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In order to study the effect of high-pressure (HP) treatment and two different methods of brine addition (important for lysosomal membrane destabilisation) on lysosomal enzymes activity and protein degradation, pork semitendinosus muscle was brine enhanced by injection or tumbling, and HP treated at 600 MPa following storage at 2 °C for up to 8 weeks. In this report a novel protocol for SDS gelatin zymography was established, and an increase of cathepsin B and L activity after HP treatment was shown followed by a decrease during storage. No calpain activity was detected following HP treatment. HP treatment was shown to induce a decrease in protein solubility in both myofibrillar and sarcoplasmic fractions. LC–MS analysis of these fractions showed changes in the peptide pattern during storage. Western blot analysis showed that troponin-T was indeed degraded during storage after HP treatment. The results therefore suggest that HP treatment induced an increase in cathepsin activity, which subsequently affected the myofibrillar protein degradation pattern in pork meat.

The objective of this study was to investigate the response of sarcoplasmic proteins in bovine longissimus muscle to low-voltage electrical stimulation (ES, 80 V, 35 s) after dressing and its contribution to meat tenderization at early postmortem time. Proteome analysis showed that ES resulted in lower (P <0.05) phosphorylation levels of creatine kinase M chain, fructose bisphosphate aldolase C-A, ß-enolase and pyruvate kinase at 3 h postmortem. Zymography indicated an earlier (P <0.05) activation of µ-calpain in ES muscles. Free lysosomal cathepsin B&L activity increased faster (P <0.05) in ES muscles up to 24 h. Immunohistochemistry and transmission electron microscopy further indicated that lysosomal enzymes were released at early postmortem time. ES also induced ultrastructural disruption of sarcomeres. In addition, ES accelerated (P <0.05) depletion of ATP, phosphate creatine and glycogen, as well as pH decline and more preferred pH/temperature decline mode. Finally, ES accelerated meat tenderization with lower (P <0.05) shear force values than control over testing time. A possible relationship was suggested between change in phosphorylation level of energy metabolic enzymes and postmortem tenderization of beef. Our results suggested the possible importance of activation of µ-calpain, phosphorylation of sarcoplasmic proteins and release of lysosomal enzymes for ES-induced tenderization of beef muscle.

In order to study the effect of high-pressure (HP) treatment and two different methods of brine addition (important for lysosomal membrane destabilisation) on lysosomal enzymes activity and protein degradation, pork semitendinosus muscle was brine enhanced by injection or tumbling, and HP treated at 600 MPa following storage at 2 °C for up to 8 weeks. In this report a novel protocol for SDS gelatin zymography was established, and an increase of cathepsin B and L activity after HP treatment was shown followed by a decrease during storage. No calpain activity was detected following HP treatment. HP treatment was shown to induce a decrease in protein solubility in both myofibrillar and sarcoplasmic fractions. LC–MS analysis of these fractions showed changes in the peptide pattern during storage. Western blot analysis showed that troponin-T was indeed degraded during storage after HP treatment. The results therefore suggest that HP treatment induced an increase in cathepsin activity, which subsequently affected the myofibrillar protein degradation pattern in pork meat.

The objective of this study was to investigate the response of sarcoplasmic proteins in bovine longissimus muscle to low-voltage electrical stimulation (ES, 80 V, 35 s) after dressing and its contribution to meat tenderization at early postmortem time. Proteome analysis showed that ES resulted in lower (P <0.05) phosphorylation levels of creatine kinase M chain, fructose bisphosphate aldolase C-A, ß-enolase and pyruvate kinase at 3 h postmortem. Zymography indicated an earlier (P <0.05) activation of µ-calpain in ES muscles. Free lysosomal cathepsin B&L activity increased faster (P <0.05) in ES muscles up to 24 h. Immunohistochemistry and transmission electron microscopy further indicated that lysosomal enzymes were released at early postmortem time. ES also induced ultrastructural disruption of sarcomeres. In addition, ES accelerated (P <0.05) depletion of ATP, phosphate creatine and glycogen, as well as pH decline and more preferred pH/temperature decline mode. Finally, ES accelerated meat tenderization with lower (P <0.05) shear force values than control over testing time. A possible relationship was suggested between change in phosphorylation level of energy metabolic enzymes and postmortem tenderization of beef. Our results suggested the possible importance of activation of µ-calpain, phosphorylation of sarcoplasmic proteins and release of lysosomal enzymes for ES-induced tenderization of beef muscle.

