The researchers, as part of the EC CRAFT project FAIR 98-9517, looked at the practical, economic, and industrial viability of waste products from juice production, waste from the canning industry, or remains from harvesting for 11 different fruits and vegetables.
Initial screening of red beet, apple, strawberry and pear residues from juice production; tomato, artichoke and asparagus from the canning industry; chicory, endive, cucumber and broccoli remains from harvesting; and golden rod herb and woad herb extracts showed that all of the wastes yielded polyphenols.
The scientists noted that the high water content of the fresh by-products needed a cost-intensive drying process, and proposed that drying should be performed immediately and close to the production site.
The best yields were obtained with polar solvents like water and methanol, with highest phenolics content found in golden rod (181 milligrams of gallic acid equivalents per gram of dry extract), red beet (150 mg GAE per g), asparagus (113 mg GAE per g), artichoke (102 mg GAE per g), and apple (52 mg GAE per g).
"Some by-products with remarkable phenolics yield were regarded as too expensive or of little promise for the market, as for instance red beet, asparagus, or woad," wrote lead author Wieland Peschel from Pharmaplant Arznei- und Gewurzpflazen Forshungs- und Saatzucht GmbH, Germany.
After initial screening the research team continued the study to look at both other extraction methods (supercritical fluid extraction) and also to scale up extraction to pilot plant scale for golden rod, artichoke and apple wastes.
The researchers found that both the golden rod and artichoke had high radical scavenging in most of the tests used, although the apple extract yield was higher (30 per cent of the raw dry material) and had high efficiency in two of the antioxidant tests.
Evaluation of the extracts for their suitability in crème formulations involved sensory analysis of odour, colour, homogeneity, and handling. Tests were also performed to investigate stability and antioxidant effect in a water-oil formulation with five per cent primrose oil as the instable lipid part.
"In two formulations, water in oil and oil in water emulsion, the golden rod extract was easily mixable and dispersible up to concentrations of three per cent. In contrast, both the apple and artichoke extracts were hard to homogenise," reported Peschel.
The crème formulations were left for five months to test their stability to oxidising conditions. For the oil in water formulation both the apple and artichoke extracts performed better than the Controx reference.
For the water in oil formulations, the scientists reported no difference between the plant extracts and the cream preserved by BHT (butylhydroxytoluene).
Although the researchers called for further tests, Peschel said: "The partial substitution of synthetic or expensive established plant antioxidants could be successful, when upper concentration limits are defined with regard to galenic stability and skin irritation, and lower limits with regard to the preservative effect."
The research, involving scientists from the University of Barcelona and companies such as Nuth-Chemie, Euromed, RAPS, Kuhs, and Becker, was published in the journal Food Chemistry (Vol. 97, pp. 137-150).