Article

The Impact of Microwave-Assisted Thermal Sterilization on the Morphology, Free Volume, and Gas Barrier Properties of Multilayer Polymeric Films

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

Microwave-assisted thermal sterilization (MATS) is an advanced thermal process that utilizes microwave (MW) energy for in-package food sterilization. Benefits include much shorter processing times than conventional retort sterilization. This research explores how MATS affects the performance of high-barrier multilayer polymeric films compared with conventional retort sterilization. The gas barrier, morphological, and free volume packaging properties of these films may influence the shelf-life of shelf-stable foods. In this study, we applied X-ray diffraction (XRD) and positron annihilation lifetime spectroscopy in order to investigate film morphology and free volume characteristics, respectively. Results show that the conventional retort process affected gas barrier properties more than MATS processing did which could be explained by the morphological and free volume changes in the polymeric films. XRD revealed improved crystalline morphology of MW-treated films in terms of overall crystallinity as compared with retort sterilization. On the other hand, higher free volume increase in MW-treated films could be explained by the different heating mechanisms involved in MATS and retort sterilization. Overall, the oxygen transmission rate for both films remained below 2 cc/m2-day after MATS and retort sterilization required for packaging applications for shelf-stable foods. This work provides the basis for understanding the gas-barrier changes of multilayer polymeric films after MATS application using Materials Science techniques. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40376.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Studies show that commercial retort-grade products (pouches or films) maintained a good shape after MATS processing, with no visible damage ( Mokwena et al., 2009;Dhawan et al., 2014a,b;Zhang et al., 2016a). However, changes in polymer morphology do occur in terms of the crystalline structure, crystallinity, polymer chain alignment, and disorderliness of polymer chain packing due to plasticization after MW sterilization ( Dhawan et al., 2014a,b). For example, films containing EVOH undergo severe plasticization due to water absorption during MW sterilization ( Mokwena et al., 2009;Zhang et al., 2016a). ...
... Positron annihilation lifetime spectroscopy (PALS) is an advanced physical method used to measure sterilization-induced free volume changes in PET-coated multilayer films. Results using this method show that MATS-pro­ cessed films contain more localized, thermally induced free volume gaps ( Dhawan et al., 2014a,b). ...
... The impact of MATS on the thermal properties of two PET-based pouches PET//Nylon 6//PP and coated-PET//oriented-Nylon 6//PP were investigated ( Dhawan et al., 2014a,b). Results showed no significant difference in melting temperature (T m ) and enthalpy of melting (⊗H m ) after MATS processing for a lethality of F 0 = 6.0 min ( Dhawan et al., 2014a,b). Pressure-assisted thermal processing was found to have no effect on 0003383265.INDD 214 12/20/2017 12:04:30 PM * Film structure was denoted as//for lamination with adhesive, denoted as/for co-extrusion. ...
... Previous studies on MATS processing demonstrate that quality is retained for a variety of foods, including asparagus, macaroni and cheese, salmon, chicken, rice, scrambled eggs, beef gravity, and mashed potatoes (Guan et al. 2002(Guan et al. , 2003Sun et al. 2007;Tang et al. 2008). Scheduled processes of packaged homogenous and nonhomogeneous foods have been accepted by the FDA (Dhawan et al. 2014). Since metal cannot be used for in-package microwave processing, the most suitable packaging for MATS must be polymer-based. ...
... This usually results in improved taste, color, and flavor of commercially sterile foods (Rodriguez et al. 2003;Byun et al. 2010a). Previous works (Dhawan et al. 2014;Mokwena et al. 2009) conducted by our group showed that ethylene vinyl alcohol (EVOH) laminates and coated poly ethylene terephthalate (PET)-based pouches were successfully used for MATS processing, although the package barrier properties deteriorated. However, this effect was less profound than that observed in conventional retort processing with similar process lethality (Dhawan et al. 2014). ...
... Previous works (Dhawan et al. 2014;Mokwena et al. 2009) conducted by our group showed that ethylene vinyl alcohol (EVOH) laminates and coated poly ethylene terephthalate (PET)-based pouches were successfully used for MATS processing, although the package barrier properties deteriorated. However, this effect was less profound than that observed in conventional retort processing with similar process lethality (Dhawan et al. 2014). If barrier properties are compromised, oxygen can enter in the packaging, causing lipid oxidation, and moisture loss can also occur (Mokwena et al. 2009). ...
Article
Full-text available
Polymer-based packaging with low oxygen (OTR) and water vapor transmission rates (WVTR) can be used to limit oxidative chemical changes in packaged foods, especially for the 3- to 5-year shelf life required for military rations and long-duration space foods. Microwave-assisted thermal sterilization (MATS) produces higher quality food with a potentially longer shelf life as a result of volumetric heating and the associated shorter process time. This study investigated the effects of the package-MATS process interactions and the resultant package barrier properties on food quality, using a mashed potato model food following MATS process of F0 = 9 min for 12 weeks at 50 °C. Two poly ethylene terephthalate (PET)-based (MFA, MFC) and one ethylene vinyl alcohol (EVOH)-based (MFB) retort pouches were tested, with OTRs of 0.20, 2.11, and 0.07 cc/m2·day and WVTRs of 2.64, 1.78, and 0.29 g/m2·day for MFA, MFB, and MFC, respectively; a foil double-sealed MFA pouch served as a control (MF0). Barrier properties did not influence oxygen content in polymer pouches during storage (p > 0.05). From the third week to the fifth week of storage, significant differences (p < 0.05) were observed in total color difference (ΔE) and oxidation indicators (TBARS, hexanal, and nonanal). The mashed potato treated in higher barrier property pouches exhibited less color change and oxidation than those in lower barrier property pouches. The performance of the MFC pouch was similar overall to that of the metal pouch. These findings suggested that high-barrier packages are suitable for MATS or other commercially sterile foods, particularly for long shelf-life purpose.
... But high gas barrier properties in polymer packages may deteriorate after undergoing high temperature and moisture processes. Our previous work has reported the effect of MATS on oxygen transmission rates (OTR) and water vapor transmission rates (WVTR) for selected polyethylene terephthalate (PET) and ethylene vinyl alcohol (EVOH) package films (Mokwena et al., 2009;Dhawan et al., 2014). The performance of polymer packages requires validation during shelf life studies of MATS foods. ...
... The MF0 pouch (230 mm  190 mm) was used to double-seal the MFA pouches after processing, and served as the control. The oxygen transmission rates (OTR) and water vapor transmission rates (WVTR) of these pouches were measured with a Mocon Ox-Tran 2/21 MH and a Mocon Permatran 3/33 permeability instrument, following the method of Dhawan et al. (2014). After MATS processing, the OTRs (23 C, 65% RH, 1 atm) and The WVTRs (38 C, 100% RH, 1 atm) were also listed in Table 1, they were used as barrier properties during storage. ...
... A description of this system can be found in Tang et al. (2006). The general processing procedure general followed that of Dhawan et al. (2014). To ensure sufficient lethality, the F 0 ¼ 9 min for MFA pouch was adopted. ...
Article
This study investigated how the shelf-life of foods processed with microwave-assisted thermal sterilization (MATS) is affected by temperature and package gas barrier properties. We conducted accelerated shelf life testing of a mashed potato-based model food processed with MATS. The model food was processed to a lethality of F0 = 9.0 min, packaged in four pouch materials with different oxygen transmission rate (OTR) and water vapor transmission rate (WVTR), and then stored at 23 °C, 37 °C and 50 °C for up to 12, 6, and 2.8 months, respectively. Findings showed that there were significant temperature effects and the combined effects of OTR and WVTR on the food color (ΔE). Moisture loss and lipid oxidation were also affected by package over the storage periods. Shelf-life predictions were based on the model at different temperatures and OTRs (23 °C storage) using ΔE = 12 as the end point for acceptable quality, with Q10 values ranged from 2.85 to 3.15. The results provide valuable information for selecting packaging materials for MATS and other thermally processed foods.
... When metal oxide coated multilayer polymeric pouches are thermally sterilized, they get exposed to high temperatures in the range of 121°C, along with high moisture and pressure. Studies demonstrate that the gas barrier properties of metal oxide coated multilayer polymeric films decrease after sterilization, due to changes in their thermal and morphological characteristics (Dhawan et al., 2014;Zhang et al., 2017). Other studies have 18 × 13 Stand-up 350 a ONy: Oriented Nylon 6; CPP: Cast Polypropylene * Information related to the type of metal oxide coating is not available for this pouch. ...
