Effect of Deep Fat Frying on Ascorbic Acid, Carotenoids an Potassium Contents of Plantain Cylinders

Effect of deep-fat frying on ascorbic acid, carotenoidsand potassium contents of plantain cylinders

JUAN A. ROJAS-GONZALEZ1,2, SYLVIE AVALLONE2, PIERRE

BRAT1, GILLES TRYSTRAM3, & PHILIPPE BOHUON1,2

1CIRAD UR-24, Montpellier, France, 2ENSIA, Montpellier, France, and 3UMR

Genial-ENSIA-CEMAGREF-INAPG-INRA, Massy, France

AbstractThe influence of thermal treatment (frying of plantain) on the micronutrients ascorbic acid,potassium and carotenoids is evaluated. Cylinders (diameter 30 mm, thickness 10 mm) ofplantain (Musa AAB ‘barraganete’) were fried at four thermal treatments (120�1808C andfrom 24 to 4 min) to obtain products with approximately the same water content (:/0.89/0.02kg/kg1) and fat content (:/0.159/0.06 kg/kg). The thermal study used the cook value and themean cook value as indicators of the effect of several different treatment temperatures and timeson quality. Deep-fat frying had no significant effect on carotenoid contents at any fryingconditions, and on potassium content, except at 1208C and 24 min (loss5/11%). There was asignificant, but not complete, loss (5/45%) of ascorbic acid. The process with the greatest effectwas low temperature and long time (1208C/24 min), as observed for potassium and ascorbicacid. These results are in agreement with other studies that demonstrated short thermaltreatments at high temperatures protect food nutritional quality, as shown by the cook value andthe mean cook value. In our work, deep-fat frying of plantain preserved most of themicronutrient contents that were evaluated.

Keywords: Deep-fat frying, ascorbic acid, carotenoids, potassium, plantain

Introduction

Deep-fat frying is a rapid, low-cost process for drying, cooking and producing

products with useful sensory attributes; that is, starchy products (Musa AAB)

produced both industrially by continuous process and at home, such as potato chips,

French fries, and plantain chips and slices (Adeva et al. 1968; Mariano et al 1969).

Fried plantains are a popular food in Africa (Onyejegbu and Orolunda 1995), Latin

America (Totte et al. 1996) and Asia. Frying is a complex process involving heat and

mass (water, fat and nutrient) transfer, resulting in physical, chemical, nutritional and

sensory changes (texture, colour, taste) (Vitrac and Bohuon 2004). Many of these

changes depend on oil temperature, product water content, oil content and product

residence time in the fryer. High-temperature conditions (:/1808 C) can generate

beneficial compounds (aromas, colour), but also undesirable effects, such as the

degradation of important nutritional compounds (vitamins, etc.) as well as the

Correspondence: Philippe Bohuon, CIRAD/ENSIA UR�/Tropiqual, TA�/40/16, 73 rue Jean Francois

Breton, 34398 Montpellier, cedex 5, France. Fax: 33 4 67 61 55 15. Email: [email protected]

ISSN 0963-7486 print/ISSN 1465-3478 online # 2006 Informa UK Ltd

DOI: 10.1080/09637480600658393

International Journal of Food Sciences and Nutrition,

February/March 2006; 57(1/2): 123�136

generation of toxic molecules (e.g. acrylamides, polar compounds of the oil, etc.)

(Pokorny 1999). High temperatures allow rapid heat transfer and short cooking times

(only a few minutes). The temperature inside the product does not usually exceed

100�/1038 C at atmospheric pressure (Valera 1988). The process involves fat

absorption or replacement and exchange, and the loss of lipid-soluble compounds

like carotenoids (Pokorny 1999). Water-soluble molecules, such as ascorbic acid and

minerals, can be transferred with the liquid water at it is lost from the product; and

complex reactions in the food can generate new compounds, such as carotenoid

isomers (Sulaeman et al. 2001) and acrylamides (Pokorny 1999; Pedreschi et al.

2005). Many studies have focused on frying oil behaviour (Carlson and Tabacchi

1986; Gordon and Kourimska 1995; Perkins and Erickson 1996), but few data are

available on the nutritional advantages and disadvantages of frying compared with

other cooking methods (Fillion and Henry 1998).

The behaviour of nutritional compounds is influenced by the solubility and

structure of the molecule as well as its thermal sensitivity. Boushell and Potter

(1980) showed that ascorbic acid (a water-soluble molecule) is easily lost by water

transfer during blanching. Losses of ascorbic acid during frying of liver and cabbage

were between 35% and 37% (Pokorny 1999). Several authors have reported activation

energy (Ea) values for ascorbic acid degradation of 58.6�/71.2, 105.59/2.1, 117.69/

4.6 and 171.7 kJ/mol, respectively, in model food systems, oranges, tomato juice and

peas (Van de Broeck et al. 1998). Lipid-soluble compounds like carotenoids and

a-tocopherol can also be lost in the frying process. In deep-fat frying of vegetables,

carotenoid losses were twice as high as in shallow-fried foods (Padmavati et al. 1992),

possibly because more carotenoids migrate into the frying oil. During frying of

cabbage, 29% of carotenoids were lost. One-half of the carotenoids were lost during

the frying of fruits and vegetables compared with other cooking methods (boiling and

blanching) (Pokorny 1999). Ahmed et al. (2002) calculated the activation energy for

carotenoid degradation as 33 kJ/mol in pasteurization of papaya puree. During frying,

the product undergoes important sensorial changes (flavour and colour) due to

chemical reactions like the Maillard reaction. Recent studies found that asparagine in

potato reacts with glucose through a Maillard reaction to form acrylamide (Becalski

et al. 2003; Rassolian et al. 2003; Pedreschi et al. 2005) and generates other

compounds with antioxidant and pro-vitamin properties, such as carotenoid isomers

(Emenhiser et al. 1995; Ferruzi et al. 1998; Sulaeman et al. 2001). Several authors

(Gall et al. 1983; Gokoglu et al. 2004) observed minor changes in the mineral

composition of both the frying oil and fatty fish (Spanish mackerel) after frying.

