# Sensory Texture and Mastication Physics of Multi-Phase Meat Products
## 1 Introduction  
Processed meat products such as ground beef, burgers, sausages, or meatloaf are well accepted food products with complex structure and texture. The structure of meat is highly directional, ranging from the orientation of actin and myosin filaments on the molecular scale to the elongated structure of muscle fiber bundles on the macroscale [1]. In general, oriented or direction dependent structures can be described as anisotropic, meaning that the direction of observation changes, opposed to isotropy, the properties of the material [2]. Processing of meat products often involves shearing or shredding followed by dissolution of the myofibrillar protein [3]. This can be either intentional, as in the production of meat batter for cooked sausage production, or unintentional due to sub-optimal processing conditions or malfunction worn processing equipment [4]. In either case, there is lysis of muscle fiber cells, leakage of sarcoplasmic and fibrillar protein, and loss of the anisotropic structure. The resulting structures can be described by the model of a multiphase system consisting of a gel-like phase and an anisotropically structured phase. To establish analytical methods that correlate with the gel-like structure, also referred to as amount of non-intact cells (ANIC) in minced meat products, [PERSON], et al. [5] developed a model system consisting of meat batter and ground meat, representing a two-phase system of anisotropic and isotropic structured matter. In their work, the histological ANIC significantly (\(p<0.01\)) correlated with metmyoglobin content (\(r=0.924\)), drip loss (\(r=-0.834\)), and firmness (\(r=-0.499\)) on samples with 0-100% replacement of minced meat by meat batter consisting of finely comminuted beef. This is a big accomplishmentfor analyzing the ANIC in raw minced meat samples with more rapid methods. The effect of ANIC in the end-product on human perception was not an issue of this work. From a quality control and economic perspective, the impact of ANIC on consumer perception is of great importance. The more precisely the threshold for the acceptable ANIC is defined, the closer the process can be steered in that direction, improving throughput and blade life, and potentially reduce waste streams by optimizing reprocessing rates. Texture studies are used to predict mechanical perception and determine this detection limit. However, due to the complexity of multiphase anisotropic systems, studying the texture of anisotropic foods can be challenging. When material is mechanically anisotropic at the macroscopic level, the anisotropic index (_AI_) calculated from deformation tests parallel and perpendicular to the direction of anisotropy showed great potential as a meaningful feature [6; 7]. Moreover, macroscopic mechanical differences often do not accurately reflect sensory impression. Current methods are a good tool to characterize materials in a macroscopic materials science approach, but do not capture the time-dependent change that a product undergoes during chewing. As an example, mastication changes foods due to cutting, shearing, and grinding between the teeth, wetting by saliva, softening by compression between the teeth or tongue and palate, or even chemical changes due to processes catalyzed by salivary enzymes [8; 9]. In this study, we characterize anisotropic structures in complex multi-phase food systems through an oral processing approach combined with sensory- and texture analysis. We focus on biomechanical characteristics of mastication in terms of kinematics of jaw movement and muscle activity. For this work, the ANIC was not determined histologically and therefore is substituted by the amount of \"batter-like substance\" (BLS) throughout the whole article. The BLS is simulated by finely committed beef, and not to be confused with conventional meat batter. It is hypothesized that the increase in BLS is reflected in reduced movement kinetics of the jaw, decreased consumption time, and less muscle activity required to break down the food.