Ethylene removal for long term conservation of fruits and vegetables

Food Quali$ and preference4 (1993) 119-126

ION ETHYLENEREMOVALFORLONGTERMCONSERVAT OFFRUITSANDVEGETABLES Altaf El Blidi, Luc Rigal, Guy Malmary, Jacques Molinier & Liberto Torres* Ecole Nationale Superieure de Chimie, 118, Route de Narbonne-31077

Toulouse Cedex-France

(Received 30 November 1992; accepted 15 Jz4y 1993)

(Sherman,

ABSTRACT

1989). synthesis

A study of ethylene removal from

the atmosphere offruit

storage rooms by catalytic oxidation was carried out. The ef$ciency of three catalysts was compared in a laboratory

1985;

Even

have been

at a low temperature enriched

However,

large volume (1800 m’) storage roomJilted with Golden Delicious apples (282 t). The conserved apples in the treated store were similar to the p-e-storage samples for

duction.

this requires

which

stimulates

vation.

age

ethylene

which

The

INTRODUCTION

atmosphere

first

one,

displaying

permanganate

storage

rooms

evolve towards senescence ant qualitative

and are subjected

and quantitive

losses

gradually

Many studies

have shown

phytohormone,

factor for rapid evolution

of post-harvest

etables

towards senescence

Dilley,

1982;

1987)

especially

Sfakiotakis

Pech

the quality

the

reorientated

is a

1986;

research

utilised

chemisorption to small

permanganate several times

(Liu and Samelson,

1986;

(200-250°C) copper

catalytic oxidation with expensive

or a copper/zinc

seems to be more

with potassium

mix-

economical

permanganate

catathan

(Blanpied

adapted

to ethylene

removal from large volume rooms. We have chosen oxidant

functioning

and adapted

of biochemical

to this hormone

season

et al., 19856) and is particularly

1974;

(Bufler,

ones

chemisorption

inductive Pratt,

ethylene

is solely adapted

since potassium

lysts based on platinum, ture. This process

et al,

field towards control

* To whom correspondence ____

con-

Lougheed

The incidence linked

which

been

on a commercial

one relies on ethylene

at high temperatures

fruits and veg-

1973;

1983;

climacteric

processes

of fruit

etable conservation

(Sacher,

and Latche,

et al., 1989).

and physiological

that ethylene, is an essential

Many

for stor-

et al., 1985a,6; Lidster et al., 1985).

The second

transport

and sale. The losses are essentially due to fungic tamination and physiological damage. maturation

Blanpied

to import-

during

have

and must be renewed

during a conservation flowers

conser-

continuous

techniques

two have met success

is rapidly consumed and

is

term

scale.

volume

vegetables

of

and colour

long

removal

pro-

properties

to avoid these draw-backs,

in a controlled

by potassium

fruits,

ethylene

acidity

reducing

which

by stored

removal from storage rooms is required.

complementary among

autocatalytic

firmness,

thereby

In order

ethylene

(Mar-

rooms

released

of the organoleptic

namely

thus accelerated

airtight

of ethylene

Degradation

the products,

in 0,

1989; Van Schik and Boerrigler,

to accumulation

products,

et

is now to

a controlled

in CO, and depleted

1986; Fontanel,

1989).

Stow,

used for some time (Lieberman under

fruits

lead

Post-harvest

1987;

of ethylene

keep

and ethylene concentration. A commercial prototype, devised from optimal operating conditions was tested in a

Keywords: Climacteric vegetable conservation, quality testing, industrial prototype for ethylene removal, isoresponse curves, chemometn‘cs.

Herner,

inhibitors

the trend

cellin,

a number of instrumentally measured quality characteristics.

1986;

chemical

al., 1974; Sister and Yang, 1984), atmosphere

pilot reactor with experimental designs fm temperature

Blanpied,

though

rooms.

on

in the vegof its emission

this second

to atmosphere

Optimal

technique

at low temperature

functioning

treatment

in a laboratory

ferent

designs

experimental

of large volume

conditions

lysts were compared

(Box

for ethylene (lOO-130°C) for three

pilot reactor

cataof dif-

et al, 1978; Coupy,

1988; Mathieu and Phan Tan Luu, 1988). The interest of the method of experimental

design,

employed in this study, is to provide a simple representation of the observed phenomenon in the form

should be addressed.

