Light-induced quality changes in plain yoghurt packed in polylactate and polystyrene

Abstract

The potential of using materials based on polylactate (PLA) for packaging of plain yoghurt has been demonstrated in the present study. Plain yoghurt (3.5% fat) was stored for 5 weeks in PLA or polystyrene (PS) cups under fluorescent light (3500 lux) or in darkness. Quality changes were studied by determination of color stability, formation of lipid hydroperoxides, development of volatile products (secondary oxidation products and release of styrene and lactate from the packaging materials) and degradation of β-carotene, and riboflavin was determined. For light-exposed yoghurts, PLA was at least as effective in preventing color changes and formation of lipid hydroperoxides as PS. During storage under fluorescence light, concentrations of n-hexanal, n-heptanal, n-octanal, n-nonanal, 3-methyl-butanal, dimethyl disulfide, and 1-octen-3-ol were lower in yoghurts packed in PLA than in PS. Furthermore, losses of riboflavin and β-carotene were less in light-exposed yoghurt packed in PLA than in PS. The amount of styrene in yoghurt stored in PS cups increased during storage, whereas lactate was not found in yoghurts stored in PLA. Practically no development of lipid hydroperoxides and secondary oxidation products or loss of riboflavin and β-carotene were observed in yoghurts stored in darkness. Thus, it can be concluded that light exposure reduced the quality of plain yoghurt and that PLA provided a better protection against photo-degradation processes than PS.