ascorbic acid mapping to study core breakdown development in ‘conference’ pears

Ascorbic acid mapping to study core breakdown developmentin ‘Conference’ pears

Christine Franck a,*, Mieke Baetens a, Jeroen Lammertyn a, Nico Scheerlinck a,Mark W. Davey b, Bart M. Nicolaı a

a Flanders Centre/Laboratory of Postharvest Technology, Katholieke Universiteit Leuven, W. de Croylaan 42, B-3001 Leuven, Belgiumb Centre for Fruit Culture, Katholieke Universiteit Leuven, W. de Croylaan 42, 3001 Leuven, Belgium

Received 2 December 2002; accepted 14 May 2003

Abstract

Core breakdown is a physiological disorder, characterised by discolouration of the inner core tissue, that can develop

during storage of pears under certain controlled atmosphere (CA) conditions. Recent research suggested a relation

between this storage disorder and ascorbic acid concentrations. Postharvest changes of ascorbic acid concentrations

and spatial distribution have been investigated. Loss of ascorbic acid during delayed CA (cooling period of 3 weeks in

air before CA storage) was observed, but further losses during subsequent CA storage were minimal. Browning-

inducing CA storage conditions resulted in a more than 4-fold faster decrease in ascorbic acid concentration. A

threshold of 0.37 mg 100 g�1 FW ascorbic acid was determined below which the incidence of internal browning was

higher than 50%. Ascorbic acid maps show a strong asymmetrical distribution and illustrate that most brown tissue was

located in the contour line of 0.4 mg 100 g�1 FW, which supports the 0.37 mg 100 g�1 FW threshold value. The

occurrence of sound spots in the brown tissue zone corresponded with higher ascorbic acid concentrations, and could be

associated to the protective capability of ascorbic acid.

# 2003 Elsevier B.V. All rights reserved.

Keywords: Browning; Controlled atmosphere; Physiological disorder; HPLC; Fruit quality

1. Introduction

Pyrus communis L. cv. Conference is commer-

cially the most important pear cultivar in Europe

with a yearly production over 500 000 tons.

Following harvest during the first weeks of Sep-

tember, the pears are immediately cooled to �/

1 8C and kept in air for 3 weeks before being

stored under controlled atmosphere conditions

(delayed controlled atmosphere, DCA). However,

suboptimal storage conditions may result in the

development of core breakdown, a physiological

disorder that can occur during the storage of pears

under high CO2 conditions. It is characterised by a

brown circular zone surrounded by sound tissue.

In contrast to the general assumption that the

disorder starts in the core and expands concen-

* Corresponding author. Tel.: �/37-16-372-413; fax: �/37-16-

372-955.

E-mail address: [email protected] (C.

Franck).

Postharvest Biology and Technology 30 (2003) 133�/142

www.elsevier.com/locate/postharvbio

0925-5214/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.

doi:10.1016/S0925-5214(03)00108-X

mailto:[email protected]

trically to the cortex in a later phase (Espin et al.,2000; Zerbini et al., 2002), non-destructive imaging

techniques indicate that incipient browning is

already present after 2 months of storage and

that the browning pattern does not develop

spatially during storage, rather the intensity of

discolouration increases (Lammertyn et al.,

2003a). Cavities can be formed subsequently. It

is known that heavy and over-mature pears inparticular are more susceptible to core breakdown

(Lammertyn et al., 2000).

The origin of this disorder, which is considered a

CO2 related injury (Kadam et al., 1995), is still

unclear. A crucial step in the browning of fruit and

vegetables is the enzymatic oxidation of polyphe-

nol compounds by polyphenoloxidase (PPO)

(Mayer, 1987). This results in the production ofo-quinones, which are very reactive and form

brown coloured polymers (Mathew and Parpia,

1971). However, neither PPO activity nor the

concentration of polyphenol compounds are limit-

ing factors in the process of core breakdown

development (Larrigaudiere et al., 1998; Veltman

et al., 1999). Since PPO and its substrate are

located in different cell compartments, enzymaticbrowning can only occur after cellular decom-

partmentation caused by membrane disintegration

has occurred. The cause of core breakdown

may therefore be related to oxidative and

senescent-related processes (Larrigaudiere et al.,

1998).

