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The effect of packaging conditions on the quality of minimally processed celeriac flakes
Food Control 18 (2007) 1191–1197 www.elsevier.com/locate/foodcont
The effect of packaging conditions on the quality of minimally processed celeriac flakes E. Radziejewska-Kubzdela a
a,*
, J. Czapski a, K. Czaczyk
b
Institute of Food Technology, The August Cieszkowski Agricultural University of Poznan´, Wojska Polskiego 31, 60-624 Poznan´, Poland b Department of Biotechnology and Food Microbiology, The August Cieszkowski Agricultural University of Poznan´, Wojska Polskiego 48, 60-627 Poznan´, Poland Received 2 January 2006; received in revised form 11 July 2006; accepted 17 July 2006
Abstract The aim of the study was to select packaging conditions of minimally processed celeriac to preserve their quality during storage for 12 days at 4 and 15 C. The quality of the product was determined on the basis of colour measured in the CIE L*a*b* system, sensory quality and total counts of mesophilic and psychrophilic bacteria, counts of moulds and yeasts, coliform counts, counts of Pseudomonas bacteria and the presence of bacteria from the genus Clostridium perfringens. Moreover, changes were determined in oxygen and carbon dioxide contents in the atmosphere within the packs, in which the product was stored. Celeriac flakes were packaged in the atmosphere with varying CO2 contents (0%, 5%, 10%, 20%, 30%, 50% plus 2% O2 and with balance N2). After 12 days at 4 C, it was found that celeriac flakes packaged in atmosphere containing 5% or 10% CO2, 2% O2 and balance N2 were characterized by better quality than samples packaged in air atmosphere or in the atmosphere with CO2 contents of 0% or higher than 10%. Modified atmosphere with the content of 5% or 10% CO2, 2% O2 and balance N2, applied in the packaging of celeriac flakes, resulted in the inhibition of growth of mesophilic, psychrophilic and coliform bacteria in the tested minimally processed product. 2006 Published by Elsevier Ltd. Keywords: Modified atmosphere; Celeriac; Minimal processing; Sensory quality; Microbiological counts
1. Introduction Minimal processing of celeriac provides convenience for consumers and many economic benefits for producers. However, little information has been published about this product. The effect of minimal processing of celeriac (peeling, shredding) can induce disadvantageous changes in tissue, which may lead to darkening of the flakes and deterioration of product sensory attributes. Moreover, shredded raw material constitutes an excellent medium for the development of micro-organisms. An uncontrolled increase in the population size of certain micro-organisms may lead
*
Corresponding author. Tel:. +48 61 848 72 90; fax: +48 61 848 73 14. E-mail address: [email protected] (E. Radziejewska-Kubzdela).
0956-7135/$ - see front matter 2006 Published by Elsevier Ltd. doi:10.1016/j.foodcont.2006.07.019
to shortened shelf life of the product. This group of micro-organisms includes e.g. bacteria from genera Pseudomonas, as well as certain types of yeasts and moulds (Beuchat, 2002; Nguyen-The & Carlin, 1994). Moreover, pathogenic micro-organisms causing a health hazard may also proliferate in the minimally processed product. Numerous studies are being carried out on the application in the packaging of minimally processed vegetables and fruits of modified atmosphere with the composition considerably differing from the recommended one, i.e. 1– 5% oxygen and 5–10% carbon dioxide. An example in this respect may be packaging chicory endive in the atmosphere containing 1.5% oxygen, 20% carbon dioxide and 78.5% nitrogen. The application of atmosphere with such a composition contributed to the maintenance of good sensory quality of the product within 13 days of storage and a 50% reduction of growth of microflora responsible for
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spoilage in comparison to air-packaged samples (Bennick et al., 1996). It was found that an increase in CO2 concentration inside the pack resulted in a reduction of the respiration rate. It was frequently explained by the effect of this gas on the activity of enzymes participating in glycolysis and the Krebs cycle (Peppelenbos & van ’t Leven, 1996). The application of too high carbon dioxide concentrations (above 30%) may contribute to physiological changes and microbial decay of minimally processed vegetables and fruits (Carlin, Nguyen-The, Chambroy, & Reich, 1990; Dixon & Kell, 1989; Ke, van Gorsel, & Kader, 1990). The selection of an appropriate composition of atmosphere used for packaging vegetables and fruits depends e.g. on the type of viable microflora, susceptibility to oxygen and carbon dioxide and the susceptibility to enzymatic browning of tissue (Church & Person, 1995). The aim of this study was to determine the effect of various CO2 contents in the atmosphere inside the pack on the quality of celeriac flakes stored for 12 days at 4 and 15 C. 2. Materials and methods 2.1. Materials Experimental material consisted of celeriac (Apium Graveolens L. var. rapaceum) cv. Mentor. The raw material came from a farm in western Poland. Celeriac was harvested in October. Celeriac roots were oval in shape and exhibited medium rooting degree. The flesh was whitecreamy in color, with low susceptibility to browning. 2.2. Preparing of the minimally processed celeriac Celeriac roots were washed in water, hand-peeled, washed again and shredded into flakes (4 · 1 · 40 mm) in a food processor (Zelmer, Polska). Flake portions of 50 g were placed in bags (15 · 21 cm) made of oriented polyamide/polyethylene laminate with layer thickness of 50/40 lm and gas permeability (in cm3/m2/24 h at 23 C) for carbon dioxide – 200, oxygen – 45 and water vapour of 2–3 g/m2/ 24 h (Multivac, Jastko´w). Bags were sealed using a vacuum packaging machine type A-300 (Multivac). Experiments were conducted for various CO2 concentrations and different temperatures of storage: (a) Samples packaged in modified atmosphere containing 10%, 20%, 30% and 50% CO2 and stored at 4 C; (b) Samples packaged in modified atmosphere containing 0%, 5% and 10% CO2 and stored at 4 C and 15 C. Contents of other gases in modified atmosphere packaged samples were 2% O2 and with balance N2. The modification of the atmosphere in the bags was achieved by using a gas packaging unit (gas mixer, WITT M6183MSO, Gasetechnik). The reference sample consisted of air-packaged celeriac flakes.
The product was analyzed after 1, 6 and 12 days of storage. Color measurements were taken of homogenized flakes and sensory examination was performed for Experiments a and b. In case of samples from Experiment b stored at 4 C changes in carbon dioxide and oxygen inside the pack were measured and microbiological quality was determined. 3. Color parameter measurements Color parameters in the CIE L*a*b* system were measured using a Hitachi U-3000 spectrophotometer. Before the measurement was taken 50 g celeriac flakes were homogenized in an IKA T-25 homogenizer with 50 ml distilled water added. Homogenized celeriac pulp was placed in a 3 · 5 · 2 cm glass cuvette. Measurements were taken immediately after homogenization. The color measurement was performed in three replications for each sample. 3.1. Sensory examination The sensory quality was evaluated by a five-member trained panel (all members of the Agricultural University of Poznan´). Before the start of the sensory experiments, panel members were familiarized with the product and scoring methods. This consisted of demonstration exercises involving examination of packs at different levels of deterioration and agreeing appropriate scores. When the panel members had become familiar with the test conditions and scoring regime, they were invited to score samples. This procedure was repeated several times until a level of consistency was obtained. Sensory examination was performed immediately after bags with celeriac flakes were opened. The examination was conducted in a 5-point scale (Baryłko-Pikielna, 1994) using a specially developed sensory examination chart (Table 1). The results of the sensory analysis were reported as means of three separate experimental determinations for each sample. 3.2. Measurement of oxygen and carbon dioxide contents in pack with celeriac flakes The measurements were taken using a PBI Dansensor Check Mate 9900 apparatus. A probe was inserted into the packaging through a rubber gasket and oxygen and carbon dioxide contents were read on the meter. Three replications were performed for each sample. 3.3. Analysis of microbiological quality of celeriac flakes 3.3.1. Sample preparation for microbiological analysis Celeriac flakes (approx. 10 g) were transferred to a sterile stomacher bag and 90 ml of a physiological salt/peptone solution (8.5 g/l NaCl, 1 g/l peptone tryptone, Difco) were added and mixed for 2 min in a DEVIMIX machine (De Ville Biotechnology, Raszyn, Poland). Ten-fold dilutions in the range from 10 1 to 10 8 were prepared from these samples.
