Wettability of commercial starches and galactomannans

ABSTRACT

This paper describes the wettability of basic commercial polysaccharides: starches (potato PS, wheat WS, corn CS, tapioca TS, kuzu KS) and galactomannans (fenugreek gum FG, guar gum GG, tara gum TG, locust bean gum LBG). The study was conducted using the Washburn capillary rise method and thermal drying. This allowed one to determine the material constant C, contact angle θ, surface free energy of solid SFE, and initial moisture content M. The measured values of contact angle θ and surface free energy SFE indicated that potato starch (70.9°, 41.1 mN · m⁻¹) and wheat starch (88.4°, 30.2 mN · m⁻¹) were characterized by the highest and lowest wettability among the examined starches, respectively. In turn, the galactomannans were poorly wettable substances. Their contact angles θ were approximately equal to 90°, showing a slight increase with increasing substitution degree. The observed decrease in surface free energy SFE from 30 to 29.6 mN · m⁻¹ indicated a very minor hydrophobization of their surfaces. Material constant C was practically independent of temperature, and an increase in initial moisture content M in the examined starches and galactomannans proceeded according to the following schemes: CS < PS < WS < TS < KS and LBG < TG < GG < FG, respectively.

GRAPHICAL ABSTRACT

KEYWORDS:

• Contact angle
• galactomannan
• starch
• Washburn method
• wettability