0 1994 Elsevier Science Publishers Ltd

of

0950-3293/94/$06.00

studied 119

polynomial

expression

and the variables

combining considered.

the

responses

The choice

of an

120

Altaf El Blidi et al. N2

C2H4

AIR

14 d--13

I__<‘___________J

4’

.

6

FIG. 1. General experimental system for ethylene removal and control: 1, two-way valve; 2, flow rate regulator; 3, pressure regulator; 4, first air heating; 5, manometers; 6, teflon PTFE coiled tube; 7, three-way valve; 8, standard circuit; 9, catalysis circuit; 10, safety valve; 11, catalyst regeneration circuit; 12, thermometer; 13, heated air ethylene mixture; 14, valve; 15, flow meters; 16, gas outlet; 17, gas chromatograph.

appropriate design matrix allows us to calculate the coefficients of this model with the best precision for a limited number of experiments. The isoresponse plots obtained from the model enable us to establish a topography of the response as a function of these factors. These data also allowed us to calculate and devise an industrial prototype which was tested. The study of the influence of an atmosphere treatment in a storage room on the subsequent quality of apples was then carried out.

MATERIALS

AND

METHODS

Laboratory experimental prototype Figure 1 represents a system composed of three basic elements: a generator of air ethylene standard gaseous mixtures, an experimental system based on previous research (Namiesnik et al, 1985) and functioning on the gaseous permeation principle (Fourcras and Rodet, 1977), an ethylene reactor heated by a heat-transfer liquid, a gas chromatograph Hewlett-Parkard 5700 A model, equipped with a FID detector and a Porapak N column (SO-80 mesh, 5 m X ‘/8in). The chromatograph analyses ethylene coming either from the generator of standard gaseous mixtures or from unoxidised ethylene from the catalytic reactor. Sample injection was carried out using a six-way valve which can be connected to the generator circuit at the end of the reactor. Prior to any experiment, this system allowed the catalyst to be conditioned by heating for 24 h at 16O’C under a nitrogen flow rate of 60 cm3 min-') . It also generated stable ethylene concentration mixtures and passed them over the heated catalyst to remove ethylene.

The study carried out concerned evaluation of the efficiency of three catalysts: P, F and S. The catalysts denoted P and F are two different forms of ‘hopkalite’ supplied by Jnowroccawskie (Poland) and Prolabo (France). They are in the form of dark grey particles whose granulometry ranges between l-5 and 3.5 mm. Catalyst P is essentially a mixture of metallic oxides (MnO, t CuO, = 82-87%). The catalyst F also consists of a mixture of oxides (MnO, t CuO, Cu,O = 60-62%) and a substantial amount of manganese carbonate (MnCO, = 29-31%). Both catalysts contain a comparably minor organic fraction, as well as traces of promoters (S, K, Ca) more abundant in P than in F and responsible for an enhancement of catalytic activity. Catalyst S is made of small heterogeneous spherical grains having a granulometry of the order of 3 mm. It results from the impregnation of refractory oxide grains by a diluted solution of chloroplatinic acid. After drying, the grains thus obtained are activated by impregnation with a fatty acid at moderate temperature. S is used in a commercialised reactor under the trade name ‘Swingtherm’ (Wojciechowski and Haber, 1982) and functions as a high temperature (200°C) catalysis.

Industrial prototype Figure 2 represents the industrial prototype devised from the laboratory model data. The principal elements are: an ethylene removal reactor heated by immersed fingers, a heat exchanger, a dust filter and an active charcoal filter to purify air which regenerates the catalyst. Prior to the prototype connection to the storage room filled with fruits, the catalyst was regenerated at 160°C for 24 h with a flow of filtered air which was

Long Term Conservation of Fruit and Vegetabkz

12 1

10

1

4

2

FIG. 2. Schematic Representation of the industrial ethylene removal prototype: 1, storage room; 2, plate heat exchanger; 3, surpressor; 4, valve; 5, manometer; 6, rotameter; 7, by-pass; 8, active charcoal filter; 9, filter; 10, ethylene removal reactor.

purified on active charcoal. This step was carried out on the day of closing the room. The temperature was lowered from 160°C to catalysis temperature (lOO120°C) and the prototype connected and put into the catalysis mode of operation.

