Food preservation frequently involves a single kill-step followed by isolation of the product within a package, with passive additional effectors or no further treatment. While this has been successful, it also represents an open-loop approach to control food quality, with no option for further active intervention should any undesirable microbial growth occur. Typically, the kill-step has various adverse effects on food quality, thus for the majority of its remaining shelf-life, the food remains at a low-quality level. An alternative vision for the food supply chain of the future is that of a closed-loop food control strategy, wherein the food is minimally processed as an initial stabilization (first kill-step) but the option for processing later as-needed is built into packages, even as late as the retail stage. This may be accomplished by implanting processing means within packages, and including sensors within the package, so that additional intervention steps are possible at the earliest indications of undesirable changes. For this purpose, unpasteurized apple cider (330 ml), packed in sterilized electrode-embedded laminate pouches, was stored at 4°C for 45 days after processed by pasteurization (water-bath; 71.1°C for 3 sec; come-up time: 5 min) and moderate processing (ohmic heating; 25 V/cm; 65°C for 30 sec; come-up time: 3 min) once or with periodic re-processing, by ohmic heating. In a meantime, pH, electrical impedance (Z), cell viability and sensory properties of the individual samples were evaluated. Through the periodic monitoring of viable cell counts, the re-processing was conducted three times (after Day 10, 24, and 42) and resulted in microbial counts maintained lower than 2.1 log CFU/mL over 45 days. Sensory evaluation indicated that, regarding visual and aroma, the juices with re-processing were the most acceptable samples over 45 days, compared to pasteurized and commercial samples. Also, we found that variance (ƒ) of electrical impedance changes (†Z) became low (1.1) as samples were re-processed, while it fluctuated highly (2.2) as spoilage proceeded. Consequently, this technology provides a new approach of processing and quality monitoring and control of liquid foods inside sealed pouches using ohmic heating, while they maintained freshness.
Electrochemical, sensory, and microbiological properties profiling and the potential application of quality trajectory tracking and as-need processing to extend the shelf-life of apple cider during cold storage
Jin Hong Mok
Food, Agricultural and Biological Engineering