ORIGINAL PAPER

Changes in Chemical and Microbial Qualities of DriedApricots Containing Sulphur Dioxide at Different LevelsDuring Storage

Meltem Türkyılmaz & Şeref Tağı & Mehmet Özkan

Received: 9 November 2011 /Accepted: 30 April 2012 /Published online: 17 May 2012# Springer Science+Business Media, LLC 2012

Abstract Effects of different sulphur dioxide (SO2) concen-trations (188, 452, 791, 1,034, 1,236, 2,899 and 3,864 mgSO2 kg

−1) and storage temperatures (5, 10, 20 and 30 °C) onthe physical, chemical and microbial qualities of sulphited-dried apricots (SDAs) were evaluated. Analysis of kineticdata suggested first-order models for losses of moisture andSO2 and formation of brown colour. Strong correlationswere found between SO2 concentrations and moisture lossconstants (r0−0.943), and brown colour values (r00.949).β-carotene contents in SDA samples ranged from 26.6 to36.2 mg 100 g−1 dry weight, depending on SO2 content ofdried apricots. The SO2 concentration over 791 mg per kg ofdried apricots effectively protected carotenoids in driedapricots during drying. While storage times had significanteffect on β-carotene contents, storage temperatures did nothave such effects. The number of total mesophilic aerobicbacteria in all SDA samples ranged from 8.20×101 to 1.84×102 CFU g−1. The number of total psychrophilic aerobicbacteria, lactic acid bacteria, yeast and mould, xerophilicmould, Staphylococcus spp. and total Enterobacteriaceaewere below the detection limits (<4 CFU g−1) in samplescontaining SO2 even at the lowest level (188 mg SO2 kg

–1)throughout the storage. Regardless of SO2 concentration indried apricots, low storage temperatures (below 20 °C)

should be preferred to prevent the characteristic goldenyellow colours of dried apricots.

Keywords Dried apricots . SO2 level . Browning .

β-carotene . Microbial growth . Storage

Introduction

Apricots are grown in many countries in the world. Turkey,Iran, Pakistan, Uzbekistan and Italy are the major apricotsproducers. Turkey is also a primary supplier of dried apri-cots to the world (FAOSTAT 2011). In fact, Turkey makesup to 84 % of the world’s total dried apricot production,supplying 98,000 tons (FAOSTAT 2011). USA, England,Russia, Germany, France and Australia are the primaryimporter countries of Turkish dried apricots with a share ofca. 60 % (Asma 2011).

Drying is an effective and low-cost preservation methodfor fruits and vegetables. As a result of removal of freewater, i.e. lowering the water activity, from fruits and veg-etables during drying, the growth of microorganisms is sup-pressed, thus preventing the spoilage of fruits andvegetables. Despite the detrimental effects on microorgan-isms, drying process has negative effect to the colour offruits and vegetables. Most dried fruits do not have attrac-tive colour for consumer appreciation since enzymatic andnon-enzymatic browning reactions lead to the loss of char-acteristic colour of fruits and vegetables, including apricots,during drying and storage.

In the presence of molecular oxygen, the polyphenol oxi-dase enzymes cause undesirable brown colour by reactingwith polyphenols to yield dopaquinone which further under-goes reactions to form brown coloured melanin pigments.According to Torre (2009), enzymatic browning results from

M. Türkyılmaz (*)Ministry of Food, Agriculture and Animal Husbandry,Golbasi District Directorate of Agriculture,Golbasi,06830 Ankara, Turkeye-mail: meltemturkyilmaz@gmail.com

Ş. Tağı :M. ÖzkanDepartment of Food Engineering, Faculty of Engineering,Ankara University,Diskapi Campus, Diskapi,06110 Ankara, Turkey

Food Bioprocess Technol (2013) 6:1526–1538DOI 10.1007/s11947-012-0884-8

(1) hydroxylation of monophenols (e.g. tyrosine), (2) oxida-tion of O-quinones (e.g. 3-4-dihydrophenylalanine, L-dopa),which are very reactive and either undergo further oxidation tobrown coloured melanin pigments or participate in the poly-merization reactions with protein functional groups to formcross-linked polymers (Wong and Stanton 1989; Dao andFredman 1992), and (3) polymerization of melanins fromthe previous oxidation products, which proceeds without theaid of enzymes.

While polyphenols as a substrate for enzymatic browningare more important in the formation of brown colour in driedapricots during drying, sugars as a substrate for non-enzymatic browning are more important during storage.The most important non-enzymatic reaction in which thereducing sugars participate during storage of dried fruits isMaillard reaction. In this reaction, the reactive anomericcarbonyl group of the reducing sugar reacts with the nucle-ophilic amino group of amino acid, causing browning infoods. The products formed during this reaction are the mainquality indicators of dried fruits since this reaction occursduring storage depending on the storage temperature andtime, and sugar and amino acid compositions of the fruit.

Dried apricots are usually treated with sulphur dioxide(SO2) for both inhibiting the enzymatic browning duringdrying and providing the protection from non-enzymaticbrowning reactions as well as prevention of microbial dete-rioration during drying and storage. The maximum limit of2,000 mg SO2 per kg of dried apricots is accepted by mostcountries, including Turkey (Codex Alimentarius Commis-sion 1989). However, both enzymatic browning reactions(depending on the origin of enzyme and polyphenol con-tents of fruits) and non-enzymatic browning reactions(depending on reducing sugar and amino acid contents offruits) have varying sensitivity to chemical inhibitors suchas SO2. Therefore, the effects of different chemical inhibitordosages on the quality of dried fruits need to be determined.

In this study, the effects of different SO2 concentrationson the physical, chemical and microbiological qualities ofdried apricots during storage at different temperatures wereevaluated since the dosages of SO2 and storage temperaturehave the most important effects on the quality parameters,especially colour, of dried apricots. Therefore, the primarypurpose was to determine which storage temperature is moresuitable for each of the dried apricot samples containing SO2

at different levels.

Materials and Methods

Materials

Fresh apricots (Prunus armenica L., var. Hacıhaliloğlu),provided by the Institute of Fruit Research Center, Malatya,

were harvested in July 2008. Hacıhaliloğlu cultivar is themost commonly grown cultivar in Malatya and is verysuitable for drying due to its high soluble solid content(brix) which is between 24 and 28. In Malatya, 70 % ofthe apricots destined for drying belong to this cultivar.

