Prediction of firmness parameters of tomato by portable visible and near-infrared spectroscopy

Authors: HUANG, YUPING - Nanjing Agricultural University; Lu, Renfu; CHEN, KUNJIE - Nanjing Agricultural University

Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2017
Publication Date: 12/1/2017
Citation: Huang, Y., Lu, R., Chen, K. 2017. Prediction of firmness parameters of tomato by portable visible and near-infrared spectroscopy. Journal of Food Engineering. 8:185-198.

Interpretive Summary: Firmness is an important parameter for determining maturity/ripeness and postharvest processing quality of tomatoes. Currently, firmness of tomatoes is measured using both destructive and nondestructive mechanical methods, including acoustic, impact, compression and puncture. Each method involves different principles and can be used for different purposes. In this research, two portable spectrometers, covering the visible and shortwave near-infrared (Vis/SWNIR) region of 400-1,100 nm and the near-infrared (NIR) region of 900-1,700 nm, were used to acquire spectra for 600 ‘Sun Bright’ tomatoes of different maturity stages. The firmness of tomatoes was then measured by the four reference mechanical methods. Mathematical prediction models were developed by relating spectral measurements to the firmness parameters by the four reference methods. Results showed that different mathematical treatment methods for the spectral data influenced firmness prediction results. Better predictions of firmness were obtained when autoscaling preprocessing was applied to the spectral data. Overall, Vis/SWNIR gave better predictions of all firmness parameters with the correlation coefficient ranging between 0.894 to 0.930, while NIR had lower correlations between 0.801 and 0.835. This research showed that Vis/SWNIR and NIR can be used as a cost-effective tool for fast assessment of different firmness parameters.

Technical Abstract: Firmness is an important parameter for determining maturity/ripeness and postharvest processing quality of tomatoes. This paper reports on the prediction of different fruit firmness parameters of tomatoes by using visible and near-infrared spectroscopy. Interactance spectra were taken from 600 freshly harvested tomatoes of six maturity stages, using two portable spectrometers for 400-1,100 nm and 900-1,700 nm, respectively. Different firmness parameters for the tomatoes were measured using acoustic, impact, compression and puncture tests. Partial least squares (PLS) regression models, coupled with four preprocessing methods (i.e., original, logarithmic, autoscaling, and logarithmic plus autoscaling), were developed to predict the firmness parameters of tomato fruit. The PLS models gave better predictions of impact firmness, compression area and puncture slope for the tomato fruit, with the correlation coefficient for prediction of 0.894, 0.914 and 0.930 for the visible and short-wave near-infrared (Vis/SWNIR) spectra of 400-1,100 nm, and 0.835, 0.801 and 0.818 for the near-infrared (NIR) spectra of 900-1,700 nm. Overall, autoscaling preprocessing performed consistently better in most cases for both Vis/SWNIR and NIR spectra. Visible and near-infrared spectroscopy in interactance mode can be useful for nondestructive assessment of tomato firmness measured by both destructive and nondestructive reference methods.