Measuring Dissolved Oxygen in Miso: Implications for Forensic Science and Semisolid Food Analysis

In a retrial, the 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, and asked him to testify. As a first step, we searched the literature for information on the levels of dissolved oxygen (DO) in miso that might affect the discoloration of blood stains, but found no relevant information. Then, 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 to 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 factors, such as taste, nutritional value, color, and aroma; our results suggest that an optical oxygen sensor could serve as a useful tool for measuring DO concentration in semisolid fermented foods, such as miso .