Study of meat qualities directly or indirectly related to mitochondria
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- Master's theses (KBM) 
Forty-one M. semimembranosus (S.M.) muscles of beef were collected from the local slaughterhouse in Norway (part I) for the study of meat quality and color stability. All the slaughter variables like pH, weight, temperature, fat content, animal group and so on were recorded. Piece B (cut from proximal side of S.M.) and Piece A (cut from distal side of S.M) were vacuum packaged in the slaughter house and were left for 3weeks in chilling room for maturation. A big S.M muscle (~5kg) was divided into various pieces for measurements that were carried out the in slaughterhouse, namely; pH, mitochondrial isolation, permeablization and oxygen consumption rate (OCR). Further measurements of the pieces were followed up three weeks later at our lab in IKBM, namely; tenderness, drip loss and cooking loss (using both piece A and B) and, color stability and OCR(using tissue from piece B). A small piece of S.M and Longismus dorsi (L.D.) muscle was used for pH measurements at time t0 (~4hrs postmortem), t1 (~8hrs postmortem) and t2 (~4hrs postmortem) with three replicate at different positions each time. Results from tenderness measurement showed that SM piece at proximal end (Piece B) was tendered than the distal end (Piece A). The rate of pH decline was different between the collected samples from number 1-20 and from 21-41. Most of the samples had good and acceptable amount of combined drip and cooking loss. Oxygen consumption rate (OCR) was measured on permeabilization fibers after 3weeks vacuum and chilled storage of the muscle. Similarly our results showed that, OCR could had some prediction ability for classifying the tender and tough group of Piece B from sample 21-41 but not for the 1-20 sample group. Regression of OCRs and WB values showed that removal of oxygen from the electron transport chain has a positive effect on tenderness. For the spectral measurements of 3 weeks stored muscle, a calibration model (part II-taken from paper (I)) for myoglobin state was required. Fresh S.M muscles (vacuum packaged 4 days postmortem) were prepared to have deoxy (DMb), oxy (OMb) and metmyoglobin (MMb) state using Chemically induced myoglobin states (CHEM) method and oxygen partial pressure packaging (OPP) method. Absorbance spectra (400-1100nm) were made on the 24 sample surface (8 samples for each myoglobin state) with 4 replicate readings at different positions of each sample for each preparation method (OPP and CHEM). Absorbance spectra were transformed by using different ways like using Kubelka-Munk (K/S) and extended multiplicative signal correction (EMSC). Calibration and validation model were made from transformed spectra by using either selected wavelengths (SW) or partial least square (PLS) regression. Post-transformation steps were used to normalize the myoglobin states so that, none of them were larger than one or negative and ensured that, sum of three states was not more than one at particular time. Low Root mean square error of cross validation (RMSECV) and high correlation coefficient (Rc) was used as criteria to choose the best calibration model for myoglobin states. Use of OPP preparation method with EMSC transformation and PLS regression on absorbance gave the best model for calibration. The color stability of 3 weeks stored S.M muscle (Part III) were measured at different times from 0-7 days using absorbance spectra (400-1100nm) and L*, a* and b* values. The calibration models were used to predict the change in myoglobin states after exposure to atmosphere using the absorbance spectra for all samples. N-partial least square (N-PLS) regression between variations in L*a*b* values and myoglobin states to OCR was carried out. The DMb concentration predicted from the calibration model decreased with time and indicated that with an increase in time of exposure to atmosphere, DMb first transforms transiently to OMb and then to MMb, whose level rose concomitantly. The change in a* values with time and OCR were highly related. It was found that pH t0 and pH t1 are important for color stability of the meat. In three weeks stored muscle, complex II of mitochondria was the most stable complex in the electron transport system and often the only viable site for accepting reducing equivalents, therefore color stability could be related to its activity. In conclusion, the activity of mitochondrial enzymes could be well related to color stability and also to tenderness for a subset of muscles that were characterized by a slower drop in pH early post mortem. No relation between mitochondrial enzyme activity and drip loss and cooking loss was found.
This thesis contains are divided into three parts with one introduction for all. Two papers were written and has been submitted but not yet published to the Journal of meat science based on this thesis. those papers are also attached after appendix.