... examined the barrier performance of metal oxide coating itself along with external factors that may lead to defects (Leterrier, Månson, & Wyser, 2001;Rochat, Leterrier, Fayet, & Månson, 2005;Singh et al., 2007;Struller et al., 2014). However, these studies have analyzed the performance of the coatings present on the exterior surface of films (Dhawan et al., 2014;Zhang et al., 2017), or of films that were not exposed to commercial sterilization conditions such as heating at 121°C under high moisture (Leterrier et al., 2001;Struller et al., 2014). Research is needed to develop an effective method to identify the changes in coating layer of metal oxide coated multilayer polymeric films after thermal processing. ...
... The structural changes in polymers also contribute to reduction in gas barrier properties after thermal treatment. However, morphological changes have less influence on the barrier properties of metal oxide coated films than EVOH-based multilayer structures Dhawan et al., 2014;Zhang et al., 2017). Nevertheless, several other factors that may have contributed to changes in film barrier properties include moisture absorption by Vol. ...
Article
Metal oxide coated multilayered polymeric pouches provide a suitable alternative to foil‐based packaging for shelf‐stable products with extended shelf‐life. The barrier performance of these films depends upon the integrity of the metal oxide coating which can develop defects as a result of thermal processing and improper handling. In this work, we developed a methodology to visually identify these defects using an oxygen‐sensitive model gel system. Four pouches with different metal oxide coatings: MOA (Coated PET), MOB (SiOx‐coated PET), MOC (Overlayer‐AlOx‐Organic‐coated PET), MOD (Overlayer‐SiOx‐coated PET) were filled with water and retort‐processed for 30 and 40 min at 121 °C. After processing, the pouches were cut open, dried and subsequently filled with a gel containing methylene blue that changes color in the presence of oxygen. The pouches were then stored at 23 and 40 °C for 180 and 90 days, respectively. Defects were identified by observing the localized color change from yellow to blue in the packaged gel. These observations were confirmed through measurement of oxygen and water vapor transmission rates, as well as SEM and CLSM analyses. The MOC pouches showed the least change in barrier properties after thermal processing. This was due to crosslinking in the organic coating and protection provided by the overlayer. The melting enthalpy of all films increased significantly (P < 0.05) after sterilization. This may increase the brittleness of the substrates after processing. Findings may be used to improve the barrier performance of metal oxide coated polymeric films intended for food packaging applications. In this study, we developed a methylene blue‐based, oxygen‐sensitive model gel system to identify defects in metal oxide coated polymeric structures induced by thermal processing and mechanical stresses. We also performed a comprehensive analysis of these defects through CLSM and SEM. The gel system and methodology developed may be useful in the design and development of high barrier metal oxide coated films.
... New polymeric packaging with improved gas barrier properties was required for military rations and space missions that specify 3 yr and 5 yr shelf lives, respectively. Metal oxide coating used for improving the barrier properties of multilayer polymeric packaging developed pinholes and cracks after packages were subjected to MATS and PATS processes (Zhang et al. 2017, Dhawan et al. 2014. During sterilization processes, mechanical and thermal stresses caused defects in the metal oxide coating, resulting in deterioration of package gas barrier properties and compromising the food's shelf life. ...
... The WSU laboratory addressed this need with a blend of advanced analytical instruments and polymer science. For example, it employed confocal laser microscopy, scanning electron microscopy, and atomic force microscopy to probe into failure mechanisms of metal oxide-coated polymeric structures subjected to sterilization processes , Parhi et al. 2019, Zhang et al. 2017, Dhawan et al. 2014. When the laboratory found that defects decreased the barrier performance of packaging, they developed oxygen-sensitive gel systems based on agar and gellan gum to quickly detect defects in metal oxide-coated film pouches (Parhi et al. 2019). ...
... In addition, positron annihilation lifetime spectroscopy and X-ray diffraction explained how an increase in fractional free volume and crystal fragmentation and other morphological changes in polymers led to an increase in oxygen and water vapor transmission rates in polymeric packaging after sterilization processes (Zhang et al. 2017, Dhawan et al. 2014. This research has been applied to assess packaging for military rations. ...
... Although polymeric-based packaging is suitable for MAPS, the packaging must maintain its visual appearance and integrity after processing. Little research has examined the influence of thermal pasteurization (Halim, Pascall, Lee, & Finnigan, 2009), microwave-assisted thermal sterilization (MATS) (Dhawan et al., 2014a;Mokwena, Tang, Dunne, Yang, & Chow, 2009), or pressureassisted thermal sterilization (PATS) (Dhawan et al., 2014b) on the barrier properties of polymeric films. Dhawan et al. (2014a) reported a reduction in gas barrier properties of PET-based multilayer films. ...
... Little research has examined the influence of thermal pasteurization (Halim, Pascall, Lee, & Finnigan, 2009), microwave-assisted thermal sterilization (MATS) (Dhawan et al., 2014a;Mokwena, Tang, Dunne, Yang, & Chow, 2009), or pressureassisted thermal sterilization (PATS) (Dhawan et al., 2014b) on the barrier properties of polymeric films. Dhawan et al. (2014a) reported a reduction in gas barrier properties of PET-based multilayer films. They demonstrated that retort sterilization had more influence compared to MATS processing due to longer processing times associated with retort processing. ...
... Therefore, nylon 66 in film C tends to absorb less moisture compared to the nylon 6 in film B because of its reduced polarity and protection from outer environment. Film A has hydrophobic PET as main barrier layer, and the increase in OTR after pasteurization can be considered as a net result of structural and morphological changes, rather than a plasticizing effect (Dhawan et al., 2014a). During pasteurization, films absorbed water, which acted as plasticizer. ...
Article
In-package pasteurization of ready-to-eat (RTE) meals using microwave-assisted pasteurization system (MAPS) has shown promise for improving the safety and quality of foods, since dielectric heating is more efficient than thermal conduction. However, MAPS can affect the oxygen transmission rate (OTR) and water vapor transmission rates (WVTR) of packaging, imparting a certain degree of quality deterioration to the pasteurized food. This study evaluates morphological changes in newly-developed 3 multilayer polymeric films used for lid-stock on trays subjected to MAPS. We measured changes in OTR and WVTR after MAPS treatment, and further correlated these measurements with melting enthalpy (?H), overall crystallinity, crystal structure, water absorption, and dielectric properties of films. The composition of tested films was: (Film A): polyethylene terephthalate (PET)/barrier PET/polyethylene (PE); (Film B): PET/Nylon-Polypropylene (PP) and (Film C): PET/low density polyethylene (LDPE)/Nylon/LDPE. Results show that the OTR and WVTR of the films significantly increased (P < 0.05) after both hot water and MAPS pasteurization. Films B and C exhibited a higher OTR after MAPS (52 mins) compared to hot water pasteurization (36 mins). The melting enthalpy (?H) of the films increased after pasteurization, and was correlated to the increase in overall crystallinity (1?4% increase) of the films. Increases in OTR and WVTR can be attributed to the fragmented crystal structures and smaller crystal size observed in X-ray diffraction. It is evident that the films absorbed water during MAPS, which altered their dielectric properties. In addition, it is likely that water absorption caused plasticization of the Nylon polymer, degrading the gas barrier properties of the film. Based on these findings, we recommend using a multilayer film with PET as barrier layer for MAPS treatment.
... Several studies have investigated the barrier performance of a range of polymeric packaging subjected to retort and high-pressure processing, including pasteurization and sterilization (Dhawan et al., 2014c;López-Rubio et al., 2005a,b;Bull et al., 2010;Koutchma et al., 2010;Halim et al., 2009). However, studies on MWassisted thermal processing are rather limited (Dhawan et al., 2014b;Mokwena et al., 2009;Zhang et al., 2016). High-temperature and prolong heating of retort processing causes severe damage to packaging material compared to HPP (López-Rubio et al., 2005b) and MATS (Dhawan et al., 2014b) and also reduces barrier performance. ...
... However, studies on MWassisted thermal processing are rather limited (Dhawan et al., 2014b;Mokwena et al., 2009;Zhang et al., 2016). High-temperature and prolong heating of retort processing causes severe damage to packaging material compared to HPP (López-Rubio et al., 2005b) and MATS (Dhawan et al., 2014b) and also reduces barrier performance. During processing, water can penetrate through protective layers plasticizing the hydrophilic EVOH layer and lowering barrier properties (López-Rubio et al., 2005a). ...
