"GADF is a good antioxidant which could not only preserve MFM from oxidation during storage but could also produce health benefits for the consumer, thanks to its bioactive compound and DF content," reported Isabel Sánchez-Alonso in the journal Food Chemistry (Vol. 101, pp. 372-378).
Oxidation processes in food can lead to organoleptic deterioration in taste, colour and texture. And fish products are particularly susceptible to oxidation processes because of the high unsaturated lipid content.
The food industry has long been aware of this, and is increasingly seeking natural solutions rather than artificial additives, such as like butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT), to extend the shelf life of milder-tasting products.
The researchers, from the Instituto del Frio (CSIC), looked at using grape antioxidant dietary fibre (GADF) as a natural antioxidant to increase the shelf life of minced fish muscle (MFM). The GADF was obtained from a winery in Spain using a patented procedure (Saura-Calixto and Larrauri, 1997).
Three different concentrations of GADF were used in the tests; zero, two and four per cent. The minced fish meat was subsequently stored at minus 20 degrees Celsius for six months.
Sánchez-Alonso and her colleagues found that the GADF had an extractable polyphenol content of 5.63 grams per 100 grams or dry matter, 53.21 grams of insoluble dietary fibre, and 20.78 grams of soluble dietary fibre per 100 grams of dry matter.
The extract had a relatively high antioxidant activity, with a ferric ion reducing antioxidant power (FRAP) of 525 micromoles of Trolox equivalents per gram.
When added to the minced fish meat and stored the researchers found that the meat with the added GADF had lower concentrations of conjugated hydroperoxides and aldehydes, products formed by oxidation of the lipid content, particularly after three months of storage.
"The rate of inhibition at 90 days of frozen storage was 57.28 per cent for the samples with 2 per cent added fibre and 54.13 per cent for samples with 4 per cent added fibre," said the researchers.
The results also suggest that the nutritional value of the meat could also be boosted by using antioxidant-rich grape pomace (peels and seeds) - a significant number of studies have reported that grape polyphenols such as gallic acid, caffeic acid, catechins, and anthocyanidins have potential benefits for heart health.
"The addition of red grape fibre considerably inhibits oxidation in horse mackerel minced muscle during the first 3 months of frozen storage. These results indicate that GADF could be used as an ingredient to prevent oxidation," concluded Sánchez-Alonso.
"The reason for this effect may be either the chelating action of fibre on some pro-oxidant metals or the action of polyphenols associated with dietary fibre," she said.
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.