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The effect of storage conditions (temperature, light, time) andvariety on the glycoalkaloid content of potato tubers and sprouts

M. Sengul a,*, F. Keles a, M.S. Keles b

a Department of Food Engineering, Agricultural Faculty, Ataturk University, 25240 Erzurum, Turkeyb Department of Biochemistry, Faculty of Medicine, Ataturk University, 25240 Erzurum, Turkey

Received 31 August 2002; received in revised form 6 April 2003; accepted 7 April 2003

Abstract

The effects of variety, tuber group, storage period and storage type on glycoalkaloid levels of potato tubers and sprouts wereinvestigated. Normal, wounded and greened tubers and sprouts from potatoes of varieties Marfona and Granola were analysed for

a-solanine, a-chaconine and total glycoalkaloid concentration by using HPLC. The potatoes were stored in normal store light,

normal store dark, retail refrigerator light, and retail refrigerator dark. Analyses were carried out at the beginning, 3rd and 6th

months for the potatoes, and at 6th month for the sprouts. The tubers had an a-solanine content ranging from 0.01 to 6.46 mg/kg

FW, a-chaconine content from 0.35 to 28.12 mg/kg FW and total glycoalkaloid content from 0.66 to 32.76 mg/kg FW.

2003 Elsevier Ltd. All rights reserved.

Keywords: Potato; Glycoalkaloid; HPLC

1. Introduction

Potatoes (Solanum tuberosum L.) have an important

role in the nutrition since they contain high amounts

of carbohydrate and high-quality protein. They also

contain toxic compounds called glycoalkaloid (GA)

(Friedman & McDonald, 1997). GA are compounds

containing nitrogen, which naturally occur in the mem-

bers ofSolanaceaeor Nightshadefamily such as potato,

tomato, eggplant, sweet pepper, nightshade, thorn apple,

and tobacco (Carman, Kuan, George, Francis, & Kirs-

chenheuter, 1986; Friedman & McDonald, 1997).

GA play an important role in the natural defence

mechanism against some organisms like fungi, insects,

viruses and herbivores (Ferreira, Moyna, Soule, &

Vazquez, 1993; Hlywka, Stephenson, Sears, & Rickey,1994; Rodriguez-Saona, Wrolstad, & Pereira, 1999). In

addition it has been reported that GA has caused illness

and even death in people, livestock, and farm animals

(Thomson & Sporns, 1995). The lower contents of gly-

coalkaloids found in potatoes has affected their tastes

positively (Abell & Sporns, 1996; Plhak & Sporns, 1992).

When the amount of glycoalkaloid reaches 15 mg glyco-

alkaloid/100 g fresh weight (FW), a bitter taste occurs

(Mondy, Tymak, & Chandra, 1978). It was stated that

the safe upper limit for human is 20 mg glycoalkaloid/

100 g FW (Hlywka et al., 1994; Papathanasiou, Mitchell,

& Harvey, 1999).

More than 95% of the total glycoalkaloids (TGA)

found in potato is composed ofa-solanine and a-chac-

onine (Mondy & Munshi, 1993; Morgan, McNerney,

Matthew, Coxon, & Chan, 1983; Percival, 1999; Saito,

Horie, Hoshino, & Nose, 1990). GA is found in flowers,

sprouts, eyes, unripe berries, young leaves that have a

high metabolic activity, and tubers and peels (Rodri-

guez-Saona et al., 1999) however, it is concentrated in

peripheral layers of the tuber and in parenchyma of

periderm cells (Mondy & Ponnampalam, 1983). Growth

condition, maturity, variety, fertilization, early harvest,exposure to phytopathogens, temperature extremes be-

fore and after harvest, exposure to light, mechanical

damages such as cutting and slicing following harvest

and sprouting are the factors affecting the amount of

TGA (Bushway, Bureau, & McGann, 1983; Bushway,

Bureau, & King, 1986; Mondy & Ponnampalam, 1985).

Before harvesting, the amount of GA is decreases with

growth and ripening of the potatoes (Lisinska & Les-

zczynski, 1989).

