Optimization of Bleaching Parameters for Soybean Oil

More documents

Recommendations

Info

200 D. [KEVIN et al.: Soybean Oil Bleaching Parameters, Food Technol. Biotechnol. 50 (2) 199–207 (2012)loss of oxidative stability can occur, trans fatty acids canform, and free fatty acid (FFA) content may increase(5–9). Optimization of bleaching parameters, mainly temperature,time, and clay content, is necessary in order tominimize these undesirable oil changes.If only the adsorbent properties of clay were importantfor bleaching, the most effective bleaching would occurat lower temperatures since at higher temperaturesthe adsorption equilibrium moves towards desorptionand some of the adsorbed molecules dissolve back intothe oil. However, decolouration is better at higher temperatures,which indicates that clay is much more thanan adsorbent. Indeed, chemical reactions take place onthe surface of the clay, and the kinetic constants of thesereactions, both desirable and undesirable, increase 2- to4-fold with a temperature increase of 10 °C (10). Therefore,there must be an optimum temperature for bleaching,and this optimum likely depends on the type of oiland levels of colour bodies, oxidation products and contaminantspresent. Most types of oil are treated in thetemperature range of 90–100 °C (11), although bleachingmay be carried out at up to 120 °C if problems are expecteddue to oil specificities (4).The optimal bleaching time depends on the bleachingtemperature and clay quality. Colour removal increaseswith time and temperature, although longer contactof oil and clay can cause colour reversion, whichalso increases with temperature. Bleaching for a longtime at high temperatures seriously damages the oxidativestability of edible oil. Bleaching time for most typesof oil is in the range of 20–30 min at 90–100 °C (4,12,13).High clay content enhances the removal of undesirablesubstances in the oil. However, the minimum clayneeded for effective bleaching is difficult to establish becausedifferent types of oil contain different amounts ofsubstances and react differently with clay. Optimal claycontent depends on the type of clay, oil pretreatments,and desired quality of the oil. It varies between 0.1 and2.0%(14), but it can be as high as 5%inspecial cases (4).These considerations make clear that bleaching parameters,i.e. temperature, duration and clay content, shouldbe determined individually for each neutralized oil usingdifferent types of bleaching clay. The aim of this study isto optimize these bleaching conditions for neutralized soybeanoil with Pure-Flo ® Supreme Pro-Active bleachingclay on the laboratory scale, since optimal conditionshave not yet been reported for this type of vegetable oilbleached with this clay. The effect of these parameterson bleaching efficiency, oxidative stability and content ofbioactive compounds (tocopherols and sterols) has beeninvestigated.Materials and MethodsStandards and chemicalsAll the standards used in this study were of HPLCgrade. The following compounds were obtained fromSigma-Aldrich (St. Louis, MO, USA): b-sitosterol (17-[5--ethyl-6-methyl-heptan-2-yl]-10,13-dimethyl-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1H-cyclopenta[a]phenanthren--3-ol), campesterol (17-[5,6-dimethylheptan-2-yl]-10,13--dimethyl-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1Hcyclopenta[a]phenanthren-3-ol),a-cholestanol (10,13-dimethyl-17-[6-methylheptan-2-yl]-2,3,4,5,6,7,8,9,11,12,14,15,16,17-tetradecahydro-1H-cyclopenta[a]phenanthren-3-ol), and stigmasterol (17-[5-ethyl-6-methyl-hept-3-en-2 --yl]-10,13-dimethyl-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1H-cyclopenta[a]phenanthren-3-ol).The compoundsa-tocopherol (2,5,7,8-tetramethyl-2-[4,8,12-trimethyltridecyl]-3,4-dihydrochromen-6-ol)and g–tocopherol (2,7,8--trimethyl-2-[4,8,12-trimethyltridecyl]-3,4-dihydrochromen-6-ol) were obtained from Merck (Darmstadt, Germany).All other chemicals were of suitable purity grade.MaterialsIndustrially neutralized