Isochoric freezing to extend the shelf-life of pomegranate juice

Authors: LEO, LOU - University Of California Berkeley; Takeoka, Gary; RUBINSKY, BORIS - University Of California Berkeley; Bilbao-Sainz, Cristina

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2023
Publication Date: 1/23/2024
Citation: Leo, L., Takeoka, G.R., Rubinsky, B., Bilbao-Sainz, C. 2024. Isochoric freezing to extend the shelf-life of pomegranate juice. Journal of Food Science. 89(3):1347-1360. https://doi.org/10.1111/1750-3841.16941.
DOI: https://doi.org/10.1111/1750-3841.16941

Interpretive Summary: Pomegranates have received “superfood” status due to numerous scientific studies claiming multiple health benefits. Pomegranate juice has become very popular because it is a convenient way to consume pomegranates. However, freshly made pomegranate juice quality will decrease after a few days in cold storage. Although pasteurization treatments are usually used to preserve pomegranate juice, thermal processing may result in nutritional losses and changes to color, flavor and taste, affecting consumer preference. This study uses a novel technology called isochoric freezing (IF) to reduce microbial load and maintain the quality of pomegranate juice during storage for four weeks. Results showed that isochoric freezing at -15 °C/130MPa for 24 hours ensured the complete microbial inactivation of pomegranate juice. Furthermore, storage under isochoric conditions at -10 °C/100 MPa inhibited microbial growth for the length of the study, whereas storage at 4 °C and 24 °C at atmospheric pressure kept microbial loads below that of fresh pomegranate juice. IF juice stored at -10 °C/100 MPa displayed great color stability and had higher nutrient contents than the heat-treated and IF juices stored at atmospheric pressure. Pomegranate juice stored for 4 weeks under isochoric conditions at -10 °C retained 72% anthocyanin content, 91% ascorbic acid content and 97% phenolics content. Subfreezing temperatures during isochoric storage might have reduced degradation of these nutraceutical compounds. In comparison, the heat-treated sample stored at 4 °C for 4 weeks showed 84% reduction in anthocyanin content, 73 % reduction in ascorbic acid content and 32% reduction in total soluble phenolic content.

Technical Abstract: Pomegranate juice was treated by isochoric freezing (-15 °C/130 MPa) for 24h and then stored under 3 different conditions for up to 4 weeks: 4°C/0.1 MPa (atmospheric pressure), 24 °C/0.1MPa and -10 °C/100 MPa. The juice microbiological stability and quality were compared to those using heat treatment at 95 °C for 15s followed by cold storage at 4 °C. Heat-treated and isochoric frozen (IF) pomegranate juice stored under isochoric conditions showed no detectable bacteria, yeasts and molds (<1 log CFU mL-1) after 4 weeks of storage. Also, IF juices stored at 4 °C or 24 °C for 4 weeks had lower microbial loads than those in fresh pomegranate juice. IF juices stored under isochoric conditions showed greater color stability, antioxidant capacity and nutrient retention (anthocyanins, ascorbic acid and total phenolic compounds) than heat-treated juices stored at 4 °C. IF juices stored at 4 °C also showed greater anthocyanins and ascorbic acid contents as well as no significant differences in phenolic content and antioxidant capacity compared with heat-treated samples stored at 4 °C. The results of this study demonstrated the benefit of isochoric freezing in maintaining the safety and quality of pomegranate juice during storage.