Application of laser and ultrasound as a pre-treatment for drying the leaf of lemon balm

Abstract

Matičnjak (Melissa officinalis L.) je ljekovita i medonosna vrsta, a često se uzgaja i kao ukrasna biljka. Njeni listovi su bogat izvor različitih bioaktivnih spojeva snažnog antioksidacijskog djelovanja. Neinvazivne tehnike kao što su ultrazvuk i laser mogu se učinkovito primijeniti kao predtretmani sušenju. Cilj ovog rada bio je utvrditi mogućnost primjene lasera i ultrazvuka kao predtretmana sušenju lista matičnjaka te utvrditi utjecaj navedenih tretmana na prinos bioaktivnih spojeva u osušenom materijalu. Analizirani su svježi listovi matičnjaka, osušeni listovi konvekcijom bez predtretmana (kontrola) te listovi predtretirani laserom (izlazne snage 100 i 200 mW) i ultrazvukom (35 kHz, 140 W). U pripremljenim uzorcima svježih i osušenih listova provedene su analize osnovnog kemijskog sastava, vitamina C, sadržaja ukupnih klorofila i karotenoida, sadržaja ukupnih fenola (flavonoida i neflavonoida) i antioksidacijskog kapaciteta. Kod kontrolnog uzorka i uzoraka predtretiranih laserom nema značajnijih razlika u brzini otpuštanja vode, dok je značajnije skraćenje vremena sušenja zabilježeno kod uzoraka predtretiranih ultrazvukom. Uspoređujući rezultate uzorka kontrole (bez predtretmana) s rezultatima uzoraka predtretiranih laserom ili ultrazvukom zamijećeno je da je uzorak kontrole imao najmanji sadržaj vitamina C, ukupnih fenola, karotenoida i ukupnih klorofila što dokazuje da su predtretmani utjecali na očuvanje tih bioaktivnih spojeva. Što se tiče antioksidacijskog kapaciteta, najveću vrijednost imao je uzorak predtretiran ultrazvukom na sobnoj temperaturi, a najmanju uzorak predtretiran laserom od 200 mW.Lemon balm (Melissa officinalis L.) is a medicinal and honey species and it is often grown as an ornamental plant. Its leaves are a rich source of various bioactive compounds that have strong antioxidant activity. Non-invasive techniques such as ultrasound and laser can be applied as pre-treatment of drying. The aim of this study was to determine the possibility of using lasers and ultrasound as a pre-treatment for drying the leaf of lemon balm, and to determine the influence of these treatments on the yield of bioactive compounds in the dried material. Fresh leaves of lemon balm, convection-dried leaves without pretreatment (control), laser pretreated leaves (output power 100 and 200 mW) and ultrasound pretreated leaves were used for analyzes. The prepared fresh and dried leaf samples were analyzed for basic chemical constituents, vitamin C, total chlorophyll and carotenoid content, total phenols (flavonoids and nonflavonoids) content and the antioxidant capacity. There was no significant difference in the rate of water release for the control and pretreated laser samples, while a significant reduction in drying time was observed for the pretreated ultrasound samples. Comparing the results of the control sample (without pretreatment) with the results of the samples pretreated with laser or ultrasound, it was observed that the control sample had the lowest content of vitamin C, total phenols, carotenoids and total chlorophylls, which proves that the pretreatments affected on conservation of these bioactive compounds. Regarding on the antioxidant capacity, the highest value had the sample pretreated by ultrasound at room temperature and the lowest sample pretreated with a 200 mW laser