Influence Of Different Roasting Temperature On Quality Characteristics Of Oil Pressed With Skins Of Apricot Kernel

The apricot kernels without skin and the apricot kernel skin were got through the peeling of kernels.The kernels and skin were roasted in different conditions,then the apricot kernel oil pressed with or without skin were made,we also made the skin flour.The effects of roasting on the physical and chemical and nutritional quality of apricot kernel oil were studied;We determined the induction period of apricot kernel oil,the total phenolics and antioxidant capacity both of apricot kernel oil and apricot kernel skin;The HPLC method was used to determine the polyphenols in the extracts of apricot kernel oil and apricot kernel skin;The effects of roasting on the volatile components of apricot kernel oil was studied by GC-MS method.The results are showing as follows:(1)The physical and chemical quality of apricot kernel oil:the results showed that the apricot kernel oil was rich in unsaturated fatty acids,accounting for 94%of the total fatty acids,of which the highest content of oleic acid,accounting for about 45%.The acid value of apricot kernel oil is between 0.41 and 0.49 mg/g,and the peroxide value is between 0.53 and 0.99 mmol/kg,both of them are in accordance with the highest level of the national edible oil standard.With the increasing of the roasting temperature,the oxidation degree of the apricot kernel oil pressed without skin is deepened,but the oxidation of the oil pressed with skin is suppressed to a certain extent.The iodine value of apricot kernel oil is between 104.2 to 106.7 g/100g,which indicating that apricot kernel oil is rich in unsaturated fatty acids and has high nutrition.The saponification value of apricot kernel oil ranges from 188.2 to 199.0 mg/g,which is lower than 200 mg/g of common edible oils.The results of sensory quality tests showed that the color of apricot kernel and oil became darker as the roasting temperature increased,exhibiting nut and baking aroma.(2)The oxidative stability and antioxidant capacity of apricot kernel oil:The results showed that the induction period of apricot kernel oil ranged from 6.56 to 8.82 h.The induction period was prolonged with the increasing of roasting temperature,and the value of oil pressed with skin was generally larger.The total phenolics content of the methanol extract of apricot kernel oil ranges from 0.22 to 3.28?g/g,and the value of oil pressed with skin is more than 2.5 times of the value of oil pressed without skin.As the roasting temperature increases,the total phenolics content of apricot kernel oil increases.The antioxidant capacity of apricot kernel oil showed the same trend.The total phenolics in the seed coat were extracted with two solvents,the results showed that the 50%ethanol extract had a higher total phenolics content,which is about 3 times of that in the water extract.With the increasing of the roasting temperature,the total phenolics content of the 50%ethanol extract increased and reached a maximum of 6.61 mg/g at 120 0C.The antioxidant capacity of apricot kernel skin showed the similar trend.Roasting enhanced the oxidative stability and antioxidant capacity of apricot kernel oil,which may due to the increase of the solubility of phenolics in the kernel skin and the promotion of its transfer to the oil.(3)The determination of polyphenols in apricot kernel oil:The results showed that the extract of apricot kernel skin contained catechin and chlorogenic acid,but both of them had little effect on the antioxidant capacity of apricot kernel oil.Two obvious chromatographic peaks appeared when the retention time was 6.684 min and 8.187 min,and the peak area changed a lot at different roasting conditions.At the two retention times,the 50%ethanol extract had a greater peak area,and the corresponding oil pressed with skin also had a greater peak area.It is presumed that new polyphenolic compounds produced at the two retention times during the roasting process,and they has a great influence on the oxidative stability of apricot kernel oil.(4)Study on the volatile components of apricot kernel oil:The results showed that the main volatile components of apricot kernel oil were 3-ethyl-2,5-dimethyl-pyrazine,2-ethyl-3-methylpyrazine,methylpyrazine,benzaldehyde,hexanal,nonanal,creosol,4,6-dimethylpyrimidine and 3,4-dimethoxytoluene,and benzaldehyde was supposed to be the characteristic flavor volatile component of apricot kernel oil.With the increasing of the roasting temperature,the content of aldehydes in the apricot kernel oil decreased,on the contary,the content of pyrazine increased,and the trend of oil pressed with skin was more obvious.Proper roasting can make apricot kernel oil produce a large number of pyrazine compounds,which can make the oil show strong nut and roasted aroma.