The combined effects of gamma irradiation and blanching process on acrylamidecontent in fried potato stripsM. Abboudi

The combined effects of gamma irradiation and blanching process on acrylamide content in fried potato strips

M. Abboudi

*, M. Albachir

, Y. Koudsi

, H. Jouhara

1

Atomic Energy Commission, P.O. Box 6091, Damascus, Syria

2

RCUK Centre for Sustainable Energy Use in Food Chains, Brunel University London, Uxbridge, Middlesex, UB8 3PH, UK, Email: hussam.jouhara@brunel.ac.uk

* Corresponding author:

E-mail addresses: Scientific@aec.org.sy ( Maher ABBOUDI)

For submission to: International Journal of Food Properties

Abstract

Potato tubers were irradiated in

Co gamma station at different doses in order to investigate the effect of gamma irradiation on acrylamide formation in fried potato strips. Acrylamide content due to the irradiation treatment was reduced by 20-54%

compared to a control after frying the irradiated tubers. While apply a blanching process, using warm tap water, to potato strips before frying has decreased acrylamide by 61%. A combination of gamma irradiation and blanching process which applied in this work, showed a maximum decrease in acrylamide formation in fried potato reach to 78 %.

Keywords: Acrylamide; Gamma irradiation; Blanching; Fried potato

Introduction

The Swedish National Food Administration reported in 2002 for the first time the presence of acrylamide (CH

CHCONH

) in some carbohydrate-rich foods cooked at high temperatures. The Acrylamide, which is a odourless white or colourless crystalline solids, formed during the heat treatment of carbohydrate-rich foods as a result of the Maillard non-enzymatic browning reaction between the amino acid asparagine and reducing sugars. Many researchers have reported that acrylamide was not detected in uncooked or boiled foods [1-5].

Acrylamide has been found i n different concentrations in a variety of popular foods, including potato chips, French fries, biscuit, coffeeand bread [6-9]. It has a toxologigical effect and so it is classified as probable human carcinogen with a potential health risk [1,10-13]. Given the popularity of fried potato strips, because of its acceptable prices and nutritional-rich value, many researchers are focusing their research activities to evaluate this food’s safety. Chen et

al. (2012) provided a link between high cancer risks in adolescents when the acrylamide concentration is higher than 168 µg/kg, based on French fries intake.

Different factors could affect the acrylamide formation in fried potato products:

production and environmental factors, cooling and post-harvest processing: pre- treatment as blanching in warm water; temperature and times of frying; the temperature of the final stage of the frying process, type of fryers [4,13,15-16].

Due to the importance of acrylamide concentration reduction in cooked food, many

studies are aimed at reducing the precursors that form acrylamide in carbohydrate-rich

food by different ways namely (1) choosing new kinds of potatoes with less reducing

sugar or/and less amino acids, (2) changing the storage conditions by modifying the

time, temperature, humidity and aeration [17-19], (3) pre-treatment such as immersion

in a salty or acidic solution, [13,16, 20-21] but this studies did not investigate the probable effects of these additions on the final products during/and after frying.

Blanching the potato strips in warm water for a few minutes before frying could improve the quality of the Frinch fries [12,19].

Gamma irradiation or electron beam treatment can be used for sprout inhibition of potato tubers in some raw food (as potato) and for insect disinfection [22-23]. The commercial food irradiation has been allowed after the recommendation of the wholesomeness of food irradiation by the joint FAO/IAEA/WHO [24]. Recently few studies investigated the effect of irradiation on the level of acrylamid in fried potato [25-26].

This present study represents an original work which aims to reduce acrylamide concentrations in fried potato by irradiating the tubers followed by thermal treatment (blanching in warm tap water) in order to reduce the amount of precursors of the Millard reaction.

Materials and methods

Samples of potato tubers cv. Spunta grown in Damascus, Syria were obtained from a local supplier, packed in cotton pouches. Then potato tubers were weighed as in the sampling plan and transferred into polyethylene plastic bags, labelled and identified with respective radiation. Each bag of potato tubers (5 kg) is considered as a replicate.

Potato treatment ( irradiation, blanching)

Potato tubers samples were exposed to gamma radiation at doses of 0, 50, 100 and

150 Gy in a

CO package irradiator (dose rate 848 Gy/h). The irradiation was

performed at room temperature. The absorbed dose was determined using alcoholic

chlorobenzene dosimeter [27]. For each treatment, 3 boxes of potato tubers were used.

All analyses were performed on controls and treated samples immediately after irradiation.

Irradiated and non-irradiated potato tubers were peeled and cut into strips of 1 cm x 1cm x 5 cm with French fries-shaped cutter. Irradiated and non-irradiated strips were divided into two lots. One lot was fried (100 g of strips in each replicate) in one liter of sunflower oil at 170±0.5 °C for 5 min in an electrical thermostated deep fryer (Molinex). The second lot was blanched using water bath equipped with a thermostat.

