Objective This paper aims to clarify and compare the characteristics of acorn qualities of Quercus and Castanopsis from different provenances, and fully tap the potential of fruit resources, then provide a reference for the selection and breeding, utilization, and protection of excellent fruit resources in China.
Method The acorns were collected, including 6 Quercus species from 28 provenances and 7 Castanopsis species from 48 provenances in 15 provinces (municipalities) in China, and the morphologies, nutrients, polyphenols and antioxidant capacities were determined, and then comprehensively evaluated by factor analysis.
Result (1) At the level of morphological traits, the Quercus acorns were mostly ellipsoidal in morphologies, while the Castanopsis acorns were mostly nearly spherical. The size and mass of the former were about 1.5‒2 times of that in the latter. (2) At the level of kernel nutrient components, the soluble sugar contents in Quercus were 18.31–79.94 mg/g, and they were higher in Q. acutissima, Q. serrata and Q. mongolica than the average value in Quercus; while those in Castanopsis were lower (about 20.16–52.08 mg/g) at the overall level, but a few species such as C. sclerophylla and C. fissa reached the average level in Quercus. The starch contents in Quercus were 169.33–382.27 mg/g, whereas those in Castanopsis were 130.29–544.12 mg/g, which were higher than that in Quercus as a whole, but the starch in C. fissa was significantly lower than that of each species. The average values of total amino acid and soluble protein contents in both Quercus and Castanopsis were relatively low, but there were significant differences between species. (3) At the level of kernel functional components, the total polyphenol contents in Quercus were 54.64–242.90 mg/g, while those in Castanopsis were 1.28–138.11 mg/g, the average contents in the former were about 4.5 times of those in the latter. Except for C. sclerophylla and C. fissa, the total polyphenol contents, between 1.28–4.66 mg/g, in other Castanopsis were extremely lower, and the changing trends of total flavonoids and soluble tannins were similar to the total polyphenols. The contents of vitamin E in Quercus were higher than those in Castanopsis, which had very low contents except for C. sclerophylla and C. fissa with high polyphenols. Further test showed that the total polyphenols in Q. serrata from provenance 25 had the highest antioxidant activity with a high DPPH value of 82.98% in both Quercus and Castanopsis. (4) Based on the comprehensive score ranking, it can be concluded that the acorns from provenance 16 had the largest seed and the higher content of polyphenols, and the acorns from provenance 20 had a larger seed size, higher starch and polyphenols, and moderate soluble protein and total amino acid contents. The ten top ranking of acorn qualities by comprehensive evaluation was provenance 16, 17, 20, 14, 2, 24, 28, 8, 3, and 19.
Conclusion The traits of phenotypes, nutrients and functional components were rich in variation as well as higher degree of variation in the selected acorns of Quercus and Castanopsis germplasm resources in China, in which, ten optimal germplasms with top ranking were selected. These findings would provide valuable resources for the selection and breeding of excellent new varieties rich in starch or polyphenols in future.
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