International Journal of Food Microbiology 153 (2012) 92–98
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International Journal of Food Microbiology
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Effects of microencapsulated Allyl isothiocyanate (AITC) on the extension of theshelf-life of Kimchi
J.A. Ko a,1, W.Y. Kim a,1, H.J. Park a,b,⁎a School of Life Sciences and Biotechnology, Korea University, Seoul, 136-701, Republic of Koreab Department of Packaging Science, Clemson University, Clemson, SC 29634-0370, USA
⁎ Corresponding author at: School of Life Sciences andsity, 1,5-Ga, Anam-Dong, Sungbuk-Gu, Seoul 136–701,3290 3450; fax: +82 2 953 5892.
E-mail address: [email protected] (H.J. Park).1 Both J.A. Ko and W.Y. Kim were equally contribut
Allyl isothiocyanate (AITC) is a well-recognized antimicrobial agent but, application of AITC to food systems islimited due to its high volatility and strong odor. This study was performed to overcome the volatility of AITCby encapsulation using gum Arabic and chitosan and to investigate the effect of microencapsulated AITC as anatural additive on the shelf-life and quality of Kimchi. AITC loaded microparticles were prepared using gumArabic and chitosan and were added to Kimchi at various concentrations (0–0.02%, w/w). The titratable acid-ity, pH, microbial changes, and sensory test of Kimchi were examined for 15 days at different fermentationtemperatures (4 and 10 °C). The pH of Kimchi containing AITC microparticles was significantly higher thanthat of control and the higher the quantity of added AITC, the higher the pH became. The titratable acidityof Kimchi increased during storage especially, titratable acidity of control increased significantly higherthan those of Kimchi with added AITC microparticles. The number of Leuconostoc and Lactobacillus speciesin Kimchi decreased with an increase in the concentration of AITC. The addition of AITC induced reductionof sour taste and improvement of the texture of Kimchi during fermentation. However, as the content ofAITC increased, the scores of overall acceptability decreased due to the odor of AITC. These results indicatethat addition of AITC (less than 0.1%) to Kimchi is an effective way of enhancing the shelf-life of Kimchi with-out reducing quality.
Kimchi is a traditional Korean fermented vegetable food whose in-creased consumption worldwide is attributable to various functionalcharacteristics, such as anti-carcinogenic (Choi et al., 1997), anti-oxidative activity (Lee et al., 2004; Ryu et al., 2004) and immunestimulatory activity (Kim and Lee, 1997). The magazine Health men-tioned Kimchi in its list of the top five “World's Healthiest Foods”(http://eating.health.com/2008/02/01/worlds-healthiest-foods-kimchi-korea/#). There are many fermentative microorganisms inKimchi, especially lactic acid bacteria such as Lactobacillus plantarumand Leuconostoc mesenteroides. These bacteria are beneficial inhabi-tants of the intestinal tract of humans and animals and produce thecharacteristic taste and flavor of Kimchi. As fermentation progresses,the lactic acid bacterial count increases, resulting in an increase inacidity and formation of CO2 gas along with production of the sourand characteristic carbonic taste of Kimchi (Shin et al., 2002). Factory
Biotechnology, Korea Univer-Republic of Korea. Tel.: +82 2
ed to this research as co-first
l rights reserved.
manufactured Kimchi is usually packaged in glass jars, plastic trays orplastic pouches without pasteurization, and therefore lactic acid fer-mentation still continues during its storage and marketing. After itreaches a well-aged step, these microbiological and enzymatic activi-ties continue and result in a sour and bitter taste, off-odor, and soften-ing due to the deterioration of Kimchi (Lee et al., 2000). Therefore,control of the fermentation process is needed to preserve the qualityof commercial Kimchi and to extend its shelf-life. Several studies havebeen conducted to extend the shelf-life of Kimchi using heat treat-ment (Kang et al., 1991), gamma radiation (Kim et al., 2008), antisep-tic treatment (Park and Woo, 1988), antimicrobial agents (Moon etal., 1995), herbal medicines (Jung et al., 2002; Kim et al., 2008), oystershell powder (Choi et al., 2006), and pH adjusters (Lee and Kim,2003). The best way to overcome the problem of over-ripening is tocontrol the growth of lactic acid bacteria without damaging the prod-uct, thus suggesting the use of the natural antimicrobial allyl isothio-cyanate (AITC).
