## 1 Introduction  
Florida citrus production has plummeted since 2005 when Huanglongbing (HLB), or citrus greening disease, was first reported in the U.S. Total citrus production has been reduced by 80% from 291.8 million boxes in 2003/2004 to 57.8 million boxes last season (2020-2021) [1]. The impact on the grapefruit (_Citrus paradisi_) industry is even more severe, with a decrease of 90% from 40.9 to 4.1 million boxes [1,2]. Citrus canker disease (_Xanthomonas citri_ subsp. citri) and associated eradication programs from the late 1990s to the early 2000s followed by catastrophic hurricanes in 2004 and 2005 were also responsible for the decrease in acreage and production [3,4].  
HLB is caused by a gram-negative bacterium, '_Candidatus_ Liberbacter asiaticus' (CLas), which is transmitted by the Asian citrus psyllid (ACP, _Diaphorina citri_) [5]. The disease has spread through the major citrus-producing regions worldwide, causing high economic losses in the citrus industry [4]. HLB seriously affects citrus production because of premature fruit drop, resulting in yield reduction [6; 7] and, eventually, tree death [3]. In oranges, fruits of HLB-affected (HLB+) trees usually are reduced in size, remain green, and are asymmetric [8]. The juice of these fruits has lower sugar and soluble solids contents (SSC), higher titratable acidity (TA), a lower SSC/TA ratio, and higher limonoid and flavonoid contents [4]. Among flavor volatiles, ethyl butanoate, valencene, decanal, and other ethyl esters are usually lower, but many monoterenes are higher in symptomatic fruit compared to healthy and asymptomatic fruit [4]. The juice is less sweet, sourer, bitter, and sometimes has a metallic and off-taste [4; 9; 10].  
Citrus volatile organic compounds (VOCs) include oil-soluble compounds commonly found in the peel and water-soluble compounds in juice [11; 12]. Citrus peel oil, a coproduct of the juice industry, is rich in terpene compounds that are used as ingredients in the food and perfume industries [13]. Graprefruit essential oil is well-known for its antioxidant, antiseptic, disinfectant, diuretic, and stimulant properties and is used for different industrial purposes [13; 14; 15]. Among the reported graprefruit volatiles, nootkatone is the most important and valuable aromatic present in the peel and juice [13; 14]. This ketone is very popular in the food and cosmetic industries. It has potential health benefits, such as the prevention of obesity and hyperglycemia, improving physical performance, and possibly having protective activity against learning and memory impairments [16; 17].  
Previous studies reported changes in the chemical composition of orange peel oil due to HLB infection [18; 19; 20]. [PERSON] et al. [20] showed that HLB+ orange peel oil contained a lower concentration of several long-chain aldehydes, such as octanal and decanal. [PERSON] et al. [18] found that severely HLB+ oranges had a lower abundance in most oxygen-containing volatile components, such as linalool, decanal, citronellol, neral, gerani, carvone, dodecanal, and 2-decenal in the peel oil, compared to less severely HLB+ fruits. However, an aroma sensory panel could not discriminate between the two oils, indicating that HLB severity may not affect flavor [19]. [PERSON] et al. [21] showed that peel oil extracted from HLB+ 'Valencia' orange fruits had lower concentrations of typical peel oil components, including valencene, octanal, and decanal, and were abundant in oxidative/dehydrogen terpen, such as carvone and D-limonene oxide. However, D-limonene, the dominant component, was not affected by disease status.  
Research on the effects of CLas bacterium on VOC profiles in citrus is sparse and nonconclusive, and most research is based on sweet oranges [4]. This study aims to evaluate the effect of CLas on VOCs in the peel oil and juice of 'Ray Ruby' graprefruit.