Viscoelastic properties of waxy maize starch and selected non-starch hydrocolloids gels

Physical Stability of Chestnut Lily Beverages (CLB): Effects of Shear Homogenization on Beverage Rheological Behavior, Particle Size, and Sensory Properties

The processing parameters have a crucial influence on the stability and sensory quality of beverages. The focus of this study is to observe the rheological behavior, particle size distribution, stability, color change, and sensory evaluation of chestnut lily beverages (CLB) at different rotational speeds (0~20,000 rpm) using a high-shear homogeneous disperser. The CLB system exhibited non-Newtonian shear-thinning behavior. As the homogenization speed increased (0~12,000 rpm), the viscosity increased (0.002~0.059 Pa.s). However, when the rotational speed shear continued to increase (12,000~20,000 rpm), the viscosity decreased slightly (0.035~0.027 Pa.s). Under all homogeneous conditions, the turbidity and precipitation fractions were the lowest when the rotational speed was 12,000 rpm: the sedimentation index was lowest at this point (2.87%), and the relative turbidity value of CLB was largest at this point (80.29%). The average beverage particle diameter and ascorbic acid content showed a downward trend at the homogenization speed from 0 to 20,000 rpm, whereas the total soluble solids (TSS) content followed the opposite trend. The results show that these physical properties can be correlated with different rotational speeds of homogenization. This study explained the effect of homogenization speed on CLB properties, which needs to be considered in beverage processing, where high-speed shear homogenization can serve as a promising technique.

Impact of Guar Gum and Locust Bean Gum Addition on the Pasting, Rheological Properties, and Freeze-Thaw Stability of Rice Starch Gel

Improving the gel texture and stability of rice starch (RS) by natural hydrocolloids is important for the development of gluten-free starch-based products. In this paper, the effects of guar gum and locust bean gum on the pasting, rheological properties, and freeze−thaw stability of rice starch were investigated by using a rapid visco analyzer, rheometer, and texture analyzer. Both gums can modify the pasting properties, revealed by an increment in the peak, trough, and final viscosities, and prevent the short-term retrogradation tendency of RS. Dynamic viscoelasticity measurements also indicated that the starch−gum system exhibits superior viscoelastic properties compared with starch alone, as revealed by its higher storage modulus (G′). Compared with the control, the hysteresis loop area of the guar gum-containing system and locust bean gum-containing system was reduced by 37.7% and 24.2%, respectively, indicating that the addition of gums could enhance shear resistance and structure recovery properties. The thermodynamic properties indicated that both gums retard short-term retrogradation as well as long-term retrogradation of the RS gels. Interestingly, the textural properties and freeze−thaw stability of the RS gel were significantly improved by the addition of galactomannans (p < 0.05), and guar gum was more effective than locust bean gum, which may be due to the different mannose to galactose ratio. The results provide alternatives for gluten-free recipes with improved texture properties and freeze−thaw stability.

Effect of potassium alum addition on the quality of potato starch noodles

The objective of this study was to investigate the effects and mechanism of potassium alum (PA) on potato starch noodles to provide a theoretical basis for future searches for new alternatives for PA that are not harmful to the body. The amount of amylose leakage significantly decreased with the PA addition. SEM showed that the honeycomb structure of potato starch noodles with 0.1% PA was diminished. The number of internal pores and average area decreased from 92 and 580.09 units to 72 and 652.58 units, respectively. NMR indicated that the water holding capacity of potato starch noodles containing PA was greater than that of the control. XRD showed that the crystal structure of potato starch noodles was destroyed and that the crystallinity of potato starch noodles with PA increased from 16.65 to 19.64%. G' and G'' increased, but tanδ decreased. FT-IR showed that PA caused the O-H stretching vibration in the absorption peak to move in the high-field direction and that the ionic bond was dominant in the PA-potato starch interaction system.

Linear Viscoelastic Properties of Selected Polysaccharide Gums as Function of Concentration, pH, and Temperature

Hydrocolloids have been intensively investigated due to their ability to modify the rheology of the system where they are employed. They find application as thickening and gelling agents in many food, cosmetic, and pharmaceutical preparations, due to their biocompatibility and biodegradability. The present study aims to provide an exhaustive and comprehensive viscoelastic characterization of a series of hydrocolloid formulations, as function of concentration, pH, and temperature. Glucomannan, xanthan gum, tara gum, guar gum, konjac gum, and gellan gum have been analyzed at two concentrations (0.5% w/w and 1.5% w/w), using three different pH conditions (pH 1.2, 5.5, and 6.8). Their viscoelastic properties have been monitored measuring the main rheological parameters, namely, storage modulus G' and loss modulus G'' as function of frequency, time, and temperature. The results obtained show a clear dependence of the linear viscoelastic properties of the systems on concentration and pH, while the temperature was not a critical factor. Glucomannan, xanthan gum, tara gum, and guar gum samples prepared in phosphate buffer (pH 6.8) at the final concentration of 1.5% (w/w) have been selected as the most promising systems for further investigations, exploring the possibility of combinations to improve the rheological properties. PRACTICAL APPLICATION: Glucomannan, xanthan gum, tara gum, guar gum, konjac gum, and gellan gum have been chosen among the most common thickening agents derived from plants to perform a systematic investigation of the influence of pH, concentration, and temperature on the rheological properties of their water dispersions. The data obtained may be useful for further application of these hydrogels in the nutraceutical field as thickeners, texture modifiers, emulsifiers, stabilizers, and gelling agents.

Understanding the viscoelastic behavior of collagen matrices through relaxation time distribution spectrum

This study aims to provide understanding of the macroscopic viscoelastic behavior of collagen matrices through studying the relaxation time distribution spectrum obtained from stress relaxation tests. Hydrated collagen gel and dehydrated collagen thin film was exploited as two different hydration levels of collagen matrices. Genipin solution was used to induce crosslinking in collagen matrices. Biaxial stress relaxation tests were performed to characterize the viscoelastic behavior of collagen matrices. The rate of stress relaxation of both hydrated and dehydrated collagen matrices shows a linear initial stress level dependency. Increased crosslinking reduces viscosity in collagen gel, but the effect is negligible for thin film. Relaxation time distribution spectrum was obtained from the stress relaxation data by inverse Laplace transform. For most of the collagen matrices, three peaks at the short (0.3s ~1 s), medium (3s ~90 s), and long relaxation time (> 200 s) were observed in the continuous spectrum, which likely corresponds to relaxation mechanisms involve fiber, inter-fibril, and fibril sliding. Splitting of the middle peak was observed at higher initial stress levels suggesting increased structural heterogeneity at the fibril level with mechanical loading. The intensity of the long-term peaks increases with higher initial stress levels indicating the engagement of collagen fibrils at higher levels of tissue strain.