Effect of hot air and freeze drying on the volatile compounds of dill (Anethum graveolens L.) herb

Rainer Huopalahti,Eila Kesälahti,Reino Linko

doi:10.23986/afsci.72194

Abstract

Volatile compounds of fresh, hot air dried and freeze dried dill (Anethum graveolens L.) herb were studied by gas chromatography-mass spectrometry. Of the 25 volatile components identified, 16 the most abundant compounds were analysed quantitatively. The major primary aroma compounds were α-phellandrene, 3,6-dimethyl-2,3,3a,4,5,7a-hexahydrobenzofuran,β-phellandrene, limonene, α-pinene, p-cymene and myristicin. Severe loss of these components occured during the drying of dill. E.g. the retention of the benzofuranoid, the most important aroma component of the dill herb, was from trace to 1.3 % in hot air dried samples and 3.5—20 % in freeze dried samples. During the drying secondary aroma compounds are formed consisting over 50 % of the total volatiles. Among these phytadienes, especially neophytadiene, were the major components. The best result was obtained by freeze drying, but the product contained only one quarter of the total aroma compounds of the fresh dill herb.

Highlights

Dill is used in Finland and in other Scandinavian countries mainly as fresh aerial part of the plant before the bud formation or at the flowering stage as well as in smaller amounts as frozen or dried chopped dill leaves.The composition and content of aroma compounds in the fresh dill herb have been studied by Huopalahti et al (1981), Schreier et al (1981), Huopalahti and Linko (1983), and Huopalahti (1985 a,b).it is well known that the quality of dill undergoes great changes during processing and subsequent storage
A decrease in the total aroma content was observed in frozen dill, already after about two months storage at —2O°C depending on the packaging material (Huopalahti, 1985 c)
In the present study the dill herb was dried in hot air at three different temperatures to reach an average moisture content of about 11 % (Table 1)

Summary

Introduction

Dill is used in Finland and in other Scandinavian countries mainly as fresh aerial part of the plant before the bud formation or at the flowering stage (dill herb) as well as in smaller amounts as frozen or dried chopped dill leaves. The composition and content of aroma compounds in the fresh dill herb have been studied by Huopalahti et al (1981), Schreier et al (1981), Huopalahti and Linko (1983), and Huopalahti (1985 a,b). The dill was harvested before the bud formation and dried with hot air (by fan) or freeze dried Both apparatus were conventional systems in the laboratory scale. Fresh or dried dill samples were chopped by cutting before analyses, which were carried out immediately after harvesting or within a few days storage after processing and packaging

Gas chromatographic and mass spectrometric analyses

Isolation of volatile compounds

Results and discussion

Freeze dried