Current antioxidants used in the food industry include butylated-hydroxyanisole (BHA), and butylated-hydroxytoluene (BHT). Some studies have suggested that synthetic antioxidants may be toxins or carcinogens, prompting interest in natural antioxidants.
Citrus peel, a major by product from juice production, is known to be rich in polyphenols, potent antioxidants. Korea annually produces about 40,000 tons of citrus peel by-products, making it a cheap and readily available source of antioxidants.
Researchers from Kyunpook National University, Korea, and Bhabha Atomic Research Centre, India, prepared citrus peel powder by finely grinding the frozen peels and extracting with 70 per cent ethanol. The powder was then irradiated to eliminate microorganisms. Previous studies by the same groups have shown that irradiation at 20kGy was optimum for sterilization without changing the physiological activities.
The powder was characterized in terms of phenolic content, and antioxidant activity against DPPH radicals, beta-caroten bleeching, and nitrite scavenging.
To measure the antioxidant activity during meat storage, the researchers studied the inhibition of lipid oxidation in salmon meat. Being a fatty fish, salmon is highly susceptible to oxidative deterioration due to its high polyunsaturated fatty acid (PUFA) content.
By measuring the secondary product of lipid oxidation, 2-thiobarbituric acid reactive substances (TBARS), the researchers could monitor antioxidative effects of the citrus peel.
"Samples containing the aqueous solution of citrus peel powder gave significant protection to lipid oxidation as indicated by the lower TBARS value," said lead-author H.J. Kang in Bioresource Technology (Vol. 97, pp. 614-620).
Although no comparison was made between the citrus peel extract and the commonly used synthetic alternative, the authors argue that more citrus peel powder could be added than the synthetic alternatives.
"The use of natural extracts as food additives can be advantageous, as it is well-known that maximum lawful levels of synthetic anti-oxidants are established from different toxicological parameters that do not apply to naturally occurring compounds," said Kang.
"These findings propose that natural antioxidant powder could be prepared from citrus peels," concluded the scientists.
BHT has been shrouded in controversy after several studies claimed it was mutagenic or carcinogenic. It has been banned as a food additive in the Japan, UK, Sweden, and Australia. The US has banned its use in infant foods.