Abstract
The effect of freezing combined with alkali treatment on physicochemical property of konjac glucomannan (KGM) with different molecular weight was investigated in this work. The properties and structure of degraded KGM was characterized by means of intrinsic viscosity measurement, atomic force microscope (AFM) and Fourier transformation infrared (FT-IR). The results suggested that the intrinsic viscosity of KGM solution gradually decreased during the ultrasonic treatment. The AFM observation indicated that KGM with lower viscosity average molecular weight had smaller height and lateral diameter of molecules. The main repeating units of the KGM chain could not be destroyed no matter how long the KGM was sonicated. Rheometrical studies revealed that with increasing alkali concentration from 0% to 0.36%, both viscosities and shear stress of deacetylated konjac glucomannan (Da-KGM) system were increased and moduli G′ were substantially higher in either freezing or unfreezing samples. Da-KGM system performed a solid-like behavior (G′ > G′′) along the frequency range after freezing treatment. With increasing sonication time, both viscosity and shear stress of unfreezing samples were decreased while had an inverse effect for freezing treated samples. The modulus G′ and G′′ declined for unfreezing samples but rise significantly for freezing treated samples with increase of sonication time.
Highlights
Konjac glucomannan (KGM) is a kind of natural neutral polysaccharide which extracted from konjac tuber
The usual ratio of mannose and glucose in KGM lies between molar ratios of 1:1.5 and 1:1.6 with a high degree of substitution (5∼10%) of the OH groups by acetyl groups (Figure 1) [1]
The intrinsic viscosity [η] is often obtained from the extrapolation of lnηrel /c or ηsp /c to infinite ined with freezing as a means to regulate the rheological properties of KGM so as dilution according to the Huggins and Kraemer empirical expressions as follows: its application in healthy food
Summary
Konjac glucomannan (KGM) is a kind of natural neutral polysaccharide which extracted from konjac tuber. Ultrasonic treatment was found to be an effective approach for KGM degradation [7]. Because ultrasonic treatment many pyrolytic and radical induced degradation processes, a series of degradation products were products were detected, and many mechanisms were proposed. It has It been investigated on involves many pyrolytic and radical induced degradation processes, a series of degradation detected, and many mechanisms were proposed It has been widely investigated on ultrasonic ultrasonic degradation of polysaccharides. It of is KGM expected to develop ultrasonic with freezing as a means to regulate the rheological properties so as to further expand its to further expand its application in healthy food. Degradation with freezing as a means to regulate the rheological properties of KGM so as application incombined healthy food
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