Isochoric impregnation of calcium to extend post-harvest shelf life of blueberries

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

Submitted to: ACS Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2024
Publication Date: 11/21/2024
Citation: McGraw, V.S., Atci, S., Powell-Palm, M.J., Rubinsky, B., Bilbao-Sainz, C. 2024. Isochoric impregnation of calcium to extend post-harvest shelf life of blueberries. ACS Food Science and Technology. 04(12):3007-3015. https://doi.org/10.1021/acsfoodscitech.4c00599.
DOI: https://doi.org/10.1021/acsfoodscitech.4c00599

Interpretive Summary: The availability of fresh produce is often limited by rapid post-harvest degradation, which shortens shelf life and contributes to food waste. Blueberries are a popular fresh fruit among consumers, but are highly perishable, undergoing weight loss, shriveling, and loss of nutrients during storage. This study investigates the physical, nutritional, and biological properties of blueberries following the infusion of calcium by isochoric impregnation, a low-temperature, high-pressure process which has been shown to help preserve foods for longer periods. Calcium interacts with cell components in blueberries to provide structural stability and combat the loss of moisture and nutrients. After five weeks of refrigeration, blueberries which underwent 1-7 days of isochoric impregnation prior to refrigeration did not lose more than 1% of their initial weight, while conventionally refrigerated blueberries lost 11% of their weight during storage. Calcium-impregnated blueberries also showed improved mechanical properties, retained their fresh appearance, and had better retention of nutrients. 3-5 day isochoric treatments led to the best mechanical properties, while 7-day treatments were the most beneficial for nutrient contents and for preventing growth of yeasts and mold. Isochoric impregnation of calcium led to a nearly ten-fold increase in calcium content relative to fresh blueberries, regardless of isochoric treatment time. Together, these results suggest that 3-7 day isochoric calcium impregnation treatments could improve the shelf life of blueberries.

Technical Abstract: Isochoric cold storage (ICS) preserves foods at subfreezing temperatures and high pressures without the formation of ice within the food product. The high pressures generated during ICS can additionally be used to impregnate foods with biologically active substances, such as calcium, which can strengthen the cell walls of plants. In this study, the effect of 1–7 day ICS treatment at -2.0 'C with calcium impregnation was investigated as a means to extend the post-treatment shelf life of blueberries over a five-week storage period at 4 'C. Mass change, water content, soluble solids content, titratable acidity, pH, color, microstructure, texture, nutrient contents, microbial growth, and calcium content were evaluated in ICS-treated, refrigerated, and fresh blueberry samples. ICS with calcium impregnation resulted in no significant mass change or water loss over the five-week storage period, and showed improved mechanical properties, cellular microstructure, and nutrient contents relative to conventional refrigeration over the same storage period. ICS treatments lasting 3–5 days imparted the most improvements to mechanical properties, while 7-day ICS treatments led to the highest nutrient contents. Calcium-impregnated blueberry samples showed a ten-fold increase in calcium concentration versus untreated blueberries and no difference in calcium concentration between 1-day and 7-day ICS treatments, suggesting that quality parameters varying as a function of ICS treatment times only do so as a result of different exposure times to low temperatures and high pressures. Together, these results suggest that 3–7-day ICS treatments with calcium impregnation could substantially extend the shelf life of blueberries.