Sulphuring and Sun-Drying

After sorting for sound fruits, fresh fruits (120 kg) wereplaced in wooden crates (90×180 cm) and the crates werestacked on top of each other in the sulphuring room. Then,the apricots were sulphured by burning of elemental sulphur.To find out the optimal SO2 levels with respect to physical,chemical and microbiological quality properties of driedapricots, different sulphur doses and exposure times wereapplied. The amount of elemental sulphur burned and thetime apricots exposed to SO2 gas formed in sulphur houseare presented in Table 1. After exposing the apricots to SO2

gas, the sulphured apricots in crates were removed from thesulphur house and placed under direct sunlight. On the thirdday of drying, the pits were removed by squeezing the fruitby hand. At the end of 6 days of drying, the drying processwas terminated.

As seen in Table 1, the amount of elemental sulphurburned for the first five sulphuring trials was the same(500 g). These five trials, in which samples contained SO2

from 188 to 1,236 mg per kg, were carried out by theauthors. For the last two trials, in which samples contained2,899 and 3,864 mg SO2 kg−1, the sulphuring was carriedout commercially; therefore, the amount of sulphur burnedwas different than our sulphuring trials. Although almosthalf of the sulphur was used in these sulphuring trialscompared to our trails, the apricots were exposed to SO2

gas in sulphur house at much longer times; i.e., 10 h for thedried apricots containing 2,899 mg SO2 kg−1 and 12 h forthe samples containing 3,864 mg SO2 kg−1. The last twosamples which contained the highest amount of SO2 wereincluded at the later stage of the study. Therefore, we had to

Table 1 The amount of elemental sulphur burned and the time apricotsexposed to SO2 gas in sulphur house, and the final SO2 concentrationof apricot samples after drying

Sulphur powdercontent (g)

Sulphuringtime (h)

SO2 concentration ofdried apricots (mg kg−1)

500 0.5 188±2.55

500 1 452±4.03

500 1.25 791±6.65

500 1.5 1,034±17.3

500 2 1,236±25.8

240 10 2,899±17.0

240 12 3,864±9.12

Food Bioprocess Technol (2013) 6:1526–1538 1527

take these samples from one of the major producers of driedapricots in Malatya. These two samples with high SO2

content were from the same cultivar and grown in the sameorchard and in the same growing season.

Sampling

The sulphured and sun-dried apricots were brought toAnkara University Food Engineering Department where allphysical, chemical and microbiological analyses were car-ried out. The samples at each sulphur level were mixedthoroughly and left in enclosed containers at 20 ± 0.5 °Cfor 2 weeks to equilibrate moisture content. Then, the dam-aged apricots were selected and removed. During sampling,equal numbers of dried apricot samples were taken from thetop, in the middle and at the bottom of each pile. Aftersampling was completed, the piles were restored to preventexcessive moisture and SO2 losses from the surface of piles,which would otherwise cause inhomogeneous sampling.

Storage

The dried apricots subsamples (25 kg for each storagetemperature) were stored in a pile without any packagingin refrigerated incubators at 5, 10 and 20 ± 0.5 °C (SanyoMIR 153 and 253, Gunma, Japan) and a non-refrigeratedincubator at 30 ± 0.1 °C (Memmert BE 400, Schwabach,Germany) for a period of 351 days. The storage of driedapricots in a pile represented the commercial conditions inMalatya. Depending on SO2 content and temperature, thedried apricots samples (1 kg) were removed from the incu-bators, and they were subjected to the following physical,chemical and microbial analyses.

Moisture Analysis

The moisture content of sulphited-dried apricots (SDAs)was determined in quadruplicate using a vacuum oven (Her-aeus VT 6025, Hanau, Germany) at 70 ± 0.1 °C for 14 h bythe method (934.06) outlined by AOAC (2000). A sampleof 500 g SDAs was taken from the bulk sample equilibratedfor moisture and ground through a plate with 4 mm orifices(Tefal Maxi Power 1800W, France). This was repeatedtwice to obtain a homogenised sample. The homogenisedsample was also used for water activity, SO2, browning, β-carotene, pH and titratable acidity analyses.

To determine the moisture contents during storage, 15SDAs for each storage temperature were randomly selectedand their weights were determined. Then, the apricots wereplaced to the incubators without any packaging. The con-tents of each SDA samples were weighed at the sameperiods when the samples were taken to physical, chemicaland microbial analyses. After weighing, the apricots were

immediately replaced to the incubators for the future mois-ture determinations. The moisture contents of SDAs duringstorage were calculated from weight loss.

Water Activity Measurements

The water activity (aw) of SDAs was measured at 25 °C witha hygrometer (AquaLab 3, Decagon Devices, Pullman, WA,USA) with an accuracy ± 0.003. The temperature of thehomogenised samples was brought to 25 °C in atemperature-controlled incubator (Sanyo MIR 253, Gunma,Japan) prior to water activity measurements. Then, the sam-ples were transferred into plastic cups which were placed inthe cell of the hygrometer. The measurements were madeafter the equilibrium was reached.

Sulphur Dioxide Analysis

SO2 was determined in duplicate by the modified Monier–Williams distillation method (Reith and Willems 1958) withthe minor revision in collecting the SO2 gas described byFranzke et al. (1968). The SO2 gas formed after heating of asulphured sample in a distillation flask with 15 % (v/v) HClwas collected into two receiver tubes containing 3 % (v/v)H2O2. By this way, if the SO2 gas escaped from the firstreceiver tube, then it was collected in the second receivertube. The contents of two receiver tubes were combined andthen titrated with standardised 0.1 N NaOH. The SO2 con-tents of SDAs were expressed as milligrams SO2 per kilo-grams of dried apricots containing 25 % moisture. Thismoisture level was taken from the Codex standard indicat-ing that dried apricots containing SO2 shall not exceed themoisture level of 25 % (Codex Alimentarius Commission1981). Reporting the SO2 content of dried apricots on thesame moisture content was necessary to compare the results.

Browning Measurements

Browning was measured in duplicate according to the meth-od developed for dried carrots by Baloch et al. (1973) withminor revision in sample preparation described by Özkanand Cemeroğlu (2002). Extraction of the water solublebrown pigment was carried out with 20 mL L−1 acetic acidcontaining 10 mL L−1 formaldehyde. Interfering carotenoidpigments were removed with lead acetate and ethyl alcohol.Formaldehyde was used to remove the interfering SO2.Absorbances of supernatants were recorded at 420 and600 nm, using an UV–VIS double-beam spectrophotometer(ThermoSpectronic Helios-α, Cambridge, England). Thebrowning was calculated by subtracting absorbances at600 nm (for turbidity) from those of 420 nm. The resultswere expressed as “absorbance at 420 nm g−1 sample driedweight.”

