Phaffia rhodozyma has drawn significant attention for its ability to synthesize high-value astaxanthin. However, since this product is contained within the cells, traditional extraction and detection procedures are extremely cumbersome. The paper highlighted in this issue reveals how the resonance Raman effect can be used to cross the barrier of the cell wall and achieve real-time, in-situ monitoring of intracellular carotenoids.
01 Research Background: The Challenge of Monitoring Intracellular Products
Carotenoids (primarily astaxanthin) account for over 80% of the total carotenoids in Phaffia rhodozyma. Because the products accumulate inside the cells, offline detection requires complex steps such as cell disruption and extraction, which are not only time-consuming but also fail to provide real-time process feedback.
The researchers posed the question: Could we "see through" the cell wall without disrupting the cells and read the product information directly?
02 Core Technology: The Resonance Raman Effect
This is the physical foundation that made the study successful.
Principle: When the laser frequency approaches the electronic absorption frequency of a molecule, the Raman scattering intensity of specific chemical bonds is enhanced by several thousand times.
Application: The vibrational peaks of the carbon‑carbon double bonds (C=C, C–C) in carotenoids become extremely strong, enough to overwhelm the complex background from the culture medium.
03 Experimental Setup: In-Situ Tracking of a Fed‑Batch Fermentation
The research team validated the technique across three consecutive batches of Phaffia rhodozyma fed‑batch fermentation.
Monitoring Target: Intracellular total carotenoid concentration.
Hardware Deployment: A 785 nm laser was used for excitation, and spectra were acquired in real time via an in-situ Raman probe.
Spectral Signatures: Three characteristic peaks were monitored—1510 cm⁻¹, 1150 cm⁻¹, and 1000 cm⁻¹—which correspond to the vibrational features of the carotenoid molecular chain.
04 Experimental Results: Accurate Mapping from Spectra to Yield
By establishing a Partial Least Squares (PLS) model, the study achieved breakthrough results:
High Correlation: The correlation coefficient (R²) between the online Raman predictions and offline HPLC measurements exceeded 0.98.
Interference Resistance: Despite the presence of substantial biomass (changes in cell concentration) and complex feed components throughout the fermentation, the resonance effect ensured that the carotenoid signals remained dominant.
Real-Time Process Insight: The online curves clearly captured the rapid accumulation phase of carotenoids in the later stage of fermentation, providing an "eye" for optimizing the feed rate and determining the harvest time.
05 Conclusion and Implications
This study demonstrates that in-situ Raman spectroscopy is an ideal tool for monitoring high‑value intracellular products. For the bio‑fermentation industry, this means we can move away from cumbersome sample pretreatment and achieve non‑destructive, real‑time monitoring of the metabolic state inside cells.
06 Reference
Christopher Cannizzaro, Martin Rhiel, Ian Marison, Urs von Stockar. On‑Line Monitoring of Phaffia rhodozyma Fed‑Batch Process With In Situ Dispersive Raman Spectroscopy. Biotechnology and Bioengineering, Vol. 83, No. 6, September 20, 2003.
Post time: Aug-26-2026