Application of imaging Raman spectroscopy to study the distribution of Kappa carrageenan in the seaweed Kappaphycus alvarezii

Abstract

Raman imaging spectroscopy has been applied to analyze carrageenan production in the red alga, Kappaphycus alvarezii. The Raman spectra of the sample suggested that the thallus of K. alvarezii mainly consists of cellulose and carrageenan. A partial least square regression prediction model for carrageenan semi-quantitative analysis was built with a simple two-material system and applied to visualize the three-dimensional carrageenan distribution in the algal body. The images clearly depicted the carrageenan distribution in carrageenan-rich and carrageenan-poor samples. Images stained for carrageenan with methylene blue showed results similar to those from analysis with Raman imaging spectroscopy. Our results suggest that Raman imaging spectroscopy, which is nondestructive and label free, is an accurate and useful method for detecting carrageenan distribution in algae.