Greater losses (22%) were encountered during milanesa meat frying (Juarez et al.

2004).

The aim of the present paper is to evaluate the effect of heat and mass transfer

during deep-fat frying of plantain cylinders (Musa AAB ‘barraganete’) on some

nutritional compounds. The water and fat contents were characterized in raw and

fried plantains. The thermal behaviour, cook value, mean cook value and several

molecules such as ascorbic acid and potassium (water-soluble) and carotenoids (lipid-

soluble) were estimated after the deep-fat frying process at different temperatures and

times (120�1808C and from 24 to 4 min).

124 J. A. Rojas-Gonzalez et al.

Materials and methods

Raw material

Plantain (Musa AAB ‘barraganete’) at commercial maturity stage 2 (peel still

completely green), from Ecuador, were purchased from a retail shop in Montpellier

(France). All the plantains were stored at 138C (9/18C) for no more than 3 days.

Before the frying treatment, the raw plantains were peeled and cut, firstly into

cylinders (diameter 30.0 9/ 0.2 mm) with a cork borer in the longitudinal direction of

the plantain; these were then trimmed to a thickness of 10.09/0.2 mm using parallel

blades. Three cylinders were used from each plantain and two plantains were used for

each frying treatment. The residual material was stored at�/208C.

Frying equipment and conditions

A large household, insulated, deep-fat fryer (model KPB 50; Kenwood, Paris, France)

was filled with 4.5 kg palm oil and heated with an electric element (effective power 1.6

kW) submerged 3 cm above the bottom of the tank. This heating configuration

generated a ‘cold’ region below the electrical resistance. The bulk oil volume above the

thermal element was stirred at 16.8 rad/s by two rushtone turbines (six blades, turbine

diameter 30 mm and blade section 15�/5 mm2) fixed on a common axis. The stirring

unit with radial flow produced turbulence without aeration and ensured the

homogenization of the temperature field. The bulk temperature, T�, was controlled

by a numerical PID controller and based on the median of five temperature

measurements. All acquisition and control algorithms were implemented by a

dedicated software application (Labview version 5.1; National Instrument, Austin,

TX, USA). Six cylinders (:/40 g) of plantain were fried at different temperatures

(T�) and times (1208C and 24 min, 1408C and 13 min, 1608C and 7 min, and

1808C and 4 min) at atmospheric pressure. When the cylinders were first plunged

into the oil, the maximum local temperature variations were T��/38C and T��/18C.

Plantain cylinders were maintained submerged by means of a wire basket.

Physico-chemical analysis

Expression of compound content in fat free dry matter. As the deep-fat frying process

combines water transfer (loss) and fat transfer (gain), the fat free dry matter in

plantain is constant. Most of the nutrient contents in this study thus correspond to a

mass content per unit mass of initial fat free dry matter. The equation for changing

X (t) (mass of compound X per unit mass of product) to X (t)s (mass of compound X per

unit mass of initial fat free dry matter) is:

X (t)s �X (t)=(1�W (0)�F (0)) (1)

where W (0) and F (0) are the initial water and fat contents of plantain. Compound X

could be water (/W ); fat (/F ); ascorbic acid (/AA); potassium (/K); a-carotene (/a);b-carotene (/b) or carotenoid isomers (Iso).

Water content. The water content, noted and expressed in kilograms of water per

kilogram of product, was determined by drying in two steps because of the high lipid

and starch content of the samples. Raw and fried plantains were firstly pre-dried at

Effect of deep-fat frying on plantain cylinders 125

508C for 12 h and secondly dried at 708C at low pressure for 12 h. The maximum

standard deviation of repeatability was9/0.001 kg/kg.

Fat content. The fat content, F(t ) and expressed in kilograms of fat per kilogram of

product, was determined with an Accelerated Solvent Extractor, DIONEX (ASE-200,

Sunnyvale, CA, USA). Lipids were extracted from the dried samples (:/2 g) with

petroleum ether at 708C for 35 min. The solvent was then evaporated and the lipids

weighed. The maximum standard deviation for repeatability was9/0.02 kg/kg.