RESULTS

AND

For each of these catalysts, an experimental composite matrix (Deming and Morgan, 1987, Massart et aZ., 1988) (Table 2) allowed calculation of the b, coefficients of a second-degree polynomial model linking the X, coded variables with ethylene removal efficiency: E= 6, + &XT t b,X,, t b,A?,

DISCUSSION

t b,,F,

t bT<:XTXC

with

Laboratory pre-pilot optimisation Comparison of the three types of catalyst (P, F, S) was carried out in a laboratory pre-pilot system (Fig. 1). The two factors outlined were: U,: catalysis temperature, U,:: initial ethylene concentration. The experimental domain chosen is represented in Table 1. The catalyst mass and the flow rate of the air/ethylene mixture were respectively fixed at 500 g and O-3 m” h-’ (Conte et al., 1992). The studied response was the ethylene removal efficiency after 72 h of non-stop functioning: E= lOO(C,C, = ethylene concentration reactor, C, = ethylene concentration reactor. TABLE 1. Experimental of the three Catalysts

Factor temperature (“C) U,: initial ethylene concentration (ppm) U,:

C,)/C, at the entry of the catalyst at the end of the catalyst

x.= h-7 X = Q-100 and (. T 6 30 Close to the centre of interest (here U, = 100°C, U,: = 7 ppm), a second degree polynomial is often, as a first approximation, a satisfactory empirical representation of the real mathematical function relating the response to the variables investigated. The 4 coefficients are unknown and represent the contribution to the efficiency of ethylene elimination of the variations within the interval [-1, tl] of the variables XT and &., of their square X2.r and Xc and of their product XT&:, of their interaction. b, represents the efficiency of ethylene elimination at the centre of the domain (X, = 0; Xc = 0). This particular choice of experimental matrix allows these six coefficients to be estimated with an excellent precision for a number of experiments limited TABLE 2. Experimental Composite Matrix Experiment

Domain for Efficiency Comparison

x,= (U,-

100)/30

-1 1 -1

Domain center

Variation step

uoi

vi

100 7

30 6

1 -1 1 0 0 0

Xc= (Uc-7)/6 -1 -1 1 1 0 0 -1 1 0

122

Altaf El Blidi et al.

TABLE 3. Operating Catalyst P Test

Conditions

Temperature

Concentration

(“C)

TABLE 4. Operating Catalyst F Test

Conditions

TABLE 5. Operating Catalyst S

Conditions

Obtained

Concentration

E72,,

1.23 1.13 13.57 12.98 7.50 8.04 1.16 13.48 7.71

to nine. The distribution

ensures

1982)

Tempkature

values

of

4

with the results

(Phan

with

@)

descriptive

model. Tan

obtained

the catalysts P (Table 3), F (Table lead to the following models:

Luu

of

4) and S (Table

5)

FIG. 4. Efficiency isoresponse curves after 72 h of catalysis for catalyst F (catalyst mass, 500 g; air flow rate, O-9 m3 h-l).

The isoresponse curves from these models sented by Figs. 3,4 and 5 and showed that: -the

1.2X,+

17.3X2,+

0.5X’,--0.6X,X,

for the catalyst F:

E=85

Tempkature (“C)

and

for each

for the catalyst P:

E= 32.3 +49.3X,-

(“C)

FIG. 3. Efficiency isoresponse curves after 72 h of catalysis for catalyst P (catalyst mass, 500 g; air flow rate, 0.9 ms h-l).

points defined

a good

quality for the polynomial

calculated

i 5

1

35 58 9 91 30 95 62 90 86

of experimental

line of the matrix

The

I

(PPm)

70.60 130.20 70.00 130.20 70.40 130.10 100.40 100.70 100.50

Mathieu,

I

21 100 9 100 7 100 63 70 100

and Results

W)

and predictive

with

E72,,(%)

1.08 0.87 12.15 12.64 7.15 6.50 1.04 13.06 6.65

Temperature

by each

and Results Obtained

(PPN

70.28 129.70 70.60 129.80 70.00 130.00 101.80 99.90 98.80

19 21 25 27 22 24 20 28 23

i

0 100 2 100 0 100 38 30 32

Concentration

m

Test

E74,,(%)

1.06 1.04 12.58 13.15 X.32 7.07 1.24 13.40 7.50

Temperature

10 12 16 18 13 15 11 17 14

2 05

with

(wm)

