NUTRITIONAL CONTENT AND CHEMICAL ANALYSIS OF SEAWEED RESIDUES EXTRACTED THROUGH VARIOUS CARRAGEENAN PROCESSING METHODS AS POTENTIAL PLANT BIOSTIMULANT

The rising interest in plant biostimulants as eco-friendly alternatives to chemical fertilizers has led to significant attention toward Kappaphycus alvarezii. This seaweed species is rich in nutrients, phytohormones, and bioactive compounds, making it a promising candidate for plant biostimulant. However, the circumstances appear to be different when considering seaweed residues. In this study, the nutritional and biochemical compounds of the seaweed residues which generated through various carrageenan extraction methods such as physical, biological and chemical treatments on Kappaphycus alvarezii were determined. Proximate analysis conducted on all residues using the AOAC method revealed moisture content at 99% (w/w), protein levels of less than 0.1% (w/w), fat content between 2.1% and 3.1% (w/w), and ash levels ranging from 0.01% to 0..1% (w/w). No detectable levels of total carbohydrates were found in any of the residues. Furthermore, nutritional analysis via inductively coupled plasma–optical emission spectroscopy (ICP-OES) identified macronutrient concentrations in the residues, including nitrogen (<0.1% (w/w)), phosphorus (675–840 mg/kg), potassium (1325 – 1470 mg/kg), magnesium (52.5 – 85 mg/kg), calcium (310 – 625 mg/kg) and sodium (525 – 745 mg/kg), as well as trace micronutrients (iron, manganese, boron, and molybdenum) at specific concentrations. Remarkably, the DPPH assay showed that all the residues exhibited antioxidant activities, ranging from 47% until 56%. This study highlights the potential of seaweed residues as plant biostimulants, offering a sustainable addition to agricultural practices while contributing to effective zero-waste management in the seaweed industry.