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A comparison was made on the use of two spectrophotometric methods, the ferric reducing antioxidant power (FRAP) method and the 2,2'-azinobis-3-ethylbenzotiazoline-6-sulfonic acid (ABTS) method, for the measurement of the total antioxidant capacity (TAC) of plant foods. The correlations of TAC measured by the two methods were highly significant in both water-soluble (r2= 0.90) and water-insoluble extracts (r2= 0.98) from 13 strawberry samples. Also a corresponding comparison of TAC in extracts from 14 plant species showed high correlation coefficients, r2= 0.98 for water-soluble extracts and r2= 0.88 for water-insoluble extracts. The ratio of TAC values obtained with the two methods (ABTS/FRAP) varied between 0.7 and 3.3 for different plant extracts indicating that they contained antioxidants with varying reactivity in the two methods. TACs in six pure antioxidant substances were ranked in the following order by both methods: quercetin > ferulic acid > catechin > rutin > caffeic acid > Trolox = chlorogenic acid. The two methods showed similar TAC values for quercetin, rutin, caffeic acid and chlorogenic acid while ferulic acid and catechin gave higher results with the ABTS method than with the FRAP method, and such differences probably explain the varying ratios of ABTS/FRAP obtained in foods. Regarding storage TAC in water-soluble strawberry extracts stored at -20 or -80 degrees C was stable for at least five months while storage at 4 degrees C decreased the TAC value with 40% during five weeks of storage. The study showed that both the ABTS and FRAP methods can be used for convenient monitoring of the antioxidant capacities in fruit and vegetables, and that different antioxidants had varying reactivity in the two methods.

The aim of the study was to investigate whether a supplement of antioxidants to subjects with a high working pace can influence the antioxidant capacity. The study was parallel and double blind with 98 subjects randomised into two groups. One of the groups was given a test drink with antioxidants for 4 weeks (450 ml/day) while the other group took a corresponding amount of placebo drink. The test drink contained: 2 mg beta-carotene/100 ml, 40 mg alpha-tocopherol/100 ml, 80 mg ascorbic acid/100 ml, 2 mg pyridoxine/100 ml, 15 mg magnesium/100 ml, 0.2 mg manganese/100 ml, 1 mg zinc/100 ml, 0.1 mg copper/100 ml and 10 microg selenium/100 ml. Consumption of the test drink for 4 weeks increased the total plasma antioxidant capacity by 7% (ferric reducing ability of plasma method, P<0.05 compared with the placebo group), and the content of selenium and selenoprotein P in serum was raised by 16-17% (P<0.001 compared with the placebo group). No significant changes were found in the placebo group. The test drink also contained Lactobacillus plantarum 299v (5 x 10(7) cfu/ml) and 4 weeks' consumption led to a significant increase of Lb. plantarum 299v in the faeces. In conclusion, consumption of a drink rich in different antioxidants can increase the antioxidant capacity in subjects with a high working pace. This can be valuable since it may increase the protection against reactive oxygen radicals.

A drink based on oats has been developed with new technology. In this study the effects of this oat milk, soya milk and cow's milk on plasma lipid, glucose, insulin, and antioxidant status (measured as the ability of serum to suppress the formation of the radical cation ABTS*+) were compared in 24 healthy men and women. Half of the subjects (group A) consumed 0.75-1 liters/day of oat milk and soya milk for 4 weeks each, and the other half (group B) consumed oat milk and cow's milk for two 4-week periods. In the combined groups A plus B the oat milk regimen resulted in decreased plasma cholesterol (4%) and low-density lipoprotein (LDL) cholesterol (9%) levels as compared with baseline, but no changes in high-density lipoprotein cholesterol (HDL) and triglyceride values were observed. Also soya milk consumption resulted in decreased LDL cholesterol concentrations. The only significant plasma lipid change observed during consumption of cow's milk was an increase in HDL cholesterol. No consistent changes in body weight, fasting blood glucose, serum insulin, and antioxidant status occurred after consumption of any milk regimen. A significant correlation between baseline antioxidant status and total plasma cholesterol was found (r = -0.56). It is proposed that the high content of beta-glucans in oat milk was responsible for the decreased plasma cholesterol and LDL cholesterol concentrations, but the effect could also be due to a replacement of saturated fat in the customary diet by unsaturated fat. It is concluded that oat milk can be used as an alternative to other milk drinks by subjects who would benefit from reduced LDL cholesterol values.