Fresh products eaten raw and minimally processed are important components of a daily diet. However, raw vegetables can harbour many microorganisms, which may be spread during washing, cutting or peeling prior to the commercial distribution. The microbial growth increases during storage. Microorganisms are the cause of food decay and reduce shelf life of fresh-cut vegetables, and potentially may be a source of foodborne illness. Polish scientists, within European Project Quafety, have found that various vegetables are more or less predisposed for fresh cut market because of strong differences in microbial development depending on processing and storage conditions. The growth of several groups of microorganisms in fresh-cut Chinese cabbage, rocket and melon stored at different temperature regimes were investigated.
The samples of cabbage or melon were cut into small pieces. Half of them was washed in tap water. Fresh rocket leaves were not washed or washed in the water. Then, plant material was packed into polystyrene foam trays and put in plastic containers lined with polyethylene film. Fresh, unprocessed and unwashed samples were used as control.
Cabbage was stored at 18-20°C for 3 days, at 0°C and at 5°C for 7 days.
Rocket was stored at 18-20°C for 4 days, at 1°C and at 5°C for 10 days.
Melon was stored at 18-20°C for 2 days, at 0°C and at 5°C for 5 days.
Microbial analyses consist in the count of mesophilic bacteria, coliforms, Escherichia coli, moulds and yeasts.
In all experiments, cutting and washing operations did not affect the number of microorganisms before storage.
Washing did not reduced the density of microbial cells on plants; however, washing and cutting operations caused significant increase of microorganisms during storage.
The highest growth of bacteria and moulds and yeasts was detected in melon. The number of mesophilic bacteria increased thousands fold, especially in cut and washed samples, in all storage conditions tested. The same was noticed for yeasts. It indicated that melons are not appropriate fruits to prepare as fresh-cut product, because the rapid growth of microorganisms in this material may cause quick food decay and reduced safety of such product.
In the case of rocket, the number of microorganisms increased significantly at all storage temperatures tested. It resulted very variable in terms of microbial groups detected suggesting that rocket is not stabile. Moreover, storing the leaves for longer time, even at low temperatures, caused high growth of coliforms.
The most predisposed for the market as ready-to-eat product seems to be Chinese cabbage. For this vegetable cutting of the leaves was the main factor stimulating microbial growth but lower temperatures (1 – 5 oC) restrained this process, and especially yeasts and coliforms development.
In all experiments and in all vegetable species E. coli was not detected.
For further info contact:
Magdalena Szczech
Research Institute of Horticulture
Skierniewice, Poland
Email: magdalena.szczech@inhort.pl