Background: The research of high pressure (HP) processing of meat based foods needs to address how pressure affects protein interactions, aggregation and/or gelation. The understanding of the gel forming properties of myofibrillar components is fundamental for the development of muscle based products (Chapleau et al., 2004;Colmenero, 2002). Object: The aim was to study the rheological properties of pork meat emulsion exposed to HP and the effect of HP on the aggregation state of myofibrillar proteins. To address the role of cathepsin in myofibrillar protein degradation the changes in the myofibrillar protein pattern and HP-induced change in activity of cathepsin B and L were investigated. Results: In this study we showed that HP treatment of pork meat emulsion, ranging from 0.1 to 800 MPa, induced protein gel formation as shown by the increased Young’s modulus (Fig.1). Analysis of SDS–PAGE gels of myofibrillar protein extract from HP treated meat showed that myofibrillar proteins form high molecular weight aggregates after HP treatment. Myofibrillar protein aggregates were stable in a reducing environment, suggesting that disulfide bonds are not the main molecular interactions responsible for these aggregations (Fig.2). Furthermore HP treatment caused an increase in cathepsin activity (Fig.3), probably due to disruption of the lysosomal membrane and leakage of enzymes, which subsequently affected the myofibrillar protein degradation pattern (Fig.4). Conclusion: HP treatment affects the rheological properties of pork meat batters by inducing formation of protein gels. HP induced protein gels are suggested to be formed by high molecular weight myofibrillar protein aggregates and by peptides formed by lysosomal enzyme-induced cleavage of myofibrillar proteins. Perspectives: The data presented suggest that the lysosomal enzymes play a potential role in pressure assisted gelation.

Background: The research of high pressure (HP) processing of meat based foods needs to address how pressure affects protein interactions, aggregation and/or gelation. The understanding of the gel forming properties of myofibrillar components is fundamental for the development of muscle based products (Chapleau et al., 2004;Colmenero, 2002). Object: The aim was to study the rheological properties of pork meat emulsion exposed to HP and the effect of HP on the aggregation state of myofibrillar proteins. To address the role of cathepsin in myofibrillar protein degradation the changes in the myofibrillar protein pattern and HP-induced change in activity of cathepsin B and L were investigated. Results: In this study we showed that HP treatment of pork meat emulsion, ranging from 0.1 to 800 MPa, induced protein gel formation as shown by the increased Young’s modulus (Fig.1). Analysis of SDS–PAGE gels of myofibrillar protein extract from HP treated meat showed that myofibrillar proteins form high molecular weight aggregates after HP treatment. Myofibrillar protein aggregates were stable in a reducing environment, suggesting that disulfide bonds are not the main molecular interactions responsible for these aggregations (Fig.2). Furthermore HP treatment caused an increase in cathepsin activity (Fig.3), probably due to disruption of the lysosomal membrane and leakage of enzymes, which subsequently affected the myofibrillar protein degradation pattern (Fig.4). Conclusion: HP treatment affects the rheological properties of pork meat batters by inducing formation of protein gels. HP induced protein gels are suggested to be formed by high molecular weight myofibrillar protein aggregates and by peptides formed by lysosomal enzyme-induced cleavage of myofibrillar proteins. Perspectives: The data presented suggest that the lysosomal enzymes play a potential role in pressure assisted gelation.