1528 Food Bioprocess Technol (2013) 6:1526–1538

pH and Titratable Acidity

Ten grams (±0.01 g) (Sartorius BP 3100S, Goettingen, Ger-many) of homogenised sample was rehydrated with 90 g ofdistilled water at 4 °C overnight. The mixture was then homo-genised for 5 min in a high-speed stainless steel blender(Waring 8012, Torrington, CT, USA), and the resulting ho-mogenate was filtered through a cheese cloth. The filtrate wasused for both pH and titratable acidity analyses. pH wasmeasured with a pH meter (WTW Inolab Level 1, Weilheim,Germany). Titratable acidity was determined according to themethod (942.15) outlined by AOAC (2000) and expressed as“grams anhydrous citric acid 100 g–1 sample.”

β-Carotene Analysis

Extraction

β-carotene was extracted following the method described bySadler et al. (1990) with minor revisions in sample prepa-ration before extraction. A 15 g (±0.01 g) of minced samplewas rehydrated in 45 mL distilled water at 4 °C overnight.This mixture was homogenised first in the Waring blenderfor 2 min and then in the homogeniser at 13,500 rpm for anadditional 2 min to obtain a thoroughly homogenised sam-ple. A 5 g (±0.0001 g) of homogenised sample was precise-ly weighed directly into a polypropylene centrifuge tubeusing an electronic balance (Mettler Toledo XS 205, Grei-fensee, Switzerland). Calcium carbonate (0.5 g) was addedas a neutralising agent. An extraction solvent of 20 mL,consisting of hexane/acetone/ethanol (50:25:25, v/v/v), wasadded to the centrifuge tube which was agitated on anorbital shaker (Heidolph Unimax 2010, Schwabach, Ger-many) at 220 rpm until the residue became completelycolourless (ca. 15 min). A 5 mL of distilled water was addedto hasten the phase separation, followed by centrifugation at9,400×g at +4 °C for 15 min. The solution was separatedinto distinct polar and nonpolar layers. Two extracts wereprepared from each sample.

Preparation of Sample for HPLC

A 5 mL of upper hexane layer containing β-carotene wastransferred to an amber coloured vial and evaporated todryness under a stream of nitrogen at 40 °C (Caliper Turbo-Vap LV, Hopkinton, MA, USA). The residue was dissolvedin 200 μL tetrahydrofuran (THF) containing 0.1 gL−1

buthylated hydroxytoluene (BHT) and diluted with1,800 μL methanol. The resulting extract was filteredthrough a 0.22-μm polytetrafluoroethylene filter (SartoriousAG, Goettingen, Germany) directly to an amber colouredauto sampler vial. The filtered extract was then immediatelyinjected to HPLC without further delay.

Instrumentation and Chromatography

Separation and quantification of β-carotene were performedon a high performance liquid chromatography (Agilent 1200series, Waldbronn, Germany) with a binary pump, a photodiode array detector, a thermostatted autosampler, a degas-ser and a thermostatted column compartment. The chro-matographic data were recorded and processed on Agilent1200 series ChemStation rev.B.02.01 software. Isocraticseparation was carried out on a C30 (5 μm) column (250×4.6 mm) (Phenomenex, Inc, Los Angeles, CA, USA) with aC30 (5 μm) guard column (10×4.0 mm) (Phenomenex, Inc).Mobile phase consisted of methanol/tert-buthyl methyl ether(65:35, v/v) solution containing 0.1 gL−1 BHT with a flowrate of 1.0 mL min−1. Sample injection volume was 50 μland column temperature was set at 30 °C. The detector wasset at 450 nm, i.e. the maximum absorption of β-carotene inmobile phase. β-carotene in dried apricot samples was iden-tified by comparing retention time and absorption spectra ofunknown peaks with external reference standard (Sigma, StLouis, MO, USA). β-carotene standard (1 mg) was dis-solved in 10 mL of THF including 0.1 % BHT for a stocksolution. Quantification of β-carotene was carried out usinga calibration curve (R200.9937). The range of the calibra-tion curve containing eight data points was 0–40 mg L−1 (0,5, 10, 15, 20, 25, 30 and 40 mg L−1).

Determination of Limit of Detection and Limitof Quantification

The limit of detection (LOD) and limit of quantification(LOQ) for β-carotene were determined based on signal tonoise (S/N) ratio. According to the ICH guideline for vali-dation of analytical procedures, an acceptable S/N is 3:1 (or2:1) for estimating the LOD and 10:1 for estimating theLOQ (ICH 1996).

Surface Colour Measurements

The surface colour of dried apricot samples was measuredwith a light reflectance spectrophotometer (Minolta CM-3600d, Osaka, Japan). The spectrophotometer had an 8-mm diameter viewing area. Before use, the instrument(45 °/0 ° geometry, 10 ° observer) was calibrated with awhite tile. During measurements, a specular component wasincluded. This gives a better estimate of colour as seen bythe human eye (Balsam et al. 1998). Measurements wererecorded in L* (lightness), +a* (redness) and +b* (yellow-ness) CIE (Commission Internationale de I'Eclairage) colourcoordinates, using the CIE C* illuminant which correspondsto the difference between average daylight and UV compo-nent. Saturation (chroma, C*) and hue angle (h°) werecalculated from a* and b* colour coordinates using the

Food Bioprocess Technol (2013) 6:1526–1538 1529

following equations:

C� ¼ a�2 þ b�2� �1=2 ð1Þ

h� ¼ tan�1 b�=a�ð Þ ð2Þ

Microbial Analyses

A representative sample (ca. 120 g) was taken from driedapricot samples, and each apricot was aseptically cut intohalves to obtain a uniform sample, and then a 30 g ofsubsample was aseptically transferred into a screw capped500-mL flask. A portion of 90 mL of sterile 0.1 % (w/v)peptone water (PW) (Merck Co., Darmstad, Germany) wasadded onto dried apricot sample just to wet and cover thesurface and left for 15 min at ambient temperature (20 °C)so as to slowly rehydrate and increase the recovery ofinjured cells and prevent microorganisms from osmoticshock (Mackey 2000). Then, the remaining portion of PWwas added to the rehydrated sample. The flasks were shakenvigorously for 1 min by a flask shaker (Griffin flask shaker,Griffin & George Ltd., UK) operating at half of the maxi-mum speed corresponding to 1,000 oscillation per min atambient temperature. Further decimal dilutions were carriedout in PW, and appropriate dilutions were later transferredonto appropriate media as follows.

