Microbial growth in fresh-cut lettuce can increase when wound-induced phenolic accumulation is suppressed
Margarita Barros and Mikal E. Saltveit
Abstracts Book, 6th International Postharvest symposium, 8-12 April 2009, Antalya, Turkey. 256 pages.
2009
บทคัดย่อ
Wounding lettuce (Lactuca sativa L. longifolia)leaves stimulates the increased synthesis and accumulation of phenolic compounds. Chlorogenic acid accumulates in excised lettuce leaf tissue held at 10°C for 2 days. The growth of five lettuce pathogens on TSA (Tryptic Soy Agar) media was not markedly reduced when it contained concentrations of chlorogenic acid that accumulated in wounded lettuce. Growth of Erwinia carotovora and Pseudomona fluorescens was stimulated when prepared with TSA media containing homogenized non-wounded lettuce mid-rib tissue, while the increase was much less when the media was prepared with 5-mm thick mid-rib tissue segments that were held for 2 days at 10°C after excision. Inhibiting the wound-induced increase in phenolic content in 2-day-old lettuce with prior 1-hexanol or heat-shock treatments allowed significantly greater growth of Erwinia carotovora compared to growth on media prepared with non-treated tissue. Neither the hexanol or heat-shock treatment made the excised lettuce tissue a better substrate for microbial growth. Rather, it appears that treatments that suppress wound-induced increases in phenolic compounds reduce the ability of excised lettuce tissue to suppress the growth of lettuce pathogens through the induced production of anti-microbial phenolic compounds.