Yeast-immobilized SPV device for koji quality control in sake brewing process

Area of Science:

• Biotechnology
• Food Science
• Microbiology

Background:

• Malted rice (koji) is crucial for sake brewing, saccharifying starch and providing yeast nutrients.
• Sake quality is highly dependent on koji quality, necessitating robust quality control methods.
• Existing methods for assessing koji quality do not directly measure yeast metabolism.

Purpose of the Study:

• To develop a novel sensor system for monitoring yeast metabolism during sake brewing.
• To establish a direct link between sensor readings and yeast activity in the brewing process.

Main Methods:

• Immobilization of Saccharomyces cerevisiae strains (K701 and K9) for use in a sensor system.
• Utilizing a Surface PhotoVoltage (SPV) device to measure pH changes related to organic acid production.
• Correlating SPV photocurrent decrease with glucose concentration to validate the sensor's metabolic response.

Main Results:

• A linear relationship (r=0.990) was found between decreased photocurrent and glucose concentration (<60 mM).
• The sensor system successfully differentiated responses between S. cerevisiae K701 and K9 when analyzing koji extract.
• Observed differences in sensor response correlated with the acidic substance productivity of the analyzed koji samples.

Conclusions:

• The developed SPV-based sensor system effectively monitors yeast metabolism in sake brewing.
• This technology offers a direct method to assess yeast activity, complementing traditional koji quality control measures.
• The sensor system shows potential for optimizing sake production by providing real-time insights into yeast performance.