Total mesophilic aerobic bacteria (TMAB) and total psy-chrophilic aerobic bacteria (TPAB) were determined onplate count agar with pour plate method. The plates wereincubated for TMAB at 28 °C for 48 h and TPAB at 7 °C for10 days. The enumeration of total yeast and moulds wascarried out in yeast extract glucose chloramphenicol(Merck) following an incubation period at 28 °C for 7 days.Meanwhile, for the enumeration of xerophilic moulds indried apricot samples, dichloran glycerol agar (DG-18;Merck) was used and the plates were incubated at 28 °Cfor 7 days. Lactic acid bacteria (LAB) were enumerated onDe Man Rogosa Sharpe agar (Merck) with pour plate meth-od, overlayed with 5 mL of the same medium and incubatedat 28 °C for 120 h. Total Enterobacteriaceae were enumer-ated in violet red bile dextrose agar (Merck) with pour platemethod by overlaying with 5 mL of the same medium andincubated at 37 °C for 24 h. For the enumeration of Staph-ylococcus spp., the serial dilutions were spread on Baird–Parker agar (fortified with egg yolk and potassium tellurite)(Merck) and the plates were incubated at 37 °C for 48 h. Allmicrobiologic analyses were done according to the APHACompendium for the Microbiological examination of foods(APHA 2002) and performed in replicate samples, anddilutions of each replicate were plated in two to four repli-cate petri dishes.

Statistical Analyses

Experimental data were analysed by using the Minitab sta-tistical software, version 15 (Minitab Inc., State College,PA, USA). Storage time was considered as the main effect.Statistical differences among means were determined by theDuncan’s multiple range tests at the 5 % significance level.

Results and Discussion

Moisture Content and Water Activity (aw)

At the beginning of storage, the moisture contents and awvalues of samples ranged from 18.9 to 24.5 % and from0.611 to 0.667, respectively. According to the Codex standard(Codex Alimentarius Commission 1981), the moisture con-tent of dried apricots shall not exceed 25 % when preserva-tives such as SO2 are used. In this study, the levels of moisturein dried apricot samples were in accordance with the Codexstandard (Codex Alimentarius Commission 1981).

Moisture contents and aw values of SDA samples de-creased gradually as the storage temperature and time in-creased. For example, the percent decreases in moisturecontents of dried apricots containing 2,899 mg SO2 kg−1

were 13.5, 43.6 and 72.9 at 10, 20 and 30 °C for 351 days ofstorage, respectively. However, when dried apricot samplescontaining SO2 at the same level were stored at 5 °C for thesame period of time, the moisture content of the samplesincreased by 23.2 %. This was explained by the differencein the vapour pressures between dried apricots and the air inthe weighing room. The vapour pressure of dried apricotsstored at 5 °C was lower than that of the air in weighingroom at ambient temperature (~20 °C). As a result of thisdifference, dried apricots stored at 5 °C absorbed the waterfrom the air in the weighing room.

The loss of moisture from SDA samples was fitted to afirst-order kinetic model (figure not shown). The reactionrate constants (k) were calculated at a given temperature andSO2 levels by the following equation (Table 2):

ln Ct=Coð Þ ¼ �kt ð3Þ

where Co is the initial moisture content of samples and Ct isthe moisture content after t min exposure to a giventemperature.

To show the effects of initial SO2 concentrations of driedapricot samples on the moisture loss rate constants, theinitial SO2 concentration of samples was plotted againstthe moisture loss rate constant in Fig. 1. A strong logarith-mic correlation (r0−0.943) was found. When the freshapricots are exposed to the SO2 gas, SO2 is absorbed bythe apricot tissues as the mixture of various sulphur

1530 Food Bioprocess Technol (2013) 6:1526–1538

Tab

le2

Kinetic

parametersforthelosses

ofmoistureandSO2,andtheform

ationof

brow

ncolour

inSDA

samples

during

storage

SO2level

Lossof

moisture

Lossof

SO2

Formationof

brow

ncolour

(mgkg

−1)

kaEqu

ations

kt 1/2a

Equ

ations

k

Storage

temperature

(°C)

3018

80.97

(0.859

2)b

logy¼

�0:0022x

þ2:2657

0:9882

ðÞ

0.06

12logy¼

0:0029

x�0:5647

0:9978

ðÞ

0.20

452

0.83

(0.903

6)logy¼

�0:0035x

þ2:6618

0:9460

ðÞ

0.10

7logy¼

0:0020

x�0:6176

0:9931

ðÞ

0.14

791

0.55

(0.943

7)logy¼

�0:0021x

þ2:8996

0:9903

ðÞ

0.06

12logy¼

0:0017

x�0:6614

0:9866

ðÞ

0.12

1,03

40.71

(0.985

3)logy¼

�0:0020x

þ3:0104

0:9932

ðÞ

0.06

12logy¼

0:0015

x�0:6979

0:9633

ðÞ

0.10

1,23

60.46

(0.988

9)logy¼

�0:0020x

þ3:0738

0:9854

ðÞ

0.06

12logy¼

0:0012

x�0:7563

0:9981

ðÞ

0.08

2,89

90.34

(0.962

0)logy¼

�0:0011x

þ3:4557

0:9702

ðÞ

0.03

23logy¼

0:0014

x�0:8830

0:9975

ðÞ

0.10

3,86

40.34

(0.961

7)logy¼

�0:0009x

þ3:5788

0:9930

ðÞ

0.02

28logy¼

0:0013

x�1:0659

0:9919

ðÞ

0.09

2018

80.55

(0.995

1)logy¼

�0:0014x

þ1:3804

0:9978

ðÞ

0.04

18logy¼

0:0005

x�0:5612

0:9944

ðÞ

0.03

452

0.18

(098

95)

logy¼

�0:0006x

þ1:2625

0:9998

ðÞ

0.02

42logy¼

0:0010

x�0:6311

0:7975

ðÞ

0.07

791

0.25

(0.926

0)logy¼

�0:0006x

þ1:2911

0:9873

ðÞ

0.02

42logy¼

0:0003

x�0:6604

0:9446

ðÞ

0.02

1,03

40.23

(0.924

7)logy¼

�0:0007x

þ1:3461

0:9852

ðÞ

0.02

40logy¼

0:0003

x�0:6699

0:9684

ðÞ

0.02

1,23

60.16

(0.948

9)–

––

––

2,89

90.16

(0.971

4)logy¼

�0:0006x

þ3:4534

0:9837

ðÞ

0.02

42logy¼

0:0005

x�0:8952

0:9898

ðÞ

0.03

3,86

40.14

(0.979

5)logy¼

�0:0006x

þ3:5832

0:9928

ðÞ

0.02

42logy¼

0:0007

x�1:0853

0:9898

ðÞ

0.05

akandt 1/2values

expressedas

mon

th−1

andmon

th,respectiv

ely

bNum

bers

inparenthesesarethedeterm

inationcoefficients

Food Bioprocess Technol (2013) 6:1526–1538 1531

oxospecies (SO2; hydrogen sulphite ion, HSO3−; sulphite

ion, SO3−2 and disulphite ion, S2O5

−2) (Wedzicha 1987). Allthese forms are easily converted to each other depending onthe pH of the foods.

