Postharvest Biology and Technology 20 2000 25 – 37
Logistic regression analysis of factors influencing core breakdown in ‘Conference’ pears
Jeroen Lammertyn
a,
, Marc Aerts
b
, Bert E. Verlinden
a
, Wendy Schotsmans
a
, Bart M. Nicolaı¨
a
a
Katholieke Uni6ersiteit Leu6en, Flanders Centre for Posthar6est Technology, W. de Croylaan
42
,
3001
He6erlee, Belgium
b
Limburgs Uni6ersitair Centrum, Center for Statistics, Uni6ersitaire Campus,
3590
Diepenbeek, Belgium Received 10 January 2000; accepted 2 May 2000
Abstract
Core breakdown of ‘Conference’ pears Pyrus communis L. is characterised by softening and browning of tissue near the core and is associated with the development of cavities. The disorder causes large economic losses of
‘Conference’ pears in Belgium, stored under controlled atmospheres. Factors that influence development of the disorder, CO
2
and O
2
concentration, the size and weight of the pear, the picking date and the storage temperature, were investigated. Multiple logistic regression was used to establish prediction and classification models for both
internal browning and cavity development. Over-mature fruit was more susceptible to core breakdown during storage. It was also found that pears with a large weight had a higher probability of developing brownheart. R
2
values from 0.7 to 0.92 were obtained between the predicted and measured percentages of brownheart and cavities. The models
classified up to 86 of the pears correctly. In a final analysis, the time sequence of the symptoms occurring during core breakdown disorder development was modelled with a generalized logits model. © 2000 Elsevier Science B.V. All
rights reserved.
Keywords
:
Carbon dioxide; Core breakdown; Logistic regression; Oxygen; Pear; Picking date www.elsevier.comlocatepostharvbio
1. Introduction
With a yearly production of over 500 000 tons, Pyrus communis L. cv. Conference is one of the
most important pear cultivars in Europe. In Bel- gium, ‘Conference’ pears usually are picked dur-
ing the first weeks of September and good postharvest storage conditions need to be applied
to maintain good fruit quality over a period of a year. Much research has been directed towards
the determination of the optimum controlled at- mosphere CA conditions to prevent postharvest
deterioration of ‘Bartlett’ pears Boersig et al., 1988; Kader, 1989; Wills et al., 1998 and ‘Confer-
ence’ pears Roelofs and de Jager, 1997. A re- duced O
2
concentration 1.5 – 2.5 and a slightly elevated CO
2
concentration 0.7 – 1 in combina-
Corresponding author. Tel.: + 32-16-322376; fax: + 32- 16-322955.
E-mail address
:
jeroen.lammertynagr.kuleuven.ac.be J. Lammertyn.
0925-521400 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 1 4 0 0 0 0 1 1 4 - 9
tion with a low temperature − 0.5 – 1°C reduces the biochemical changes associated with respira-
tory metabolism, physical injuries, and physiolog- ical and pathological breakdown Brady and
Romani, 1988; Kerbel et al., 1988; Chavez-Franco and Kader, 1993; Mathooko, 1996. However, an
elevated CO
2
concentration during postharvest storage can cause CO
2
-related injuries such as core breakdown, also called brownheart or
browning Kadam, 1995. This is a physiological disorder characterised by browning and softening
of tissue near the core. It is often coupled with the development of cavities. The time course of inter-
nal browning and appearance of cavities suggests that cavities arise from the brown areas Roelofs
and de Jager, 1997. These authors also found that over-mature ‘Conference’ pears are more sus-
ceptible to core breakdown during storage. A serious breakdown is often observed when the
pears are removed from CA conditions for selling. Late harvested ‘Bartlett’ pears also show an in-
crease in CO
2
in the tissue around the core, until the onset of core breakdown Kadam, 1995. Velt-
man et al. 1999 associated browning in ‘Confer- ence’ pears with the disappearance of ascorbic
acid. Larrigaudiere et al. 1998 and Lentheric et al. 1999 discussed the relation between harvest
date, ascorbic acid concentration and internal browning. The physiological and quality re-
sponses of ‘Bartlett’ pears to modified gas atmo- spheres were studied by Ke et al. 1990. Exposure
of the fruits to O
2
-reduced and CO
2
-enriched at- mospheres resulted in reduced respiration and
increased ethanol and acetaldehyde concentra- tions. Pears stored for a long time under high CO
2
levels showed CO
2
injury. However, the literature concerning the development of this disorder in
other European pear cultivars is scarce. In addi- tion to this, no literature on a statistical modelling
approach to predict core breakdown was found. However, such a predictive model can be valuable
in predicting the susceptibility of pears to core breakdown as affected by their intrinsic quality
attributes soluble solids content SSC, firmness, weight and storage conditions. Storage condi-
tions could then be fine-tuned for a particular fruit lot. A predictive model can also give insight
into the role of interaction between two or more storage parameters.
The specific objectives of this study were 1 to determine the effect of the storage gas composi-
tion, the storage temperature, the storage time, the picking date and quality parameters of ‘Con-
ference’ pears on the incidence of core breakdown as well as to determine the interaction effects
between the storage parameters; and 2 to de- velop a statistical model that can predict brown-
ing
incidence of
pears given
the quality
parameters and the storage conditions. In this way, postharvest storage simulations can be per-
formed. A storage scenario to obtain pears with brownheart, for further research, can be derived
from this statistical model.
2. Materials and methods