100 g of strips from non-irradiated (control) and from irradiated potato strips were heated at 85±0.5°C for 5 min in 500 mL tap water and then drained before frying at 170±0.5 °C for 6 min. One litre of sunflower oil was used for each replicate. The fried potatoes were stored at 4°C until analysis.

Potato characterization

Approximately 150 g of raw potato tubers (washed and peeled) were blended for 15 s

in a laboratory blender, and were used in all the chemical analysis. Each sample was

homogenized and analyzed in triplicates. To determine the moisture content, samples

were dried at 105

C for 6h To measure the ash content, samples were incinerated in a

muffle furnaceat 550

C for 4 h, crude fat (as extractable component in Soxhlet

apparatus), crude protein (as Kjeldahl nitrogen) were measured using standard

methods [28]. Total sugar was analysed using Anthrone indicator method by

measuring the absorbance at 620 nm with a T70 UV/VIS Spectrophotometer (PG

Instrument Ltd). The reducing sugar was measured by iodometric determination of the

unreduced copper remaining after reaction, and the concentration of reducing sugar

was expressed as g glucoseper 100 g powders of dried potato [28]. Total volatile basic

nitrogen (TVBN) in the sample was determinedin term of mg TVBN per kg potato

[27].

Acrylamide analysis Reagent and standard:

Acrylamide (>99%) was obtained from Fluka, methanol analytical grade from Merck.

Water used throughout the experiments was bidistilled deionized and passed through 0.22 µm filters. Strata X (SPE) cartridges were supplied by phenominex.

Stock solution of acrylamide was prepared by dissolving 1mg of acrylamide in 1L of distilled water. A set of standards for HPLC analysis were prepared by appropriate dilution of the stock solution in concentrations from 3 to 35 mg/Kg with distilled water. All stock and standard solutions were kept at 4ºC.

Sample preparation:

Fried potato strips (100 g) were ground and homogenized and then 10 g were

weighed. The sample was suspended in 25 ml mobilephase (water-methanol 95:5,v/v) and vortexed for homogenizing for 15 min. Then the suspension was centrifuged at 10000 rpm at 0°C for 20 min, the clear supernatant was quantitatively collected and loaded through the Strata X (SPE) cartridges. The cartridges were preconditioned 2 time suing 2 ml methanol and 2 ml of water at a rate of 2 ml per min. The acrylamide residues in the cartridges were eluted with 1ml of water and collected. All resultant eluents were passed through a 0.45µm filter and analyzed directly by the HPLC.

HPLC analysis:

The quantification of acrylamide was performed using Agilent- 1100 Series HPLC

system, the chromatographic separations were performed on Agilent-ZORBAX-E

clipse XDB-C8 (4.6x150mm) 5 µm column. The flow rate of the mobile phase

(water-methanol 95:5,v/v) was 0.5 ml/min, the injection volume was 50µl. The

analysis was performed at un ambient temperature using Vis-UV detector at detection

wavelength of 210 nm.

Statistical analysis

The four irradiation doses and two heating treatments were distributed in a completely randomized design with three replicates. Data were subjected to the analysis of variance test (ANOVA) using the SUPERANOVA computer package (Abacus Concepts Inc, Berkeley, CA, USA; 1998). A separation test on treatment means was conducted using Fisher’s least significant differences (LSD) methods at 95% confidence level [29].

Results and discussion

Effect of gamma irradiation on chemical composition of raw potato

Characterization of potato tubers are listed in Table (1). No significant differences in dry protein, moisture, ash, crud protein, total carbohydrate, starch and reduction sugar were observed in potato tubers post irradiation.

Immediately after irradiation, TVBN value of non-irradiated control sample of potato was 114 mg/kg potato. TVBN values decreased significantly (p>0.05) according to irradiation doses (Table 1). The TVBN is related to protein breakdown [30], and the observed increases may be attributed to the formation of ammonia or other basic compounds. It is obvious that as irradiation doses increased, high energy is absorbed by the food substrate given rise to generation of new volatile compounds through oxidation [31].

