## 3 Materials and Methods
### Quality Evaluation  
#### 3.3.1 Analysis of Volatile Compounds  
* Extraction of volatile compounds  
The extraction of volatile compounds was performed following the method described by [PERSON] et al. (2018) using solid-phase microextraction (SPME), with minor modifications. Chopped samples (2.5 g) were homogenized and transferred into a headspace bottle (20 mL, ANPEL Laboratory Technologies Inc., Shanghai, China) containing 50 mL of 1000 times diluted cyclohexanone as an internal standard. The bottles were sealed using a PTFE-silicone septum and equilibrated at 50 \({}^{\circ}\)C for 15 min with agitation. Next, a 50/30 \(\upmu\)m divinybenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) SPME fiber (Supelco, Bellefonte, PA, USA) was exposed to the headspace of the samples for 40 min at the same temperature without stirring. Finally, the fiber was withdrawn and introduced into the GC injector at 250 \({}^{\circ}\)C for 5 min.  
* Gas chromatography-mass spectrometry (GC-MS) analysis  
GC-MS measurements were conducted following the method of previous studies ([PERSON], 2018), with minor modifications, using an Agilent 7890 gas chromatography system (Agilent Technologies, Santa Clara, CA, USA) equipped with an Agilent 5975C series mass spectrometer. The volatile compounds were isolated with a DB-WAX (30 m \(\times\) 320 \(\upmu\)i.d. \(\times\) 0.25 \(\upmu\)m) fused silica capillary column (Agilent Technologies). Helium (purity \(\geq\) 99.999%) was used as the carrier gas at a rate of 1.0 mL/min constant flow. The oven temperature was maintained at 40 \({}^{\circ}\)C for 12 min, increased at a rate of 3 \({}^{\circ}\)C/min to 108 \({}^{\circ}\)C, and then maintainedat 108 \({}^{\circ}\)C for 2 min, followed by an increase to 250 \({}^{\circ}\)C at a rate of 5 \({}^{\circ}\)C/min for 5 min. Mass spectrometry was performed in the electron impact mode of 70 eV with a scan range of 450-550 m/z.
* Identification and quantification analysis  
The volatile compounds in HPP and TS marinated lotus root slices were identified by comparing sample mass spectra with those of the standard NIST12 database and by comparing the calculated linear retention indices (LRIs) with the open-access data of the NIST WebBook. The LRIs of volatile compounds were calculated using the retention times (RTs) of a liquid injection of 1 \(\mu\)L of C\({}_{7}\)-C\({}_{30}\)\(n\)-alkane standards obtained using the same GC-MS temperature program. A difference value below 20 between the calculated LRI values and those from the NIST Chemistry WebBook ([[https://webbook.nist.gov/chemistry/](https://webbook.nist.gov/chemistry/)]([https://webbook.nist.gov/chemistry/](https://webbook.nist.gov/chemistry/)) (accessed on 31 October 2021)) was considered acceptable. LRI was calculated using the following equation:  
\[\mathrm{LRI}=100\mathrm{N}+\frac{100\mathrm{n}(\mathrm{t}_{\mathrm{R}_{2}}- \mathrm{t}_{\mathrm{R}_{\mathrm{N}}})}{\mathrm{t}_{\mathrm{R}_{\mathrm{N}}( \mathrm{N}+\mathrm{n})}-\mathrm{t}_{\mathrm{R}_{\mathrm{N}}}} \tag{9}\]  
where N is the number of carbon atoms of \(n\)-alkanes immediately before the RT of the compound, n is the difference in the number of carbon atoms of \(n\)-alkanes immediately before and after the RT of the compound, \(\mathrm{t}_{\mathrm{R}_{\mathrm{A}}}\) is the RT of the compound, \(\mathrm{t}_{\mathrm{R}_{\mathrm{N}}}\) is the RT of \(n\)-alkanes immediately before the compound, and \(\mathrm{t}_{\mathrm{R}_{\mathrm{N}}(\mathrm{N}+\mathrm{n})}\) is the RT of \(n\)-alkanes immediately after the compound.  
Quantification of volatile compounds in HPP and TS marinated lotus root slices was performed using cyclohexanone as an internal standard. The peak areas were normalized to the cyclohexanone added to each sample. The concentrations of the identified compounds were calculated from the ratio of the peak area to that of the internal standard.