# Rapid In-Field Volatile Sampling for Detection of _Botrytis cinerea_ Infection in Wine Grapes
## 2 Results and Discussion
### Correlation between Volatile Detection and B. cinerea Infection Severities  
The correlations between the _B. cinerea_ infection levels and the targeted compounds detected using thermal desorption GC-MS with ZIF-8 as adsorbent materials in a controlled environmental condition are shown in Figure 2 (left). _B. cinerea_ infection severities were  
Figure 1: Relative responses to internal standards of some key compounds detected from synthetic grape juice with spiked standard and whole bunches of infected grapes, using ZIF-8 (red) and Tenax®-TA (green) as absorbent materials, detected using thermal detection GC-MS. The median marks the mid-point of the data; the middle ‘box’ represents the middle 50% of scores; the upper and lower whiskers represent scores outside the middle 50%; and the circles represent outliers of 1.5 \(\times\) the interquartile range. 1,5-DMT, 1,5-dimethyltetralin; 1,5-DMN, 1,5-dimethylnaphthalene; PEA, phenylethyl alcohol; * significantly different (_p_ < 0.05). determined by the concentration of species-specific antigens, using a lateral flow device (LFD). Lateral flow devices are reported to have an excellent performance for the detection and quantification of infection levels in naturally infected grapes compared with other measures of infection, such as measurement of ergosterol [5]. In this experiment, positive correlation coefficients were observed between the LFD scores and the concentrations of 3-methyl-1-butanol, 1,5-dimethylletralin, and 1,5-dimethylhaphthalene. 1,5-dimethylletralin and 1,5-dimethylhaphthalene are reported as key markers for _B. cinerea_ infection in grapes [5] and are thought to arise from the breakdown of berry carotenoids [29]. 3-Methyl-1-butanol was reported as a key volatile organic compound for the discrimination of bunch rot and noble rot detected in the progression of grey mould disease in grape berries [30]. In some cases, noble rot caused by _B. cinerea_ is desirable, as the growth of fungi may weaken the grape skin, accelerate water evaporation, and lead to high concentrations of sugars and acids, especially for dessert wines. However, with high-humidity environments, the growth of grey mould results in the reduction of sugar accumulation and the increase of acetic acid in the juice of the grape berries which may significantly impact the wine quality. Thus, the detection of 3-methyl-1-butanol is important for harvest decisions, and volatile analysis on berries before sample crushing using a non-invasive sampling technique directly from the gas space around intact bunches provides a potential pathway for more rapid and thorough analytical support tools. Significant correlations were observed between the LFD scores and 1,5-dimethylhaphthalene, 1,5-dimethylletralin, and 3-methyl-1-butanol, with the \(p\)-values of 0.011, <0.001, and 0.004, respectively (Supplementary Table S1). These metabolites are indicators of _B. cinerea_ infection in grapes and strongly correlated with the infection severity. Significant differences (Supplementary Table S2) were also observed in the detection of hexanal, 3-methyl-1-butanol, 3-octanone, 1-hexanol, 3-octanol, 1,5-dimethylletralin, benzyl alcohol, phenylethyl alcohol, and 1,5-dimethylhaphalene between healthy (LFD signal intensity 12-14) and infected bunches (LFD signal intensity 37-97), demonstrating the potential application for _B. cinerea_ infection discrimination in grapes using such an enclosure glass sampling system with ZIF-8 as an absorb  
Figure 2: Correlation coefficients for _B. cinerea_ infection levels measured with LFD scores (12–97) and volatile concentrations detected by thermal desorption GC-MS with ZIF-8 as absorbent materials, using an enclosed glass container system for volatile sampling (left), and SPME GC-MS (right). Green shows positive correlation, red shows negative correlation, and the dot sizes represent the absolute values of correlation coefficients. LFD, lateral flow device; 1,5-DMT, 1,5-dimethylletralin; PEA, phenylethyl alcohol; 1,5-DMN, 1,5-dimethylhaphthalene.