# Compositional Analysis and Aroma Evaluation of Feijoa Essential Oils from New Zealand
## 1 Introduction  
Essential oils are aromatic volatile liquids which can be extracted from various plant materials, including flowers, leaves, herbs, and fruits. The history of essential oil extraction and application can be traced back to the Middle Ages [1]. Due to the extremely low extraction yield, essential oils are often deemed as 'liquid gold'.  
Plant derived essential oils have been widely applied in the food, perfume, pharmaceutical, and aromatherapy industries [1; 2; 3; 4]. For instance, essential oils from oregano, cinnamon, thyme, and rosemary are employed in food packaging to extend shelf life [5; 6; 7; 8], launder essential oils are famous for their relaxing effects [9; 10], and citrus essential oils are reported to have antimicrobial, antioxidant, anti-inflammatory, and anti-cancer properties [11; 12; 13; 14]. Particularly in the flavor and fragrance industries, compared with artificial compounds, natural essential oils could be a safer choice for food flavoring and hygiene products.  
Feijoa (_Acca sellowiana_ ([PERSON]) is a subtropical fruit with intense aroma. It was originally discovered in South America [15] and is now widely grown in New Zealand. The fruit has a green skin and a jelly pulp with a sweet-sour taste. The unique aroma/flavor of feijoa fruit is one of its most characteristic features and is believed to contribute greatly to its increasing consumption. However, very limited research has focused on volatile compounds in feijoa fruit and feijoa essential oil and the aromatic properties of feijoa have not been thoroughly reported. [PERSON] and [PERSON] [16] are among the earliest researchers of feijoa volatiles and they found that methyl benzoate and ethyl benzoate were dominant aroma active volatile compounds, accounting for over 90% of the total feijoa volatile oil. Despite this early publication, to date, fewer than five published works have mentioned the extraction and component analysis of feijoa essential oil and the aroma active compounds largely remain unknown.  
Cultivar variation exists in many well-known fruits, such as apple [17], grape [18], and strawberry [19]. Cultivar may affect fruit size, color, texture, aroma, flavor, and nutritional and bioactive compound composition. Feijoa cultivars can be roughly divided according to their ripening season. Previous studies have reported the diversity of the compound composition as well as the aroma experience in the essential oils from different plant cultivars [20; 21]. In addition, the components of essential oils could also serve as biomarkers for the identification of different cultivars [22]. Therefore, a systematic comparison of the compound composition and aroma profile of essential oils from different feijoa cultivars could be vital in feijoa cultivar selection and differentiation.  
In this study, four feijoa cultivars, namely Unique (early season cultivar), Apollo (early to mid-season cultivar), Wiki Tu (mid to late season cultivar), and Opal Star (late season cultivar), were carefully selected following suggestions from local growers. This is the first report that optimized the extraction method, investigated the aroma active compounds, and established the aroma profile of feijoa essential oils, with a comparison of four New Zealand grown cultivars. Moreover, the peel of feijoa fruits is normally a waste material from the juicing industry and when consumed as a fresh fruit. Obtaining highly valuable essential oils from waste materials could therefore provide additional value to the feijoa industry.