| Apricot(Armeniaca vulgaris Lam.)belongs to the genus Armeniaca of the subfamily Prunoideae in the family Rosaceae.China is one of the distribution centers of apricots,with abundant germplasm resources,ranking first in the world in terms of varieties and number.The apricot tree has strong ecological adaptability and grows well in harsh environments.It is a pioneer tree species for windbreak and sand fixation,afforestation and soil conservation,and improvement of the ecological environment,and has irreplaceable ecological value in semi-arid areas with fragile ecological environment.Apricot kernels is rich in protein,oil,essential oil,sugar,various inorganic salts and vitamins.Especially apricot kernel oil has high nutritional value and medical value attributing to unsaturated fatty acid structure and biologically active ingredients.The apricot has become an important pillar industry of the rural economy in arid areas.However,there has been a long-term limiting factor in the development and utilization of apricot kernel,that is,a large amount of amygdalin is synthesized and accumulated during the growth and development process,and its content is uneven.All products including intensive and deep processing inevitably contain cyanide,which brings confusion to the production process,management departments and consumers.The lack of high-quality cultivation and processing technology in production has severely restricted the development of the apricot industry.The above mentioned is closely related to the insufficient understanding of the accumulation pattern and genetic regulation mechanism of cyanogenic glycosides and oil components during the development of apricot kernel.Based on the above problems,this study measured and compared the fruit and kernel physical properties(weight,linearity dimension,shape index),cyanogenic glycoside content(amygdalin,prunasin),amygdalin synthesis key enzyme UDP-glucosyltransferase,amygdalin degradation key enzyme ?-glucosidase activity,apricot kernel oil and nutrient components(fatty acids,tocopherols,squalene)of the hybrid combination and the parent's open pollination and 10 cultivars at different development stages.The genetic basis,differential accumulation modes,and the effects of different cross combinations and cultivars on the phenotypic quality,amygdalin content,oil components and heredity of apricot fruits and kernels were clarified.The inherent correlation among the phenotypic quality,and differential accumulation of amygdalin and oil components in apricot kernels was explained as well.The study has provided the theoretical basis for scientific regulation of apricot quality and development and utilization,for the rational preparation of pollination trees,and efficient selection of varieties with high/low content of cyanogenic glycosides,and provided scientific basis for development and utilization,analysis and testing,detoxification technology,and risk evaluation of bitter apricot functional products.The main conclusions of this research are as follows:(1)Different hybrid combinations have significant effects on the content of amygdalin and the activities of related metabolic enzymes(?-glucosidase and UDP-glucosyltransferase)in apricot kernels.Taking open pollination from the female parent as a control,different cross combinations can significantly increase or decrease the amygdalin content in apricot kernels.From the perspective of reducing the content of amygdalin,'ZK' and 'DG' are more suitable as pollination trees for 'SK-1',and 'ZK' is more suitable as a pollination tree for 'JD';from the perspective of increasing the content of amygdalin,'DG' and 'JG' are more suitable as pollination trees for 'CZH' and 'YS',and 'DG' is more suitable as a pollination tree for 'JG'.Different cross combinations have significant effects on the fruit setting rate of apricots,the physical properties of the fruit and kernel(weight,linear dimension),the kernel oil content,the fatty acid composition ratio,the total tocopherol content and the content of each isomer(?-,?-and ?-Tocopherol)and squalene content,but there were no significant differences in shape index of fruits and kernels and saturated fatty acid content in different crossbred combinations.From the perspective of increasing the content of tocopherols in apricots,'JG'and 'DG' are more suitable as pollination trees for 'SK-1',while 'ZK' is not suitable as a pollination tree for 'SK-1'.Taking open pollination as a control,different hybrid combinations significantly increased the squalene content in 'SK-1'.To increase squalene in the production,'JG' and 'DG' could be selected as the 'SK-1' pollination tree.'DG' as the pollination tree of 'SK-1','YS' and 'CZH',and 'QH' as the pollination tree of 'JD',significantly increased the fruit-setting rate.Therefore,in order to achieve high-quality and high-yield apricot,it is necessary to choose good pollination tree varieties.(2)Amygdalin and its precursor prunasin can hardly be detected in sweet apricot kernels,and are only synthesized and accumulated in bitter kernel varieties.In the early stage of bitter kernel development(20 ? 