AITC (CH2_CHCH2N_C_S), the majority pungent compound inplants, belongs to the Cruciferae family, which includes cabbage, broc-coli, horseradish, and mustard (Delaquis and Sholberg, 1997). AITC isknown to possess strong antimicrobial activity, capable of killingfungal and bacterial pathogens on plant seeds, fresh produce, bread,meat, and cheese (Lee et al., 2009; Li et al., 2007; Nadarajah et al.,2005; Nielsen and Rios, 2000). Therefore, it might be a potential
93J.A. Ko et al. / International Journal of Food Microbiology 153 (2012) 92–98
natural antimicrobial agent for food preservation. However, any ap-plication of AITC to food systems is limited due to its high volatility,strong odor, poor water solubility, and reactivity with natural foodnucleophiles (Chacon et al., 2006; Kim et al., 2008). To solve theseproblems, a microencapsulation method was considered. Microen-capsulation can provide protecting sensitive food components, mask-ing taste and odor as well as promoting controlled lease of corematerials (Ko et al., 2008).
Gum Arabic (gum acacia) is a negatively charged polyelectrolytethat is commonly used as a flavor-encapsulating material due to itshigh water solubility, low viscosity in concentrated solution relative toother hydrocolloid gums, and good retention of volatile compounds(Ko et al., in press; Shiga et al., 2001). Chitosan [poly(ß -(1→4)-2-amino-2-deoxy-Dglucose)], a natural cationic polysaccharide derivedfrom chitin, has been studied by the food industry since it has film-forming properties, nutritional quality, and antimicrobial agents(Shahidi et al., 1999). Therefore, the combined use of gum Arabic withchitosan could provide an inter-biopolymer electrostatic complex thatwould form strong viscoelastic films around AITC and provide goodbarrier properties against its unique flavor.
The objective of this study was to overcome the volatility of AITCby encapsulation using gum Arabic and chitosan and to evaluate theeffects of AITC microparticles as a natural additive on the shelf-lifeand quality of packaged Kimchi during the storage.
2. Materials and methods
2.1. Materials
Gum Arabic HPS Powder (Food grade, IRX 50924) was supplied byCNI (France). AITC (>98% GC purity, Nature) was purchased fromHyangwon-Spice (Seoul, Korea). Chitosan (MW: 30,000 and DOD90%) was purchased from BioTech Inc. (Mokpo, Korea). L. plantarumKCCM 11322 and L. mesenteroides KCCM 11324 strains were obtainedfrom the Korean Culture Center of Microorganisms (KCCM; Seoul,Korea). Other chemicals were reagent grade and used without furtherpurification. Kimchi was purchased from Pungmi Foods Co., Ltd(Suwon, Korea).
2.2. Antimicrobial test of AITC
The antimicrobial activity of encapsulated AITC against L. plan-tarum and L. mesenteroides was evaluated using liquid culture testmethods. Microorganisms were grown in 20 mL of Tryptic soy broth(TSB; Difco, St. Louis, USA) in an incubator at 37 °C. L. plantarumand L. mesenteroides (0.3 mL) was inoculated into 30 mL of MRSbroth (Difco, St. Louis, USA) supplemented with 0 to 0.50% (w/w) ofAITC, respectively and incubated at 30 °C for 24 h. Each culture wassampled (1.5 mL) periodically every 4 h during the incubation period.The optical density of each culture sample was measured atλ=600 nm using an UV/visible spectrophotometer to represent thecell concentrations of the microorganisms in the media.
