Quality Aspects of Modified Atmosphere Packaged Broccoli

Sammanfattning: The modified atmosphere packaging (MAP) of vegetables is used with the aim of prolonging the shelf-life of the packaged produce. The packaging material consists of a permeable film and as a result of the respiration of the produce and gas diffusion through the film, the O2 decreases and the CO2 increases inside the package. This thesis has focused on the MAP of broccoli and the effect of the packaging material on the quality of broccoli. The influence of temperature was also investigated. The quality parameters studied were flavour, aroma, weight, colour and texture. Oriented polypropylene (OPP), polyvinyl chloride (PVC), and two different low-density polyethylene (LDPE) films were used as packaging materials. One of the LDPE packages contained an ethylene-absorbing sachet. In all the studies, significantly different atmospheres developed inside the different packaging materials. At steady state, the O2 levels ranged between 2-18 % while the CO2 concentration was between 4-13 %. MAP was found to significantly affect the investigated quality parameters of the broccoli. Significant differences in the smell and flavour of cooked broccoli were found, depending on the packaging material used to store the raw broccoli. However, no such differences could be found in raw broccoli prior to cooking. A high CO2 level of 10-14 %, in combination with an O2 level of 12-14 % differed significantly from the other material used when raw as well as after heat treatment. The high CO2 level enhanced the sulphur compounds of the broccoli. The different atmospheres were also found to influence the weight, colour, appearance and texture of the raw broccoli. The texture of the broccoli was affected differently, depending on the storage atmosphere, and softening occurred at a CO2 level above 10 % in combination with an O2 level of 12-14 %. The yellowing of the broccoli decreased upon introducing an ethylene- absorbing sachet into the package. It was observed that the quality parameters did not change at the same rate during storage. Thus, the shelf-life of the broccoli was found to be dependent not only on the choice of packaging material, but also on the choice of quality parameter. The shelf-life was prolonged by up to 14 days using MAP. However, the quality parameter limiting the shelf-life differed between the packaging materials. Storage at a combination of 4 and 10 °C for one week was found to affect the aroma production of MAP broccoli differently to storage solely at 10 °C. A change in temperature during storage resulted in the presence of dimethyl sulphide in raw broccoli and an increased amount of methanethiol in cooked broccoli, which could not be found for broccoli stored solely at 10 °C. The altered aroma production resulted in noticeable differences in the smell and flavour of the cooked broccoli. In addition to the quality evaluations, the precooling of broccoli using forced-air cooling was simulated in order to predict the airflow rate and the cooling time of the broccoli. The study showed that the porous media approach to flow could be extended to irregularly shaped produce, i.e. broccoli. However, simulations of the heat transfer of irregular produce were more difficult than for regularly shaped products, e.g. potatoes.