Taze meyve sebze ürünlerinin modifiye atmosferde paketlenmesine yönelik ambalaj malzemesi geliştirme
Development of a packaging material for modified atmosphere packaging of fresh produce products
Yazar: DENİZ TURAN KUNTER
Danışman: PROF. DR. GÜRBÜZ GÜNEŞ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Gıda Mühendisliği Ana Bilim Dalı / Gıda Mühendisliği Bilim Dalı
Derece: Doktora, 2018
Konu: Gıda Mühendisliği = Food Engineering

Özet:
Bütün halde veya doğranmış, dilimlenmiş kullanıma hazır taze meyve-sebzeler metabolik olarak aktiftirler ve solunum yaparak O2 tüketip CO2 üretirler. Taze meyve sebzeler genellikle havadaki oranlara göre çok daha düşük O2 ve daha yüksek CO2 içeren, ürüne özgü optimum modifiye atmosfer (MA) koşullarında ambalajlanır. Diğer taraftan taze meyve sebzeler bazı düşük O2 ve yüksek CO2 içeren atmosferlerde fizyolojik olarak zarar görmektedir. Taze meyve sebze ürünleri için geçerli olan bu minimum O2 ve maksimum CO2 düzeyleri üründen ürüne değişmekte olup modifiye atmosferde ambalajlamada (MAA) bu değerler dikkate alınmaktadır. Bu kritik değerlerin ötesinde O2 ve CO2 oranlarına maruz kalan ürünlerde anaerobik solunum gerçekleşmekte ve fizyolojik olarak ürün kalitesi ve raf ömrü hızlı bir şekilde düşmektedir. Bu fizyolojik degradasyon çoğu zaman mikrobiyolojik bozulmalardan daha hızlı gerçekleşmektedir.
Taze meyve ve sebzeler için MAA tasarımı ürüne uygun bir soğuk depolama sıcaklığı dikkate alınarak yapılmaktadır. Bu sıcaklıktaki ürün solunum hızı ve ambalaj gaz geçirgenliği sonucu ambalaj içinde denge MA oluşmakta ve ürün stabilitesi sağlanmaktadır. Ancak, MA ambalajlanmış taze meyve sebze ürünleri özellikle depolama, taşıma ve pazarlama aşamalarında kısa süreli soğuk zincirin kırılması sonucu ortam sıcaklıklarına maruz kalmaktadır. Taze meyve sebze ürünlerinin solunum hızlarının sıcaklığa duyarlılığı (Q10 değerleri), mevcut ticari ambalaj malzemelerinin gaz geçirgenliklerine ait Q10 değerlerinden daha yüksek olduğundan ambalaj içindeki ürünün solunum hızı ambalaj malzemesinin gaz geçirgenliğinden daha fazla artarak ambalaj içinde ürün için uygun olmayan çok düşük O2 veya anaerobik ortam ile çok yüksek CO2 birikmesine neden olmakta ve bunun sonucunda ürün bozulmaktadır. Bu problemin çözümü için gaz bariyer özellikleri iyileştirilmiş yeni ambalaj malzemelerine ihtiyaç vardır. Bu yeni nesil ambalaj malzemelerinin gaz geçirgenlik Q10 değerlerinin (sıcaklık duyarlılığı) mevcut ambalaj malzemelerininkinden daha yüksek olması ve taze meyve sebzelerin solunum hızı Q10 değerlerine yakın olması gerekmektedir. Bu malzemelerle MA ambalajlanmış taze meyve sebze ürünlerinde üretim sonrasında olası sıcaklık dalgalanmaları ambalaj içi denge atmosferi etkilemeyeceğinden fizyolojik açıdan ürün kalitesi korunacaktır.
Bu çalışmanın amacı, taze meyve sebze ürünlerinin modifiye atmosferde ambalajlanmasına yönelik, gaz geçirgenliğinin sıcaklığa duyarlılığı mevcut ticari ambalaj filmlerinden daha yüksek olan, bu duyarlılığı meyve-sebzelerin solunum hızlarının sıcaklığa duyarlılığına yakın olan yeni bir ambalaj malzemesi geliştirmektir. Bu tez çalışması kapsamında, sıcaklık etkisi ile şekil hafıza özelliği gösteren poliüretan (ŞHPU) filmler çalışılmıştır. Literatürdeki bilgiler doğrultusunda yapmış olduğumuz çalışmalar sonucu şekil hafıza özelliği oda sıcaklığı civarında olan poliüretan film sentezlenmiş ve bu sıcaklıkta gaz geçirgenliğinin oldukça yüksek düzeyde arttığı görülmüştür. Gıda ambalajına uygun olması için polimer sentezinde katalizör ya da çözücü kullanılmamıştır. Tez çalışması kapsamında farklı fiziksel ve kimyasal özelliklere sahip monomerler (polietilen glikol, hint yağı, 1,4- bütandiol, hegzametilen diizosiyanat) değişen oranlarda kullanılarak farklı kompozisyonlarda ŞHPU filmler sentezlenerek gaz geçirgenliğinin arttığı geçiş sıcaklıkları 20 ve 25 oC olan 2 farklı grupta ŞHPU filmler dökme yöntemiyle üretilmiştir. Elde edilen filmler, gaz geçirgenliklerinin sıcaklığa duyarlılıkları, fiziksel, bariyer ve mekanik özellikleri ve aynı zamanda migrasyon açısından incelenerek taze meyve sebzelerin ambalajlanmasına uygunluğu değerlendirilmiştir. Çalışmanın sonraki kısmında bu yaklaşım sonucu elde edilen ve gaz geçirgenliği sıcaklığa yeterince duyarlı olan ŞHPU polimer malzemesinden sıcak pres yöntemi denenerek ince ambalaj filmleri üretilmiştir. Üretilen ambalaj filminin, model olarak seçilen taze dilimlenmiş elma dilimlerinde test edilerek performansları değerlendirilmiştir.