Colour and drip loss were measured. A faster decrease in pH resulted in reduced level of l-calpain activity and increased autolysis of the enzyme, and hence an earlier loss of activity due to activation of l-calpain in muscles with a fast pH decline. Paralleling the l-calpain activation in muscles with a fast pH decline a higher myofibril fragmentation at 24 h post-mortem was observed, which was no longer evident in the later phase of the tenderization process. In conclusion, the rate of early pH decline influenced l-calpain activity and the rate but not the extent of myofibrillar degradation, suggesting an early effect of proteolysis on myofibril fragmentation that is reduced during ageing due to an earlier exhaustion of lcalpain activity.

Colour and drip loss were measured. A faster decrease in pH resulted in reduced level of l-calpain activity and increased autolysis of the enzyme, and hence an earlier loss of activity due to activation of l-calpain in muscles with a fast pH decline. Paralleling the l-calpain activation in muscles with a fast pH decline a higher myofibril fragmentation at 24 h post-mortem was observed, which was no longer evident in the later phase of the tenderization process. In conclusion, the rate of early pH decline influenced l-calpain activity and the rate but not the extent of myofibrillar degradation, suggesting an early effect of proteolysis on myofibril fragmentation that is reduced during ageing due to an earlier exhaustion of lcalpain activity.

Background: The research of high pressure (HP) processing of meat based foods needs to address how pressure affects protein interactions, aggregation and/or gelation. The understanding of the gel forming properties of myofibrillar components is fundamental for the development of muscle based products (Chapleau et al., 2004;Colmenero, 2002). Object: The aim was to study the rheological properties of pork meat emulsion exposed to HP and the effect of HP on the aggregation state of myofibrillar proteins. To address the role of cathepsin in myofibrillar protein degradation the changes in the myofibrillar protein pattern and HP-induced change in activity of cathepsin B and L were investigated. Results: In this study we showed that HP treatment of pork meat emulsion, ranging from 0.1 to 800 MPa, induced protein gel formation as shown by the increased Young’s modulus (Fig.1). Analysis of SDS–PAGE gels of myofibrillar protein extract from HP treated meat showed that myofibrillar proteins form high molecular weight aggregates after HP treatment. Myofibrillar protein aggregates were stable in a reducing environment, suggesting that disulfide bonds are not the main molecular interactions responsible for these aggregations (Fig.2). Furthermore HP treatment caused an increase in cathepsin activity (Fig.3), probably due to disruption of the lysosomal membrane and leakage of enzymes, which subsequently affected the myofibrillar protein degradation pattern (Fig.4). Conclusion: HP treatment affects the rheological properties of pork meat batters by inducing formation of protein gels. HP induced protein gels are suggested to be formed by high molecular weight myofibrillar protein aggregates and by peptides formed by lysosomal enzyme-induced cleavage of myofibrillar proteins. Perspectives: The data presented suggest that the lysosomal enzymes play a potential role in pressure assisted gelation.

Background: The research of high pressure (HP) processing of meat based foods needs to address how pressure affects protein interactions, aggregation and/or gelation. The understanding of the gel forming properties of myofibrillar components is fundamental for the development of muscle based products (Chapleau et al., 2004;Colmenero, 2002). Object: The aim was to study the rheological properties of pork meat emulsion exposed to HP and the effect of HP on the aggregation state of myofibrillar proteins. To address the role of cathepsin in myofibrillar protein degradation the changes in the myofibrillar protein pattern and HP-induced change in activity of cathepsin B and L were investigated. Results: In this study we showed that HP treatment of pork meat emulsion, ranging from 0.1 to 800 MPa, induced protein gel formation as shown by the increased Young’s modulus (Fig.1). Analysis of SDS–PAGE gels of myofibrillar protein extract from HP treated meat showed that myofibrillar proteins form high molecular weight aggregates after HP treatment. Myofibrillar protein aggregates were stable in a reducing environment, suggesting that disulfide bonds are not the main molecular interactions responsible for these aggregations (Fig.2). Furthermore HP treatment caused an increase in cathepsin activity (Fig.3), probably due to disruption of the lysosomal membrane and leakage of enzymes, which subsequently affected the myofibrillar protein degradation pattern (Fig.4). Conclusion: HP treatment affects the rheological properties of pork meat batters by inducing formation of protein gels. HP induced protein gels are suggested to be formed by high molecular weight myofibrillar protein aggregates and by peptides formed by lysosomal enzyme-induced cleavage of myofibrillar proteins. Perspectives: The data presented suggest that the lysosomal enzymes play a potential role in pressure assisted gelation.

