Comprehensive evaluation and analysis of kernel quality of Torreya grandis ‘Merrillii’from different soil types

Abstract: 【Objective】Torreya grandis is a large, evergreen and economic plant belonging to Taxaceae family and Torreya genus. As the representative and commonly cultivated T. grandis variety in China,Merrillii is well known for its edibility and its seed is one of the world's rare dry fruits with distinctive texture, charming flavor and physiological function. Previous studies suggest that the nut quality is obviously influenced by nutrition management and ecological condition. With the increasing of the plantation area of T. grandis, many trees have been planted in variable types of soil, while the effect of soil types on nuts quality is still unclear. To provide a reference for high quality T. grandis cultivation, The kernel quality traits of Merrillii from different soil types were evaluated and the correlations between soil nutrients and kernel quality traits were analyzed in this study.【Methods】The 15-20 years old Merrillii plantations with five soil types including volcanic ash soil, granite weathered soil, sandy soil, yellow loam and calcareous soil in Zhejiang province were selected to analyze soil nutrients and kernel quality traits. The p H value, organic matter, hydrolytic nitrogen, available phosphorus, available potassium, calcium, magnesium, manganese, ferrum and zinc contents in different soil types, and the contents of oil,protein, hydrolytic amino acids, starch, soluble sugars, potassium, calcium, magnesium, manganese, ferrum, zinc and vitamin E in fully ripe kernel were determined by standard chemical processes. The processing sensory quality of kernel including biting sense, fragrance, sweet taste and texture were measured using expert marking method. The relations between soil nutrients and kernel quality traits were analyzed by Pearson correlation analysis. The processing sensory flavor and kernel quality traits were evaluated based on grey relation analysis.【Results】The nutrient contents in different types of soil varied greatly and the coefficient of variation of pH value, organic matter and mineral elements content was in the range of 19.02%-177.20%. A significant positive correlation was found between soil pH value and the content of calcium, magnesium and zinc. There was also a significant positive correlation between the content of organic matter and hydrolytic nitrogen. And the content of zinc was significantly related with magnesium and manganese in the soil as well. The average contents of oil, protein and hydrolytic amino acids in kernel of Merrillii from different types of soil were 59.56%, 12.20 g · 100 g-1and11.96 g·100 g-1, respectively, and their coefficient of variation was between 3.42% and 4.85%. The average contents of starch, soluble sugars and vitamin E were 4.97 g·100 g^-1, 3.36 g·100 g^-1 and 1.26 g·kg^-1,respectively, with a coefficient of variation of 13.91%, 13.38% and 11.94%, respectively. The kernel was also rich in mineral elements and vitamin E. The average contents of potassium, magnesium and calcium reached 5.47, 2.37 and 0.55 g·kg^-1, respectively. The average contents of microelements e.g.manganese, ferrum and zinc were 16.92, 45.02 and 18.54 mg·kg^-1, respectively. The average coefficient of variation of mineral elements was 18.27%. Unlike those of the oil, protein and hydrolytic amino acids, the coefficients of variation of starch, soluble sugar, mineral elements and vitamin E were higher and ranged from 7.11% to 38.09%. The correlation coefficient between soil organic matter content and starch, soluble sugar content in kernel was 0.902 and 0.893(p<0.05), respectively. And the correlation coefficient between soil hydrolytic nitrogen content and starch in kernel was 0.965(p<0.01). The mineral elements in the soil were also significantly correlated with those the in kernel. For instance, a significant positive correlation was found between the calcium content in kernel and the content of available phosphorus, manganese, ferrum and zinc in the soil, and between the magnesium content in kernel and the content of available potassium, magnesium and zinc in the soil as well. The results of grey relation analysis showed that the flavor traits, inner nutritional traits and processing sensory flavor of nuts from sandy soil ranked first, second and first, respectively. And the nuts from granite weathered soil showed the best inner nutritional quality, but the flavor quality was poor relatively. The correlation coefficient of flavor traits and processing sensory flavor reached 0.958(p<0.01), while no significant correlation was found between inner nutritional traits and processing sensory flavor as well as between flavor traits and inner nutritional traits of the kernel.【Conclusion】The soil nutrients and kernel quality traits of Merrillii from different types of soil varied greatly. Compared with the contents of starch, soluble sugars, mineral elements and vitamin E, the contents of oil, protein and hydrolytic amino acids in kernel were relatively stable under different soil conditions. The starch, soluble sugar, and mineral element content in the kernel had a significant correlation with organic matter and mineral elements content in soil. Overall, the kernel from the sandy soil showed the best comprehensive quality in terms of flavor and inner nutritional traits. And the kernel quality traits including oil, protein, hydrolytic amino acids,starch, and soluble sugars could be used as quantitative indicators to evaluate the nut processing sensory quality based on grey relation analysis.