Bu çalışmalarla, gaz geçirgenliklerinin sıcaklığa duyarlılığı (Q10 değerleri) taze meyve sebzelerin solunum hızlarının sıcaklığa duyarlılıklarına yakın olan ŞHPU filmler elde edilmiştir. Ticari potansiyeli olan tez çalışmasının çıktısı ambalaj malzemesinin, taze meyve sebzelerde hasat sonrası kayıpların azaltılmasına, tüketime hazır katma değerli ürünlerin geliştirilmesine katkı sağlayarak sektöre ve ekonomiye olumlu etkisi olacağı beklenmektedir. Ayrıca ŞHPU malzemeler esnek ambalaj malzemesi olarak akıllı ambalaj konseptinde ilk kez değerlendirilmiş olup bu alanda yeni bilgilerin üretilmesine katkı sağlayacağı da düşünülmektedir.

Abstract:
Fresh fruits and vegetables (whole or fresh-cut) are metabolically active, respiring products consuming O2 and producing CO2. Fresh produce products are packaged under a specific optimum modified atmosphere with reduced O2 and elevated CO2 compared to air. On the other hand too low O2 and too high CO2 levels (which varies with the product) can physiologically damage the fresh produce products. These critical O2 and CO2 levels depend on the product and considered in modified atmosphere packaging of fresh produce. Exposure of the fresh produce O2 and CO2 beyond these levels results in anaerobic respiration that caused a reduction in product quality and shelf life. These physiological degradations are usually faster than microbiological spoilage in these products.
A specific cold storage temperature is considered when designing a modified atmosphere package for fresh produce product. Respiration rate of the product and the gas transmission rate through the package surface at this temperature results in an equilibrium modified atmosphere which stabilize the product. However, MA packaged fresh produce products are usually subjected to temperature abuse during transportation, storage and marketing even for short periods due to broken cold chain for various reasons. The fact that respiration rate increases at a faster rate than the gas transmission rate through the package film is because the temperature dependence of respiration rate (expressed by Q10 value) is higher than the temperature dependence of permeability of the packaging films. As a result, too low or anaerobic conditions are occured in the package and this too high CO2 accumulation causes spoilage of the packed product. New packaging materials with increased temperature sensitivity for gas permeabilities are necessary to solve these problems. The Q10 values of these new materials need to be higher than that of commercial films and need to be close to the Q10 values of the respiration rate of fresh produce. Temperature fluctuations after packaging of fresh produce with these new packaging materials would not change the equilibrium MA and thus the quality of the product would be maintained from the physiological point of view.
The objective of this thesis study is to develop a new packaging material with increased temperature sensitivity for gas permeabilities compared to available commercial films, and to have this temperature sensitivity close to the temperature sensitivity of the fresh produce respiration rate. Thermoplastic polyurethane films with shape memories induced by temperature change was studied. The information in literature and the experiments showed that the shape memories of the films occured at room temperature and the gas permeability of films increased at a very high rate with temperature change from refrigerated to near room temperature. Any solvent or catalyst was not used in synthesis of the shape memory thermoplastic polyurethane (SMPU) film to get a food contact compatible material. In the first part of the study, series of shape memory polyurethane (SMPU) were synthesized using poly(ethylene glycol) (PEG), 1,6-hexamethylene diisocyanate (HDI), 1,4-butanediol (BDO) and castor oil (CO), and casted into films. The reaction was monitored by Fourier transform infrared (FTIR) spectroscopy. The changes in thermal, viscoelastic, shape memory properties, and gas permeabilities of the films were studied. All the diisocyanate and BDO were consumed in the reaction. 1500 g mol-1 PEG based polyurethane films showed a phase transition (switching) temperature between 20 and 27 oC. The SMPU consisting of 50/50 CO/PEG had log E' value of 8.32 Pa, and showed good elasticity as low density polyethylene (LDPE). SMPU prepared from 1500 g mol-1 PEG with 50/50 CO/PEG and 40/60 BDO/(PEG+CO) ratios showed excellent shape memory properties with shape recovery ratio > 85 % and shape fixity ratio > 90 %. This film had higher oxygen permeability, and showed up to 67 % increase in Q10 value for oxygen permeability compared to commercial packaging films like LDPE. Permselectivity (PCO2/PO2) of the SMPU film was 15, which is approximately three times higher than for LDPE.
