Moisture absorption and aw changing during storage, which can lead to quality degradation in terms of hydrolytic rancidity and sensory attributes such as texture (crispness) and ultimately resulting in shorter shelf-life and rejection of the product (Labuza, 1980; Taoukis et al., 1988; Tiwari et al., 2011) were not significant in this study (data not shown). Thewater activitywas well below0.3 under which food products are largely protected against lipid oxidation, non-enzymatic browning, enzymatic activity and microbial spoilage (Belitz et al., 2009). Usually, the rate of oxidation decreases as the water activity is lowered towards the monolayer, but the rate of many lipid oxidation reactions increase under very low aw (<0.2). Thus, some oxidation might be expected. However, there was a small increase in peroxide values of all products during storage (<1.00 meq/kg) but it was not significant. Low PV of 5 meq/ kg has been as a reference value of oxidation in dried foods (Tiwariet al., 2011). There were also no significant changes in the TBARS values (0.02e1.1 mmol/kg) during the 6 months storage period (data not shown) indicating the stability of the prototypes against oxidation probably due to low water activity of the product (Belitz et al., 2009). The low peroxide and TBARS values after production of the snacks indicates that the thermal processing during extrusion did not accelerate lipid oxidation as previously reported (Shaviklo, Olafsdottir et al., 2011). It also reveals that the seasoning time (15 min) and temperature (<60 C) did not either increase oxidation.The selected puffed corn-shrimp snacks and control had high fat content (>28 g/100 g) but the hydrogenated vegetable oil used for seasoning and the low water activity may explain the low peroxide and TBARS values (Belitz et al., 2009). After 6 months storage the PV (1 < meq/kg), TBARS (<1.1 mmol/kg) and TVBN (2.8 mg N/100 g) of corn-shrimp and control snacks did not increased significantly (data not shown) indicating proper storage conditions.
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