Technofunctional Properties of Stinging Nettle (Urtica dioica L.) Leaf Flour and Its Enhancing Pasting, Physical and Sensory Characteristics in Gluten-Free Rice Waffles

The study investigated the technofunctional properties of Urtica dioica L. leaf flour and its effect on the pasting, physical and sensory characteristics of gluten-free rice waffles. Compared with commonly used gluten-free rice and corn flour, Urtica dioica L. leaf flour had the lowest swelling capacity (2.71 mL), oil absorption capacity (89.55%) and water activity (0.31), and the highest nitrogen solubility index (20.85%), foaming capacity (13.91%) and stability (93.66%). Its Carr’s index, Hausner’s ratio and angle of repose were 20.05%, 1.24° and 32.76°, respectively, which indicated a fair flowability. In addition, the incorporation of nettle leaf flour did not affect (p > 0.05) the fat and starch contents of waffles, but significantly (p < 0.05) increase the ash, protein, fibre, total phenolic, antioxidant and total flavonoid contents. The peak and trough velocity significantly decreased about 876 times and 1022 times in the 20% nettle-incorporated waffle mix, respectively. Although this decrease indicated a lesser ability for nettle-incorporated waffle mixes to absorb water, the breakdown viscosity (ranging from 644.71 cP to 352.0 cP) showed that the formed paste, and subsequently the cooked waffles, could resist disintegration and became stable against increasing cooking temperature and shear forces. Furthermore, the sensory test indicated no significant (p > 0.05) difference in the sweetness and overall liking of all formulated waffle samples; however, attributes such as appearance, aroma, flavour, bitterness, mouthfeel and aftertaste slightly varied when compared with the control (100% rice waffles). The findings revealed promising characteristics of Urtica dioica L. leaf flour as a low-cost natural functional food ingredient, particularly in gluten-free bakery products. The study offers novel insights into gluten-free food formulations and contribute to the development of technofunctional nettle leaf flour for the food industry.