## 1 Introduction  
Asparagus (_Asparagus officinalis_) is a perennial crop, where the spears (shoots) can be eaten as a nutritious vegetable. It has two main types: green and white which can be derived from the same variety, depending on the cultivation method. Green asparagus is harvested above-ground, while white asparagus grows fully immersed in soil wherein it is also harvested [1]. The key difference in cultivation relates to growth with or without sunlight. Green asparagus is, by far, the most widely grown whereas white asparagus is more country-specific. In Europe, for example, green asparagus is more commonly grown and consumed in, e.g., the UK and Spain while white asparagus is more popular in, e.g., Germany and The Netherlands. In some countries, consumers speak about \"asparagus\" without distinguishing the type as they are unaware of the white alternative [1]. For cultivating asparagus, the crowns should be planted such that they are ca. 40 cm deep. For green asparagus, once the shoots start to grow, they emerge above the soil, are exposed to sunlight, and elongate further. For white asparagus, ridges are made using an extra ca. 20 cm of topsoil and the shoots are harvested while still beneath the soil as they must remain in the dark [1]. Exposure to light not only induces the synthesis of pigments such as chlorophyll and anthocyanins, but also strongly determines spear morphology (Figure 1a). Green asparagus bears bear more prominent cladodes (leaf-like organs) (Figure 1b). Furthermore, white spears are generally significantly thicker, as in darkness, cells from the primary thickening meristem proliferate both periclinally and anticlinally [2; 3]. The composition of secondary metabolites in plants is tissue-specific and is influenced by developmental stage and genetic/environmental perturbation [4]. Many different pathways are involved in secondary metabolite biosynthesis, including the phenylpropanol, methyl-erythritol-4-phosphate (MEP) and mevalonate (MVA) pathways, which lead to the formation of many different volatile and non-volatile (poly)phenolic and terpenoid compounds [4]. Volatile organic compounds (VOCs) formulate the aroma profile and, in addition to the aforementioned pathways, many other aroma compounds are formed by the conversion/degradation of fatty acids and amino acids into straight and branched medium-chain aldehydes, alcohols and esters [4; 5; 6], as well as heterocyclic compounds such as methoxypyrazines [7]. Aroma is one of the two key determinants of asparagus flavour [8; 9; 10; 11]. Thanks to the studies of [PERSON], [PERSON] et al. on the aroma profile of cooked white asparagus [10; 11; 12; 13], we can now refer to specific VOCs (e.g., dimethyl sulfide, 2-methoxy-3-isopropyl pyrazine, methional) as being the \"key odorants\" also currently used as industrial references for flavour quality. Remarkably little research has been done on the metabolite profile of the raw vegetable. Such investigations are needed to provide the fundamental chemical basis to understanding the physiology and chemistry of the crop and to explore precursor pathways involved in the formation of flavour also after food preparation. It is hypothesised that the flavour chemistry of green and white asparagus should have many commonalities, as they both have a recognisable asparagus taste, while contrasting compounds will be the basis of the nuances in green/white flavour. Several studies on green or white asparagus have focused on the chemical composition of the crop, including, e.g., minerals [14], flavonoids [15; 16] and saponins [17; 18]. However, most studies only involve green asparagus although sometimes the type is not actually mentioned. A few studies have compared the chemical composition of both types,  
Figure 1: Clear differences in appearance are visible between white and green asparagus spears: (**a**) three freshly harvested white and green spears; (**b**) zoom in to reveal the cladodes and general tip morphology.