| Popis: |
The viability of a near infrared (NIR) method based on a dual-beam, fibre-optic portable spectrophotometer was tested to determine soluble solids non-destructively in apples ( Malus domestica Borkh.). A total of 340 apples (190 of cv. `Golden Delicious' and 150 of cv. `Jonagold') sampled from two positions in the canopy to increase variation in soluble solids concentration, were measured after 5-months storage and the measurements randomly assigned to a calibration data set and a prediction data set. Thus the calibration set and the prediction set represented exactly the same distribution. The calibration data set was used to select the wavelengths best correlated with °Brix and to fit a multiple linear regression (MLR) equation that was applied to calculate the °Brix value in the prediction data set. The most significant R 2 (0.56) was found with the first derivative of log(1/ R ) (where R =reflectance), yielding standard error of calibration (S.E.C.)=1.01 °Brix, standard error of prediction (S.E.P.)=1.14 °Brix and bias=−0.13 °Brix. When MLR was carried out separately on each cultivar, the R 2 value was higher for `Golden Delicious' (0.65), but not for `Jonagold' fruit. Analysis of variance performed on the actual and the predicted °Brix showed no difference in statistical significance, although the bias was higher (±5% of actual °Brix) at the extremities of the °Brix range. The scoring of the fruits according to soluble solids content measured by NIR enabled correct classification of 72 and 76% of the fruits, with a threshold of 12 and 13 °Brix, respectively. This NIR method seems reliable for determining soluble solids contents non-destructively, and could prove useful in the orchard. |
Full Text from ScienceDirect