**2.2 Analytical determinations**

Oil was extracted from the treated solid obtained by SES and ST with n-hexane using a Soxhlet apparatus. The obtained oils were filtered and stored at -20 °C until analysis. Oil content and fat enrichment (pitted dry matter) were determined and compared with the values for untreated alperujo samples.

Determination of the concentrations of aliphatic alcohols, sterols and triterpenic dialcohols (erythrodiol and uvaol) was performed according to the Commission Regulation (EEC) No 2568/91 for olive oil and pomace oil. After the silylation reaction, 1 mL of heptane was added to the mixture, and 1 μL of the solution was injected into an Agilent 7890A gas chromatograph system (Agilent Technologies, Palo Alto, USA) equipped with an FID detector. The analytical column was an HP-5 (5%-phenyl)-methylpolysiloxane column (30 m x 0,32 mm i.d., 0,25 μm film thickness). The results were expressed as mg/kg of oil.

First, the application of SES on alperujo in order to obtain pomace olive oil was studied with or without acid as a catalytic agent. Due to the technical disadvantages of SES and to make the use of thermal pre-treatment in OPO mills easier and more convenient low severities, no

Samples of stored olive pomace or alperujo were collected from the COPO extraction factory Oleícola El Tejar (Córdoba, Spain) with 70% humidity. This by-product is generated as a

The thermal treatments were carried out in the Instituto de la Grasa (CSIC) pilot plant by the

a. The SES was carried out using a flash hydrolysis laboratory pilot unit with a 2 L reactor. The reactor was equipped with a quick-opening ball valve for the final explosion into the expansion chamber. Alperujo samples of 250 g were treated with saturated steam in a 2 L reactor with a maximum operating pressure of 40 Kg/cm2. The reactor was equipped with a quick-opening ball valve and an electronic device programmed for the accurate control of steam time and temperature for the final steam explosion. Prior to the treatment, some of the samples were acidified with H3PO4. The acid was added to the moist sample so as to reach a final concentration of 2,5 % (v/v). After the treatment, the samples were collected and filtered in vacuo through filter paper using a Buchner funnel. b. The new ST reactor has recently been patented (Fernández-Bolaños et al., 2011). It has a 100 L capacity stainless steel reservoir that can operate at temperatures between 50 and 190 °C by direct heating and at a maximum pressure of 9 Kg/cm2. The system allows the appropriate treatment of alperujo without steam explosion or high pressures and temperatures. The wet treated material was filtered by centrifugation at 4700 g

After solid separation, the solid phase was dried in a stove at 50 °C, and the reduction (%) in

Oil was extracted from the treated solid obtained by SES and ST with n-hexane using a Soxhlet apparatus. The obtained oils were filtered and stored at -20 °C until analysis. Oil content and fat enrichment (pitted dry matter) were determined and compared with the

Determination of the concentrations of aliphatic alcohols, sterols and triterpenic dialcohols (erythrodiol and uvaol) was performed according to the Commission Regulation (EEC) No 2568/91 for olive oil and pomace oil. After the silylation reaction, 1 mL of heptane was added to the mixture, and 1 μL of the solution was injected into an Agilent 7890A gas chromatograph system (Agilent Technologies, Palo Alto, USA) equipped with an FID detector. The analytical column was an HP-5 (5%-phenyl)-methylpolysiloxane column (30 m

x 0,32 mm i.d., 0,25 μm film thickness). The results were expressed as mg/kg of oil.

(Comteifa, S.L., Barcelona, Spain) to separate the solids and liquids.

depressurisation or acid addition were used in the new system (ST).

waste from the two-phase olive oil extraction system.

steam explosion system and a new thermal system:

the mass of the solid phase was determined.

**2.2 Analytical determinations** 

values for untreated alperujo samples.

**2. Experimental procedures** 

**2.1 Thermal treatments** 

Tocopherols were evaluated using the IUPAC 2.432 method. Results were expressed as mg/kg of oil.

The wax and squalene compositions were determined according to the European Regulation EEC/183/93, by separation on a silica gel 60 (70-230 mesh ASTM) chromatographic column (Merck KGaA, Darmstadt, Germany) using hexane/ether (98:2) as the eluent with a few drops of Sudan I as a colorant. Dodecyl arachidate (Sigma) and squalane (Fluka) were added as internal standards. The results were expressed as mg/kg of oil.

Polar compounds, triglycerides and their derivatives oxidise and hydrolyse were prepared using solid-phase extraction and size-exclusion chromatography and monostearin as internal standard (Márquez -Ruiz et al., 1996). An aliquot (20 μL) of the final solution was injected into a Hewlett Packard Series 1050 HPLC system equipped with a refractive index detector (LaChrom L-7490 Merck) and a 100-Å PL gel column (5 μm) (Agilent). Elution was performed at 0,6 mL/min, with tetrahydrofuran as the mobile phase.

Determination of fatty acid, free acidity and peroxide value (PV) was carried out according to the Official Methods described in the European Community Regulation EEC/2568/91. The results were expressed as the percentage of oleic acid. The peroxide value was expressed in milliequivalents of active oxygen per kilogram of oil (mequiv O2/kg oil).

The indexes K232, K270 and *∆K* were determined using the European Communities official methods (European Union Commission, 1991). Oil samples were diluted in isooctane and placed into a 1 cm quartz cuvette; for values calculation, each solution was analysed at 270 and 232 nm, with isooctane as a blank.