Packing of the potatoes with some packaging mate-

rials to protect them from light, irradiating, treating

* Corresponding author. Tel.: +90-442-231-2490; fax: +90-442-236-

0958.

E-mail address: [email protected](M. Sengul).

0956-7135/$ - see front matter 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0956-7135(03)00077-X

Food Control 15 (2004) 281286

www.elsevier.com/locate/foodcont
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with chemicals and storing in controlled atmosphere can

prevent synthesis of chlorophyll and alkaloid, and

sprouting (Wu & Salunkhe, 1972).

The amount of glycoalkaloid is usually determined by

spectrophotometry, titration, and colorimetry, HPLC,

TLC, ELISA and MALTI-TOF MS. The analysing

both glycoalkaloids and aglycons individually and the

performing of the analysis at room temperature are the

important advantageous of HPLC (Hsl, 1994; Husgen

& Schuster, 1996; Yetim, 2001).

When the potatoes with increased GA levels were

consumed, very bad off-flavor were feeled. Acute and

chronic poisoning and even death can be caused by

taking up GA in high dosages. So, the condition of

potatoes storage were critical importance. The aim of

this study is to investigate the effects of the several fac-

tors including variety, tuber group, storage period, and

storage type on the glycoalkaloid contents of tubers and

sprouts in Marfona and Granola varieties, and to de-

termine storage conditions.

2. Materials and methods

2.1. Materials

2.1.1. Potatoes

Two potato cultivars, Marfona and Granola were

used in this study. Marfona was obtained from the

Agricultural Research and Extension Centre, at the

University of Ataturk, Faculty of Agriculture, Granola

was obtained from the Eastern Anatolia Agricultural

Research Institute during the 1999 growing season.

Potatoes of medium size and uniform shape were

selected from each variety in order to limit the variations

from size differences. After curing period, the tubers

from each cultivar were divided into three groups as

normal (unwounded, ungreened), wounded (mechani-

cally damaged) and greened, then the initial GA deter-

minations were analysed. The remainder of tubers were

placed into the stores for six months. The GA analysis

was performed to the tubers of potatoes at the beginning

and at the end of the 3rd and 6th months. GA was also

determined in the sprouts of the potatoes at the end of

the 6th month.Four types of stores were used in the research. Tubers

were placed into store at 10.219.2 C, 4053% RH for

normal store light (NSL) and the normal store dark

(NSD). For the retail refrigerator light (RL) and the

retail refrigerator dark (RD) stores, tubers were stored

at 58 C, 5560% RH.

2.1.2. Reagents

HPLC grade acetonitrile, tetrahydrofuran, methanol,

water (Lab-Scan), ACS grade ammonium hydroxide

(Sigma), GR HCl (Merck), extra pure H2SO4 (Merck),

a-solanine, a-chaconine (Sigma) were used in the re-

search. HPLC grade water was used for the preparation

of the HPLC mobile phase and extracting solutions.

2.2. Methods

2.2.1. Sample preparation

The potatoes peeled were diced and placed in refrig-

erator bags then were frozen by dipping into liquid ni-

trogen ()196 C). On the other hand, the sprouts formed

during storage of six months were chopped and frozen

as recited. The frozen potatoes and sprouts were lyo-

philised and kept in the deep-freeze ()2 0 1 C) until

the analysis had been done. The lyophilised potatoes

were ground by laboratory mill and screened by 38 mesh

screen to become powder and then extracted as follows

(Friedman & Dao, 1992).

2.2.2. Extraction method

Determination of glycoalkaloid was done accordingto Friedman and Dao (1992) and Bushway, Barden,

