Correlations between physical properties and major chemical components of shells in apricot

Abstract:【Objective】Kernel-using apricots (Prunus armeniaca L.) are unique apricot resources in Chi- na, and they are often used as the main economic tree species in arid and semidesert areas in Northern China due to their excellent characteristics of cold and drought resistance and barren tolerance. Difficul- ty in opening the shells and low kernel-yield-rate are two major concerns both for growers and breed- ers. The evaluation of the physical properties and the chemical components of the kernel-using apricots would be valuable for speeding up the selection of new variety【. Methods】The physical characteristics of kernel thickness, hardness, and breaking force were investigated using TMS-Pro physical property analyzer (Food Technology Corporation in USA). The contents of cellulose, hemicellulose, and lignin in the kernel of different germplasms were determined using general detection methods such as Klason lignin method and Kurschner-Hoffer method【. Results】The order of the mean value of the shell thick- ness were ansu apricot (P. sibrica L.) population (1.37 mm) < Fresh-using apricot (P. armeniaca L.) (1.74 mm) < Kernel-using apricot (P. armeniaca L.) (2.00 mm); the average value of breaking force were ansu apricot population (149.57 N) < Fresh- using apricot (149.57 N) < Kernel- using apricot (209.65 N); the average value of kernel hardness were ansu apricot population (613.26 N) < Kernel-us-ing apricot (733.73 N) < Fresh-using apricot (873.62 N). Analysis of variances showed that there were significant differences in the thickness, breaking force, and hardness of the apricot shells among differ- ent types of apricot germplasms. There were abundant genetic variations in apricot shells, but the genet- ic variation of the kernel-using apricot was smaller than other types. In the process of artificial selec- tion, there were some undesirable traits such as the kernel thickness and hardness of shell in the kernel- using apricot, however, some germplasm such as Lve, Luren, You No.1, and Xin No.4, exhibited great utilization potential for improving the kernel yield in apricot. The main components of apricot shell were cellulose, hemicelluloses, and lignin, and their contents were 19.08%, 47.55%, and 28.78%, respectively. The mean content lignin in kernel-using apricots, fresh-using apricots and ansu apricot popu- lation were 28.22%, 30.2%, and 28.34%, respectively. Analysis of variances showed that the mean con- tents of cellulose, hemicellulose, and lignin were not significantly different among different types of apricot germplasms. The variation coefficient of lignin content was larger than that of holocellulose, which indicated that lignin content varied obviously with different accessions. It was found that shell thickness and hardness (r = 0.544**), breaking force and hardness (r = 0.600**), cellulose and hemicel- lulose (r = 0.976**), acid-insoluble lignin content and the total lignin content (r = 0.999**) were ex- tremely significantly and positively correlated. Among the physical properties and chemical composi- tion of the apricot shells, there was only one correlation, that is, the correlation between the shell hard- ness and the total content of lignin (r = 0.343*), and the contents of cellulose and hemicelluloses, which were the cell wall framework materials, were not significantly correlated with shell thickness. It indicated that the lignin content of shell had the greatest impact on the hardness of the apricot stone.【Conclusion】There were abundant genetic variations in thickness, breaking force, and hardness of the apricot shells among different types of germplasms. The apricot shell was mainly chemically composed of cel- lulose, hemicelluloses, and lignin; the proportions of these compositions showed no significant differ- ence among different types of germplasms. The hardness of the shell was correlated with thickness and lignin content of the shell in apricot.