Microbial and endogenous polygalacturonase activity in broccoli during storage

Broccoli florets were cut into 3 to 10 g and, washed in a 200 ppm chlorine solution or left unwashed. The florets were packaged and stored at 7 and 13°C for a 16- d period. The initial washing reduced the microbial counts by 2 log CFU/g on the florets. After 16-d storage at 7 and 13°C, there were significant differences in microbial counts between washed and unwashed broccoli (P>0.05). There was a greater increase in microbial counts on broccoli stored at 13° C, 3.5 log CFU/g, than on broccoli stored at 7°C, 2.5 log CFU/g. Temperature had more effect on controlling microbial growth over the 16-d period than washing the broccoli. Endogenous polygalacturonase (PG) activity in the broccoli did not increase during16-d storage at 7, or 12-d storage at 13° C. However, PG increased for the broccoli stored 16-d at 13° C (P<0.05).

Endogenous PG activity of broccoli florets stored at 13°C did not increase during an 8-d storage period. Internal broccoli tissue did not soften for the 8-d period (P>0.05). A method for measuring enzyme activity due to PG produced by spoilage microorganisms was developed. Total PG activity levels increased during 8-d storage indicating increased microbial activity.

Broccoli cores softened after 4-d storage at 13°C in broccoli medium that was inoculated with indigenous broccoli aerobic spoilage microorganisms. At that time, aerobic microbial counts in the medium were 7.5 log CFU/g. Broccoli cores stored in sterile broccoli medium did not soften after 4-d. This would indicate that PG produced by the high level of microorganisms has a softening effect on the broccoli texture.