Recent research links core breakdown develop-

ment to decreased ascorbic acid (AA) concentra-tions in the fruit (Lentheric et al., 1999; Veltman et

al., 1999). Ascorbic acid is abundantly present in

all plant cells and has many biological functions.

As an antioxidant, it protects plants directly and

indirectly against oxidative damage resulting from

aerobic metabolism, photosynthesis and environ-

mental pollution (Smirnoff, 1996). Pinto et al.

(2001) described a relationship between corebreakdown and ascorbic acid starting from the

fact that CA-conditions cause a change in the

buffering capacity of the tissue and impairment of

the mitochondrial function. Reduced equivalents

(e.g. NAD(P)H) accumulate, resulting in increased

production of reactive oxygen species (ROS). The

activities of antioxidative enzymes such as super-

oxide dismutase (SOD), ascorbate peroxidase

(APX) and glutathione reductase (GR) can in-

crease, and consequently, the consumption of

ascorbic acid increases. Imbalances between as-

corbic acid consumption and regeneration, and

increased non-enzymic removal of radicals by

ascorbic acid result in a lowered ascorbic acid

concentration. Moreover, insufficient ascorbic

acid causes APX inactivation (Asada, 1992),

hence, oxidative damage cannot be

prevented any more resulting in membrane lipid

peroxidation and subsequent decompartmenta-

tion.A hypothesis has been developed (Veltman et

al., 1999; Zerbini et al., 2002), which states that the

higher the ascorbic acid concentration is, the less

susceptible a pear is to this storage disorder, and

that pears will be affected when ascorbic acid

drops below a certain value (ascorbic acid thresh-

old hypothesis). Following this hypothesis, a

threshold value of 1.3 mg 100 g�1 FW, defined

as the ascorbic acid concentration of cortex tissue

at which the brown index exceeded 0.35 was found

(Veltman et al., 1999). Zerbini et al. (2002)

determined a critical ascorbic acid concentration

of 0.2 mg 100 g�1 FW based on analysis of core

tissue of sound pears. The ascorbic acid threshold

value was in this study defined as the concentra-

tion at which the first appearance of browning was

noticed and appeared to be 5% of the concentra-

tion at harvest.Although the literature stresses the importance

of ascorbic acid in the development of core

breakdown in pears, the variability of proposed

threshold values is high and no correspondance

between brown tissue and local ascorbic acid

concentrations have been reported. Therefore, we

investigated first the ascorbic acid changes in pears

stored under optimal and browning-inducing CA

conditions. Secondly, we derived a ascorbic acid

threshold value and tested the ascorbic acid

threshold hypothesis. Finally, ascorbic acid maps

were constructed to study the spatial distribution

of ascorbic acid in pear slices and this

was compared with the distribution of brown

tissue.

C. Franck et al. / Postharvest Biology and Technology 30 (2003) 133�/142134

2. Materials and methods

2.1. Fruit material

Pears (Pyrus communis L. cv. Conference) were

picked at the optimal maturity for commercial CA

storage (10 September 2001) in the orchard of the

Fruit Culture Centre (K.U. Leuven) in Rillaar

(Belgium). After a cooling period of 3 weeks in airat �/1 8C (delayed CA, DCA), pears were stored

at conditions comparable to commercial storage

(2.5% O2, 0.7% CO2, �/1 8C).

To induce the development of core breakdown,

pears were picked 16 days later (26 September

2001) in a commercial orchard in Meensel (Bel-

gium) and stored at browning-inducing CA con-

ditions (1% O2, 10% CO2, �/1 8C) without DCA.

2.2. Ascorbic acid changes in function of storage

time

To compare the decrease in ascorbic acid

concentration after harvest in pears stored in

commercial (with DCA) and browning-inducing

(without DCA) CA conditions (see Section 2.1),

ten pears were sampled respectively 3, 9, 11, 13 and20 weeks after harvest for the optimally stored

pears and 4, 8 and 12 weeks after harvest for the

browning-induced ones. For the optimally stored

pears, the sampling at 3 weeks was at the end of

the cooling period in air, just before CA storage

started. Pear slices (0.7 cm thick) were cut perpen-

dicular to the longitudinal axis 5 cm from the calyx

end of a pear and immediately frozen in liquidnitrogen. The frozen and weighed pear slices (9/18

g, varying with pear size) were ground with 20 ml

extraction buffer consisting of 3% metaphosphoric

acid and 1 mM EDTA (Davey et al., 1997). The

extract was centrifuged, filtered and stored on ice

until analysis (see Section 2.5).

