Effect of Thermal and Freeze-Drying on the Volatile Composition of Mountain Horopito (Pseudowintera colorata) and Kawakawa (Piper excelsum).

Mountain horopito (Pseudowintera colorata) and kawakawa (Piper excelsum) are plants endemic to Aotearoa|New Zealand with cultural and medicinal importance for Indigenous Māori. These plants have also become popular in food applications. Drying is an important preservation technique for extending the shelf life of herbs, which alters the volatile composition and aroma of food products. This study evaluates the effects of thermal and freeze-drying on the volatile compound profiles of mountain horopito and kawakawa. Volatile compounds were extracted from both fresh and dried leaves using headspace solid-phase microextraction (HS-SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 105 volatiles were identified in horopito and 102 in kawakawa. Limonene was the most abundant compound in fresh horopito, whereas myristicin was the most abundant in fresh kawakawa. Both thermal and freeze-drying led to large changes in volatile composition, with freeze-dried samples mirroring those of thermally dried leaves rather than those of fresh material. Drying notably reduced key terpenes and alcohols in horopito, such as limonene, α-cubebene, and terpinen-4-ol, likely diminishing "herby," "peppery," "spicy," and "citrus" odor notes. Decreased terpenes and aldehydes in kawakawa, such as limonene and n-hexanal, are likely to lessen "sweet," "floral," and "fruity" odors. The present results highlight that thermal and freeze-drying reduced the abundance of key volatile compounds in horopito and kawakawa compared to fresh samples. These findings provide valuable guidance to the commercial food industry for selecting drying techniques based on desired odor qualities.