Cocoa wafer cream is a mixture of fat, sugars, cocoa powder and other compounds including flavour. Due to the high lipid content this product is prone to peroxidation during storage. Wafers with cream usually have a long shelf life (about 12 months), thus the oxidative stability becomes crucial to their quality during long-term storage. The aim of this study was to investigate the effect of the addition of commercially available citrus fruit extract on the oxidative stability of lipids, extracted from cream from fresh and stored samples (3, 6, 8, 10, 12 and 13 months) at 18 °C. Differential scanning calorimetry (DSC), diene content (CD) for assessing oxidative stability and 2,2-diphenyl-1-pikrylhydrazyl (DPPH) radical scavenging activity for antioxidant activity were used. Additionally the color of the samples was measured in the CIE L*a*b* color space. The thermo-oxidative stability was expressed as the oxidation induction time measured at temperature 160 °C (OIT160) by the DSC isothermal mode. Based on the DSC results it was observed that the fruit extract addition effectively slowed down the oxidation process of lipids in cream during storage of wafers. After 13 months of storage, the OIT160 values for both samples (WT, WTE) were about two times lower, however, until 12th month of storage, the OIT160 values for WTE were always higher than those for WT. The slope of the linear plot for the OIT160 changes was lower for WTE (-1.81) than for WT sample (-3.41) during storage. Similar trend was observed for CD, as the slope for exponential plot of CD values vs. storage time was two times higher for WT than for WTE sample during the first eight months. This indicates the protective effect of fruit extract on the lipid fraction of cocoa cream. The color of the product is the quality attribute affecting its acceptance by the consumers. It was stated that L*a*b* color coordinates were significantly correlated with the OIT160 values. Moreover it was also observed that from the eighth month of storage, L* values for the WT sample were increasing, indicating a lightening of the cocoa cream, while for the sample WTE the opposite trend was noted till the end of storage.
This research was funded by the Ministry of Science and Education as the part of “Industrial doctorate”, Poland, grant number: DWD/3/35/2019.