50 DAF),it is dominated by prunasin,while in the late development period(50 DAF to full maturity),only amygdalin is accumulated.The accumulation of cyanogenic glycosides is a shift from a prunasin-dominated to an amygdalin-dominated state during bitter apricot kernel development and ripening;the accumulation of cyanogenic glycosides in apricot kernel depends on the variety and the developmental stage.The accumulation of amygdalin may not be a single control point,but may be the result of more factors.The dynamic accumulation of amygdalin is not correlated or has a weak positive correlation with the linear dimensional parameters and shape index of apricot kernel development,and has a significant positive correlation with other indicators.The oil dynamic accumulation has little correlation with amygdalin and prunasin in apricot kernels.(3)Apricot varieties are rich in oil,14 fatty acids were detected in different varieties of apricot kernel oil,the main fatty acid is oleic acid(64.35 ? 74.04%),followed by linoleic acid(18.50 ? 27.22%),palmitic acid(4.63 ? 5.53%),stearic acid(1.22 ? 1.73%),palmitoleic acid(0.41 ? 0.71%)and linolenic acid(0.22 ? 0.38%);There are significant differences in the content of oils,fatty acids,saturated fatty acids,monounsaturated fatty acids,and polyunsaturated fatty acids of different apricot varieties.The oil content of 'ZK' was the highest(53.31%),followed by 'QH'(52.46%).The oleic acid content in 'DG' was the lowest(64.35%),linoleic acid and linolenic acid were the highest(27.22%,0.38%).The monounsaturated fatty acid content of all tested cultivars was more than 92%,and the monounsaturated fatty acid content in 'ZK'(74.73%)and saturated fatty acid in 'QH'(7.07%)was significantly higher than that of other cultivars.Oleic acid/linoleic acid ratio of all tested cultivars was moderate(2.37 ? 3.94),among which the ratio of 'ZK' had the highest ratio(3.94).The ratio of unsaturated fatty acid to saturated fatty acid in 'WX-1'(15.55)was significantly higher than that of other cultivars.The oil accumulation presents an S-curve pattern with the development of apricot kernels;for the purpose of oil production,the best harvesting period of some cultivars should be harvested before the full ripening period.The contents of total tocopherol,various tocopherol isomers and squalene in different cultivars apricot kernel oil are significantly different.The highest contents of total tocopherol(334.7mg/kg oil),?-tocopherol(316.21 mg/kg oil)and ?-tocopherol(13.14 mg/kg oil)were found in 'DG',followed by 'SK-1'.The squalene content of 'DG'(105.09 mg/kg oil)was significantly higher than that of other cultivars.During the rapid accumulation period of oil,there are significant differences in the fatty acid composition ratio,total tocopherol,various tocopherol isomers,and squalene content at different development stages and at the same development stage of different cultivars.Linoleic acid,linolenic acid,palmitic acid,and stearic acid show a decreasing trend.Oleic acid and linoleic acid form opposite accumulation patterns during the rapid accumulation period of almond oil;unsaturated fatty acid/saturated fatty acid,oleic acid/linoleic acid,the ratio of monounsaturated fatty acid/polyunsaturated fatty acid basically showed an S-shaped increase pattern with the apricot kernenl development;the ?-tocopherol content in each developmental stage was extremely significantly higher than other tocopherol isomers.The content of total tocopherol,each tocopherol and squalene showed a decreasing trend with the apricot kernel development.(4)Bitter apricot oil and its alkaline hydrolysis components can react with cyanide to form some unknown oil-cyanide complex,which may be an important factor affecting the stability,reproducibility and accuracy of the results of the existing methods for the determination of cyanide in oil.In summary,the accumulation mode of amygdalin is a shift from a prunasin-dominated to an amygdalin-dominated state during bitter apricot kernel development and ripening.The production of amygdalin depends on the genotype of the mother tree.Different hybrid combinations can significantly increase or decrease the content of amygdalin in apricot kernels.The differential accumulation of amygdalin is mainly regulated by apricot genotype,and is also regulated by hybrid combination,developmental stage,and maturity,to a certain extent,which is a comprehensive result of changes in the activities of related metabolic enzymes.Apricot kernel oil,O/L,UFA/SFA,MUFA/PUFA show an S-curve pattern with the development of apricot kernels;Apricot kernel oil content,fatty acid composition,tocopherol composition,and squalene are unique attributes of apricots,and their content and quality are coordinatly regulated by genotypes,hybrid combination and developmental stage.The content of tocopherol and squalene in apricots shows a sharp decline during the rapid accumulation period of oil,which is a comprehensive result of external phenology and internal synthesis pathways(substrates,precursor substances,enzyme activities).Cyanide can be present as some unknown compound in bitter almond oil,which may affect the stability,reproducibility and accuracy of quantitative analysis results.The results of this study provided a basis for further research on the genetic basis of amygdalin and the accumulation of oil components,and provided a reference basis for the testing standards,detoxification technology,and risk evaluation of functional products of bitter apricot oil. |
PDF Full Text Request