It is assumed that the decrease in ascorbic acid

concentration (d[AA ]/dt) is proportional to theactual ascorbic acid concentration (/[AA]) (Eq. (1)).

Eq. (2) is the solution of equation 1 and was used

to describe the ascorbic acid evolution as a

function of storage time (exponential-decay

model). An optimisation routine was written in

Matlab version 6 (The MathWorks Inc., Natick,

MA) for estimation of the parameter k by fittingthe model to the experimentally obtained ascorbic

acid concentration profile. The estimation proce-

dure was accomplished using a gradient-search-

based least square method (Lawson and Hanson,

1976).

d[AA]

dt��k [AA] (1)

[AA]� [AA]0 exp(�kt) (2)

with [AA ], ascorbic acid concentration (mg 100

g�1 FW), [AA ]0, ascorbic acid concentration at

harvest (mg 100 g�1 FW), k , rate constant (1/week), t , time (weeks).

2.3. Determination of the ascorbic acid threshold

value

To investigate the relationship between the

occurrence of browning and the present ascorbic

acid concentration, 40 pears, all stored immedi-

ately after harvest in 1% O2 and 10% CO2 at �/

1 8C, were analysed 13 weeks after storage and

categorised in two groups: sound and disordered

pears. From the disordered pears, the brown zone(inner cortex�/core) was cut out and analysed

separately from the remaining sound border (outer

cortex�/peel). Similarly, from the sound pears, an

approximately 1 cm thick border (outer cortex�/

peel) was cut from the slice and analysed sepa-

rately from the remaining part of the slice (inner

cortex�/core). Extraction was carried out as de-

scribed in Section 2.2. A logistic regression modelwas used to predict the probability of browning

given the ascorbic acid concentration ([AA ]). This

approach is based on the construction of a

statistical model describing the relationship be-

tween the observed response and the explanatory

variable, also called independent variables (Hos-

mer and Lemeshow, 1989; Collett, 1991). The

dependence of the occurrence of browning on theascorbic acid concentration is modelled as in Eq.

(3). The SAS/STAT software package, version 8.2

(SAS Institute, Cary, NC) was used to estimate the

regression parameters, a and b . The graphical

representation of the model was based on Eq. (4)

where the probability on browning, p , was plotted

C. Franck et al. / Postharvest Biology and Technology 30 (2003) 133�/142 135

as a function of the ascorbic acid concentration.

logit(p)� log

�p

1 � p

��a�b [AA] (3)

p�exp(a� b [AA])

1 � exp(a� b [AA])(4)

2.4. Ascorbic acid mapping

To construct ascorbic acid maps, analyses werecarried out on pears of the late harvest after 11�/12

weeks storage at browning-inducing conditions.

Twelve pear slices of 7 mm thickness, were cut

perpendicular to the longitudinal axis at 5 cm from

the bottom of the pear. Pictures of the 12 slices

were taken with a digital camera. Subsequently,

the slices were divided into cubes of 0.7 cm3

according to a regular grid. Each cube was quicklytransferred to a numbered tube and submerged in

liquid nitrogen. After weighing the tubes, 3 ml

extraction buffer was added and the tissue (9/0.75

g) was homogenised using mortar and pestle. On

average, 25 cubes were prepared from one pear

slice. Ascorbic acid maps were constructed using

MATLAB 6 (The Mathworks, Natick, MA). The

ascorbic acid concentrations in the slices werevisualised by means of a colour map with resolu-

tions of 0.5 mg and 0.2 mg 100 g�1 FW.

2.5. HPLC analysis

Immediately after extraction, HPLC analyses

were carried out on a HP 1100 system (Hewlett

Packard, Agilent Technologies, Palo Alto, USA)

using a Lichrospher RP18 (non-endcapped) col-

umn (150 mm�/4.6 mm ID, 3 mm particle

diameter) (Alltech, Lokeren, Belgium). The mobilephase (0.5% MeOH, 1 mM KCl and 400 ml l�1

phosphoric acid) was, after being filtered and

degassed, flushed through the column at a con-

stant rate of 0.8 ml min�1. The column tempera-

ture was kept at 25 8C and ascorbic acid was

detected with a diode array detector at 242 nm.