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Table 1 A sensory examination chart Quality attribute
Weighting coefficient
Point scores 5
4
3
2
1
Colour of flesh
4
White-creamy
Creamy-yellow
Creamy-yellow with scarce brown spots
Brown on whole surface
Aroma desirability
4
Good, celery
Just acceptable
Deteriorated
Intensity Taste desirability
2 4
Intensive Good, celery
Medium intensive Just acceptable
Weakly detectable Just unacceptable
Undetectable Deteriorated
Intensity Texture
2 4
Very good, celery Very intensive Very good, celery Very intensive Very firm
Creamy-yellow with numerous brown spots Just unacceptable
Intensive Firm
Medium intensive Loosened or hardening
Weakly detectable Loose or lignified
Undetectable Sticky or lignified
Total counts of mesophilic and psychrophilic bacteria and counts of moulds and yeasts were determined using a quantitative culture according to the Koch plate method (Burbianka & Pliszka, 1983). In case of the total mesophilic and psychrophilic bacteria counts media were prepared according to Burbianka and Pliszka (1983). Peptone agar with glucose was the medium for aerobic mesophilic and psychrophilic bacteria (10 g/l bacteriological pepton, 10 g/l glucose, 15 g/l bacteriological agar, pH 7, BTL, Poland). The medium used for analysis of yeasts and moulds containing: 5 g/l yeast extract, 20 g/l glucose, 0.1 g/l chloramfenicol, 15 g/l bacteriological agar, pH 6.6, (BTL, Poland). The analyses were carried out on duplicate agar plates for each replication of sample. Reported microbiological counts therefore represent the means of six values. The applied incubation parameters were as follows: mesophilic bacteria – incubation time 48 h–72 h, incubation temperature 30 C; psychrophilic bacteria – incubation time 72 h–120 h, incubation temperature 15 C. Incubation time for the determination of moulds and yeasts was 72 h– 96 h, while temperature was 30 C. The filtration method was applied to determine coliform bacteria counts and counts of Pseudomonas bacteria (Libudzisz, 2000). The Endo–Total Coliform Broth (Millipore) was used as a medium for coliform bacteria. Incubation time was 24 h– 48 h, while incubation temperature was 30 C. The Pseudomonas Selective Broth (Millipore) was used as a medium for Pseudomonas bacteria. Incubation time was 48 h–72 h and incubation temperature was 37 C. The determination of anaerobic bacteria consisted in the detection of the presence of anaerobic bacteria from the genus Clostridium perfringens. Quantitative culture using the Koch plate method was applied in the analysis. Agar TSC (Merck) was used as a medium. Incubation time was 48 h, while incubation temperature was 37 C. Black colonies on the medium constituted a positive culture result. Morphology of the micro-organisms was examined in microscopic slides: live specimens for moulds and fixed Gram-stained for bacteria (Burbianka & Pliszka, 1983).
3.4. Statistical analysis of results All experiments were carried out in duplicate and each duplicate was repeated twice. For each set of conditions three samples (three bags) were prepared and analyzed. Statistical analysis was performed using computer software Statistical version 6.0 applying the analysis of variance (ANOVA), the Fisher’s least significant difference (LSD) multicomparison test and multiple linear regression. Statistically significant differences were reported at p 6 0.05.
4. Results Packaging of celeriac flakes in modified atmosphere containing 5% or 10% CO2, 2% O2 and balance with N2 had an advantageous effect on their color. On the basis of color sensory examination it was found that these flakes were creamy after 1, 6, as well as 12 days of storage at the temperature of 4 C. In samples packaged in the atmosphere with a higher CO2 content (20%, 30%, 50%) or without CO2, as well as those which were air packaged, a significant (p 6 0.05) deterioration of the product color was observed. After 12-day storage these samples were defined as creamyyellow with scarce brown spots (Table 2). Instrumental color measurement confirmed the results of sensory examination. Flakes packaged in the atmosphere with 5% or 10% CO2 (2% O2 and balance with N2) after 12-day storage had lightness values L* significantly (p 6 0.05) higher, while colour parameter a* was lower than in the other samples (Table 3). A statistically significant correlation (R2 = 0.99) was found between the lightness L* value, the color parameter a* and the sensory examination results for shredded celeriac color (Table 4). As far as the other sensory examination indexes are concerned, it was found that celeriac flakes packaged at the initial CO2 contents of 0%, 5% and 10% (2% O2 and balance with N2) had good taste and aroma. The samples packaged in air atmosphere and in modified atmosphere with CO2 contents of 20% (2% O2 and balance with N2) or more, after 12-day storage, were characterized by sour taste and
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Table 2 A list of sensory examination results for celeriac flakes packaged in air atmosphere and in modified atmosphere with various CO2 contents stored at 4 C CO2A content [%]
Storage time [day]
Sensory attributes Color
Aroma
Taste
Texture
Overall score
1 6 12
4.9 4.2b 3.1b
2.8 2.1b 2.8
4.4 2.4b 2.8b
4.8 3.2b 3.7b
3.9a 2.9b 3.1b
10
1 6 12
5.0 4.3b 3.6a,b
5.0 4.4a,b 4.2a,b
4.4 3.9a 3.8a,b
4.8 3.9b 4.1a,b
4.8a 4.1a 3.9a,b
20
1 6 12
5.0 4.2b 3.0b
4.2 3.1a,b 3.1b
4.4 3.4a,b 3.4a,b
4.8 3.7b 4.0a,b
4.4 3.6a,b 3.4b
30
1 6 12
5.0 4.3b 3.0b
3.6 2.6b 2.6b
4.4 2.6b 2.8b
4.8 3.2b 4.0a,b
4.4 3.2b 3.2b
50
1 6 12
5.0 4.3b 3.0b
4.0 2.3a,b 2.8b
4.4 2.6b 3.3b
4.8 3.8b 4.2a,b
4.3 2.9b 3.1b
1 6 12
3.3 3.1 3.0
4.7 4.6 3.9
4.5 4.6 4.1
4.7 4.5 4.1
4.4 4.3 3.9b
5
1 6 12
4.0a 4.0a 4.0a
4.5 4.3 3.9
4.5 4.7 4.3
4.8 4.6 4.1
4.5 4.4 4.1b
10
1 6 12
5.0a 4.9a 4.8a
4.5 3.7a 3.8
4.8 4.7 4.6
4.7 4.6 4.6
4.7 4.5 4.3a,b
Experiment a Air
Experiment b 0
A
Contents of individual gases in modified atmosphere: O2-2% and with balance N2. Statistically significant difference (p 6 0.05) between: the scores for modified atmosphere packaged samples and the score for air packaged sample (control) (Experiment a); the scores for samples packaged in atmosphere with 5% and 10% CO2, and the score for sample packaged in atmosphere with 0% CO2 (Experiment b) after the same storage time, for individual sensory attributes. b Statistically significant difference (p 6 0.05) between the score (for individual attributes) of sensory examination after 6 and 12 days of storage and the score after 1 day of storage within the sample. a
