Shear stiffness and density in potato parenchyma

To understand textural changes that occur during processing of potatoes, a more comprehensive understanding of the mechanical properties of potato tub ers is desirable. Specimens of potato parenchyma had their turgor osmotical ly adjusted to be either fully turgid or flaccid. Control specimens at norm al turgor were also studied. Density of the specimens was measured using Ar chimedes' principle. The storage (G') and loss (G ") moduli of the complex shear stiffness were measured in a rheometer. A weak positive relationship between G' and density was apparent, but only for the osmotically adjusted specimens. This was true regardless of whether specimens were fully turgid or flaccid. However, no such relationship was observed for the control (nor mal turgor) specimens, which was probably due to slight variation in turgor pressure affecting G' independently of the effect of density on G', and so masking the effect of density on shear stiffness. A positive relationship between G " and density was observed, but only for flaccid specimens. This relationship was putatively assigned to shear strain energy dissipation by starch granule movement in a viscous protoplasm.