Biodegradable Materials for Dairy Product Packaging
Polylactic acid (PLA) is currently used for packaging (cups, bowls, foils, and food storage containers) in the food industry. Foamed polylactide is used as an insulator and is an alternative to foamed polystyrene (styrofoam). Polylactates have good mechanical properties, similar to polyethylene terephtalate (PET) and polypropylene (PP).
In 2011, Dannon began using PLA packaging for its Activia yogurt in Germany. The new yogurt pack is the result of a close cooperation between Dannon and NatureWorks. The switch to this material will reduce packaging carbon footprint and the use of fossil resources compared to the previous packaging, according to a life cycle assessment study (Detzel et al., 2013; Natureworks, 2011).
Scannell et al. (2000) evaluated the application of cellulose-based packaging paper (Perganorm, Germany), including nisin, as an insert interleaved between slices of cheddar cheese packaged under a modified atmosphere (polystyrene/ethyl vinyl alcohol/ polyethylene containers; 60% N2/40% CO2). They observed that the population of L. innocua and S. aureus dropped dramatically in the first week of storage at 4°C and, as a result, nisin-adsorbed bioactive inserts reduced levels of Listeria innocua by >2 log units and Staphylococcus aureus by ~ 1.5 log units. The shelf life of cheddar cheese was significantly extended with respect to control systems (absence of nisin).
Holm et al. (2006a) studied the application of polylactic acid (PLA) on the quality of Danbo cheese during light exposure and storage in the dark. Results showed that moisture loss from cheeses packaged in PLA was approximately 10 times higher than those observed for the samples packaged in polyethylene terephthalate/polyethylene, but dry surface spots were not observed before 56 days of storage in the PLA packages. During light exposure, lipid oxidation of cheeses packaged in PLA was rather limited for the first 56 days of storage, and lipid oxidation was almost negligible after 84 days when the cheeses were protected from light.
Holm et al. (2006b) performed a study in order to evaluate the impact of a polylactic acid (PLA) package relative to a polyester packaging material on quality of semi-hard Danbo cheese during light exposure and storage in the dark and when applying as oxygen scavengers, sachets containing iron-based compounds (Mitsubishi Chemicals, Japan). As more oxygen was present in the PLA packages than in the reference packages due to a higher oxygen transmission rate of PLA, a higher degree of lipid oxidation was noted in cheeses packaged in PLA. The degree of lipid oxidation was reduced when applying oxygen scavengers, but to a lesser extent than when the products were stored in the dark. The results indicate that dark storage and reduction of the water vapor transmission rate are recommended when using PLA for packaging of semi-hard cheeses in order to protect the products against both lipid oxidation and moisture loss. dos Santos Pires et al. (2008) developed antimicrobial films by the incorporation of nisin (NI), natamycin (NA), and a combination of both (NI+NA) into a cellulose-derivative polymer provided by Rhodia Co (France). The antimicrobial activity of the films was evaluated on sliced mozzarella cheese against molds and yeasts, Staphylococcus sp., and psychrotrophic bacteria. Over 9 days of storage, the films containing NA and NI + NA showed inhibition of yeast and mold growth on sliced mozzarella cheese. These films improved the shelf life of the cheese by 6 days compared with the control. Film containing NI was able to delay psychrotrophic bacteria growth in the cheese by 6 days, while the films (NI and NI + NA) showed only a limited effect against Staphylococcus sp. present in the sliced mozzarella.
Gammariello et al. (2011) evaluated the effects of a biobased coating containing silver-montmorillonite nanoparticles combined with modified-atmosphere packaging (MAP) on microbial and sensory quality decay of Fior di latte cheese. Different concentrations of silver nanoparticles (0.25-1.00 mg/mL) were dispersed in a sodium alginic acid solution (8% wt/vol) before coating the cheese. Each coated sample was packaged in a commercially available bag, obtained by laminating a nylon layer with a polyolefin layer. All bags were sealed under MAP conditions (30% CO2, 5% O2, and 65% N2). Fior di latte packaged in brine, coated with a simple coating without any active compound, showed a shelf life of 3 days. The nanocomposite system allowed a significant prolongation of shelf life to more than 5 days. The authors stated that the developed coating containing nanoparticles must be removed before eating Fior di latte and that extensive research is essential to assess the safety concerns related to silver migration to the food for compliance with the European Union regulation.
Conte et al. (2013) studied the development of nanocomposite coatings embedding copper nanoparticles as active packaging for fresh dairy products. The particles were incorporated in a biodegradable polymer matrix of polylactic acid (PLA). The polylactic acid films delayed proliferation of main spoilage microorganisms in Fior di latte samples stored at 4°C during 9 days with a consequent preservation of sensory attributes. Also in this case, studies must be performed to assure the safety of the nanocomposite proposed. In addition, it must be determined whether the inclusion of inorganic nanoparticles affects packaging biodegradability.
The influence of the packaging with biodegradable PLA and PLA coated with a barrier of pure silicon oxide and in combination with modified atmosphere (MAP) on the shelf life of soft cheese Kleo produced in Latvia, was studied by Dukalska et al. (2011). Modified atmosphere consisted of 30% carbon dioxide and 70% nitrogen. The samples were stored at 4.0°C up to 32 days. The best results were obtained for cheese packaged with PLA, coated with a barrier of pure silicon oxide and in combination with MAP, observing that, in this case, the cheese quality evaluated through the color was acceptable and molds were not observed after 32 days storage.
Balaguer et al. (2014) developed gliadin films crosslinked with cinnamaldehyde (5%) and with natamycin (0.5%) incorporated. Films were prepared by casting and used in the packaging of cheese slices (soft and semi-hard cheeses) showing fungistatic action that was proved to be exerted by cinnamaldehyde. The greatest effectiveness was observed for soft cheese, probably due to its higher water activity that favored the release of the active substances. No considerations were performed by the authors in relation to the biodegradability of the matrix developed after crosslinking.
Plain yogurt (3.5% fat) shelf life was studied by Frederiksen et al. (2003). This food was stored for 5 weeks in PLA or polystyrene (PS) cups under fluorescent light (3500 lux) or in darkness. Practically no development of lipid hydroperoxides and secondary oxidation products or loss of riboflavin and p-carotene were observed in yogurts stored in darkness. For yogurts exposed to light, PLA was at least as effective in preventing color changes and formation of lipid hydroperoxides as PS. Losses of riboflavin and p-carotene were less in yogurt packed in PLA than in PS. The amount of styrene in yogurt stored in PS cups increased during storage, whereas lactate was not found in yogurts stored in PLA.