2.3. Preparation of microparticles
An aqueous solution of gum Arabic (25% w/w) was prepared andstirred overnight at room temperature. Emulsions were prepared byadding AITC oil to the gum Arabic solution with tween 20 (0.5%),and the mass ratio of gum Arabic to AITC was 3:1. The mixture wasthen homogenized using a high-speed mixer (T25-basic, IKA, Germa-ny) set at 11,000 rpm for 3 min. Then, the chitosan solution (2.5%, w/v), which was dissolved in 50 mM lactic acid solution, was added tothis mixture. The final mixture was homogenized at 11,000 rpm for10 min. The AITC emulsion was fed through a spray dryer (LabPlant-SD05, Huddersfield, UK) equipped with a centrifugal atomizer.The operation conditions of spray drying were as follows: inlet air
temperature of 200 °C, outlet temperature of 115 °C, feed rate of5 mL/min, air flow rate of 73 m3/h, and atomizer rotational speed of30,000 rpm. Finished powder was stored in a hermetically-sealedbottle at −20 °C.
2.3.1. Characterization of microparticlesThe particle size distribution of the spray-dried microparticles was
determined using a particle size analyzer (CILAS-1064, Orleans,France) fitted with a small volume sample presentation unit and inte-gration software. Calculation of the particle size distribution wasbased on a relative particle refractive index of 1.1500 and particle ab-sorption of 1.0000. Powder particle size distributions were deter-mined following their dispersion in propan-2-ol.
The external structures and microcapsule morphology wereassessed using a cold stage scanning electron microscope (JEOL,JSM-5300, Tokyo, Japan) at an accelerating voltage of 15 kV. Micro-capsules were placed on stubs using double-sided sticky carbontape. Stubs were then coated with a gold-palladium layer using aSEM magnetron sputter coater.
2.3.2. Quantification of encapsulated AITCThe total content of AITC in the powder was measured according
to the solvent extraction method. One gram of powder was weighedinto a 50 mL glass bottle and mixed with 4 mL of distilled water,after which 4 mL of diethyl ether with phenyl isothiocyanate as an in-ternal standard was added. This was followed by violent shaking andthen centrifugation at 3000 rpm for 10 min to separate the organicphase from distilled water. The flavor content in the organic phasewas measured using a gas chromatograph (HP 5890 series, Hewlett-Packard Co. Avondale, PA). The column used was a HP-1 cross linkedmethyl siloxane column (30 m×0.25 mm inner diameter, 0.25 μmfilm thickness, Agilent Technologies, Inc., Palo Alto, CA, USA). Theoven temperature was programmed from 50 °C for 1 min to 200 °Cfor 3 min at 10 °C/min. The injection port temperature and detectortemperature were kept at 160 °C and 250 °C, respectively. The carriergas was nitrogen at a split ratio of 1:30. Peaks areas were recordedand calculated using HP Chemstation software.
2.3.3. Release of AITC from microparticlesIn other to evaluate release of AITC from microparticles, 0.1 g of
powder was put in 5 mL vial capped with septum. The volume wasup to 1 mL with sodium phosphate citrate buffers adjusted to pH 4,and the vial capped with Teflon lined cap equipped septum. Then,the mixture was stored at 10 °C for 15 days. The amount of AITCretained in the powder was quantified by the method describedabove and expressed as a percentage of the initial amount.
2.4. Characteristics of packaged Kimchi during storage
2.4.1. Preparation of KimchiKimchiwas prepared on the basis of the following composition (%,
w/w) — radish (7.5%), red pepper (2.8%), leaf mustard (0.7%), garlic(1.2%), ginger (0.4%), onion (0.7%), green onion (0.5%), liquefied fishsauce (0.8%), salted shrimps (1.0%), white sugar (0.6%), and refinedsalt (0.38%). Each quarter head of blended cabbage was anaerobicallypackaged in a polyethylene vinyl pouch (500 mL). AITC microparti-cles (0–0.2% against the weight of Kimchi) were added to the condi-ment and spread onto the cabbage for preparation of Kimchi. AITC0% means only gum Arabic–chitosan microparticles without core ma-terial, AITC. The prepared Kimchi was fermented in a refrigerator for15 days at 4 and 10 °C, respectively. The temperature of a showcaseof Kimchi at the market is about 10 °C.
