Measuring dissolved oxygen in Miso for forensic medicine and semisolid food analysis

During a retrial, a prosecutor sought a scientific opinion from one of the authors on whether blood stains on cotton clothes placed in miso, a traditional Japanese fermented food, for 1 year and 2 months would remain reddish in color and asked this author to testify in court. We first searched the literature for information on the levels of dissolved oxygen (DO) in miso that may affect the discoloration of blood stains due to methemoglobin formation and subsequent degradation of hemoglobin but found no relevant information. Next, we investigated whether the DO concentration in miso could be measured using an optical oxygen sensor by analyzing freshly prepared and commercially available ripened miso. The DO concentration in miso decreased to below the detection limit (0.002%) within 9.5-23.2 h after preparation and remained low, even after the miso ripened. Thus, the low DO concentration may have affected the redness of the bloodstain. The amount of oxygen in foods must be controlled because it affects essential properties such as taste, nutritional value, color, and aroma. An optical oxygen sensor may serve as a useful tool for measuring DO concentration in semisolid fermented foods, such as miso.