70.4 130.2 70.25 130.50 70.40 130.30 100.40 100.70 100.50

1 3 7 9 4 6 2 8 5

and Results Obtained

t 44*6X,-- 1~5~,:-22~7X2,-10~9X’,,t4~2XTXc

for the catalyst S: E=86.8+28.1X,t7.2&-26.2X2,-11.6X”,+

12.8X,&

influence

case of catalyst

of ethylene

are repre-

concentration

P, is negligible

compared

in the to the

temperature effect (Fig. 3). This is particularly important for a complete removal of ethylene produced in cold fruit storage rooms. catalyst requires in these conditions to obtain a 100% ethylene

However, this at least 130°C

degradation

efficiency.

Long Term Ccmsmation

of Fruit and Vegetables

123

harvest time and during post-harvest conservation in storage rooms with and without ethylene removal were carried out. The analysis used, described in full by Afnor (1981)) consists of: -evaluation of total sugars by measuring the refractive index, -titration of malic acid (g litre-‘) in the juice with a pH-meter, -determination of the firmness (kgf) by using a penetrometer -determination of the colour by using a Minolta chromometer. ,.

\

-r

70

1 Tcmphlure

(“C)

FIG. 5. Efficiency isoresponse curves after 72 h of catalysis for catalyst S (catalyst mass, 500 g; air flow rate, 0.9 m3 h-l).

F leads to 100% efficiency at lower tem(115°C) and average ethylene concentrations (Fig. 4). However, this efficiency is not total at low and high ethylene concentrations. -catalyst S seems the least capable since an efficiency of 100% is not achieved even at the highest temperatures (Fig. 5). The maximum efficiency in this case was 90% with an increase in temperature.

-catalyst

peratures

Industrial test and quality tests The long term storage industrial test was carried out with catalyst P. The industrial prototype containing 90 kg of catalyst P was tested in a 1800 ms cold room with 282 t of Golden Delicious apples, harvested in the region of Montauban (France) a few days before and had therefore started to mature before the start of the trial. During the experiment, oxygen variation (2.5-8%) and carbonic anhydride variation (3-3.5%) were observed in the composition of the controlled room atmosphere. The objectives of these tests were to study the functioning of the prototype to collect scientific and technical data to evaluate the efficiency of ethylene removal and optimise design of the industrial reactor. Thus, atmospheric samples were withdrawn from the room equipped with the ethylene adsorbent and from a standard room without an absorbent and matching samples were taken from air at the entry and at the end of the reactor. These samples were analysed by gas chromatography. A control of 0, and CO, concentrations of both rooms was also carried out. The ethylene removal effect on the physical properties of stored apples and quality tests on apples at

These measures were carried out on 30 apples. Figure 6 shows the study of ethylene contents during the test. A 33 days breakdown in the electric heating circuit occurred after 17 days functioning of the prototype. The treated and standard rooms respectively had 37 and 247 ppmV of ethylene. After repairing the reactor, the ethylene level in the purified room was maintained at 30 ppmV for 50 days with a 68.5 mS h-’ purification flow rate. An increase in the flow rate to 80 ms h-’ during a short period (28 days) bought down the concentration to 16 ppmV. This modification clearly shows that the impact of the flow rate on the residual ethylene concentration. A return of the flow rate to 68.5 m3 h-’ lead to a slight increase in the concentration in the treated room. The residual ethylene values obtained during this storage experiment were higher than the expected concentration of 1 ppm at which fruits may be sensitive. Nevertheless, during this test, we have outlined the principal factors responsible for the high residual ethylene concentrations observed. They are mainly: -the low purification flow rate (68.5-80 m3 h-‘). A 100 m3 h-’ value may be required. -the poor functioning of the thermal regulation of the catalyst temperature variation over a large range compared to the recommended value (115°C). Furthermore, the heating system used induced a thermal heterogeneity of the catalyst. A new system with a heating ribbon around the reactor is now in place. This will eliminate the drawbacks observed. -partial filling of the storage room (282 t of fruit instead of 450 t) . -advanced maturation of the apples during harvest. Nevertheless, the results of the quality tests reported in Table 6 indicate that the apples stored under a purified atmosphere retained their initial sugar content and their initial colour. The firmness of the apples as well as their acidity were preserved under an atmosphere containing a reduced ethylene concentration. The quality indices were evaluated according to the formula: IQ = Total sugars + 10 Acidity