3. Results

3.1. Ascorbic acid changes in optimally stored and

browning-induced pears

A clear difference in the rate of ascorbic acid

loss between sound and disordered pears was

noticed. Fig. 1 shows the fitted exponential-decay

curves according to Eq. (2), which describes the

change in ascorbic acid concentration as a func-

tion of the time after harvest under the two storage

conditions. The parameter estimates for k are

given in Table 1. Under browning-inducing con-

ditions, the exponential-decay parameter k is more

than four times higher than under optimal storage

conditions. This difference can be explained by

following factors: picking date (optimal/late),

DCA (yes/no) and CA conditions, in particular

the CO2 concentration (low/high).

During the cooling period of 3 weeks in air, the

optimally stored pears lost 30% of the initial

ascorbic acid concentration. Comparison of the

AA decay rate at week 1 and 11 (Table 1) makes

clear that most losses occur immediately after

harvest while further losses during subsequent

CA-storage occur more slowly. This result corre-

sponds with earlier observations (Veltman et al.,

2000; Larrigaudiere et al., 2001). No pears with

disorders were found in optimal storage condi-

tions, while the first brown pears were seen after 2

months of storage at 1% O2, 10% CO2 and �/1 8Ccorresponding with an average ascorbic acid con-

centration of 1 mg 100 g�1 FW. This value is

based on the analysis of entire slices.

In this experiment, a rapid decline during the

first 3 weeks after harvest and a slower decline

during CA storage was observed. It is likely that

loss of ascorbic acid concentration is a natural

phenomenon related to fruit ripening. Selvarajah

et al. (2001) discovered that application of 1-MCP,

an ethylene antagonist, reduced the rate of ascor-

bic acid decline. This finding supports the idea that

ascorbic acid decline is ripening-related and that

ascorbic acid metabolism might be under control

of ethylene.


3.2. Ascorbic acid threshold hypothesis

To investigate the ascorbic acid threshold hy-

pothesis, the central and border tissue from 20

sound and 20 disordered pears, stored under

browning-inducing conditions, were analysed se-

parately. Whether the pear was disordered or not,

similar ascorbic acid concentrations were mea-

sured in the border tissue (data not shown),

whereas the ascorbic acid concentration in the

central tissue was significantly lower in the dis-

ordered pears. A logistic regression model (Eq. (3))

was used to predict the probability that browning

occurs with the ascorbic acid concentration in the

Fig. 1. Comparison of the change in ascorbic acid concentration under optimal (k) and browning-inducing (m) conditions. For the

optimally stored pears, the second measuring point is taken after the cooling period (delayed CA), just before CA (2.5% O2, 0.7% CO2,

�/1 8C) storage starts; the browning-induced pears are stored immediately under CA (1% O2, 10% CO2, �/1 8C) conditions. Each

measurement is the mean of ten pear slices. Error bars indicate 95% confidence intervals around the means.

Table 1

Exponential-decay curve characteristics for AA changes in function of storage time

k (1/week) Decay rate at week 1 ([AA ]/week) Decay rate at week 11 ([AA ]/week)

Optimala 0.0429/0.008 �/0.201 �/0.132

BIb 0.1969/0.026 �/0.945 �/0.129

a Optimal storage: 3 weeks cooling in air, followed by CA storage (2.5% O2, 0.7% CO2, �/1 8C).b BI: browning-inducing storage: no DCA, CA storage (1% O2, 10% CO2, �/1 8C).


border as an independent variable. The estimated

model parameters were a�/ 6.68 and b�/�/17.96

(both parameters were significant at the 5% level

with standard errors respectively 2.54 and 6.05).

The high and negative estimate for the regression

parameter, b , indicates that a small decrease in

ascorbic acid concentration results in a strong

increase in the probability that browning will

occur. The model (Fig. 2) illustrates that the

concentration at which there is 50% probability

that core breakdown develops was 0.37 mg 100

g�1 FW. This threshold value lies between 0.2 and

1.3 mg 100 g�1 FW as measured by Veltman et al.

(1999) and Zerbini et al. (2002), respectively.

