Study shows plant extracts could be potent antibacterials

Researchers based at two universities in Taiwan said their study was triggered by food safety concerns following a number of foodborne disease outbreaks in Taiwan related to bacteria such as Salmonella typhimurium​ DT104, Escherichia coli​ O157:H7, Listeria monocytogenes​, Staphylococcus aureus​ and Bacillus cereus. ​​

The objective of the study, said the scientists, was to determine whether the aqueous and ethanol extracts of the plant Roselle calyx could exhibit antibacterial protection against the five bacteria (listed above) at higher temperatures; it the extracts proved effective, they could be useful in a wide variety of food systems.

“Roselle calyx is an edible plant; thus, both aqueous and ethanol extracts should be safe when they are used for food systems to prevent bacterial contamination,”​ claim the authors.

Method​​

The researchers said they examined the antibacterial effects of the extracts coupled with protocatechuic acid against the five bacteria in ground beef and apple juice. ​

The test spoilage bacteria were recovered from contaminated beef, chicken, milk, or seafood from March 2007 to June 2007 by using a surface swab technique, according to the authors of the study.

Roselle calyx extracts or protocatechuic acid at 5 or 10 mg was mixed with 100g of ground beef or 100mL of apple juice, while a control group was also set up that contained neither roselle calyx extracts nor protocatechuic acid.

And one millilitre of each test bacterial culture was added into beef and apple juice previously treated with or without roselle calyx extracts or protocatechuic acid.

Outcome ​

The results showed that the antibacterial effects of roselle calyx ethanol extract and protocatechuic acid were dose dependent and heat resistant.

The scientists maintain that after three days storage at 25°C, the addition of roselle calyx extracts and protocatechuic acid exhibited dose-dependent inhibitory effects against test bacteria in ground beef and apple juice, in which the roselle calyx ethanol extract showed greater antibacterial effects than the aqueous extract.

And, according to the findings, the antibacterial activity of roselle calyx ethanol extract and protocatechuic acid was not affected by heat treatments from 25°C to 75°C and 25°C to 100°C, respectively.

The authors concluded that the results indicate that roselle calyx extracts can be considered as effective agents for beef, apple juice or other foods to prevent contamination from bacteria such as Salmonella ​and E. coli.​​

Source: Foodborne Pathogens and Disease​Published online ahead of print: DOI: 10.1089/fpd.2008.0187Title: Antibacterial Effects of ​Roselle​ Calyx Extracts and Protocatechuic Acid in Ground Beef and Apple Juice​Authors: C. Chao; M. Yin.