Optical and AFM microscopy of grape juices treated with UHPH: Effects of microstructure and nanostructure

Abstract

UHPH treatment of Vitis vinifera must for winemaking leads to fragmentation of colloidal particles into smaller structures. The shear and fracture forces experienced by grape juice during valve pressurization are sufficient to reduce the particle size of grape juice to below 500 nm. As a result, the applied force can disrupt bacterial and yeast cell structures, altering or breaking down proteins, polysaccharides and enzymes. This effect is not observed for low molecular weight compounds such as monomeric pigments and phenolic structures, varietal aroma precursors, fermentable sugars, etc. Treated and untreated samples can be compared using optical and atomic force microscopy. Optical microscopy images show reduction or elimination of bacteria and yeast and changes in microstructure. On the other hand, in addition to describing topography in the nanometer range, AFM can also measure particles in comparison to other techniques such as laser diffraction (LD). This work contributes to the characterization and better understanding of the effects of UHPH on grape juice for winemaking.