The objective of this study was to evaluate the oxidative stability of the PS-enriched chocolate bars during 5 months of storage, see more and its main effects on color, texture, sensory quality and potential bioactivity of the functional food product. As the oxidation of sterols reaction can start with the hydroperoxides formation (Lengyel et al., 2012), the primary oxidation of unsaturated lipids was measured
by the hydroperoxide concentration (Fig. 1). When stored at 20 °C (Fig. 1A), the hydroperoxide peak (1.39 mmol/kg) occurred after 60 days of storage. Thereafter, the hydroperoxide decomposition rate was greater than its formation. At 30 °C (Fig. 1B), the maximum value (1.06 mmol/kg) was reached after 30 days, thus being earlier but lower than the peak observed at 20 °C. Hamid and Damit (2004) evaluated cocoa butter stability during storage at 15 and 70 °C and observed that the increase of temperature anticipated the peroxide peak from 6 to 4
months, even though the maximum values were similar in both storage conditions. The peroxide value observed in the chocolate samples during the shelf-life study was lower than 3.0 milli equivalent O2/kg (or 1.5 mmol/kg). This value can be considered low when compared with PV of other fresh vegetable oils, such as coconut (4.9 milli equivalent CYC202 nmr O2/kg), soybean (2.4 milli equivalent O2/kg) or canola (5.0 milli equivalent O2/kg) (Chaiyasit, Elias, McClements, & Decker, 2007). This low hydroperoxide content observed in chocolates was consequence of
the high proportion of saturated (50 g/100 g) and monounsaturated (40 g/100 g) fatty acids present in the cocoa butter. Only less than 10 g/100 g of the fatty acids observed in our samples were polyunsaturated, being the proportion of the most susceptible fatty acid (α-linolenic acid) lower than 1 g/100 g. Major fatty acids levels observed in the treatments during storage at 30 °C suggested that no significant alterations were detected during the shelf-life. Fatty acids proportion observed in the CONT samples after 150 days at 30 °C were: 27.94 ± 0.06, 18.79 ± 0.51, Ribose-5-phosphate isomerase 41.104 ± 0.06, 7.82 ± 0.29 and 0.26 ± 0.01 g/100 g; for C16:0, C18:0, C18:1, C18:2 n6 and C18:3 n3 respectively; while the mean values obtained to PHYT and PHAN samples were: 22.19 ± 0.12, 24.64 ± 0.21, 40.91 ± 0.15, 7.58 ± 0.10 and 0.90 ± 0.03 g/100 g for C16:0, C18:0, C18:1, C18: 2 n6 and C18:3 n3 respectively. In both storage conditions (20 and 30 °C) it was observed a trend of the PS-enriched bars to oxidize more than the bars formulated with palm oil (Fig. 1). In our chocolate bars, it was expected that C18:3 n3 had been the major responsible for the hydroperoxide formation, since no differences were observed for C18:2 n6 levels between the samples. In fact, the chocolates bars formulated with phytosterols (PHYT and PHAN) presented 236% more C18:3 n3 than those formulated with palm oil (CONT).