2.4.2. Measurement of pH and titratable acidityKimchi juice was centrifuged at 3100 rpm for 10 min. The pH
of the supernatant was determined using a pH meter. Titratable
Ab
sorb
ance
at
600n
m
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 4 8 12 16 20 24
0.0
0.5
1.0
1.5
2.0
2.5
Ab
sorb
ance
at
600n
m
(a) Leuconostoc mesenteroides
(b) Lactobacillus plantarum
Incubation time (hrs)
Fig. 1. Changes in the growth of (a) Leuconostoc mesenteroides and (b) Lactobacillusplantarum in medium containing allyl isothiocyanate (AITC). ●: control, ○: 0.1%, ▼:0.2%, △: 0.3%, ■: 0.4%, □:0.5%.
Time (days)0 3 6 9 12 15
Rel
ease
of
AIT
C (
%)
50
60
70
80
90
100
Fig. 3. Release behavior of AITC from gum Arabic–chitosan microparticles.
5.0
5.5
6.0
(a) 4 oC
94 J.A. Ko et al. / International Journal of Food Microbiology 153 (2012) 92–98
acidity (TA) was measured by titrating with 0.1 N NaOH solution untila pH of 8.3, and total acidity was calculated as a percentage of lacticacid.
pH
3.5
4.0
4.5
2.4.3. Microbial analysisThe supernatant (100 μL) of centrifuged Kimchi juice was diluted
1000-fold with 0.1% peptone water. And the dilution (100 μL) wereinoculated on Plate count agar (Difco, St. Louis, USA) for the determi-nation of total microbial counts and also inoculated on MRS agar(Difco, St. Louis, USA) and PES (Difco, St. Louis, USA) for Lactobacillusand Leuconostoc species, respectively. All plates were prepared in
Fig. 2. Scanning electron micrograph (SEM) of AITC-loaded gum Arabic–chitosanmicroparticles.
triplicate, incubated at 30 °C for 48 h, and viable cell numbers weredetermined as colony forming units (log cfu/mL).
2.4.4. Sensory evaluationSensory properties of Kimchi samples during storage for 15 days
were assessed by a taste panel consisting of eight people. All panelistswere semi-trained for Kimchi evaluation. Sensory evaluation of sour-ness, texture, flavor, color, and overall acceptability was scored on ascale from 0 to 15. The degree of sourness and texture was representedas very weak (1–3 points), weak (4–6 points), moderate (7–9 points),strong (10–12 points), or very strong (13–15 points). The degree of fla-vor, color, and overall acceptability was represented as very poor (1–3
Fermentation time (days)
0 3 6 9 12 15
pH
3.0
3.5
4.0
4.5
5.0
5.5
3.0
(b) 10 oC
Fig. 4. Changes in pH of Kimchi during fermentation period. ●: control, ○: G-C, ▼:0.05%, △: 0.1%, ■: 0.15%, □:0.2%.
95J.A. Ko et al. / International Journal of Food Microbiology 153 (2012) 92–98
points), very (4–6 points), moderate (7–9 points), good (10–12 points),or very good (13–15 points).
2.5. Statistical analysis
One-way analysis of variance (ANOVA) was used to determine theeffect of microencapsulated AITC on the Kimchi using SPSS software(version 12.0, SPSS Korea). The mean values were compared with sig-nificance defined at pb0.05 using Duncan's multiple rang test. In thisstudy, all the experiments were performed in at least triplicate and alldata were expressed means±standard deviation (SD).
