PROPERTIES FROM SELF-SUPPORTING HYDROGELS MADE WITH WHOLE MACROALGAE

Seaweeds are abundant along the Brazilian coast and an underexploited source of sustainable materials. They have polysaccharides and proteins with great structuring properties, but these have been limited to the prospection of individual components. For the comprehensive utilization of seaweeds in their integrity, ultrasonic waves and controlled heat treatment can induce conformational changes in biopolymers and modulate the gelling capacity of both polysaccharides and proteins, making it practical to expand their applications, such as stabilizers, edible packaging, controlled release vehicles, biotissues, and biosorbents. Herein, the effects of conventional heat treatments with and without ultrasonic pretreatment on the self-supporting hydrogel properties of Gracilaria sp. flour (GF) were evaluated. Samples with 1, 2, and 3% w/v GF at pH 3 and 7 were pretreated at 600W/5 min, followed by heat treatment at 80 °C/20min (U80). Control samples were obtained without ultrasonic pretreatment (T80).  The U80 samples with 1 and 2% concentrations and pH 3 did not form self-standing gels. Higher GF concentrations presented lower gel syneresis, although all U80 samples had more water loss than T80. The same behavior was found in the water holding capacity (WHC) of the hydrogels, reaching up to 67%. This trend with the hydrogel concentration was repeated in the mechanical properties of the samples, but the sonicated gels at 3% concentration and pH 7 achieved the highest values of gel fracture stress and strain (with U80 reaching stress fracture of 14.4 kPa, while T80 in the same conditions reached 11.9 kPa). The elastic modulus of these sonicated samples had no statistically significant difference from that of other treatments at 3% concentration and pH 7 (22 kPa). This implies that, although ultrasonic pretreatment did not contribute to the formation of self-standing gels, it is possible to modulate the mechanical properties of the Gracilaria sp. flour hydrogels, broadening their use as food matrices.