| In this paper,the oxidative stability,antioxidant capacity and physical-chemical characteristics of apricot kernel skin,S-AKO(oil obtained from apricot kernel with skins)and N-AKO(oil obtained from apricot naked-kernel)were studied under different roasting condition.Meantime,the correlations between oxidation stability and polyphenols and Maillard reaction products were also analyzed.The results was as following:(1)The effects of different roasting conditions and apricot kernel skin on the physical and chemical qualities of apricot kernel oil were studied.With the increase of the roasting temperature,the value acid of apricot kernel oil(0.71-0.94 mg/g)increased,the peroxide value(0.7-2.31mg/g),and the S-AKO peroxide value tended to fluctuate.N-AKO peroxide value gradually increased.There was no significant difference(p>0.05)in iodine value of apricot kernel roasted at low temperature(130?,160?),and iodine value of roasted apricot kernel oil increased gradually at high temperature(190?).The saponification value was slightly reduced and there was no significant difference in the roasting process(p>0.05).Apricot kernel color deepened.The content of almond oil fatty acid was not affected by low-temperature roasted(130?,160?),but the total amount of unsaturated fatty acids in apricot kernel that was baked for a long time decreased.N-AKO has higher acid,peroxide and iodine values than S-AKO.There is no significant difference in the saponification value.The high-temperature roasting S-AKO has more unsaturated fatty acids than N-AKO.The results showed that the quality of apricot kernel oil obtained by roasting at low temperature(130?,160?)for a short time(5 min,10 min)was improved.The quality of almond oil obtained by roasting at a high temperature of 190?gradually decreased.The quality of S-AKO is better than that of N-AKO,mainly because that the presence of apricot kernel skin inhibited the oxidation of almond oil.(2)The total phenol content and in vitro antioxidant capacity of S-AKO and N-AKO in different roasting conditions were evaluated by using total phenol content,lipid oxidation induction time,total reducing power,DPPH radical scavenging capacity,and ABTS scavenging capacity as indicators.The results showed that the induction time,total phenolic content and antioxidant capacity of apricot kernel oil increased with the increase of roasting temperature and time.N-AKO increased by 36.73%,89.44%and 78.28%,respectively,and S-AKO increased by 34.07%.,64.39%and 78.55%,the total phenolic content and antioxidant capacity of apricot kernel skin showed that a trend of increased first and then decreased.Oxidation induction time of S-AKO is slightly lower than that of N-AKO.The correlation shows that there is a highly significant positive correlation between total phenolic content and antioxidant activity in apricot kernel oil(r=0.857).The total phenolic content and antioxidant capacity of apricot kernel skin cultivars were significantly negatively correlated with the total phenolic content and antioxidant capacity of S-AKO(r=-0.779),the main factors that deter mine the increase in the total phenolic content of apricot kernel oil and the enhancement of antioxidant capacity are the active ingredients produced by apricot kernel during roasting.(3)The changes of phenolic substances in apricot kernel oil were analyzed by HPLC.The results were as follows:The type and content of phenolic compounds in apricot kernel oil gradually increased as the roasting temperature increased,except for the propyl gall ate contained in control apricot kerne oil.Five kinds of phenolic substances were found in the roasted apricot kernel oil:catechin,epicatechin,quercetin,epigallocatechin gallate,and homovanillic acid.During the roasting process,the content of propyl gallate in S-AKO gradually decreased,and the content of propyl gallate in N-AKO increased.Compared with N-AKO,the content of propyl gallate in S-AKO was higher,the contents of other five polyphenols gradually increased during the roasting process,and the N-AKO changes were more obvious.Due to the small peak area of these phenolic compounds in the HPLC chromatogram,it has no decisive effect on the total phenolic content of apricot kernel oil.In addition to the known polyphenols,there were 8 unknowns with large peak areas.The peak times were 6.295 min,8.042 min,11.608 min,14.051 min,15.09 min,22.835 min,25.38 min,and 28.594 min.As the roasting temperature risen and the time increased,the peak area gradually increased,the peak areas appearing at 6.295 min and 8.042 min change more obviously during the roasting process.During the whole roasting process,the peak areas of the unknown substances in S-AKO and N-AKO were compared and it was found that the substances deter mining the total phenol content of S-AKO higher than N-AKO were present at 6.295 min,8.042 min,and 28.594 min.(4)Separation of browning substances in oil by column chromatography and thin layer chromatography.The results are as follows:for two full-band scans of apricot kerneloil,two absorption peaks appear at 234 nm and 271 nm in the ultraviolet region and at 435 nm and 459 nm in the visible region,respectively.As the roasting temperature increased,the light absorption value gradually increased.Compared with S-AKO,the light absorption value of N-AKO is larger,indicating that the N-AKO has a deeper Maillard reaction and produces more beauty,produced more Maillard reaction products.The absorbance at 420 nm gradually increases,and the absorbance of N-AKO is greater than that of S-AKO,indicated that N-AKO contains more black sperm.The browning substances extracted from N-AKO are more resistant to oxidation than S-AKO.The liquid chromatograms of the browning material extracted from almond oil at 190 ? for 20 min showed a large peak at 8.042 min.The same substance appeared in the phenolic liquid chromatography.lt is assumed that the material appearing at 8.042 min is one of the browning substances of the Maillard reaction product,and it is combined with phenolic substances to play an antioxidant role.A Fourier-spectrum scan of apricot kernel oil and browning substances revealed that N-AKO contains more aromatic hydrocarbon groups.The browning material may contain a longer carbon chain,intramolecular hydrogen bonding carboxylic acid,aromatic hydrocarbons,and fat.Primary a mines,C-Cl functional groups.lt is assumed that it is a hemi-class polymer consisting of furan or pyrrole repeat units. |
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