Formålet med dette projekt var at undersøge den kombinerede effekt af marinering med kiwifrugtpulver og høj-intensitet ultralyd på mørheden af yderlår (M. biceps femoris) fra svin. Det var forventet, at både marinering med kiwifrugtpulver og høj-intensitet ultralyd ville resultere i en forbedret mørhed, samt at kombinationen af behandlingerne eventuelt ville resultere i en yderligere forbedring af mørheden pga. en bedre fordeling af marinaden forårsaget af ultralyden.Yderlår (24 h post-mortem) blev injiceret med kiwi-marinade til en tilvækst på 10 % og en koncentration af kiwifrugtpulver på 0,075 % i musklen. Efterfølgende blev halve muskler vakuum-pakket og ultralydsbehandlet i 40 minutter (1 MHz, 150 W og 500 W, 25 kHz). Prøver blev udskåret og opbevaret ved 2°C i henholdsvis 0, 2 og 7 dage. Mørheden blev undersøgt ved Warner-Bratzler shear force-analyse, hvor parametrene initial yield, peak force og final yield blev bestemt. For at forklare den forventede, mørnende effekt af marinering med kiwifrugtpulver og høj-intensitet ultralyd blev yderligere analyser foretaget for at undersøge, hvilke komponenter (myofibrillære eller bindevævs) der blev påvirket af behandlingerne. Analyserne omfattede bestemmelse af aktiviteten af de proteolytiske enzymer samt myofibrillær fragmentering. De struktur-relaterede proteiner F-aktin, desmin, integrin og collagen blev desuden undersøgt ved immunfluorescens kombineret med konfokal laserscanning-mikroskopi. For at undersøge om marinering med kiwifrugtpulver og høj-intensitet ultralyd påvirkede andre kvalitetsparametre, blev pH, ekssudat og kogetab bestemt. Resultaterne for Warner-Bratzler peak force-målingerne viste, at høj-intensitet ultralyden ikke havde nogen signifikant mørnende effekt på yderlåret, samt at marineringen med kiwifrugtpulver kun resulterede i en numerisk stigning i mørheden. Resultaterne viste yderligere, at kombinationen af marinering med kiwifrugtpulver og høj-intensitet ultralyd resulterede i en signifikant fo, The objective of the current study was to investigate the combined effect of marination with kiwi fruit powder and high power ultrasound on tenderness of porcine M. biceps femoris. The hypotheses were that both high power ultrasound and marination with kiwi fruit powder would enhance tenderness, and the combined effect would maybe lead to a further increase in tenderness caused by a better distribution of the marinade by ultrasonication.Muscles (24 h post-mortem) were injected with kiwi fruit marinade to a 10 % weight increase and a final concentration of 0.075 % kiwi fruit powder. Subsequently, half muscles were vacuum packed and ultrasonicated for 40 minutes in an ultrasound bath (1 MHz, 150 W and 500 W, 25 kHz). Samples were cut and stored at 2°C for either 0, 2 or 7 days. Tenderness was investigated by Warner-Bratzler shear force analysis, where the parameters initial yield, peak force and final yield were determined. To explain effects on tenderness further analyses were conducted to investigate which fractions (myofibrillar and connective tissue fraction) that were affected by kiwi fruit marination and high power ultrasound. The activity of the proteolytic enzymes and the myofibril fragmentation were investigated, and structural components including F-actin, desmin, integrin, and collagen were investigated by immunofluorescence combined with confocal laser scanning microscopy. To investigate if kiwi fruit marination and high power ultrasound affected other meat quality characteristics, the pH, exudate, and cooking loss was also determined. Results of Warner-Bratzler peak force measurements revealed that high power ultrasound did not significantly enhance the tenderness of porcine M. Biceps femoris, and kiwi fruit marination only resulted in a numerical increase in tenderness. However, the combination of the treatments resulted in significantly increased tenderness. Results of Warner-Bratzler initial yield and final yield measurements indicated that the tenderi

