Analysis of WMP and SMP Reconstitute Headspace Volatiles and Correlations with Sensory Properties

Abstract

This research demonstrates through the use of Solid Phase Micro-Extraction Gas- Chromatography Mass-Spectrometry (SPME-GCMS), that volatile (aldehyde and methyl ketone) headspace expression in milk powder reconstitute is variable over time, influenced primarily by hydrophobicity and functionality. Increased hydrophobicity was shown to be synonymous with increased retention, while increased functional reactivity (aldehyde>ketone) linked to decreased temporal headspace stability. This variation can be minimised through effective normalisation, such as in utilising 2-methyl 3-heptanone (2M3H) to normalise methyl ketones (2-heptanone and 2-nonanone) within the SMP reconstitute headspace. Successful methyl ketone and aldehyde normalisation allowed for comparisons to be made between different SMP and WMP samples. However, such comparisons required minimum product variation (starting milk feed, processing parameters and product specification) to ensure differences in volatile expression, were most likely a result of matrix structural differences, rather than of differences in starting volatile content. Thus correlations with sensory scores were limited to a select product of typical specification made within the same facility. The headspace concentration of volatiles observed in milk powder reconstitute has been previously used and successfully correlated with milk powder flavours and aromas. The effective comparisons achieved between methyl ketone and aldehyde expression, in this instance afforded correlations of varying degrees with sensory properties including; sweetness (flavour), fatty mouthfeel (texture), yellowness (appearance), milky (aroma), viscosity (texture) and creaminess (flavour). Some sensory property correlations were likely not resultant from matrix reconstitute changes, including milky (aroma) and sweetness (flavour). In these instances methyl ketone increases likely coincided with increases in other volatiles known to decrease sweet aromatic flavours and increase aroma perception. With respect textural attributes, SMP reconstitute matrix structural changes (protein structure and fat globule size distribution) were thought to increase lipid surface area and fatty mouthfeel, increasing protein denaturation and volatile headspace expression. This correlation likely afforded the link between volatiles and creaminess (flavour) of SMP reconstitute. The WMP reconstitute matrix structure however, did not seem to influence volatile headspace expression. For WMP, starting volatile content seemed the primary variable, with texture (viscosity) correlations afforded indirectly through volatile correlations with other sensory properties (yellow appearance).