Optical Non-Intrusive Measurement of Dissolved Oxygen and pH in Wine Processing
Setup
Components for Oxygen:
NeoFox Phase Fluorometer
RedEye® Oxygen Patches (Headspace and In-Solution measurement)
Bifurcated Fiber Optic probe
Components for pH:
Jaz Spectrometer
LS-1 Tungsten Light Source
Bifurcated Fiber Optic Probe
Reflective pH Patches
Experimental Procedure:
• Oxygen Patches were placed inside the Bio-flask to monitor the oxygen in headspace and in solution.
• pH patch was placed in solution to monitor pH changes during the fermentation process.
• Fresh red grapes were mashed and the must was left to sit for 2 days.
• The liquid was added in the bio-flask. Initial measurements were recorded and yeast cells and nutrients were added to start the fermentation process.
• This process was observed over a period of 60 hours.
Optical Oxygen Sensors:
• Prominent method for luminescence sensing in which the lifetime of the indicator compound changes in response to the analyte sensed (phase measurement).
• A fluorescence method measures the partial pressure of dissolved or gaseous oxygen. The fluorescence is generated at the tip of the optical electrode by a light source.
• When oxygen in the gas or liquid samples diffuses into the thin film coating, it quenches the fluorescence.
• The degree of quenching correlates to the level of oxygen pressure.
RedEye Oxygen Sensor Patch:
• RedEye is a revolutionary oxygen sensing product designed specifically to measure oxygen.
• RedEye consists of a sensor coating formulation trapped in a sol gel matrix, immobilized and protected from the package contents
• The RedEye patch has no minimum and maximum diameter sizes, but typically sizes will vary from a few millimeters to several centimeters
• RedEye can be easily integrated into any system because of its self-adhesive acrylic patch having the sensor coating formulation.
O2 Sensing Electronics – NeoFox:
NeoFox is an instrument platform for measurement of fluorescence lifetime and phase for oxygen sensing
• The frequency domain electronics uses a blue LED excitation and an avalanche photodiode for detection.
• A bifurcated optical fiber carries excitation light produced by the blue LED to the thin-film coating of the RedEye Oxygen Sensor
• Fluorescence generated at the surface of the RedEye Patch is collected by the probe and carried by the optical fiber to the detector.
Lifetime Measurement Technique:
The phase shift between the blue LED excitation and emission signal of fluorescence is used to calculate lifetime.
Advantages of Optical Oxygen Sensors:
• Uses fiber optic cable for non-intrusive measurements
• Not contaminated by water or other solutions
• Immune to EMI
• Non-electrical, non-conductive
• Operable in temperature and concentration range of various applications
• Simple calibration
• Works with colored samples without any color or light interference
Smart pH Technology:
• pH buffers used for calibration, references taken by software
• Absorbance curves seen as pH increases
• Absorbance peak at 620nm, baseline correction at 512 nm
Temperature Compensation:
Compensation for temperature effects is achieved through the van’t Hoff equation:
• Isothermal correction corrects pH value based on user-input temperature
• Dynamic temperature correction available for non-isothermal systems with temperature monitoring
Result Analysis and Conclusion:
• The graph shows the complete measurement of both oxygen and pH over a period of 60 hours.
• The next graph shows the measurements over the first two hours. The oxygen sensor in solution quickly dropped from air saturation as soon as the yeast cells and nutrients were added. The pH sensor in solution dropped slightly as the oxygen decreased and CO2 is released. Hence the drop in pH value.
• The following graph indicates the oxygen sensor in the headspace stays at air saturation approximately the first 2.5 hours. Once the oxygen in solution is completely quenched, the yeast cells and nutrients start consuming oxygen from the headspace.
• Conclusion: Ocean Optics sensor patches are able to monitor both oxygen and pH non-intrusively which can be used in the fermentation industries.
