RELATIONSHIP BETWEEN METABOLISM AND GLYCOGEN CONTENT IN SKELETAL MUSCLE FIBERS OF LARGE WHITE AND HAMPSHIRE CROSSBRED PIGS

Glycolytic potential (an estimator of intra vitam glycogen level) was determined at slaughter in the M. longissimus lumborum muscle from 6 Large White pigs and 6 Pen Ar Lan pigs (Pen Ar Lans are Hampshire × Pietrain × Large White crossbred pigs). Muscle samples (M. longissimus lumborum) were taken at slaughter and 24 h later. Muscle glycolytic potential was much higher in Pen Ar Lans than in Large Whites. Samples were cut at – 25°C for histochemistry. Serial cuts were stained for ATPase activity, succinate dehydrogenase activity     

ULTIMATE pH EXPLAINS VARIATION IN PORK QUALITY TRAITS

The objective of this study was to determine the relationship between pH and fresh pork quality. Pigs ( n =  988) were harvested at one plant on 6 days over a 2-month period. Loin pH was recorded at 45 min, and 3 and 24 h postmortem. Loins ( n =  840) were classified based on ultimate pH into four categories: low ( ≤ 5.44), low/normal (5.45–5.74), high/normal (5.75–6.04) and high ( ≥ 6.05). A majority of loins (53.3%) were classified as low/normal, while only 1.3% were classified as low. It was confirmed that 24 h pH was the best predictor of key meat quality traits because 45 min and 3 h pH accounted for less than 5% of the total variation in quality traits. The pH at 24 h postmortem is the best predictor of quality of the three time points tested in this population, because it accounted for over 10% of the variation in several quality attributes.

PRACTICAL APPLICATIONS

Ultimate pH is becoming more widely used in industry applications to segregate carcasses prior to fabrication. The pH has been linked to several important attributes of pork quality, including water-holding capacity, tenderness and color. While it has been suggested that the pH measured at earlier time points postmortem can be used to predict pork quality, the results of this study suggest that the pH at 24 h postmortem is the best predictor of these characteristics. The addition of 45 min or 3 h pH is of little predictive value for meat quality characteristics in this population. While 24 h pH accounts for some variability in pork quality attributes, more work is still needed to determine factors impacting the quality of pork.     

GENETIC AND ENVIRONMENTAL VARIATION OF GUM CONTENT IN BARLEY

The influence of genetic vs environmental factors on the gum content of the barley grain has been studied by growing 4 varieties of barley, at 4 locations in the South of Spain, with 6 sowing dates at each location. The genetic factors proved to be the more important, accounting for 89% of the variation over locations and 71·5% of the variation among locations and sowing dates. Of the environmental factors studied, the sowing date was the most important. The variety × sowing date interaction was also statistically significant. Furthermore, the later the sowing date the higher the gum content of the grain. There was no variety × location interaction and, therefore, the varieties ranked in the same order at each location. It was also demonstrated that there was a different pattern of response for the varieties when grown in environments which were able to induce high or low gum content, suggesting that low gum content-low response varieties should be grown if the grain is to be used as an adjunct in brewing.     

VARIATION IN THE SELENIUM CONTENT OF INDIVIDUAL BRAZIL NUTS

Brazil nuts are high in selenium content relative to other human foods. Since the limits between human selenium essentiality and toxicity are narrow, it is important to know the variation in selenium content of individual nuts. Analysis was performed on 72 individual nuts obtained in stores as shelled nuts in bulk and shelled and unshelled nuts in packages. Their average selenium content was 14.66 ppm with a range of 0.2 to 253.0. The agronomic and health aspects of these findings are discussed.     

DEGRADATION OF ATP AND GLYCOGEN IN COD (GADUS MORHUA) MUSCLE DURING FREEZING

Changes in ATP, IMP, lactate and glycogen contents in the muscle of cod were followed during freezing at temperatures of ?20C and ?45C. ATP degradation was accompanied by a corresponding increase in IMP content. Simultaneous measurement of temperature showed that at both freezing rates, the greatest decrease in ATP content was observed when the temperature reached ‐0.8C. Glycolysis occurred during freezing of cod as indicated by an increase in lactate content. The changes found in all measured metabolites were more pronounced when freezing was performed at a slow rate compared to a fast rate due to the thermal arrest time at about 0.8C.     

ROLE OF INITIAL MUSCLE pH ON THE SOLUBILITY OF FISH MUSCLE PROTEINS IN WATER

The solubility of the myofibrillar and cytoskeletal proteins in water was determined for the muscle tissue often species offish. The flesh of six white-muscled fish had pH's at the time of processing above pH 6.6 and greater than 80% of their myofibrillar/cytoskeletal proteins were soluble in water. The flesh of three pelagic species and a shark had pH values when processed below 6.6 and the water solubility of their myofibrillar and cytoskeletal proteins was less than 40%. When the washed minced muscle of one of the white-fleshed species, cod, was exposed to low pH, the solubility of its myofibrillar and cytoskeletal proteins decreased substantially. The water solubility of the cod myofibrillar and cytoskeletal proteins could be reestablished by washing the acid-treated cod flesh with neutral salt solutions. It is suggested that pH values below 6.6 modify certain proteins which prevent the water-extractability of the rest of the myofibrillar and cytoskeletal proteins from being expressed.     

