# Food Processing with UHP Waterjets
## 4 Selected Cutting Applications
### Vegetables
#### 4.4.2 Potatoes, Onions, Carrots, and Sugarcane  
Potatoes and onions are \"round\" vegetables and are challenging to slice with waterjets as the standoff distance will vary across the vegetable and thus the cuts may not be consistent from edge to middle. However, carrots are more \"cylindrical\", with reasonable size diameters, making them easy for waterjet cutting. [PERSON] and [PERSON] [26] evaluated waterjet slicing of potatoes. They found that, in general, the best cuts were obtained with the smallest orifice, regardless of water pressure or cutting speed. As orifice size increased, effects of water pressure and cutting speed became more apparent, with the most subsurface cellular damage occurring at lower cutting speeds and intermediate water pressures. When higher cutting speeds are desired, the smallest orifice (0.076 mm) was acceptable if it completely cuts through the sample. Because of the atomized spray from the waterjet column, standoff distances should always be minimized, preferably 0.5 cm or less. Recently, the author conducted exploration tests on cutting potatoes at 600 MPa of pressure with an 0.13 mm orifice size and a cutting speed ranging from 0.13 to 0.85 m/s. The cuts at 0.64 m/s were found to be acceptable with minimal striations over 75 mm which was the potato diameter. The process of trimming green onions and leeks is similar to the trimming of celery and lettuce and similar systems are used for this purpose. The main motivation is extended shelf life due to less cell destruction and high productivity. Figure 22 shows the surfaces cut with a waterjet and a blade after 6 days with browning starting on the blade-cut surface earlier than when a waterjet is used. Onion slicing with waterjets has been tested using a UHP nozzle manifold, as shown in Figure 23. The spacing between the jets was minimized without compromising the ability of the manifold to work at 600 MPa of pressure. While onions can be sliced at lower pressures, the use of higher pressures results in lower forces for the same jet power and thus a smaller-diameter orifice and less kerf waste. Minimizing the forces is important to keep the onion slices stuck together during slicing and feeding out of the slicing area. The slice thickness can be reduced based on the angle of the manifold with the direction of travel. For example, an angle of 45 degrees will cut the slice thickness in half. \begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**Cutting Method**} & **Microlora Count** &
\begin{tabular}{c} **Days of Acceptable** \\ **Sensory Quality (2)** \\ \end{tabular} \\ \cline{2-3}  & **CFU/g (1)** & **10** \({}^{\circ}\)**C** \\ \hline Kitchen paring knife & \(2\times 10^{11}\) & 12 \\ \hline Commercial rotary blade cutter & \(4\times 10^{11}\) & 13 \\ \hline Single Edge razor blade & \(1\times 10^{9}\) & 24 \\ \hline Sharp thin blade knife sawing motion & \(5\times 10^{6}\) & 25–40 \\ \hline Waterjet & \(5\times 10^{4}\) & 25–40 \\ \hline (1) Colony Forming Units, (2) at 10 \({}^{\circ}\)C. & & \\ \end{tabular}
\end{table} 
Table 2: Comparison of celery cutting methods. Similarly to celery, waterjet cutting of carrots is well-established; for example, baby carrots are actually crowned and cut carrots. [PERSON] et al. [27] studied carrot slicing with waterjets and treatment with a NaCl solution to evaluate reducing the amount of white tissue development on carrot stick surfaces. The NaCl treatment caused a weight loss of 4-10% (not commercially acceptable). Waterjet slicing resulted in the striation of surface tissue and left loose layers of cells, as observed with the scanning electron microscope. These cells dehydrated rapidly and formed as much white tissue as on carrots sliced with a culinary knife. However, they realized that based on the findings of [PERSON] and [PERSON] [26] on cutting potatoes, the whitening and loose layers of cells might have been avoided or eliminated by using a smaller waterjet orifice or adjusting cutting speeds.