ARS | Publication request: NIR MEASUREMENT OF APPLE FRUIT SOLUBLE SOLIDS CONTENT AND FIRMNESS AS AFFECTED BY POSTHARVEST STORAGE

Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: May 16, 2005
Publication Date: July 17, 2005
Citation: Lu, R., Bailey, B.B. 2005. NIR measurement of apple fruit soluble solids content and firmness as affected by postharvest storage. ASAE Annual International Meeting. Paper No. 056070.

Interpretive Summary: Nondestructive sensing technology is critical to assuring the quality and consistency of fresh apples to meet consumer expectation and satisfaction. Near-infrared (NIR) technology has been researched extensively for measuring sugar or soluble solids content (SSC) and other quality attributes of apples. The technology is currently being used in some modern packing facilities for sorting and grading apples for sweetness or SSC. NIR measures diffusely reflected light from the fruit sample at different wavelengths in the near-infrared (longer than the visible) spectral region. NIR measurements of SSC are affected by postharvest storage condition/time and instrument configuration. Appropriate calibration procedures are critical to accurate measurement of fruit SSC. This research showed that NIR measurements of SSC were strongly influenced by postharvest storage time and inappropriate calibration procedures could lead to unsatisfactory predictions of fruit SSC. SSC measurements were also related to instrument configuration. The sensing mode used in this research was good for measuring the SSC and firmness of apples. To achieve accurate measurements of fruit SSC, calibration samples must be such selected that they are representative of the entire lot of fruit. The research provides critical information for equipment manufacturers and NIR instrument users on appropriate procedures and potential pitfalls for developing NIR calibration models for predicting apple fruit SSC.

Technical Abstract: Near-infrared (NIR) measurements of fruit quality are influenced by instrument configuration, fruit growth condition, and postharvest storage condition. The objective of this research was to determine how NIR measurements of soluble solids content (SSC) and firmness were affected by postharvest storage and were related to instrument setting. A low-cost CCD-based visible/NIR spectrometer and an InGaAs-based NIR spectrometer were used in interactance mode for collecting spectra from three groups of ‘Golden Delicious’ apples with different postharvest conditions (freshly harvest and one and two months in cold storage at 0 deg C). Calibration models were developed using the partial least squares method for each group of apples. Model performances were evaluated for within groups and cross groups. The coefficients of determination R**2 (standard errors of validation or SEV) for within-group predictions of SSC were in the range 0.57-0.71(0.67-0.76%) for the Vis/NIR spectrometer and 0.77-0.85(0.41-0.55%) for the NIR spectrometer. Poor predictions of SSC were obtained (SEV = 0.7-1.4%) with both spectrometers when the calibration model for one group was used to predict other groups (cross-group validation). Excellent firmness predictions (R**2=0.839 and SEV=4.8 N) were obtained for the pooled data with the NIR spectrometer. To ensure accurate and reliable NIR measurement of fruit SSC, calibration samples must be representative of the population of fruit to be measured and different post-storage conditions/times.