The Effects of Using Shortwave Infrared Lamp-Drying and Alkali Pretreatment on the Color, Texture, and Volatile Compounds of Gongliao Gelidium amansii Seaweed and Its Jelly Qualities

Abstract

This study investigated the effects of alkaline pretreatment and drying methods on the physicochemical properties of Gelidium amansii and the quality of the resulting agar jelly. Seaweeds with or without alkaline pretreatment were subjected to either sun-drying or shortwave infrared (SWIR) lamp-drying for three or seven cycles to evaluate whether SWIR drying could replace conventional sun-drying by reducing drying time and whether alkaline pretreatment could enhance gel hardness. The results showed that both drying methods effectively reduced moisture content, while the alkaline pretreatment significantly increased the ash content, likely due to the removal of water-soluble components. Marked color improvement was observed after seven cycles of sun-drying or following alkaline pretreatment, with the appearance changing from purplish red to bright golden yellow, which is closer to traditional quality expectations. Although SWIR lamp-drying was more energy-efficient, it resulted in limited color improvement. Volatile compound analysis revealed that deviations from the fresh control increased with the number of sun-drying cycles, whereas alkaline pretreatment and infrared-drying induced more pronounced changes in volatile profiles. Among all of the treatments, Gelidium subjected to seven sun-drying cycles produced jellies with the most favorable texture, indicating enhanced agar gel formation through repeated washing and drying. In contrast, the combination of alkaline pretreatment and infrared-drying restricted agar extraction, likely due to tissue hardening and insufficient light intensity, resulting in weak or negligible gel formation. Overall, both the drying method and alkaline pretreatment significantly influenced the Gelidium quality and agar gel properties; despite being labor-intensive, traditional washing and sun-drying processes remain critical for achieving desirable product quality.