Thermoresponsive films are favorable for the packaging of fresh fruits and vegetable products as their gas permeabilities increase to a greater extent than commercial films when temperature abuse occurs during refrigerated storage. Thermoresponsive polyurethane (PU) films were synthesized from polyethylene glycol (PEG) with three different molecular weights (400, 1000, and 1500 g mol⁻¹), castor oil (CO) with two different proportions (30 and 50 %, CO/PEG ratio) and a constant level of 1,4-butanediol (BDO). The effects of these compositional factors on the thermal, mechanical, physical, structural, and gas barrier properties of the films were investigated. Melting temperatures (T_m) of the PU films varied from 25 to 29 °C and decreased with CO content. Glass transition temperatures (T_g) of the films were all below −32 °C and decreased by increased CO content. PU films with 1500 g mol⁻¹ PEG and 30 % CO/PEG ratio had better shape memory (R_r) and shape fixity (R_f) properties than others. O₂ permeabilities of the PU films were in the range of 1.99–7.25 barrer while their CO₂ permeabilities were between 10.3 and 18.3 barrer. The temperature sensitivity of the gas permeabilities of the PU films was higher than that of a commercial LDPE film, which makes them more appropriate for fresh produce packaging. Nevertheless, PU films were mechanically weaker and they had higher water vapor permeability compared to the LDPE film. These properties of the PU films need further improvements for potential packaging applications.

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A thermoplastic polyurethane (PU) polymer was synthesized, casted into films, and specific and overall migration (OM) tests were applied. A new method with gas chromatography–flame ionization detector was proposed to measure specific migration (SM) of 1,4-butanediol from the PU film. OM values in the four established simulants were under the legal limits. Determination of 1,4-butanediol migrating from PU film to the three established simulants showed maximum SM result as 1.5 mg/kg which was far below the legal limits. Therefore, the PU film has a good potential as a safe food contact material. Moreover, the analytical method used for determination of SM of 1,4-butanediol resulted in good analytical characteristics and detection limits at ppm level.

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The conjugation reaction of electrospun fibers of a mixture of whey protein isolate (WPI) and dextran using different molecular weights (40, 70, and 100 kDa) and mixing ratios was studied. This study includes the electrospinnability of a mixture of WPI and dextran, and the conjugation reaction between them via the initial stage of the Maillard reaction. The WPI-dextran fibers were characterized using optical and transmission electron microscopy. The covalent attachment of dextran to WPI was confirmed using sodium-dodecyl-sulfate-polyacrylamide gel-electrophoresis with protein and glycoprotein staining. Both 70 and 100 kDa of dextran and WPI at mixing ratios of 2:1 and 3:1 in phosphate buffer (30 mM, pH 6.5) were electrospun using needleless electrospinning. The solution concentration of the mixture was 50 wt% (33.3/37.5 wt% for dextran/16.5/12.5 wt% for WPI). The optimal conjugation conditions chosen from the experiments were a mixture of dextran (70 kDa)-WPI at 3:1 (75% relative humidity, 60 °C, 48 h).

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Thermoplastic shape memory polyurethane (SMPU) polymers were synthesized, cast to films, and their gas barrier properties were characterized. In addition, performance of an optical method was assessed by measuring oxygen permeability (PO2) of the films. PO2 of the SMPU film was at least two times higher than that of low density polyethylene (LDPE and increased at higher relative humidity. Permselectivity (PCO2/PO2) of the SMPU film was 15, which is approximately three times higher than for LDPE. The film absorbed circa 18% water vapor at 98% relative humidity. The optical method agreed very well (maximum 20% deviation) with a standard carrier gas method in PO2 measurement. Overall our results show that SMPU is an attractive polymer for fresh produce packaging.@en

There is an increasing concern on the environmental issues related to petroleum-based plastics as packaging materials. Therefore, the interest for biodegradable packaging materials from renewable sources (biopolymers) has been increased steadily, particularly for the utilization in short-term packaging and throwaway applications. However, biopolymers have usually low barrier and mechanical characteristics with poor processability resulting in limitations for their scalable production and industrial use. To overcome these limitations, bio-nanocomposites with enhanced packaging characteristics such as mechanical strength, barrier properties against gases and water, and optical clarity have been developed. Moreover, bioactive ingredients can be added to give the targeted functional properties to the subsequent packaging materials. This chapter reviews distinctive sorts of new biobased nanocomposite materials, for example, biodegradable and edible nanocomposite films, and their commercial applications as packaging materials, and relevant regulations.

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The demand for minimally processed fresh fruits and vegetable products by consumers has been increasing around the world. Minimally processed fruits and vegetables are convenient fresh products with high nutritional quality. They are prone to microbiological and biochemical degradations, and thus, technologies to prevent these degradations without adversely affecting the fresh quality are desired. Conventional thermal preservation treatments are not suitable for these products. Several emerging nonthermal technologies have great potential alone or in combination for preserving minimally processed fresh produce products. This chapter provides a brief overview of the nonthermal technologies such as ozone, electrolyzed water, gamma irradiation, ultraviolet light (UVC), pulsed light, ultrasound, cold plasma, dense-phase CO2 processing, high-pressure processing, pulsed electric field, and edible coatings. Their applications alone or in combination on minimally processed fresh produce products including fresh cuts and freshly squeezed juices are discussed.@en

The aim of this work was to investigate the effect of film formulations in an effort to obtain a fresh produce packaging film with increased temperature sensitivity for gas permeability. Series of shape-memory polyurethane (SMPU) were synthesized using poly(ethylene glycol) (PEG), 1,6-hexamethylene diisocyanate, 1,4-butanediol and castor oil (CO) and casted into films. The changes in thermal, viscoelastic, shape-memory properties and oxygen permeability of the films were studied. The polyurethane films with 1500 g mol−1 PEG showed a phase transition temperature (switching temperature) between 20 and 27°C. The SMPU consisting of 50/50 CO/PEG had a log E′ value of 8.32 Pa and showed good elasticity as low density polyethylene. SMPU prepared from 1500 g mol−1 PEG with 50/50 CO/PEG and 40/60 butanediol/(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 with commercial packaging films like low density polyethylene. This film can be used to develop smart packaging with increased thermally responsive gas permeability to similar levels observed in respiration rates of fresh produce.@en