SO2ðgasÞ ! SO2ðaqueousÞSO2ðaqÞ þ H2O ! H2SO3

H2SO3 ! Hþ þ HSO3�

HSO3� ! Hþ þ SO3

2�

2HSO3� ! S2O5

2� þ H2O

In the presence of water, SO2 gas is dissolved in water,forming sulphurous acid (H2SO3). At the pH of dried apri-cots, bisulphite ion (HSO3

−) was the predominant form. TheHSO3

− ion may lead to hydrolysis of protopectin and this, inturn, probably increased the ability of pectin to bind to waterin SDA samples (Walker 1985). And thus, dried apricotsamples containing SO2 at relatively higher concentrationinclude unbound water at lower concentration comparedwith those samples containing SO2 at lower concentration.As known, the rates of first-order reactions change depend-ing on initial substrate concentration. Therefore, as the con-centration of unbound water in dried apricot samplesdecreases, the rate of moisture loss also decreases. Mean-while, mass transfer has also important effects on the rate ofmoisture loss. As the moisture content decreases dependingon increase in SO2 concentration of SDAs, the differencebetween concentrations of water molecules in SDAs and airalso decreases. Thus, the decrease in the relative concen-trations of water molecules in SDAs and air also causes todecrease in the rate of moisture loss.

While the loss of moisture for the dried apricots stored at10 °C was limited, the loss was significantly high at 20 and30 °C. Therefore, the SDA samples stored at 10 °C could bemarketed without rehydration even after a long storageperiod (2–8 years). However, samples stored at 20 and

30 °C should be definitely rehydrated before marketingdue to high moisture loss.

pH and Titratable Acidity

There were no significant changes found in the pH values ofSDA samples during storage (P>0.05). On the contrary,titratable acidity values increased during storage. For exam-ple, titratable acidity values of dried apricots containing2,899 mg SO2 kg−1 increased from 2.2414 g 100 g−1 dryweight to 2.2854 g at 10 °C, 2.3229 g at 20 °C and 2.4108 gat 30 °C after storage for 351 days. However, there were nosignificant changes found in titratable acidity values(2.2404 g 100 g–1 dry weight) of samples stored at 5 °Cfor the same storage time (P<0.05).

The increase in titratable acidity of samples may be attrib-uted to enzymatic breakdown of pectin to α-1,4 galacturonicacid by polygalacturonase (PG). This was observed in a studycarried out by Levi et al. (1988) who reported that pectincontents of peaches decreased from 509 mg to 430 mg100 g−1 fruit after sulphuring, 381 mg after drying and358 mg after storage at 15 °C for a year. These results clearlyshowed that, in addition to sulphuring and drying, pectin wasalso degraded during storage. Moreover, storage temperaturehad significant effect on pectin degradation by enzymes. Arteset al. (1996) indicated that at storage temperature lower than8 °C, while pectin methyl esterase (PME) in peaches wasactive, PG was inactive. As known, PMEs catalyse the deme-thylesterification of polygalacturonans present in the cell wallof plants and then PGs degrade polygalacturonans by thehydrolysis of the glycosidic bonds that link galacturonic acidresidues. These findings also agree with our results.

Kinetics of SO2 Removal

As the storage temperature increased, the rate of SO2 re-moval from SDAs increased. Thus, the decreases in SO2

contents of samples containing 2,899 mg SO2 kg−1 andstored at 20 and 30 °C were 38 and 61 %, respectively.However, almost no changes in SO2 contents of samplesstored at 5 and 10 °C for 351 days were observed. Similarresults were reported for intermediate moisture apricotsstored at 5 °C (Sağırlı et al. 2008).

The kinetics of SO2 removal was also investigated in SDAsamples. The removal of SO2 during storage was fitted to afirst-order kinetic model (figure not shown) which agreedwithprevious studies (Stadtman et al. 1946; Davis et al. 1973;Sağırlı et al. 2008). The calculated reaction rate constants (k)were presented in Table 2. Increasing temperature from 5 to30 °C resulted in significant decrease in SO2 content in allSDA samples (P<0.05). However, when k values were com-pared with respect to initial SO2 concentrations of samples, nosystematic changes in k values were found. These results

log y = – 0.3736 log x – 1.1316 r = – 0.943

Moi

stur

e lo

ss r

ate

cons

tant

x 1

03 (da

y−1)

SO2 concentration (mg kg−1)

Fig. 1 The effects of initial SO2 concentrations of SDA samples on themoisture loss rate constants at 30 °C

1532 Food Bioprocess Technol (2013) 6:1526–1538

showed that not only initial SO2 concentrations had effect onSO2 removal rate constants but also other factor(s) had effect(s). One of these factors would be different in moisture con-tents of samples. Eheart and Stoles (1945) also reported thatthe loss of SO2 from dried fruits depended on the moisturecontent of dried fruits. This loss was especially high in sam-ples with high moisture content (18–20 %). Additionally,some reactions between sulphites and carbonyl groups alsolead to the loss of SO2 in dried fruit and vegetables.

Various carbonyl intermediates are generated by non-enzymatic browning reactions, including reducing sugar,simple carbonyls, dicarbonyls and α, β-unsaturated carbon-yls (Taylor et al. 1986). Moreover, the sulphites can reactwith all of these intermediates. Thus, they block the forma-tion of brown pigments. However, some of the sulphite–carbonyl reaction products are more stable than the others(Taylor et al. 1986). While the sugar hydroxy sulphonatesformed between reducing sugar and sulphites are very un-stable, the sulphonated carbonyls formed on reaction of thesulphites with the α,β-unsaturated carbonyls are extremelystable. Moreover, the reaction between sulphites and theα,β-unsaturated carbonyls is generally considered to beirreversible (Taylor et al. 1986). Furthermore, the irrevers-ible reactions remove sulphite permanently from the reser-voir of free SO2. Similarly, Wedzicha (1984) showed thatmost of sulphites’ losses in dehydrated vegetables is due toreactions between sulphites and the carbonyls formed bynon-enzymatic browning.