... During processing, water can penetrate through protective layers plasticizing the hydrophilic EVOH layer and lowering barrier properties (López-Rubio et al., 2005a). This phenomenon is time dependent, so that the longer the processing time, the higher the water absorption and the higher the OTR and WVTR of the packaging films (Dhawan et al., 2014b;Mokwena et al., 2009). Many approaches, including Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and positron annihilation lifetime spectroscopy, have been employed to correlate changes in barrier properties with morphological and structural changes in polymers. ...
Chapter
Gas barrier packaging prolongs the shelf life of foods by protecting food quality and providing consumer safety. Advances in food processing technology have led to the development of new gas barrier materials to replace glass and metal packaging. Although the use of polymeric packaging is now commonplace, researchers still strive to improve gas barrier packaging and thus the quality of the food supply. Polymers such as ethylene vinyl alcohol, nylons, and polyethylene terephthalate in a multilayer structure significantly enhance the barrier functionality. However, there is a need of further improvement in barrier performance. Nanotechnology and other techniques such as layer multiplication and smart blending have shown considerable promise in high-barrier food packaging innovations. This article summarizes recent advances in high-barrier food packaging technology.
... Food Packaging and Shelf Life 25 (2020) 100514 compared to 30 and 40 min in retort at 121°C. The lower change in OTRs after MATS may be attributed to the shorter exposure time to elevated temperatures during processing (Dhawan et al., 2014;Zhang et al., 2017). In fact, film MO-E showed no oxygen permeation for the unprocessed and R30 samples. ...
... The effectiveness of the MO-coating depends on the presence of pinholes and cracks that allow oxygen molecules to navigate through the coating, the polymer substrate underneath and into the packaged food. Previous studies have reported that oxygen permeation occurs primarily through the macro defects (> 1 nm) in MO-coated films (Roberts et al., 2002).These defects can be generated on exposure to thermal processing and handling (Dhawan et al., 2014;Parhi et al., 2019;Zhang et al., 2017). In fact, studies showed a 12-fold increase in OTRs of MO-coated films after MATS processes (Zhang et al., 2017) which is similar to our measurements. ...
... Reduced heat exposure overall may have led to lesser deterioration in the MO-coating and the polymer substrate. Thermal processing can also alter the morphological properties such as free volume and crystallinity (Dhawan et al., 2014;Parhi et al., 2019;Zhang et al., 2017). As a result, the oxygen barrier ability of the coatings can decrease with longer processing time. ...
Article
Defects in metal oxide (MO)-coated polymer films increase their oxygen and water vapor transmission rates (OTRs, WVTRs), lowering the shelf-life of packaged food. In this study, we investigated the effects of thermal processing on six multilayered MO-coated films: MO-A (MO-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (50 μm)), MO-B (SiOx-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (60 μm)), MO-C (Overlayer/AlOx-organic-coated PET(13 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (50 μm)), MO-D (Overlayer/SiOx-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (60 μm)), MO-E (AlOx-coated PET(12 μm)//AlOx-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (70 μm)) and MO-F (AlOx-coated PET(12 μm)//AlOx-coated PET(12 μm)//AlOx-coated PET(12 μm)//Oriented-Nylon 6 (15 μm)//Cast-Polypropylene (70 μm)). Water filled film pouches were processed with a pilot-scale retort (30 and 40 min at 121 °C; F0 = 6–9 min) and microwave-assisted thermal sterilization unit (25-kW, single-mode, 915 MHz MATS system; F0 = 10.9 min). Subsequently, the pouches were emptied, filled with a color-changing oxygen sensor and stored at 23 ± 2 °C for 180-days. MO-F with three AlOx-coated PET layers, showed no oxygen permeation before and after retort and MATS processes. Compared to other films, MO-F exhibited low WVTRs after processing. Oxygen sensor in MO-F changed color at limited locations, indicating fewer defects. Confocal laser scanning microscope and scanning electron microscope images also showed less deterioration in MO-F. The dielectric loss factor (εr") for MO-F was significantly less than other films (P < 0.05) after thermal processing, indicating limited moisture absorption. Altogether, this study presents food industry with an alternative to foil-based packaging for sterilized products having an extended shelf-life.
... Traditional high-barrier packaging materials containing aluminum foil are not suitable for MATS, as they block microwave energy from reaching the food product to achieve the targeted lethality value. High barrier polymer packaging materials are,therefore,used for in-package thermal sterilization in MATS systems (Dhawan et al., 2014;Zhang et al., 2017). Several polymer-based structures can provide high barrier to water vapor, and most importantly, to oxygen. ...
... The oxygen transmission rate (OTR) and WVTR of the polymeric films were measured using an oxygen permeation analyzer (Mocon Ox-Tran 2/21 MH, Modern Control, Minneapolis, MN, USA) at 23°C, 55% RH, and 1 atm and a water vapor permeation analyzer (Mocon Permatran 3/33, Modern Control) at 100% RH and 38°C, respectively, following the method of Dhawan et al. (2014). Duplicate film samples were measured before and after MATS processing, and at the end of storage at 37.8°C. ...
... The highest weight loss (16.7%) was observed in pouch P3. Over the 6 months of storage, pouches with high WVTR lost more weight during storage due to moisture migration from the food to the atmosphere (Dhawan et al., 2014). At the end of storage, the weight loss percentage in the P3 differed significantly (P < 0.05) from the other pouches. ...
Article
The U.S. Army and NASA need ready‐to‐eat meals with extended shelf‐life for military operations and future manned space missions. For traditional heat sterilization methods, aluminum foil laminated pouches are used to achieve a shelf‐life of 3 to 5 years at room temperature. However, those packages are not suited for advanced thermal processing technologies based on microwave energy. This research investigated the effect of polymeric packaging materials on storage stability of garlic flavor, vitamin C, and color of garlic mashed potatoes processed with microwave‐assisted thermal sterilization (MATS) technology. Three types of high‐barrier metal oxide‐coated polymer pouches were used for MATS process, designed to achieve lethality approximately F0 = 6 min. Aluminum foil‐based pouches were used for retort process as control. Results demonstrated that both oxygen and water vapor barrier properties (oxygen transmission rate [OTR] and water vapor transmission rate [WVTR]) of the polymer pouches were affected by MATS processing. OTR increased by three to nine times, while WVTR increased by 5 to 20 times after processing. The MATS process resulted in 13% to 16% vitamin C loss, while retort process resulted in 18% loss in garlic mashed potato. The kinetics of vitamin C indicated that metal oxide‐coated high‐barrier packages (after processing OTR <0.1 cc/m².day; WVTR <1.0 g/m².day) could replace aluminum foil‐based pouches for MATS processed shelf‐stable ready‐to‐eat garlic mashed potatoes. Practical Application Garlic mashed potatoes in polymer packages processed in a microwave‐assisted thermal sterilization (MATS) system had better retention of vitamin C compared to samples packaged in aluminum laminated pouches and processed in retort. Polymer packages combined with MATS processing could potentially provide safe, better quality, and nutritious shelf‐stable food products for military and space missions.
... increases the free volume and could be one reason for the increase in gas and vapor barrier properties . In the case of control film, where hydrophobic PET is the main barrier layer, structural and morphological changes resulting in higher chain mobility and increased free volume resulted in barrier property changes rather than plasticization Dhawan et al., 2014). ...
... On the contrary, for PLA-PBAT and control film, the DSC results were not conclusive. Apart from plasticization and chain hydrolysis, morphological changes such as free volume increase and changes in crystallinities of individual layers/polymers can influence the changes in barrier properties after thermal processing Dhawan et al., 2014). The chemical modification of PLA-PBAT film could have helped in resistance towards thermal changes during processing. ...
Article
This study examined the feasibility of biobased/biodegradable films for in-package thermal pasteurization. Salmon in sauce and beet mixed mashed potato were vacuum packed in polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT)-based pouches (oxygen transmission rate (OTR): 330–619 cm³ m⁻² day⁻¹ and water vapor transmission rate: 38–49 g m⁻² day⁻¹), pasteurized targeting 6-log reduction of L. monocytogenes (P70°C7.5°C = 3 min), and stored at 4°C for 10 days. The gas barrier properties of all films decreased significantly (P<0.05) after processing, and some haziness developed in PLA films. Although the OTR increased, the microbial, physical, and chemical qualities were maintained at the end of storage. The lipid oxidation, based on TBARS, was within the acceptable limit in salmon in sauce. However, the vitamin C in mashed potato packed in biobased/biodegradable films demonstrated losses 2–3 times higher than in the control (polyethylene) film. Overall findings indicate that selected PLA and PBAT-based films are suitable for in-package pasteurization and can replace polyethylene for ≤10 days of shelf life at 4°C. Industrial significance Increasing consumer awareness about plastic waste disposal and demand for sustainable products has prompted food and polymer companies to develop sustainable solutions for food packaging. The use of biobased and biodegradable packaging could be one solution to address this challenge. However, current applications of biobased/biodegradable films are limited to fresh produce, meat, yogurt, some beverages, and dry products. Our findings extend the application of these films to in-package thermal pasteurization of high-moisture products, such as ready-to-eat meals.