aroma. The texture of flakes in all the examined samples was evaluated as desirable (Table 2). During storage, a significant (p 6 0.05) decrease in scores in overall sensory examination, both in air and modified atmosphere packaged samples, was observed (Table 2). Storage of celeriac flakes packaged in modified atmosphere at the temperature of 15 C (Experiment b) resulted in a deterioration of quality. A significant (p 6 0.05) lowering in lightness values L* (Table 3) was observed along with a visible microbial spoilage, which made it impossible to conduct sensory assessment of these samples. On the basis of the results obtained in Experiment b it was found that carbon dioxide content after storage in samples packaged in the initial atmosphere containing 0%, 5% or 10% CO2 (2% O2 and balance with N2) was 14.3%, 19.2% and 24.3%, respectively. In contrast, in air packaged samples it was markedly higher, amounting to 34.1% (Fig. 1). Both in samples packaged in modified atmosphere at the initial oxygen content of 2% and air packaged samples, after 6 and 12 days of storage, a complete disappearance of oxygen was observed. Thus, only
anaerobic respiration processes occurred in the tissue. In spite of that, the taste and aroma of modified atmosphere packaged flakes (0%, 5% and 10% CO2, 2% O2 and balance with N2) were defined as good (Table 2). Moreover, microbiological quality was also determined for samples from Experiment b. During 12-day storage in celeriac flakes packaged in the atmosphere without carbon dioxide content (0% CO2, 2% O2 and balance with N2) and in air atmosphere the counts of mesophilic bacteria increased from 102–103 CFU/g to 106–107 CFU/g, while the counts of psychrophilic bacteria increased from 105 CFU/g to 107–108 CFU/g, respectively. An inhibition of growth in bacteria from the above mentioned groups was observed after the introduction of CO2 to the atmosphere at packaging (Table 5). No significant (p 6 0.05) effect of the composition of atmosphere inside the packaging was found on moulds and yeasts counts (Table 5). During storage, in samples packaged in atmosphere with no carbon dioxide content (0% CO2, 2% O2 and balance with N2) and in air atmosphere, coliform bacteria counts
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Table 3 The color parameters L*, a* and b* after 12-day storage of celeriac flakes packaged in air atmosphere and in modified atmosphere with various CO2 contents: (a) – Experiment a; (b) – Experiment (b). Storage temperature: 4 C; 15 C CO2A content [%]
Color parameters L*
Experiment a Air 10 20 30 50
a*
57.18 ± 1.31 59.10 ± 0.55a 57.33 ± 1.33 57.35 ± 1.19 56.80 ± 1.44
L*
a*
Experiment b 4 C 0 56.92 ± 0.70 5 61.11 ± 0.61a 10 62.64 ± 0.87a
0.35 ± 0.23 0.93 ± 0.18a 2.13 ± 0.18a
b*
0.63 ± 0.37 1.51 ± 0.42a 0.04 ± 0.12 0.50 ± 0.58 0.53 ± 0.31 b*
L*
23.26 ± 1.07 22.43 ± 1.16 21.19 ± 1.12
15 C 56.51± 0.38 55.76 ± 0.79 54.05 ± 0.33a
21.65 ± 0.40 20.06 ± 0.38a 20.38 ± 0.72a 21.55 ± 0.97 20.52 ± 0.41 a*
1.41± 0.11 0.96 ± 0.23a 1.36 ± 0.10
b*
21.73 ± 1.55 19.93 ± 0.44 20.34 ± 0.80
A
– Contents of individual gases in modified atmosphere: O2- 2% and with balance N2. Statistically significant difference (p 6 0.05) between: the values for modified atmosphere packaged samples and the values for air packaged sample (control) (Experiment a); the values for samples packaged in atmosphere with 5% and 10% CO2, and the values for sample packaged in atmosphere with 0% CO2 (Experiment b) for individual color parameters. a
40
after 1 day after 6 day
35 CO2 content [%]
after 12 day
30 25 20 15 10 5 0
air
0%
5%
10%*
Fig. 1. Changes in carbon dioxide contents in atmosphere inside the pack with celeriac flakes during storage at 4 C. Reported values represent the means of nine values. Error bars show standard deviation. *contents of individual gases in modified atmosphere: CO2, O2-2% and with balance N2.
Table 4 A summary of regression describing the dependence between the sensory examination results for shredded celeriac of color and lightness L* value, the color parameter a* and b* after 12 days of storage Regression equation Color =
13.26 + 0.794L*
0.22a* + 0.01b*
was observed in Pseudomonas bacteria counts in comparison to the air packaged sample (Table 5). In the tested celeriac flakes packaged in modified atmosphere and stored for 12 days at the temperature of 4 C no anaerobic bacteria from the genus Clostridium perfringens were found in 1 g of product. The examination of the morphology of mesophilic and psychrophilic bacteria in the analyzed samples showed the presence of Gram-negative bacteria. Live specimens from mould colonies showed that moulds belonged to the genera Aspergillus, Rhizopus and Penicillium.
R2
p-level
0.99
0.000077 (L*) 0.001017 (a*) 0.088490 (b*)
increased from 102 CFU/g to 103–104 CFU/g. The introduction of 5% or 10% CO2 (2% O2 and balance with N2) to the atmosphere inside the packaging resulted in a reduction in the growth of this group of bacteria at the level of 101–102 CFU/g (Table 5). After 1 and 6 days of storage of modified atmosphere packaged celeriac flakes a significant (p 6 0.05) decrease
5. Discussion On the basis of the results of these experiments it was found that celeriac flakes packaged in atmosphere containing 5% or 10% CO2, 2% O2 and balance with N2 exhibited better values of sensory attributes (colour, taste and aroma) than samples packaged in air atmosphere or in the atmosphere with 0% or more than 10% CO2 contents (2% O2 and balance with N2). After 12 days storage, in the sample packaged in air atmosphere and atmosphere 0% CO2, 2% O2 and balance with N2, CO2 concentrations inside the pack increased to 34% and 14.3%, respectively. The high CO2 contents, in the air packaged sample and that with more than 10% CO2 contents (2% O2 and balance with N2), may contribute to the deteriorating quality of flakes. Carlin et al. (1990), Dixon and Kell (1989) and Ke et al. (1990) reported that CO2 concentrations above 30% could have induced physiological injuries and microbial decay of minimally processed vegetables and fruits. No extension of consumer acceptability time of the product was found by Diaz and Hotchkiss (1996), who stored fresh-cut lettuce in the atmosphere containing 10% CO2, 0% O2, 90% N2 at 13 C. On the basis of our results, it was found that the
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Table 5 The effect of the composition of atmosphere inside packaging on microbiological quality of celeriac flakes stored at 4 C Analyzed index [CFU/g]
Storage time [day]
Composition of atmosphere inside pack CO2 content [%]A
Air
0 2
5 3
10 2
Total mesophilic bacteria counts
1 6 12
2.3 · 10 4.2 · 104 2.7 · 107b
1.9 · 10 5.0 · 103 2.2 · 106a,b
5.9 · 10 1.6 · 103 Not found in 0.1 ga
4.3 · 102 2.9 · 102 9.0 · 102a
Total psychrophilic bacteria counts
1 6 12
4.9 · 105 7.6 · 106 1.5 · 108b
1.3 · 105 3.8 · 105 7.7 · 107a,b
