Abstract:

【Objective】Soapberry (Sapindus mukorossi) is an important raw material species for biochemical, biomass energy industries. In recent years, China’s soapberry industry has seen booming growth. The fruiting period of soapberry is several months long and there is no clear harvesting period or method to determine the harvesting time during production. In this study, we conducted observations of fruit growth and development dynamics, as well as dynamic changes in the contents of inclusions, to clearly determine the harvesting time of soapberry fruits during production.【Method】Five eight-year-old living soapberry trees with medium growth and good flowering, and fruit set were selected. Three fruit sequences were randomly chosen from each tree every four days from the end of the fruit expansion period to the fruit abscission period. The ten phenotypic indicators, seed kernel oil content, mass of single kernel oil, pericarp saponin content, mass of single pericarp saponin and water content were determined.【Result】① The change in fruit color from green to golden yellow occurred at the end of September, followed by a water loss in the first half of October, along with wrinkling of the pericarp surface. A 7.95% decrease in the transverse diameter and a 10.71% decrease in the lateral diameter of the fruit were also observed. ② The seed kernels were small and green from the end of August to the beginning of September; these then grew gradually before changing from green to yellow around September 20 and completely changed to yellow at the end of September. The transverse diameter, longitudinal diameter and lateral diameter of the seeds decreased significantly in early October, with the transverse diameter decreasing by 10.81%, the longitudinal diameter by 4.87%, and the lateral diameter by 8.96%. ③ The dry mass of the fruit and pericarp showed the same trend, both rising until October 15 and then fluctuating slightly. We innovatively found that the dry mass of seeds decreased when the se-cond significant rise in pericarp dry mass occurred. The fruits finished drying in mid-October. ④ The content of single kernel oil was higher in mid-September and thereafter, whereas the content of single pericarp saponin was higher in early and mid-October.【Conclusion】 The accumulation of saponins in the peel and the oil of the seed kernels was the highest in early October, and the best fruit harvesting periods for peel saponin and the oil of single seed kernels were in early and mid-October. Judging from the fruit’s appearance, the optimum fruit harvesting period was within 20 days after the fruit completely turned golden yellow and the peel started to wrinkle in production.

Key words: Sapindus mukorossi (soapberry), fruit, saponin, inclusion, energy tree