and Texture Measurements of Potato


Potatoes are the largest non-grain food commodity in the world and the consumption is expanding rapidly. Unlike grains and cereals, the potato is it not a globally traded product. It is most often produced and consumed locally around the world. Its nutritional value is high, containing vitamins and minerals that are essential to health. A medium sized potato contains nearly half of the daily recommended (adults) in-take of vitamin C. It is also a good source for vitamin B.

There are many companies producing various forms of peeled potato products to restaurants, schools, hospitals etc. and a common customer complaint of these products is that a leathery layer is formed on the surface of the cooked ready-peeled potatoes. This film formation is a defense mechanism of the potato and is initiated during the peeling of the potato when the outer cell layers are damaged. The potato undergoes various stages of maturation during growth and the storage. This affects the storage stability and the quality for further processing and cooking. Different varieties and growing conditions influence the final product as well. This increases the demands of an optimized peeling and cooking process when it comes to times and temperatures.

To gain a deeper understanding of the formation of the leathery layer on the surface of the potato, there is an ongoing study at the moment at Lund University, Sweden. The project is called School meal potato for the future – quality throughout the value chain. In the project, they are using the TVT Texture Analyzer to measure the properties of the leathery layer. The BVM Volumeter is used to measure both the variation in volume within and between the potato varieties and to measure the volume reduction after the peeling process.

Volume and Texture Measurements

All potato samples were peeled and stored for 8 days prior to measurement. The volume measurements presented in Table I were performed using a BVM-L100 with a profile scanning time of 60sec and without any attachments. Figure 1, shows two example graphs from two scans of different potato samples.

Table I: BVM results for some measurements.






X and Y are two different potato varieties; A1 and A2 are two different locations with different type of soil, and pot1 and pot2 are replicate samples.









Figure 1: Example pictures for two different potatoes

After the volume measurements, the potatoes were cut into smaller samples with a height of 33± 0.5mm before the texture measurements. The texture measurements were performed using a TVT-XP equipped with a 7kg load cell and a 2mm cylinder probe. The test speed was set to 1mm/sec with a trigger point of 5g. Typical graphs from each potato sample can be seen in Figure 2.

Figure 2: Puncture graphs for the potato samples.

The peak force is the force required to puncture the surface of the potato, and thereby also the leathery layer. The toughness of the layer is measured by how deep the probe can penetrate the potato before the layer breaks. It is clearly seen that there are differences in both hardness and toughness of the leathery layers formed on the surfaces of the potatoes.