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Rapid Characterization of Garlic Volatiles—No Sample Prep Required!

Using Headspace GC/MS and an Rxi-5ms Capillary Column


By Julie Kowalski, Innovations Chemist; Michelle Long, Innovations Chemist; Jason Thomas, Innovations Chemist; and William Goodman†, GC/MS Applications Specialist
  • No sample preparation! Eliminate complicated steps required by other methods.
  • Rapid screening of garlic-specific flavor and odor compounds.
  • Speedy determination of volatiles profile.

Introduction

Garlic, Allium sativum (L)., is a member of the onion family and is related to onions, shallots, and leek. It has a rich history in cooking and is characterized by a strong hot flavor which sweetens as it is cooked. Garlic has also been used for medicinal purposes for thousands of years and, at times, has been claimed to help prevent everything from high cholesterol to cancer. Recently, garlic supplements have gained popularity for boosting immune and cardiovascular health. Determining garlic flavor and odor components is important to the food industry since the quality of garlic and garlic powder affects overall food quality. Similarly, chromatographic methods for garlic are used by the dietary supplements industry to detect garlic volatiles that may affect the acceptability of supplements to the consumer.

Garlic odor and flavor components are produce enzymatically from precursors when the plant is cut or crushed. Allicin is the key compound of interest produced in this manner but it degrades quickly to other sulfide compounds. These sulfide degradents help produce garlicky odor and taste and are more stable than allicin and retain health benefits. Many of these components are volatile and thus are well-suited for headspace analysis.

This work describes the determination of garlic flavor and odor components by headspace gas chromatography mass spectrometry (HS GC/MS). The method shown here requires no sample preparation making the bench work simple and fast. Other methods of analysis involve steam distillation, solid phase trapping solvent exchange, headspace solid phase microextraction, and simultaneous distillation and solvent extraction which can be difficult and time-consuming.

Method

This comparative analysis of fresh garlic and garlic powder was done on a PerkinElmer TurboMatrix 40 Trap Headspace Sampler. Several headspace conditions were adjusted to optimize the comparison. The column and injection pressures used were 15psi. Column flow is dictated by the headspace unit pressure when the headspace unit is directly coupled to the GC column. The vial was pressurized for 1 min., with a thermostat time of 15min. The oven, needle, and transfer temperatures were 80°C, 90°C and 110°C respectively. A 0.32mm ID IP deactivated guard column was used as a transfer line from the headspace unit to the GC oven. The transfer line was inserted into the injector of the Clarus 500 in a manner which allowed the flow from the HS-trap to be split (10:1). The analytical column used was a 30m x 0.25mm ID x 1.0µm Rxi-5ms column. The GC oven temperature program started with an initial temperature of 35°C (1 min.) increasing at 15°C/min. to 20°C then increasing at 45°C/min. to the final temperature of 300°C. The mass spectrometer was used as the detector with a scan range of 35-350amu.

Results

Several sulfur components were identified including allyl methylsulfide, 3,3'-thiobis-1-propene, allyl mercaptan and diallyl disulfide. Diallyl disulfide appeared to be the dominant component for both garlic preparations. The fingerprint, or relative ratios, of the other components were distinct for fresh garlic and powdered garlic. Figure 1 shows the total ion chromatograms and for both fresh garlic and garlic powder.

Conclusions

This work demonstrates the simplicity of using headspace GC/MS for rapid characterization of garlic and garlic powder samples. The experimental set-up is ideal for both screening analysis and low-level trace analysis. This method will allow for rapid determination of garlic quality and could be used for the determination of low levels of sulfur containing compounds from odorless supplements.

Figure 1  Rapid screening of garlic volatiles—analyze samples in less than 11 minutes!

Peaks
1.Allyl methylsulfide
2.3,3'-Thiobis-1-propene
Peaks
3.Allyl mercaptan
4.Diallyl disulphide
Fresh Garlic on Rxi-5ms
GC_FF00958
ColumnRxi -5ms, 30 m, 0.25 mm ID, 1.00 µm (cat.# 13453)
using IP Deactivated Guard Column 5 m, 0.32 mm ID (cat.# 10044)
SampleFresh garlic
Injectionheadspace-trap
Headspace-Trap
Instrument:PerkinElmer Turbomatrix 40 Trap Headspace Sampler
Column Pressure:15 psi
Inj. Time:0.02 min
Inj. Temp.:220 °C
Inj. Pressure:30 psi
Withdraw Time:0.2 min
Transfer Line Temp.:110 °C
Oven Temp.:80 °C
Needle Temp.:90 °C
Vial Pressurize Time:1 min
Thermostat Time:15 min
Oven
Oven Temp.:35 °C (hold 1 min) to 220 °C at 15 °C/min to 300 °C at 45 °C/min
Carrier GasHe, constant flow
Flow Rate:1.5 mL/min
DetectorMS
Mode:Scan
Ionization Mode:EI
Scan Range:35-350 amu
NotesInjection: split (10:1)
Peaks
1.Allyl methylsulfide
2.3,3'-Thiobis-1-propene
Peaks
3.Allyl mercaptan
4.Diallyl disulphide
Garlic Powder on Rxi-5ms
GC_FF00959
ColumnRxi -5ms, 30 m, 0.25 mm ID, 1.00 µm (cat.# 13453)
using IP Deactivated Guard Column 5 m, 0.32 mm ID (cat.# 10044)
SampleGarlic Powder
Injectionheadspace-trap
Headspace-Trap
Instrument:PerkinElmer Turbomatrix 40 Trap Headspace Sampler
Column Pressure:15 psi
Inj. Time:0.02 min
Inj. Temp.:220 °C
Inj. Pressure:30 psi
Withdraw Time:0.2 min
Transfer Line Temp.:110 °C
Oven Temp.:80 °C
Needle Temp.:90 °C
Vial Pressurize Time:1 min
Thermostat Time:15 min
Oven
Oven Temp.:35 °C (hold 1 min) to 220 °C at 15 °C/min to 300 °C at 45 °C/min
Carrier GasHe, constant flow
Flow Rate:1.5 mL/min
DetectorMS
Mode:Scan
Ionization Mode:EI
Scan Range:35-350 amu
NotesInjection: split (10:1)

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