... Microwave-assisted thermal sterilization (MATS) offers a shorter processing time than retort processing, with similar lethality (Tang 2015). This minimizes quality degradation and is less detrimental to package barrier properties (Dhawan et al. 2014). ...
... However, after MATS processing, the OTR increased significantly (p < 0.05) to 0.03-0.34 cc/m 2 day, except for package A. The increase in OTR was due to changes in polymer morphology and minor cracks in the metal oxide coating after thermal processing (Zhang et al. 2017;Dhawan et al. 2014;Mokwena et al. 2009). Package A sustained thermal and mechanical stresses during sterilization and the OTR change was not significant. ...
Article
Full-text available
Ready-to-eat macaroni and cheese filled in novel oxygen scavenger and metal oxide–coated high-barrier polymer packages were processed in pilot scale 915-MHz microwave-assisted thermal sterilization system (MATS). Also, aluminum foil packages were processed in Allpax retort system to compare packaging performance. Physicochemical and sensory attributes of macaroni and cheese packaged in different oxygen and water vapor transmission rates were evaluated and stored for 6 months at 37.8 °C. Findings showed oxygen transmission rate (OTR) increase by 2–7 times and water vapor transmission rate (WVTR) increase by 2.5–24 times after MATS processing. OTR of polymeric packaging had no significant effect on vitamin A and vitamin E, shear force, and food color. Comparable results between polymeric and aluminum foil packaging were observed throughout the shelf life. This indicates that oxygen scavenger and high-barrier packaging with OTRs ~ 0.03–0.34 cc/m² day and WVTRs ~ 0.62–7.19 g/m² day can be used for ready-to-eat meals with extended shelf life for soldiers and astronauts.
... The changes occurring in the crystal structure and crystal size of the polymers when undergone processing can be visualized in X-ray diffraction (Al-Ghamdi, Rasco, Tang, Barbosa-Cánovas, & Sablani, 2019). Positron annihilation lifetime spectroscopy (PALS) is an informative technique that can be used for characterization of valance defects in crystals and voids volumes in polymers (Tang, Selim, Dhawan, Varney, & Barbosa-c, 2014). ...
... MATS requires the food to be processed inside the packaging and multilayer polymeric films appear to be a viable candidate for this advanced sterilization process. An improvement in morphology in terms of overall crystallinity after MATS would increase the order of polymeric chains and reduce the voids that enhance gas barrier properties (Tang et al., 2014). PET-based polymeric packaging films have been found suitable for microwave-assisted pasteurization of ready-to-eat (RTE) foods (Bhunia et al., 2016). ...
Article
In recent years, with advantages of versatility, functionality, and convenience, multilayer food packaging has gained significant interest. As a single entity, multilayer packaging combines the benefits of each monolayer in terms of enhanced barrier properties, mechanical integrity, and functional properties. Of late, apart from conventional approaches such as coextrusion and lamination, concepts of nanotechnology have been used in the preparation of composite multilayer films with improved physical, chemical, and functional characteristics. Further, emerging techniques such as ultraviolet and cold plasma treatments have been used in manufacturing films with enhanced performance through surface modifications. This work provides an up‐to‐date review on advancements in the preparation of multilayer films for food packaging applications. This includes critical considerations in design, risk of interaction between the package and the food, mathematical modeling and simulation, potential for scale‐up, and costs involved. The impact of in‐package processing is also explained considering cases of nonthermal processing and advanced thermal processing. Importantly, challenges associated with degradability and recycling multilayer packages and associated implications on sustainability have been discussed.
... This observation is confirmed by an X-ray diffraction pattern test for the PET/EVOH/PP multilayer polymeric films before and after the pressure-assist thermal sterilization (PATS) process, shown in Fig. 10 (b) [82]. The result highlights a decrease in crystallinity and changes in the crystal morphology of MLPs after pasteurization treatment [81,84]. ...
Article
The global market of multilayer polymer (MLP) films accounted for $5.50 billion in 2017 and is expected to reach $9.58 billion by 2026. In this paper, a comprehensive review on morphology, interfacial characteristics, and rheological behavior, as three main effective interim parameters on the overall properties of MLPs, has been presented. It has been shown that the morphology of MLPs is strongly governed by layer thickness, type of polymers, annealing, and the conditions in secondary processes. By manipulating these parameters in MLPs, various morphologies such as random 3-D spherulites, on-edge crystals, and planar lamellas are observed, leading to changes in properties such as gas permeability. Moreover, different levels of interfacial adhesion in MLPs are obtained by altering the interfacial entanglement density, highlighting that the interfacial entanglement density is a defining factor for many properties such as peeling strength. Addition of blends or copolymers to improve compatibility, use of adhesives, introduction of micro- or nanoparticles to the interface, and annealing have been shown to be effective techniques to improve the interfacial entanglement density. Followingly, the review of the rheological behavior in MLPs revealed that slip at the interface of MLPs is dependent at interactions between constitutive polymers. Also, it has shown that MLPs can present hardening in extension that contributes to improved properties such as reduced dripping in fire. This review provides a summary of the current status of MLPs from a structure-process-property perspective while shedding light on existing knowledge gaps to be addressed by future research works.
... In our previous works, we have demonstrated that microwave can change the lamellar architecture of rice starch 12 , which suggested that it might play an important role in regulating the FV of starch. However, there are no available publications regarding the effects of microwave heating on the FV holes of starch although it can manipulate FV of other polymer materials 13 . In addition, it is noteworthy that water is a vital dipole molecule, which had a high response to the applied microwave electromagnetic field 14 . ...
Article
Full-text available
The aim of this work was to investigate the role of microwave parameters and moisture content on the free volume (FV) changes of rice starch by positron annihilation lifetime spectroscopy analysis (PALS) and to explore the potential relationship between the changes of FV and physicochemical properties of rice starch. Microwave heating and water molecules lead to the increasing of FV of starch. However, this result is largely influenced by the plasticization of water molecule. The anti-plasticization caused by water evaporation resulting in a decrease in the size and concentration of FV during microwave heating. Significant decrease (p < 0.05) in the thickness of amorphous region of microwave-heated rice starch was found by small angle X-ray scattering (SAXS), and the glass transition temperature (Tg) and gelatinization temperature significantly increase (p < 0.05) after microwave heating. According to correlation analysis, the power intensity and heating time were correlated negatively with the lifetime of o-Ps. In addition, the changes of amorphous region and Tg of rice starch were strongly related to FV changes. These results provided a theoretical basis for further research on the directional regulation of FV and improvement the quality of starch-based food by using microwave treatment.
... The shorter processing time associated with MATS is mainly responsible for the better food quality based on reduced shrinkage, less loss of texture, and greater retention in fresh-like appearance. The gas barrier and morphological properties and free volume of the polymer films used in food packaging application can influence the shelf life of shelf-stable foods (Dhawan et al., 2014a). However, the gas barrier properties in polymer packages may deteriorate under high-temperature and high-moisture processes. ...
Article
Full-text available
Fossil-based plastic materials are an integral part of modern life. In food packaging, plastics have a highly important function in preserving food quality and safety, ensuring adequate shelf life, and thereby contributing to limiting food waste. Meanwhile, the global stream of plastics into the oceans is increasing exponentially, triggering worldwide concerns for the environment. There is an urgent need to reduce the environmental impacts of packaging waste, a matter raising increasing consumer awareness. Shifting part of the focus toward packaging materials from renewable resources is one promising strategy. This review provides an overview of the status and future of biobased and biodegradable films used for food packaging applications, highlighting the effects on food shelf life and quality. Potentials, limitations, and promising modifications of selected synthetic biopolymers; polylactic acid, polybutylene succinate, and polyhydroxyalkanoate; and natural biopolymers such as cellulose, starch, chitosan, alginate, gelatine, whey, and soy protein are discussed. Further, this review provides insight into the connection between biobased packaging materials and innovative technologies such as high pressure, cold plasma, microwave, ultrasound, and ultraviolet light. The potential for utilizing such technologies to improve biomaterial barrier and mechanical properties as well as to aid in improving overall shelf life for the packaging system by in-pack processing is elaborated on.
