Farklı Yıkama Çözeltisi Ve Ambalaj Malzemesinin Modifiye Atmosferde Depolanan Kültür Mantarı (agaricus Bisporus) Kalitesine Etkileri

Abstract

u çalışmada, iki farklı yıkama çözeltisi ve dört çeşit ambalaj malzemesi kullanılarak modifiye atmosfer koşullarında, 5 ile 15°C'de depolanan kültür mantarlarında (Agaricus bisporus) meydana gelen kalite değişimleri incelenmiştir. İkinci parti kesimden alınan kültür mantarları, sodyum metabisülfit, sodyum hipoklorit içeren birinci çözelti veya sodyum askorbat, sodyum EDTA, sodyum hipoklorit içeren ikinci çözelti ile yıkanmıştır. Yıkanmamış mantarlar kontrol örneği olarak kullanılmıştır. Ambalaj malzemesi olarak piyasada yaygın olarak kullanılan streç film (PVC), morötesi ışığa karşı geçirgenliği az olan bir diğer streç film (green streç, PVC), 30um düşük yoğunluklu polietilen film (LDPE) ve iğne ile perfore hale getirilen 30u,m düşük yoğunluklu polietilen film (perfore LDPE) kullanılmıştır. Depolama süresince örneklerde her gün gaz ölçümü yapılarak ambalaj içi gaz bileşimi belirlenirken, birinci, üçüncü ve yedinci gününde ayrıca fiziksel (şapka rengi, sap rengi, iç renk, sap ve şapkada tekstür), kimyasal (pH, toplam asittik, nem, kül, protein, ağırlık kaybı, kükürt miktarı) ve mikrobiyolojik (toplam aerob bakteri, Pseudomonas türleri ve anaerob bakteri) analizler yapılmıştır. Ambalaj içi gaz konsantrasyonu üzerinde yıkama işleminin bir etkisi görülmezken, ambalaj malzemesi ve depolama süresinin etkileri önemli bulunmuştur (p<0.05). Streç filmlerle sanlı ambalajlarda O2 konsantrasyonu LDPE filmlere göre daha yüksekken (sırasıyla, %1 1-15; %2-8), buna karşın C02 konsantrasyonu daha düşük (sırasıyla, %7-10; %13-19) seviyelerde dengeye ulaşmıştır. Yıkama işleminin mantar rengi üzerindeki etkisinin önemli olduğu (p<0.05), ancak hangi çözelti ile yıkandığının sonucu etkilemediği gözlenmiştir. Mantarlarda şapka renk değerleri (L değeri) genel olarak 70-85 arasında değişim göstermiştir. Mantar dokusu 7 günlük depolama süresince önemli ölçüde yumuşamış ve Instron pik kuvveti bu süre içinde 85 Newton'dan 45 Newton seviyelerine düşmüştür. İstatistiki sonuçların genel bir değerlendirilmesi yapıldığında kültür mantarının kalitesini öncelikle yıkama işleminin ve depolama süresinin belirlediği; ambalaj malzemesinin bu iki faktöre göre daha az etkili olduğu gözlenmiştir.

