In hamburger manufacturing, meat is subjected to four main processing steps (pre-grinding, mixing, grinding, and forming), whereby muscle fibers are disintegrated. In this study, the influence of these process steps was characterized by structural (amount of non-intact cells (ANIC), CLS-Microscopy), functional (drip loss) and qualitative (soluble protein content, lactate dehydrogenase (LDH) activity, myoglobin content (Mb)) parameters of the meat. Therefore, meat samples were analyzed after each process step. Histological analyses revealed an increased ANIC with progressive processing. Thereby, the first and second grinding steps caused the strongest increases (factors 2.43 and 2.69). Comparable results were found in the relative LDH activity (factor 2.20 and 1.62) and the Mb concentration (factor 2.24 and 1.33) of the extracted meat solution. The findings suggest that the disintegration of the meat structure increases with progressive processing, causing more vulnerable structures which result in increased leakage of intramuscular substances. Further, the type of stress acting on the meat determines the extent of the changes. The presented findings enable manufacturers to precisely adjust their process towards more gentle production parameters and thus, to meet the legal regulations.

The determination of the amount of non-intact cells (ANIC) in ground beef products is usually performed using a time-consuming and subjective histometric approach neglecting structural properties, which is why more objective and faster methods including evaluation of quality parameters are needed. To determine, whether the addition of meat batter increases the histologically determined ANIC ground beef samples containing increasing shares of meat batter (non-intact cells) were investigated histologically and results were compared to other methodological approaches, namely lactate dehydrogenase activity (LDH), soluble protein content, metmyoglobin content, drip loss, firmness, and cooking loss. Histological measurements showed that ANIC increased linearly with the addition of meat batter to ground beef. The quality parameters drip loss (r = − 0.834, p < 0.01) and firmness (r = − 0.499, p < 0.01), and the structural parameter metmyoglobin content (r = 0.924, p < 0.01) revealed significant correlations with the amount of added meat batter, and detected differences between ground beef samples when the difference in the amount of added batter-like-substance was ≥ 25%. Therefore, those methods might be useful to estimate and extrapolate ANIC, and assess product quality of ground beef samples in a faster and simpler way. The cooking loss was not affected by meat batter addition, whereas LDH activity revealed non-repeatable results. Taken together, histometric methods are useful to measure ANIC, nevertheless, it is limited in terms of characterization of morphological and structural changes in the meat. However, other parameters were correlated and could, in addition, be used for assessing the quality of ground meat.

Larger processing equipment to produce minced meat could affect its structure due to intensive processing and a high energy intake in the meat mass. To assess if this would result in alterations in the minced meat quality, finely chopped meat (FCM) was added in different concentrations (15, 30, 45, 60, 75, 90, and 100%) to minced meat and quality parameters were analyzed. FCM was used to simulate different intensity of an unintended destruction of meat cells due to various processes. The amount of non-intact cells (ANIC) was determined histologically and furthermore, soluble protein content, water holding capacity, mechanical and sensory texture, and scanning electron and confocal laser scanning microscopy was applied to analyze the meat structure and quality. ANIC indicated that even adding 15% FCM was statistically (p < 0.05) distinguishable from 100% minced meat and 30% FCM had already 50 Vol.-% ANIC. In contrast, the addition of 15% or 30% FCM did not result in significant differences in drip loss of raw and cooked meat as well as mechanical and sensory texture analysis. This study showed that intensive processing might be detectable via ANIC, but that the minced meat quality was not affected.

Food products often consist of several phases. Comminuted meat products, for example, are multiphase systems consisting of structured meat particles and unstructured batter-like substance. To develop and understand the processing of these products, it is important to understand the sensory and mechanical perception principles. To this end, two-phase food prototypes consisting of mixtures of ground beef and beef batter were prepared and subjected to sensory, texture, and oral processing analysis. The oral processing analysis focused on the biomechanical data of the chewing process, namely the kinematics of jaw movement and electromyographic activity. The ground meat served as the anisotropic phase and the meat dough as the isotropic phase. A significant increase in muscle activity, duration per bite, and occlusion time with increasing proportion of fibrous particles was demonstrated (p < 0.05). In contrast, a higher proportion of isotropic substance resulted in significantly higher amplitudes of jaw movement and faster jaw kinetics (p < 0.05). In mixed regimes, the system responded mainly according to the dominant phase, with sensory or mechanical response changing at a critical point. In combination with texture and sensory data, a holistic characterization of the food models could be performed.

The meat industry is typically using a mixture of fresh and frozen meat batters for minced meat production. Our goal was to find the exact threshold for fresh to frozen meat ratio capable of controlling the meat temperature during processing, but without having an adverse effect on the sensory quality of minced pork. To achieve this, the percentage of frozen meat used for the minced pork production was increased from 0% (control) to 50% (maximum) in 10% increments. To keep the minced meat temperature in control and make the processing resistant to fat smearing, the addition of 30% of frozen meat to the meat batter is sufficient. The soluble protein content, instrumental cutting force, and the sensory perceived firmness, juiciness, and inner cohesion were not affected by the addition of frozen meat. However, it has contributed to a significant increase of the drip loss and the amount of non-intact cells (ANIC). With the addition of frozen meat into the minced pork, the compliance to ANIC regulation by the German regulatory authorities is technologically (practically) almost impossible.