Formålet med dette projekt var at undersøge den kombinerede effekt af marinering med kiwifrugtpulver og høj-intensitet ultralyd på mørheden af yderlår (M. biceps femoris) fra svin. Det var forventet, at både marinering med kiwifrugtpulver og høj-intensitet ultralyd ville resultere i en forbedret mørhed, samt at kombinationen af behandlingerne eventuelt ville resultere i en yderligere forbedring af mørheden pga. en bedre fordeling af marinaden forårsaget af ultralyden.Yderlår (24 h post-mortem) blev injiceret med kiwi-marinade til en tilvækst på 10 % og en koncentration af kiwifrugtpulver på 0,075 % i musklen. Efterfølgende blev halve muskler vakuum-pakket og ultralydsbehandlet i 40 minutter (1 MHz, 150 W og 500 W, 25 kHz). Prøver blev udskåret og opbevaret ved 2°C i henholdsvis 0, 2 og 7 dage. Mørheden blev undersøgt ved Warner-Bratzler shear force-analyse, hvor parametrene initial yield, peak force og final yield blev bestemt. For at forklare den forventede, mørnende effekt af marinering med kiwifrugtpulver og høj-intensitet ultralyd blev yderligere analyser foretaget for at undersøge, hvilke komponenter (myofibrillære eller bindevævs) der blev påvirket af behandlingerne. Analyserne omfattede bestemmelse af aktiviteten af de proteolytiske enzymer samt myofibrillær fragmentering. De struktur-relaterede proteiner F-aktin, desmin, integrin og collagen blev desuden undersøgt ved immunfluorescens kombineret med konfokal laserscanning-mikroskopi. For at undersøge om marinering med kiwifrugtpulver og høj-intensitet ultralyd påvirkede andre kvalitetsparametre, blev pH, ekssudat og kogetab bestemt. Resultaterne for Warner-Bratzler peak force-målingerne viste, at høj-intensitet ultralyden ikke havde nogen signifikant mørnende effekt på yderlåret, samt at marineringen med kiwifrugtpulver kun resulterede i en numerisk stigning i mørheden. Resultaterne viste yderligere, at kombinationen af marinering med kiwifrugtpulver og høj-intensitet ultralyd resulterede i en signifikant fo, The objective of the current study was to investigate the combined effect of marination with kiwi fruit powder and high power ultrasound on tenderness of porcine M. biceps femoris. The hypotheses were that both high power ultrasound and marination with kiwi fruit powder would enhance tenderness, and the combined effect would maybe lead to a further increase in tenderness caused by a better distribution of the marinade by ultrasonication.Muscles (24 h post-mortem) were injected with kiwi fruit marinade to a 10 % weight increase and a final concentration of 0.075 % kiwi fruit powder. Subsequently, half muscles were vacuum packed and ultrasonicated for 40 minutes in an ultrasound bath (1 MHz, 150 W and 500 W, 25 kHz). Samples were cut and stored at 2°C for either 0, 2 or 7 days. Tenderness was investigated by Warner-Bratzler shear force analysis, where the parameters initial yield, peak force and final yield were determined. To explain effects on tenderness further analyses were conducted to investigate which fractions (myofibrillar and connective tissue fraction) that were affected by kiwi fruit marination and high power ultrasound. The activity of the proteolytic enzymes and the myofibril fragmentation were investigated, and structural components including F-actin, desmin, integrin, and collagen were investigated by immunofluorescence combined with confocal laser scanning microscopy. To investigate if kiwi fruit marination and high power ultrasound affected other meat quality characteristics, the pH, exudate, and cooking loss was also determined. Results of Warner-Bratzler peak force measurements revealed that high power ultrasound did not significantly enhance the tenderness of porcine M. Biceps femoris, and kiwi fruit marination only resulted in a numerical increase in tenderness. However, the combination of the treatments resulted in significantly increased tenderness. Results of Warner-Bratzler initial yield and final yield measurements indicated that the tenderi

