Post-Cooking Quality Deterioration of Wheat (Triticum durum) During Bulgur Production

This study characterized the pattern and timing of post-cooking quality deterioration in durum wheat held at 25, 35, and 45 °C by performing physicochemical, microbiological, and volatile compound analyses combined with a sensorially defined off-odor onset endpoint. The bulk moisture content remained high throughout holding at all temperatures. Titratable acidity increased from 1.49 to 2.15, and pH at off-odor onset decreased from 6.63 to 6.49 with increasing temperature. Off-odor was detected after 50, 45, and 34 h at 25, 35, and 45 °C, respectively. Microbial growth was fastest at 35 °C (μmax = 0.0651 h−1). Thiobarbituric acid reactive substances (TBARS) values were slightly lower at 45 °C than at 25 °C, despite the shorter holding duration, whereas lipid oxidation-derived volatile aldehydes declined more sharply over the same comparison. This pattern, together with the earliest off-odor onset occurring at 45 °C, suggests that non-lipid-derived volatiles increasingly drive off-odor perception as holding temperature increases. Gas chromatography–mass spectrometry (GC–MS)-based relative odor activity value (ROAV) analysis identified 2-methoxy-4-vinylphenol, 2,4-decadienal, 2-nonenal, 2,3-butanedione, nonanal and 2-methoxyphenol as the principal contributors to the aroma profile. These findings indicate that off-odor development during post-cooking holding results from a temperature-dependent interplay between microbial and chemical deterioration pathways and provide a basis for optimizing holding time and temperature to delay off-odor onset and limit quality losses in bulgur production.