124

AltafEl Blidiet

al.

and were respectively

141.5

for apple of the standard

stock and 151 for the fruits stored ethylene

partial pressure.

under

CONCLUSION

low residual

After the harvest,

this meter

was 156.8. Yet, the advanced considered

good

physical

efficiently

fully reflect

concentration

Indeed,

shown that, regardless

various devices used to eliminate of any attempt

the benefits

to preserve

on the initial condition

Dover

moval

that a low (1989),

of the accuracy ethylene,

technology

carried

has

-the

of the

ethylene

conre-

out

at low

economical.

results obtained

study of catalytic efficiency

temperatures

concerned:

of ethylene

removal on

a laboratory pilot scale, carried out according

the success

mental

composite

catalyst P chosen

105

115 STOP ‘ROTOTYP

80

removal

of a physicochemical

which was energetically

The most significant

of these products.

Flow rate (m3.h-')

on catalytic

to the development

(lOO-130°C)

in

the quality of fruits depends

Catalysis temperature ("C)

investigation

tributed

the tests are

would have on fruits being

condition.

This

of the apples

here is such that, even though

positive, they cannot ethylene

state of maturation

designs,

for development

115

125

80

68.5

68,s

which

showed

to experithat the

of our process was

"l-

\ JL

4

40

I

I

60

80

z 120

140

160

Storage time (days) 11-3-90

12-6-90

FIG. 6. Evolution of ethylene contents in Golden Delicious apples storage rooms equipped (0) or not (X) with the removal prototype, also at the entry (0) or at the end (W) of the reactor: room atmosphere without prototype, 3.5% Os, 3.5% CO,, 0.3”C; room atmosphere with prototype, 2.5-8% O,, 3.5% COP, 0.3”C.

TABLE 6. Quality Tests for Golden Delicious Apples Stored with the Industrial Prototype. Conservation Time 134 days TeStS

Firmness (kgf) Acidity (g. of malic acid/litre Refractive index Total sugars (g) Colour coordinates

nStandard deviation sampling: 30 apples.

Analy&

at harvest time

Post conservation adysk Room without ethylene absorbent

Room with ethylene absorbent

2.98 (O-37”) 3.79 13.20 118.90

2.32 (0~26~) 2.8 12.7 113.5

2.50 (0.27”) 3.21 13.20 118.90

Y= 45.153 x= 0.385 y = 0.444

Y = 46-2 x= 0.400 y = 0.442

Y= 45-6 X = 0.400 y = O-442

Long Term Conservation of Fruit and Vegetables 125 the most adequate as it leads to complete oxidation of ethylene whatever its concentration at low temperature. -the ethylene removal tests carried out in a 1800 m3 room with our industrial prototype lead to excellent results for Golden Delicious apples which, after 134 days of conservation, retained properties close to the fruits at harvest time. This test shows the industrial scale realisation of ethylene removal by catalytic oxidation at low temperature. Its application for the treatment of conventional controlled atmospheres used for high added value fruits like the kiwi fruit or Granny Smith apples would appear to be economical thereby allowing long-term storage of these ethylene sensitive fruits with its catalytic ethylene removal in mild energetic conditions.

ACKNOWLEDGEMENTS First and foremost, we wish to thank Mr J. C. Pech and Mr A. Latch6 for their help and advice. We also thank Lhotelier Montrichard for the design of the prototype used and Sica Sagef from the international market of Montauban (Tarn et Garonne, France) for the storage apple rooms in which tests were carried out.

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Commodities,

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Sfakiotakis, E., Ververidis, P. & Stavroulakis, G. (1989). The control of autocatalytic ethylene production and ripening in kiwi fruit by temperature and controlled atmosphere storage. Acta. Hart., 258, 115-23. Sherman, M. (1985). Control of ethylene in the post-harvest environn1ent.j. Hart. Sci., 20, 57-60. Sister, E. C. & Yang, S. F. (1984). Anti-ethylene effects of cis2-butene and cyclic olefins. Phytochemistq 23, 2765-8. Stow, J. R. (1989). Effects of oxygen concentration on ethylene synthesis and action in stored apple fruits. Acta Hurt., 258,97-106.

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