The current study delineates the effect of incubation temperature on mechanical and electrical properties of ketchup. The analysis was done in the temperature range of 5oC and 25oC. Microstructure analysis of ketchup suggested the presence of cell wall components. Mechanical properties of ketchup were analyzed by spreadability and stress relaxation studies. Electrical properties of ketchup were analyzed by measuring the impedance in the frequency range of 100 Hz and 15 KHz. Spreadability study showed a higher firmness and cohesiveness in samples incubated at a lower temperature. The stress relaxation study suggested that inherent mechanical stability of the samples reached a critical lower limit at 15oC. Stability of the electrical equivalent circuit of samples was highest at 5oC. An increase in temperature drastically compromised the stability of electrical equivalent circuit of the samples. In gist, a variation in incubation temperature of the tomato ketchup can allow modulating not only the mechanical and viscoelastic properties, but also the electrical properties of ketchup.
TopIntroduction
Tomato ketchup is one of the commonly used food products across the globe (Berta, Wiklund, Kotzé, & Stading). It may be produced either by cold or hot extraction process (Sánchez-Moreno, De Ancos, Plaza, Elez-Martínez, & Cano, 2008). The rheological properties of the tomato ketchup have been found to modulate the consumer acceptability. The thickening property of the starch and other hydrocolloids is dependent on temperature (Juszczak, Oczadły, & Gałkowska, 2013). Some of the commonly used hydrocolloids include guar gum, sodium alginate, pectin, carboxymethyl cellulose, xantham gum and gum acacia (Ma & Boye, 2015; Mert, 2012; Villay, et al., 2012). The use of these hydrocolloids reduces the chances of occurrence of serum separation (Mert, 2012). Usually, an increase in the temperature of hydrocolloids leads to a decrease in the thickening property of the hydrocolloids containing sols (Xu, Gong, Dong, & Li, 2015). Hence, it is quite expected that the rheological properties of the hydrocolloids containing tomato ketchup will also show altered rheological properties. The viscosity enhancing properties of the hydrocolloids is due to their ability to form physically crosslinked network structure (Kadam, Pochat-Bohatier, Sanchez, & El Ghzaoui, 2015). Hence, the addition of these hydrocolloids plays an important role in altering the rheological properties of ketchup (Foster, 2011). The physical properties of the hydrocolloid gels are altered by the alteration in the storage temperature (Albano, Franco, & Telis, 2014). Hence, the properties of the ketchup are also altered when stored at different temperatures. Since there is an alteration in the rheological properties of the ketchup with the variation in the storage temperature, it is highly likely that there will have a marked variation in the electrical properties of the ketchup. But a thorough literature survey indicated no study on the variation in the electrical properties of the ketchup and their relationship with the viscoelastic properties. Taking a note of the above, in this study, the alteration in the viscoelastic and electrical properties of the commercially available ketchup were studied in the temperature range of 5 oC to 25 oC. The viscoelastic properties of the ketchup were estimated from the large-scale stress relaxation study. The viscoelastic parameters were calculated using Kohlarusch (Enrione, et al., 2012) and Maxwell-Weichert (Fu, Chang, & Shiau, 2015) model of stress relaxation. The electrical properties were modeled using (RQ)Q1 model (Biswal, et al., 2016), a commonly used electrical model for the analysis of soft materials. In addition to the above studies, the microstructure and the spreadability of the ketchup, incubated at different temperatures, were also studied.