The half-life periods (t1/2), i.e. the time needed for 50 %loss of SO2, were calculated at a given temperature by thefollowing equations:

t1=2 ¼ � ln 0:5� k1�1 ð4Þ

As the storage temperature increased, half-life periods forSO2 loss from SDA samples decreased. For example, half-life periods for SO2 loss from dried apricots containing2,899 mg SO2 kg−1 and 20.9 % moisture were 42 and23 months at 20 and 30 °C, respectively (Table 2).

The general practice in Malatya was to oversulphite theapricots if stored for a long time especially for the years whenthe crop yield would be low. During storage especially at highstorage temperatures, SO2 is naturally removed from the apri-cot tissues. In fact, Özkan and Cemeroğlu (2002) showed thatincreasing temperature from 40 to 60 °C resulted in significantincreases for SO2 loss from the oversulphited apricots. Forexample, the SO2 content of dried apricots after exposure for96 h of hot air declined by 19.6 % at 40 °C, 27.6 % at 50 °Cand 64.2 % at 60 °C. Therefore, in this study, at which storagetemperature (5–30 °C) and storage time, SO2 contents ofoversulfited dried apricots (2,899 and 3,864 mg SO2 kg−1)would reach to 2,000 mg SO2 kg−1, was also determined(Table 3). As seen from Table 3, SO2 contents of these

samples (2,899 and 3,864 mg SO2 kg−1) would reach to2,000 mg SO2 kg

−1 at the end of 0.7–1.3 years at 20 °C andat the end of 0.4–0.9 years at 30 °C.

Browning Values

Almost no changes in browning values of samples stored at5 and 10 °C for 351 days were observed while a littleincrease at 20 °C and significant increase at 30 °C (P<0.05) were observed. Meanwhile, when browning valuesof dried apricot samples were compared with respect toSO2 concentrations, the colour of samples was generallyacceptable when the samples were stored at 20 °C even atthe end of 351 days of storage in almost all samples. How-ever, only, the colour of the samples containing 188 and452 mg SO2 kg

–1 reached to unacceptable colour levels in avery short time (2.6 and 3.6 months, respectively) at 20 °C.Similarly, very high browning values in all samples stored at30 °C even in a short time were also observed.

Browning values formation in all apricot samples wasfitted to a first-order reaction model. Our results agree withthose from the previous studies, reporting a first-order reac-tion model for the formation of browning colour in SDAs(Sadler et al. 1990; Özkan and Cemeroğlu 2002). On thecontrary, there were also some studies reporting a zero-ordermodel for browning reaction in pineapple juice (Rattanatha-nalerk et al. 2005), Sultan raisins (Aguilera et al. 1987) andrehydrated ground dried apricots (Lee et al. 1979).

The formation of brown colour was significantly affectedby storage temperature (P<0.05). As expected, higher stor-age temperatures increased the rate of brown colour forma-tion in all samples (Table 2). For example, the k valuescalculated for brown colour formation at 20 and 30 °C were0.0193 and 0.0553 month–1, respectively, in samples con-taining 1,236 mg SO2 kg

−1. In a previous study, the higher kvalues (0.0488 and 0.2411 month−1 at 20 and 30 °C, respec-tively) for brown colour formation in high moisture(36.6 %) dried apricots containing 1,458 mg SO2 kg

−1 werereported (Sağırlı et al. 2008). Similarly, Coşkun (2010) alsoreported higher k values (0.0345 and 0.2257 month−1 at 20and 30 °C, respectively) for brown colour formation in driedapricots (with 22 % moisture) containing 2,364 mg SO2

kg−1. Although samples at both studies had higher SO2

concentration than our samples, k values for brown colourformation in these samples were higher than those in ours.This was attributable to differences between the rates ofmoisture loss. At the other two studies, samples were storedin plastic bags and thus the loss of moisture from thesesamples was limited. In our study, since the samples werestored in a pile without any packaging, the loss of moisturewas very fast and thus the Maillard reaction causing thebrowning in dried apricots during storage occurred at amuch lower rate.

Food Bioprocess Technol (2013) 6:1526–1538 1533

The dependence of the formation of brown colour inSDA samples on temperature was determined by calculatingthe temperature quotient (Q10) values from the followingequation:

Q10 ¼ ðk2=k1Þ10=ðT1�T2Þ ð5ÞQ10 values obtained for the formation of brown colour in

SDA samples during storage ranged from 1.85 to 5.85.Similar to our results, Q10 values for brown colour forma-tion were found ranging from 1 to 8 in a previous studycarried out by Tsai et al. (1991) who investigated the effectsof the storage temperature (5 to 45 °C) and aw (0.6 to 0.85)in the presence of glucose and celite on browning ratepatterns of 22 amino acids in dried squid and simulatedmodel system.

Moreover, to determine the effect of percentage decrease inSO2 concentration on brown colour formation in dried apricotsamples, the values of SO2 concentration were plotted againstthe browning values obtained during storage. A strong linearcorrelation (r00.949) was found between these two variables.Before storage, the browning values of SDA samples rangedfrom 0.28 to 0.08 A420 g

−1 dry weights, depending on SO2

content of dried apricots. The browning values of dried apri-cots containing 188 and 452 mg SO2 kg

−1 were 0.28 and 0.25A420 g

−1 dry weight, respectively. Nury et al. (1960) definedthe limit for acceptability of colour of dried apricots as theabsorbance values reach to a value of 0.30 at 440 nm (Davis etal. 1973). Taking into account this limit, dried apricot samplescontaining SO2 at low levels should be definitely stored at lowtemperatures (5–10 °C). The colour of SDA samples evenwith SO2 content lower than 452 mg SO2 kg−1 was stillacceptable right after sulphuring. However, the colour of thesesamples easily exceeded the acceptable limit at a very shortperiod when stored over 10 °C.

Storage lives, which are the time the absorbance valuereached to 0.30 at 440 nm of the dried apricot samples con-taining SO2 at different levels at 20 and 30 °C, were presentedin Table 3. At both temperatures, the storage lives of driedapricots containing SO2 over 2,000 mg kg–1 were, asexpected, found considerably higher than those of dried apri-cots containing SO2 at relatively low levels, below 452 mg

SO2 kg−1 (Table 3). Figure 2 shows the SO2 concentration of

SDA samples when the storage life of samples expired basedon the browning value reaching up to 0.3. Comparing the SO2

contents of samples stored at higher temperatures once thecolour of the samples was not acceptable anymore, significantdifferences were found between SO2 contents of samplesstored at 20 and 30 °C, and generally samples stored at 30 °C had higher SO2 contents than that of samples stored at 20 °C(Fig. 2). This is easily explained by comparing the values ofQ10 for brown colour formation and SO2 loss. On the average,Q10 values for browning reactions were 3.85 whileQ10 valuesfor SO2 loss were 2.82. As known, if the Q10 value of areaction is higher than the Q10 value of other reaction, thereaction with highQ10 values is more affected by temperaturechanges. In other words, 10 °C increase in the storage tem-perature accelerated the rate of brown colour formation 1.4times more than the rate of SO2 loss.

