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Experimental design is introduced as a novel procedure to optimise solid-phase microextraction for the determination of orange juice flavour using gas chromatography and mass spectrometry. A central composite design was chosen to study the effects of variation in levels of extraction time (3-15 min), extraction temperature (30-80°C) and pH value (3-11). The models fitted for the prediction of the extraction of terpene flavour compounds (limonene, myrcene, pinene, copaene, caryophyllene), as indicated by r 2 values of more than 0.97. Various surface plots were generated to describe the relationship between operating variables and predicted extraction yields. Optimum conditions with the highest desirability (minimal extraction time, highest yield for all components) were 9 min, 40°C and pH 11.

Aloe vera beverages have to be produced exclusively using material of the plant species Aloe barbadensis MILLER. Commercial material was reported to be frequently adulterated by artificial preservatives or to lack significant amounts of Aloe ingredients. HPTLC and HS-SPME/GC/MS methods to assess the authenticity of Aloe vera beverages were developed in this study, allowing to differentiate between authentic and adulterated products. In one case a commercially available Aloe vera juice could be proven to be exceedingly watered down. Parallel to the authenticity control, the HS-SPME method employed in this work allowed to detect the preservatives benzoic acid, sorbic acid and pHB-esters. In 17 of 24 (71%) currently available Aloe-food products an illegal addition of preservatives of up to 1000 mg/l could be ascertained. The presented analyses of Aloe vera beverages lead to the conclusion, that this product line does not give any cause for hygienic but rather legal concerns: controls have to be intensified to ensure sufficient product quality with regard to preservatives.