## 3 Results and Discussion
### Water Activity, Density, Mechanical Properties, and Acoustic Emission  
Table 3 shows the water activity, density, and texture parameters (acoustic and mechanical) of instant noodles. The water activity of the tested instant noodles did not differ statistically (p = 0.441), regardless of the type of additives used. However, the density of the samples depended on the type of the additive (p = 0.030). The addition of Psyllium in the amount of 3% caused a decrease of the density value in comparison with the control sample, but the addition of Psyllium in the amount of 5% had no influence on the density. The smallest density was found in instant noodles with the addition of Psyllium in the amount of 3%, while the largest was observed in instant noodles with Maltodextrin 5%. In the sample with the addition of Psyllium in the amount of 3%, a high content of fat and a low level of moisture was observed which caused the low density value of the instant noodle. However, the addition of Maltodextrin in the amount of 5% caused the instant noodle to have a similar fat and moisture content as samples with addition of Psyllium in the amount of 3%, but the density was significantly higher. Both ingredients: Psyllium and maltodextrin were added to the dough bind water [43], which evaporates during frying. Differences in the density of the tested instant noodles may result from the strength of water binding and the possibility of its release during frying. In addition, it can be assumed that Psyllium has greater gas retention ability during frying than Maltodextrin. Samples with a higher concentration of MCG (0.8%) HPMC (0.5%) in comparison with instant noodles with maltodextrin, had a density value on the similar level, higher moisture content and the lower fat content. One can conclude that higher concentrations of MCG and HPMC result in less moisture loss and reduces the absorption of fat during instant noodles' frying. Cellulose derivatives such as CMC, HPMC, and hydroxypropyl cellulose (HPC) and amylose have been evaluated as oil barriers in a deep-fat fried African cowpea paste-based food, comparing the coatings obtained by spraying and dipping the cowpea balls [22]. This oil barrier effect was related to the thermal gelation capacity of HPMC. Above the incipient gelation temperature, the viscosity increases dramatically as intermolecular associations occur very rapidly, and the solutions gel at the point which for HPMC is found lies in a temperature range of 50-90 \({}^{\circ}\)C. The gel layer controls the migration of water and oil during frying. Acoustic emission (AE) is a phenomenon of generation and propagation of elastic waves in various materials. The basis for the creation of such waves are microcracks, mutual shifts, or friction of surfaces of materials. In order to characterize the observed AE signal, acoustic descriptors are determined [31]. AE descriptors strongly depend on the composition of the product, the type of structure, and mechanical properties such as hardness or tendency of the material to experience plastic deformation [44]. Pasta textural parameters are recognized as one of the most important features for consumers and are one of the critical aspects for quality assessment. Statistical analysis showed that the type of additives significantly affected the acoustic parameters: The number of AE events (p < 0.001), the amplitude of the sound (p < 0.001), and the energy of a single AE event (p < 0.001) (Table 3). The lowest number of AE events was generated by the control sample, while the largest number was observed in the sample with the addition of Psyllium 5% (Table 3). Instant noodles with Maltodextrin, MCG, and HPMC generated a significantly higher number of AE events than the control sample, but smaller than instant noodles with Psyllium. Higher density, as well as the lower fat content of samples with maltodextrin, MCG, and HPMC addition, influenced the generated number of AE events.