Seyed Mehdi Niknam

Olive mill wastewater (OMWW) is an extremely polluting dark liquid generated in large quantities during the extraction of olive oil. OMWW is also an interesting source of high-added value natural compounds such as biophenols, especially hydroxytyrosol (HT), a powerful antioxidant with proven nutritional and pharmaceutical properties. The main objective of this work was to explore the use of membrane technology for the treatment of OMWW in order to obtain a retentate stream rich in hydroxytyrosol and a permeate with low chemical oxygen demand (COD). Pretreatment was firstly performed by a combined centrifugation and acidification process. Then, several membrane operations were tested and phenolics rejection, HT content, COD removal and membrane fouling were examined. Best results were obtained using a single ultrafiltration process with a 10 kDa ST polyethersulfone membrane at 8 bar. Improved results were reached using a two-stage integrated system with 100 kDa US100 ultrafiltration and 200 Da NF90 nanofiltration membranes, at 5 and 10 bar, respectively. Volume reduction factor of 1.9 in ultrafiltration and 1.6 in nanofiltration yielded to 234.49 ± 26.08 mg/L of HT in the retentate (9-fold the HT content in the raw OMWW) and 94.15% COD removal.

In this study, we aimed to prepare stable water-in-oil (W/O) nanoemulsions loaded with a phenolic-rich aqueous phase from olive cake extract by applying the response surface methodology and using two methods: rotor-stator mixing and ultrasonic homogenization. The optimal nanoemulsion formulation was 7.4% (w/w) of olive cake extract as the dispersed phase, and 11.2% (w/w) of a surfactant mixture of polyglycerol polyricinoleate (97%) and Tween 80 (3%) in Miglyol oil as the continuous phase. Optimum results were obtained by ultrasonication for 15 min at 20% amplitude, yielding W/O nanoemulsion droplets of 104.9 ± 6.7 nm in diameter and with a polydispersity index (PDI) of 0.156 ± 0.085. Furthermore, an optimal nanoemulsion with a droplet size of 105.8 ± 10.3 nm and a PDI of 0.255 ± 0.045 was prepared using a rotor-stator mixer for 10.1 min at 20,000 rpm. High levels of retention of antioxidant activity (90.2%) and phenolics (83.1–87.2%) were reached after 30 days of storage at room temperature. Both W/O nanoemulsions showed good physical stability during this storage period.

Currently, industry is requesting proven techniques that allow the use of encapsulated polyphenols, rather than free molecules, to improve their stability and bioavailability. Response surface methodology (RSM) was applied in this work to determine the optimal composition and operating conditions for preparation of water-in-oil-in-water (W/O/W) emulsions loaded with phenolic rich inner aqueous phase from olive mill wastewater. A rotor-stator mixer, an ultrasonic homogenizer and a microfluidizer processor were tested in this study as high-energy emulsification methods. Optimum results were obtained by means of microfluidizer with 148 MPa and seven cycles input levels yielding droplets of 105.3 ± 3.2 nm in average size and 0.233 ± 0.020 of polydispersity index. ζ-potential, chemical and physical stability of the optimal W/O/W emulsion were also evaluated after storage. No droplet size growth or changes in stability and ζ-potential were observed. Furthermore, a satisfactory level of phenolics retention (68.6%) and antioxidant activity (89.5%) after 35 days of storage at room temperature makes it suitable for application in the food industry.