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Summary In this study, the flux decline mechanisms were identified during membrane clarification of red plum juice at several processing parameters, including pore size, membrane type, transmembrane pressure, temperature and velocity. The results were used to investigate the effect of changes in operating conditions on the intensity of membrane fouling. Also, scanning electron microscopy (SEM) was used for analysing fouling‐layer morphology. These results showed that the main mechanism responsible for membrane fouling was cake formation (over 95% fitness) occurring in the first stage of the process. Intermediate, standard and complete blockings were formed during most of the runs as filtration proceeded. The results also indicated that increasing the temperature from 30 to 40 °C was the most effective factor in decreasing cake‐layer fouling, reducing it by about 66.7%. Furthermore, an increase in processing velocity of up to 0.5 m s−1 had the greatest effect on intermediate blocking, reducing it by about 86.1%. Also, increasing pressure up to 2.9 bar completely eliminated standard blocking and complete blocking. Finally, microstructure analysis of membrane using SEM confirmed that cake formation had the greatest impact on membrane fouling.

This study evaluated the total (R t ), reversible (R rev ), irreversible (R irr ), and cake (R c ) resistances during microfiltration of watermelon juice (as a juice with colloid particles) and red plum juice (as a juice without colloid particles). Results showed that the total resistance decreased by about 45% when the feed velocity was increased during clarification of red plum juice due to change in cake resistance. Also, increasing the feed temperature from 20 to 30°C decreased the total fouling resistance by about 9% due to decreases in the irreversible and reversible fouling resistances. Also, mixed cellulose ester (MCE) membrane (which is hydrophilic) had a lower cake resistance compared to polyvinylidene fluoride (PVDF) membrane (which is hydrophobic). Examination of the microfiltration of watermelon juice showed that R t decreased by about 54% when the feed temperature was increased from 20 to 50°C, partially due to the reduction of reversible fouling resistance by 78%. Also, increasing transmembrane pressures from 0.5 to 2.5 bars greatly increased total fouling resistance. The feed velocity had a different effect on fouling resistances during microfiltration of watermelon juice compared to red plum juice: in contrast with red plum juice, increasing the feed velocity for watermelon juice increased cake resistance.

A whey protein isolate solution was heat-denatured and treated with the enzyme transglutaminase, which cross-linked ≈26% of the amino groups and increased the magnitude of the ζ-potential value. The protein solution was microemulsified, and then the resulting water-in-oil microemulsion was dispersed within a gallic acid-rich model wastewater. Gallic acid extraction by the outlined microemulsion liquid membrane (MLM) from the exterior aqueous phase (wastewater) and accumulation within the internal aqueous nanodroplets induced protein cold-set gelation and resulted in the formation of gallic acid-enveloping nanoparticles. Measurements with a strain-controlled rheometer indicated a progressive increase in the MLM viscosity during gallic acid recovery corresponding to particle formation. The mean hydrodynamic size of the nanoparticles made from the heat-denatured and preheated enzymatically cross-linked proteins was 137 and 122 nm, respectively. The enzymatic cross-linking of whey proteins led to a higher gallic acid recovery yield and increased the glass transition enthalpy and temperature. A similar impact on glass transition indices was observed by the gallic acid-induced nanoparticulation of proteins. Scanning electron microscopy showed the existence of numerous jammed/fused nanoparticles. It was suggested on the basis of the results of Fourier transform infrared spectroscopy that the in situ nanoparticulation of proteins shifted the C-N stretching and C-H bending peaks to higher wavenumbers. X-ray diffraction results proposed a decreased β-sheet content for proteins because of the acid-induced particulation. The nanoparticles made from the enzymatically cross-linked protein were more stable against the in vitro gastrointestinal digestion and retained almost 19% of the entrapped gallic acid after 300 min sequential gastric and intestinal digestions.