| Pine nut oil is a multipurpose plant oil with many beneficial effects,such as anti-oxidation,cholesterol-lowering effect,lipid metabolism regulation,and weight loss promoting agents.It is rich in unsaturated fatty acids,tocopherols,sterols,and many other nutrients.The selection of high-quality pine nut strains could provide a better quality of pine nut oil resources.However,systematic research to determine the high-quality of pine nut oil is still lacking.In this study,the physical quality,chemical components,and antioxidant properties of 10 pine nut oils were analyzed and studied.Furthermore,the storage stability of oils under different conditions was also evaluated.Multiple established fingerprints based on their fatty acids,tocopherols,Fourier Transform Infrared(FTIR)data,and volatile components,along with the principal component analysis and cluster analysis methods,were used to determine the differences between pine nut oil strains,and select the better strain among them.These results could provide a basis literature to evaluate a better pine nut strain and define the quality parameters to control the pine nut oil properties.The specific research results are as follows:(1)Research on the differences in phychemical properties of pine nut oils.The oil yield,phychemical index,color,and FTIR of 10 pine nut oils were analyzed.The oil yields were obtained to be ranged from 54.99%to 60.213%,and the#1 was observed to be the highest.Acid values ranged from 0.60 to 1.07 mg KOH/g,saponification values were between 127.48 and 154.28 mg KOH/g,peroxide values were between 0.14 and 0.38 meq/kg,and iodine values were between 96.25 and 142.43 g I2/100g.Significant differences were observed between physical quality of pine nut oils among different strains(p<0.05).1#has the lowest acid value,which indicated the freshness of the pine oil compared to other strains.3#has the highest iodine value,which observed to be less in other strains,and also characterized with the higher saturated fatty acids.4#has the smallest peroxide value,which is less prone to rancidity compared to other strains.8#has the smallest saponification value and higher purity than other strains.There is no significant difference in the a*value among the color of oils(P>0.05).The main differences were obtained in the L*and b*values(p<0.05),while 2#show the highest L*and b*value.FTIR data could show that hydrolysis of triacylglycerol in pine nut oil was relatively low.(2)Research on the differences in chemical composition of pine nut oils.The fatty acid composition,tocopherol composition,and volatile substances of 10 pine nut oils were determined,along with their contents of total phenolic and total flavonoid.Results showed significant differences in chemical parameters among the pine nut oils(p<0.05).The average relative contents of polyunsaturated fatty acids,monounsaturated fatty acids,and saturated fatty acids were 56.88%,34.07%,and 11.50%,respectively.Pinolenic acid was accounted to present in sample between 9.19-17.15%,and 10#was the highest.There were significant differences in total phenolics and flavonoids between different strains.The total phenolic content ranged between 287.04-450.19 mg GAE/kg,while the total flavonoid content were 35.91-47.27 mg RE/kg.Total tocopherol content ranged between 25.05 mg/100g(2#)and 32.36 mg/100g(1#).The highest content of ?-tocopherol was observed in 1#(19.89 mg/100g),while the highest content of ?-tocopherol was in 7#(13.03 mg/100g),and the highest content of ?-tocopherol was in 6#(1.17 mg/100g).A total of 163 volatile substances have been identified in the pine nut oil,mainly as hydrocarbons,aldehydes,alcohols,and esters.The main flavor-contributing substances were aldehydes(2,4-decadiene aldehydes,3-methyl-2-butyraldehyde,octyl aldehyde,nonanal),alcohols(cyclohexanol,2-cyclohexen-1-ol,3-hexen-1-ol and 2-hexen-1-ol,1-dodecen-3-ol,cyclopentanol),and esters(ethyl acetate).(3)Research on the differences in antioxidant activities of pine nut oils.The scavenging abilities of DPPH free radicals,hydroxyl free radicals,ABTS free radical,and FRAP of pine nut oils were measured.The IC50 value for DPPH,ABTS,and FRAP assay ranged between 28.28-41.52 mg/mL,65.94-81.24 mg/mL,and 2.01-6.92 mmol/L,respectively.7#was found to have less scavenging ability for FRAP free radical,but strongest for scavenging DPPH,OH,and ABTS free radicals(p<0.05).Meanwhile,the strongest strain that exhibited the highest antioxidant activity measured by FRAP assay was found in 6#.Results showed that different pine nut oils have different antioxidant capacity,and the different responsible components for antioxidants(fatty acids,tocopherols,total polyphenols,total flavonoids)have different scavenging abilities of free radicals.The correlation analysis between antioxidant capacity and active ingredients showed that the content of tocopherols had a greater influence on the antioxidant capacity.(4)Evaluation of storage stability of pine nut oils.The changing trends of the acid value and peroxide value of pine nut oil during storage time under different storage temperatures(4,25,40,60?)were evaluated.The kinetic model for fitting was performed,and pine nut oil under the storage condition of 25? was adopted.The acid value and peroxide value of the oil were verified against the model.The results showed that the acid value and peroxide value increased with the increasing of storage time and temperature,while the higher temperature resulted with the faster changing rate.The correlation coefficients at different temperatures were greater than 0.72 and 0.83 for acid value and peroxide value,respectively.These changes were in accordance with the first-order kinetic equation.Moreover,results also verified that this prediction model could more accurately predict the changing trend of acid value and peroxide value of pine nut oils during storage temperature at 25?.(5)Construction fingerprints of pine nut oils.The fingerprints based on the fatty acid,tocopherol composition,volatile compounds,and FTIR spectrum data were constructed.A total of three principal components analyses(PCA)were also performed.Results showed that the similarity of fatty acid profiles between samples was extremely high,which the value was above 0.95.The cumulative variance contribution rate of fatty acid PCA was 73.15%,which C18:1,C16:0,C18:0,C20:2 were observed to be the main characteristic fatty acid components in Korean pine nut oil.Furthermore,cluster analysis classified pine nut oils into three categories based on their fatty acid compositions.The tocopherol spectrum fingerprint showed that the similarity between sample with the standard fingerprint was above 0.965,and cluster analysis differentiated into three categories.The fingerprint for the FTIR data showed that the similarity between infrared spectrum of samples and standard spectrum was up to 0.98.The total contribution rate of the two main components of FTIR PCA was 80.36%.PC1 was characterized with wavelength 3010 cm-1,which is related to the characteristic absorption of-OH,and the two largest positive wavelengths on PC2 were 1432 cm-1 and 2036 cm-1,which is related to the cellulose CH bond of carbohydrates and the secondary over frequency vibration of the carbonyl group,respectively.Significant differences in the content of volatile components among pine nut oils were also observed among samples.The electronic nose data were subjected into principal component analysis and linear discriminant analysis,with the cumulative contribution rate of principal components reached 97.17%and 88.81%,respectively.These results indicated that sensors have a high degree of recognition and a well degree of discrimination between various strains. |
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