Non-destructive determination of soluble solids in apple fruit by near infrared spectroscopy (NIRS)
Maurizio Ventura, Anton de Jager, Herman de Putter and Frans P. M. M. Roelofs
Postharvest Biology and Technology. Vol. 14, No.1. 1998. pp. 21-27.
1998
บทคัดย่อ
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 R2 (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 R2 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.