Comprehensive insights into color, oil content, and chemical component variations and mediated browning mechanistic DFT study in crude pine oleoresin (Pinus massoniana) melt processing

Abstract

Pine oleoresin's color, oil content, and specific chemical composition remain significant industry concerns related to economic benefits. However, quality deterioration of crude pine oleoresin during melt processing will directly affect its market value and end-use. The present study evaluated the different melt processing conditions (90–120 °C, 0.5–3 h) on the color, oil content, and chemical components of crude pine oleoresin using CIE- L * a * b * color space and GC-MS and insight into the biomass impurities (pine needles and bark) mediated browning mechanisms via UHPLC-Q-Exactive Orbitrap MS/MS and density functional theory (DFT). Results showed that the lightness L * of crude pine oleoresin was decreased with enhanced melt processing, while the redness a * and yellowness b * increased, as well as color difference Δ E * , browning index BI, and Gardner color scale. Color kinetic models were developed to describe variations in L *, a *, and b * with activation energies of 7.19–74.68 kJ/mol. The residual reducing sugar content of impurities in crude pine oleoresin was decreased and significantly negatively correlated with oleoresin color deterioration. The browning products, such as representative marker 5-hydroxymethylfurfural and 2-furoic acid, were found in melted crude pine oleoresin. DFT studies revealed that the browning reactions of impurities were exothermic and proceeded spontaneously. The rate-determining step to generate 5-hydroxymethylfurfural in the Maillard reaction had an energy barrier of 275.9 kJ/mol, while the caramelization reaction to form corresponding 5-hydroxymethylfurfural and furfural had energy barriers of 345.4 kJ/mol and 367.0 kJ/mol, respectively. Moreover, the decrease in oil content was inextricably related to terpenes volatilization, especially α and β-pinenes. Overall, melt processing of crude pine oleoresin at 90–100 °C and within 1 h can avoid significant quality deterioration and obtain lighter-colored rosin products. This study could provide an experimental and theoretical basis for controlling the quality deterioration of pine oleoresin and other biomass products during thermal processing. • Variations in color, oil content, and chemical components of crude pine oleoresin during melt processing were examined. • Twelve mediated browning products, such as 5-HMF and 2-furoic acid, were found in melted crude pine oleoresin. • Density functional theory studies mechanistically revealed the mediated browning effects on crude pine oleoresin. • Minimizing quality deterioration and obtaining lighter-colored rosin products are desired in oleoresin thermal processing.

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