Ascorbic acid content. The ascorbic acid content, AA(t ) and expressed in milligrams per

100 g product, was measured by the chromatographic method of Polesello and

Rizzolo (1990). Raw and fried samples (:/7 g) were cut and put in a beaker with 50 ml

methaphosphoric acid buffer solution (0.6 mM, pH 2.5) and immediately homo-

genized at ambient temperature by a rotating blade at 105 rad/s for 10 s (IKA-Werk,

Staufen, Germany). The resulting mixtures were centrifuged for 15 min (1571 rad/s,

48C) to coagulate the fat gained during the deep-fat frying process. The aqueous

extract was collected and 10 ml hexane was added to remove the fat. The final

aqueous volume was then measured. The supernatant was filtered through a 0.45 mm

cellulose filter (Millipore Corporation, Billerica, MA, USA). Quantification was

performed with an Agilent 1100 series chromatograph equipped with a LC-18

monomeric column (4.6 mm�/250 mm, 5 mm particle size) (LichoCART 250-4;

Merck, Darmstadt, Germany). Methaphosphoric acid buffer (0.6 mM, pH 2.5) was

used as eluent at a flow rate of 0.7 ml/min. Detection was carried out at l�/254 nm

and identification and quantification were based on the retention time and standard

co-injection. The maximum standard deviation for repeatability was9/0.5 mg/100 g.

Potassium content. The potassium content, k(t ) and expressed in milligrams of

potassium per 100 g product, was measured with an inductively coupled plasma

spectrometer. Raw and fried samples were dried in a vacuum oven at 708C (9/18C)

for 24 h, then ground and mineralized at 6008C. After solubilization, potassium was

quantified with an inductively coupled plasma spectrometer, type JY50 poly (spectral

range 175�800 nm; generator, 40.68 MHz, 2400 lines/min, power 1.5 kW). The

maximum standard deviation for repeatability was9/0.03 mg/100 g.

Carotenoid content. The carotenoid and carotenoid isomer contents were noted, a(t ),

b(t ) and Iso(t ), and expressed in micrograms of carotenoids per 100 g product. Frozen

samples were pulverized for 3 min in liquid nitrogen with a Dangoumeau 300 ball mill

(Prolabo, Lyon, France). Carotenoid extraction was adapted from the method of

Kimura and Rodriguez-Amaya (2002). Tert-butyl-methyl-phenol (0.1%, v/v) was

added to all the extraction and high-performance liquid chromatography solvents. For

fried samples, a preliminary fat removal step was performed (De-Sa and Rodriguez

Amaya 2003). Under red light, powdered samples (:/1 g) were mixed for 5 min in a

tube glass with 10 ml acetone and 0.5 g MgCO3 to neutralize the organic acids and

then left for 2 h at�/208C. The solution was then filtered through a cold glass funnel

to separate liquid organic extract and solidified lipids. The organic solution was then

transferred to a separating funnel and 10 ml petroleum ether was added. The extract

was washed with 10% NaCl and distilled water and left for 10 min for partitioning.

The organic extract was then concentrated in a rotary evaporator at 328C (9/18C)


and the residue dissolved in 10 ml tert-methyl-butyl-ether:methanol:dichloromethane

(40/10/50, v/v/v). Samples were filtered through a 0.45 mm PVDF (polyvinylidene

fluoride) filter and injected immediately into the high-performance liquid chromato-

graph. The carotenoid analysis was performed with an Agilent 1100 series

chromatograph. The column was a polymeric YMC-30 (4.6 mm inner diameter�/

250 mm, 5 mm particle size) (YMC, Inc., Wilmington, NC, USA) thermostated at

258C, and the mobile phase was composed of distilled water, methanol and tert-

butyl-methyl-ether at a flow rate of 1 ml/min. A gradient was applied from 40/60/0 to

4/81/15 v/v/v over 10 min and then from 4/81/15 to 4/11/85 v/v/v over 50 min until the

end of the run (Dhuique-Mayer et al. 2005). A UV�visible photodiode array detector

was used and chromatographs were analysed at the wavelength of maximum

absorption of the carotenoids in the mobile phase (l�/450 nm). The carotenoids

were identified and quantified by comparing their retention times with a reference

standard when available (Sigma, Lyon, france). Carotenoid isomerization was

suspected when a maximum absorption appeared between 320 and 340 nm in the

carotenoid spectra. The standard deviation of repeatability was9/0.2 mg/100 g.

Thermal behaviour and determination of the cook value

Temperatures at three different depths inside the plantain cylinder (Figure 1) were

monitored using 0.5 mm thick K-type micro-thermocouples (Model 12MK 0.25; TC,

Dardilly, France). Temperature data were acquired using a dedicated software

application (Labview version 5.1; National Instrument). Each time�temperature

profile at a given position (r; y); T (t)(r;y); was fitted with a cubic smoothing spline

(Matlab†

Version 5.2; The Mathworks Inc., Natick, MA, USA). The degree of

cooking and thus the thermal impact on the nutritional quality attributes was

expressed in terms of the cook value. The cook value at a given position C (t)(r;y) was

calculated as the direct analytical integral of the cubic smoothing spline function on

T (t)(r;y) by:

C (t)(r;y)�g

t

0

10(T (t)(r;y)

�Tref )=zdt (2)

The mean degree of cooking (in terms of average volume) C(t)

was calculated as the

direct analytical integral of the cubic smoothing spline function on /C (t)(r;y):

5

10

Thermal sensors

R = 30 mm

10 mm

rr = 15 mm

10 mm

3 mm

y1

2

3

21

3

( ∞T )oil

Figure 1. Thermal sensor in bulk oil (T��/120, 140, 160 and 1808C) and transversally cut plantain

cylinder at different depths: (1) 15 mm, (2) 10 mm and (3) 3 mm.


