Isochoric Impregnation of Calcium to Extend Postharvest Shelf Life of Blueberries

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- to 7-day ICS treatments at −2 °C with calcium impregnation was investigated as a means to extend the post-treatment shelf life of blueberries over a 5-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 5-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 10-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- to 7-day ICS treatments with calcium impregnation could substantially extend the shelf life of blueberries.