Advantages of UHT in retaining coconut milk aroma and insights into thermal changes of aroma compounds

Abstract

Coconut milk products are susceptible to bacterial damage, necessitating sterilization methods that often compromise nutrient and aroma integrity. This study investigates the effects of different thermal sterilisation methods on coconut milk aroma using headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). We assessed the impact of pasteurisation (PAS, 70 °C, 25 min), high-temperature sterilisation (HTS, 121.1 °C, 15 min), and ultra-high temperature sterilisation (UHT, 130 °C, 5 s) through clustered heat maps and correlation analyses. Significant differences were observed (p < 0.05), with 37 and 52 substances detected by HS-GC-IMS and HS-SPME-GC-MS, respectively, identifying 12 key aroma compounds. UHT treatment primarily reduced 8 acids, maintaining a compositional structure and sensory profile similar to raw coconut milk. PAS and HTS treatments decreased the sensory intensity of overall coconut milk aroma, creamy, and floral notes, correlating with the presence of 2-heptanol, nonanal, 4-methylvaleric acid, and 2-tridecanone. These methods increased cooked notes, associated with 5-methyl-3-heptanone, 3-butyn-1-ol, hydroxyacetone, and acetoin. Rancidity was linked to acids such as isobutyric acid, isovaleric acid, and heptanoic acid, with high temperatures effectively reducing these compounds. Prolonged temperature changes in PAS and HTS accelerated lipid oxidative degradation and the Maillard reaction, involving free fatty acids in the formation of alcohols, aldehydes, esters, and lactones. These findings provide a theoretical basis for studying coconut milk flavour deterioration.