... The DSC analysis was performed under a nitrogen atmosphere at a flow rate of 50 mL/min. The first heating scan was performed at a heating rate of 10 • C/min from 30 to 280 • C, then cooled to 30 • C at a cooling rate of 10 • C/min, followed by a second heating scan at a heating rate of 10 • C/min from 30 to 280 • C. DSC thermograms were analyzed to determine the melting temperatures (T m ) and heat of fusion (ΔH) of each layer in the multilayer structure (Dhawan et al., 2014;Júnior et al., 2020c). ...
Article
Different laminated pouches (PET12/Alu7/Ny15/CPP90, PET12/Ny15/CPP90, Ny15/CPP90, and Ny15/LLDPE60) filled with food simulants (3% acetic acid, 20%, and 50% ethanol) at different head spaces (10% and 20%) were subjected to varying process conditions in a 30-liter pilot scale high-pressure processing (HPP) system. Results from appearance, mechanical, and barrier properties revealed that metal-based pouch was more resistant to high-pressure treatment than others. Defects with white opaque areas and lines were observed in approximately 60% of the total transparent pouches, and were more pronounced in samples from improper placement in HPP basket. Ny15/LLDPE60 was the most susceptible to pressure force, which resulted in delamination and improved seal strength and barrier properties. The overall migration values of packaging were slightly increased by HPP and storage time, but, less than 10 mg/dm² considered safe by the Commission Regulation (EU) No 10/2011. The study discovered that the primary factor lowering the properties of laminated films was food simulant rather than high-pressure treatment.
... Chemical vapor deposition, such plasma-enhanced and atomic layer deposition processes [92] are recently developed coating processes expected to have an increasing application in the production of packaging materials for food and in particular for those with long shelf-life. For non-rigid materials, the gas barrier properties, which are required for the chemical stability of long shelf-life products, typically decrease after thermal treatment [93] and this is a key aspect to be taken into consideration when designing the packaging system. ...
Article
Thermal processing is still the most important method to ensure food safety, however, there is a need for further improvements, from basic data to advanced optimization methods. Due to the competitive market, customer demands and environmental concerns, several challenges have been raised. In this review, some important topics are discussed, including inactivation kinetics, engineering properties, process design and control, packaging systems and regulatory, environmental, and economic aspects. This position paper describes our opinion about the main challenges associated with thermal processing (conventional and alternative technologies, as microwave and ohmic heating), as well as some possibilities to deal with them.
Article
Polypropylene composites containing modified kaolinite were prepared using melt processing and the morphological, thermal, mechanical and their water barrier properties were analyzed. To improve compatibility with polypropylene, kaolinite was modified with silane as a coupling agent. Characterization techniques (X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy) confirmed the effective grafting of these compounds on the surface and edges of the kaolinite with no functionalization on the inner surface. The differential scanning calorimetry and X-ray diffraction techniques demonstrated that the addition of grafted kaolinite affected the iPP crystallinity. The thermogravimetric analysis helped to determine the thermal stability of the composites, being this, dependent on the amount of kaolinite and silane. The stress–strain tests demonstrated an increase in Young's modulus and obtained a 70% reduction in water vapor permeation. These improvements were mainly related to the increased compatibility between the iPP/Kaol interfaces promoted by the silane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 135, 45785.
Chapter
Microwave energy has inherent advantages for heat treatment of foods due to the ability to penetrate food and microwave permeable materials to volumetrically heat the contents rather than rely solely on thermal conduction. It can be applied to both flow-through heat exchange systems for pumpable foods and to prepackaged foods. However, successful commercialization of continuous microwave-assisted pasteurization and sterilization of meals and meal components has only been slowly progressing since the 1970s. The first successful development was the Multitherm hot air and microwave energy based system out of Alpha-Laval. It was subsequently abandoned commercially, but other technology manufacturers in Europe included, e.g., Officine Meccaniche Attrezzature per Ceramiche (OMAC). They sold over 200 machines in the period circa. 1980–2000, which were based on a 2.45 GHz continuous microwave sterilization process. Products such as pasta meals became common in Italy in the 1990s and in other parts of the world excluding the United States. Also in Europe, an industrial continuous in-pack meal pasteurization system by MicVac uses 2.45 GHz microwaves. This system utilizes a one-way steam valve on the food package, which releases excess energy as steam allowing rapid heating and vacuum sealing when the product cools below boiling point. Other current reported systems include a 2.45 GHz continuous pressurized microwave sterilization system manufactured by Gustosi, and 915 MHz pressured pasteurization and sterilization systems developed out of Washington State University for US Defense and commercial consortia backers. These systems are finding growing markets enabled by many factors. The development of improved heat- and oxygen-resistant packaging allows better quality preservation. The rise of meals not prepared at home and the developments of centralized institutional catering systems has greatly expanded the range of applications. Improvements in technology, such as computer controlled processing, allow dynamic control of microwave energy to minimize any overprocessing during sterilization with consequential loss of organoleptic qualities.
Article
Full-text available
Food safety is becoming an increasing concern in the United States. This study investigated the effects of ultraviolet-C (UV-C) light as a postpackaging bactericidal treatment on the quality of English cucumber packaged in polyethylene (PE) film. Escherichia coli k-12 was used as a surrogate microbe. The microbial growth and physical properties of packaged cucumbers were analyzed during a 28-d storage period at 5 °C. Inoculating packaged cucumbers treated at 23 °C for 6 min with UV-C (560 mJ/cm(2) ) resulted in a 1.60 log CFU/g reduction. However, this treatment had no significant effect (P > 0.05) on the water vapor transmission rate or oxygen transmission rate of the PE film. Results show that UV-C light treatment delayed the loss of firmness and yellowing of English cucumber up to 28 d at 5 °C. In addition, UV-C light treatment extended the shelf life of treated cucumber 1 wk longer compared to untreated cucumbers. Electron microscopy images indicate that UV-C light treatment influences the morphology of the E. coli k-12 cells. Findings demonstrate that treating cucumbers with UV-C light following packaging in PE film can reduce bacterial populations significantly and delay quality loss. This technology may also be effective for other similarly packaged fresh fruits and vegetables.
Article
Full-text available
It is a priority to develop polymeric packaging that can withstand microwave-assisted thermal sterilization (MATS) and maintain the quality of low-acid foods during long-term storage. In this study, we explored changes in the morphology of pouch films with two multi-layer structures. The films are based on barrier layers of metal oxide-coated poly(ethylene terephthalate) (PET) (film A) and ethylene vinyl alcohol (EVOH) (film B). A 8-oz model food in pouches was processed with MATS (F0 = 9.0 min) and stored at 23, 35 and 45 °C for up to 12 months. Findings reveal that the oxygen barrier of film A was influenced by the coating and crystallinity of PET. The oxygen barrier of film B was primarily affected by the moisture content of the EVOH polymer. Results also show that changes in barrier properties depended on storage temperature. Recrystallization in polymer might be an important morphological change that occurs during storages. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45481.
Article
We introduce a new computational methodology for the identification and characterization of free volume within/around atomistic configurations. This scheme employs a three-stage workflow, by which spheres are iteratively grown inside of voxels, and ultimately converted to planar graphs, which are then characterized via a graph-based order parameter. Our approach is computationally efficient, physically intuitive, and universally transferable to any material system. Validation of our methodology is performed on several sets of materials problems: (1) classification of unique free volumes in various crystal phases, (2) autonomous detection and classification of complex surface defects during epitaxial growth simulations, (3) characterization of free volume defects in metals/alloys, and (4) quantification of the spatio-temporal behavior of nano-scale free volume morphologies as a function of both temperature and free-volume size. Our method accurately identifies and characterizes unique free volumes over a multitude of systems and length scales, indicating its potential for future use in understanding the relationship between free volume morphology and material properties under both static and dynamic conditions.
