(NaturalNews) Olive and grape extracts derived as byproducts of oil and wine manufacturing proved to be more effective food preservatives than pure antioxidant chemicals in a new study conducted by Portuguese researchers and published in the journal "Innovative Food Science and Emerging Technologies."
"We can assume that the natural extracts grape extract and olive extract are promising natural preservatives, with application in food industry," lead author Ana Teresa Serra said.
Researchers derived the extracts from the residue left behind as a byproduct of pressing grapes for wine and olives for olive
oil. These extracts, along with three
antioxidant chemicals, were tested against three
bacteria species and two yeast species. The bacteria were E. coli, S. Poona, and B. cereus, while the yeasts were S. cerevisiae and C. albicans.
The three
antioxidants tested were quercetin,
hydroxytyrosol and oleuropein.
Of the five substances tested, the grape extract proved most effective. It inhibited growth among all three species of bacteria, with inhibition increasing along with the dose applied. Quercetin also suppressed all three bacteria species, although not as effectively as grape extract.
Olive extract, hydroxytyrosol and oleuropein were less effective still. Olive extract proved more effective against Gram–positive bacteria than Gram-negative bacteria.
Both olive and grape extracts suppressed the yeast species more effectively than
quercetin or hydroxytyrosol at similar concentrations. The suppressing effects of the extracts against the yeasts were also dose-dependent.
While quercetin, hydroxytyrosol and oleuropein are all naturally occurring antioxidants, the higher effectiveness of the extracts suggests that antioxidants are not as effective when isolated from the other plant components they occur with. The researchers hypothesized that the extracts might be more effective because of "a positive synergetic effect within the constituents of grape extract, that reinforce the response and/or, the presence of other components in the matrices with antimicrobial activity."
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