1.3 · 104 1.9 · 104 5.8 · 106a
5.5 · 103 3.2 · 103 1.2 · 103a
Moulds and yeasts counts
1 6 12
1.0 · 102 1.4 · 102 4.3 · 101
1.3 · 101 1.1 · 102 1.5 · 101
3.5 · 101 9.5 · 101 Not found in 0.1 g
2.0 · 101 2.0 · 101 Not found in 0.1 g
Coliform bacteria counts
1 6 12
9.6 · 102 3.0 · 104b 4.7 · 103b
4.2 · 102 4.2 · 103a,b 4.2 · 103a,b
7.0 · 101 1.8 · 102a 3.0 · 101a
2.7 · 102 6.0 · 101a 5.8 · 102a
Pseudomonas bacteria counts
1 6 12
2.8 · 104 2.7 · 104 2.8 · 103b
1.3 · 104a 1.3 · 104a 7.6 · 103
3.8 · 103a 6.5 · 103a Not found in 0.1 g
4.6 · 102a 2.5 · 102a 5.0 · 102
a
A
– Contents of individual gases in modified atmosphere: O2-2% and with balance N2. Statistically significant difference (p 6 0.05) between microbial counts in samples with 0, 5 or 10% C02 contents and microbial counts in air packaged sample (control) after the same time of storage, for individual microbiological analysis indexes. b Statistically significant difference (p 6 0.05) between microbial counts (for individual microbiological analysis indexes) after 6 and 12 days of storage and microbial counts after 1 day of storage, within sample. a
disappearance of oxygen and an increase in carbon dioxide content (19.2% and 24.3%, respectively) in the atmosphere inside the pack during the storage of celeriac flakes packaged in the atmosphere with the initial CO2 contents of 5% and 10% did not result in changes in their sensory attributes. Disadvantageous sensory changes were not found by Barry-Ryan, Pacussi, and O’Beirne (2000) Kakiomenou, Tassou, and Nychas (1996) at the storage of shredded carrot in anaerobic atmosphere, in case of the study by Barry-Ryan et al. (2000) increasing to 30% CO2 content. However, it needs to be stressed that the exposure to low O2 levels or the absence of O2 may result in anaerobiosis, tissue necrosis and growth of anaerobic micro-organisms. The latter may include species that constitute serious health hazards for humans if the produce is consumed. Higher levels of CO2 than the tolerance limit may also induce anaerobiosis and tissue injury. Different vegetables have unique tolerance limits to low O2 and high CO2. Therefore, the ranges of O2 and CO2 must be defined for each product (Kader, Zagory, & Kerbel, 1989; Fonseca, Oliveira, Brecht, & Chau, 2005). In the results of investigations concerning the microbiological quality of stored shredded celeriac, presented in our study, no inhibition of growth was observed in case of mesophilic, psychrophilic or coliform bacteria when air or the atmosphere with 0% CO2, 2% O2 and balance with N2 were used at packaging. It results from a study by Diaz and Hotchkiss (1996) that storage of fresh-cut lettuce in the atmosphere containing 30% CO2, 5% O2, 65% N2 at 13 C resulted in a significant inhibition of growth of aerobic bacteria. In the tested celeriac flakes packaged in air atmo-
sphere, despite an increase of CO2 contents in the atmosphere inside the pack to 34%, no effect of CO2 was found on a reduction in counts of mesophilic and psychrophilic bacteria. However, in those samples after 1 day storage O2 content was 15.9% ±0.1. Carlin, Nguyen-The, Da Silva, and Cochet (1996) reported that endive leaves stored in 30% CO2/10% O2 or 50% CO2/10% O2 showed extensive spoilage after 14 days of storage. The performed tests indicate however that the application of modified atmosphere containing 5% or 10% CO2 (2% O2 and balance with N2) inhibits the growth of mesophilic, psychrophilic and coliform bacteria in celeriac flakes stored for 12 days. King, Magnusson, To¨ro¨k, and Goodman (1991) reported a reduction in the counts of mesophilic bacteria in shredded iceberg lettuce stored in sealed bags in which CO2 increased to 19% after 14 day storage. There are few papers discussing the effect of the composition of atmosphere on coliform bacteria counts. Abdul-Raouf, Beuchat, and Ammar (1993) and Diaz and Hotchkiss (1996) stated that CO2 does not effectively inhibit the growth of Escherichia coli 0157:H7 on fresh-cut lettuce stored at the temperature of 13 or 22 C. In samples they analyzed, packaged in the atmosphere of 30% CO2, 5% O2 and 65% N2, the count of this group of microorganisms was higher than in air packaged samples. In turn, the results of a study by Amanatidou, Smid, and Gorris (1999) under model conditions showed a reduction in the growth of this group of bacteria in the atmosphere with the addition of CO2. In this study a decrease was observed in the counts of bacteria from the genus Pseudomonas in sample of modi-
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fied atmosphere packaged celeriac flakes (Experiment b) after 1 and 6 days of storage in comparison to the air packaged samples. Both after 1- and 6-day storage oxygen was detected in samples packaged in air atmosphere (15.9% and 0.2%, respectively). In the other samples the atmosphere did not contain oxygen. It results from a study by Bennick et al. (1996) that in general Pseudomonas counts were lower under 0% O2, irrespective of CO2. The same authors found for CO2 levels upto 20% a slight reduction in the in vitro growth rate of P. fluorescens. 6. Conclusions On the basis of the conducted tests concerning the selection of packaging conditions for minimally processed celeriac it was found that celeriac flakes packaged in atmosphere containing 5% or 10% CO2, 2% O2 and with balance N2 exhibited better sensory attributes (colour, aroma and taste) than air packaged samples or samples packaged in atmosphere with 0% or more than 10% CO2, 2% O2 and with balance N2. Modified atmosphere used in packaging celeriac flakes containing 5% or 10% CO2, 2% O2 and with balance N2 resulted in an inhibition of growth of mesophilic, psychrophilic and coliform bacteria in the minimally processed product stored during 12 days at the temperature of 4 C. References Abdul-Raouf, U. M., Beuchat, L. R., & Ammar, M. S. (1993). Survival and growth of E coli 0157:H7 on salad vegetables. Applied and Environmental Microbiology, 55, 2167–2171. Amanatidou, A., Smid, E. J., & Gorris, L. G. M. (1999). Effect of elevated oxygen and carbon dioxide on the surface growth of vegetableassociated micro-organisms. Journal of Applied Microbiology, 86, 429–438. Barry-Ryan, C., Pacussi, J. M., & O’Beirne, D. (2000). Quality of shredded carrots as affected by packaging film and storage temperature. Journal of Food Science, 65, 726–730. Baryłko-Pikielna, N., (1994). Zarys analizy sensorycznej z_ ywnos´ci .WNT, Warszawa (in Polish). Bennick, M. H. J., Peppelenbos, H. W., Nguyen-The, C., Carlin, C., Smid, E. J., & Gorris, L. G. M. (1996). Microbiology of minimally processed, modified atmosphere packaged chicory endive. Postharvest Biology and Technology, 9, 209–221.