Article
Full-text available
In this study, we investigated the effects of package barrier properties on shelf-life of vitamin C-fortified sweet potato puree (SPP) processed with microwave-assisted thermal sterilization (MATS). Results show a change in SPP color during both processing and storage. The vitamin C in SPP decreased from 201.7 ± 4.7 to 185.8 ± 15.6 mg/100g during MATS and further decreased to as low as 13.6 ± 4.1 and 10.0 ± 0.3 mg/100g the end of 9 or 18 month, depending on the oxygen barrier and temperature. The total β-carotene content after processing and storage was slightly higher than before processing. Pouches with oxygen transmission rates (OTRs) of less than 0.3 cc/m2⋅day showed higher retention of color, vitamin C, and predicted shelf life than other pouches. However, this did not affect the consumer acceptance. Most panelists considered MATS processed SPP as a desirable baby food throughout the 18 months. Efforts are still needed to stabilize vitamin C content for over 3 years for military and NASA missions.
Article
Encapsulation may solve thermal and storage stability issues for vitamins in foods. Here, the role of encapsulation in improving thermal and oxidative stability of vitamin C (encapsulated (EVC) and non-encapsulated (NVC), lipid-soluble vitamins (A & E together, esterified forms) was determined in mashed potato. The product was vacuum packed in four different oxygen barrier films, pasteurized using a microwave-assisted system or conventionally, and then stored at 5 °C for 90 days. We observed 4–5 % losses of NVC, while no losses occurred in EVC, vitamin A & E after thermal processing. At the end of storage, NVC and EVC losses in mashed potato varied between 12–76 % and 13–31 %, respectively depending upon film type, while vitamin A & E remained stable. TPC and pH of mashed potato were stable over the storage period in all selected films, but the color changed significantly in the lowest barrier film. Processing affected the gas barrier, dielectric, and thermal properties of films to a variable extent. This study demonstrated the effectiveness of encapsulation in improving the stability of vitamin C and can help processors in selecting optimal packaging film.
Article
This accelerated shelf life study of a ready-to-eat meal processed with a microwave-assisted thermal sterilization (MATS) system aimed to evaluate the performance of double metal oxide coated polyethylene terephthalate (PET) layers-based ultra-high barrier packaging along with ethylene vinyl alcohol (EVOH)-based pouches, and aluminum (AL) foil-based pouches (served as control). First, we evaluated barrier changes in the two types of pouches (double-layered PET and EVOH) caused by MATS processing. Next, we determined the influence of barrier properties on the physical, chemical and sensory quality of MATS-processed chicken pasta meals at accelerated storage conditions at 49 °C. Sensory evaluation was also done at lower storage temperature of 38 °C. Results demonstrated that MATS processing did not affect the barrier properties of double metal oxide coated PET pouches, however, it significantly influenced the barrier properties of EVOH-based pouches. After storage at 49 °C for 60 days, there was a small total color change (ΔE = 3.5) in chicken pasta meals in the double coated film pouches. This result was similar to that obtained for aluminum foil pouches (p > 0.05), but significantly lower than that for the EVOH pouches (ΔE = 5.5). The double metal oxide coated PET packaging provided an excellent barrier against lipid oxidation similar to that of aluminum (AL) foil-based pouches. A trained sensory panel scored the recipe between 6.0 and 6.45 immediately after MATS processing on a labelled effective magnitude (LAM) scale from 1 to 9 (worst to best quality). Results indicate that the newly developed double-layered PET pouches offer an excellent alternative to higher density metal foil-based packaging.
Article
The goal of this research was to design a thinner wall tray for microwave-assisted thermal processing technologies. Three-layer (PP//EVOH//PP) sheets of different EVOH- and PP-layer thicknesses were coextruded. The sheets were then thermoformed into 8-oz trays with dimensions of 150 × 100 × 50 mm (L × W×D). Trays were filled with model foods and subjected to conventional and microwave-assisted pasteurization and sterilization processes. Barrier and mechanical properties were assessed before and after processing. Oxygen ingress, weight loss, and color kinetics were measured over a storage period of 3–6 months at 7, 23, and 37 °C. The newly-designed trays showed comparable or better performance in terms of O2 ingress and weight loss, with a 24 % reduction in wall thickness. Therefore, thinner EVOH and PP-based trays hold promise for use in microwave-assisted sterilization and pasteurization processes. This will result in a reduced carbon footprint and provide more economical alternatives to other forms of packaging that are currently available.
Article
Positron is the only probe that can detect individual atomic vacancies and small and large vacancy clusters induced by irradiation with remarkable sensitivity, providing information about their size, concentration, and chemical environment. The focus of this review article is to provide guidance to facilitate applications of positron annihilation spectroscopy (PAS) in irradiation-induced defect studies to advance the development of new radiation-tolerant materials. The principle of PAS, its techniques, and data analysis methods are described. PAS studies of defects in nuclear and irradiated materials are reviewed and discussed in depth. Future developments to advance PAS applications in nuclear materials research and studies of materials under extreme environments are presented.
Chapter
In this chapter, we discuss sterilizations based on microwave-assisted methods. The application of microwave-assisted sterilization method in several areas such as in the medical field, food industry, and material processing field is included. Microwave-assisted plasma sterilization methods and combined microwave systems are also included in this chapter.
Chapter
The selection of appropriate packaging is important for in-package thermal processing technologies. The package should be able to withstand thermal processes while maintaining its visual integrity and barrier properties after processing and during storage. Oxygen and water vapor barrier properties of packages are critical for retaining food quality during the storage. In-package thermal processing, to a certain degree, deteriorates the package barrier properties, which may accelerate food quality losses during storage. A better understanding of oxygen sensitivity of food components such as pigments, vitamins, and lipids during storage is important for the design and selection of appropriate barrier packaging for the desired shelf life of pasteurized products. Flexible packaging with a low and medium gas barrier is adequate for pasteurized products with a shelf life of 10 days to 12 weeks.
Article
The aim of this study was to examine the influence of pressure-assisted thermal sterilization (PATS) on properties of polymer packaging and packaged avocado puree. High pressure of 600 MPa and initial vessel temperature of 90 °C were used over 5 min processing time. We used two high barrier film pouches: Film A-PE/PA6//EVOH//PA6/PE and film B-AlOx-coated PET//AlOx-coated PET//PA//CPP. Oxygen transmission rates (OTR) changed from 0.16 ± 0.07 to 3.24 ± 0.52 cm³/m².day for film A after processing while OTRs were not detected for film B. Water vapor transmission rates changed from 3.72 ± 0.06 to 4.97 ± 0.14 g/m².day for film A and 0.11 ± 0.02 to 0.62 ± 0.0.6 g/m².day for film B. The dissolved oxygen in packaged avocado puree reduced from 21% to 3% after PATS for both films. Reduced oxygen level in packaged avocado may help extend its shelf life. Dielectric properties and X-ray diffraction helped explain PATS induced changes in film barrier properties. The total chlorophyll, greenness, and lightness decreased significantly (p < 0.05) after PATS. The thiobarbituric acid activity reduced after PATS. PATS showed potential to produced shelf-stable avocado puree; however, shelf-life studies are needed to further develop PATS process.
Article
Full-text available
Sustainability and recyclability are among the main driving forces in the plastics industry, since the pressure on crude oil resources and the environment is increasing. The aim of this research is to develop a sustainable thermoformable multilayer food packaging, based on co-polyesters, which is suitable for hot-fill applications and allows for recycling in a conventional waste stream. As a polymer material for the outer layer, we selected a modified polyethylene terephthalate (PETM), which is an amorphous co-polyester with a high glass transition temperature (±105 °C) and thus high thermal stability and transparency. The inner layer consists of 1,4-cyclohexylene dimethanol-modified polyethylene terephthalate (PETg), which is allowed to be recycled in a PET stream. Multilayers with a total thickness of 1 mm and a layer thickness distribution of 10/80/10 have been produced. To test the recyclability, sheets which contained 20% and 50% regrind of the initial multilayer in their middle PETg layer have been produced as well. The sheet produced from virgin pellets and the one containing 20% regrind in the middle layer showed no visible haze. This was not the case for the one containing 50% regrind in the middle layer, which was confirmed by haze measurements. The hot-fill test results showed no shrinkage or warpage for the multilayer trays for all temperatures applied, namely 95, 85, 75 and 65 °C. This is a remarkable improvement compared to pure PETg trays, which show a visible deformation after exposure to hot-fill conditions of 95 °C and 85 °C.
