Microbiological Design and Validation of Thermal and High Pressure Processing of Acidifield Carrots and Assessment of Product Quality

Abstract

Modification of pH and combined use of novel processing methods may be a good strategy to improve the quality of canned vegetables. In this study, selected thermal (TP) and high pressure-assisted thermal (HP-T) processing methods were validated for citric acid-infused carrots (pH≤4.5) using Bacillus licheniformis spores. Previously established thermal inactivation kinetics data were used to setup the target process times (to achieve 7-log kill ofB. licheniformis). The microbial spores were inoculated at the center of simulated carrot alginate beads and subjected to different processing methods. Delivered process lethalities, evaluated by the microbial count/re-count method and measured time–temperature data, were equal to or higher than the targeted values. No survivors were found after the treatments, demonstrating the adequacy of the processes. Texture, color and β-carotene retention in processed carrots, evaluated and compared with those processed under conventional canning, showed higher texture retention (P<0.05) in the modified processing methods. Residual hardness values of carrots were 86% with HP-T, 70% with ohmic heating and 8% with conventionally canned product. The same trend was observed with chewiness value. However, processing methods showed no differences (P>0.05) with respect to color change. In terms of β-carotene, carrots subjected to a relatively more severe heat treatment (water immersion mode in static retort) showed better β-carotene extractability than samples from HP-