3. Results and discussion
3.1. Antimicrobial effect of AITC
The effects of AITC on the growth of L. plantarum and L. mesenter-oides are shown in Fig. 1. The growth profiles of L. plantarum weresimilar to those of L. mesenteroides. The microbial growth of L. plan-tarum and L. mesenteroides at 0.10% AITC decreased significantly(pb0.05) to almost half of those of the control after 24 h. The bacteri-cidal effect of AITC was concentration-dependent. In other words, asthe concentration of AITC solution increased, the growth of L. plan-tarum and L. mesenteroides decreased. AITC has been shown to haveantimicrobial activity against some pathogenic bacteria, yeasts, ormolds and is permitted for use as a food preservative in Japan, butuse of AITC in food systems is limited because due to its strong odor(Inatsu et al., 2005; Jin and Gurtler, 2011). Thus, reduction of theodor of AITC is necessary for food applications. Therefore, we choselow concentration (a lower than 0.2%) of AITC and microencapsula-tion technique for the study of Kimchi fermentation.
Tit
rata
ble
aci
dit
y (%
as
lact
ic a
cid
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Fermentation time (days)0 3 6 9 12 15
Tit
rata
ble
aci
dit
y (%
as
lact
ic a
cid
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
(a) 4 oC
(b) 10 oC
Fig. 5. Changes in titratable acidity of Kimchi during fermentation period.●: control,○:G-C, ▼: 0.05%, △: 0.1%, ■: 0.15%, □:0.2%.
3.2. Preparation and characterization of gum Arabic–chitosanmicroparticles
Gum Arabic–chitosan microparticles were prepared based on theionic interaction between the carboxylic groups (\COO−) of gum Ar-abic and the amino groups (\NH3
+) of chitosan using an air-atomizer.Fig. 2 shows the shapes and surface morphologies of the chitosan-gum Arabic microparticles. Similar to the observations of Bertolini etal. (2001) and Rosenberg et al. (1990), the gum Arabic microparticleshad a rounded external surface with concavities and dents due toshrinkage of the droplets during drying. The particle size of the micro-particles ranged mainly between 10 and 50 μm, and efficiency of AITCwas about 77%. Fig. 3 shows the behavior of AITC release from thegum Arabic–chitosan microparticles. Approximately 20% of the load-ed AITC was released from the microparticles during storage for15 days. As fermentation proceeded, AITC was released continuously,thereby increasing the shelf-life of Kimchi.
3.3. Characteristics of packaged Kimchi during storage
3.3.1. pH and titratable acidityFig. 4 shows changes in the pH levels of the Kimchi samples trea-
ted with various concentrations of AITC during fermentation at 4and 10 °C. It is well established that the pH of Kimchi decreases withthe fermentation period. The pH value of the control decreased from5.7 to 3.76 (at 4 °C) and 3.31 (at 10 °C) during storage for 15 days.The pH of Kimchi containing AITC was significantly higher than thatof the control (pb0.05), and the pH decreased slightly when AITCcontent increased from 0.05 to 0.2%.
The changes in the titratable acidity values of the Kimchi samplesduring fermentation at 4 and 10 °C are shown in Fig. 5. After fermen-tation for 15 days, the titratable acidity of the control increased
To
tal m
icro
bia
l nu
mb
er (
log
CF
U/m
l)
4
5
6
7
8
9
Fermentation time (days)0 3 6 9 12 15
4
5
6
7
8
To
tal m
icro
bia
l nu
mb
er (
log
CF
U/m
l)
(a) 4 oC
(b) 10 oC
Fig. 6. Changes in total microbial count of Kimchi during fermentation period. ●: con-trol, ○: G-C, ▼: 0.05%, △: 0.1%, ■: 0.15%, □:0.2%.