Article
Full-text available
Microwave is an effective means to deliver energy to food through polymeric package materials, offering potential for developing short-time in-package sterilization and pasteurization processes. The complex physics related to microwave propagation and microwave heating require special attention to the design of process systems and development of thermal processes in compliance with regulatory requirements for food safety. This article describes the basic microwave properties relevant to heating uniformity and system design, and provides a historical overview on the development of microwave-assisted thermal sterilization (MATS) and pasteurization systems in research laboratories and used in food plants. It presents recent activities on the development of 915 MHz single-mode MATS technology, the procedures leading to regulatory acceptance, and sensory results of the processed products. The article discusses needs for further efforts to bridge remaining knowledge gaps and facilitate transfer of academic research to industrial implementation. © 2015 Institute of Food Technologists®
Article
Full-text available
Positron annihilation lifetime spectroscopy (PALS) was employed to study the free volume properties of polystyrene (PS) containing three different types of carbon nanoparticles: polystyrene-grafted single wall carbon nanotubes (SWCNTs-g-PS), single wall carbon nanotubes (SWCNTs), and carbon nanofibers (CNFs). The glass transition temperature measured via PALS was significantly lower than that from differential scanning calorimetry (DSC), although qualitatively the two methods agreed in that the Tg measured increased as nanotubes were added to the material. There were some specific differences between the two measurements which may have been related to the fact that DSC does not measure Tg of a portion of the material which is immobilized on the surface of the particle, while PALS measures all polymer, whether immobilized or not. PALS was also used to measure the thermal expansion coefficient and distributions of the free volume of the polystyrene.
Article
Full-text available
A pilot-scale 915 MHz Microwave-Circulation Water Combination (MCWC) sterilization system was used to treat macaroni and cheese entrees prepared according to recipes selected to minimize treatment effects on sensory quality. Modifications to the traditional commercial boxed macaroni and cheese recipe included the selection of a noodle better suited for applications requiring prolonged heat treatments and the addition of twice the amount of cheese sauce to optimize heating uniformity. The MCWC system provided desired sterility (with a F0 value of 7 min) within one fourth of the time required by conventional retort methods to produce shelf-stable products. Descriptive analysis was used to identify the quality attributes most significantly affected by MCWC processing. Formulation changes, such as noodle type and amount of cheese sauce present, affected the overall quality of MCWC treated macaroni and cheese entrees. Durum semolina noodles were superior to box-type noodles (a blend of durum and common wheat) in applications involving heat treatment. A consumer panel rated microwave treated macaroni and cheese as being acceptable when compared to freshly cooked controls.
Article
Pressure-assisted thermal sterilization (PATS) alters the morphology and free volume distributions of polymers leading to a decrease in gas-barrier properties of polymer packaging materials, and hence compromising the quality and shelf life of PATS processed foods. Two multilayer ethylene–vinyl alcohol (EVOH) films, intended for high pressure applications, were investigated to understand the influence of free volume characteristics and film morphology on gas-barrier properties of PATS processed EVOH films. X-ray diffraction (XRD) and positron annihilation lifetime spectroscopy (PALS) were applied to investigate film morphology and free volume characteristics, respectively. Film A was comprised of polyethylene terephthalate (PET)/EVOH/polypropylene (PP). Film B consisted of PET laminated to a co-extruded structure of PP/tie/Nylon6/EVOH/Nylon6/tie/PP. Both oxygen and water vapor transmission rates increased in the two films after the selected treatments. However, the increase in film A is much larger which can be understood from the change in free volume distributions measured by positron lifetime and overall crystallinity observed from X-ray diffraction. This work shows that PALS and XRD are suitable tools to reason out the gas-barrier changes in multilayer EVOH films after PATS treatment.
Article
This paper brings to perspective issues related to research initiatives for the application of microwave (MW) and radiofrequency (RF) applications in foods. Both MW (300 MHz and 300 GHz) and RF waves (3 kHz — 300 MHz) are part of the electromagnetic spectrum that result in heating of dielectric materials by induced molecular vibration as a result of dipole rotation or ionic polarization. They have been credited with volumetric heat generation resulting in rapid heating of foodstuffs. Due to their lower frequency levels, RF waves have a larger penetration depth than MW and hence could find better application in larger size foods. Besides the popular domestic use of MW ovens, commercialized applications of MW/RF heating include blanching, tempering, pasteurization, sterilization, drying, rapid extraction, enhanced reaction kinetics, selective heating, disinfestations, etc. This paper reviews the current status and research needs for in-packaged sterilization technologies for commercial applications. Technological challenges include process equipment design, microbial destruction and enzyme inactivation kinetics, temperature and process monitoring, and achieving of temperature uniformity. Other issues also relate to the use of packaging material in in-package sterilization applications, package/container concerns in domestic MW ovens, receptor technology for creating dry-oven conditions, modeling and time-temperature process integrators. There is also the issue of non-thermal and enhanced thermal effects of microwave heating on destruction kinetics.
Article
Interfaces in binary polymer blends play a pivotal role in moulding their physical properties. We observe a diffused interface in immiscible and partially miscible binary polymer blends for which the methods of preparation characterize the interface widths. The interface widths for three binary blends of PVC/PS, PS/PMMA, and PVC/SAN are in the maximum range of 2.15, 5.04 and 6.24 nm respectively. We establish a correlation between hydrodynamic interaction and the Flory–Huggins interaction parameter which is consistent with self-consistent mean field theory and the usual constructed density profile across the interface. Our approach is based on the hydrodynamic interaction which is derived from free volume data measured by positron lifetime spectroscopy.
Article
In this paper, I summarize the subject of positron annihilation in polymers. The subject is very broad and practically impossible to treat comprehensively in the allowed space. After an introduction to the special problems of positron interactions in polymers and a brief summary of the important developments occurring between 1950 and 1990, I concentrate on methods of free-volume determination at both qualitative and quantitative levels that have been developed in the past three years. Several notable applications of positron annihilation to polymeric materials - hole size, content, distribution, and anisotropic structure - are discussed in detail; and applications to the study of physical aging, interfacial problems, and mechanical problems are introduced. I conclude the review by presenting some unsolved problems in this area of research.
Article
An X-ray diffraction procedure for the crystallinity of polymer blends determination was verified by comparison with the DSC method. Crystallinity of polyamide 6/sulfonated polysulfone (PA-6/SPS) blends was investigated using X-ray and DSC methods. A good consistency of the results was observed. Both methods showed the same trends in the variations of crystallinity as a function of blend composition. © 1997 Elsevier Science Ltd
Article
Crystalline polymers are not in thermal equilibrium and thermodynamic parameters such as enthalpy of fusion as determined by differential scanning calorimetry from the area under the melting endotherm over a wide temperature range have not been measured under equilibrium conditions. Accordingly measurements of the degree of crystallinity based on the enthalpy of fusion reflect experimental conditions, are incorrect in that they do not usually agree with those determined by other analytical procedures, such as density and WAX scattering, particularly when measured at ambient temperatures. While this has been repeatedly pointed out procedures used to determine the fractional crystallinity of polymers based on the enthalpy of fusion continue to be widely used.Using the First Law method, the enthalpy of fusion and fractional crystallinity have been measured as a function of temperature for metallocene polyethylene and polyethylene terephthalate during heating. The crystallinity measured on the sample prior to heating is in good agreement with that determined by density and wide angle X-ray diffraction.
Article
This study investigated the influence of high-pressure processing on the morphology and permeability of low-density polyethylene (LDPE) films used for food packaging. This was done by monitoring the crystallinity, melting temperature (Tm), and oxygen transmission rate (OTR) of the materials before and after the pressure treatments. A first set of pouches made from the LDPE films were filled with 95% ethanol then pressured at 200, 400, 600, and 800 MPa for 5 and 10 min at 25 and 75°C. The crystallinity and Tm of the films were measured using differential scanning calorimetry (DSC). X-ray diffraction (XRD) was also used to determine the crystallinity. A second set of LDPE pouches were similarly made but a half of them were filled with 95% ethanol and the other half filled with distilled water. These second set of pouches were pressured at 200, 600, and 800 MPa then their OTR tested. Results of the DSC experiments showed that the Tm increased with increasing pressure intensity but the crystallinity changes were not detectible. The XRD method on the other hand, showed significant (P < 0.05) crystallinity increases with increasing pressure treatments. The gas permeability analyses showed decreasing OTR's with increasing high-pressure intensity treatments. The OTR in the pouches filled with the 95% ethanol was slightly lower than that of the pouches filled with water. These findings allowed us to better anticipate the behavior of LDPE films used to package high-pressure processed foods. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Article
The objective of this article was the determination of the degree of crystallinity of a series of heat-set poly(ethylene terephthalate) (PET) films and their study by thermomechanical analysis (TMA) in order to elucidate a peculiar behaviour that takes place around the glass transition region. For this purpose, amorphous cast Mylar films from DuPont were annealed at 115 °C for various periods of time. Four methods were used to study the crystallinity of the samples prepared: differential scanning calorimetry (DSC), density measurements (DM), wide-angle X-ray diffraction (WAXD), and Fourier transform infrared spectroscopy (FT-IR). From the results obtained, the following conclusions are drawn: amorphous PET Mylar films can be crystallized in a degree of about up to 30% after thermal treatment for 30 min (cold crystallization) above glass transition temperature. When these semicrystalline samples are subjected to TMA, they show a two step penetration of the probe into them, which decreases with the increase of the degree of crystallinity. The first step of penetration was attributed to the shrinkage of the amorphous or semicrystalline sample, which takes place on the glass transition temperature, while the second step was attributed to the continuous softening of the sample, and the reorganization of the matter which takes place on heating run due to cold crystallization.