soybean oil (Zvijezda d.d.,Zagreb, Croatia) was bleached using Pure-Flo ® SupremePro-Active bleaching clay (Oil-Dri Corporation of America,Chicago, IL, USA). This is an adsorbent manufacturedusing a proprietary surface modification technology (SMT).Raw material of the adsorbent is an intergrowth of hormiteand smectite minerals. SMT processing, combinedwith the intrinsic qualities of the mineral, produces ahighly active, fast-filtering product that removes coloursfrom corn, canola and soybean oil, in addition to removingsoaps, phospholipids and metals such as Ca, Fe,Mg and Ni. Manufacturer specifications of the bleachingclay (Oil-Dri Corporation of America) indicate a freemoisture content of 14–18 % at 105 °C and pH=2.4 to 3.3(5 % solids in deionized H 2 O).Bleaching of oil under laboratory conditionsLaboratory bleaching was performed in a round--bottom, three-necked flask of 500 mL equipped with athermometer and attached to a vacuum pump and nitrogensource (Fisherbrand bleaching equipment, Fisherscientific Ltd, Loughborough, UK and Gast 0211 vacuumpump, Gast, Benton Harbor, MI, USA). Bleaching wasconducted using an electromagnetic mixer with adjustableheater. All bleaching parameters are given in Table1. Briefly, 200 g of industrially neutralized soybean oilwas weighed into a round-bottom, three-necked flaskTable 1. Bleaching parameters of soybean oil samplesSamplew(clay)%Bleaching parametersTimeminTemperature°C120 1052950.5303 1154 40 105595206 1157 130 105895409 1151020 10511951.53012 11513 40 105
D. [KEVIN et al.: Soybean Oil Bleaching Parameters, Food Technol. Biotechnol. 50 (2) 199–207 (2012)201and heated with mixing under a partial vacuum of 0.4bar. Bleaching clay was added to a final concentration of0.5, 1.0 or 1.5 % to the oil preheated to approx. 60 °C.The oil was then gradually heated to the desired bleachingtemperature (95, 105 or 115 °C) with constant mixingunder vacuum to disperse the clay completely. Afterreaching the desired temperature, the heating was temporarilyturned off to allow the temperature to fall byapprox. 2–3 °C. Then the heating was turned on againand kept constant for the desired bleaching time (20, 30or 40 min). At the end of bleaching, heating and vacuumwere turned off and nitrogen supply was turned on.After bleaching, hot sludge from the flask was filteredthrough filter paper (Whatman no. 541) under vacuum.Samples of bleached oil were stored at –18 °C untilfurther analysis.Analytical methodLovibond colour was determined according to theISO method (15) using Lovibond Colourscan (TintometerLtd., Amesbury, UK). Transparency was measured at 455nm on a Cary 100 Scan spectrophotometer (Varian, PaloAlto, CA, USA) following the method of O{tri}-Matija-{evi} et al. (16). Transparency of samples was measuredin undiluted oil using distilled water as a blank.The elements P, Fe and Cu in oil were determinedusing an inductively coupled plasma atomic emissionspectroscopy (ICP-AES) method (17,18) on a Vista-MPX(Varian). The three elements were analyzed by directinjection of a sample dissolved in PremiSolv ICP solvent(SCP Science, Conostan, Montreal, Quebec, Canada). Determinationof the peroxide value (PV) was carried outfollowing ISO 3960:2007 analytical method (19) and theanisidine value following ISO 6885:2006 method (20).These two values were used to calculate the Totox (totaloxidation) value using formulae from O{tri}-Matija{evi}and Turkulov (21). Specific UV absorption at 232 and 270nm (K 232 and K 270 , respectively) was measured followingISO 3656:2011 method (22). Free fatty acid (FFA) contentwas determined using ISO 660:2009 method (23).Sterol content and composition were determinedusing gas chromatography and ISO 12228:1999 method(24). The prepared sterol fraction (1 µL) was injectedinto a gas chromatograph (series 610, ATI Unicam, Cambridge,UK) equipped with a DB-17 capillary column (30m×0.32 mm×0.25 mm) containing 50 % phenyl-methylpolysiloxanestationary phase. Helium was used as carriergas at a flow