C(t)�

1

Vcylinderg

Vcylinder

0

C (t)(r;y)dV (3)

where Vcylinder was the total volume of the plantain cylinder. Tref ; the reference

temperature, was set at 1008C as used for cooking processes by Bimbenet et al.

(2002). z is the temperature increase that induces a 10-fold increase in the rate of the

reference chemical reaction; we chose the z value to be set at 258C. This value is often

used to characterize the thermal sensitivity of ascorbic acid (Ohlson 1980) and

corresponds to Ea:/100 kJ/mol.

Statistical analyses

Differences in the mean values of fat free dry matter of water (/W ); fat (/F ); ascorbic

acid (/AA); potassium (/K); a-carotene (/a); b-carotene (/b) and carotenoid isomers (Iso)

contents, were tested by analysis of variance, and the significance of differences

between samples was determined using Fisher test.

Results and discussion

Chemical composition of raw plantain

Preliminary studies (data not presented) showed that water, fat and micronutrients

were distributed homogeneously along the length of the plantain. The average water

and fat contents of raw plantain cylinders were 60.19/1.8 (standard deviation) and

0.19/0.02 kg/100 kg fresh weight (n�/28), similar to values published by Chandler

(1995), which ranged from 59 to 74 and from 0.2 to 0.3 kg/100 kg plantain,

respectively. The fat content of plantain is very low, only 1�2%. The average

micronutrient content of the raw plantain was 24.59/0.5 mg ascorbic acid/100 g flesh,

and this value is higher than that found by Chandler (1995) (i.e. 20 mg/100 g flesh).

The ascorbic acid concentration was close to that of pineapple, raw tomato and

melon, which varies from 18 to 25 mg ascorbic acid/100 g flesh (Guilland 2003 ). The

potassium content was 3989/18 mg/100 g plantain, which is also similar to that found

by Chandler (1995), plantain being particularly rich in comparison with other staple

foods. The average a-carotene and b-carotene contents were 8509/410 and 6009/290

mg/100 g fresh plantain, respectively. The large standard deviations indicate

considerable biological variability, which can result from differences in variety,

maturity, growing conditions and season (Hart and Scott 1995). Plantain is

particularly rich in a-carotene, although not as rich as vegetables such as pumpkin

and carrot, which average 3700 mg/100 g flesh. Our b-carotene content was close to

that found in several fruits and vegetables, such as broccoli, asparagus, cabbages,

guava and tomatoes, which average about 600 mg/100 g flesh (Guilland 2003). Pro-

vitamin capacity can be affected by the quality of the molecule, bio-availability and

adsorption (Azaıs-Braesco and Grolier 2001).

Water content of fried plantain

After each frying treatment (1208C for 24 min, 1408C for 13 min, 1608C for 7 min

and 1808C for 4 min), the average water loss from the plantain cylinders was 0.719/

0.04 kg/kg (about 50 g water/100 g product) (Table I) for the different frying


conditions (thermal history). The final average water content for all frying products

was 0.809/0.04 kg/kg (:/30 g water/100 g in the fried product). Thus losses and gains

of micronutrients (acid ascorbic, potassium and carotenoids) were compared in

products at similar final water contents.

Fat content of fried plantain

The fat gains (/F (t)s ) per plantain cylinder for each frying treatment are presented in

Table I. The fat gain was greatest (0.279/0.02 kg/kg, :/10 g fat/100 g fried product) at

1208C and 24 min, which are unusual frying conditions. At 1408C and 13 min the fat

gain was less (0.159/0.03 kg/kg, :/7 g fat/100 g fried product), and was still less at

1608C and 1808C for 7 and 4 min, respectively (0.119/0.01 kg/kg, :/5 g fat/100 g

fried product). For all frying conditions (except 1208C and 24 min), the fat gain

observed in our plantain cylinders was generally lower than in several pre-treated

thicker products (e.g. potatoes) in which the fat gain ranged from 0.17 to 0.35 kg/kg

(:/15�20% of fried product) (Garcia et al. 2002; Krokida et al. 2000). The low fat

gain observed in plantain cylinders is a valuable/useful nutritional attribute.

Thermal behaviour and cook value

Typical temperature profiles inside the plantain cylinders measured at different depths

(3, 10 and 15 mm) are shown in Figure 2. Temperature profiles were similar in shape

for all tested oil temperatures. During the heating phase, the temperature in the centre

and at the surface of the product increased with time, as expected. The frying process

was broken down into three stages in all frying conditions. The first stage was

characterized by a rapid temperature increase up to boiling (Tsat :/102�/1038C). At

1208C this stage took around 100 sec, while at 1808C the heat transfer was faster (70

sec) for the whole product to reach Tsat . The second stage was characterized by a

constant temperature around saturation temperature. The same temperature was

maintained for half (ranged from :/40�50%) of the total time in all the frying

processes. The temperature located at the centre remained constant until the end of

the deep fat frying process due to the high water content at the centre of the plantain

cylinder. The third stage was characterized by a slight change in the temperature in all

frying treatments. Overheating (T �/Tsat) was greater towards the peripheral zones

of the product. The temperature range at the surface of the plantain cylinder was from

:/115 to 1308C until the end of frying process. The rise in temperature could be due

Table I. Cook value (/C(t)); water content (/W (t)s ) and fat content (/F (t)

s ) in plantains after time t at several frying

temperatures T.