Article
The structure and free volume properties of semi-crystalline poly(3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV) were investigated in this study. The structure change and conformational motion of PHBV during melting and crystallization process were discussed by in situ FTIR. The free volume within the amorphous phase and its temperature dependence in the PHBV membrane, which was prepared by the compression molding method with isothermal crystallization processes, were characterized by using positron annihilation lifetime (PAL) spectroscopy. From the lifetime parameters, the temperature dependence of free volume size, amount, distribution, and fractional free volume, and the thermal expansion of free volume and/or polymer were discussed. Furthermore, the knee temperature was first observed in the melting process of the crystallized PHBV membranes. It indicated that there was structural transition of polymer chains during melting as the corresponding results observed with in situ FTIR measurement.Graphical abstract
Article
Pressure-assisted thermal processing (PATP) is an advanced thermal process involving application of elevated pressures above 600 MPa on a preheated food for a holding time of 3 to 5 min, causing the volumetric temperature of food to increase above 100°C, to inactivate bacterial spores and enzymes. This study evaluated the influence of PATP on two state-of-the-art multilayer EVOH films. Flexible pouches containing water as the food simulant were made from the two films and processed at 680 MPa for 3 min at 105°C and 680 MPa for 5 min at 100°C. Each film was investigated for its oxygen transmission rates (OTRs), melting temperature (Tm), enthalpy of melting (ΔH), and overall crystallinity before (control) and after processing. The changes in OTRs and total ΔH of the two films were also analyzed during a storage period of 240 days in ambient conditions after processing. Results showed a significant (P < 0.05) increase in the OTRs of the two films after PATP. However, PATP did not cause a significant (P > 0.05) change in the Tm and ΔH of the two films. The overall crystallinity of film A decreased, but improved slightly for film B after PATP. A recovery in the OTRs of the two films occurred during storage. The films also showed changes in the total ΔH measured during the storage period, which was used to explain the changes in the oxygen barrier properties. The OTR of both films remained below 2 cc/m2 day, which is required in packaging applications for shelf-stable foods with a 1-year shelf life. This work demonstrates the advantages of using multilayer films containing EVOH as the barrier layer in PATP applications to produce shelf-stable foods. This work also highlights the advantage of, DSC analysis for studying the physical ageing of polymers during storage. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Article
High hydrostatic pressure has become an industrial reality, and although there are still many aspects under research, today it is possible to buy high-pressurized products in many countries. Indeed, pasteurization of food products using elevated pressure at room temperature has been accepted by regulatory agencies for commercial use. The quality displayed in such products includes better nutritional retention, fresh-like flavor, improved color, texture, and taste, and extended shelf life compared to thermally pasteurized products. There are several applications of high hydrostatic pressure (HHP) use today in processing fruits, vegetables, meats, seafood, dairy and egg products, including the intelligent combination of pressure, temperature, and time to generate specific characteristics in certain products. One of the biggest challenges in high-pressure application is in the sterilization of low-acid foods with combined elevated pressure (600–800 MPa), moderate temperatures (30–90 °C), and short processing times (less than 5 min). Combined pressure and temperature, also known as pressure-assisted thermal sterilization (PATS), was recently approved by the FDA in 2009 for commercial sterilization. This manuscript is an update of the state-of-the-art in high-pressure technology, showing the advances achieved in past years and its most recent applications today in food processing. Inactivation of different microorganisms and the potential use of mathematical models to describe and validate the process are also mentioned, including using PATP to achieve sterilization parameters. Facts pertaining to equipment and operation costs are included as well to show that as a new technology, high-pressure use would likely require high initial investment. However, given the productivity and capability of this technology to enhance food quality, it may well deserve this initial investment, as many food companies have indicated in their annual cost reports.
Article
The measurements of free-volume hole property by positron annihilation lifetime spectroscopy (PALS) have been carried out for polymer–clay nanocomposite materials that consist of styrene–butadiene rubber (SBR) and layered silicate clay of rectorite and conventional composite materials N326 (carbon black) /SBR. The PALS and differential scanning calorimeter (DSC) results show layered rectorite has a stronger effect on restraining polymer chain mobility which results in the decrease of fraction free volume and gas permeation than carbon black. The dispersion of nanoscale rectorite clay in SBR largely enhances gas barrier property in contrast to results obtained in N326/SBR system. Experimental results reveal that gas permeability in rectorite/SBR nanocomposite is mainly influenced by fractional free volume and tortuous diffusional path effects attributed to the clay plateletlike morphology.
Article
Classical industrial retort sterilization processes expose food packages to high temperature, moisture, and pressure conditions. Migration of water into hydrophilic polymers such as ethylene vinyl alcohol (EVOH) sharply reduces their oxygen barrier ability. This research studied the effect of short time microwave sterilization on oxygen transmission rates (OTR) of two multilayer films containing EVOH and compared with that of conventional retorting. Film A had a laminated structure of EVOH sandwiched between oriented polyethylene terephthalate (PET) and cast polypropylene (PP). Film B consisted of PET laminated to a 7-layer co-extruded structure of PP/tie/Nylon 6/EVOH/Nylon 6/tie/PP. The films were used as lidstocks for trays containing mashed potato and processed by microwave or retort sterilization to achieve lethality of F0 = 3 min or F0 = 6 min. For both films the classical retort treatments resulted in higher OTR than the microwave treatments. In all cases, the oxygen barrier property of film A was better than that of film B. Storage of the food packages for 2 months at room temperature helped with recovery of more than 50% of the oxygen barrier lost by the films. The oxygen barrier slowly deteriorated beyond 2 months in storage. Over the 12 months storage, the OTR for both films after F0 = 3 min microwave process remained below 2 cc/m2 day, a value comparable to commercially available polyvinylidene chloride (PVDC) laminated films currently used in the USA as lid film for shelf-stable products.
Article
A major challenge in developing advanced thermal processess based on electromagnetic heating is to determine the location of cold spots in foods. A rapid and reliable method was developed in this study with the aim to effectively locate the cold spot in model food sterilized in microwave systems. The developed method involved application of chemical marker M-2 yield to a model food, mashed potatoes, using computer vision system and an image processing software IMAQ Vision Builder to capture and analyze color patterns after thermal processes. A systematic study was conducted to establish relationships among M-2 yields, color values from captured images of cut food samples, and thermal lethality (F0). Several factors including consistency of imaging background and positions of lights over the diffuser box were considered to standardize the method. To facilitate the comparative study of heating characteristic for different combinations of power levels and F0, a mapping scale using unheated and saturated mashed potato samples was developed by fixing the lowest and upper most gray-scale values. Color values equivalent to gray-level values were positively correlated to F0 and M-2 yield. The specified cold spot location determined by computer vision method was validated in a 915 MHz single-mode microwave sterilization system. The results showed that the computer vision method can potentially be used as an effective tool in microwave sterilization process development for regulatory acceptance and industrial applications.
Article
A user friendly program (LT) for analysis of the lifetime spectra has been designed for personal computers. The program is compared with other existing programs such as POSITRONFIT, CONTIN and MELT. LT enables one to analyse both discrete and continuous spectra as well as mixed- partially linear and partially continuous spectra. The searched parameters are found by using a fully automatic procedure and/or by a nonlinear optimising procedure, starting from a set of chosen parameters. The program is tested for series of simulated data as well as some chosen experimental ones, especially for the two polymers PTFE and hard polyethylene. The analysis of these polymer spectra is carried out on the basis of the log-normal distribution model and a new model of the lifetime spectrum developed by Dauwe et al., recently adapted to LT.