Thermal decomposition of cow ghee by multi-stage heating and preliminary study of interactions of pyrolysis products with water vapour

Abstract

Cow ghee is a clarified dairy fat used across South Asian food and Ayurvedic practice. Its thermal degradation chemistry from hydrolysis to pyrolysis has not been reported systematically, and no ghee-specific emission profile or pyrolysis-product interaction with water vapour has been characterised. Samples of 50 ± 2 g were heated under nitrogen in three stages. Stage 1 was mild at 60 to 70 °C. Stage 2 was intermediate at 220 to 340 °C in 20 °C steps. Stage 3 used a muffle furnace set to a nominal 500 °C for 90 s. Here 500 °C denotes the furnace set point. Products were characterised by FTIR, GC-MS, HPLC-DNPH and PTR-ToF-MS. Pyrolysis gas of 100 mL was introduced into a 2.5 L chamber at 25 °C and 65% relative humidity, and the water response was followed by Raman spectroscopy and gravimetric uptake. Mild heating produced ester hydrolysis, with free fatty acid rising from 0.42 to 0.71% (n = 5, p = 0.018). Intermediate heating produced acrolein, reaching 112.6 ± 8.2 micrograms per gram at 300 °C within the HPLC-DNPH series, equal to 64.2 ± 6.8% of total carbonyls (F = 42.3, p < 0.0001). The high-temperature stage produced a transient unassigned ion at nominal m/z 27 with a decay time of 90 to 140s. Its identity could not be established, because the raw high-resolution files were not retained. Pyrolysis gas produced a chamber water uptake of 1.3 ± 0.2 mg against 0.3 ± 0.3 mg for the blank (p = 0.012). The Raman signal reflects an integrated chamber water response with a condensed-phase contribution. The chamber result is a laboratory feasibility observation and carries no atmospheric inference.