Formålet med dette projekt var at undersøge den kombinerede effekt af marinering med kiwifrugtpulver og høj-intensitet ultralyd på mørheden af yderlår (M. biceps femoris) fra svin. Det var forventet, at både marinering med kiwifrugtpulver og høj-intensitet ultralyd ville resultere i en forbedret mørhed, samt at kombinationen af behandlingerne eventuelt ville resultere i en yderligere forbedring af mørheden pga. en bedre fordeling af marinaden forårsaget af ultralyden.Yderlår (24 h post-mortem) blev injiceret med kiwi-marinade til en tilvækst på 10 % og en koncentration af kiwifrugtpulver på 0,075 % i musklen. Efterfølgende blev halve muskler vakuum-pakket og ultralydsbehandlet i 40 minutter (1 MHz, 150 W og 500 W, 25 kHz). Prøver blev udskåret og opbevaret ved 2°C i henholdsvis 0, 2 og 7 dage. Mørheden blev undersøgt ved Warner-Bratzler shear force-analyse, hvor parametrene initial yield, peak force og final yield blev bestemt. For at forklare den forventede, mørnende effekt af marinering med kiwifrugtpulver og høj-intensitet ultralyd blev yderligere analyser foretaget for at undersøge, hvilke komponenter (myofibrillære eller bindevævs) der blev påvirket af behandlingerne. Analyserne omfattede bestemmelse af aktiviteten af de proteolytiske enzymer samt myofibrillær fragmentering. De struktur-relaterede proteiner F-aktin, desmin, integrin og collagen blev desuden undersøgt ved immunfluorescens kombineret med konfokal laserscanning-mikroskopi. For at undersøge om marinering med kiwifrugtpulver og høj-intensitet ultralyd påvirkede andre kvalitetsparametre, blev pH, ekssudat og kogetab bestemt. Resultaterne for Warner-Bratzler peak force-målingerne viste, at høj-intensitet ultralyden ikke havde nogen signifikant mørnende effekt på yderlåret, samt at marineringen med kiwifrugtpulver kun resulterede i en numerisk stigning i mørheden. Resultaterne viste yderligere, at kombinationen af marinering med kiwifrugtpulver og høj-intensitet ultralyd resulterede i en signifikant fo, The objective of the current study was to investigate the combined effect of marination with kiwi fruit powder and high power ultrasound on tenderness of porcine M. biceps femoris. The hypotheses were that both high power ultrasound and marination with kiwi fruit powder would enhance tenderness, and the combined effect would maybe lead to a further increase in tenderness caused by a better distribution of the marinade by ultrasonication.Muscles (24 h post-mortem) were injected with kiwi fruit marinade to a 10 % weight increase and a final concentration of 0.075 % kiwi fruit powder. Subsequently, half muscles were vacuum packed and ultrasonicated for 40 minutes in an ultrasound bath (1 MHz, 150 W and 500 W, 25 kHz). Samples were cut and stored at 2°C for either 0, 2 or 7 days. Tenderness was investigated by Warner-Bratzler shear force analysis, where the parameters initial yield, peak force and final yield were determined. To explain effects on tenderness further analyses were conducted to investigate which fractions (myofibrillar and connective tissue fraction) that were affected by kiwi fruit marination and high power ultrasound. The activity of the proteolytic enzymes and the myofibril fragmentation were investigated, and structural components including F-actin, desmin, integrin, and collagen were investigated by immunofluorescence combined with confocal laser scanning microscopy. To investigate if kiwi fruit marination and high power ultrasound affected other meat quality characteristics, the pH, exudate, and cooking loss was also determined. Results of Warner-Bratzler peak force measurements revealed that high power ultrasound did not significantly enhance the tenderness of porcine M. Biceps femoris, and kiwi fruit marination only resulted in a numerical increase in tenderness. However, the combination of the treatments resulted in significantly increased tenderness. Results of Warner-Bratzler initial yield and final yield measurements indicated that the tenderi