Wilson, and Bushway (1980). Some compulsory modi-

fications were made in the extraction process. Forty

mililitres of tetrahydrofuranwateracetonitrile (5:3:2,

v/v) was added to 5 g of potatoes in powdered form and

then the mixture was homogenized in a Waring blender

for 15 min. Two grams of powdered sprouts were taken

as sample. The mixture was centrifuged for 10 min by

using a DAMON/IEC DIVISION B-60 Model ultra-

centrifuge at 18,300 rpm (30,000 g) to collect the su-

pernatant. The supernatant was concentrated to 1015

ml in the rotary evaporator (Heidolph-5111 Model). 0.2

N HCl (15 ml) was added to this concentrated solution

slowly with continuous stirring. The mixture was soni-

cated for 5 min using an ultrasonic cleaner Bandelin

Sonorex Super RK 103H. After the suspension was

centrifuged at 10 C for 25 min in 30,000 g, the su-

pernatant was transferred in round bottom flasks and

pH was adjusted to 1011. The basic solution was al-

lowed to stand in a water bath at 70 C for 30 min. After

cooling the solution in the refrigerator overnight, the

precipitate was washed up with 1% ammonium hy-

droxide solution, then centrifuged at 4 C for 25 min and

the pellet was collected. The air-dried pellet was then

dissolved in 20 ml of methanol and boiled for 10 min.The hot suspension was filtered by using a 0.45 lm

membrane filter. The solution was concentrated to 1 ml

in the rotary evaporator and of 20 ll was used for

HPLC analysis.

2.2.3. HPLC procedure

A high performance liquid chromatography (HPLC)

method based on Friedman and Dao (1992) was used. A

Hewlett Packard 1100 Model HPLC system with iso-

cratic pump and diode array detector was used. The

column was Alltech Hypersil BDS C18 5l cartridge

282 M.Sengul et al. / Food Control 15 (2004) 281286


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column + guard column with dimensions of 250 4.6

mm was used. The mobile phase consisted of 50%

acetonitrile containing 5 mM sodium lauryl sulfate

(Sigma) and 5 mM sodium sulfate decahydrate (ACS

grade). The pH of the solution was adjusted to 4.5 with

1% of sulphuric acid. The solvent flow rate was 1ml/min,

and the UV absorbance was monitored at 200 nm. A

glycoalkaloid stock solution (1 mg/ml) was prepared by

dissolving a-solanine and a-chaconine in methanol.

2.3. Statistical analysis

In the study, four different storage type (NSL, NSD,

RL, RD), three different storage period (0, 3 and 6

months) three different potato group (normal, wounded,

greened) and two variety (Marfona and Granola) were

selected as experimental factors. The analysis was car-

ried out according to completely randomized blocks

design with four replications. The MINITAB package

programme was applied to the data obtained from the

research to perform variance analysis (Gurbuz, 1993).

The averages belong to the main parameters that found

statistically important were compared with the Duncan

multiple comparison test method (Yldz & Bircan,

1989).

3. Results and discussion

Total glycoalkaloid, a-solanine and a-chaconinecontent of potatoes are given in Table 1. There were

significant differences between the mean tuber a-sola-

nine, a-chaconine and total glycoalkaloid contents of

cultivars P


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a-solanine and a-chaconine were lowest in the normal

potatoes. Usually, the potatoes stored under light were

found to contain morea-solanine and a-chaconine than

those stored in the dark. It was determined that the

potatoes stored in the NSL and RL contained higher

amount ofa-solanine and a-chaconine than those in the

other two stores potatoes.

Clearly tuber glycoalkaloid production is affected by

mechanical damage, greening, temperature and day-

light. Light and mechanic damage were reported asbeing the most important environmental stress agents on

the synthesis of glycoalkaloid in the potato tubers after

the harvesting (Wu & Salunkhe, 1977), nevertheless the

effect of light was found to be greater (Edwards & Cobb,

1996). Such a response is now well established and has

been reported by workers elsewhere (De Maine, Bain, &

Joyce, 1988; Gosselin & Mondy, 1989; Haddadin, Hu-

meid, Qaroot, & Robinson, 2001; Plhak & Sporns,

1992).

The effect of storage period tuber group interaction

were significant on a-chaconine and total glycoalkaloid

amount at P


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other groups. Dao and Friedman (1994) found out that

when the potatoes were stored for three days, a-chaco-

nine was increased by 62%, and when they were stored

for 16 days, it was increased 300%, but decreased at the

end of the day twentieth.

The amounts of total glycoalkaloid of the potatoes

were affected by storage period and storage type inter-

action P


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