96 J.A. Ko et al. / International Journal of Food Microbiology 153 (2012) 92–98
sharply from 0.33 to 0.74 (at 4 °C) and 1.28 (at 10 °C). Meanwhile, thetitratable acidity values of the Kimchi samples containing AITC micro-particles (0.05, 0.1, 0.15, and 0.2%) increased slightly to 0.63, 0.64,0.59, and 0.55 acidity at 4 °C and to 0.77, 0.88, 0.65, and 0.60 acidityat 10 °C, respectively. The titratable acidity also increased dependingon the concentration of AITC. One of the most important factors af-fecting Kimchi fermentation is temperature, as the ripening time ofKimchi depends on the fermentation temperature. At 10 °C, pH de-creased sharply with increasing titratable acidity, whereas pH and ti-tratable acidity at 4 °C changed more slowly compared.
The pH and titratable acidity are considered to be the major qual-ity attributes affecting the characteristic sour taste of Kimchi (Hongand Park, 1999). The pH and titratable acidity ranges of commerciallyavailable Kimchi are from 4.1 to 4.5 and from 0.28 to 1.00%, respec-tively (Ku et al., 2003). In this study, the pH and titratable acidity ofKimchi with added AITC were within this available range or not yetreached. Therefore, it means that addition of AITC microparticlescan affect the extension of fermentation of Kimchi.
3.3.2. Microbial analysisThe total growth of microbes during fermentation of the Kimchi
samples at 4 and 10 °C is shown in Fig. 6. At the initial stage of fer-mentation, the number of total microbes of the control group was ap-proximately 4.50±0.01 log cfu/mL at 4 and 10 °C. Generally, the totalnumber of microbes increased markedly until 6 days of fermentationand remained constant thereafter. However, the total number of mi-crobes in Kimchi containing 0.2% AITC increased steadily during the15 day fermentation period at both 4 and 10 °C. As the concentrationof AITC in Kimchi increased, the total number of the microbes in Kim-chi increased slowly.
Fig. 7 shows the number of Leuconostoc species of Kimchi contain-ing encapsulated AITC from 0.05 to 0.20% during fermentation.
Leu
con
ost
oc
nu
mb
er (
log
CF
U/m
l)
4
5
6
7
8
9
Fermentation time (days)0 3 6 9 12 15
Leu
con
ost
oc
nu
mb
er (
log
CF
U/m
l)
4
5
6
7
8
(a) 4 oC
(b) 10 oC
Fig. 7. Changes in Leuconostoc species count of Kimchi during fermentation period. ●:control, ○: G-C, ▼: 0.05%, △: 0.1%, ■: 0.15%, □:0.2%.
L. mesenteroides is a major bacterial population of Kimchi from the ini-tial to the middle stage of fermentation. This bacterium produces var-ious metabolites such as lactic acid, acetic acid, ethanol, carbondioxide, mannitol, and dextran, which are associated with the tasteof Kimchi (Mheen and Kwon, 1984). During the optimum-ripeningperiod, the number of L. mesenteroides reaches its highest point anddecreases when the pH of Kimchi is decreased to 4.0–4.5 (Lee et al.,1992). This is in good agreement with our study. The number of Leu-conostoc species increased rapidly at the initial stage of fermentationand then decreased or was maintained. However, the addition ofmore than 0.10% encapsulated AITC continuously increased the num-ber of Leuconostoc species during Kimchi fermentation.
On the other hand, Lactobacillus species have strong pH toleranceunder high organic acid concentration (Mheen and Kwon, 1984).Therefore, the number of Lactobacillus species increased continuouslyduring fermentation at both 4 and 10 °C (Fig. 8), and it possibly in-duces the acidification of Kimchi.
As the concentration of AITC in Kimchi increased, the number ofLeuconostoc and Lactobacillus species decreased. AITC has been reportedto have antibacterial and antifungal properties against a wide variety ofmicroorganisms (Delaquis and Sholberg, 1997; Isshiki et al., 1992; Lin etal., 2000). Inatsu et al. (2005) reported that the addition of AITC sup-presses the growth of LAB from 2.85 log CFU/g to 2.0 log CFU/g after4 days of storage in fermented Chinese cabbage.
