Systematic application of UPLC-Q-ToF-MS/MS coupled with chemometrics for the identification of natural food pigments from Davidson plum and native currant

Abstract

This study investigates the potential of Australian Traditional foods as novel sources of natural colourants for food applications, employing untargeted metabolomics and chemometrics. Two native species were analysed: Davidson plum and native currant. The species were quantitatively assessed for colour properties using the CIELAB colour system in conjunction with Ultra Performance Liquid Chromatography-Quadrupole Time of Flight Tandem Mass Spectrometry (UPLC-Q-ToF-MS/MS). The results highlight diverse phenolic, flavonoid, and significant anthocyanin levels in Davidson plum and native currant, contributing to their robust red hues, comparable to commercial blueberry standards. Davidson plum and native currant exhibited high phenolic, flavonoid, and anthocyanin levels, contributing to vibrant red hues and significant bioactivity. Compared to blueberry, these species showed greater redness (a*) and chroma. Native currant demonstrated the highest phenolic content (146.73 mg g^-1), anthocyanin content (14.48 mg g^-1), and antioxidant activity (95.48 μmol Trolox equivalents/g). The chemometric analysis identified 46 key pigment metabolites, including anthocyanins and flavonoids, directly correlating to observed colour properties. UPLC-Q-ToF-MS/MS combined with CIELAB colourimetry facilitated pigment identification and colour analysis. These findings position Davidson plum and native currant as promising natural food colourants and functional ingredients. Additionally, the study underscores the efficacy of integrating chemometric analysis with CIELAB and UPLC-Q-ToF-MS/MS methodologies for pinpointing specific metabolites that influence the colour properties of these Traditional foods. This approach facilitates a deeper understanding of how indigenous Australian bushfoods can be innovatively incorporated into the food industry, aligning with consumer demand for natural and sustainable food options.

Keywords: Anthocyanins; CIELAB; Chemometrics; Colour; Metabolomics; Traditional foods; UPLC-Q-ToF-MS/MS.

Graphical abstract

Fig. 1

Blueberry (Vaccinium corymbosum), davidson plum (Davidsonia puriens), and native currant (Antidesma erostre). The native currant shows a range of colours during ripening, from yellow to black. Ripened fruits were used for colour extracts. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Metabolites of native currant, davidson plum, and blueberry. Stepwise multivariate analysis shows trimming the dataset to only include pigment compounds as having no impact on class groupings. QC = quality control, where a mixture of the replicates was injected. Mixed QC is a mix of all samples included in the analysis. Centred mixed QC represents a good model fit for shared features. Fig. 2a: PCA scores and loadings plots of total metabolomic features (n = 306); R² (cum) = 81.8 % (PC1 = 38.9 %, PC2 = 27.3 %, PC3 = 15.6 %) Q² (cum) = 75.7 %. Fig. 2b: PCA scores and loadings plot using pigment metabolomic data (n = 54); R² (cum) = 87.5 % (PC1 = 42.4 %, PC2 = 31.7 %, PC3 = 13.4 %) Q² (cum) = 75.7 %.

Fig. 3

Predictive multivariate analysis of CIELAB and pigment compounds in davidson plum, native currant, and blueberry. Fig. 3a: PLS scores and loadings plots of the pigment; R² (cum) = 76.7 % (PC1 = 39.7 %, PC2 = 36.9 %) Q² (cum) = 97.1 %. Fig. 3b: PLS biplot of pigment compounds and CIELAB colour metrics.

Fig. 4

Coefficient of metabolite contribution to CIELAB metric separation in native currant, davidson plum and blueberry. The positive coefficient means that as the metabolite concentration increases, the colour metric's value (L*, a*, or b*) also increases. The positive coefficient for a* indicates that higher levels of a particular metabolite are associated with a shift towards red in the colour spectrum. The negative coefficient means that as the metabolite concentration increases, the colour metric's value decreases. For example, a negative coefficient for L* would indicate that higher levels of a specific metabolite result in a darker colour (lower lightness). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)