The use of natural alternatives to synthetic preservatives such as like butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT) to slow down the oxidative deterioration of food is gaining interest.
According to a 2003 report by Frost and Sullivan, the synthetic antioxidant market is in decline, while natural antioxidants, such as herb extracts, tocopherols (vitamin E) and ascorbates (vitamin C) are growing, pushed by easier consumer acceptance and legal requirements for market access.
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.
The study focussed on two important aspects for the extracts: Firstly, the general potential of the plant waste extracts as antioxidants compared to established ones, and, secondly, if the research could lead to practical and economic applications.
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 wastes yielded polyphenols.
The scientists noted that the high water content of the fresh byproducts needed a cost-intensive drying process. The best yields were obtained with polar solvents like water and methanol, with highest phenolics content found in golden rod, red beet, asparagus, woad, artichoke, strawberry and apple.
"Some byproducts 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 economically based exclusion of some active extracts at an early stage of screening might be different when other companies pursue other product sectors and efficiency limits differ," said Peschel.
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.
When compared to the commercially available synthetic antioxidant BHT, the three chosen extracts did not perform as efficiently in all of the tests used, although both the golden rod extract and the apple extracts did perform better in the DPPH free radical scavenging test.
It was also reported that the pilot plant extracts could be enriched by purification. For example, the artichoke extract yield was increased from 145 mg per g of dry extract to 193 mg per g dry extract.
The possibilities and advantages of using these natural antioxidants could offer important opportunities for food preservative producers.
The researchers highlighted the apple extract of particular interest, but cautioned: "Such substantial changes in the production chain would require a guaranteed demand for high amounts of byproduct to be processed for phenol extraction."
"Following the strategy of lower total antioxidant concentrations and higher consumer acceptance an extended pool of non-toxic natural antioxidants would be available even if the price of the extracts is still higher than that of ascorbic acid derivatives, modified tocopherol products or BHT," concluded Peschel.
Antioxidant revenues are predicted to grow from 46m ($55m) in 2004 to 58m ($70m) in 2008, according to Frost and Sullivan.
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).