Several workers have reported that chitosan is effective in extend-ing the edible period of Kimchi (Lee and Lee, 2000; Lee and Jo, 1998;Yoo et al., 1998). Ahn and Lee (1995) reported that chitosan delaysthe softening of Kimchi tissues during fermentation. However, in ourstudy, we found that chitosan did not have an effect on the numberof microorganisms in Kimchi. In the case of gum Arabic–chitosantreatment, the number of microorganisms was similar to that of con-trol. This is in good agreement with the results of Inatsu et al. (2005)
Lac
tob
acill
us
nu
mb
er (
log
CF
U/m
l)
3
4
5
6
7
8
9
Fermentation time (days)0 3 6 9 12 15
Lac
tob
acill
us
nu
mb
er (
log
CF
U/m
l)
3
4
5
6
7
8
(a) 4 oC
(b) 10 oC
Fig. 8. Changes in Lactobacillus species count of Kimchi during fermentation period. ●:control, ○: G-C, ▼: 0.05%, △: 0.1%, ■: 0.15%, □:0.2%.
97J.A. Ko et al. / International Journal of Food Microbiology 153 (2012) 92–98
and Savard et al. (2002), and who indicated that chitosan does notsuppress the growth of LAB in vegetable juice and fermented Chinesecabbage, respectively.
3.3.3. Sensory evaluationThe sensory evaluation results of Kimchi containing various con-
centrations of AITC microparticles are shown in Fig. 9. It shows the re-sults for five sensory evaluation items (sourness, texture, flavor, color,and overall acceptability) acquired during 15 days of fermentation at4 and 10 °C. The scores for texture of the control decreased signifi-cantly compared to those of AITC-treated Kimchi (pb0.05). Generally,the edible, good taste of Kimchi is obtained before texture-softeningand acidification. Further, softening of Kimchi is one of the main
Fig. 9. Quantitative description analysis (QDA) profiles of sensory evaluation scores ofKimchi containing different concentrations of AITC microparticles during fermentationfor (a) 0 days, (b) 4 °C, 15 days, and (c) 10 °C, 15 days.○: control,△: 0.05%,□: 0.1%,▲:0.15%, ■:0.2%.
causes of deterioration of Kimchi (Song et al., 2009). Therefore, theaddition of AITC had a beneficial effect on delaying the softening ofKimchi.
Color, flavor, and texture were not affected by temperature, butsourness increased at 10 °C compared to 4 °C. As the fermentationprogressed, major changes in the sour taste were observed in all ofthe treated samples. The sour taste of Kimchi containing encapsulatedAITC was significantly lower than that of the control (pb0.05). As thecontent of AITC increased, the scores for sour taste decreased. Howev-er, 0.15% and 0.2% AITC-treated Kimchi had lower scores for flavor andoverall acceptability compared to those of other samples. The addi-tion of AITC increased the unique flavor in Kimchi due to its strongodor, resulting in a large effect on overall acceptability. After15 days, the growing difference between the flavors of the controland treated Kimchi might have been due to the release of AITC frommicroparticles during fermentation. From the results, it was conclud-ed that 0.15 and 0.2% AITC treatment affected the sensory qualities ofKimchi. Thus, treatment with less than 0.1% is recommendable forKimchi.
4. Conclusions
This study was performed to investigate the effects of encapsulat-ed AITC as a natural additive on the fermentation and quality ofKimchi in order to extend shelf-life. Encapsulated AITC addition toKimchi resulted in positive changes in pH, titratable acidity, and mi-crobial analysis compared to that of control. However, with regardsto sensory analysis, AITC concentrations of 0.10% or lower are recom-mended for manufacturing Kimchi. These results constitute a theoret-ical foundation for the application of AITC as a nature additive in thefood industry.
Acknowledgments
This study was supported by a grant from Korea Universityand the Korea Health 21 R&D Project, Ministry of Health and Welfare,Republic of Korea (A050376).
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