Study On The Different Extraction Methods And Oxidation Stability Of Walnut Oil

This paper studied the extraction methods, qualities changes and refining technics, antioxygen effect, and oxidation stability of walnut oil. The main conclusions are as follows:(1) The optimization conditions of walnut oil extraction were studied; the results showed that the extraction rate of squeeze method was 60.85%, and the oil has high quality in flavour and no solvent residue, but not good in colour and transparency. The optimization condition of soxhlet extraction was:ratio of solvent to material was 8:1, extraction temperature was 75℃, extraction time was 6h and the maximum extraction yield was 81.73%. The optimization condition of ultrasonic extraction was:n-hexane as extraction solvent, ratio of solvent to material was 7:1, extraction temperature was 53℃, extraction time was 48 min, ultrasonic power was 120W and the maximum extraction yield was 94.95%. The optimization condition of aqueous extraction was:caking temperature was 100℃, caking time was 110min, ratio of solvent to material was 1.5:1, water temperature was 75℃, water pH=8 and the maximum extraction yield was 72.35%. The optimization condition of SCF-CO2 was:extraction pressure was 32 MPa, temperature was 43℃, time was 4.5 h and the maximum extraction yield was 90.87%.(2) The influence of extraction method on quality of walnut oil was also studied. The physico-character indexes (colour, favlour, relative density, refractive index), chemi-character indexes (acid value, iodine value, saponification valu, peroxide value), content of phospholipid, content of flavone, composition and content of VE and composition and content of fatty acid were studied. The results showed that:the influence of different extraction methods on relative density, refractive index and fat acids was not significant, but it was significantly changed for colour indexes, flavour, acid values, iodine values, saponification values and peroxide values. The relative density, refractive index, iodine value and saponification number of soxhlet and SFE-CO2 oil were not changed significantly, but the colour, acid walue and peroxide value changed obviously. The phospholipid content in soxhlet and aqueous oil were 0.1035% and 0.024%. The total flavone content in SFE-CO2 and pressing oils were 31.64 mg/100ml and 25.55 mg/100ml, and the contents in phospholipid and total flavone were decreased with refining. The VE content in supersonic oil was 45 mg/100g, but it's only 30.26 mg/100g in SFE-CO2 oil. The VE content decreased obviously duiring refining process expecially after deordorization process. The main fat acids in walnut oil were palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. The unsaturated fatty acid content was above 90%. The fat acids content changed after different refine process, but not significant. So the ultrasonic and SCF-CO2 extraction were better methods for walnut oil extraction compared with the other methods.(3) At room temperature, The acid values and peroxide values all increased with extending of storage time and the oxidation stability of different samples were soxhlet extraction, ultrasonic extraction, aqueous extraction, expression extraction and SCF-CO2 extraction in order.(4) The oxidation stability can be reinforced by adding antioxidant, citric acid and antiscorbic acid showed synergistic effect. and the theory shelf life of walmut can extend to 18 months by adding 0.015%TBHQ+0.01%Vc.