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On-line-monitoring of food fermentation processes using infrared and Fourier-transformed infrared spectroscopy


Key words Fermentation, IR, FTIR, infrared spectroscopy, on-line monitoring, ATR, process control, MIR, NIR, non-invasive
Latest version 2012/07/17
Completed by DIL

How does it work?

Primary objective Infrared (IR) - spectroscopy offers the possibility to measure substrate conversion or product/ biomass formation directly in food fermentation processes, eliminating the need for additional off-line assays.
Working principle On-line process control of fermentation processes is often limited to the measurement of chemical and physical parameters like temperature, gas composition or pH. Information on substrate conversion or product/ biomass formation must be obtained by off-line assays. These are time-consuming and bear a risk of process contamination and are therefore performed rather periodically.

Spectroscopic measurements with suitable on-line sensors provide the opportunity to monitor the conversion and formation of a broad variety of biomolecules like sugars, organic acids, alcohols and proteins. The method can be applied to the actual fermentation process and facilitates a nearly real-time detection of the above mentioned biomolecules.

Infrared (IR) – spectroscopy:

IR – spectroscopy is a method that makes use of the specific physical properties of simple to complex molecules in the infrared range of the electromagnetic light spectrum (0.8 – 1000 µm), namely in the near-infrared (NIR, 0.8 – 2.5 µm), the mid-infrared (MIR, 2.5 - 25 µM) and the far-infrared (FIR, 25 – 1000 µm) region. Molecules active in the IR – region possess at least one asymmetrical chemical bond. CO for example has a distinct IR – signal whereas N2 does not. The more complex a molecule is the more signals it exhibits. This results in a specific “fingerprint” of the molecule which allows predictions of a sample composition and the concentration of compounds.
Identification and quantification of the obtained spectra is performed by comparison with reference spectra of specific compounds of interest. Reference spectra are commercially available but, depending on the respective application and sample composition, may have to be recorded and stored in databases beforehand. Additionally, the need might occur to enhance the overall sensitivity of the detection since it depends on the sample composition as well as on the detector and the light source used. Two possibilities to enhance the sensitivity and applicability of IR – spectroscopy are the use of Fourier-Transformed-Infrared-Spectroscopy (FTIR) and/ or Attenuated Total Reflectance (ATR).

FTIR (Fourier-Transformed-Infrared-Spectroscopy):

In FTIR – measurements, a broad range of spectral data is collected in a wide spectral range. This leads to an improved signal-to-noise-ratio. After the raw data acquisition, the actual spectrum is evaluated by a mathematical algorithm, the Fourier transform. FTIR – spectrometers are preferentially applied in the MIR or FIR region. In the NIR, conventional IR – spectrometers are widely distributed.

ATR (Attenuated Total Reflectance):

ATR is a sampling technique in which the sample is in direct contact with a reflective crystal surface. The IR – beam is passed through the crystal, resulting in an evanescent wave that extends into the sample for only a few micrometres. This constitutes a huge advantage over conventional transmission measurements, especially for aqueous or highly absorbing samples.

Additional effects
Important process parameters overall sensitivity of the detection system (wavelength range, light source, detectors, CO2 adherence to ATR surface, biofilm formation, temperature)
Important product parameters compounds in the fermentation process, sample absorbance

What can it be used for?

Products Liquid products, fermented products (e.g. ethanol or lactic acid fermentations), beverages, food waste
Operations On-line detection, fermentation process control
Solutions for short comings Infrared-on-line-monitoring is needed in food fermentation processes which afford rapid, constant and effective control of the fermentation progress and identification of the included biomolecules. It therefore enhances the quality and safety of the final product [1], [2], [4].

What can it NOT be used for?

Products Non-fermented foods, dry foods
Operations The application of IR/ FTIR online monitoring is restricted in operations that do not provide suitable physical parameters for optical detectors (e.g. high optical density or dispersion). Operations which do not include the turnover of biomolecules/ biomass with additional need of their identification/ quantification may not benefit from this technique.
Other limitations
  • Applicability might be restricted by gas or biofilm formation on the detection surface.
  • Fermentation media with high absorption may not be measured or require pre-measurement treatment.
  • Measurements without suitable reference spectra may lead to false results concerning fermentation medium composition and compound concentration [3].
Risks or hazards


Maturity Industrially available
Modularity /Implementation Easy implementation in old and new fermentation equipment.
Consumer aspects Since IR/ FTIR spectroscopy provides a method for the online monitoring of industrial processes it is unlikely that consumers are generally aware of the application of this technique. Given the fact that infrared light does not cause any changes in the molecular composition of a product and does not cause the formation or liberation of allergenic or toxic by- products, this application can be viewed as completely harmless for the production of foodstuffs. Furthermore, since it is a non- invasive tool of process control, the need for off-line measurements with a risk of process contamination is reduced, leading to enhanced products safety and freshness [5].
Legal aspects None to be expected. The method does not influence or alter the product properties.
Environmental aspects -

Further Information

Institutes UTCN, DTU Food, University of Vienna
Companies Bartec Benke GmbH, Vital Sensors Technologies, Bellingham & Stanley
  1. Gonzalez-Saiz, J. M., Pizarro, C., Esteban-Diez, I., Ramirez, O., Gonzalez-Navarro, C. J., Saiz-Abajo, M. J., Itoiz, R.; Monitoring of Alcoholic Fermentation of Onion Juice by NIR Spectroscopy: Valorization of Worthless Onions; Journal of Agricultural and Food Chemistry; 2007; 55; 2930-2936.
  2. Veale, E. L., Irudayaraj, J., Demirci, A.; An On-Line Approach To Monitor Ethanol Fermentation Using FTIR Spectroscopy; Biotechnology Progress; 2007; 23; 494-500.
  3. Mazarevica, G., Diewok, J., Baena, J. R., Rosenberg, E., Lendl, B.; On-Line Fermentation Monitoring by Mid-infrared Spectroscopy; Applied Spectroscopy; Volume 58; Number 7; 2004; 804-810.
  4. Fayolle, Ph., Picque, D., Corrieu, G.; On-line monitoring of fermentation processes by a new remote dispersive middle-infrared spectrometer; Food Control 11; 2000; 291-296.
  5. Liu, Y., Ying, Y.; Use of FT-NIR spectrometry in non-invasive measurements of internal quality of ‘Fuji’ apples; Postharvest Biology and Technology 37; 2005; 65–71.

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Created by Claudia Siemer on 13 June 2012, at 16:43