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Beuchat, L. R. (2002). Ecological factors influencing survival and growth of human pathogens on raw fruits and vegetables. Microbes and Infection, 4, 413–423. Burbianka, M., Pliszka, A. (1983). Mikrobiologia z_ ywnos´ci. PZWL, Warszawa (in Polish). Carlin, F., Nguyen-The, C., Chambroy, Y., & Reich, M. (1990). Effect of controlled atmospheres on microbial spoilage, electrolyte leakage and sugar content of ready-to-use grated carrots. Journal of Food Science and Agriculture, 25, 110–119. Carlin, F., Nguyen-The, C., Da Silva, A. A., & Cochet, C. (1996). Effects of carbon dioxide on the fate of Listeria monocytogenes, of aerobic bacteria and on the development of spoilage in minimally processed fresh endive. International Journal of Food Microbiology, 32, 159–172. Church, I. J., & Person, A. L. (1995). Modified atmosphere packaging technology: a review. Journal of Science and Agriculture, 67, 143–152. Diaz, C., & Hotchkiss, J. H. (1996). Comparative growth of Escherichia coli 0157:H7, spoilage organisms and shelf-life of shredded iceberg lettuce and shelf-life of shredded iceberg lettuce stored under modified atmospheres. Journal of Food Science and Agriculture, 70, 433–438. Dixon, N. M., & Kell, D. B. (1989). The inhibition by CO2 of the growth and metabolism of microorganisms. Journal of Applied Bacteriology, 67, 109–136. Fonseca, S. C., Oliveira, F. A. R., Brecht, J. K., & Chau, K. V. (2005). Influence of low oxygen and high carbon dioxide on shredded Galega kale quality for development of modified atmosphere packages. Postharvest Biology and Technology, 35, 279–292. Kader, A. A., Zagory, D., & Kerbel, E. L. (1989). Modified atmosphere packaging of fruits and vegetables. Critical Reviews Food Science and Nutrition, 28, 1–30. Kakiomenou, K., Tassou, C., & Nychas, G. J. (1996). Microbiological, physicochemical and organoleptic changes of shredded carrots stored under modified storage. International Journal of Food Science and Technology, 31, 359–366. Ke, D., van Gorsel, H., & Kader, A. A. (1990). Physiological and quality responses of Barlett pears to reduced O2 and enhanced CO2 levels and storage temperature. Journal of The American Society for Horticultural Science, 115, 435–439. King, A. D., Jr., Magnusson, J. A., To¨ro¨k, T., & Goodman, N. (1991). Microbial flora and storage quality of partially processed lettuce. Journal of Food Science, 56, 459–461. Libudzisz, Z. (2000). Mikrobiologia przemysłowa. Wydawnictwo Politechniki Ło´dzkiej, Ło´dz´ (in Polish). Nguyen-The, C., & Carlin, F. (1994). The microbiology of minimally processed fresh fruits and vegetables. Critical Reviews Food Science and Nutrition, 34(4), 371–401. Peppelenbos, H. W., & van ’t Leven, J. (1996). Evaluation of four types of inhibition for modeling the influence of carbon dioxide on oxygen consumption of fruits and vegetables. Postharvest Biology and Technology, 7, 27–40.
The effect of packaging conditions on the quality of minimally processed celeriac flakes E. Radziejewska-Kubzdela a
a,*
, J. Czapski a, K. Czaczyk
b
Institute of Food Technology, The August Cieszkowski Agricultural University of Poznan´, Wojska Polskiego 31, 60-624 Poznan´, Poland b Department of Biotechnology and Food Microbiology, The August Cieszkowski Agricultural University of Poznan´, Wojska Polskiego 48, 60-627 Poznan´, Poland Received 2 January 2006; received in revised form 11 July 2006; accepted 17 July 2006
Abstract The aim of the study was to select packaging conditions of minimally processed celeriac to preserve their quality during storage for 12 days at 4 and 15 C. The quality of the product was determined on the basis of colour measured in the CIE L*a*b* system, sensory quality and total counts of mesophilic and psychrophilic bacteria, counts of moulds and yeasts, coliform counts, counts of Pseudomonas bacteria and the presence of bacteria from the genus Clostridium perfringens. Moreover, changes were determined in oxygen and carbon dioxide contents in the atmosphere within the packs, in which the product was stored. Celeriac flakes were packaged in the atmosphere with varying CO2 contents (0%, 5%, 10%, 20%, 30%, 50% plus 2% O2 and with balance N2). After 12 days at 4 C, it was found that celeriac flakes packaged in atmosphere containing 5% or 10% CO2, 2% O2 and balance N2 were characterized by better quality than samples packaged in air atmosphere or in the atmosphere with CO2 contents of 0% or higher than 10%. Modified atmosphere with the content of 5% or 10% CO2, 2% O2 and balance N2, applied in the packaging of celeriac flakes, resulted in the inhibition of growth of mesophilic, psychrophilic and coliform bacteria in the tested minimally processed product. 2006 Published by Elsevier Ltd. Keywords: Modified atmosphere; Celeriac; Minimal processing; Sensory quality; Microbiological counts
1. Introduction Minimal processing of celeriac provides convenience for consumers and many economic benefits for producers. However, little information has been published about this product. The effect of minimal processing of celeriac (peeling, shredding) can induce disadvantageous changes in tissue, which may lead to darkening of the flakes and deterioration of product sensory attributes. Moreover, shredded raw material constitutes an excellent medium for the development of micro-organisms. An uncontrolled increase in the population size of certain micro-organisms may lead
*
Corresponding author. Tel:. +48 61 848 72 90; fax: +48 61 848 73 14. E-mail address: [email protected] (E. Radziejewska-Kubzdela).
0956-7135/$ - see front matter 2006 Published by Elsevier Ltd. doi:10.1016/j.foodcont.2006.07.019
to shortened shelf life of the product. This group of micro-organisms includes e.g. bacteria from genera Pseudomonas, as well as certain types of yeasts and moulds (Beuchat, 2002; Nguyen-The & Carlin, 1994). Moreover, pathogenic micro-organisms causing a health hazard may also proliferate in the minimally processed product. Numerous studies are being carried out on the application in the packaging of minimally processed vegetables and fruits of modified atmosphere with the composition considerably differing from the recommended one, i.e. 1– 5% oxygen and 5–10% carbon dioxide. An example in this respect may be packaging chicory endive in the atmosphere containing 1.5% oxygen, 20% carbon dioxide and 78.5% nitrogen. The application of atmosphere with such a composition contributed to the maintenance of good sensory quality of the product within 13 days of storage and a 50% reduction of growth of microflora responsible for
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spoilage in comparison to air-packaged samples (Bennick et al., 1996). It was found that an increase in CO2 concentration inside the pack resulted in a reduction of the respiration rate. It was frequently explained by the effect of this gas on the activity of enzymes participating in glycolysis and the Krebs cycle (Peppelenbos & van ’t Leven, 1996). The application of too high carbon dioxide concentrations (above 30%) may contribute to physiological changes and microbial decay of minimally processed vegetables and fruits (Carlin, Nguyen-The, Chambroy, & Reich, 1990; Dixon & Kell, 1989; Ke, van Gorsel, & Kader, 1990). The selection of an appropriate composition of atmosphere used for packaging vegetables and fruits depends e.g. on the type of viable microflora, susceptibility to oxygen and carbon dioxide and the susceptibility to enzymatic browning of tissue (Church & Person, 1995). The aim of this study was to determine the effect of various CO2 contents in the atmosphere inside the pack on the quality of celeriac flakes stored for 12 days at 4 and 15 C. 2. Materials and methods 2.1. Materials Experimental material consisted of celeriac (Apium Graveolens L. var. rapaceum) cv. Mentor. The raw material came from a farm in western Poland. Celeriac was harvested in October. Celeriac roots were oval in shape and exhibited medium rooting degree. The flesh was whitecreamy in color, with low susceptibility to browning. 2.2. Preparing of the minimally processed celeriac Celeriac roots were washed in water, hand-peeled, washed again and shredded into flakes (4 · 1 · 40 mm) in a food processor (Zelmer, Polska). Flake portions of 50 g were placed in bags (15 · 21 cm) made of oriented polyamide/polyethylene laminate with layer thickness of 50/40 lm and gas permeability (in cm3/m2/24 h at 23 C) for carbon dioxide – 200, oxygen – 45 and water vapour of 2–3 g/m2/ 24 h (Multivac, Jastko´w). Bags were sealed using a vacuum packaging machine type A-300 (Multivac). Experiments were conducted for various CO2 concentrations and different temperatures of storage: (a) Samples packaged in modified atmosphere containing 10%, 20%, 30% and 50% CO2 and stored at 4 C; (b) Samples packaged in modified atmosphere containing 0%, 5% and 10% CO2 and stored at 4 C and 15 C. Contents of other gases in modified atmosphere packaged samples were 2% O2 and with balance N2. The modification of the atmosphere in the bags was achieved by using a gas packaging unit (gas mixer, WITT M6183MSO, Gasetechnik). The reference sample consisted of air-packaged celeriac flakes.
