Determining the Authenticity of Spirulina Dietary Supplements Based on Stable Isotope and Elemental Composition

Abstract

While the demand for Spirulina dietary supplements continues to grow, product inspection in terms of authenticity and safety remains limited. This study used the stable isotope ratios of light elements (C, N, S, H, and O) and the elemental composition to characterize Spirulina dietary supplements available on the Slovenian market. Forty-six samples were labelled as originating from the EU (1), non-EU (6), Hawaii (2), Italy (2), Japan (1), Portugal (2), Taiwan (3), India (4), and China (16), and nine products were without a declared origin. Stable isotope ratio median values were -23.9‱ (-26.0 to -21.8‱) for δ¹³C, 4.80‱ (1.30-8.02‱) for δ¹⁵N, 11.0‱ (6.79-12.7‱) for δ³⁴S, -173‱ (- 190 to -158‱) for δ²H, and 17.2‱ (15.8-18.8‱) for δ¹⁸O. Multivariate statistical analyses achieved a reliable differentiation of Hawaiian, Italian, and Portuguese (100%) samples and a good separation of Chinese samples, while the separation of Indian and Taiwanese samples was less successful, but still notable. The study showed that differences in isotopic and elemental composition are indicative of sample origins, cultivation and processing methods, and environmental conditions such that, when combined, they provide a promising tool for determining the authenticity of Spirulina products.

Keywords: Arthrospira spp.; Spirulina; authenticity; dietary supplements; elements; geographical origin; quality; stable isotope ratio.

Figure 1

A plot of δ²H and δ¹⁸O relationship in Spirulina food supplements. The blue dots in the plot represent the analyzed Spirulina samples and the dotted line through the data points indicates a correlation of the data (y = 7.8x − 308.8; r² = 0.82, p < 0.001).

Figure 2

(a) PCA score plot of Spirulina food supplements (n = 46) available on the Slovenian market and (b) PCA variables loading plot. Orange circles in figure (a) mark the samples of undeclared origin (NS).

Figure 3

Box plots of selected elemental and nitrogen isotopic composition of Spirulina food supplements according to declared geographical origin, with specifically marked samples of undeclared origin (NS). (a) δ¹⁵N, (b) Cl, (c) Fe, (d) Zn, (e) Br, and (f) Rb. The values presented under the label ‘Asia’ include Japanese, Indian, Chinese, and Taiwanese samples.

Figure 4

Discriminant function score plot (a) and discriminant loadings plot (b) for Spirulina food supplements available on the Slovenian market (China (n = 16), Hawaii (n = 2), India (n = 4), Italy (n = 2), Portugal (n = 2), and Taiwan (n = 3)). Red vectors indicate the most, and blue vectors are the least significant variables for sample separation.

Figure 5

OPLS-DA score plots and VIP values in the pairwise comparisons between different declared countries of origin of Spirulina products derived from all isotopic and elemental composition data. The ellipse on the score plot represents the 95% confidence interval. Red dotted line indicates a criteria for identification of the variables, important for the developed model. Separation of the most numerous class, China, is presented, from Hawaii (a), India (b), Italy (c), Portugal (d), and Taiwan (e).