Comparing threshold values from the literature is

difficult and must be done carefully. Like other

biochemical components, the ascorbic acid con-

centration in fruit strongly depends on growth

conditions such as light intensity and temperature

(Nagy, 1980; Klein and Perry, 1982). Moreover,

the methodology used to determine the threshold

value, the intrinsic pear characteristics, the age of

the pears at analysis time and the definition for

this value may differ considerably.

Fig. 2. Relation between the occurrence of core breakdown and the ascorbic acid concentration in the central tissue (k: data, */:

model).

Fig. 3. Asymmetrical distribution of ascorbic acid (mg 100 g�1 FW). Ascorbic acid map (A and B) with corresponding pear slice

picture below (C and D).

Fig. 4. Pictures of a brown pear slices overlaid by the corresponding ascorbic acid contour plots (values on the contour lines indicate

the ascorbic acid concentration in mg 100 g�1 FW).


Fig. 2 shows that, after 13 weeks of storage, theascorbic acid concentration in the centre of sound

pears is always higher than 0.4 mg 100 g�1 FW

and that the brown tissue has ascorbic acid

concentrations ranging from 0 to 0.4 mg 100 g�1

FW. If brown tissue is supposed to be ‘dead’,

ascorbic acid is expected to be completely broken

down. The fact that a measurable amount of

ascorbic acid in brown tissue was found in thisstudy can be explained by the presence of a fair

amount of healthy cells within the brown tissue at

the moment of sampling, and hence, the ascorbic

acid concentration was not (yet) zero.

3.3. Ascorbic acid mapping

In pears affected by core breakdown, the brown

inner tissue is always surrounded by a border ofsound tissue (Fig. 4). Peel and cortex tissue just

beneath the peel are almost never affected by

browning and since it is known that the highest

ascorbic acid concentrations can be found in these

tissue types, a relationship between ascorbic acid

and browning seems plausible. Ascorbic acid maps

were constructed to test this hypothesis. Fig. 3

shows ascorbic acid maps (Fig. 3A and B) with thecorresponding pictures of the analysed pear slice

(Fig. 3C resp. D). In general, the concentrations of

all the analysed cubes varied between almost 0 and

4 mg 100 g�1 FW, with occasionally higher values

reaching 8.58 mg 100 g�1 FW (Fig. 4A). From the

analysis of the ascorbic acid maps, it was found

that the ascorbic acid concentration is asymme-

trically distributed within a pear slice. This asym-metrical distribution, which was very pronounced

in all pears analysed, might be due to the position

of the pear on the tree with regard to the sun. The

large spatial differences in ascorbic acid concen-

trations makes sampling very critical and increases

the variability of measurements since concentra-

tion differences up to 4 times between sun and

shadow side were registered.Ascorbic acid mapping experiments illustrated

that sound and disordered pears can have similar

maps (compare Fig. 3A and B). All pears had

more or less the same average ascorbic acid

concentration after 11 weeks of storage whether

they were disordered or not. If ascorbic acid is a

limiting factor in the development of browning, aradial ascorbic acid pattern would be expected. In

reality, it appeared that only one half (the sun side)

of the border tissue has a pronounced higher

ascorbic acid concentration. Hence, the reason

why there is always a sound border surrounding

the brown zone had, at first sight, nothing to do

with ascorbic acid concentrations alone. However,

looking in detail to the maps by reducing theresolution to 0.2 mg 100 g�1 FW (more colour

levels) instead of 0.5 mg 100 g�1 FW as was done

in Fig. 4(B and D), a more detailed view on the

ascorbic acid distribution emerged. In general, a

good correspondence between the brown pattern

and the ascorbic acid contours was observed. The

brown tissue is located more or less in between the

contour lines of 0.2 and 0.4 mg 100 g�1 FW,which gives evidence for the estimated threshold

value of 0.37 mg 100 g�1 FW.

Pears with a low ascorbic acid concentration are

probably more susceptible to internal browning.