The product was analyzed after 1, 6 and 12 days of storage. Color measurements were taken of homogenized flakes and sensory examination was performed for Experiments a and b. In case of samples from Experiment b stored at 4 C changes in carbon dioxide and oxygen inside the pack were measured and microbiological quality was determined. 3. Color parameter measurements Color parameters in the CIE L*a*b* system were measured using a Hitachi U-3000 spectrophotometer. Before the measurement was taken 50 g celeriac flakes were homogenized in an IKA T-25 homogenizer with 50 ml distilled water added. Homogenized celeriac pulp was placed in a 3 · 5 · 2 cm glass cuvette. Measurements were taken immediately after homogenization. The color measurement was performed in three replications for each sample. 3.1. Sensory examination The sensory quality was evaluated by a five-member trained panel (all members of the Agricultural University of Poznan´). Before the start of the sensory experiments, panel members were familiarized with the product and scoring methods. This consisted of demonstration exercises involving examination of packs at different levels of deterioration and agreeing appropriate scores. When the panel members had become familiar with the test conditions and scoring regime, they were invited to score samples. This procedure was repeated several times until a level of consistency was obtained. Sensory examination was performed immediately after bags with celeriac flakes were opened. The examination was conducted in a 5-point scale (Baryłko-Pikielna, 1994) using a specially developed sensory examination chart (Table 1). The results of the sensory analysis were reported as means of three separate experimental determinations for each sample. 3.2. Measurement of oxygen and carbon dioxide contents in pack with celeriac flakes The measurements were taken using a PBI Dansensor Check Mate 9900 apparatus. A probe was inserted into the packaging through a rubber gasket and oxygen and carbon dioxide contents were read on the meter. Three replications were performed for each sample. 3.3. Analysis of microbiological quality of celeriac flakes 3.3.1. Sample preparation for microbiological analysis Celeriac flakes (approx. 10 g) were transferred to a sterile stomacher bag and 90 ml of a physiological salt/peptone solution (8.5 g/l NaCl, 1 g/l peptone tryptone, Difco) were added and mixed for 2 min in a DEVIMIX machine (De Ville Biotechnology, Raszyn, Poland). Ten-fold dilutions in the range from 10 1 to 10 8 were prepared from these samples.
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Table 1 A sensory examination chart Quality attribute
Weighting coefficient
Point scores 5
4
3
2
1
Colour of flesh
4
White-creamy
Creamy-yellow
Creamy-yellow with scarce brown spots
Brown on whole surface
Aroma desirability
4
Good, celery
Just acceptable
Deteriorated
Intensity Taste desirability
2 4
Intensive Good, celery
Medium intensive Just acceptable
Weakly detectable Just unacceptable
Undetectable Deteriorated
Intensity Texture
2 4
Very good, celery Very intensive Very good, celery Very intensive Very firm
Creamy-yellow with numerous brown spots Just unacceptable
Intensive Firm
Medium intensive Loosened or hardening
Weakly detectable Loose or lignified
Undetectable Sticky or lignified
Total counts of mesophilic and psychrophilic bacteria and counts of moulds and yeasts were determined using a quantitative culture according to the Koch plate method (Burbianka & Pliszka, 1983). In case of the total mesophilic and psychrophilic bacteria counts media were prepared according to Burbianka and Pliszka (1983). Peptone agar with glucose was the medium for aerobic mesophilic and psychrophilic bacteria (10 g/l bacteriological pepton, 10 g/l glucose, 15 g/l bacteriological agar, pH 7, BTL, Poland). The medium used for analysis of yeasts and moulds containing: 5 g/l yeast extract, 20 g/l glucose, 0.1 g/l chloramfenicol, 15 g/l bacteriological agar, pH 6.6, (BTL, Poland). The analyses were carried out on duplicate agar plates for each replication of sample. Reported microbiological counts therefore represent the means of six values. The applied incubation parameters were as follows: mesophilic bacteria – incubation time 48 h–72 h, incubation temperature 30 C; psychrophilic bacteria – incubation time 72 h–120 h, incubation temperature 15 C. Incubation time for the determination of moulds and yeasts was 72 h– 96 h, while temperature was 30 C. The filtration method was applied to determine coliform bacteria counts and counts of Pseudomonas bacteria (Libudzisz, 2000). The Endo–Total Coliform Broth (Millipore) was used as a medium for coliform bacteria. Incubation time was 24 h– 48 h, while incubation temperature was 30 C. The Pseudomonas Selective Broth (Millipore) was used as a medium for Pseudomonas bacteria. Incubation time was 48 h–72 h and incubation temperature was 37 C. The determination of anaerobic bacteria consisted in the detection of the presence of anaerobic bacteria from the genus Clostridium perfringens. Quantitative culture using the Koch plate method was applied in the analysis. Agar TSC (Merck) was used as a medium. Incubation time was 48 h, while incubation temperature was 37 C. Black colonies on the medium constituted a positive culture result. Morphology of the micro-organisms was examined in microscopic slides: live specimens for moulds and fixed Gram-stained for bacteria (Burbianka & Pliszka, 1983).
3.4. Statistical analysis of results All experiments were carried out in duplicate and each duplicate was repeated twice. For each set of conditions three samples (three bags) were prepared and analyzed. Statistical analysis was performed using computer software Statistical version 6.0 applying the analysis of variance (ANOVA), the Fisher’s least significant difference (LSD) multicomparison test and multiple linear regression. Statistically significant differences were reported at p 6 0.05.
4. Results Packaging of celeriac flakes in modified atmosphere containing 5% or 10% CO2, 2% O2 and balance with N2 had an advantageous effect on their color. On the basis of color sensory examination it was found that these flakes were creamy after 1, 6, as well as 12 days of storage at the temperature of 4 C. In samples packaged in the atmosphere with a higher CO2 content (20%, 30%, 50%) or without CO2, as well as those which were air packaged, a significant (p 6 0.05) deterioration of the product color was observed. After 12-day storage these samples were defined as creamyyellow with scarce brown spots (Table 2). Instrumental color measurement confirmed the results of sensory examination. Flakes packaged in the atmosphere with 5% or 10% CO2 (2% O2 and balance with N2) after 12-day storage had lightness values L* significantly (p 6 0.05) higher, while colour parameter a* was lower than in the other samples (Table 3). A statistically significant correlation (R2 = 0.99) was found between the lightness L* value, the color parameter a* and the sensory examination results for shredded celeriac color (Table 4). As far as the other sensory examination indexes are concerned, it was found that celeriac flakes packaged at the initial CO2 contents of 0%, 5% and 10% (2% O2 and balance with N2) had good taste and aroma. The samples packaged in air atmosphere and in modified atmosphere with CO2 contents of 20% (2% O2 and balance with N2) or more, after 12-day storage, were characterized by sour taste and
