The compounds hexylresorcinol, N-acetylcysteine, and glutathione all reduced the browning of Fuji apple pieces over a 14 day period, with results significantly better than vitamin C (ascorbic acid), according to findings published in the Journal of Food Science .
Tapping into the search for natural ingredients, researchers from the Department of Food Technology at the University of Lleida report that the sulphur-containing compounds may be an interesting alternative to vitamin C-based anti-browning agents, which dominate the commercial market.
"Because the individual effect of ascorbic acid is temporary, other alternatives should be searched to control browning," wrote the researchers.
N-acetylcysteine and glutathione are thiol-containing compounds, while hexylresorcinol is a compound with anaesthetic and antiseptic properties, commonly used as an ingredient in throat lozenges.
"The results obtained corroborated the effectiveness of other natural anti-browning agents over the traditional use of ascorbic acid in the control of the enzymatic browning in the fresh-cut fruit industry," wrote the researchers.
Fresh-cut fruits and vegetables are a rapidly growing segment of the market, and chlorine solutions are widely used by the industry to sanitise and prolong the shelf-life.
But concerns about the potential formation of carcinogens from chlorine usage have prompted some to investigate alternative sources including essential oils and irradiation.
Browning inhibition The main problem facing the fresh-cut products is the loss of water, which promotes the growth of, predominantly, fungi and moulds that lead to spoilage.
As a result, various approaches have been proposed to prolong the shelf-life of these products, including the use of edible films and active packaging.
Another problem is browning, which occurs in the presence of oxygen when the enzyme polyphenol oxidase (PPO) converts phenolic compounds into dark coloured pigments.
The Spanish researchers measured levels of PPO to quantify the anti-browning activity of ascorbic acid, 4-hexylresorcinol, N-acetylcysteine, and glutathione on fresh-cut Fuji apple slices stored at four degrees Celsius for 14 days.
The compounds were studied individually or in combination.
An inhibition of PPO activity was observed when both thiol-containing compounds were used individually, and when N-acetylcysteine was used at a one per cent concentration, the colour of the apples was maintained over 14 days, they report.
"The individual use of ascorbic acid and 4-hexylresorcinol was not an effective antioxidant for fresh-cut Fuji apples, at least in the concentrations used in this study," wrote the authors.
Moreover, combining ascorbic acid with N-acetylcysteine, glutathione, or 4-hexylresorcinol did not improve the results, they said.
"The results obtained with [colour and lightness measures] corroborated the positive effect of N-acetylcysteine as an alternative method in the control of the enzymatic browning as compared with the traditional anti-browning agent, ascorbic acid.
"Nevertheless, it is necessary to evaluate the effect of this anti-browning agent on sensory and nutritional quality attributes to determine not only the quality of fresh-cut Fuji apples but also its acceptance by consumers," they concluded.
Source: Journal of Food Science Published online ahead of print, doi: 10.1111/j.1750-3841.2008.00794.x "Effect of Natural Antibrowning Agents on Color and Related Enzymes in Fresh-Cut Fuji Apples as an Alternative to the Use of Ascorbic Acid" Authors: M.A. Rojas-Grau, R. Soliva-Fortuny, O. Martin-Bellosa