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Invloed van vleesgrondstoffen en temperatuur op de macroscopische eigenschappen van kookworst Kernwoorden: kookworst, macroscopische eigenschappen, verhittingstemperatuur, spiervezeltypes Een kookworst is een homogeen mengsel dat bestaat uit mager spierweefsel, vet en ijs, waar eventueel additieven aan toegevoegd worden. Het hoofddoel bij de productie van kookworst is het vormen van een gel tijdens het koken door het emulgeren van vet en het immobiliseren van water. De functionele eigenschappen van de vlees- en vetgrondstoffen, zoals gelering en kristallisatie, dragen bij tot de structurele en texturele eigenschappen van de kookworst. Ook de keuze van procesparameters, bijvoorbeeld temperatuur en tijd van verhitten spelen hierin een belangrijke rol. Om een microbieel stabiel product te verkrijgen werd als eerste bepaald hoelang een kookworst verhit moet worden bij twee verschillende kerntemperaturen: 60 °C en 70 °C. Vervolgens werden kookworsten bereid volgens twee kritische recepturen en verhit bij deze twee kerntemperaturen. De twee kritische recepturen verschilden in eiwitgehalte en hoeveelheid water. Deze kookworsten werden vergeleken met elkaar naar macroscopische eigenschappen, zoals het bepalen van de emulsiestabiliteit, kookverlies en hardheid. Naarmate het eiwitgehalte daalde en het de hoeveelheid water steeg, werd meer vloeistof geëxtraheerd uit het vleesdeeg, dit was ook het geval bij een stijging in verhittingstemperatuur. Deze twee fenomenen doen de emulsiestabiliteit van een vleesdeeg significant dalen. Ook het kookverlies was significant lager en de hardheid significant hoger bij kookworsten bereid volgens de receptuur met het hoogste eiwitgehalte en de laagste hoeveelheid water. In het tweede deel van het onderzoek werd één kritische receptuur geselecteerd en werd het effect van temperatuur en vleesgrondstof op de macroscopische eigenschappen nagegaan. De emulsiestabiliteit van een deegsysteem bereid met varkensschouder was significant lager dan bij een systeem op basis van wit kippenvlees. De emulsiestabiliteit daalde significant bij verhitten op 70 °C in vergelijking met 60 °C. Het kookverlies van de kookworst bereid met varkensschouder was significant hoger dan dat van kookworsten met wit en rood kippenvlees. De hardheid van kookworst bereid met wit kippenvlees was significant hoger in vergelijking met rood kippenvlees en varkensschouder. De hardheid van de verschillende deegsystemen die verhit werden op 60 °C is significant hoger dan wanneer verhit werd op 70 °C. Naast de temperatuur werden verschillen in macroscopische eigenschappen tussen de verschillende deegsystemen mogelijks veroorzaakt door een variërend eiwitgehalte, de pH van de grondstoffen en vezeltype. Deze kennis laat mogelijks toe de gewenste productstructuur te bekomen door intelligente keuze van grondstoffen en procesparameters, waardoor de nood aan additieven beperkt zal zijn.

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Cooked sausages can be classified as gel-type emulsified meat products. They are produced by finely comminuting a lean meat fraction, fat, ice and additives in order to obtain a raw meat batter. The raw meat batter is stuffed into casings, heated (pasteurized) and cooled to obtain the final meat product. The fat fraction, generally pork back fat, in raw meat batters is macroscopically solid due to the low temperature during processing. As such, meat products do not form a true emulsion. Still, the existence of an interfacial protein film (IPF) formed by myofibrillar proteins (from the meat) around the fat particles is described.This IPF stabilizes the fat phase that becomes liquid during the pasteurization process, thereby preventing fat coalescence and outward flow. Myofibrillar proteins form a three dimensional gelled protein network during heating (gelation) wherein fat and water are physically entrapped. Upon cooling, the protein network is further stabilized and the fat fraction partially crystallizes. Because the fat particles are coated with an IPF which interacts with the continuous protein network, they act as 'active filler particles', contributing to the overall gel rigidity. As such, it is clear that the structure of cooked sausages mainly depends on the properties of the continuous myofibrillar protein network (matrix) and the crystallized fat particles (the filler), all of which are in turn affected by the processing conditions. The product structure greatly influences the macroscopic properties of the meat product, such as the mechanical (rheology and texture) and stabilization properties (water- and fat-holding capacity).This doctoral research focuses on understanding the relationship between the structure-forming potential of the raw materials (gelation of proteins from the meat fraction and crystallization of lipids from the fat fraction), thermal processing, and the micro- and macrostructure of the final product. Additionally, the effect of the raw material composition, that is, meat consisting of different muscle fiber types (white vs. red muscle fiber type) and pork fats with a distinct chemical composition, was evaluated.First, the isothermal gelation behavior of white and red chicken myofibrillar proteins (CMP) (extracted from chicken meat consisting of predominantly white or red muscle fiber types, respectively) at different temperatures (20 to 80 °C) was studied. Special attention was paid to the molecular interactions involved in the aggregation mechanism, that is, hydrophobic interactions and disulfide formation. From 20 to 60 °C, an increase in aromatic surface hydrophobicity (SoANS) was found, suggesting partial protein unfolding and potential formation of hydrophobic interactions between CMP. From 60 to 80 °C, high SoANS and a significant decrease in total sulfhydryl amount (SH-amount) strongly indicated the presence of hydrophobic interactions and disulfide bonding, resulting in aggregation, as confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The elastic modulus G' after 60 min isothermal heating (G'60min) significantly increased at 70 or 80 °C, depending on the type of CMP. At low temperatures (20 to 60 °C), differences in G'60min between white and red CMP were rather small. However, at 70 °C, white CMP reached a significantly higher G'60min compared to red CMP, while at 80 °C, red CMP reached a slightly (but not significantly) higher G'60min compared to