Measuring antioxidant effectiveness

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The makers of a new natural rosemary extract claim that it has superior antioxidative effects when compared to other sources of vitamin E. German firm RAPS GmbH explains the scientific basis for this claim.

RAPS GmbH & Co KG

Evening primrose oil is a high-quality seed oil, extracted from the seeds of Oenothera biennis by means of cold pressing. It is often used in the area of cosmetics and nutraceuticals. An unusually high content of unsaturated fatty acids, mainly gamma linolenic acid, gives evening primrose oil its valuable character and is at the same time responsible for its susceptibility against oxidation.

Refining is one technique that allows for the stabilisation of an oil. However, this process detracts from the oil’s natural characteristics, due to several chemical treatments, while at the same time reducing the desired effectiveness on the skin.

Another possibility for the stabilisation of sensitive oils is the addition of antioxidants. Synthetic antioxidants such as alpha-Tocopherols, BHA or BHT are mainly used. However, the information available to consumers regarding possible undesired side effects caused by the use of synthetic antioxidants has resulted in an increased demand for natural active ingredients made from plant extracts.

A study by RAPS GmbH was set up to show that the company’s natural rosemary extract Stabiloton OS Ultra (Art 39370) is highly effective compared to conventional antioxidants such as Tocopherols, and therefore aids the effective stabilisation of products based on oils and fats.

Method

For the test, cold-pressed evening primrose seed oil is mixed with Stabiloton OS Ultra (approx. 40 per cent carnosic acid), Tocopherol E306 (consisting of a natural mixture of different Tocopherols) and a conventional synthetic Tocopherol (consisting of 100 per cent alpha-Tocopherol). The samples then undergo a Rancimat test compared to a blank sample as standard (Rancimat 743 Metrohm Ltd, Switzerland). The temperature is maintained at 90°C. The air in-flow is maintained at 10ltr/h and the sample size is 3g.

The samples are oxidised by addition of oxygen. The electrical sensitivity and induction time is determined based on the resulting oxidation product.

The shorter the induction time, the faster the oil oxidation. A short induction time when testing a stabilised oil indicates a low antioxidative activity of the applied antioxidant.

Evaluation of the results

The test results are summarised in the following chart:

Induction period (absolute) = Induction time (sample stabilised) – Induction time (sample not stabilised)

Stabiloton OS Ultra

A concentration of 0.015 per cent of Stabiloton OS Ultra results in a comparable absolute induction time as 1 per cent alpha-Tocopherol. With a concentration of 0.03 per cent, the antioxidative effect lies far beyond the 2 per cent concentration of alpha-Tocopherol and is comparable to the concentration of natural Tocophero at 1 per cent.

Stabiloton OS Ultra is therefore approximately 60 times more effective than conventional alpha-Tocopherol.

The high antioxidative properties of the extract are a result of the chemical structure of carnosic acid, the active substance in the Rosemary Extract, which is known for its strong antioxidative effect.

Carnosic acid contained in Stabiloton OS Ultra is a very effective antioxidant, since resulting degradation products of carnosic acid such as carnosol and rosmanol also have antioxidative effects. Like other phenolic antioxidants, the phenolic diterpenes in Stabiloton OS Ultra are also capable of disturbing the lipidoxidation by quickly donating a hydrogen ion to a free lipid radical. As a result, the chain reaction of the oxidation process is interrupted.

Comparison between the antioxidative potentials

The following result can be ascertained from Figure 1: with the same applied concentration of 0.5 per cent, 1.0 per cent and 2.0 per cent, synthetic alpha-Tocopherol shows a shorter absolute induction period than natural Tocopherol. This is illustrated by the lower bars.

A comparison of the absolute induction times shows that the effectiveness of natural Tocopherol is approximately three times higher than conventional alpha-Tocopherol.

The question that arises is, why do two vitamin E products show different antioxidative effects? The answer lies in the chemical structure.

Rosmarinus officinalis L. and its main anti-oxidative components (left to right): Carnosic acid, Carnosol amd Rosmanol

Whilst Tocopherol E306 is a natural mixture of alpha-, beta-, gamma- and delta- Tocopherol, the synthetic vitamin E product consists of 100 per cent alpha-Tocopherol. Numerous scientific studies have already demonstrated that the antioxidative effectiveness of Tocopherol increases in the order from alpha à delta.

The three-times higher antioxidative effectiveness of natural Tocopherol E306 can be ascribed to the unadulterated natural mixture of the different tocopherol in the extract.

Summary: Based on the study carried out in the Rancimat, it can be proven that the purely natural plant extract Stabiloton OS Ultra offered by RAPS GmbH & Co KG provides a higher antioxidative effectiveness.

Alternatively it is possible to use the liquid form of Stabiloton OS Ultra ‘Stabiloton OS Ultra liquid’ (approximately 4 per cent carnosic acid) which enables the stabilisation of liquid formulations based on oils or fats.

For more information contact birgit.volk@raps.de

www.raps-industrieservice.de

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