Evaluation of a novel pre-treatment, flash vacuum expansion, on grape juice yield and quality

Shriram Paranjpe, Purdue University

Abstract

Due to the increased importance of phytochemicals in the daily diet, grape juice is gaining importance in the US. Presently, it is produced by pressing grapes immediately after an enzyme treatment. However, the treatment takes 30-60 minutes and can destabilize some phytochemicals. Flash vacuum expansion is a novel technology with the potential to substitute for this pre-treatment. However, it has not been studied for the extraction of juices. This dissertation aims to understand the process and develop it into one applicable to the industry. For better understanding of the process, the effects of key of flash vacuum expansion parameters (temperature and initial pressure) were studied on juice yield and quality from Thompson seedless grapes. Lower initial pressures and higher temperatures improved both the yield (61.3% to 75.5%) and phenolic content (3.7mg/mL to 7.5mg/mL) of juice. Additionally, a comparison of cell damage caused by the different treatments indicated that flash vacuum expansion-caused more cell rupture than heat treatment or enzyme processing. To verify the effect of the process on common juice grapes, it was applied to Concord grapes. The juice obtained was compared to enzyme treated, heat treated, and cold pressed juice samples. Results showed that flash vacuum expansion provided the same yield of grape juice (∼84%) as enzyme processing which was significantly higher than the other two treatments. The treatment also yielded a higher concentration (315mg/L v/s 253mg/L) and extraction efficiency (87% v/s 72%) of anthocyanins than enzyme processing without significantly affecting their profile. To further develop the process with an industry perspective, a system capable of continuously processing grapes by flash vacuum expansion was developed and applied to Niagara and Concord grapes. After this treatment, Niagara grapes yielded more juice (92% v/s 90%) and polyphenols (2.65mg/mL v/s 1.98mg/mL) than enzyme processing. Cost analysis on this system indicated that flash vacuum expansion would be financially comparable to enzyme processing if the cost of enzyme were 7.82 cents per kilogram. These studies indicate that flash vacuum expansion is a potential substitute for enzyme pre-treatment of grapes prior to juice extraction. However, more research is needed to improve and develop the continuous process prior to application in the industry.

Degree

Ph.D.

Advisors

Morgan, Purdue University.

Subject Area

Agronomy

COinS