3.2.1. Total expressible fluid (TEF)
Figures 5A and B represent the results of TEF of different purees by water bath, and microwave oven heating, respectively.
(Place for figure 5)
Fig.5. Effect of incorporation of 10% psyllium husk (PH) emulsion gel with 0%, 10% and 20% inulin in puree samples (A) at 70℃ water bath heating for 30 min, and (B) at microwave oven heating with power 700W for 2 min and then centrifugation at 3750 g for 3 min. Different letters represent significant different at p<0.05.
TEF of water bath-heated or microwave-heated pure puree (chicken, salmon, chicken stew and beef without emulsion gel incorporation) was significantly higher than that of puree with 10% w/w husk-0% inulin emulsion gel incorporation. Water bath and microwave oven heating methods were selected in this study because they are common household heating methods. Increased inulin concentration in emulsion gel (from 0% to 20%) incorporation in the purees further reduced their TEF. So, the puree with husk-20% inulin emulsion gel had the lowest TEF among the same puree group. For example, within the chicken puree group (Figure 3.7), the pure puree (no emulsion gel incorporation) had the highest TEF (31.77% mean value), while the puree with 10% w/w replaced by husk-20% inulin emulsion gel had the lowest TEF (17.22% mean value). Microwave-heating method (Figure 3.8) produced similar result; the puree with husk-20% inulin emulsion gel incorporation still had the lowest TEF within the same puree group. TEF reduction with the inclusion of husk emulsion gel may be due to ingredients in the emulsion gel crosslinking with the polar groups of protein matrix. The cross-linking can strengthen the puree three-dimensional network structure, leading to stronger binding properties and smaller fluid release during heating (Colmenero et al., 2005; Kumar, 2021). Previous study (Kumar, 2021) has shown that inulin has water and fat retention capacity, which also help TEF reduction.
In comparison to water bath heated-meat puree, the microwave-heated meat puree had higher TEF, which agrees with Colmenero et al., (2005). This may be due to the internal microwave heating creating higher center temperature of the puree, and the high steam pressure driving more water from within the sample to the surface (Wang et al., 2020).