Aqueous extraction optimisation of okra (Abelmoschus esculentus) mucilage for food processing applications: Rheological, FTIR, and TGA characterisation

Abstract:

Hydrocolloids, such as plant mucilage, are increasingly utilised in food and non-food applications due to their multifunc­tional properties, including thickening, emulsifying, and foaming. However, limited availability and processing challenges have prompted exploration of alternative sources and optimised extraction techniques. This study aimed to optimise the extraction conditions of crude okra (Abelmoschus esculentus) mucilage using Response Surface Methodology (RSM) and to characterise its rheological properties and structural composition via Fourier-Transform Infrared (FTIR) spectroscopy. A Central Composite Design was used to evaluate the extraction temperature (X₁), okra mass (X₂), and water volume (X₃) as independent variables, with mucilage Yield (Y) as the response variable. Rheological measurements were performed using a Brookfield RST-SST Rheometer and modelled with the Herschel–Bulkley equation. FTIR spectroscopy was used to identify functional groups in the mucilage. The quadratic polynomial model reliably predicted mucilage yield (R^²=0.8673 and adjusted R^²=0.7578, p<0.0001). Extraction water (p=0.0001) and okra mass (p=0.0294) significantly influenced yield, while temperature showed no significant linear effect. Optimal extraction conditions were 619.3 mL of extraction water and 131.4g of okra, at 80^°C, resulting in a predicted yield of 11.87%. Rheological analysis revealed a pseudoplastic, shear-thinning behavior (flow index n=0.708) with a moderate thickening capacity, suitable for suspension and gel formation. FTIR analysis confirmed polysaccharide composition with hydroxyl, carbonyl, ester, and β-glycosidic functional groups. TGA analysis confirmed that okra mucilage thermal stability is sufficient for most food processing involving moderate heat treatments. Okra mucilage demonstrates properties ideal for use as a natural thickener, emulsi­fier, binder, and gelling agent in the food industry, offering a reliable basis for its incorporation into functional formula­tions and innovative applications. FTIR and TGA analyses confirm that the extracted okra mucilage is chemically pure, structurally uniform, and free of significant protein or lipid contamination, making it suitable for food, pharmaceutical, and nutraceutical applications.