In the second part of the study, performance of an optical method was assessed by measuring oxygen permeability (PO2) of the films at different temperatures (5, 15, 24, 31, 38 and 55 oC) and humidities (0, 60, 80 and 98%). Water vapor transmission rate (WVTR) was measured according to the gravimetric method. The moisture absorption of the film was measured as a function of time at an RH of 98% at 25 °C. Tensile test was conducted to determine the stress/ strain behavior of film. PO2 of the SMPU film was at least two times higher than that of low density polyethylene (LDPE) and increased at higher relative humidity. There was a sudden increase in Po2 at higher RH after phase transition temperature. WVTR of PU film was found 3830 g∙m-2∙day-1 at 38 oC and 90% RH. It was almost 100-fold higher than the WVTR of commercial LDPE. The film absorbed circa 18% water vapor at 98% relative humidity. Young modulus of SMPU film was found as 90 MPa which was compatible with commercial packaging films such as LDPE. The optical method agreed very well (maximum 20% deviation) with a standard carrier gas method in PO2 measurement.
In the third part of the study, thin film method was developed by using a hot press method. Hot pressed SMPU films were subjected to specific and overall migration tests. A new method with gas chromatography-flame ionization detector was proposed to measure specific migration of 1, 4-butanediol from the SMPU film. Both specific and overall migration values in the established simulants were under the legal limits. Therefore, the SMPU film can be considered safe as a food contact material. Moreover, the analytical method used for determination of specific migration of 1, 4-butanediol resulted in good analytical characteristics and detection limits at ppm level.
Finally, selected SMPU film was tested on fresh-cut Starking apple to evaluate their performance. Respiration rates of fresh-cut apples were measured using closed jar system and modelled using enzyme kinetic model. Fresh-cut Starking apple was packaged under designed MA using the SMPU film and LDPE as control. The packages were stored at 4 oC, 20 oC and also at fluctuating temperatures for a week. At first, the headspace O2 concentration was aimed at 10% level in order to avoid any damage because of anaerobic enviroment as a result of temperature fluctuation. Then, the headspace O2 and CO2 levels were measured during weekly storage. Respiration rates showed good fit between experimental and modelled values. For SMPU film, steady-state atmospheres of % 10,5 O2 -% 2 CO2 and % 10,1 O2 -% 2 CO2 were maintained in the package headspace at 4 oC and 20 oC, respectively. However, the steady state atmosphere in the headspace of LDPE packages were % 10,1 O2 -% 2.3 CO2 and % 6,1 O2 -% 4.3 CO2 at 4 oC and 20 oC, respectively during storage. While temperature fluctuations during storage had a major impact on equilibrium atmosphere composition in LDPE packages; no significant change was observed in the SMPU packages. Afterwards, fresh-cut Starking apples were packaged again using the SMPU film and LDPE as control, but this time under MA as stated in the literature (2% O2 and 7% CO2 (balanced with N2)) for fresh-cut apple. Packaged products stored at 4 oC; and subjected to temperature fluctuations between 4 and 20 oC for 20 day (5 cycles of 3 days at 4 °C and 1 day at 20 °C). Quality attributes (weight loss, color change, texture, soluble solid content, pH, microbial load and sensory analysis) were evaluated. Temperature fluctuations had a major impact on the composition of the package atmospheres and on product quality for LDPE packages. CO2 concentrations increased rapidly, reaching maxima of 21%. The quality of the apples packed with LDPE stored under the temperature fluctuating regime was severely affected as indicated by extensive browning, loss of firmness, weight loss increase, infection due to physiological damage and excessive condensation, compared to products stored at constant temperature. It was clear that temperature fluctuation, even if it should occur only once, can seriously compromise the benefits of modified atmosphere packaging and safety of the packaged produce.
Overall, a new SMPU film was obtained with Q10 values of their permeabilities close to the Q10 values of respiration rate of fresh produce in this thesis study. Moreover, the film may prevent water vapor condensation for moisture sensitive fresh products without the need of microperforation. This film can be used to develop smart packaging with increased thermally responsive gas permeability to a similar levels observed in respiration rates of fresh produce products. This product will likely have commercial potential and can support reduction of postharvest losses, development of value added new fresh products and thus can provide benefits for the industry and economy of the country. Moreover, SMPU films were evaluated as a flexible intelligent food packaging for the first time by this study which generates new information and new project ideas.