Differences in Surface Colour

Hue angle (h°) describes the colour as 0 °/360 ° for red-purple, 90 ° for yellow, 180 ° for green and 270 ° for blue.

Table 3 Shelf lives of SDAsamples and time for the samplesreaching to 2,000 mg SO2 kg

−1

at different storage temperatures

SO2 concentration Shelf lives (month) Time for the samples reaching to 2,000 mg SO2 kg–1 (month)

(mg kg–1) 20 °C 30 °C 5 °C 10 °C 20 °C 30 °C

188 2.6 0.5 – – – –

452 3.6 1.6 – – – –

791 15.3 2.7 – – – –

1,034 16.3 3.9 – – – –

2,899 24.8 8.6 53.6 26.9 8.5 4.7

3,864 26.8 13.9 95.5 95.4 15.7 10.3

0

400

800

1200

1600

SO2 c

once

ntra

tion

(m

g kg

−1)

Initial SO2 concentration (mg kg−1)

188a 452 791 1034 1236 2899 3864

20 °C

30 °C

Fig. 2 SO2 concentrations of SDA samples when their storage livesexpire with respect to brown colour formation at 20 and 30 °C. a InitialSO2 concentrations (in milligrams SO2 per kilogram)

1534 Food Bioprocess Technol (2013) 6:1526–1538

The chroma (C*) value describes colour saturation or inten-sity, which is scaled from 0 (dull) to 60 (vivid). L* value is ameasure of lightness, which is scaled from 0 (black) to 100(white) and used as a browning index in dried fruits (Agui-lera et al. 1987; Sağırlı et al. 2008).

During storage at 5, 10, 20 and 30 °C for 351 days, nosystematic changes in L*, a*, b*, C* and h° were detectedfor the samples containing SO2 at different levels. Thiswould be attributed to different moisture contents of sam-ples (data not shown). To show whether the moisture con-tent has any effect on the surface colours of the samples,dried apricots containing 2,899 mg SO2 kg–1 were rehy-drated to initial moisture content at the end of the storageat 20 and 30 °C for 351 days and then the reflectance colourvalues were determined. After rehydration, all reflectancecolour values, except a* values, increased. Meanwhile,changes in all reflectance colour values of samples storedat both storage temperatures were similar. In fact, theincreases in L*, b*, C* and h° values of samples stored at20 and 30 °C were 8.3–8.2, 6.4–6.5, 5.8–6.1 and 8.5–9.4units, respectively. Before and after rehydration processes,the colour values of samples stored at 20 °C were higherthan those of samples stored at 30 °C. These findings werein agreement with the findings of Özkan et al. (2003) whofound that as the moisture content of dried apricots in-creased, the L*, b*, C* and h° colour values also increasedwith the exception of the a* value.

At the end of storage, all dried apricot samples werephotographed to show the effects of storage temperatureson the perceived colour of dried apricots by human eye(Fig. 4). As the SO2 concentration increased, the colour ofdried apricots was lighter. This clearly shows the importanceof SO2 concentration in preventing the undesirable browncolour formation in samples during drying and storage.However, storage temperature had an opposite effect whichmeans that as storage temperature increased, the colour ofdried apricots turned brown. These findings clearly showthat regardless of SO2 concentration in dried apricots, lowstorage temperatures (lower than 20 °C) should be preferredto preserve the characteristic golden yellow colours of driedapricots.

Changes in β-Carotene Content

The major carotenoid identified by HPLC in SDA sampleswas β-carotene (Fig. 3). Previous studies also showed thatthe major carotenoids in apricots are β-carotene, γ-caroteneand lycopene (Sass-Kiss et al. 2005), with β-carotene rep-resenting more than 60–70 % of the total carotenoids (Sass-Kiss et al. 2005; Sağırlı et al. 2008).

Zhao and Chang (1995) and Eheart and Sholes (1945)indicated that sulphite could retard β-carotene breakdownduring drying and storage. However, to date, the minimumnecessary SO2 concentration for preserving the β-carotenein dried apricots during storage at different temperatures hasnot been determined. β-carotene contents in SDA samplesranged from 26.6 to 36.2 mg 100 g−1 dry weight. The SO2

concentration over 791 mg per kg of dried apricots effec-tively protected carotenoids in dried apricots during drying.

-carotene

Non-identified

Fig. 3 The HPLCchromatogram of thecarotenoids in SDA samplesincluding 3,864 mg SO2 kg

−1

B.S. A.S. (10 °C)

A.S. (20 °C)

A.S. (30 °C)

A.S. (5 °C)

0

10

20

30

40

-car

oten

e co

nten

t (m

g 10

0g d

ry m

atte

r-1)

Fig. 4 The effects of storage temperatures on the visual colours and β-carotene contents of SDAs containing 3,864 mg SO2 kg

−1. B.S. At thebeginning of storage, A.S. At the end of 351 days of storage at a givenstorage temperature

Food Bioprocess Technol (2013) 6:1526–1538 1535

The effects of storage temperature and time on the β-carotene contents in dried apricots were also observed. Theresults indicated that while storage temperatures did nothave significant effect on β-carotene contents, storage timehad significant effect. Generally, β-carotene contents de-creased 24–28 % at the end of 351 storage days. The highestloss in β-carotene contents were found in samples stored at30 °C and containing 188, 451 and 791 mg SO2 kg

−1. Thismay be attributed to the relatively low SO2 concentrations inthese samples at the end of the storage at 30 °C. These lowlevels of SO2 contents may probably promoted oxidationduring storage. Except for these particular samples, storagetemperatures had similar effects (Fig. 4) on the β-carotenecontents of SDA samples containing varying SO2 contents.However, as clearly seen in Fig. 4, brown colour had stron-ger effect on the perceived colour of SDAs by human eyethan β-carotene contents of samples.