Demand for cultivated mushrooms in Turkey has been increasing since 1960. Consequently, the amount of cultivated mushroom produced in the sountry greatly increased in the past two decades (Figure 1). Among the many regions for growing cultivated mushrooms in Turkey, the Mediterrainean leads the production with a share of 43.9% (Figure 2). §1 8000 7000 6000-- 5000-- İS ?O « 4000 ?e = i I u 3000' 2000 1000 ?? 3052 2560 1400 tMMâtt£tâtât * ffi 1973 1983 1987 Year 1991 7728 V' - 1995 Figure 1. Cultivated mushrooms production in Turkey xni 45 40 35 30 25 20 1 5 1 0 5 0 T 4 3,9 i& 2 8,3 t''. S*& 7,5 6,1 0,0 6 0,0 4 Regions Figure 2. Production of cultivated mushrooms in different regions in Turkey The objective of this study was to determine effects of two washing solutions and four packaging materials on the quality of cultivated mushrooms (Agaricus bisporus) stored at 5 and 15°C under modified atmosphere (MA) conditions. Cultivated mushrooms were obtained from a local commercial producer. All mushrooms were taken from second flush. The flow chart of the experimental procedure is shown in Figure 3. Four packaging materials used in this study were a) stretch film currently used by commercial producers, b) another stretch film that was more opaque to ultraviolet light than the normal stretch film, c) 30um low density polyethylene (LDPE) bag and d) 30um LDPE bag with one hole on each side. Gas composition analyses of the internal atmosphere of packages were conducted in triplicate every day up to one week using Chrompack Micro GC Gas Analyser. The quality parameters measured during MA storage were; physical tests (color of cap, stem and cut surface; texture of cap and stem; weight loss), chemical tests (moisture content, protein content, ash content, pH and total acidity), and microbiological tests (total aerobe bacteria count, anaerobe bacteria count and Pseudomonas count). Moreover, development stage of mushrooms during storage was visually evaluated. xiv Figure 3. Flow chart of the experimental procedure followed in this study xv Experimental data were evaluated statistically by running analysis of variance (ANOVA) at a significance level of 0.05. Mushrooms stored at 15°C were deteriorated within two days of storage. Therefore incomplete data pertaining to this temperature were not included in statistical evaluation. Mushroom respiration rates were determined as 28 and 55 ml CC^/kg. h for 5 and 15°C respectively. There was a rapid decrease in O2 concentration and rapid increase in CO2 concentration during first day of MA storage. Thereafter, equilibrium conditions prevailed at 7-9% for 02 and 12-14% for C02 (Figure 4). Equilibrium levels of 02 and CO2 varied with the packaging material (Table 1). Results in this table also indicate that the stretch group, owing to their high gas permeability, attained higher equilibrium levels of 02 and lower equilibrium level of C02 than the LDPE group. Moreover, one small perforation on each side of the LDPE bag did not appreciably alter the equilibrium levels of the gases in these packages. Table 1. Equilibrium atmosphere conditions in packages at 5°C Statistical results are summarised in Table 2. It is seen that two main indices of mushroom quality, namely color and texture, are influenced significantly (p<0.05) by all the experimental variables. Moreover, as visual observations we noted the followings: a) mushrooms packed with normal LDPE film had a good quality at the end of 9th day of MA storage, b) although the appearance was acceptable, there was an unpleasant odour in mushrooms packed with stretch film or perforated LDPE film, and c) the color of washed mushrooms was generally darker than that of unwashed mushrooms. xvi Figure 4. Gas composition in cultivated mushroom packages during MA storage at 5°C Table 2. Summary of statistical results on effects of washing process, packaging material and storage time on measured parameters of cultivated mushrooms +: effect is significant (p<0.05); -: effect is not significant (p<0.05) The L color value of the cultivated mushrooms decreased during MA storage (Figure 5). The lowest values of L was observed for the stipe of the mushrooms, whereas cap and xvu cut surface had similar L values throughout the storage period. Moreover, the L value of cut surface did not change during the first 3 days of MA storage. Despite of the decreasing trend seen in Figure 5, the L values did not reach the unacceptable lower limit of 70 as suggested in the literature. 90t 0 3 7 Storage period (day) 9 ?stipe ?cut surface Figure 5. Changes in L color value of stipe, cap and cut surface of cultivated mushrooms during MA storage at 5°C The peak force in compression of the cap of cultivated mushrooms decreased from 90 N to 50 N in the first 3 days and remained nearly unchanged in the rest of the storage period (Figure 6). This was in concert with the increased softness of the produce perceived by touching. The change in texture of the stipe of mushrooms was relatively small (Figure 6). The decrease in pH during MA storage of mushrooms (Figure 7) was accompanied by an increase in total acidity (Figure 8). The decrease or increase in total acidity was probably due to accumulation of organic acids resulting from physiologycal processes under high CO2 and low O2 during storage. It has been reported that malic and fumaric acid contents of cultivated mushrooms increased during storage at 3°C for 6 days. A steady decrease in weight of mushrooms packages (about 400g) observed during 6 day storage (Figure 9). However, weight losses recorded in this study was about 0.5%, which was comparably less than the values reported in the literature. It has been reported that weigth losses up to 4.5% for cultivated mushrooms stored at 12°C and 90% RH. The lower weigth losses in this work was probably due to the high RH and low temperature during storage. xvm Figure 6. Changes in peak force in compression of stipe and cap of cultivated mushrooms during MA storage at 5°C Figure 7. pH of cultivated mushrooms during MA storage at 5°C The total aerobe bacteria count generally increased from an initial value of lxl05cfu/ml to lxl09cfu/ml during one week of MA storage. Lower counts were obtained for mushrooms treated with second solution and higher counts were observed for unwashed mushrooms. The Pseudomonas count changed from an initial value of 5x 10s cfii/ml to 5xl08cfu/ml during one week of MA storage. Similar findings were reported at literature for mushrooms stored at 10°C for 8 days. In our study, neither washing process nor a particular packaging material appeared to have a significant retarding effect on microbial growth. XIX "w o H 0,03 0,025 + 0,02 0,015 -f 0,01 0,005 + 0 + + + 0 2 4 6 Storage period (day) 8 Figure 8. Total acidity of cultivated mushrooms during MA storage at 5°C. This work on cultivated mushrooms (Agaricus bisporus) grown in Turkey indicated that LDPE bags, whether perforated or not, did not present any advantage in terms of color and texture of the produce as compared to PVC stretch films. It seems that both PVC and LDPE films can benefit from more and larger perforations as the CO2 and O2 equilibrium levels were different from those reported in the literature as "optimum". Although washing fresh produce may be necessary for consumer appeal, it did not seem to improve (on contrary it was detrimental sometimes) the quality of the cultivated mushrooms. Packaging materials with gas permeabilities that closely matches the optimum CO2/ 02 ratio of the produce must be developed to extend shelf life of the produce. Storage period (day) Figure 9. Weight loss of cultivated mushrooms during MA storage at 5°C. Mushroom weight