# Influence of Processing Steps on Structural, Functional, and Quality Properties of Beef Hamburgers
## 3 Results and Discussion
### Changes in Chemical and Quality Properties  
To check changes in the chemical and quality properties, \(EMS\) were analyzed for their relative \(LDH\) activity, their \(SPC\), and \(Mb\). As the aim of the study was to detect changes in the structural, functional, and chemical properties of samples with different mechanical treatment, the \(EMS\) were produced by a gentle extraction process without homogenization. A homogenization would mechanically disrupt the muscle fiber structure completely; this structural damage would superpose the process related changes and would, thus, rule out the differentiation between the samples. \(LDH\) doubled (factor 2.20) during the first grinding step and further increased during the second grinding (Figure 4A). Only slight changes were caused by mixing, whereas forming caused a comparable increase to the second grinding (factor 1.70, Figure 4B). This might be attributed to a stronger \(LDH\) release from the muscle fibers due to the applied pressure. Considering the statics, the statistically significant increases in \(LDH\) were caused by the first and second grinding steps and forming. This result is partly comparable to the histologically determined \(ANIC\) (Figure 2A). Moreover, this shows that \(LDH\) might serve as a chemical indicator for muscle fiber disintegration when the raw material is known and analyzed as a reference. An \(LDH\) increase was expected, as a disruption of muscle fibers by grinding and a subsequent release of muscle fiber content leading to an increase in \(LDH\) activity was reported earlier [12; 15]. Similarly, \(LDH\) activity determination is a common measure to distinguish between chilled and frozen meat caused by increased enzyme release upon freezing [15]. A slight increase in the amount of _SPC_ during processing could be found (Figure 4B). However, statistically significant differences were only analyzed between the second grinding step and forming and the meat piece. Moreover, _SPC_ did not change in the same manner as the histologically determined _ANIC_. An increase in the soluble protein content was expected, as [PERSON] et al. [12] stated, that a mechanical rupture of the meat muscle fibers opens the internal structure of meat tissue, thus making the (myofibrillar) proteins available for extraction. They found a significantly higher proportion of extracted water-soluble (sarcoplasmic) protein in the ground sample compared with the sample treated with the tenderizer or activator. However, this trend was only slightly pronounced in the study. This might be traced back to the use of different analytical methods. [PERSON] et al. [12] used the Helander procedure [29] which is used to detect the protein availability, whereas in this study the total amount of nitrogen compounds was determined. It is possible that other soluble nitrogen compounds, such as non-protein nitrogen compounds, dipeptides, or amino acids remain in the extract upon filtration and overlay the effect of the processing steps on the _SPC_. During the first grinding step, _Mb_ approximately doubled from 0.15 \(\pm\) 0.05 mg/mL in raw material to 0.33 \(\pm\) 0.04 mg/mL after the first grinding (Figure 4C). The mixing and second grinding step further increased _Mb_ (0.62 \(\pm\) 0.08 mg/mL after second grinding). The subsequent forming step slightly reduced _Mb_. It can be concluded that the first and second grinding steps increase _Mb_ the strongest. The _Mb_ analysis is based on specific absorbance spectra of myoglobin derivates [30]. As myoglobin is present in cardiac and skeletal muscles and is released upon muscle fiber damage during acute myocardial infarctions, it serves as a biochemical indicator [31,32]. Meat grinding also disintegrates muscle structures, thus an increase of _Mb_ with increasing _ANIC_ is assumed. The strongest increase in the myoglobin content in the first and second grinding steps is in accordance with the findings of the histologically determined _ANIC_ (Figure 2A) and _SPC_ (Figure 4B).