Perishable foods are packaged during storage and distribution to prevent them from spoiling, so ensuring their safety and quality and improving their shelf life. Traditional packaging consists of polymeric materials, plastic containers, metal foil and metal cans which act by forming a barrier between the food and external influences such as air, bacteria and impact. But recently, a new form of packaging has emerged, which has a different mode of action.
Active packaging is impregnated with substances that will actively work to preserve food. These additives can be released from the packing to kill microorganisms, infuse preservatives or top up the aroma. Alternatively, they remain in the packaging and remove undesirable compounds such as oxygen, ethylene, free radicals and taints. Some food packaging is even prepared from edible material like starch or protein, permeated with these additives.
Natural compounds are perceived by the consumer as safe and healthy, so food extracts are being considered as active additives for packaging. However, they must still pass safety checks and, in Europe, these consist of migration tests with liquid simulants that imitate real food. Portions of the packaging are immersed in the simulant then the compounds that migrate into the liquid are detected and measured.
Several techniques are used regularly for the final preconcentration and extraction of the migrants from the liquid simulants, including SPME, SPE and headspace extraction. One technique that has not yet been applied is hollow fibre liquid-phase microextraction (HFLPME) in which a hollow fibre made from a porous membrane is filled with an exchange liquid and inserted into the sample. Compounds in the sample diffuse though the membrane into the exchange liquid, which is removed for analysis.
In the dynamic version of HFLPME, the exchange liquid is continuously cycled through the membrane, rather than just sitting there. Now, scientists in Spain have designed an automated dynamic HFLPME system which they have used to test food packaging migration. Jesus Salafranca and co-researchers from the University of Zaragoza used a multichannel syringe pump to supply exchange solvent continuously to six hollow fibre membranes in six solutions.
The spent liquid was collected in individual vials for analysis by GC/MS for compound identification and by GC-FID for compound measurement. Toluene was used as the exchange liquid because it did not migrate through the membrane into the aqueous sample, but it contributed to poor reproducibility during GC. However, the performance was adequate for this proof-of-concept study.
The team tested the system with standard compounds, achieving concentration factors of 83-338. Detection limits were in the ng/g range, relative standard deviations were below 13% and calibration graphs were linear over four orders of magnitude.
Active packaging materials were prepared in-house from high-barrier ethylene-vinyl alcohol copolymer films. Each film was impregnated with an essential oil extract prepared from ginger, oregano and cinnamon, chosen because of their natural antioxidant content. The food simulant was water, which is known to predict the behaviour of many foodstuffs. After immersion of sections of the packaging material for 10 d at 40 °C, the water was subjected to HFLPME in the automated system.
Oregano- and cinnamon-based packaging released eugenol into the liquid simulant at concentrations well above the legal limit of 0.02 mg/kg set by the EU. Benzaldehyde and camphor also migrated. They have no restrictions in this context but must comply with a different set of regulations covering the deterioration of organoleptic characteristics of food. So, from these materials, only the ginger-based packaging material is regarded as safe for consumers.
This preliminary research has shown that HFLPME can be applied to the migration analysis of food packaging materials and the automated system will magnify throughput while reducing operator participation.
Source |
