The antioxidant activity of aspalathin, the major flavonoid of unfermented rooibos tea, was compared with that of other polyphenols present in rooibos tea, α-tocopherol, BHT, and BHA using the β-carotene bleaching, α,α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging, and automated Rancimat methods. The phenolic compounds include the flavonoids vitexin, rutin, quercetin, luteolin, isoquercitrin, (+)-catechin, and the phenolic acids protocatechuic acid, caffeic acid, p-hydroxybenzoic acid, p-coumaric acid, ferulic acid, syringic acid, and vanillic acid. (+)-Catechin had the longest induction period according to the Rancimat method, while BHT was the most effective inhibitor of β-carotene bleaching. Compounds with the highest degree of DPPH radical scavenging and highest rate of scavenging were caffeic acid and aspalathin, respectively. Aspalathin offered less protection against lipid oxidation than BHT and α-tocopherol according to the Rancimat and β-carotene methods, but it displayed a higher ability to scavenge the DPPH radical. Keywords: Antioxidant; aspalathin; polyphenols; rooibos; Rancimat; β-carotene bleaching; DPPH; BHA; BHT; α-tocopherol

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2~~~ Private Bag X5013Stellenbosch, 7599, Republic of South Afnca ABSTRACT Green bell pepper dices were dipped in two metabisulphite solutions, 2400 and 3600 mg.kg", respectively, and dehydrated. The dehydrated peppers were sealed in laminated pouches of different oxygen and moisture transmission rates, and stored in the dark at 0, 10 and 20C for 12 weeks. Color was evaluated by objective color measurement and a sensory panel during storage. The different packaging materials did not significantly influence color retention, while the SO, treatments showed only limited differences in their effect, but storage temperatures significantly affected visual and objective color. The best correlation between visual color evaluation and the objective color measurements, was obtained for the a* (greenness) measurements. Panelists could discriminate between samples stored at 0 and ZOC in contrast to a* measurements which did not differ significantly. Calculated hue angles exhibited the highest discriminatory ability of any of the objective color parameters.

The antioxidant activity of aqueous extracts of rooibos tea (Aspalathus linearis) as affected by extraction time and additional exposure to heat was determined using the Rancimat and β-carotene bleaching methods. Two fractions of the aqueous extract, consisting of phenolic compounds soluble in ethyl acetate and, after removal of these substances, the remaining polymeric fraction only soluble in water, were analyzed for antioxidant activity. The effect of concentration of the soluble solids of rooibos tea on the oxidation of lard and linoleic acid were assessed by the Rancimat and β-carotene bleaching methods, respectively. Increasing extraction time resulted in increasing induction time for a fixed ratio of soluble solids to lard. Additional heat treatment of tea extracts also increased antioxidant activity according to the Rancimat method, without exhibiting a prooxidative effect at high concentrations. Antioxidant activity of rooibos was demonstrated for both the ethyl acetate soluble phenolic compounds and the highly polymerized polyphenols only soluble in water. Keywords: Antioxidant; rooibos; extraction time; heat treatment; Rancimat; β-carotene bleaching

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