Algae are becoming a strategic source of fuels, food, feedstocks, and biologically active compounds. This potential has stimulated the development of innovative analytical methods focused on these microorganisms. Algal lipids are among the most promising potential products for fuels as well as for nutrition. The crucial parameter characterizing the algal lipids is the degree of unsaturation of the constituent fatty acids quantified by the iodine value. Here we demonstrate the capacity of the spatially resolved Raman microspectroscopy to determine the effective iodine value in lipid storage bodies of individual living algal cells. The Raman spectra were collected from three selected algal species immobilized in an agarose gel. Prior to immobilization, the algae were cultivated in the stationary phase inducing an overproduction of lipids. We employed the characteristic peaks in the Raman scattering spectra at 1,656 cm−1 (cis C═C stretching mode) and 1,445 cm−1 (CH2 scissoring mode) as the markers defining the ratio of unsaturated-to-saturated carbon-carbon bonds of the fatty acids in the algal lipids. These spectral features were first quantified for pure fatty acids of known iodine value. The resultant calibration curve was then used to calculate the effective iodine value of storage lipids in the living algal cells from their Raman spectra. We demonstrated that the iodine value differs significantly for the three studied algal species. Our spectroscopic estimations of the iodine value were validated using GC-MS measurements and an excellent agreement was found for the Trachydiscus minutus species. A good agreement was also found with the earlier published data on Botryococcus braunii. Thus, we propose that Raman microspectroscopy can become technique of choice in the rapidly expanding field of algal biotechnology.
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机译：藻类正成为燃料，食品，原料和生物活性化合物的战略来源。这种潜力刺激了针对这些微生物的创新分析方法的发展。藻类脂质是燃料和营养方面最有希望的潜在产品之一。表征藻类脂质的关键参数是通过碘值量化的组成脂肪酸的不饱和度。在这里，我们展示了空间分辨拉曼光谱技术确定单个活藻细胞脂质存储体中有效碘值的能力。从固定在琼脂糖凝胶中的三种选定藻类收集拉曼光谱。在固定之前，将藻类在固定相中培养，诱导脂质的过量生产。我们在拉曼散射光谱中以1656 cm -1 （顺式C═C拉伸模式）和1,445 cm -1 （CH2剪切模式）的特征峰作为标记定义藻类脂质中脂肪酸的不饱和碳原子键与饱和碳碳键之比。首先对已知碘值的纯脂肪酸定量这些光谱特征。然后，将所得的校准曲线用于从活藻细胞的拉曼光谱中计算其储存脂质的有效碘值。我们证明了三种研究的藻类物种的碘值显着不同。我们的碘值的光谱估计值已通过GC-MS测量得到了验证，并且对于曲霉属物种发现了极好的一致性。也发现了与早先发布的关于布氏葡萄球菌的数据的良好协议。因此，我们建议拉曼光谱技术可以成为藻类生物技术迅速发展领域中的首选技术。
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