rate of 0.36 mL/min. The temperatureof the injector was set to 280 °C and the temperature ofthe detector to 290 °C. The temperature of the columnoven was programmed to increase at 6 °C/min from aninitial value of 180 to 270 °C, and then to remain at thisvalue for 30 min. Peaks were identified by comparingthe retention times of sterols with those of the standards.Quantification of all sterols was based on an internal standardmethod using a-cholestanol.Tocopherol content and composition were determinedusing a standard ISO method (25). Analysis wasperformed by high-performance liquid chromatography(HPLC) using a ProStar 363 (Varian) equipped with aProStar fluorescent detector and a Restek Pinnacle II silicacolumn (15 cm×4.6 mm, 5 µm). Sample was preparedby dissolving 0.1 g of soybean oil in 10 mL of n-hexane,and 20 µL of the solution was injected in the column.Detection of tocopherols was performed at an excitationwavelength of 295 nm and emission wavelength of 330nm. Isocratic chromatography at room temperature wasused with a mobile phase of 0.7 % propan-2-ol in n-hexaneat a flow rate of 0.6 mL/min. Quantification of tocopherolswas performed using standard calibration curvesof a- and g-tocopherol covering the mass fraction rangeof 5–750 mg/kg.Statistical analysesA Box-Behnken design for three factors was used todesign the samples (26). The Friedman-type statistics forranking the data was calculated to rank the samples accordingto bleaching efficiency and oxidative stability.Nonparametric analogues to Fisher’s least significantdifferences (LSD) for ranking the sums were calculated,and a multiple comparison procedure was performed todetermine the significance of differences between thebleaching efficiency and oxidative deterioration parametersevaluated by the ranking test (27). Principal componentanalysis (PCA) was performed to reduce thenumber of correlated variables, and to determine whichparameters significantly affected bleaching outcomes. Allstatistical analyses were performed using the softwarepackage STATISTICA v. 9 (28).Results and DiscussionBleaching was performed on industrial neutralizedsoybean oil in the laboratory under vacuum and nitrogenatmosphere, using Pure-Flo ® Supreme Pro-Activebleaching adsorbent. The values for temperature, durationof bleaching and clay content tested in this studywere based on the literature (2,4,5,29) and on previousexperience with bleaching at the refining plant of theZvijezda oil factory, Zagreb, Croatia. Three bleachingtemperatures (95, 105 and 115 °C), three clay amounts(0.5, 1 and 1.5 %) and three bleaching durations (20, 30and 40 min) were tested. A Box-Behnken design forthree factors was used to design the samples. The designconsisted of 12 different cases, with the 13th centralcase representing an average valuation of variables (Table1). All reported results are mean values of duplicate analyticaldeterminations.Bleaching efficiency was monitored by measuring thereduction in colour bodies, metal contaminants and oilretention by the bleaching clay. Colour bodies of oils andfats are pigments, primarily chlorophylls and carotenoids.Soybean oil contains small amounts of chlorophylls,and the main carotenoids are xanthophylls. Reduction ofcolour bodies in this work was measured according tothe Lovibond method (Table 2). The greatest reductionin red (72 %) and yellow units (26 %) in neutralized oilwas achieved using the highest clay content (1.5 %) atthe highest temperature (115 °C) during 30 min. Substantialremoval of colour substances makes the oil highlytransparent. The highest transparency, 12-fold greater thanthat of neutralized oil, was obtained with the highest claycontent, at higher temperature (105 and 115 °C) andthrough all time durations.
Page 4 and 5: 202 D. [KEVIN et al.: Soybean Oil B
Page 6: 204 D. [KEVIN et al.: Soybean Oil B
Page 9: D. [KEVIN et al.: Soybean Oil Bleac

Optimization of Bleaching Parameters for Soybean Oil

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?