Effects of subzero isochoric cooling at low- and high-pressure conditions on the shelf life and physicochemical qualities of cut bell peppers

Authors: MCGRAW, VALERIE - University Of California Berkeley; Atci, Sumeyye; LI, JIAYUAN - Volunteer; POWELL-PALM, MATTHEW - Texas A&M University; RUBINSKY, BORIS - University Of California Berkeley; Bilbao-Sainz, Cristina

Submitted to: Journal of Food Processing and Preservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2026
Publication Date: 7/1/2026
Citation: McGraw, V., Atci, S., Li, J., Powell-Palm, M.J., Rubinsky, B., Bilbao-Sainz, C. 2026. Effects of subzero isochoric cooling at low- and high-pressure conditions on the shelf life and physicochemical qualities of cut bell peppers. Journal of Food Processing and Preservation. 2026(1). Article 3596521. https://doi.org/10.1155/jfpp/3596521.
DOI: https://doi.org/10.1155/jfpp/3596521

Interpretive Summary: Fresh, pre-cut produce is popular among consumers and food producers, but spoils quickly. Cut bell peppers are a common ingredient in ready-to-eat or ready-to-cook products and thus could benefit from improved preservation methods. Subzero isochoric cooling (ICC), which combines low temperatures and high pressures to preserve food at subfreezing temperatures without forming ice within the food product, has shown promising results as a means to preserve variety of fresh produce. ARS scientists in Albany, CA, conducted experiments to investigate the efficacy of short-term (five-day) exposure to ICC conditions on the long-term (four-week) refrigerated shelf life of cut green peppers. The key finding of this study was that five days of ICC, carried out at two different temperatures/pressures, was highly effective at preventing bacterial growth over 4 weeks of refrigerated storage. ICC was also somewhat beneficial in terms of retaining the texture and nutrient contents of peppers, but further work is needed to optimize ICC to improve these attributes. The findings of this work contribute to the field of food preservation research by demonstrating the ability of ICC to slow the spoilage of cut bell peppers. Additionally, the study showed that two different ICC pressure conditions can achieve comparable results, which is a helpful step towards implementing ICC in the food industry, where specific temperature/pressure conditions may be required.

Technical Abstract: Cut bell peppers are commonly sold in ready-to-eat food products but are susceptible to rapid spoilage. Subzero isochoric cooling (ICC) preserves foods at subzero temperatures without the formation of ice within the food itself, while passively generating high pressures. High pressures, combined with low temperatures, are effective at reducing microbial activity, and exposure to isochoric conditions can slow loss of physicochemical quality. In this study, cut bell peppers (raw or blanched) were stored in 3% NaCl solution for four weeks and underwent ICC at either -3 °C/35 MPa or -10 °C/110 MPa for five days followed by conventional refrigerated storage. ICC treatments at both -3 and -10 °C reduced microbial activity and growth over the four-week storage period, while control samples rapidly underwent microbial spoilage that affected texture and acidity. Storing samples in NaCl solution was somewhat detrimental to certain mechanical properties and resulted in loss of some bioactive compounds, with ICC samples exhibiting the negative effects slightly more than control samples. Treatment with ICC halted microbial activity over the entire storage period, demonstrating a promising route towards scaling ICC technology by using lower, industrially-feasible pressures.