THE EFFECT OF COMPOSITION OF MODIFIED ATMOSPHERE AND TYPE OF PACKAGING FILM ON SENSORY QUALITY AND PHYSICO-CHEMICAL PROPERTIES OF COLESLAW MIX

Elżbieta Radziejewska-Kubzdela, Róża Biegańska-Marecik
Institute of Plant Origin Food Technology, Poznań University of Life Sciences, Poland

ABSTRACT

The study was to determine the effect of the composition of modified atmosphere and the type of packaging material on physico-chemical properties and sensory quality of minimally processed coleslaw mix stored for 12 days at 4°C. Samples were packaged in Flow HB 50 EZ Peel (OPP/PEEVOH) film with oxygen permeability of 3 cm³/m²/24 h or in Opalen 55 AF (OPA/PE) film with oxygen permeability of 35 cm³/m²/24 h, with and without microperforation. Tested vegetable salads were packaged in air atmosphere or in modified atmosphere with an O₂/CO₂ percentage ratio of 70/30 and 80/20. It results from conducted analyses that the application of Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h) with 2 x 10 microperforation and modified atmosphere containing 70%O₂/30%CO₂ and 80%O₂/20%CO₂ makes it possible to maintain good sensory quality of coleslaw mix during 12-day storage at 4°C. In all analyzed samples a significant decrease (p ≤ 0.05) of solids content was recorded during storage. After 12 days pH in samples packaged in modified atmosphere, irrespective of the applied type of film, was significantly (p ≤ 0.05) lower that in air atmosphere packaged vegetable salads.

Key words: coleslaw mix, modified atmosphere, packaging film.

INTRODUCTION

Common cabbage (Brassica oleracea L. ssp. Oleracea convar capitata) is one of the most commonly grown vegetables in Poland. It is consumed e.g. in the form of fresh salads, such as coleslaw, a product popular both in Poland and worldwide and based on common cabbage. The other component is carrot (20%).

Shelf-life of vegetable salads produced in Poland is 5 days. One of the more effective methods to extend shelf-life of such products is minimal processing. This technology consists of washing of raw material, comminution and most frequently packaging in modified atmosphere on trays wrapped in clingfilm or in plastic bags. Requirements imposed on minimally processed products are very high.An advantage of such products is their "clean label", i.e. an adequately high quality provided without the application of chemical preservatives. The consumption of minimally processed vegetables and fruit has been increasing constantly in such countries of the United States, Spain or Great Britain. Also in Poland the number of such products has been growing. Initially minimally communited vegetables and fruit were used only marginally, primarily in catering. At present demand for them has been extended to include supermarkets and food wholesalers, thus facilitating their introduction to retail.

Modified atmosphere packaging applied by producers does not always guarantee good quality of comminuted vegetables throughout their storage. The atmosphere composition most frequently recommended for packaging of fruit and vegetables is 1%–5% oxygen and 5%–10% carbon dioxide (balanced with nitrogen) [5].  However, fruit and vegetables are characterized by varied metabolism, thus numerous studies are conducted on the use of atmosphere of optimal gas composition, adapted specifically for the packaging of these raw materials. A new trend is to apply atmosphere with a high oxygen content (even up to 100%) and an elevated proportion of CO₂ (15%–30%). It results from literature data that an elevated oxygen content in the atmosphere may both inhibit and stimulate physiological activity of fruit and vegetable tissues. It is dependent on the species, ripeness, storage temperature and time as well as the concentrations of oxygen, carbon dioxide and ethylene in the atmosphere surrounding the product [7]. Minimally processed vegetables and fruit exhibit varied sensitivity to high carbon dioxide concentrations. The tolerance limit depends e.g. on the cultivar, differences in diffusional resistance for gases or storage temperature. Thus the content of both carbon dioxide and oxygen in the atmosphere surrounding the product needs to be determined individually for every product [6]. The type of applied packaging material plays an essential role in the establishment of an appropriate composition of modified atmosphere inside a packaging with a minimally processed product. It results from studies conducted to date that the packaging film used in the production of modified atmosphere with high oxygen content and elevated carbon dioxide content needs to exhibit high barrier properties towards these gases.

The aim of this study was to determine the effect of the composition of modified atmosphere and the type of packaging material on physico-chemical properties and sensory quality of coleslaw-type minimally processed vegetable salad, stored for 12 days at 4°C.

MATERIAL AND METHODS

Material for analysis consisted of coleslaw mix, containing 80% common cabbage (Brassica oleracea L. Convar. Capitata) cv. Galaxy, supplemented with 20% carrot (Daucus carota L.) cv. Perfekcja.

