Purpose: This study aimed to optimize the maximum temperature of leafy greens during supply chain taking into account cost of refrigeration, sensory quality parameters (fresh appearance, wilting, browning, and off-odor), and microbial safety of leafy greens using nonlinear programming (NLP).
Methods: The coefficient of performance (COP) was used to determine the cooling costs of refrigeration. The loss of sensory quality parameters (for fresh-cut iceberg and Romaine lettuce and fresh-cut chicory) was expressed using Arrhenius equation, and pathogen growth was represented by a three-phase linear (primary) and square-root (secondary) models. The objective function representing cost was minimized. The nonlinear constraints were growth of pathogens (E. coli O157:H7, Salmonella and L. monocytogenes), and loss of sensory characteristics. An interactive graphical user interface, ‘SHELF’ was developed in the MATLAB (MathWorks, ver. 2013b) software.
Results: For a desired shelf life of 2-3 days, pathogen growth poses a higher concern than loss of sensory quality. However, for longer shelf times it is difficult to maintain sensory qualities. The results vary for different leafy greens. E. coli O157:H7 and Salmonella do not grow at lower temperature, whereas L. monocytogenes is capable of growing at refrigerated temperatures. Browning poses the worst concern for iceberg and Romaine lettuce, whereas off-odor is the biggest concern for fresh-cut chicory.
Significance: The results can inform decisions on the maximum refrigeration temperature for leafy greens along the supply chain.