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Table 2 A list of sensory examination results for celeriac flakes packaged in air atmosphere and in modified atmosphere with various CO2 contents stored at 4 C CO2A content [%]
Storage time [day]
Sensory attributes Color
Aroma
Taste
Texture
Overall score
1 6 12
4.9 4.2b 3.1b
2.8 2.1b 2.8
4.4 2.4b 2.8b
4.8 3.2b 3.7b
3.9a 2.9b 3.1b
10
1 6 12
5.0 4.3b 3.6a,b
5.0 4.4a,b 4.2a,b
4.4 3.9a 3.8a,b
4.8 3.9b 4.1a,b
4.8a 4.1a 3.9a,b
20
1 6 12
5.0 4.2b 3.0b
4.2 3.1a,b 3.1b
4.4 3.4a,b 3.4a,b
4.8 3.7b 4.0a,b
4.4 3.6a,b 3.4b
30
1 6 12
5.0 4.3b 3.0b
3.6 2.6b 2.6b
4.4 2.6b 2.8b
4.8 3.2b 4.0a,b
4.4 3.2b 3.2b
50
1 6 12
5.0 4.3b 3.0b
4.0 2.3a,b 2.8b
4.4 2.6b 3.3b
4.8 3.8b 4.2a,b
4.3 2.9b 3.1b
1 6 12
3.3 3.1 3.0
4.7 4.6 3.9
4.5 4.6 4.1
4.7 4.5 4.1
4.4 4.3 3.9b
5
1 6 12
4.0a 4.0a 4.0a
4.5 4.3 3.9
4.5 4.7 4.3
4.8 4.6 4.1
4.5 4.4 4.1b
10
1 6 12
5.0a 4.9a 4.8a
4.5 3.7a 3.8
4.8 4.7 4.6
4.7 4.6 4.6
4.7 4.5 4.3a,b
Experiment a Air
Experiment b 0
A
Contents of individual gases in modified atmosphere: O2-2% and with balance N2. Statistically significant difference (p 6 0.05) between: the scores for modified atmosphere packaged samples and the score for air packaged sample (control) (Experiment a); the scores for samples packaged in atmosphere with 5% and 10% CO2, and the score for sample packaged in atmosphere with 0% CO2 (Experiment b) after the same storage time, for individual sensory attributes. b Statistically significant difference (p 6 0.05) between the score (for individual attributes) of sensory examination after 6 and 12 days of storage and the score after 1 day of storage within the sample. a
aroma. The texture of flakes in all the examined samples was evaluated as desirable (Table 2). During storage, a significant (p 6 0.05) decrease in scores in overall sensory examination, both in air and modified atmosphere packaged samples, was observed (Table 2). Storage of celeriac flakes packaged in modified atmosphere at the temperature of 15 C (Experiment b) resulted in a deterioration of quality. A significant (p 6 0.05) lowering in lightness values L* (Table 3) was observed along with a visible microbial spoilage, which made it impossible to conduct sensory assessment of these samples. On the basis of the results obtained in Experiment b it was found that carbon dioxide content after storage in samples packaged in the initial atmosphere containing 0%, 5% or 10% CO2 (2% O2 and balance with N2) was 14.3%, 19.2% and 24.3%, respectively. In contrast, in air packaged samples it was markedly higher, amounting to 34.1% (Fig. 1). Both in samples packaged in modified atmosphere at the initial oxygen content of 2% and air packaged samples, after 6 and 12 days of storage, a complete disappearance of oxygen was observed. Thus, only
anaerobic respiration processes occurred in the tissue. In spite of that, the taste and aroma of modified atmosphere packaged flakes (0%, 5% and 10% CO2, 2% O2 and balance with N2) were defined as good (Table 2). Moreover, microbiological quality was also determined for samples from Experiment b. During 12-day storage in celeriac flakes packaged in the atmosphere without carbon dioxide content (0% CO2, 2% O2 and balance with N2) and in air atmosphere the counts of mesophilic bacteria increased from 102–103 CFU/g to 106–107 CFU/g, while the counts of psychrophilic bacteria increased from 105 CFU/g to 107–108 CFU/g, respectively. An inhibition of growth in bacteria from the above mentioned groups was observed after the introduction of CO2 to the atmosphere at packaging (Table 5). No significant (p 6 0.05) effect of the composition of atmosphere inside the packaging was found on moulds and yeasts counts (Table 5). During storage, in samples packaged in atmosphere with no carbon dioxide content (0% CO2, 2% O2 and balance with N2) and in air atmosphere, coliform bacteria counts
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Table 3 The color parameters L*, a* and b* after 12-day storage of celeriac flakes packaged in air atmosphere and in modified atmosphere with various CO2 contents: (a) – Experiment a; (b) – Experiment (b). Storage temperature: 4 C; 15 C CO2A content [%]
Color parameters L*
Experiment a Air 10 20 30 50
a*
57.18 ± 1.31 59.10 ± 0.55a 57.33 ± 1.33 57.35 ± 1.19 56.80 ± 1.44
L*
a*
Experiment b 4 C 0 56.92 ± 0.70 5 61.11 ± 0.61a 10 62.64 ± 0.87a
0.35 ± 0.23 0.93 ± 0.18a 2.13 ± 0.18a
b*
0.63 ± 0.37 1.51 ± 0.42a 0.04 ± 0.12 0.50 ± 0.58 0.53 ± 0.31 b*
L*
23.26 ± 1.07 22.43 ± 1.16 21.19 ± 1.12
15 C 56.51± 0.38 55.76 ± 0.79 54.05 ± 0.33a
21.65 ± 0.40 20.06 ± 0.38a 20.38 ± 0.72a 21.55 ± 0.97 20.52 ± 0.41 a*
1.41± 0.11 0.96 ± 0.23a 1.36 ± 0.10
b*
21.73 ± 1.55 19.93 ± 0.44 20.34 ± 0.80
A
– Contents of individual gases in modified atmosphere: O2- 2% and with balance N2. Statistically significant difference (p 6 0.05) between: the values for modified atmosphere packaged samples and the values for air packaged sample (control) (Experiment a); the values for samples packaged in atmosphere with 5% and 10% CO2, and the values for sample packaged in atmosphere with 0% CO2 (Experiment b) for individual color parameters. a
40
after 1 day after 6 day
35 CO2 content [%]
after 12 day
30 25 20 15 10 5 0
air
0%
5%
10%*
Fig. 1. Changes in carbon dioxide contents in atmosphere inside the pack with celeriac flakes during storage at 4 C. Reported values represent the means of nine values. Error bars show standard deviation. *contents of individual gases in modified atmosphere: CO2, O2-2% and with balance N2.
Table 4 A summary of regression describing the dependence between the sensory examination results for shredded celeriac of color and lightness L* value, the color parameter a* and b* after 12 days of storage Regression equation Color =
13.26 + 0.794L*
0.22a* + 0.01b*
was observed in Pseudomonas bacteria counts in comparison to the air packaged sample (Table 5). In the tested celeriac flakes packaged in modified atmosphere and stored for 12 days at the temperature of 4 C no anaerobic bacteria from the genus Clostridium perfringens were found in 1 g of product. The examination of the morphology of mesophilic and psychrophilic bacteria in the analyzed samples showed the presence of Gram-negative bacteria. Live specimens from mould colonies showed that moulds belonged to the genera Aspergillus, Rhizopus and Penicillium.
