Magnetic field hydrocooling system: Effect of field intensities on the cooling characteristics of three different leavy vegetables

The physiological changes occurring during postharvest of leafy vegetables affect quality. To address this, several cooling technologies that utilize physical fields like magnetic fields (MFs) have been proposed. The application of MFs in the cooling of leafy vegetables however remains a substantial controversy among the food engineers. Therefore, the effectiveness should be clarified by experiments. In the current study, the effect of MFs (at 534.1 mT, 458.0 mT, and 396.8 mT) on hydrocooling process of three different leafy vegetables including jute mallow, fluted pumpkin, and bitter leaf was investigated by using a specially designed hydrocooling system facilitated with magnetic field (also known as magnetic field hydrocooling; MFHC) generated from a Neodymium perma-nent magnet. The investigation included the comparison of the cooling curves, physiological loss in weight (PLW), microbial loads, and observation of microstructures. Based on the results of the experiment, it was observed that the weak magnetic fields provided significant improvement on the hydrocooling technique as well as the quality of hydrocooled vegetables. The MFHC assisted by Neodymium magnet (at 396.8 mT) provided higher cooling rate (at P <= 0.05) when compared with conventional room cooling, reduced microbial loads significantly from 8.40 x 105 to 5.86 x 105 CFU/ml, 7.03 x 105 to 5.89 x 105 CFU/ml and 6.00 x 105 to 4.0 x 105 CFU/ml (at P <= 0.05) for jute mallow, fluted pumpkin and bitter leaf respectively. In addition, hydrocooling-assisted by magnetic field (at 396.8 mT) is more effective in the preservation of the microstructures. The study indicates that the MFHC technology enhances cooling process and preserves the leafy vegetables, thus pose great potential in the food industry.Practical applications: Leafy vegetables deteriorate faster after harvest; hence, there is a need to cool them in order to extend their shelf-life. MFHC technique has great potentials in preservation of leaves, with the advantage of minimum quality loss due to reduction in cooling time and microbial activities. Currently, innovative studies have been carried out on the use of MFHC technique to improve the cooling process and achieve better quality preservation. However, the findings presented in this work can provide detail insights on the quality of some leafy vegetables that were cooled by MFHC, and give some guidance for further developments of MFHC technology.