Raw material was washed under running water and next inedible parts were removed. Carrots were hand-peeled. Vegetables were washed again and next dried on blotting paper. After drying raw material were mechanically comminuted – cabbage with a Nagema HU-1 cabbage slicer (Dresden, Germany), while carrots with a Robot Coupe CL 50 Ultra (Vincennes, France). Comminuted product was weighed in the amount of 200 g (160 g common cabbage and 40 g carrot) to polypropylene trays of 205 x 160 x 60 mm, with oxygen permeability of 7–8 cm³/m²/24 h. Trays with prepared vegetable mix were sealed with Flow HB 50 EZ Peel film (OPP/PEEVOH; Bemis, Duchnice, Polska) with oxygen permeability of 3 cm³/m²/24 h and carbon dioxide permeability of 13.5 cm³/m²/24 h (experiment 1), and Opalen 55 AF film (OPA/PE; Bemis, Duchnice, Polska), with oxygen permeability of 35 cm³/m²/24h and carbon dioxide permeability of 158 cm³/m²/24 h (experiments 2 and 3). In experiment 3 samples were packaged using 2x10 film microperforation applied with two rollers (Ø 7 cm with 10 needles of Ø 0.7 µm). Tested vegetable salads were packaged in air atmosphere or in modified atmosphere with percentage ratios of O₂/CO₂ of 70/30 and 80/20. Salads were stored for 12 days at 4°C.

Product quality was analyzed after 0, 1, 3, 6, 9 and 12 days.
Sensory analysis. Sensory evaluation was conducted immediately after packagings with coleslaw-type vegetable salad were opened. The analysis was performed using a 5-point scale in three replications for each sample [1].

Measurement of oxygen and carbon dioxide contents. Analyses were performed using a Gaspace 2 apparatus by Systech Instruments BV (Oxon, UK). Three replications were performed for each sample.
Physico-chemical analysis. Active acidity [9] and soluble solid [8] were determined according to respective standards.

Statistical analysis of results. Results were analyzed using the analysis of variance and Fisher's LSD test. Statistically significant differences were determined at p ≤ 0.05.Analysis was conducted using STATISTICA ver. 7.0 (StatSoft, Kraków, Poland).

RESULTS AND DISCUSSION

Assessment of sensory quality
In samples packaged using barrier films both in air and in modified atmosphere with a high oxygen aroma was an attribute reducing sensory quality. When applying film with oxygen permeability of 3 cm³/m²/24 h in packaging in air atmosphere and in the atmosphere of 70% O₂ and 30% CO₂, a desirable aroma of a sample was maintained for 3 days of storage. In case of samples packaged in atmosphere of 80% O₂ and 20% CO₂ the aroma perceived as intrinsic was found up to 6 days of storage (Table 1). The application of film with a slightly higher oxygen permeability (35 cm³/m²/24 h) in case of air atmosphere samples resulted in the extension of sensory acceptability of aroma to 6 days. In turn, salads packaged in modified atmosphere exhibited intrinsic aroma only during 1 day (when sealed at an atmosphere of 80% O₂ and 20% CO₂) or during 3-day storage (when sealed in an atmosphere of 70% O₂ and 30% CO₂) (Table 2).

The sensory acceptance period for analyzed samples was significantly (p ≤ 0.05) extended when they were packaged in Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h) with 2 x 10 microperforation. In salads packaged in atmospheres with high oxygen contents using microperforated film intrinsic aroma was maintained for 12 days of storage. In turn, when air atmosphere was used to package samples, aroma was perceived as desirable up to the 9^th day of storage (Table 3). In overall sensory evaluation after 12-day storage samples packaged using Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h) with 2 x 10 microperforation in an atmosphere with a high oxygen content received scores which were significantly (p ≤ 0.05) higher (4.4) than those of salads packaged in air atmosphere (3.7) (Table 3).

An unpleasant aroma originating from the accumulation of sulphur compounds in the packaging as a factor limiting shelf-life in case of products based on common cabbage was discussed e.g. by Chin and Lindsay [2]. When describing the effect of the type of packaging material on sensory quality of stored coleslaw packaged in air atmosphere, Cliffe-Byrnes and O`Beirne [3] stated that samples packaged in microperforated OPP film (PA160) retained good sensory quality for a longer time (up to 5 days) than those packaged in film with no microperforation (up to 2 days). The additional variant applied in this study, i.e. packaging of vegetable salad in an atmosphere with high oxygen and carbon dioxide contents resulted in an extension of sensory acceptability of the tested product up to 12 days. The advantageous effect of such a composition of modified atmosphere on the extension of sensory stability of e.g. sliced peppers was discussed by Conesa et al. [4].

Changes in oxygen and carbon dioxide contents in atmosphere inside packaging
Based on measurements of oxygen and carbon dioxide ratios in the atmosphere inside the packaging it was found that in samples packaged in air atmosphere using barrier films for analyzed gases anaerobic atmosphere was produced as early as after 1 day of storage. In case of salads packaged in an atmosphere with a high oxygen content (70% and 80%) a statistically significant (p ≤ 0.05) decrease of oxygen content was recorded during storage. After 12 days the proportion of this gas in the atmosphere inside packaging ranged from 34.7% to 48.1% (Tables 4, 5). In samples packaged in Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h) with 2 x 10 microperforation, both in case of air atmosphere and modified atmosphere, oxygen was found throughout the entire storage period. After 12 days the content of this gas in the above mentioned samples ranged from 13.3% to 14.6% (Table 6).

