Abstract:
Red algae (Class Rhodophyceae) are seaweeds with a high economic trend in agar
production. As Sri Lanka is equipped with a high diversity and endemism of Gracilaria
species, we have a high potential for producing agar-based extracts in commercial scale
reaching sustainability. Therefore, this work reports on the production of agar extracts
from the seaweed Gracilaria lemaneiformis by means of selected simple protocols
based on hot water extraction, with a future direction on developing a useful agar-based
product with prescreening for plastic pollutants because macroalgae have a resilient
capacity to trap both mesoplastics (5–10 mm) and microplastics (less than 5 mm). The
collected plants from Trincomalee and Morawala, Negombo, Sri Lanka using random
quadrat sampling method in September, 2023 were screened for debris prior storage.
The agar production was performed in four different methods with and without
pretreatment of 2% sodium hydroxide as per the literature using simplified water
extraction protocols with slight modifications and prescreening for microplastics (MPs).
According to the results, extraction efficiency increases with the use of dry powder
form, rather than the direct extraction of thalli. A significantly higher percentage agar
extraction had recorded when extracting using the dry powder form regardless of
pretreatment with a percentage extraction of 19.46%. The selected species has been
contaminated with microplastics (0.417±0.188 items/5 g), among which the majority
are fibers of secondary MPs. It is highlighted that there is a significant difference
among the concentration of microplastics in filtrates of the washing steps. It is evident
that the mean MPs concentration present in the initial dried sample is decreasing with
the number of washing steps (DW3-0 items/5 g) starting from the sodium hydroxide
pretreated sample (NaOH—0.667±0.210 items/ 5 g) (p<0.05). Thus, more the washing
steps would ensure the decreased contamination of MPs entrusting reduced MPs
toxicity and enhancement of the good quality of the extracted product in commercial
process. A conclusion can be made that G. lemaneiformis has been significantly
contaminated with microplastics and the agar extraction protocol with pretreatment of
sodium hydroxide followed by thorough water washing could be recommended for
enhancing the quality of agar extracts. Further, this research should be developed to a
better way of extracting agar with higher efficiency and producing a useful agar-based
product.