Changes in Microbial Counts

The number of TPAB, yeast and mould, xerophilic mould,LAB, Staphylococcus spp. and Enterobacteriaceae werebelow the lowest detection limit (<4 CFU g−1), and nogrowth of these bacteria was detected in all SDA samplesinitially and throughout the storage, while the number ofTMAB were detectable during storage. Similarly, the

presence and growth of Staphylococcus aureus and Clos-tridium spp. (Mahmutoğlu et al. 1996) and Staphylococcusspp. and Enterobacteriaceae (Sağırlı et al. 2008) were foundbelow detection limits by other authors in SDAs samplesstored up to 12 months. Before storage, initial microbialcounts on the samples of SDAs showed that the number ofTMAB was relatively very low, 8.2×101and 18.4×101 CFU g−1 being the lowest and the highest countsobtained, respectively (Table 4).

Table 4 Changes in TMAB counts of SDA samples containing SO2 at different levels during storage at different temperatures

SO2 concentration (mg kg−1) Time (day) 5 °C 10 °C 20 °C 30 °C

188 0 9.70×101±0.19×101 9.70×101±0.19×101 9.70×101±0.19×101 9.70×101±0.19×101

186 3.84×102±1.30×101 2.03×102±0.80×101 3.15×102±1.10×101 2.70×101±0.20×101

351 8.45×102±1.29×101 7.93×102±0.22×101 5.70×101±1.18×101 2.40×101±0.19×101

452 0 8.40×101±0.00×101 8.40×101±0.00×101 8.40×101±0.00×101 8.40×101±0.00×101

186 5.10×101±1.10×101 5.90×101±0.40×101 5.10×101±0.60×101 1.18×102±1.30×101

351 6.00×101±1.19×101 4.00×101±0.76×101 4.70×101±0.76×101 2.00×101±0.38×101

791 0 1.38×102±1.56×101 1.80×101±1.56×101 1.38×102±1.56×101 1.38×102±1.56×101

186 1.43×102±1.50×101 1.71×102±0.30×101 4.90×101±0.30×101 3.20×101±0.70×101

351 4.70×101±0.38×101 4.10×101±0.38×101 4.40×101±0.19×101 2.00×101±0.38×101

1034 0 8.90×101±0.00×101 8.90×101±0.00×101 8.90×101±0.00×101 8.90×101±0.00×101

186 5.60×101±0.90×101 5.30×101±0.90×101 1.09×102±0.80×101 6.40×101±0.00×101

351 7.60×101±0.19×101 5.20×101±0.35×101 3.50×101±0.19×101 2.50×101±0.76×101

1236 0 8.20×101±1.27×101 8.20×101±1.27×101 8.20×101±1.27×101 8.20×101±1.27×101

186 1.30×101±0.50×101 1.90×101±0.20×101 6.50×101±1.30×101 2.90×101±0.50×101

351 2.90×101±0.33×101 2.40×101±0.45×101 1.60×101±0.34×101 1.20×101±0.09×101

2988 0 1.84×102±1.39×101 1.84×102±1.39×101 1.84×102±1.39×101 1.84×102±1.39×101

186 4.80×101±0.89×101 8.40×101±1.54×101 4.12×102±3.34×101 3.41×102±3.60×101

351 1.09×102±0.63×101 2.02×102±0.38×101 8.90×101±0.52×101 4.40×101±1.04×101

3864 0 1.07×102±1.26×101 1.07×102±1.26×101 1.07×102±1.26×101 1.07×102±1.26×101

186 3.84×102±1.30×101 2.03×102±0.80×101 3.15×102±1.10×101 2.70×101±0.20×101

351 2.58×102±4.20×101 2.20×102±0.75×101 2.25×102±1.59×101 3.20×101±0.22×101

For TMAB counts, values are expressed in mean ± standard error

TMAB

SO2

conc

entr

atio

n (m

g kg

−1)

Mic

robi

al lo

ad (

cfu

g−1)

Fig. 5 The effects of storage time, different SO2 concentrations andwater activity of SDA samples on microbial growth during storage at30 °C

1536 Food Bioprocess Technol (2013) 6:1526–1538

Compared with the counts at the beginning of storage, thenumber of TMAB of dried apricots, containing SO2 at differ-ent levels and stored at different temperatures (5, 10, 20 and30 °C) for 351 days, slightly decreased. As mentioned before,at the end of the storage period at 5, 10, 20 and 30 °C, SO2

contents of samples decreased to 8, 12, 38 and 61 %, respec-tively. However, with the decreasing SO2 contents of samplesduring storage at 30 °C, the number of TMAB also decreasedin the range of 0.5–0.8 log cycles in the SDAs samples at theend of 351 days of storage at 30 °C. This may be attributed tothe significant decreases in aw values during storage. In fact,the decreases in aw values were 31% at 20 °C and 43% at 30 °C for 351 days of storage. Moreover, TMAB counts of driedapricot samples including 188 mg SO2 kg

−1 increased 0.9 logcycle both at 5 and 10 °C since the aw values of these samplesstored at 5 and 10 °C increased from 0.616 to 0.690 and 0.711,at the end of 351 days of storage, respectively.

During storage, the correlation between TMAB countswith SO2 contents and water activity values of samples con-taining 188 mg SO2 kg−1 was presented in Fig. 5 as anexample. At 30 °C, TMAB counts, SO2 contents and awvalues of the samples decreased. The restriction for microbialgrowth in SDA samples was due to the decrease in aw as wellas the antimicrobial activity of SO2 (Christian 2000).

Conclusion

The results of this study showed that moisture and SO2

levels in dried apricots as well as storage temperature andtime had all important effects on the colour of SDA samples.If SDA samples, especially with low SO2 content, are storedfor a long time, they should be stored at low temperatures,preferably at 10 °C rather than 5 °C, with respect to cost andquality. Although the losses of SO2 from the samples storedat both temperatures were similar, the increase in moisturecontent of the samples stored at 10 °C for 351 days waslower than that of samples stored at 5 °C for the sameperiod. Therefore, especially in samples containing SO2 atlow levels, microbial stability may be maintained at 10 °Cfor a longer time compared to the samples stored at 5 °C.Also, regardless of the SO2 levels, dried apricots should notbe stored at 30 °C. Otherwise, the colour of samples wouldreach the unacceptable state in a very short time.

Acknowledgments This study is in part of Miss Türkyılmaz's Ph.D.thesis. Miss Türkyılmaz would like to thank The Scientific and Tech-nological Research Council of Turkey-Graduate Research ScholarshipProgramme (TUBITAK-BIDEP) for their financial support during herPh.D. studies. The authors would like to acknowledge the valuablehelp of Mr. Kadir Öztürk and Mr. Bülent Öztürk at The Institute ofFruit Research Center, Malatya during sulphuring of apricots. Theauthors would also like to thank Malatya Apricot Foundation forproviding the apricots.

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