However, this does not imply that ascorbic acid is

the only factor important in the development of

core breakdown. The fact that later harvested

pears lose ascorbic acid more rapidly than theearly picked ones (data not shown) suggests that

the harvest time has an important impact on the

biochemical status of the fruit cells. Besides the

ascorbic acid distribution, also gas gradients

(Lammertyn et al., 2003b), influencing the cellular

energy levels, and differences in tissue character-

istics between outer cortex and cortex can explain

the typical radial browning pattern. Outer cortextissue differs from the cortex by younger cells, the

presence of more scleroids (Bain, 1961), a higher

cell density and smaller but rounder cells (Schots-

mans, 2003). Even though the ascorbic acid

concentration is probably not the only important

factor in the origin of brown, it probably provides

protection against tissue browning. The white spot

within the brown zone (see arrow in Fig. 4A)corresponds with an extremely high ascorbic acid

concentration of 8.58 mg 100 g�1 FW. The

occurrence of these spots and the heterogeneous

and asymmetrical distribution of the ascorbic acid

concentration raise questions on the site of ascor-

bic acid biosynthesis. It is still unknown where the

site of biosyntheses is located (in leaves or in fruit


tissue) and how the eventual translocation isregulated. It has been shown that ascorbic acid

concentrations can increase during storage at low

CO2 conditions (Larrigaudiere et al., 2001),

although this is not a proof for de novo synthesis.

4. Conclusion

Changes in ascorbic acid concentration during

storage and its distribution were investigated for

pear fruit. The highest rate of ascorbic acid decline

was found during the DCA of 3 weeks directly

after harvest while further losses during CA

storage occur slower. The rate of decline of

ascorbic acid was more than 4-fold faster under

browning-inducing conditions than under opti-mally postharvest conditions. The ascorbic acid

concentration in pears is asymmetrical indicating

that the sampling position is quite crucial and that

analysing tissue cut randomly can give misleading

results. It was found that all the brown tissue lay in

between the contour line of 0.4 mg 100 g�1 FW,

which corresponded very well with the threshold

value of 0.37 mg 100 g�1 FW, derived from alogistic regression analysis of the ascorbic acid

concentration of the inner core of 20 sound and 20

disordered pears.

Rather than supporting the ascorbic acid thresh-

old hypothesis, which is not well-defined due to

differences in methodology, age of pears at analy-

sis time and pear characteristics, we prefer to

assign a strong protection capability to ascorbicacid, proven by the correspondence between white

spots in brown tissue and locally high ascorbic

acid concentrations. Since all analyses were un-

avoidably done post-factum, no direct causal

relationship can be deduced and, hence, it is not

clear whether a low ascorbic acid concentration in

brown tissue is the cause or the consequence of

browning. The importance of ascorbic acid withrespect to core breakdown may not be over-

estimated since it is not the only plant compound

with strong antioxidative effects, however, max-

imal maintenance of ascorbic acid during post-

harvest storage is highly recommended, being

favourable for both growers and consumers.

Acknowledgements

The research was financially supported by the

Ministery of SME and Agriculture (project S-

5901) and the Research Council of the K.U.

Leuven (project IDO 00/008). Christine Franck is

doctoral fellow of the Institute for the Promotion

of Innovation by Science and Technology in

Flanders (IWT); Jeroen Lammertyn and NicoScheerlinck are postdoctoral fellows of the Fund

for Scientific Research-Flanders (FWO-Vlaande-

ren).

References

Asada, K., 1992. Ascorbate peroxidase-hydrogen peroxide-

scavenging enzyme in plants. Physiol. Plant. 85, 235�/241.

Bain, J.M., 1961. Some morphological, anatomical and phy-

siological changes in the pear fruit (Pyrus communis var.

Williams Bon Chretien) during development and following

harvest. Austr. J. Bot. 9, 99�/123.

Collett, D.R. (Ed.), 1991. Modelling Binary Data. Chapman

and Hall, London.

Davey, M.W., Bauw, G., Van Montagu, M., 1997. Simulta-

neous high-performance capillary electrophoresis analysis of

the reduced and oxidised forms of ascorbate and glu-

tathione. J. Chromatogr. B 697, 269�/276.

Espin, J.C., Veltman, R.H., Wichers, H.J., 2000. The oxidation

of L-ascorbic acid catalysed by pear tyrosinase. Physiol.

Plant. 109, 1�/6.

Hosmer, D.W., Lemeshow, S. (Eds.), 1989. Applied Logistic

Regression. Wiley, New York.

