The scientists, from the Food Science Department at University College Dublin (UCD), report that a brined onion extract significantly reduced lipid oxidation in turkey rolls over seven days of storage, relative to controls, and was seen to improve flavour when tasted by 30 volunteer tasters.
"While the production of an antioxidant effect by the flavonoid components of the added onion juice was obviously a positive effect, the broader influence of the juice on the overall sensory quality of the cooked turkey breast may well be of greater importance in terms of its potential to yield a commercial product with superior shelf life and improved sensory attributes," wrote the researchers in the journal Food Chemistry.
Interest is growing in plant-derived food additives as replacements to synthetic antioxidants like butylhydroxyanisole (BHA) and butylhydroxytoluene (BHT) to slow down the oxidative deterioration of food.
Indeed, according to a 2003 report by Frost and Sullivan, the synthetic antioxidant market is in decline, while natural antioxidants, such as herb extracts (particularly rosemary), tocopherols (vitamin E) and ascorbates (vitamin C) are growing, pushed by easier consumer acceptance and legal requirements for market access.
"The overall aim of the present study was to evaluate the feasibility of producing a premium quality turkey breast roll product incorporating a purely natural flavour-preserving/enhancing ingredient," said the researchers.
But while interest in natural sources is increasing, the authors of the new study, Xueyan Tang and Denis Cronin, report that, despite limited research into the applicability of onion extracts, the results appear to show that the use of the onion extract was feasible.
"Flavour in cooked meats is a key attribute of quality and its retention during storage is of considerable importance to producers of commercially prepared meat products," explained the UCD researchers.
"However, without protection, the flavour of cooked meats deteriorates quite rapidly during storage or on reheating due to a process of free radical-induced oxidation of intramuscular membrane phospholipids, which contain relatively high levels of polyunsaturated fatty acids," they said.
Tang and Cronin prepared brined onion extract and then tumbled the turkey breast meat in the liquid, and then packed into plastic casings and sealed. They prepared three turkey breast products by adding 10 per cent brine (control product), 25 per cent brined onion extract (O25), or a 50 per cent brined onion extract (O50).
Using the thiobarbituric acid (TBA) assay to measure lipid oxidation, the researchers report that the 50 per cent onion extract reduced oxidation of the fat in the meat by about 25 per cent, compared to controls.
The quercetin content, the main onion antioxidant, was found to decrease by an initial 65 per cent in freshly cooked rolls (one kg) compared with raw rolls but then did not change significantly further during storage.
While the onion extract was not found to have an effect on the colour of the meat, a 30-member untrained sensory panel were found to express a preference for the onion extract product when four millimetre thick meat slices were stored in air for an further 24 hours.
"The onion juice probably exerts its beneficial effect by a combination of its antioxidant properties and a masking of off flavours in the meat by certain cooked onion flavour compounds which are compatible with cooked turkey flavour," suggested the researchers.
"The results of the present study suggest that the incorporation of onion juice during the preparation of encased turkey breast rolls leads to the production of a premium quality product possessing improved flavour quality and stability in sliced form," they said.
Source: Food Chemistry Volume 100, Issue 2, Pages 712-718 "The effects of brined onion extracts on lipid oxidation and sensory quality in refrigerated cooked turkey breast rolls during storage" Authors: X. Tang and D.A. Cronin