Study On The Quality And Oxidation Stability Of Palm Oil During Heat Processing

Palm oil because of its light color,good thermal stability,not easy to polymerization,wide application,low price and other characteristics,has been widely used in the world of Fried industry.In Chinese traditional cooking methods,the oil temperature is usually heated to 150?200?.Under the influence of oxygen,water and high temperature,a series of complex reactions,such as hydrolysis,oxidation and polymerization,occur in the heat process of unsaturated fatty acids in palm oil.The formation of some new substances such as free fatty acid,peroxide,polar material,polymer,free radicals and other characteristics of small molecular substances,not only makes the properties of palm oil change,quality deterioration,produce toxic or harmful substances will affect human health,causing harm to human life,safety and food safety.As a result,the quality change and quality safety of palm oil during heat processing has become one of the hot spots in recent years.Therefore,this paperuses the catering of palm oil(24?)as raw materials,at different temperatures(160,180,200?)and time under the conditions of heat processing of palm oil,and then compare the acid value(AV),free fatty acid(FFA),peroxide value(POV),malondialdehyde(MDA),p-anisidine value(PAV),the total oxidation value(TOTOX)and total polar material(TPC)changes.On this basis,the changes of fatty acid composition,main components and free radical content,volatile component,the structural and thermal oxidative stability of palm oil under the condition of heat processing at 180? were studied.The main contents and conclusions are as follows:(1)The main physical and chemical indexes(acid value,free fatty acid,peroxide value,malondialdehyde value,p-anisidine value,total oxidation value and total polar substance)changes of palm oil were measured by national standard method and so on at different heating temperatures(160,180,200?)with time.The results showed that the higher the heating temperature and the longer the heating time,the higher the physical and chemical index of palm oil,and the peroxide value increased first and then decreased,and the degree of oxidation of palm oil was deepened.(2)Gas chromatography(GC-MS),gas chromatography(GC)and high performance liquid chromatography(HPLC)were used to determine the changes of fatty acids content and composition,trans fatty acid content and composition and five volatile aldehyde carbonyl compounds content and composition in the heat processing(180?)of palm oil.The results showed that the ratio of saturated fatty acid to unsaturated fatty acid in palm oil was about 1:1 with the increase of heating time,and the ratio was basically unchanged.The content of trans fatty acids was increasing,but at the later stage of oxidation the content of trans fatty acids was almost unchanged.The total amount of five kinds of volatile aldehydes increased with the increase of heating time,and the content of nonylaldehyde was the highest among the five aldehydes.(3)The changes of volatile components in palm oil(180?)were determined by headspace solid phase microextraction and gas chromatography-mass spectrometry(HS-SPME/GC-MS).The results showed that 63 volatile compounds were identified in palm oil during the heat processing,including aldehydes,alcohols,acids,ketones,hydrocarbons and heterocycles.The volatile components in palm oil increased first and then decreased with the increase of heating time.After the heat processing,the main volatile components of palm oil were aldehydes and hydrocarbons,and the content of aldehydes was the highest,and the content of 12 h was up to 80.41%of total volatile components.In addition,the detection of 1-octen-3-ol,hexanoic acid,2-pentadecanone and 2-pentylfuran showed that linoleic acid in palm oil was oxidative and decomposed.The change trend indicates that the degree of oxidation of the palm oil is prolonged with the heat treatment time,and the deterioration of the oil quality is serious;(4)The structural changes and thermal oxidation stability of palm oil during heat processing(180?)were analyzed by Fourier transform infrared spectroscopy(FTIR),hydrogen spectroscopy(1H NMR),electron spin resonance(ESR)and differential scanning calorimetry(DSC).The results show that the oxidation of palm oil in the maximum extent,the content of trans fatty acid is far less than the infrared spectra of trans fatty acids,the detection limit is 5%,so the experiment in FTIR at 966 cm-1 did not see obvious trans double bond absorption peak.With the heating time prolonged,1HNMR experiments showed that linoleic acid content was significantly reduced.ESRexperiments showed that,with the heating time extended,the more free radicals detected in the system,and the deeper the degree of oxidation of palm oil.At the same time,DSC experiments show that the palm oil has good oxidation stability.