Effects of Physical and Drying Treatments on Near-Infrared Spectroscopic Characterization of Starch, Sucrose, and Protein Peaks in Ulva ohnoi with Respect to Model Spectra

Ulva ohnoi had different drying techniques applied, including air-drying, oven-drying, microwave-assisted, and freeze-drying (lyophilization), and three other physical treatments such as osmosis, boiling, and ultrasonication. The effects of these treatments on the near-infrared spectra, water activity, and weight of Ulva ohnoi samples were studied. Also, the protein, polysaccharide (mainly starch), and disaccharide (mainly sucrose) peaks in the obtained spectra were defined and characterized using different models.

The results showed that microwave-assisted, oven-drying, and freeze-drying have significant effects on the spectra, with lyophilization being the most effective drying technique. Using the potato starch spectrum model, three peaks and one valley corresponding to starch were detected at 4750 cm^-1, 5186 cm^-1, 6900 cm^-1, and 4500 cm^-1, respectively.

In addition, two peaks corresponding to sucrose at 5186 cm¹ and 6980 cm^-1 and three peaks corresponding to proteins were detected using model spectra. The comparison of the dry U.ohnoi spectrum with the studied models suggests that the Ulva ohnoi proteins have an alpha-helix-dominated secondary structure.

Moreover, after rehydration, spectra of some treated samples returned to the initial conformation as the fresh ones, which is a significant preservative characteristic for the food industry. This study contributes to the growing body of research on algae as a sustainable food source, and it offers insights into the practical application of NIR spectroscopy for analysis of protein and carbohydrate content.