Frying condition /C(t) (min) Content (kg/kg fat-free dry matter)

T (8C) t (min ) Cook value in the centre Mean cook value /W (0)s /W (t)

s /F (t)s

120 24 21.49/0.8a 32.59/4.0a 1.559/0.04a 0.759/0.03a. 0.279/0.02a

140 13 11.39/1.1b 14.49/0.9b 1.489/0.07b 0.749/0.04a 0.159/0.03b

160 7 5.89/0.7c 10.29/4.0b 1.549/0.04a,b 0.869/0.05b 0.119/0.01c

180 4 3.09/0.4d 8.79/3.0b 1.469/0.09b 0.849/0.04b 0.129/0.02c

Values presented as the mean9/SD (n�/7 per group). In columns, values with different letters are

significantly different (PB/ 0.05) between the four frying conditions.


to the water lost at the surface and the close contact with the hot frying oil. This

situation is known to occur at the surface of starchy products when a vapourization

front separates a superficial dried region and an internal region partially saturated in

water (Vitrac et al. 2002). This slight increase in temperature can be explained by the

movement of water (liquid water) into the plantain cylinder through the surface

(drying phenomena). This liquid water supply moderates the degree of overheating

(Vitrac et al. 2002; Vitrac and Bohuon 2004; Vittadini et al. 2005).

After each frying process, one-half of the water content was lost. Moreover, the

product received the same quantity of heat (latent) to evaporate water, but a different

thermal course. In order to facilitate the comparison between the four thermal

courses, the cook value was estimated (n�/7) with the profile temperature at the

centre for each frying treatment, and is presented in Table I. The cook value located at

the centre of the plantain is close to the total process time, as the temperature at the

centre remains constant (Tsat :/102�/1038C). All cook values at the centre of

the plantain were significantly different (PB/ 0.05). The temperature gradient inside

the plantain induced a gradient in the cook value (the cook value was higher towards

the periphery). Thus, to compare the unfavourable effects of heat transfer on

nutritional compounds (acid ascorbic) in the whole plantain cylinder, the mean

cook value was estimated. This mean cook value was affected by the temperature

profile at the centre and at the surface. The mean cook value was higher than the total

frying times used (from 24 to 4 min), because the peripheral temperature was higher.

The mean cook values obtained from 140 to 1808C were the same (PB/ 0.05), but the

0

50

100

150

200

0 100 200 300 400

0

50

100

150

200

0 200 400 600 8000

50

100

150

200

0 300 600 900 1200

0

50

100

150

200

0 50 100 150 200 250

Tem

pera

ture

(°C

)

Time (s)

(a)

(c) (d)

(b)

1

T∞

T∞

T∞

T∞

321

321

23

123

Figure 2. Time�temperature profiles during the deep-fat frying process at different oil temperatures

(T� : 1208C (a ) 1408C (b ) 1608C (c ) and 1808C (d )) and different depths: (1) 15 mm, (2) 10 mm and

(3) 3 mm.


mean cook value at 1208C was significantly different (PB/ 0.05) and higher. From the

point of view of acid ascorbic, we would expect that the losses obtained from 140 to

1808C will be the same and higher than at 1208C.

Effect of frying on micronutrients

Loss of ascorbic acid. For analytical reasons, a preliminary study was performed to

evaluate the influence of fat removal by hexane on the ascorbic acid content of the

aqueous extracts. The ascorbic acid extraction of raw and fried plantain was carried

out with and without the addition of hexane to the supernatant solution. No

significant effect (PB/ 0.01) was observed on ascorbic acid content and, as a result,

hexane was added for fat removal.

Ascorbic acid content (/AA(t)s ) was reduced by deep-fat frying (Table II). An average

loss of 28% ascorbic acid was observed for the 1408C for 13 min, 1608C for 7 min

and 1808C for 4 min processes (Table II). The loss was significantly greater (45%) at

1208C and 24 min.

With mean cook values between 8 and 15 min (high temperature and short time),

ascorbic acid losses ranged from 20 to 30%. On the other hand, with a mean cook

value close to 32 min (low temperature and long time), the ascorbic acid loss was

45%. The ascorbic acid losses observed are in agreement with the two levels of mean

cook value. In our case, the mean cook value seems to be a relevant parameter to

analyse the unfavourable effects of heat transfer on acid ascorbic compounds during

the deep fat frying process. Many studies have shown losses of ascorbic acid of

between 17 and 52% in French fries prepared during foodservice operations or deep-

fat-fried at home or under industrial conditions (blanching and pre-frying) (Agustin

et al. 1981; Carlson and Tabacchi 1986; Hasse and Weber 2001). The final loss of

ascorbic acid, which depends on how the raw product is prepared, can be very high

(Boushell and Potter 1980). High temperatures and short processing periods have

been reported to better protect vitamins than low temperature and long treatment

time (Bhaskarachary et al. 1995).

Loss of potassium. The only significant loss (P B/0.05) of potassium (/K (t)s ) was observed

at 1208C for 24 min (11% loss) (Table II). This could be due to a leaching effect

during prolonged low-temperature frying (Pokorny 1999). Potassium ions may

migrate during frying and be deposited in a very thin water layer at the surface of

the fried food from which they are lost to the oil. Other studies have shown that the

Table II. Ascorbic acid (AAs(t )) and potassium (Ks

(t )) contents in plantains after t time at several frying

temperatures T.

