Formation and predictive modeling of harman and norharman in Pictet–Spengler model systems: Effects of intramuscular fat and reducing sugars

Harman and norharman were the most representative β-carboline heterocyclic amines (HAs). Their formation mechanisms were investigated in model systems containing intramuscular fat, D-glucose, D-ribose, and D-glucose-6-phosphate under varying conditions, and predictive models were developed. Results showed that at 90–210 °C, reaction times of 10–60 min, pH 5.5–8.0, and different additive levels, intramuscular fat increased harman and norharman formation by 16–275% and 16–284%, respectively, compared with the control group without additives, while D-glucose, D-ribose, and D-glucose-6-phosphate exhibited stronger enhancing effects, promoting the formation of harman by 50–753%, 18–718%, and 46–1586%, and norharman by 68–396%, 36–391%, and 11–107%, respectively, relative to the control. This indicated that sugar-derived reactive carbonyl species (RCSs) play a stronger role in promoting harman and norharman formation than lipid-derived RCSs under identical processing conditions. Furthermore, both linear and polynomial regression models effectively described the formation trends, with R 2 values of 0.916 and 0.981, respectively, and a range of 0.608 to 0.999. For the optimal Partial Least Squares Regression (PLSR) models, harman achieved calibration ( R 2 c ) and prediction ( R 2 p ) values of 0.75–0.87 and 0.73–0.86; for norharman, 0.75–0.78 and 0.74–0.75. These results confirmed that harman and norharman can be accurately quantified and monitored during the smoking and roasting of meat products. • Both reducing sugars and intramuscular fat enhance the formation of harman and norharman. • D-glucose-6-phosphate significantly promoted harman formation at moderate temperatures (90–150 °C). • D-glucose and D-ribose markedly enhanced norharman formation across a wide range of temperatures (90–210 °C). • Reducing sugars demonstrated a stronger promotional effect on harman and norharman formation than intramuscular fat.