Effect of gamma irradiation and blanching on acrylamide formation

Figure (1) presents the variation of acrylamide concentration of irradiated potato at low doses: 0Gy, 50Gy, 100Gy, 150Gy and potato irradiated at the same doses and then blanched in warm tap water. The concentrations of acrylamide at the first

treatment only irradiated with 0Gy, 50Gy, 100Gy, 150Gy were 4551±456, 3629±248,

3310±273, 2073±247μg/Kg, respectively; while at the second combined treatment

(irradiated and blanched) the acrylamide concentrations were1768±323, 1487±106, 1339±54, 1010±141 μg/Kg, respectively. Gamma irradiation in the raw potato tuber induced a significant decrease in acrylamide formation in frying; this decrease was of 20, 27, and 54% in irradiated potato by 50Gy, 100Gy and 150Gy, respectively, compared to the control. Blanching un-irradiated potato strips decreased acrylamide significantly by 61% the acrylamide concentration compared to the control. Blanching irradiated potato at the same radiation dosesas 50Gy, 100Gy and 150Gy above caused a decrease of 67, 70 and 78 % respectively, in acrylamide concentration, compared to un-irradiated un-blanched potato (control). Figures 2 and 3 represent typical

chromatograms of acrylamide and they show the decrease in the peaks area due to the

applied dose of gamma irradiation (Fig.2) and also the decrease in peaks area in the

second combined treatment (Fig.3) of irradiation dose and blanching with warm

water. The acrylamide concentration in our study has ranged within the value that was

indicated by Brunton (2007)

, Mestdagh et al. (2007)

, Pedreschi et al. (2008)

, Ou

et al. (2008)

, Vinci et al. (2012)

. The low dose of gamma irradiation has a good

effect on the quality of potato [22] and also the inhibition of potato sprouting in

addition it would decrease the reducing sugars during storage and consequently

reduce the concentration of acrylamide by influencing the Maillard reaction [25]. The

obtained results showedthat gamma irradiation caused a decrease in acrylamide

concentration proportionally to the applied dose (Figure 1). No significant differences

in reducing sugars of potato tubers were observed in the current investigation due to

irradiation (table 1). On the other hand, Lu et al. (2012)

indicated that gamma

irradiation induced an increase in glucose content by the degradation of starch in

potato tuber which could in turn increase the acrylamide formation during frying. The

different effects seen of the gamma irradiation on the potato tubers could be attributed

to the type of potato and to its chemical properties. So it can be assumed that gamma irradiation affected other acrylamide precursors -principally Asparagine-which had the ability to reduce the acrylamide content in the fried potato. Previous studies were interested in the reduction of the acrylamide precursor by blanching the potato slices in preheated water (50-90ºC) for different periods (2-70min), this pre-treatment could reduce sugars and/or asparagine and then could reduce the acrylamide formation (51- 81%) [20,19,35-36]. Other studies suggested reducing the formation of acrylamide in fried potato and crisps by using some additives such as organic acids (citic, acetic, lactic acid), salts (NaCl, CaCl

, MgCl

), hydrocollids, enzymes, an agent's inhibitors as reported by Ou et al. (2008)

, Zeng (2010)

, Vinci et al. (2012)

, Kalita and Jayanty (2013)

. According to our knowledge there are no studies that evaluated impacts of these additives on the fried potato and on the oil used in frying, which may influence the quality and the safety of fried potato. Therefore, it is suggested that blanching the potato strips solely by warm water is more likely to be a safer procedure compared to the additives. It is important to expand the research by examining the impact of storage, on the changes in the chemical composition of the irradiated potato, measuring the asparagines and reducing sugar content and their effects on acrylamide formation before and after each treatment. Thus, optimizing the gamma irradiation dose and the blanching process could significantly reduce the acrylamide content in fried potato.

Conclusion

Gamma irradiation was capable of reducing the acrylamide formation by 20-54%

where as the combination of gamma irradiation with blanching the potato strips in

warm tap waterprior to frying reduced the acrylamide concentration by 67-78%. The

treatment of tubers by gamma irradiation in order to prevent sprouting could be

considered as an effective process to reduce the acrylamide content in fried potato,

and a further simple technique of blanching the potato strips prior to frying accounted

for a more significant decline in the acrylamide level. Hence, the combination of the

two treatments could be potentially useful on an industrial scale to lower acrylamide

in fried potato strips.

Acknowledgements

The authors wish to express their deep appreciation to the Director General of Atomic Energy Commission of Syria, and the Head of chemical department, and to A. Odeh, A. Alkaid.

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Figure 1: Acrylamide concentrations in fried potato in two different treatments (A:

irradiating by low gamma doses + Frying; B: combined treatment of irradiation at 4 low gamma doses+

Blanching by warm water + Frying).

Figure 2: Typical chromatogram of acrylamide for the first treatment (potato tubers irradiated with low doses of gamma irradiation [ (1) Blanc, (2) 50Gy, (3) 100 Gy, (4) 150 Gy]

before fraying .

Figure 3: Typical chromatogram of acrylamide for the combined treatment (potato tubers irradiated with low doses of gamma irradiation [ (1) Blanc, (2) 50Gy, (3) 100 Gy, (4)

150 Gy] and then blanching the strips by warm tap water before fraying .