Formålet med dette projekt var at undersøge den kombinerede effekt af marinering med kiwifrugtpulver og høj-intensitet ultralyd på mørheden af yderlår (M. biceps femoris) fra svin. Det var forventet, at både marinering med kiwifrugtpulver og høj-intensitet ultralyd ville resultere i en forbedret mørhed, samt at kombinationen af behandlingerne eventuelt ville resultere i en yderligere forbedring af mørheden pga. en bedre fordeling af marinaden forårsaget af ultralyden.Yderlår (24 h post-mortem) blev injiceret med kiwi-marinade til en tilvækst på 10 % og en koncentration af kiwifrugtpulver på 0,075 % i musklen. Efterfølgende blev halve muskler vakuum-pakket og ultralydsbehandlet i 40 minutter (1 MHz, 150 W og 500 W, 25 kHz). Prøver blev udskåret og opbevaret ved 2°C i henholdsvis 0, 2 og 7 dage. Mørheden blev undersøgt ved Warner-Bratzler shear force-analyse, hvor parametrene initial yield, peak force og final yield blev bestemt. For at forklare den forventede, mørnende effekt af marinering med kiwifrugtpulver og høj-intensitet ultralyd blev yderligere analyser foretaget for at undersøge, hvilke komponenter (myofibrillære eller bindevævs) der blev påvirket af behandlingerne. Analyserne omfattede bestemmelse af aktiviteten af de proteolytiske enzymer samt myofibrillær fragmentering. De struktur-relaterede proteiner F-aktin, desmin, integrin og collagen blev desuden undersøgt ved immunfluorescens kombineret med konfokal laserscanning-mikroskopi. For at undersøge om marinering med kiwifrugtpulver og høj-intensitet ultralyd påvirkede andre kvalitetsparametre, blev pH, ekssudat og kogetab bestemt. Resultaterne for Warner-Bratzler peak force-målingerne viste, at høj-intensitet ultralyden ikke havde nogen signifikant mørnende effekt på yderlåret, samt at marineringen med kiwifrugtpulver kun resulterede i en numerisk stigning i mørheden. Resultaterne viste yderligere, at kombinationen af marinering med kiwifrugtpulver og høj-intensitet ultralyd resulterede i en signifikant fo, The objective of the current study was to investigate the combined effect of marination with kiwi fruit powder and high power ultrasound on tenderness of porcine M. biceps femoris. The hypotheses were that both high power ultrasound and marination with kiwi fruit powder would enhance tenderness, and the combined effect would maybe lead to a further increase in tenderness caused by a better distribution of the marinade by ultrasonication.Muscles (24 h post-mortem) were injected with kiwi fruit marinade to a 10 % weight increase and a final concentration of 0.075 % kiwi fruit powder. Subsequently, half muscles were vacuum packed and ultrasonicated for 40 minutes in an ultrasound bath (1 MHz, 150 W and 500 W, 25 kHz). Samples were cut and stored at 2°C for either 0, 2 or 7 days. Tenderness was investigated by Warner-Bratzler shear force analysis, where the parameters initial yield, peak force and final yield were determined. To explain effects on tenderness further analyses were conducted to investigate which fractions (myofibrillar and connective tissue fraction) that were affected by kiwi fruit marination and high power ultrasound. The activity of the proteolytic enzymes and the myofibril fragmentation were investigated, and structural components including F-actin, desmin, integrin, and collagen were investigated by immunofluorescence combined with confocal laser scanning microscopy. To investigate if kiwi fruit marination and high power ultrasound affected other meat quality characteristics, the pH, exudate, and cooking loss was also determined. Results of Warner-Bratzler peak force measurements revealed that high power ultrasound did not significantly enhance the tenderness of porcine M. Biceps femoris, and kiwi fruit marination only resulted in a numerical increase in tenderness. However, the combination of the treatments resulted in significantly increased tenderness. Results of Warner-Bratzler initial yield and final yield measurements indicated that the tenderi