Determining the Identity of Spices Using UV-Vis Spectroscopy
Spices have a long and rich history around the world. In some ways, the cuisine of a particular region is distinguished by local spices. For centuries, spices and spice extracts have been used to modify the flavor of prepared foods, help preserve foods and act as herbal remedies for a wide variety of ills.
Spices also have interesting spectral characteristics. In this application note, we use a Flame-CHEM spectrophotometer to identify an unknown spice extract. Flame-CHEM combines a UV-Vis or Vis-NIR spectrometer, light source and cuvette holder in a single-footprint system, simplifying the setup and freeing up bench space. It is a simple yet elegant option for basic absorbance measurements.
When used in a teaching lab, the absorbance procedure described here can help students to understand principles of absorbance spectroscopy and the preparation of extracts for sampling. For researchers and other users, similar procedures can be applied to measure the concentration of various solutions, including spices used in food dyes and colorants.
Spices have myriad uses in flavoring and coloring foods, and have grown in popularity as health-conscious consumers seek to reduce salt intake and expand their palates. In naturopathic medicine, spices are sometimes used for their antimicrobial or therapeutic effects, contributing to their value and making them a frequent target of adulteration with various fillers.
Spectroscopy is an excellent tool for determining unknown spices and identifying adulterants. For example, reflectance spectroscopy can reveal that certain spices have greater reflectivity at longer wavelengths, or characteristic peaks that adulterants do not.
For this experiment, we’re creating extracts of different cooking spices, measuring their absorbance and then comparing the results to unknown spice extracts.
Modular spectrometers and accessories from Ocean Optics make it possible to configure dozens of different setups for absorbance measurements. For a teaching lab setting, where a streamlined setup may be preferable, we offer the Flame-CHEM spectrophotometer – a spectrometer with direct-attach light source-cuvette holder combination. UV-Vis (250-800 nm) and Vis-NIR (350-1000 nm) versions are available.
The Flame-CHEM’s direct-attach light source with cuvette holder avoids the potential problem of fiber breakage, and keeps the system to a single piece (plus interface cables). Also, the Vis-NIR version of the Flame-CHEM system draws all the power it needs to run the spectrometer and light source through the USB cable that connects to the PC.
Users are not limited to the Flame-CHEM for cuvette-based absorbance measurements. A good alternative for the teaching lab is the ultra-compact STS-VIS spectrometer (350-800 nm) with an ecoVis light source (which also has a built-in cuvette holder) and 400 µm optical fiber. This setup is flexible enough for absorbance, fluorescence or — with the addition of a reflectance probe — reflection measurements of solid samples.
Sample preparation was performed by using common cooking spices and creating extracts using isopropyl (rubbing) alcohol and disposable pipettes. Standard labware such as beakers and transfer pipettes are also necessary but not included with the systems described here.
|Featured System|| |
Flame-CHEM-Vis-NIR (350-1000 nm)
STS-VIS (350-800 nm)
|Light source:||Tungsten halogen with a violet LED (~390-1000 nm); attaches to spectrometer||ecoVis krypton source (400-2500 nm)|
|Cuvette holder:||QP400-2-VIS-NIR 400 µm patch cord||1 cm pathlength; built in to light source|
|Optical fibers/probe:||NA||400 µm patch cord, Vis-NIR, 2 m length|
|Software:||OceanView spectroscopy software||OceanView spectroscopy software|
|Also notable:||Light source-cuvette holder can be removed and the spectrometer used with discrete sampling devices||Includes a reflective insert piece that adapts the cuvette holder for fluorescence and can be used to block the light path for dark measurements|
This experiment comprises three primary steps:
1) preparation of spice extracts using a 70% isopropyl alcohol solution
2) measurement of the visible light absorbance of several known spice extracts
3) determination of unknown spice samples by comparing results to the spectral database the user creates
Because Ocean Optics systems are modular, students and others can understand how the components of each system go together and can be reconfigured for different types of measurements. Optimizing system and acquisition parameters for absorbance are among the concepts covered in the absorbance of spice extracts experiment.
Application Notes and Technical Resources
- Absorbance as a measurement technique – the comprehensive guide
- Adulteration of Spices
- Measuring Curcumin Concentration Using Absorbance Spectroscopy
- Measuring DNA Absorbance with the STS-UV Microspectrometer
- Sampling Accessories for Absorbance
- Stray Light and Absorbance