Effects of rainwater on the carrageenan yield and quality and dry yield biomass of eucheumatoid seaweed Kappaphycus alvarezii

Abstract

Kappaphycus alvarezii, a commercially valuable eucheumatoid seaweed, is widely cultivated in equatorial regions for its kappa-carrageenan. A common post-harvest practice among local farmers involves drying the seaweed using the hanging method, often with exposure to rain. This study investigates the effects of rainwater exposure on the carrageenan yield and quality, as well as the dry yield biomass, of K. alvarezii. Four rainwater soaking times (0, 30, 60, and 90 min) were applied to both fresh and dried forms of K. alvarezii. The samples were then dried or re-dried, and their carrageenan properties were analyzed. Results indicate that rainwater significantly reduces dry yield biomass in both fresh and dried forms, while substantially improving carrageenan yield. In its fresh form, exposure to rainwater notably increased gel strength after 90 min of soak. However, when dried seaweed was soaked and re-dried, gel strength was reduced. Rainwater generally had no effect on viscosity or syneresis index. Gelling temperature was significantly affected by rainwater exposure in fresh seaweed but not in dried samples. Melting temperature in fresh forms was unaffected, but rainwater exposure reduced it in dried seaweed after 90 min of soak. Moisture content was significantly reduced by rainwater in both fresh and dried forms. This research highlights the potential impacts of rainwater on the post-harvest processing of Kappaphycus.