Frying condition Content (mg/100 g fat-free dry matter)

T (8C) t (min ) AAs(0) AAs

(t ) Ks(0) Ks

(0)

120 24 61.39/2.3a 33.39/5.0a 10109/31a,x 8999/23a,y

140 13 61.39/2.3a 42.49/4.1b 10009/38a,x 9609/47b,x

160 7 61.39/2.3a 49.69/2.9c 10009/32a,x 9909/38b,x

180 4 61.39/2.3a 41.99/5.2b 9909/23a,x 9659/35b,x

Values presented as the mean9/SD (n�/7 per group). In columns, values with different letters (a�c) are

significantly different (PB/ 0.05) between the four frying conditions. In rows, values with different letters

(x, y) are significantly different (PB/ 0.05) between raw and fried plantain.


losses of minerals during deep-fat frying for short times at temperatures from 165 to

1858C were not significant (Gall et al. 1983; Gokoglu et al. 2004). On the other hand,

high temperature (1808C) and long frying times (15�30 min) have been shown to

cause serious losses of minerals of about 22% (Juarez et al. 2004).

Losses of carotenoids. The carotenoids of the raw and fried plantains are mainly

a-carotene and b-carotene, with a predominance of the a molecule. The average loss

of carotenoids (/a(t)s ; b(t)

s ) ranged from 9 to 13% at all frying temperatures. There was a

tendency for greater loss of carotenoids with longer frying time, but the losses were not

statistically significant (P B/0.05), because of the great variability in raw plantain

(Table III). Other authors have observed rather good stability of carotenoids during

thermal treatment (Sant’Ana Pinheiro et al. 1998; Sungpuag et al. 1999; Ravichandra

2001; Sulaeman et al. 2001; De-Sa and Rodriguez-Amaya 2004). In some cases, the

carotenoid content was higher in some fried samples than in the raw samples because

interactions between carotene and protein or others molecules were disrupted, making

the carotenoids easier to extract (Sulaeman et al. 2001; De-Sa and Rodriguez-Amaya

2004). Although isomers of carotenoids were detected (Table IV), their identification

was not possible (Figure 3). There was no apparent increase in isomer contents in

fried samples at different temperatures (120�1808C) and times (from 24 to 4 min) as

previously observed by De-Sa and Rodriguez-Amaya (2004). The high resistance of

carotenoids to thermal treatment (Ea:/33 kJ/mol and z value corresponding:/818C)

limits the use of the mean cook value as an indicator of losses during the deep-fat

frying process.

Table III. a-carotene (as(t )) and b-carotene (bs

(t )) content in plantains after time t at several frying

temperatures T.


T (8C) t (min ) as(0) as

(t ) bs(0) bs

(t )

120 24 8609/450a,x 5709/120a,x 5709/280a,y 4609/150a,y

140 13 9409/570a,x 8609/170a,x 6309/390a,y 6209/80a,y

160 7 9309/540a,x 8909/500a,x 6309/370a,y 5709/90a,y

180 4 6509/80a,x 6109/90a,x 5309/120a,y 5209/80a,y

Values presented as the mean9/SD (n�/7 per group). In columns, values with different letters (a�c) are

significantly different (PB/ 0.05) between the four frying conditions. In rows, values with different letters

(x, y) are significantly different (PB/ 0.05) between raw and fried plantain.

Table IV. Carotenoid isomers (Isos(t ) 1�4) content in plantains after time t at several frying temperatures T.


T (8C) t (min ) Isomer 1 Isomer 2 Isomer 3 Isomer 4

120 24 289/12a 319/6a 69/6a 609/10a

140 13 499/5b 449/6b 879/1b 809/10b

160 7 259/12a 269/5a 659/1c 609/10a

180 4 269/13a 289/3a 779/7c 709/9a

Values presented as the mean9/SD (n�/7 per group). In columns, values with different letters are

significantly different (PB/ 0.05) between the four frying conditions.


Conclusion

The plantain lost the same quantity of water (:/0.3 kg/1 kg initial plantain), gained

similar quantities of oil (:/0.05�/0.1 kg/1 kg initial plantain) and consumed the same

quantity of heat to vapourize the water (:/670 kJ/1 kg initial plantain) in all frying

conditions (French fried). On the other hand, the products were not subjected to the

same thermal treatments (120�1808C and from 24 to 4 min). In the comparison of

the heat treatments, our results showed that the mean cook value is a good qualitative

α -carotene

β-carotene

isomers

12

3

4

4

0

2

-2

14

12

mAU

10

8

6

332

416

440

466

(1)

332

418

438

464

338

450

424472

338

420

445

467

(2)

(3) (4)

6

2

1

0

3

5

4

2.5

1

0.5

2

1.5

2

1

0

3

5

4

1

0

3

5

4

2

mA

U

340 380 420 460 nm340 380 420 460 nm

340 380 420 460 nm 340 380 420 460 nm

20 22.5 25 27.5 30 32.5 35 37.5 min

Figure 3. Carotenoid isomers 1, 2, 3 and 4 found after the different deep-fat frying processes of plantain

cylinders.


