Simplifed Analysis of Flavor in Shiikuwasha Products Using Monolithic Silica Adsorbents “MonoTrap” and GC-MS

Importance of the Topic

The peel and processing residues of shiikuwasha (Citrus depressa Hayata), a tangerine native to Okinawa, contain valuable aroma compounds but are often discarded. Efficient analysis of these volatile flavor components supports product development, waste valorization and quality control. A streamlined method that mimics human aroma perception and reduces laborious extraction steps is of high practical value for food, beverage and fragrance industries.

Objectives and Study Overview

This work aimed to develop a simplified headspace sampling approach for shiikuwasha vinegar extract using a monolithic silica adsorbent (MonoTrap) coupled to thermal desorption GC-MS. Secondary goals included identifying the major volatile components and evaluating the stability of flavor compounds adsorbed on the trap during frozen storage up to four weeks at –20 °C.

Methodology and Instrumentation

Sample preparation involved vortexing ground shiikuwasha peel with vinegar or adding internal standard to the liquid extract. A MonoTrap RGPS TD adsorbent housed in an MT holder was heated at 50 °C for 60 min in a sealed vial to collect headspace volatiles. Adsorbents were transferred to a thermal desorption liner, capped with a CDC cap, and either analyzed immediately or stored frozen.

Main Results and Discussion

GC-MS analysis with an OPTIC-4 multimode inlet identified 19 volatile compounds originating from shiikuwasha, including limonene, γ-terpinene, p-cymene and various monoterpene alcohols. Relative proportions differed from peel headspace, reflecting solvent polarity and extraction efficiency. Notably, monoterpene alcohols (linalool, terpinen-4-ol, α-terpineol) were effectively trapped despite aqueous matrix. Frozen storage of loaded MonoTrap units for up to four weeks did not significantly affect total ion chromatograms or relative peak areas, with coefficients of variation below 11 % for all analytes.

Benefits and Practical Applications

A headspace-MonoTrap-TD GC-MS workflow offers:

• Elimination of complex solvent extraction and liquid nitrogen cryofocusing during sampling
• Enhanced throughput and storage flexibility through frozen preservation of adsorbents
• Accurate profiling of key flavor compounds for product development and quality assurance

Used Instrumentation

• Adsorbent: MonoTrap RGPS TD with PDMS coating
• Inlet: Shimadzu OPTIC-4 multimode inlet with cryotrap
• Autosampler: AOC-5000 Plus with LINEX liner exchanger and CDC station
• GC-MS: Shimadzu GCMS-QP2010 Ultra using WAX ProG capillary column
• Software: GCMSsolution, Cycle Composer, Evolution Workstation
• Mass spectral libraries: NIST 11, FFNSC 2

Future Trends and Potential Applications

Advances may include integrating this approach with two-dimensional GC or time-of-flight MS for deeper aroma profiling, miniaturized field-portable sampling devices for on-site monitoring, and adaptation to other citrus or botanical byproducts. Coupling with sensory analysis and chemometric tools can further link chemical data with perceived flavor quality.

Conclusion

The simplified headspace trapping of shiikuwasha vinegar extract on MonoTrap adsorbents combined with thermal desorption GC-MS enabled rapid, reproducible flavor profiling. The method’s ability to preserve adsorbed volatiles frozen expands flexibility for batch analysis and quality control in food and fragrance research.

Reference

1) Koji Wada. Aroma, taste and biological function of Okinawan citrus fruit, shiikuwasha (Citrus depressa Hayata). The Koryo, 260, 47–59 (2013).
2) Naoto Hirose, Goki Maeda, Satoshi Onda, Moriyuki Shoda, Kazuna Miyagi, Koji Wada, Hideaki Ohta. Development of vinegar extract from the waste peels of Shiikuwasha. Journal of the Japanese Society of Food Science, 64(2), 81–89 (2017).