Controlled and modified atmosphere storage of tomatoes

Abstract

From the literature it was concluded that various factors could influence the storage life of tomatoes. These included harvest maturity, storage temperature, storage humidity and the level of gases in the storage atmosphere using modified atmosphere packaging (MAP) and controlled atmosphere storage (CAS). However, what was not clear from the literature was how (many of) these factors interacted and there was little information on the effect at long term MAP or CAS on eating quality of tomatoes. A series of experiments were, therefore, carried out to investigate the above factors. In order to carry out experiments preliminary tests were performed on tomatoes and compared to those given in the literature. These were to establish relevant quality criteria for the fruit in order to judge the comparative effects of the various treatments and included a texture measuring test and minimum criteria for objective colour measurements. Storage humidity was shown to interact with fruit harvest maturity in that ripening time of fruits increased in high humidity levels. The quality of tomatoes harvested at the mature green stage of development and stored in low or medium humidity was approximately the same when they were ripe. However, fruit ripened at high humidity had a significantly better colour, were more acidic and firmer than those ripened at low humidities. Tomatoes harvested at the pink stage of maturity and ripened at low humidity levels were firmer, probably because the time taken to ripen was shorter than those ripened in medium and high humidity. There were interactions between MAP and temperature in that MAP was more effective in delaying ripening at 13°C than at 20°C. MAP interacted also with tomato harvest maturity where it was more effective in delaying ripening of fruit harvested at the mature green stage of maturity. Colour development was affected by storage temperature. In storage at 13°C maximum reddening occurred about 10 days later than in those stored at 20°C. There was an interaction between packaging films and ripening time of fruits. Tomatoes ripened later when they were sealed in films which were less permeable to O2 , CO2 and water vapour than when they were sealed in higher permeable films. Packaging films also affected fruit firmness of tomatoes. All green tomatoes sealed in 25 micron thick polypropylene (PP) film were very firm even after 60 days of storage at 13°C or 20°C, compared to other films. Ripening time and subsequent quality of fruits were influenced by their harvest maturity. Tomatoes harvested at the mature green stage and sealed in 50 micron thick polyethylene (PE50) or PP films had delayed development of the red colour after 30 days of storage and those tomatoes also had the lowest weight loss and the highest soluble solids after 60 days of storage. Storage temperature affected the acidity and total soluble solids (TSS) contents of fruits. These were higher at 13°C than at 20°C for those harvested at either the mature green or pink stage. The CO2 levels affected the colour changes of the tomatoes. The colour of tomatoes harvested at the pink stage of maturity did not change when they were stored in 6.4 % CO2 with 5.5 % O2 and 9.1 % CO2 with 5.5 % O2 even after 50 days and in some cases after 70 days storage. The red colour development of the tomatoes exposed to less than 6.4 % CO2 increased, whereas red colour (Minolta a*.b*-1 values) decreased with CO2 levels above 9.1 % during storage. There were differences in ripening of tomatoes between MAP and CAS where mature green fruits in MAP ripened earlier than the same fruits in CAS. The differences were probably due to ethylene accumulation in MAP which would not occur in CAS because of the continuous gas flushing. It was concluded that with the combination of reduced temperature and MAP or CAS, fruit could be stored for 60 or 70 days and still be marketable in terms of appearance, firmness, flavour and overall acceptability.