indicator, relevant and consistent with the unfavourable effects of heat transfer on acid

ascorbic compounds in the whole plantain cylinder. Two ranges of mean cook values

were obtained: firstly, low temperature (1208C) and long time (24 min), with a high

mean cook value of 32.59/4.0 min; secondly, high temperatures (]/1408C) and short

times (5/13 min), with a low mean cook value of 11.49/2.7 min. The lowest average

loss for ascorbic acid (28%) was found at high temperatures and short times, and the

biggest loss for ascorbic acid (45%) was found at low temperatures and long times;

this phenomenon can be explained by the thermal effect on ascorbic acid at longer

frying times. In the same way, the high temperatures and short times caused no

significant losses of potassium. The biggest losses (11%) were observed at low

temperatures and long times. This loss can be explained by leaching phenomena of the

mass transfer (water and oil) (not typical for frying processes). No significant effect of

the deep-fat frying process (P B/0.05) was observed on carotenoid compounds

(a-carotene, b-carotene and isomers) at the different temperatures and times used.

These results confirm the high resistance to thermal treatment of carotenoids in

plantain foodstuff. The deep-fat frying process of plantain thus appears to preserve

most of the micronutrients evaluated, whether water-soluble (ascorbic and potas-

sium), lipid-soluble (carotenoids), or sensitive to heat (ascorbic acid).

Acknowledgements

Particular thanks to Guy Self, Claudie Dhuique-Mayer and Marc Lebrun for their

support. All belong to the investigating team of UR TROPIQUAL�/CIRAD�/

FRANCE.

References

Adeva IV, Gopez MD, Payumo EM. 1968. Studies on the preparation and storage qualities of banana chips.

Philippine J Sci 97(1):27�35.

Agustin J, Marousek GI, Artz WE, Swanson BG. 1981. Retention of some water-soluble vitamins during

home preparation of commercially frozen potato products. J Food Sci 46:1697�1700.

Ahmed J, Shivare US, Shandu KS. 2002. Thermal degradation kinetics of carotenoids and visual colour of

papaya puree. J Food Sci 67(7):2692�2695.

Azaıs-Braesco V, Grolier P. 2001. Vitamines liposolubles. In: Ambroise M, editor. Apports nutritionnels

conseilles pour la population francaise. Paris: Editions Tec and Doc. pp 221�248.

Becalski A, Lau PYB, Lewis D, Seaman SW. 2003. Acrylamides in food: occurrence, source and modelling.

J Agric Food Chem 51:802�808.

Bhaskarachary K, Sankar Rao DS, Deosthale YG, Vinodini Reddy K. 1995. Carotene content of some

common and less familiar foods of plant origin. Food Chem 54:189�193.

Bimbenet J-J, Duquenoy A, Trystram G. 2002. Genie des procedes alimentaires, des bases aux applications.

Paris: Dunob.

Boushell R, Potter NN. 1980. Effect of soaking-blanching conditions on vitamin C losses and other

properties of frozen French fried potatoes. J Food Sci 45:1207�1213.

Carlson BL, Tabacchi MH. 1986. Frying oil deterioration and vitamin loss during foodservice operation. J

Food Sci 51(1):218�221.

Chandler S. 1995. The nutritional value of bananas. In: Gowen S, editor. Bananas and plantains. London:

Chapman & Hall. pp 468�480.

De-Sa MC, Rodriguez-Amaya DB. 2003. Carotenoid composition of cooked green vegetables from

restaurants. Food Chem 83:595�600.

De-Sa MC, Rodriguez-Amaya DB. 2004. Optimization of HPLC quantification of carotenoids in cooked

green vegetables*Comparison of analytical and calculated data. J Food Comp Anal 17:37�51.


Dhuique-Mayer C, Caris-Veyrat C, Ollitrault P, Curk F, Amiot M-J. 2005. Varietal and interspecific

influence on micronutrient contents in citrus from the mediterranean area. J Agric Food Chem 53:2140�2145.

Emenhiser C, Sander LC, Schwartz SJ. 1995. Capability of a polymeric C30 stationary phase to resolve cis-

trans isomers in reversed-phase liquid chromatography. J Chromatogr 707:205�216.

Ferruzi MG, Sander LC, Rock CL, Schwartz SJ. 1998. Carotenoid determination in biological

microsamples using liquid chromatography with a coulometric electrochemical array detector. Anal

Biochem 256:74�81.

Fillion L, Henry CJK. 1998. Nutrient Losses and gain during frying: a review. Int J Food Sci Nutr 49:157�168.

Gall KL, Otwell WS, Koburger JA, Appledorf H. 1983. Effects of four cooking methods on the proximate,

mineral and fatty acid composition of fish fillets. J Food Sci 48:1068�1074.

Garcia MA, Ferrero C, Bertola N, Martino M, Zaritsky N. 2002. Edible coatings from cellulose derivatives

to reduce oil update in fried products. Innovative Food Science and Emerging Technologies 3:391�397.

Gokoglu N, Yerlikaya P, Cengiz E. 2004. Effects of cooking methods on the proximate composition and

mineral contents of rainbow trout (Oncorhynchus mykiss ). Food Chem 84:19�22.

Gordon MH, Kourimska L. 1995. Effect of antioxidants on losses of tocopherols during deep-fat frying.

Food Chem 52:175�177.

