New Studies on the Galactomannan Extracted from Trigonella foenum-graecum (Fenugreek) Seed: Effect of Subsequent Use of Ultrasound and Microwave on the Physicochemical and Rheological Properties

Abstract

The effect of subsequent use of ultrasound and microwave on the physicochemical and rheological properties of galactomannan extracted from fenugreek seed (locally called as Shanbalileh) was investigated. Maximum yield of 18.54% was gained at optimized conditions: ultrasound power of 150 W, microwave power of 500 W, seed to water ratio of 1:30, and extraction time of 150 min. Chemical composition of the galactomannan was 7.03% (wb) moisture, 5.35% (db) ash, 0.85% (db) protein, 0.59% (db) lipid, and 85.89% (db) carbohydrate, respectively. FT-IR analysis admitted representative peaks of polysaccharide at 3400, 2920, 1620, 1400, and 1050/cm. Thermal analysis results revealed a melting range of 60–135 °C and degradation temperature of 280.54 °C. XRD pattern illustrated a large degree of crystallinity in the galactomannan structure. The results of SEM imaging indicated that the obtained galactomannan had a smooth surface. The steady shear flow experiments showed that the shear stress–shear rate, apparent viscosity–shear rate, and shear stress–time well fitted in Herschel–Bulkley, Carraeu, and Figuni–Shoemaker models. The samples with 0.5 and 1% w/v concentration demonstrated viscous-like and sample with 1.5% w/v indicated gel-like behavior upon strain and frequency sweep tests. Other parameters including bulk and tapped density, powder cohesiveness, powder compressibility index, DPPH-free radical scavenging activity, powder solubility, water holding capacity (WHC), and oil holding capacity (OHC) were also evaluated.