Increasing the Safety and Storage of Pre-Packed Fresh-Cut Fruits and Vegetables by Supercritical CO2 Process

Abstract

This work presents a feasibility lab-scale study for a new preservation method to inactivate microorganisms and increase the shelf life of pre-packed fresh-cut products. Experiments were conducted on coriander leaves and fresh-cut carrots and coconut. The technology used the combination of hydrostatic pressure (<15 MPa), low temperature (≤45 °C), and CO2 modified atmosphere packaging (MAP). The inactivation was achieved for the naturally present microorganisms (total mesophilic bacteria, yeasts and molds, total coliforms) and inoculated E. coli. Yeasts and molds and coliform were under the detection limit in all the treated samples, while mesophiles were strongly reduced, but below the detection limit only in carrots. Inoculated E. coli strains were completely inactivated (>6.0 log CFU/g) on coconut, while a reduction >4.0 log CFU/g was achieved for carrots and coriander. For all the treated products, the texture was similar to the fresh ones, while a small alteration of color was detected. Microbiological stability was achieved for up to 14 days for both fresh-cut carrots and coconut. Overall, the results are promising for the development of a new mild and innovative food preservation technique for fresh food.

Keywords: carbon dioxide; high pressure; modified atmosphere packaging; ready-to-eat; shelf life.

Figure 1

Microbial counts of total mesophiles, yeasts and molds, total coliforms, and spiked E. coli, measured on coriander (a), carrot (b), and coconut (c), in the untreated samples (), the ones treated directly with high-pressure carbon dioxide (HPCO₂, ) and the ones treated inside the packaging (HPMAP-CO₂, ). Treatment conditions were: 120 bar/40 °C/20 min for carrots, 100 bar/40 °C/1 min for coriander, and 120 bar/45 °C/30 min for coconut. * ND—Not detected. No colonies were found at the lowest dilution possible (<2.0 log CFU/g for yeasts and molds, coliforms, and E. coli, <1.0 log CFU/g for mesophiles).

Figure 2

Microbial counts of total mesophiles, yeasts and molds, and total coliforms, on coriander (a), carrot (b), and coconut (c), in the untreated samples (), the ones treated inside the packaging with air (HPMAP-air, ), the ones packaged in CO₂ and maintained at the processing temperature and time (TMAP-CO₂, ), and the ones treated inside the packaging in CO₂ (HPMAP-CO₂, ). Treatment conditions were: 120 bar/40 °C/20 min for carrot, 100 bar/40 °C/1 min for coriander, and 120 bar/45 °C/30 min for coconut. Means with different small superscript letters in the same group of microorganisms are significantly different (p < 0.05). * ND—Not detected. No colonies were found at the lowest dilution possible (<2.0 log CFU/g for yeasts and molds, coliforms, and E. coli, <1.0 log CFU/g for mesophiles).

Figure 3

Fresh-cut carrot microbial levels of total mesophiles (a), yeasts and molds (b), and total coliforms (c), and gas composition (d), in the control packaged in air (MAP-air) (), control packaged in CO₂ (MAP-CO₂) (), and the treated packaged in CO₂ (HPMAP-CO₂) (), during a shelf-life trial at 4 °C. Treatment conditions were 120 bar—40 °C—20 min. Points with different small letters at the same time point represent significantly different values (p < 0.05). * ND—Not detected. No colonies were found at the lowest dilution possible (< 1.0 log CFU/g).

Figure 4

Fresh-cut coconut microbial levels of total mesophiles (a), yeasts and molds (b), and total coliforms (c), and gas composition (d), in the control packaged in air (MAP-air) (), control packaged in CO₂ (MAP-CO₂) (), and the treated packaged in CO₂ (HPMAP-CO₂) (), during a shelf-life trial at 4 °C. Treatment conditions were 120 bar—45 °C—30 min. Points with different small letters at the same time point represent significantly different values (p < 0.05). * ND – Not detected. No colonies were found at the lowest dilution possible (<1.0 log CFU/g) in at least one repetition.