M.abboudi et al. Gamma irradiation, blanching, acrylamide
The combined effects of gamma irradiation and blanching process on acrylamidecontent in fried potatostrips
M. Abboudi1*, M.Albachir1, Y.Koudsi1,H.Jouhara2
1 Atomic Energy Commission, P.O. Box 6091, Damascus, Syria
2RCUK Centre for Sustainable Energy Usein Food Chains, Brunel University London, Uxbridge, Middlesex, UB8 3PH, UK, Email:
* Corresponding author:
E-mail addresses: (Maher ABBOUDI)
For submission to: International Journal of Food Properties
Abstract
Potato tubers were irradiated in60Cogamma 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, topotato stripsbefore frying has decreased acrylamide by 61%.A combination of gamma irradiation and blanchingprocesswhich 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 (CH2CHCONH2) in some carbohydrate-rich foods cooked at high temperatures. TheAcrylamide, which isa odourlesswhite or colourlesscrystalline solids,formedduring the heat treatment of carbohydrate-rich foods as a result of the Maillardnon-enzymatic browning reactionbetweenthe amino acid asparagine and reducing sugars. Many researchers havereported that acrylamidewas notdetected in uncooked or boiled foods[1-5].
Acrylamidehas been found in different concentrations in a variety of popular foods, including potato chips, French fries, biscuit, coffeeand bread [6-9].Ithas a toxologigical effect and so it is classified as probablehuman carcinogen with a potential health risk[1,10-13].Given the popularity of fried potatostrips, becauseof its acceptable prices and nutritional-rich value, many researchers are focusing their research activities to evaluate this food’ssafety.Chenet14 al.(2012) provided a link between high cancer risksin adolescents whentheacrylamide concentration is higher than 168 µg/kg,based on French fries intake.
Different factors could affect the acrylamide formationin 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 aimedat 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)changingthe storage conditions by modifyingthetime, temperature, humidity and aeration[17-19], (3) pre-treatment such asimmersion in a saltyor acidic solution, [13,16, 20-21]but this studies did not investigate the probable effects of theseadditions on the final products during/and after frying.Blanching the potato strips in warm water for a few minutes before fryingcould 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 investigatedthe 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 irradiatingthe tubers followed bythermal treatment (blanching in warm tapwater) in order to reduce the amount of precursors of the Millard reaction.
Materials and methods
Samples of potato tubers cv. Spuntagrown in Damascus, Syriawere 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)
Potatotuberssamples were exposed to gamma radiation at doses of 0, 50, 100 and 150 Gy in a 60CO 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.Allanalyses were performed on controls and treated samples immediately after irradiation.
Irradiated and non-irradiated potato tubers werepeeledand cut into strips of 1 cm x 1cm x 5 cm with French fries-shaped cutter. Irradiated and non-irradiated stripswere divided into twolots. One lot was fried (100 g of strips in each replicate)in one literof 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 equippedwith a thermostat. 100 g of strips fromnon-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 gof raw potato tubers (washed and peeled)were blended for 15 s in a laboratory blender, and wereused in all the chemical analysis. Each sample was homogenized and analyzed in triplicates.Todetermine the moisturecontent,samples were driedat 105oC for6h Tomeasure theash content,samples were incinerated in a muffle furnaceat 550oC for4 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 measuredby 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 perkgpotato[27].
Acrylamide analysis
Reagent and standard:
Acrylamide (>99%) was obtained from Fluka, methanol analytical grade fromMerck.Water used throughout the experimentswas bidistilled deionized and passed through 0.22 µmfilters. 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 inconcentrations from 3 to 35 mg/Kg with distilled water. All stock and standard solutions were kept at 4ºC.
Sample preparation:
Friedpotato 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 thesuspension was centrifuged at 10000 rpm at0°C for 20 min, the clear supernatant was quantitativelycollectedand loaded through the Strata X (SPE) cartridges.Thecartridgeswere preconditioned 2 timesuing 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. Allresultant eluentswere passed through a 0.45µm filter and analyzeddirectly by the HPLC.
HPLC analysis:
The quantification of acrylamide was performed usingAgilent- 1100 Series HPLC system, the chromatographic separations were performed onAgilent-ZORBAX-Eclipse 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 usingVis-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 irradiationonchemical composition of raw potato
Characterization of potato tubers are listedin 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 potatoirradiatedat the same doses and thenblanchedin warmtap water. The concentrations of acrylamide at the first treatment only irradiated with0Gy, 50Gy, 100Gy, 150Gy were4551±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 induceda significant decrease in acrylamide formationinfrying; this decrease was of 20, 27, and 54% in irradiated potato by 50Gy, 100Gy and150Gy, respectively, compared to the control. Blanching un-irradiated potato stripsdecreased acrylamide significantly by 61% the acrylamide concentration compared to the control.Blanching irradiated potato at the same radiation dosesas 50Gy, 100Gy and150Gy abovecaused 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 chromatogramsof 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 peaksarea in the second combined treatment (Fig.3)of irradiation dose and blanchingwithwarm water. The acrylamide concentration in our studyhas ranged within the value that was indicated byBrunton(2007)32, Mestdagh et al.(2007)33, Pedreschi et al. (2008)34, Ou et al. (2008)21, Vinci et al. (2012)16.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 decreaseinacrylamide concentration proportionallyto the applied dose (Figure 1).No significant differences in reducingsugars of potato tubers were observed in the current investigation due to irradiation (table 1). On the other hand, Lu et al.(2012)26 indicated that gamma irradiation induced an increase in glucose contentby the degradation of starch in potato tuberwhichcouldin turn increase the acrylamide formation during frying. The differenteffects seen of the gamma irradiation on the potato tubers could be attributed to the type of potato and to its chemical properties. Soit 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 interestedinthe reduction ofthe 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 studiessuggested reducing the formation of acrylamide in fried potato and crisps by using some additives such as organic acids(citic, acetic, lactic acid), salts(NaCl, CaCl2, MgCl2), hydrocollids, enzymes, anagent's inhibitors as reported byOu et al. (2008)21, Zeng (2010)37, Vinci et al. (2012)16, Kalita and Jayanty (2013)13.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 solelyby 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 compositionof the irradiated potato,measuringthe asparagines and reducing sugar content and their effects on acrylamide formationbefore and after each treatment. Thus, optimizing the gamma irradiation dose and the blanching process could significantly reduce the acrylamide content in fried potato.
Conclusion
Gammairradiation wascapable of reducing the acrylamide formation by 20-54% whereasthe combination of gamma irradiation with blanching thepotato 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 sproutingcould be considered as aneffective 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 scaleto loweracrylamide in fried potato strips.
Acknowledgements
The authors wish to express their deep appreciation to theDirector General of Atomic Energy Commission of Syria, and the Head of chemical department, and to A.Odeh, A. Alkaid.
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