[Determination of hard rate of licorice (Glycyrrhiza uralensis F.) seeds using near infrared reflectance spectroscopy].

With 112 licorice seed samples with different hard rates ranging from 0.3% to 99.3%, harvested in different years from 2002 to 2007 and from different locations of China including Xinjiang municipality, Ningxia province, Inner-Mongolia municipality, Gansu province, Shanxi province and Heilongjiang province, a model for determining hard rate of licorice seeds was tried to be built by near infrared reflectance spectroscopy with quantitative partial least squares (QPLS). All the seeds samples were divided into two groups: calibration set (including 84 samples) and validation set (including 28 samples). The influences of different spectral regions, different main components and different calibration samples on the prediction results were compared. The result indicated that the spectral regions of 4000-8000, 5000-9000, 5000-8000, 5000-7000 and 5000-6000 cm(-1) all had satisfied and similar prediction results, then 5000-6000 cm(-1) was regarded as the optimum spectral region for building the model because of its faster operation speed. The model with 6 main components had better relative high determination coefficient (R2) and low standard errors and absolute errors. With the spectral range from 5000 to 6000 cm(-1) and 6 main components, there was a better fitting between the predictive value and true value. Determination coefficients (R2) of calibration and validation sets are 90.23% and 91.24%, the coefficients of correlation are 0.9532 and 0.9579, the standard errors are 10.31 and 9.72, and the average absolute errors are 8.01% and 7.45% respectively. Even with different calibration samples, the models have high determination coefficient (R2 over 90%), low standard errors (about 10.00) and low absolute errors (about 7.90%). The building of NIR model for determining hard rate of licorice seeds could promote the application of hard seeds in cultivation.