Evaluation of rheological and textural properties of hybrid hydrogel containing Whey protein isolate – Opuntia

cactus pear (Opuntia stricta) is known as a source of polysaccharide compounds (mucilage) that can trap water by the three-dimensional network. Hydrogels are three-dimensional polymer networks with cross-links that can absorb large amounts of water. In recent years, the use of these compounds as a thickening or gelling agent has increased. In these systems, whey protein hydrogel due to its high nutritional value, good functional properties, and biocompatibility has attracted the attention of the food industry. In this study, the production of new hydrogels (hybrid hydrogels) in combination with a polysaccharide component for improving the functional properties of whey protein was investigated. The purpose of this study was to evaluate the behavior of Whey Protein Isolated-Opuntia hybrid hydrogels in terms of rheological behavior and textural properties as a subordinate of protein and polysaccharide concentrations.

Opuntia fruit powder was prepared from the fruit pulp by a hot air dryer. To prepare the main/final mixture of the hydrogel, two hydrogel bases including Opuntia pulp hydrogel (Op) (20% w/w) and whey protein isolate hydrogel (W) (15% w/w) were mixed in different ratios (W/Op: 80-20, 70-30, 60-40, 50-50) by an electric mixer at low speed for 1 minute. Finally, textural properties including (viscosity, consistency, hardness, adhesiveness), water holding capacity, swelling ratio, and rheological properties were tested. Data were analyzed using SAS software and the mean values were compared using Duncan's multiple range test at the 5% level.

Increasing ratio of Opuntia hydrogel to Whey protein hydrogel caused a significant increase in Viscosity, Consistency, Hardness, and Adhesiveness of hybrid hydrogels (W-Op H) compared to protein control (Whey protein) (p≤0.05). Also, Water Holding Capacity and Swelling ratio increased with increasing the ratio of Opuntia hydrogel in the samples (p≤0.05). Opuntia and Whey Protein Isolate hydrogel had the highest (694.71± 42.89 %) and lowest (340.22 ± 7.19 %) swelling ratios among the other samples, respectively. On the other hand, the addition of Opuntia hydrogel to Whey Protein Isolate hydrogel enhanced the viscoelastic behavior of the mixture, so that with increasing Opuntia hydrogel ratio, the storage and loss modulus was increased. The loss factor of hydrogel samples was between 0.24-0.36, which can be obtained as semi-gel material and the elastic behavior was more dominant than the viscose behavior.

hybrid hydrogel (W/Op: 60-40) due to its highest viscosity, maximum water holding capacity, and swelling ratio, as well as the presence of appropriate rheological behavior, was suggested as the best sample for thickening agent and texture improvement in food products such as ice cream, sauces, meat products, dairy products, Tofu, Noodles, etc.