In all samples packaged in barrier films a statistically significant (p ≤ 0.05) increase in the proportion of carbon dioxide was recorded in the atmosphere inside packaging.  The highest content of this gas after 12-day storage was found in salads packaged in atmosphere of 70% O₂ and 30% CO₂ (Tables 4, 5). For samples sealed in such an atmosphere using Flow HB 50 film (with oxygen permeability of 3 cm³/m²/24 h) CO₂ content was 60.9% and it was 56.8% for salads sealed with Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h). However, it needs to be stressed that the highest increase of carbon dioxide content in relation to its initial content in the atmosphere was recorded in air-packaged samples (Tables 4, 5).

Packaging of tested salads in modified atmosphere (%O₂/%CO₂: 70/30; 80/20) in Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h) with 2 x 10 microperforation resulted in a statistically significant (p ≤ 0.05) decrease in carbon dioxide content (to 17.0% and 15.6%, respectively) recorded as early as after 1 day of storage. In turn, in air-packaged salads after an identical storage time a statistically significant (p ≤ 0.05) increase in CO₂ content to 5.7% was found (Table 6). After 6 days CO₂ content was observed to decrease in all samples analyzed in this experiment. The proportion of this gas in the atmosphere inside the packaging ranged from 4.0% to 4.9%. After the assumed storage time in all tested salads a significant (p ≤ 0.05) increase was recorded in carbon dioxide content up to the final values of 9.8%–11.8% (Table 6). Carbon dioxide concentrations over 20% are not recommended in packaging of respiring products, such as coleslaw-type vegetable salad. However, it results from a study by Fonseca et al. [6] that vegetables vary in their tolerance to high carbon dioxide concentrations. Based on results obtained in this study it may be assumed that the application of high carbon dioxide concentrations in packaging, followed by a considerable drop in its content during storage as a result of film microperforation, is one of the factors contributing to the extension of sensory acceptability of the tested product.

Physico-chemical attributes ( soluble solid, pH)
In all analyzed samples, irrespective of the type of film used in packaging and the composition of the atmosphere, a significant (p ≤ 0.05) decrease in soluble solid content was observed during storage in relation to its level in fresh salad. In salads packaged in modified atmosphere in barrier films for oxygen and carbon dioxide, this decrease was significantly smaller (p ≤ 0.05) than in air-packaged samples (Tables 4, 5). When applying Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h) with 2 x 10 microperforation in sample packaging the composition of atmosphere inside the packaging did not have a significant (p ≤ 0.05) effect on changes in soluble solid content during storage (Table 6).

In samples packaged in the air atmosphere, using both barrier films for oxygen and carbon dioxide and microperforated film, a significant (p ≤ 0.05) increase in pH was recorded after 12-day storage in relation to that of fresh salad (Tables 4, 5, 6). In turn, in modified atmosphere packaged samples an initial increase and then a decrease in active acidity were observed. After 12-day storage the recorded value in samples packaged in barrier films was comparable to pH in fresh salad (Tables 4, 5). In case of modified atmosphere samples packaged in Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h) with 2 x 10 microperforation, the pH level was significantly (p ≤ 0.05) lower than that of air-atmosphere samples (Table 6).

This study analyzed only the effect of atmosphere composition and the type of packaging material on sensory quality, changes in oxygen and carbon dioxide contents in the atmosphere inside the packaging as well as selected physico-chemical properties of stored vegetable salad. It needs to be stressed that in order to obtain a safe product, which shelf-life could be 12 days, it will be necessary to supplement these investigations with an evaluation of microbiological quality.

CONCLUSIONS

Based on the conducted analyses concerning the effect of the composition of atmosphere and the type of packaging material on sensory quality, changes in oxygen and carbon dioxide contents in the atmosphere inside the packaging and selected physico-chemical properties of coleslaw-type vegetable salad stored for 12 days at 4°C it was found that:

1. The application of Opalen 55 AF 50 film (with oxygen permeability of 35 cm³/m²/24 h) with 2 x 10 microperforation and modified atmospheres of 70%O₂/30%CO₂ and 80%O₂/20%CO₂ contributed to the maintenance of good sensory quality of coleslaw-type vegetable salad during 12-day storage at 4°C.

2. Throughout storage in modified atmosphere samples packaged using microperforated Opalen 55 AF 50 film the proportion of carbon dioxide was found to decrease considerably and the presence of oxygen was detected.

3. In all tested samples a significant (p ≤ 0.05) decrease was recorded in soluble solid  content during storage.

4. After 12-day storage pH of modified atmosphere packaged samples, irrespective of the used film type, was significantly (p ≤ 0.05) lower than that in salads packaged in air atmosphere.

REFERENCES

The study was financed from funds for research in the years 2008–2011 as a research project.

Accepted for print: 15.11.2009

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.