|Noh, Hyun Kwon|
Submitted to: Proceedings of SPIE
Publication Type: Proceedings
Publication Acceptance Date: 10/19/2005
Publication Date: 12/15/2005
Citation: Noh, H., Lu, R. 2005. UV/blue light-induced fluorescence for assessing apple maturity. Proceedings of SPIE. 5996:59960I.
Interpretive Summary: The maturity of apples is a key factor in determining harvest time and their postharvest quality and end uses. Accurate determination of apple maturity is challenging since individual fruit vary greatly on the same tree or between the trees of the same orchard. The current maturity determination requires measuring skin and flesh color, fruit firmness, sugar (or soluble solids), starch, acid, and ethylene production. These measurements are destructive, time consuming, inefficient, and prone to operational error. Nondestructive sensing would offer great advantages in maximizing fruit postharvest quality and solving the inconsistent fruit quality problem that is still commonplace in the marketplace. The objective of this research was to develop a fluorescence spectroscopy technique for measuring multiple quality attributes of apple fruit. Fluorescence is a technique for measuring the light of longer wavelengths released from a fluorescing object after it absorbed short-wavelength light. Most plant materials are fluorescing, which is related to their physiochemical activities. Research was performed on collecting fluorescence spectra from ‘Golden Delicious’ and ‘Red Delicious’ apples. Statistical models were developed on relating fluorescence spectra data to standard destructive measurements. Fluorescence spectroscopy provided accurate measure of fruit skin and flesh color. Fluorescence measurements were also correlated to fruit firmness, sugar, and acid, but the correlation was relatively low. This research showed that fluorescence spectroscopy can be potentially useful for measuring quality and condition of apples and other fruits. The technique is complementary with other nondestructive sensing techniques in measuring multiple quality attributes of fruit, and hence it can be a valuable tool for quality and maturity evaluation of apples and other fruits.
Technical Abstract: Chlorophyll fluorescence has been researched for assessing fruit post-harvest quality and condition. The objective of this preliminary research was to investigate the potential of fluorescence spectroscopy for measuring apple fruit quality. Ultraviolet (UV) and blue light was used as an excitation source for inducing fluorescence in apples. Fluorescence spectra were measured from 'Golden Delicious’ (GD) and 'Red Delicious’ (RD) apples by using a visible/near-infrared spectrometer after one, three, and five minutes of continuous UV/blue light illumination. Standard destructive tests were performed to measure fruit firmness, skin and flesh color, soluble solids and acid content from the apples. Calibration models for each of the three illumination time periods were developed to predict fruit quality indexes. The results showed that fluorescence emission decreased steadily during the first three minutes of UV/blue light illumination and was stable within five minutes. The differences were minimal in the model prediction results based on fluorescence data at one, three or five minutes of illumination. Overall, better predictions were obtained for apple skin chroma and hue and flesh hue with values for the correlation coefficient of validation between 0.80 and 0.90 for both GD and RD. Relatively poor predictions were obtained for fruit firmness, soluble solids content, titrational acid, and flesh chroma. This research demonstrated that fluorescence spectroscopy is potentially useful for assessing selected quality attributes of apple fruit and further research is needed to improve fluorescence measurements so that better predictions of fruit quality can be achieved.