R2
p-level
0.99
0.000077 (L*) 0.001017 (a*) 0.088490 (b*)
increased from 102 CFU/g to 103–104 CFU/g. The introduction of 5% or 10% CO2 (2% O2 and balance with N2) to the atmosphere inside the packaging resulted in a reduction in the growth of this group of bacteria at the level of 101–102 CFU/g (Table 5). After 1 and 6 days of storage of modified atmosphere packaged celeriac flakes a significant (p 6 0.05) decrease
5. Discussion On the basis of the results of these experiments it was found that celeriac flakes packaged in atmosphere containing 5% or 10% CO2, 2% O2 and balance with N2 exhibited better values of sensory attributes (colour, taste and aroma) than samples packaged in air atmosphere or in the atmosphere with 0% or more than 10% CO2 contents (2% O2 and balance with N2). After 12 days storage, in the sample packaged in air atmosphere and atmosphere 0% CO2, 2% O2 and balance with N2, CO2 concentrations inside the pack increased to 34% and 14.3%, respectively. The high CO2 contents, in the air packaged sample and that with more than 10% CO2 contents (2% O2 and balance with N2), may contribute to the deteriorating quality of flakes. Carlin et al. (1990), Dixon and Kell (1989) and Ke et al. (1990) reported that CO2 concentrations above 30% could have induced physiological injuries and microbial decay of minimally processed vegetables and fruits. No extension of consumer acceptability time of the product was found by Diaz and Hotchkiss (1996), who stored fresh-cut lettuce in the atmosphere containing 10% CO2, 0% O2, 90% N2 at 13 C. On the basis of our results, it was found that the
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Table 5 The effect of the composition of atmosphere inside packaging on microbiological quality of celeriac flakes stored at 4 C Analyzed index [CFU/g]
Storage time [day]
Composition of atmosphere inside pack CO2 content [%]A
Air
0 2
5 3
10 2
Total mesophilic bacteria counts
1 6 12
2.3 · 10 4.2 · 104 2.7 · 107b
1.9 · 10 5.0 · 103 2.2 · 106a,b
5.9 · 10 1.6 · 103 Not found in 0.1 ga
4.3 · 102 2.9 · 102 9.0 · 102a
Total psychrophilic bacteria counts
1 6 12
4.9 · 105 7.6 · 106 1.5 · 108b
1.3 · 105 3.8 · 105 7.7 · 107a,b
1.3 · 104 1.9 · 104 5.8 · 106a
5.5 · 103 3.2 · 103 1.2 · 103a
Moulds and yeasts counts
1 6 12
1.0 · 102 1.4 · 102 4.3 · 101
1.3 · 101 1.1 · 102 1.5 · 101
3.5 · 101 9.5 · 101 Not found in 0.1 g
2.0 · 101 2.0 · 101 Not found in 0.1 g
Coliform bacteria counts
1 6 12
9.6 · 102 3.0 · 104b 4.7 · 103b
4.2 · 102 4.2 · 103a,b 4.2 · 103a,b
7.0 · 101 1.8 · 102a 3.0 · 101a
2.7 · 102 6.0 · 101a 5.8 · 102a
Pseudomonas bacteria counts
1 6 12
2.8 · 104 2.7 · 104 2.8 · 103b
1.3 · 104a 1.3 · 104a 7.6 · 103
3.8 · 103a 6.5 · 103a Not found in 0.1 g
4.6 · 102a 2.5 · 102a 5.0 · 102
a
A
– Contents of individual gases in modified atmosphere: O2-2% and with balance N2. Statistically significant difference (p 6 0.05) between microbial counts in samples with 0, 5 or 10% C02 contents and microbial counts in air packaged sample (control) after the same time of storage, for individual microbiological analysis indexes. b Statistically significant difference (p 6 0.05) between microbial counts (for individual microbiological analysis indexes) after 6 and 12 days of storage and microbial counts after 1 day of storage, within sample. a
disappearance of oxygen and an increase in carbon dioxide content (19.2% and 24.3%, respectively) in the atmosphere inside the pack during the storage of celeriac flakes packaged in the atmosphere with the initial CO2 contents of 5% and 10% did not result in changes in their sensory attributes. Disadvantageous sensory changes were not found by Barry-Ryan, Pacussi, and O’Beirne (2000) Kakiomenou, Tassou, and Nychas (1996) at the storage of shredded carrot in anaerobic atmosphere, in case of the study by Barry-Ryan et al. (2000) increasing to 30% CO2 content. However, it needs to be stressed that the exposure to low O2 levels or the absence of O2 may result in anaerobiosis, tissue necrosis and growth of anaerobic micro-organisms. The latter may include species that constitute serious health hazards for humans if the produce is consumed. Higher levels of CO2 than the tolerance limit may also induce anaerobiosis and tissue injury. Different vegetables have unique tolerance limits to low O2 and high CO2. Therefore, the ranges of O2 and CO2 must be defined for each product (Kader, Zagory, & Kerbel, 1989; Fonseca, Oliveira, Brecht, & Chau, 2005). In the results of investigations concerning the microbiological quality of stored shredded celeriac, presented in our study, no inhibition of growth was observed in case of mesophilic, psychrophilic or coliform bacteria when air or the atmosphere with 0% CO2, 2% O2 and balance with N2 were used at packaging. It results from a study by Diaz and Hotchkiss (1996) that storage of fresh-cut lettuce in the atmosphere containing 30% CO2, 5% O2, 65% N2 at 13 C resulted in a significant inhibition of growth of aerobic bacteria. In the tested celeriac flakes packaged in air atmo-
sphere, despite an increase of CO2 contents in the atmosphere inside the pack to 34%, no effect of CO2 was found on a reduction in counts of mesophilic and psychrophilic bacteria. However, in those samples after 1 day storage O2 content was 15.9% ±0.1. Carlin, Nguyen-The, Da Silva, and Cochet (1996) reported that endive leaves stored in 30% CO2/10% O2 or 50% CO2/10% O2 showed extensive spoilage after 14 days of storage. The performed tests indicate however that the application of modified atmosphere containing 5% or 10% CO2 (2% O2 and balance with N2) inhibits the growth of mesophilic, psychrophilic and coliform bacteria in celeriac flakes stored for 12 days. King, Magnusson, To¨ro¨k, and Goodman (1991) reported a reduction in the counts of mesophilic bacteria in shredded iceberg lettuce stored in sealed bags in which CO2 increased to 19% after 14 day storage. There are few papers discussing the effect of the composition of atmosphere on coliform bacteria counts. Abdul-Raouf, Beuchat, and Ammar (1993) and Diaz and Hotchkiss (1996) stated that CO2 does not effectively inhibit the growth of Escherichia coli 0157:H7 on fresh-cut lettuce stored at the temperature of 13 or 22 C. In samples they analyzed, packaged in the atmosphere of 30% CO2, 5% O2 and 65% N2, the count of this group of microorganisms was higher than in air packaged samples. In turn, the results of a study by Amanatidou, Smid, and Gorris (1999) under model conditions showed a reduction in the growth of this group of bacteria in the atmosphere with the addition of CO2. In this study a decrease was observed in the counts of bacteria from the genus Pseudomonas in sample of modi-
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fied atmosphere packaged celeriac flakes (Experiment b) after 1 and 6 days of storage in comparison to the air packaged samples. Both after 1- and 6-day storage oxygen was detected in samples packaged in air atmosphere (15.9% and 0.2%, respectively). In the other samples the atmosphere did not contain oxygen. It results from a study by Bennick et al. (1996) that in general Pseudomonas counts were lower under 0% O2, irrespective of CO2. The same authors found for CO2 levels upto 20% a slight reduction in the in vitro growth rate of P. fluorescens. 6. Conclusions On the basis of the conducted tests concerning the selection of packaging conditions for minimally processed celeriac it was found that celeriac flakes packaged in atmosphere containing 5% or 10% CO2, 2% O2 and with balance N2 exhibited better sensory attributes (colour, aroma and taste) than air packaged samples or samples packaged in atmosphere with 0% or more than 10% CO2, 2% O2 and with balance N2. Modified atmosphere used in packaging celeriac flakes containing 5% or 10% CO2, 2% O2 and with balance N2 resulted in an inhibition of growth of mesophilic, psychrophilic and coliform bacteria in the minimally processed product stored during 12 days at the temperature of 4 C. References Abdul-Raouf, U. M., Beuchat, L. R., & Ammar, M. S. (1993). Survival and growth of E coli 0157:H7 on salad vegetables. Applied and Environmental Microbiology, 55, 2167–2171. Amanatidou, A., Smid, E. J., & Gorris, L. G. M. (1999). Effect of elevated oxygen and carbon dioxide on the surface growth of vegetableassociated micro-organisms. Journal of Applied Microbiology, 86, 429–438. Barry-Ryan, C., Pacussi, J. M., & O’Beirne, D. (2000). Quality of shredded carrots as affected by packaging film and storage temperature. Journal of Food Science, 65, 726–730. Baryłko-Pikielna, N., (1994). Zarys analizy sensorycznej z_ ywnos´ci .WNT, Warszawa (in Polish). Bennick, M. H. J., Peppelenbos, H. W., Nguyen-The, C., Carlin, C., Smid, E. J., & Gorris, L. G. M. (1996). Microbiology of minimally processed, modified atmosphere packaged chicory endive. Postharvest Biology and Technology, 9, 209–221.
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