Colours and flavours determine the freshness perception of meat products. However, oxidative processes in meat form off-flavours and toxic compounds, change colour, lower shelf-life and cause nutrient and drip losses during storage and distribution. Adding antioxidants may delay or decrease the rate of oxidative processes. Consumers have concerns about the safety of synthetic antioxidants. Hence, researchers compared natural antioxidants and synthetic antioxidants in several studies.
Results are not conclusive; however, several natural sources have been identified as potential alternative to synthetic antioxidants. The effectiveness of natural antioxidants depends on circumstances, such as specific type of meat, type of fat, type of product, pH, processing, other ingredients, package conditions, exposure to oxygen, concentration and more. For example, minced meats are exposed more to air and bacteria than intact muscles due to the larger surface area and therefore develop more rancidity. Therefore, natural antioxidants need to be tested per product to know which antioxidants works for each product. Below, results of two experiments with beef patties are given as an example.
Researchers from Lincoln University in New Zealand added antioxidants on meat during the grinding process of beef patties. They compared the natural antioxidants resveratrol, carnosine, quercetin and rutin. Their results indicated that the antioxidant activity of resveratrol is superior to quercetin, rutin and carnosine. The effect of resveratrol is dependent on concentration and method of application to meat. Carnosine was not effective at normal pH<6 but may have an application in food products in which the pH can be adjusted.
Researchers from China Agricultural University also added antioxidants on meat during the grinding process of beef patties. They compared natural antioxidants vitamin E, carnosine, grape seed and tea catechins compared with the synthetic antioxidant BHA. Addition of all antioxidants inhibited fat oxidation and retarded the formation of metmyoglobin. Metmyoblobin gives the meat the characteristic brown colour occurs as it ages. Carnosine and grape seed extract preserved red colour best. However, fat oxidation was prevented most by the synthetic antioxidant BHA, followed by tea catechins and vitamin E.
The colour of meat is influenced by the form of myoglobin. Myoglobin is a pigment in muscles that contains iron, just like haemoglobin in blood. The purple colour of fresh red meat is a reflection of the dominance of native myoglobin. When oxygen binds to the myoglobin, the meat becomes bright red, which consumers associate with freshness. However, when the meat becomes older, the iron in the myoglobin loses an electron and the meat becomes brown. Free radicals are produced during fat oxidation. They can change myoglobin, which causes discolouration. Some antioxidants preserve the colour because they are free radical scavengers.
Fat oxidation occurs under influence of light, enzymes or by exposure to atmospheric oxygen, named auto-oxidation. Oxidized fats cause the development of rancid flavour. Antioxidants disrupt fat oxidation by scavenging free radical generated during oxidative processes or chelating transit elements that initiate oxidative processes.
“Use specific natural antioxidants for specific purposes”, advices Alaa Bekhit, expert in natural antioxidants from Otago University in New Zealand. “Antioxidants that inhibit fat oxidation maybe cannot stop colour change and those that stop colour change may not be the best ones to stop fat oxidation. Also some natural antioxidants that are obtained from herbs and spices may have strong flavours and this needs to be evaluated for each product.” If you have more questions for Alaa Bekhit, you can fill out the get in touch section below.
This article was adapted from
The effects of natural antioxidants on oxidative processes and metmyoglobin reducing activity in beef patties. 2003. A.E.D. Bekhit, G.H. Geesink, M.A. Iliana, J.D. Morton, R. Bickerstaffe. Food Chem. 81, 175-187.
Effects of natural antioxidants on colour stability, lipid oxidation and metmyoglobon reducing activity in raw beef patties. 2015. Fang Liu, Qian Xu, Ruitong Dai, Yuanying Ni. Acta Sci. Pol. Technol. Aliment. 14(1), 37–44
Read more about the separate antioxidants
Free radicals are produced during fat oxidation. They can oxidise and decompose myoglobin, causing discolouration of meat. Resveratrol is a free radical scavenger, found in certain plants and grapes. Resveratrol was also reported to reducing lipoxygenase to its inactive ferrous form. From the reported work on resveratrol as an inhibitor of lipoxygenase and as a scavenger of free radicals, it is reasonable to hypothesise that applying resveratrol to meat should contribute to maintaining meat colour and extending shelf-life.
Quercetin and rutin
Quercetin and rutin are water-soluble flavonoids, present in many plant foods, that have also been shown to have antioxidant activities. Quercetin and its derivatives have effective antioxidant activity in heme-catalysed systems, and this is attributed to their ability to break the lipid oxidation chain reaction cascade.
Because of its antioxidant properties carnosine has been suggested as a useful natural food antioxidant. However, its antioxidant activity is probably pH-dependent, which limits its potential. Carnosine inhibits the formation of thiobarbituric acid reactive substances in various oxidative model systems, but its antioxidant behaviour depends on the catalyst of oxidation.
Vitamin E and grape seed
Vitamin E, especially in the form of a-tocopherol, is widely used as an antioxidant. It reduces lipid oxidation, drip losses and provides colour stability. Grape seed extracts contain a number of polyphenols including procyanidins and proanthocyanidins and are powerful free radical scavengers. Free radicals catalyse fat oxidation. Researchers tested grape seed in mutton slices, cooked beef, pork patties and burgers).
Tea catechins are polyphenolic antioxidants, which possess a range of health promoting properties. Tea catechins have demonstrated significant antioxidant, anti-carcinogenic, anti-mutagenic properties in numerous human, animal and in vitro studies. Tea polyphenols are metal chelating agents and also act on free radicals, since their benzene rings, inhibit chain reactions during lipid oxidation.
Butylhydroxyanisol (BHA) is a synthetic antioxidant that is often added to foods.