Rheological and stability properties of Citrullus lanatus mucosospermus, lanatus citroides and moringa oleifera seed hydrocolloids in oil-in-water

Abstract

When mixed with water, hydrocolloids create gel-like structures and have grown in popularity due to their wide range of applications in food, medicine, and other industries. The extraction of hydrocolloids from natural sources, such as seeds, is an exciting idea because of the potential diversity in composition and function. In a variety of sectors, the use of seeds from Citrullus lanatus mucosospermus (egusi, EG), Citrullus lanatus citroides (makataan, MA), and Moringa oleifera (moringa, MO) as a hydrocolloid is in line with the growing demand for sustainable and natural products worldwide. This study examined hydrocolloids derived from EG, MA, and MO seeds, highlighting their diverse physicochemical and functional properties. Hydrocolloids were extracted from the seeds and analysed for their proximate composition, particle size distribution, and interfacial tension using the hot water extraction method. The raw oilseed flours had varying amounts of protein. Hydrocolloids had a higher protein concentration than raw oilseeds, greatly improving the amino acid profile. Furthermore, the hydrocolloid ash concentration ranged from 4.09% to 6.52% w/w dry weight, accompanied by low-fat levels. Smaller particles in all hydrocolloid samples showed a more narrow and uniform size distribution, suggesting a better degree of homogeneity in particle size within this range, according to the examination of particle size distribution. This implies a lower chance of size variation for small particles, which may affect their rheological and functional characteristics in different applications. This study also investigated the rheological behaviour of three novel hydrocolloids: egusi seed hydrocolloid (EGH), makataan seed hydrocolloid (MAH), and moringa seed hydrocolloid (MOH) in semi-concentrated (20-50 wt) as well as concentrated (50-75 wt%) slurries, when subjected to a shear steady flow, to reversible minor strain in amplitude as well as frequency sweep modes deformation. The high protein content of these hydrocolloids (48.12%, 34.00%, and 35.00% for MOH, MAH, and EGH, respectively—reduced the interfacial tension. Regardless of the hydrocolloid type and process parameters (pH = 4– 9; temperatures =30-75 oC; mixing time = 1–10 minutes; concentration = 20–50 wt%), semi concentrated slurries were pseudoplastic materials that behave like viscous liquids with no yield stress; G” > G’ in the entire range of strain (0.1–200%). The storage modulus, yield stress, and slurry concentration correlation showed two deflection points/transitional points, 50 wt% and 67 wt%, respectively. The first transition point was present in all three hydrocolloids, whereas the second was only related to EGH and MAH slurries; MOH-based slurries did not display such a point. The first transition point (50 wt%) was associated with the onset of structure formation. The bottle test further confirmed that slurries containing more than 50% by mass hydrocolloids did not flow when inverting the vessels. The second transitional point marked the boundary between the region of the slow or rapid response of the strength or rigidity of the structure of the slurry of EGH and MAH with changes in hydrocolloid concentration. The strength of the structure increased rapidly with the hydrocolloid concentration below this point, whereas a slow increase was observed above the critical point. Conversely, the rigidity of the structure of the slurries displayed an opposite effect. Interestingly, because of its high content of hydrophobic proteins, the dominating mechanism of structure formation within MOH slurries was the entanglement network of polymers (proteins and polysaccharides) whose yield stress originated from the presence of high concentrations of dispersed particulate material within the structure. This gave rise to a weak, predominantly elastic rather than viscous gel with a cohesive energy range of 0.2 – 0.7 kJ. On the other hand, due to their high hydrophilic protein content, the dominant mechanism of structure formation within EGH and MAH slurries could be cross-liking rather than entanglement. This cross linking generated a predominantly elastic gel with a relatively high cohesive energy of 2-7 kJ. The effects of extracted hydrocolloid on the stability and rheological behaviours of oil in-water (O/W) emulsions (MOH, MAH, and EGH) were investigated using plant-based emulsifiers from moringa, makataan, and egusi hydrocolloids. In this work, the mixture design was optimised for each level of limitation between hydrocolloid, oil, and water. Stability testing was used to experiment with and optimise the mixture. The droplet size distributions, morphology, creaming index, and polydispersity index were all measured on 11 emulsions, and the best emulsion with a stable profile was chosen for further investigation. The rheological characteristics and the microscopic morphology were acquired to understand the mechanism and interaction of droplets in the O/W emulsion. The results indicated that optimal for O/W emulsions was found in samples with 20-30% hydrocolloid, 37-40 % oil and 25-45 % water while using the three hydrocolloids. EGH and MAH, with the lowest hydrocolloid composition, showed the smallest droplet size and highest creaming index values. The study concludes by highlighting the promising potential of hydrocolloids generated from egusi (EG), makataan (MA), and moringa (MO) seeds. These plant-based hydrocolloids displayed different functional features, including increased protein content, considerable rheological behaviour, and excellent stabilisation in oil-water emulsions. Their capacity to produce gel-like structures, lower interfacial tension, and increase structural rigidity is useful in food systems, particularly for thickening, emulsifying, and texture modification. These findings add to the growing interest in using sustainable, natural ingredients to improve food formulation and product durability.