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 eff ects of material crystallinity and polarity on the quality of fermented mil k were studied. The fermented milk is a high-quality Swedish product, simil ar 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 polyethyl ene, high-density polyethylene and aluminium laminate as packaging material s. Aluminium was used on account of its '100%' gas-tightness. The polarity was varied by comparing an aliphatic polyketone with polyethylene of simila r crystallinity. The carbon dioxide (CO2) and oxygen (O-2) contents in the headspace of the pouches were determined. The food quality was determined b y measuring whey syneresis, viscosity and the content of desired Bifidobact eria, as well as of undesired yeast and mould. A trained taste panel determ ined the degree of acidity and of the sparkling taste. It was found that th e content of CO2 increased and that of O-2 decreased in the pouches with in creasing degree of crystallinity and increasing polarity. The sparkling tas te 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 crys tallinity. Whey syneresis, viscosity and content of Bifidobacteria were fou nd to be independent of pouch material. While the degree of whey syneresis and the viscosity increased with increasing storage time, the content of Bi fidobacteria 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 an d polyketone pouches, although the differences in acidulous taste between t he various pouch materials were small. Copyright (C) 2001 John Wiley & Sons , Ltd.