Analysis of Volatile Compounds in Pumpkin with ‘Taro-like’ Aroma Using Solid Phase Micro-extraction and Gas Chromatography-Mass Spectrometry Combined with Chemometrics

Significance of the Topic

Pumpkin with a distinctive ‘Taro-like’ aroma represents a valuable cultivar for flavor improvement, consumer appeal, and breeding programs. Detailed profiling of its volatile constituents is essential for understanding aroma formation, guiding quality control, and enhancing sensory traits in commercial varieties.

Aims and Study Overview

This work aimed to characterize volatile metabolites in a ‘Taro-like’ aromatic pumpkin (YJ) and distinguish them from two non-aromatic controls (EY and 278). Key objectives included:

• Comprehensive identification of headspace volatiles in mature YJ fruit
• Statistical comparison of aroma profiles across cultivars
• Monitoring of key aroma compound dynamics during fruit development

Methodology and Instrumentation

Sampling and Sample Preparation:

• Mature fruits (~45 days post-pollination) harvested in triplicate for each cultivar; additional samples collected at unpollinated, 25-day, and 45-day stages
• Freeze-drying and fine grinding of fruit tissue; 1 g aliquots used for analysis with 3-nonanone as internal standard

SPME and GC-MS Conditions:

• Headspace SPME: equilibration at 70 °C for 2 min, fiber exposure for 35 min at 70 °C, desorption at 270 °C for 4.5 min
• GC-MS: Agilent 7890B system with DB-5MS column; Agilent 7000D MS in full-scan mode (35–500 m/z); helium carrier gas at 1.0 mL/min

Chemometric Analysis:

• Data deconvolution in MassHunter Qualitative; export as .cef files
• Filtering criteria: frequency > 60%, CV < 30%
• Principal Component Analysis to differentiate sample groups

Used Instrumentation

• Agilent 7890B Gas Chromatograph
• Agilent 7000D Triple Quadrupole Mass Spectrometer
• DB-5MS capillary column (60 m × 0.32 mm × 0.25 μm)
• SPME fiber assembly and autosampler

Main Results and Discussion

Volatile Profile in YJ Pumpkin:

• Identification of 31 compounds: 12 aldehydes, 6 ketones, 5 heterocycles, 4 alcohols, 1 ester, 1 lactone, 1 benzene derivative, 1 alkene
• Highest concentrations: trans-2-hexenal (0.0182 mg/kg dw) and 2-acetyl-1-pyrroline (0.0133 mg/kg dw)

Discrimination of Cultivars:

• PCA separated YJ from EY and 278, accounting for over 78% of variance in first two components

Key Aroma Compound:

• 2-Acetyl-1-pyrroline (2-AP) was uniquely present in YJ versus both controls, confirming its role as the signature ‘Taro-like’ aroma compound

Developmental Dynamics of 2-AP:

• Comparable 2-AP levels in unpollinated and 25-day fruit
• Significant decline by 45 days, indicating early accumulation and late-stage reduction

Contributions and Practical Applications

• Establishes a robust HS-SPME-GC-MS and chemometric workflow for flavor compound analysis in pumpkin
• Provides a detailed volatile fingerprint to support targeted breeding of aromatic cultivars
• Identifies 2-AP as a reliable marker for quality control during harvest and postharvest handling

Future Trends and Potential Applications

• Integration of metabolomic data with genomics to unravel biosynthetic pathways of key aroma compounds
• Development of rapid sensory screening tools (e-noses) focused on 2-AP detection for breeding and quality assurance
• Metabolic engineering approaches to enhance ‘Taro-like’ aroma in commercial varieties
• Optimization of storage and processing protocols to preserve volatile aroma profiles

Conclusion

HS-SPME-GC-MS coupled with chemometric analysis effectively revealed the volatile composition underlying the ‘Taro-like’ aroma in pumpkin. The unique detection of 2-acetyl-1-pyrroline in the YJ cultivar underscores its central role as the aroma determinant. These insights pave the way for aroma-driven breeding strategies and improved quality control in pumpkin production.