white CMP. Overall, for every temperature studied, SoANS and SH-amount of red CMP were higher compared to white CMP. The differences in G'60min, SoANS, and SH-amount between white and red CMP were probably due to different isoforms.Next it was investigated to which extent the 'equilibrium' crystallization state of lard (i.e. the fat obtained from pork back fat by a rendering process), and as a result, its textural properties depended on the chemical composition of lard from different pork fats. More specifically, the effect of fatty acid, triglyceride, diglyceride and FFA composition on the melting properties (melting peak area (indication of the solid fat content) and peak temperature) and hardness of lard at 'equilibrium' state was investigated. It could be concluded that differences in chemical composition definitely lead to differences in the physical properties of lard. The melting and textural properties of lard samples could be accurately predicted by the ratio of saturated to unsaturated fatty acids and the ratio of trisaturated and mono- and di-unsaturated triglycerides not containing linoleic acid to the tri-unsaturated and other mono- and di-unsaturated triglycerides. Although the diglyceride content in lard samples was small, they slightly affected the peak temperature and hardness of lard at 'equilibrium' state. The effect of these minor components should therefore not be overlooked. Additionally, the fatty acid profile solely also seemed to be a good predictor for the amount of solid fat and lard hardness at 'equilibrium' state.The aim of the third experimental chapter was to simultaneously study the effect of meat type (chicken breast and leg meat, predominantly high in white and red muscle fiber types, respectively), animal fat type (lard from selected pork back fats having a low and high degree of saturation), and isothermal temperature (50, 60, 70, and 80 °C) on the viscoelastic properties of meat batters during and after application of different time-temperature profiles. Results indicated that gelation of the meat proteins contributed most to the viscoelastic properties of meat batters during heating, whereas crystallization of the lipids especially contributed to the viscoelastic properties during the cooling phase. Lean meat model systems and meat batters prepared with chicken breast or leg meat yielded similar G' values at the end of the process (G'end). Therefore, it could be concluded that the meat type had little effect on the final viscoelastic properties. However, the fatty acid composition had a clear impact on the final viscoelastic properties of meat batters prepared with different types of fats, with higher G' values for the most saturated animal pork fat. The effect of fat type clearly transcended the effect of the meat type with regard to G'end. Viscoelastic properties of meat batters also clearly increased with increasing isothermal temperature. As such, it could be said that the structural properties of meat batters mainly depended on the heating temperature and the fatty acid composition of the pork fat, rather than the meat type. Last, the effect of meat type (chicken breast and leg meat), animal fat type (selected pork back fats having a low and high degree of saturation) and cooking temperature (60 and 70 °C) on the microstructural and macroscopic properties (water and fat binding, texture and pH) of cooked sausages was studied simultaneously. Sausages were produced at pilot scale. It should be noted that for the effect of temperature, the sausages were cooked to two different core temperatures until an F0-value of 40 min was attained, resulting in a considerably longer heating time for the sausages heated at 60 °C compared to 70 °C. This approach is different compared to the 60 min isothermal heating in the first and third experimental chapter. With regard to the stabilization properties, the emulsion stability was significantly lower and the greater part of the total expressible fluid (water- and fat loss) was fat in sausages prepared with the most saturated pork back fat, while the reverse was seen for the more unsaturated pork back fat. In accordance with these results, fat coalescence was observed at the microstructural level for sausages prepared with the most saturated back fat. During processing of the raw meat batter, the fat particles need to be partially melted in order to become coated with an IPF. Fat too high in saturated fatty acids probably resulted in a decreased ability of the myofibrillar proteins to properly coat the fat particles. The cooking loss was slightly lower for sausages prepared with the most saturated pork back fat. With regard to the textural properties, the fat type clearly affected the hardness of the cooked sausages, irrespective of the type of meat or temperature. Cooked sausages prepared with the most saturated back fat resulted in the highest hardness values. It could be concluded that small differences in fatty acid composition between the different pork back fats had a great effect on the microstructural and macroscopic properties of the cooked sausages, while the meat type (muscle fiber type) or cooking temperature only had a slight effect.Overall, the results in this doctoral study proved that the effect of muscle fiber was rather limited. The (isothermal) heating temperature affected myofibrillar protein gelation and viscoelastic properties of meat batters (G'60min and G'end values increased with increasing temperature), but only moderately affected the microstructural and macroscopic properties of cooked sausages. However, the latter was probably due to the different heating regime in this study. The chemical composition of pork fats strongly affected the physical properties of lard, in turn affecting viscoelastic properties of meat batters and macroscopic properties of cooked sausages. The higher the hardness of the fat, the higher G'end of meat batters and hardness of the final sausages. However, pork fats high in saturated fatty acids negatively affected the product stability. It is hypothized that apart from the importance of myofibrillar protein gelation in the matrix of meat batters, their ability to form a proper IPF around fat particles to stabilize the fat fraction in cooked sausages should not be overlooked. Based on these insights, the structure of meat products may be steered more effectively through an intelligent choice of raw materials and/or processing conditions.