Lyophilization and its effects on the essential oil content and composition of herbs and spices - A review

Herbs and spices have a prolonged history of use in culinary purposes, as preservatives and also as pharmaceuticals. Their characteristic flavour and aroma is mainly due to the volatiles accumulated within them. These compounds are very sensitive to different factors (e.g. high temperature, moisture or oxygen), therefore the methods used for preserving herbs and spices can influence not only their healing characteristics but also organoleptic properties and enjoyment value. During the drying process, the temperature of plant parts is increased, which results in the loss of essential oils. Among the artificial drying methods, lyophilization or freeze-drying helps to obtain dried products with good organoleptic properties, as this method uses a low temperature and a shorter processing time. In recent times, lyophilization has become an accepted method for preserving different herbs and spices as it has many advantages compared with other drying and preservation techniques. However, only relatively little and contradictory information is available in relation to the formation of essential oils during freeze-drying. This review aims to summarize the effects of lyophilization on the essential oil content and composition of herbs and spices.