Effect of a flash vacuum expansion process on grape juice yield and quality

Abstract

Flash vacuum expansion is a process where a heated product is rapidly exposed to low pressure, or vacuum, causing interstitial water in the product to rapidly flash and rupture a portion of the tissue. This process has potential to aid juice expression and improve extraction of potentially healthy components from fruits and vegetables. In this study, the yield and quality of juice extracted from grapes treated by flash vacuum expansion, heat and enzymes, heat only, and no treatment were compared. The flash expansion process was first studied using Thompson seedless grapes. Lower chamber pressures and higher fruit temperatures were found to improve juice yield and phytochemical composition. While the process could improve polyphenol content and extraction over traditional methods, juice yield was lower than enzyme processing. Tissue damage on grape skins, measured via electrical impedance, was highest after flash vacuum expansion and resulted in higher polyphenol extraction. Juice pressed from concord grapes treated with flash vacuum expansion was compared with heat and enzyme processing, heat treatment only, and cold pressing. Flash vacuum expansion provided juice yields similar to enzyme processing and higher than heat treatment or cold pressing. The process also improved juice anthocyanins over enzyme processing, heat processing, and cold pressing. This investigation provides a comparison of the flash vacuum expansion process and more traditional grape processing methods. It also provides insight into the role of key operating conditions on juice yield and quality.