Packaging materials for fermented milk Part 2 : Solute-induced changes and effects of material polarity and thickness on food quality

• This work is a continuation of the application of a developed methodology for the selection of packaging material for a specific food product, in this case the 'demanding' food product. fermented milk. The effects of different packaging material parameters on the quality of fermented milk were studied. Food quality after storage was determined as a function of material polarity and pouch thickness by storing the liquid in pouches of different materials. The material polarity was varied by using laminates with polyethylene, poly(ethylene-co-vinyl alcohol) with two different ethylene contents and an aliphatic polyketone. The effects of pouch thickness were studied using high-density polyethylene films of different thicknesses between 25 mum and 200 mum. The interactions between the milk product and the pouch material were analysed by oxygen and water permeability, gas chromatography-mass spectrometry and tensile testing. The CO2 and O-2 contents in the headspace of the pouches were determined. The food quality was determined by measuring whey syneresis and the contents of Bifidobacteria, Enterobacteriaceae, yeast and mould. A trained taste panel determined the sensory properties. The content of CO2, and consequently the sparkling taste, increased with increasing polarity and/or pouch thickness. The CO2 content was affected more easily by changes in material polarity than by changes in pouch thickness. The increase in whey syneresis and the decrease in Bifidobacteria content with time were independent Of material polarity and pouch thickness. The contents Of Enterobacteriaceae, yeast and mould in the liquid were always below existing limits for foodstuffs. A newly developed method was used by which the CO2 and 02 permeabilities of the pouch/packaging could be estimated, using the kinetics of the gas composition in the pouch headspace. Permeability values, as estimated by the method, revealed that the CO2 production and the O-2 consumption rates of the fermented milk were dependent on the CO2 and O-2 headspace concentrations. An increase in permeability, determined by conventional methods, suggested that both the non-polar and the polar polymers were plasticized by fermented milk. The plasticization was, however, modest and undetectable when the polyethylene tensile test data were analysed.

Nyckelord

food quality

fermented milk

headspace

polarity

film thickness

plasticization

permeability

sensory properties

shelf-life

ultrapasteurized milk

pasteurized milk

carbon-dioxide

films

bifidobacteria

diffusion

products

oxygen

flavor

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