Packaging materials for fermented milk : Effects of material crystallinity and polarity on food quality

• The ability of a packaging material to protect the food product and extend its shelf-life depends on several material properties. In this work the effects of material crystallinity and polarity on the quality of fermented milk were studied. The fermented milk is a high-quality Swedish product, similar to yoghurt. The quality of the food product was determined as a function of storage time by containing the liquid in pouches of different materials. The material crystallinity was varied by using very low-density polyethylene, high-density polyethylene and aluminium laminate as packaging materials. Aluminium was used on account of its '100%' gas-tightness. The polarity was varied by comparing an aliphatic polyketone with polyethylene of similar crystallinity. The carbon dioxide (CO2) and oxygen (O-2) contents in the headspace of the pouches were determined. The food quality was determined by measuring whey syneresis, viscosity and the content of desired Bifidobacteria, as well as of undesired yeast and mould. A trained taste panel determined the degree of acidity and of the sparkling taste. It was found that the content of CO2 increased and that of O-2 decreased in the pouches with increasing degree of crystallinity and increasing polarity. The sparkling taste of fermented milk was a clear function of the headspace CO2 content. The data presented here could thus be used to 'design' a package for a desired sparkling taste of the fermented milk by selecting a certain material crystallinity. Whey syneresis, viscosity and content of Bifidobacteria were found to be independent of pouch material. While the degree of whey syneresis and the viscosity increased with increasing storage time, the content of Bifidobacteria slowly decreased. The content of yeast and mould in the liquid was below the existing limit values for foodstuffs. The degrees of acidity and sparkling taste were highest for the liquids contained in aluminium and polyketone pouches, although the differences in acidulous taste between the various pouch materials were small.

Nyckelord

food quality

fermented milk

headspace

crystallinity

polarity

polyketone

barrier selection

carbon-monoxide copolymers

shelf-life

ethylene

polymers

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art (ämneskategori)