Article
Postharvest Monitoring of Tomato Ripening Using
the Dynamic Laser Speckle
Piotr Mariusz Pieczywek
1,
*, Małgorzata Nowacka
2
, Magdalena Dadan
2
, Artur Wiktor
2
,
Katarzyna Rybak
2
, Dorota Witrowa-Rajchert
2
and Artur Zdunek
1
1
Institute of Agrophysics, Polish Academy of Sciences, Do´swiadczalna 4, 20-290 Lublin, Poland;
a.zdunek@ipan.lublin.pl
2
Department of Food Engineering and Process Management, Faculty of Food Sciences,
Warsaw University of Life Sciences (SGGW), Nowoursynowska 159c, 02-776 Warsaw, Poland;
malgorzata_rzaca@sggw.pl (M.N.); magdalena_dadan@sggw.pl (M.D.); artur_wiktor@sggw.pl (A.W.);
katarzyna_rybak@sggw.pl (K.R.); dorota_witrowa_rajchert@sggw.pl (D.W.-R.)
* Correspondence: p.pieczywek@ipan.lublin.pl; Tel.: +48-81-744-50-61
Received: 26 February 2018; Accepted: 30 March 2018; Published: 4 April 2018
Abstract:
The dynamic laser speckle (biospeckle) method was tested as a potential tool for the
assessment and monitoring of the maturity stage of tomatoes. Two tomato cultivars—Admiro
and Starbuck—were tested. The process of climacteric maturation of tomatoes was monitored
during a shelf life storage experiment. The biospeckle phenomena were captured using 640 nm and
830 nm laser light wavelength, and analysed using two activity descriptors based on biospeckle
pattern decorrelation—C4 and
ε
. The well-established optical parameters of tomatoes skin were
used as a reference method (luminosity, a*/b*, chroma). Both methods were tested with respect
to their prediction capabilities of the maturity and destructive indicators of tomatoes—firmness,
chlorophyll and carotenoids content. The statistical significance of the tested relationships were
investigated by means of linear regression models. The climacteric maturation of tomato fruit
was associated with an increase in biospckle activity. Compared to the 830 nm laser wavelength
the biospeckle activity measured at 640 nm enabled more accurate predictions of firmness,
chlorophyll and carotenoids content. At 640 nm laser wavelength both activity descriptors (C4 and
ε
)
provided similar results, while at 830 nm the
ε
showed slightly better performance. The linear
regression models showed that biospeckle activity descriptors had a higher correlation with
chlorophyll and carotenoids content than the a*/b* ratio and luminosity. The results for chroma were
comparable with the results for both biospeckle activity indicators. The biospeckle method showed
very good results in terms of maturation monitoring and the prediction of the maturity indices of
tomatoes, proving the possibility of practical implementation of this method for the determination of
the maturity stage of tomatoes.
Keywords:
biospeckle; optical sensor; video processing; tomato; maturation; shelf life; postharvest quality
1. Introduction
Tomato is a climacteric fruit, with a relatively short postharvest life determined by ethylene [
1
].
As for many other climacteric fruit and vegetables ripeness assessment of the agricultural crop ensures
optimal harvest time, which has a huge impact on the postharvest quality of the yield. Harvesting at
the full ripening stage results in poor transport and storage capabilities and unacceptable organoleptic
quality, while premature harvesting prevents the development of the characteristic flavor and aroma
of tomatoes.
During the ripening period, this fruit undergoes a number of physiological and biochemical
processes, which change its chemical composition and cellular structure [
2
]. The ripening process
Sensors 2018, 18, 1093; doi:10.3390/s18041093 www.mdpi.com/journal/sensors