Kadam, S.S., Dhumal, A., Shinde, N.N., 1995. Pear. In:

Salunkhe, D.K., Kadam, S.S. (Eds.), Handbook of Fruit

Science and Technology. Marcel Dekker, New York, pp.

183�/202.

Klein, B.P., Perry, A.K., 1982. Ascorbic acid and vitamin A

activity in selected vegetables from different geographical

areas of the United States. J. Food Sci. 47, 941�/945.

Lammertyn, J., Aerts, M., Verlinden, B.E., Schotsmans, W.,

Nicolaı, B.M., 2000. Logistic regression analysis of factors

influencing core breakdown in ‘Conference’ pears. Post-

harvest Biol. Technol. 20, 25�/37.

Lammertyn, J., Dresselaers, T., Van Hecke, P., Jancsok, P.,

Wevers, M., Nicolaı, B.M., 2003a. Analysis of the time

course of core breakdown in ‘Conference’ pears by means of

MRI and Xray CT. Postharvest Biol. Tech. 29, 19�/28.

Lammertyn, J., Scheerlinck, N., Jancsok, P., Verlinden, B.E.,

Nicolaı, B.M. 2003b. A respiration-diffusion model for

‘Conference’ pears II: simulations and relation to core

breakdown. Postharvest Biol. Technol. (in press).

Larrigaudiere, C., Lentheric, I., Vendrell, M., 1998. Relation-

ship between enzymatic browning and internal disorders in


controlled-atmosphere stored pears. J. Sci. Food Agric. 78,

232�/236.

Larrigaudiere, C., Pinto, E., Lentheric, I., Vendrell, M., 2001.

Involvement of oxidative processes in the development of

core browning in controlled-atmosphere stored pears. J.

Hort. Sci. Biotechnol. 76, 157�/162.

Lawson, C.L., Hanson, R.J. (Eds.), 1976. Solving Least Squares

Problems, Prentice-Hall, Old Tappan, NJ, USA.

Lentheric, I., Pinto, E., Vendrell, M., Larrigaudiere, C., 1999.

Harvest date affects the antioxidative systems in pear fruits.

J. Hort. Sci. Biotechnol. 74, 791�/795.

Mathew, A.G., Parpia, H.A.B., 1971. Food browning as a

polyphenol reaction. Food Res. 19, 75�/145.

Mayer, A.M., 1987. Polyphenoloxidases in plants*/recent

progress. Phytochemistry 26, 11�/20.

Nagy, S., 1980. Ascorbic acid concentrations of citrus fruit and

their products: a review. J. Agric. Food Chem. 28, 8�/18.

Pinto, E., Lentheric, I., Vendrell, M., Larrigaudiere, C., 2001.

Role of fermentative and antioxidant metabolisms in the

induction of core browning in controlled-atmosphere stored

pears. J. Sci. Food Agric. 81, 364�/370.

Schotsmans, W. 2003. Gas diffusion properties of pome fruit in

relation to storage potential. PhD dissertation, Katholieke

Universiteit Leuven, Belgium.

Selvarajah, S., Bauchot, A.D., John, P., 2001. Internal brown-

ing in cold-storage pineapples is suppressed by a postharvest

application of 1-methylcyclopropene. Postharvest Biol.

Technol. 23, 167�/170.

Smirnoff, N., 1996. The function and metabolism of ascorbic

acid in plants. Ann. Bot. 78, 661�/669.

Veltman, R.H., Sanders, M.G., Persijn, S.T., Peppelenbos,

H.W., Oosterhaven, J., 1999. Decreased ascorbic acid

concentrations and core breakdown development in pears

(Pyrus communis cv. communis). Physiol. Plant. 107, 39�/45.

Veltman, R.H., Kho, R.M., van Schaik, A.C.R., Sanders,

M.G., Oosterhaven, J., 2000. Ascorbic acid and tissue

browning in pears (Pyrus communis L. cvs Rocha and

Conference) under controlled atmosphere conditions. Post-

harvest Biol. Technol. 19, 129�/137.

Zerbini, P.E., Rizzolo, A., Brambilla, A., Grassi, M., 2002.

Loss of ascorbic acid during storage of Conference pears in

relation to the appearance of brown heart. J. Sci. Food

Agric. 82, 1�/7.


ascorbic acid mapping to study core breakdown development in ‘conference’ pears

Documents