Thermal and Modern, Non-Thermal Method Induction as a Factor of Modification of Inulin Hydrogel Properties

Abstract

The aim of the study was to compare the properties of inulin hydrogels obtained with different methods, e.g., the traditional–thermal method and new, non-thermal methods, used in food production, like ultrasonic, high-pressure homogenization (HPH), and high hydrostatic pressures (HHPs). It was found that each of the compared induction methods allowed for obtaining inulin hydrogels. However, the use of non-thermal induction methods allows for obtaining a gel structure faster than in the case of thermal induction. In addition, hydrogels obtained with new, non-thermal methods differ from gels obtained with thermal treatment. They were characterized by higher stability (from 1.7 percent point-of-stability parameters for HHP 150 MPa to 18.8 for HPH II cycles) and in most cases, by improved microrheological properties–lower solid–liquid balance toward the solid phase, increased elasticity and viscosity indexes, and lowering the flow index. The gels obtained with the new, non-thermal method were also characterized by a more delicate structure, including lower firmness (the differences between thermal and non-thermal inductions were from 0.73 N for HHP at 500 MPa to 2.39 N for HHP at 150 MPa) and spreadability (the differences between thermal and non-thermal inductions were from 7.60 Ns for HHP at 500 MPa to 15.08 Ns for HHP at 150 MPa). The color of ultrasound-induced inulin gels, regarding the HPH and HHP technique, was darker (the differences in the L* parameter between thermal and non-thermal inductions were from 1.92 for HHP at 500 MPa to 4.37 for 10 min ultrasounds) and with a lower a* color parameter (the differences in the a* parameter between thermal and non-thermal inductions were from 0.16 for HHP at 500 MPa to 0.39 for HPH II cycles) and b* color parameter (the differences in the b* parameter between thermal and non-thermal inductions were from 1.69 for 5 min ultrasounds to 2.68 for HPH II cycles). It was also found that among the compared induction methods, the high-pressure technique has the greatest potential for modifying the properties of the created inulin hydrogels. Thanks to its application, depending on the amount of applied pressure, it was possible to obtain gels with very different characteristics, both delicate (i.e., soft and spreadable), using HHP at 150 MPa, and hard, using HHP at 500 MPa, the closest in characteristics to gels induced with the thermal method. This may allow the properties of hydrogels to be matched to the characteristics of the food matrix being created.

Progress in the Preparation and Application of Inulin-Based Hydrogels

“…Avoids thermal degradation, higher elasticity, higher viscosity, and lower fluidity Requires specialized equipment; the operation may be more complex [18,[35][36][37][38] Chemical Methods…”

“…It still has limitations, particularly when processing components with poor thermal stability. To address these issues, investigators and food manufacturers have developed alternative, non-thermal techniques which have been indicated in the previous literature and applied in inulin gelation, including ultrasonic treatment [ 35 ], high-pressure homogenization (HPH) [ 18 ], and high hydrostatic pressure (HHP) [ 36 , 37 , 38 ].…”

“…High-pressure techniques showed significant potential for modifying hydrogel properties, enabling the production of gels with varied textures—from soft and spreadable to firm—depending on the applied pressure. This adaptability indicates that high-pressure methods can be applied in tailored inulin hydrogels to meet specific requirements in various food matrices [ 36 , 38 ]. In summary, the non-thermal induction methods generally resulted in the faster gelation, higher elasticity, higher viscosity, and lower fluidity of the inulin hydrogels compared to thermal induction.…”