Aqueous extracts of Hibiscus sabdariffa as antimicrobials in foods

Hibiscus sabdariffa L. is a tropical shrub species cultivated in multiple countries and is mainly produced for its red calyces that are used for a tea beverage. Aqueous, lyophilized extracts of Hibiscus were examined for their chemical composition and antimicrobial activity against Escherichia coli O157:H7, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and Listeria monocytogenes.

Lyophilized, dialyzed extracts of commercially aquired calyces were examined in microbiological medium and milk at various fat levels for antimicrobial activity against E. coli O157:H7 and S.aureus. Extracts were either filtered or autoclaved to sterilize and tested in microbiological medium. Autoclaved extracts were more effective in microbiological medium and were subsequently tested in ultrahigh temperature-processed (UHT) milk with various fat percentages. E. coli O157:H7 was inactivated after 96 h using 60 mg/ml extracts in all milk fat levels while S. aureus was inactivated after 168 h using 40 mg/ml extracts in both skim and whole milk.

Lyophilized, undialyzed extracts were tested as an antimicrobial rinse on hot dogs against L. monocytogenes and MRSA. Inoculated hot dogs were rinsed with autoclaved extracts (0, 120 and 240 mg/ml) for 5, 15, 30, or 60 min and stored for 0 or 24 h. Reductions of ca. 3.7 log CFU/g and 5.5 log CFU/g were observed for L. monocytogenes and MRSA respectively when rinsed in extracts at 240 mg/ml for 60 min and after 24 h.

Extracts produced from commercial brands were compared to greenhouse grown varieties of Hibiscus. Anthocyanin and phenolic contents were determined to compare chemical profiles. Extracts at 60 mg/ml were adjusted to pH 7, autoclaved, and antimicrobial activity was determined against S. aureus ATCC 27708. Growth of S. aureus was inhibited when grown in the presence of extracts at 60 mg/ml at pH 7. Phenolic content remained similar after autoclaving; however autoclaved extracts had less anthocyanin content than filtered extracts.

H. sabdariffa extracts were effective against foodborne pathogens in a microbiological media and in two food systems, UHT milk and as an antimicrobial rinse on hot dogs. Hibiscus extracts have the potential to be a natural alternative to antimicrobials currently used in foods.