Analysis And Assessment Of Chilled Pork Color And Its Color Stability

The paper is consisted of four chapters. In chapter I , color, temperature, pH of muscle longissimus dor si of chilled pork were surveyed and their correlations were studied, chapter II focused on objectively assessing chilled pork color by instrumental measurement and digital image processing. The color stability of chilled pork from PSE , Normal, DFD muscles during refrigerated storage were comparatively studied in chapter III and the mechanisms for their different color stabilities were intensively explored in chapter IV.Chapter I : The objectives of this study were to determine a pork carcass population in term of color ,temperature, pH of the muscle longissimus dor si and thereafter assign pork carcass population into different pork quality groups; to determine the correlations among, color ,temperature, pH. 500 pork carcasses under conventional cooling method were selected randomly and data collected on these carcasses' longissimus dor si muscles included measurements of pH45min,T45min,pH24h ,T24h, instrumental color features (L*, a*, b*, Chroma , Hue angle) and sensory color scores . Frequency distributions of the above parameters and their correlations were calculated and analyzed; and all the carcasses were classified into three quality groups of PSE, RFN, DFD based on given standards. The results showed a* values were normally distributed whereas the values of L* , pH43min, T45min,pH24h,b*,Chroma,Hue angle, sensory score and T24h (not shown)were all abnormally distributed (p < 0.05) .The percentage of PSE pork in all 500 carcasses was 18.6% and that of RFN pork and DFD pork were 80.4% and 1.0% respectively. T45mjn was correlated(p < 0.01) with pH45min(-0.370),L*(0.445)and sensory score(-0.389); pH45min was correlated(p < 0.01) with pH24h (0.427), L* (-0.468 ), Hue angle (-0.415) and sensory score (0.455); pH24h wascorrelated(p< 0.01) with L* (-0.415), a* (-0.358) , b* (-0.453), Hue angle (-0.475) and sensory score (0.439); Sensory score was correlated(p < 0.01) with L*(-0.802), Hue angle(-0.724), b*(-0.629) but not correlated with a*, Chroma (p,0.05) . Carcass cooling regime (conventional cooling method and two-stage rapid cooling method) was designed to comparatively study its effects on pork quality. 240 pork carcasses for each cooling method were selected and their longissimus dorsi muscle pH and temperature were measured during cooling period and another 200 carcasses for two-stage rapid cooling method were classified into three quality groups of PSE, RFN, DFD based on given standards. Temperatures of longissimus dorsi muscles at the same early post mortem time were significantly reduced(p < 0.05)and pH values dropped slowly in the two-stage rapid cooling method . 12.0% of the 200 pork carcasses cooled through the two-stage rapid cooling method were classified into PSE pork group, lower than 18.6% through the conventional cooling method ; 87.0% into RFN pork group ,higher than 80.4% in the conventional cooling method and 1.0% into DFD pork group, equal to the number (1.0%) from the conventional cooling method. The results indicated two-stage rapid cooling method could reduce the incidence of PSE pork, thus improve pork color.Chapter II: To objectively assess chilled pork color by instrumental measurement and digital image processing, pork carcass longissimus dor si muscles were cut at 3-4th rib and blooming for 60min. The surface color features (L*, a*, b* , Chroma, Hue angle) were measured by instrument chromameter and the surface sensory color scores were evaluated by 6 panelists thereafter. Digital images were captured by digital camera and processed to extract image color features (as above). Color features from 80 carcass longissimus dorsi muscles were used to establish color score prediction models by stepwise regression and BP artificial neural net work(ANN) and the prediction models were evaluated comparatively. The results showed the color score prediction model (stepwise regression)based on image color features from digital image processing was better than any others and its predicti...