AbstractUltrasonication (20 kHz, 19.9 W/10 mL sample) was used to form O/W emulsions stabilised by quinoa protein isolate (QPI) particles at 3 wt%. Effects of pH (3, 5, 7, 9) and oil volume fractions (20%, 40%, and 60%) on rheological properties and microstructural characteristics of emulsions were investigated. All emulsions show viscoelastic behaviours and form a network structure comprising aggregated oil droplets and QPI particles. Emulsions stabilised by QPI at pH 5 showed largest droplet sizes and lowest gel strength due to extensive aggregation of proteins around the isoelectric point (pI ~ 4.5). The gel strength (G´(1 Hz)) were enhanced when the oil volume fraction increased and reached ~ 1100–1350 Pa at 60% oil volume fraction at different pH. This could be attributed to a tighter packing of oil droplets at 60% oil. Confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) revealed that interdroplets bridging and voids filling of QPI particles between oil droplets are critical in formation of aggregated emulsions network. Emulsions stabilised by QPI at pH 7 and 9 possessed thinner interfacial layers compared to those at pH 3 and 5. Finally, this study shows a potential of using ultrasonication to prepare gel-like emulsions stabilised by QPI, broadening applications of quinoa proteins in making dairy substitutes with semi-solid textural characteristics.

AbstractThis work aims at examining the impact of generated CO2 nanobubbles (NBs) via the membrane-based method on physicochemical properties and surface tension of commercial clarified apple juice. The gas was injected at 300 kPa pressure for variable liquid circulation times (5, 13 and 26 min) to produce the CO2 NBs. Sets of 13- and 26-min circulation time to mix CO2 and liquid gave the desirably nano-size (~ 80–200 nm) NBs and significantly (p ≤ 0.05) reduced surface tension (by ~ 20–25%) of the juice dispersed with these formed tiny gas bubbles (NB-juice). An increase in circulation time also resulted in more negative zeta potential and higher dissolved CO2 concentration of the NB-juice. Density values of apple juice remained unchanged with and without incorporating CO2 NBs. These experimental outcomes provide the potential use of NBs in controlling the characteristics of liquid food as an environment-friendly approach to minimise chemical usages.

AbstractHeat moisture treatment (HMT) was used to improve the functionalities of elephant foot yam starch (EFYS) by using selected heating techniques such as hot air oven (HAO), autoclave (AL), and microwave (MW). The swelling power and solubility were reduced significantly after HMT modification, whereas an increase in amylose content was detectable after HMT modification, and the maximum changes were identified in HAO-modified EFYS (28.48%) as compared to its native counterpart (18.01%). The study demonstrates that the maximum drop in peak viscosity (1045 cP) was perceived in HAO-modified EFYS, which confirms its thermostability as compared to native (1114 cP) and other treated starches (1059 to 1098 cP). All the starch pastes exhibited shear-thinning behavior, however, isothermal heating of starch paste at 95 °C revealed a rise in apparent viscosity with increasing shear rate in all HMT-modified EFYS. Large amplitude oscillatory shear (LAOS) measurements of modified starch samples showed the predominating solid-like behavior in modified EFYS. The HAO-treated EFYS had the highest elasticity of the others, which represents the enhanced structural rigidity due to the formation of transient network structures. Furthermore, Lissajous-Bowditch plots confirmed the early deviation of the structural integrity from elastic to viscous behavior in HAO-treated EFYS. Overall, the HAO-modified EFYS showed significant improvement in functionalities and structural integrities under high shear and high oscillation strain, which infers its potential industrial applications. Based on our results, we propose specific physical models suggesting the effect of molecular structural arrangements of amylose and amylopectin expressing the essential rheological differences between native and HMT EFYS.