Guilland J-C, Grolier P. 2003. Repartition les vitamines dans la nature. In: Bourgeois CF, editor. Les

vitamines dans les industries agroalimentaires. Paris, France: Lavorsier. pp 25�56.

Hart DJ, Scott KJ. 1995. Development and evaluation of an HPLC method for the analysis of carotenoids in

foods, and the measurement of the carotenoid content of vegetables and fruits commonly consumed in

the UK. Food Chem 54:101�111.

Hasse NU, Weber L. 2001. Ascorbic acid losses during processing of French fries and potatoes chips. J Food

Eng 56:207�209.

Juarez MD, Alfaro ME, Samman N. 2004. Nutrient retention factors of deep-fried milanesa. J Food Comp

Anal 17:119�124.

Kimura M, Rodriguez-Amaya DB. 2002. A scheme for obtaining standards and HPLC quantification of

leafy vegetable carotenoids. Food Chem 78:389�398.

Krokida MK, Oreopoulou V, Maroulis ZB. 2000. Water loss and oil uptake as a function of frying time. J

Food Eng 44:39�46.

Mariano LA, Gonzalez AN, Pablo IS. 1969. Effect of maturity of chips prepared from saba banana (Musa

sapientum, Linn var. compressa ). Philippine J Nutr :171�180.

Ohlson T. 1980. Optimal temperature for sterilization of flat containers. J Food Sci 45:848�859.

Onyejegbu CA, Orolunda AO. 1995. Effect of raw materials, processing conditions and packaging on the

quality of plantain chips. J Sci Food Agric 68:279�283.

Padmavati K, Udipi SA, Rao M. 1992. Effect of different cooking on b-carotene content of vegetables. J

Food Sci Technol 29(3):137�140.

Pedreschi F, Moyano P, Kaack K, Granby K. 2005. Colour changes and acrylamide formation in fried

potatoes slices. Food Res Int 38:1�9.

Perkins EG, Erickson M, editors. 1996. Deep frying: chemistry, nutrition, and practical applications.

Champaign, IL: AOCS Press.

Pokorny J. 1999. Changes of nutrients at frying temperatures. In: Boskou D, Elmadfa I, (editors). Frying of

food: oxidation, nutrient and non-nutrient antioxidants, biologically active compounds and high

temperatures. Lancaster, PA: Technomic Publishing Company Inc. pp 9�25.

Polesello A, Rizzolo A. 1990. Application of HPLC to the determination of water-soluble vitamins in foods.

J Micronutr Anal 8:105�158.

Ravichandran R. 2001. Carotenoid composition, distribution and degradation to flavour volatiles during

black tea manufacture and the effect of carotenoid supplementation on tea quality and aroma. Food

Chem 78:23�28.

Rassolian M, Chass GA, Setiadi DH, Csizmadia IG. 2003. Asparagine: ab initio structural analyses. J Mol

Struct Theochem 666:273�278.

Sant’Ana Pinhero HM, Stringheta PC, Cardoso Brandao SC, Cordeiro de Azeredo RM. 1998. Carotenoid

retention and vitamin A value in carrot (Daucus carota L.) prepared by food service. Food Chem 61:145�151.

Sulaeman A, Keeler L, Giraud DW, Taylor SL, Wehling RL, Driskell JA. 2001. Carotenoid content and

physicochemical and sensory characteristics of carrot chips deep-fried in different oils at several

temperatures. Food Chem Toxic 66(9):1257�1264.


Sungpuag P, Tangchitpianvit S, Chittchang U, Wasantwitsu E. 1999. Retinol and b-carotene content of

indigenous raw and home-prepared foods in northeast Thailand. Food Chem 64:163�167.

Totte A, Diaz A, Marouzec, Raoult-Wack AL. 1996. Deep-fat frying of plantain (Musa paradisiaca L.). II.

Experimental study of solid/liquid phase contacting systems. Lebensm-Wiss u-Technol 29:599�605.

Valera G. 1988. Current facts about the frying of food. In: Valera G, Bender AE, Morton ID, (editors).

Frying of food: principles, changes, new approaches. Chichester: Ellis Horwood Ltd. pp 9�25.

Van de Broeck I, Ludikhuyze L, Weemaes C, Van Loey A, Hendrickx M. 1998. Kinetics for isobaric-

isothermal degradation of L-ascorbic acid. J Agric Food Chem 46:2001�2006.

Vitrac O, Bohuon Ph. 2004. Internal coupled heat and mass transfer during deep-frying of materials with

high water contents: application to apple chips fried at atmospheric pressure. In: International

Conference Engineering and Food, Montpellier, 7�11 March, pp. 1�6.

Vitrac O, Dufour D, Trystram G, Raoult-Wack A-L. 2002. Characterization of heat and mass transfer

during deep-fat frying and its effect on cassava chip quality. J Food Eng 53:161�176.

Vittadini E, Rinaldi M, Chiavaro E, Barbanti D, Massini R. 2005. The effect of different convection cooking

methods on the instrumental quality and yield of pork Longissimus dorsi . Meat Sci 69:749�756.

Zerrudo HD, editor. 1985. Banana and plantain. Cavendish banana chips and powder. Proceedings of the

International Seminar-Workshop on banana and plantain. Research and Development, Davao City,

Philippines, 1985.


Documents

Effect of Deep Fat Frying on Ascorbic Acid, Carotenoids an Potassium Contents of Plantain Cylinders