EFFECT OF ULTIMATE pH UPON THE WATER-HOLDING CAPACITY AND TENDERNESS OF MUTTON

SUMMARY— Ultimate pH values in the musculature of sheep ranging from 5.6–7.0 have been obtained by using pre-slaughter injections of epinephrine. A high speed centrifugal method was used to measure the water-holding capacity of raw M. semitendinosus (ST), semimembranosus (SM) and biceps femoris (BF). Results showed a high correlation with ultimate pH. Cooking losses end the amounts of centrifugally expressed juice were determined for the SM and BF cooked for 1 hr at either 65°C or 90°C. Cooking losses at 65°C decreased linearly with increasing pH while the losses at 90°C showed little change up to o raw meat pH of ca. 5.9, then decreased linearly with increasing pH. The amount of juice centrifugally expressed from the cooked meat, which has a high positive correlations with organoleptic juiciness, increased linearly with pH. Tenderness of the cooked SM and BF muscles was measured using o Warner-Bratzler shearing device and an Instron Universal Testing Machine: both gave high objective-subjective correlations. Instron measurements have high negative linear correlations with ultimate pH for both the 65°C and 90°C cooked samples. Hardness of these muscles, cooked at 65°C or 90°C. decreased approximately three-fold as ultimate pH increased from 5.6–6.9. Results obtained using the Warner-Bratzler device showed linear regressions with a significant quadratic component for one muscle at both 65°C and 90°C.     

METABOLISM AND HISTOCHEMISTRY OF SKELETAL MUSCLE FROM STRESS-SUSCEPTIBLE PIGS

The metabolism and histochemical characteristics of muscle from stress-susceptible and stress-resistant animals were studied. ATP values were. higher and lactic acid values lower in muscle of stress-resistant animals than stress-susceptible animals at the time of exsanguination. Results from oxygen uptake studies revealed that muscle from stress-susceptible animals had a lower ability for aerobic metabolism or alternatively was more labile to damage during the isolation procedure. Our oxygen uptake values for pig muscle were lower than those reported for muscle from other species. The muscle from stress-susceptible animals, when incubated under anoxic conditions, produced more lactic acid than did muscle from stress-resistant pigs under conditions where the muscle from both types of animals had similar CP and ATP levels. Samples for histochemical analysis were examined from restrained and unrestrained muscle strips. There was a trend for the restrained samples to have somewhat smaller fibers. The muscle fiber size from Poland China animals was greater than that from Chester White animals. A large number of intermediate-type fibers, on the basis of DPNH-TR and phosphorylase staining, were found in the muscle of stress-susceptible animals.     

THE DETERMINATION OF GLYCOGEN IN YEASTS

Four methods for the determination of glycogen in yeast have been compared in five strains of Saccharomyces cerevisiae over a range of glycogen contents. A new method has been developed which is specific, precise and more exhaustive than previously published procedures. After extraction with sodium carbonate and perchloric acid, the glycogen was hydrolysed with amyloglucosidase to glucose, which was estimated enzymically. The greater extraction of glycogen using this method cannot be explained by acid hydrolysis of glucans prior to treatment with amyloglucosidase. Further, the older data using the non-specific methods can now be equated with values obtained using a specific method.     

A REVIEW OF SENSORY AND INSTRUMENTAL METHODS USED TO EVALUATE THE TEXTURE OF FISH MUSCLE

The texture of fish muscle is an important quality attribute that depends on several parameters, both intrinsic and extrinsic. Its evaluation by sensory means is the result of a combination of several parameters that cover every impression from when the fish first comes into contact with a surface in the mouth, until it is completely masticated. This makes texture difficult to describe and evaluate. In addition the muscle structure of fish is not homogenous, and this has important implications on texture measurements by instrumental means. Numerous instrumental and sensory methods have been used to evaluate the texture of fish and fish fillets, with varying results and there exists no universal recommended method.     

VARIATION OF CELL WALL CONTENT IN FLOCCULENT AND NON-FLOCCULENT YEAST STRAINS

Estimation of the wall content of a number of flocculent and non-flocculent yeast strains taken in both the growth and stationary phases reveals that flocculent yeasts almost invariably increase their wall content to a greater extent as the cells pass to the stationary phase than do non-flocculent strains. This variation of increase is observed whether the yeasts are grown in hopped wort or in a synthetic malt-yeast-peptone-glucose medium. There are considerable variations in wall content from strain to strain in both types of yeast. Cells of flocculent strains are more difficult to disrupt than those of powdery strains. The nitrogen, phosphate and carbohydrate contents of the walls of all strains varied between the growth and stationary phases but no significant trends were noted in any of the components which could be related to flocculent or non-flocculent behaviour.     

黄曲霉生长预测模型的建立及毒素含量变化

黄曲霉在适合条件下易污染储藏的粮食、饲料，产生对人畜有害的黄曲霉毒素。用两种模型模拟黄曲霉的生长规律，测定了黄曲霉毒素含量的变化情况，初步探索了二者之间的关系，并为风险评估提供了数据基础。     

MUSCLE CONTRACTION AND POSTMORTEM pH CHANGES IN PIG SKELETAL MUSCLE

SUMMARY– The initial (5 min) pH of longissimus dorsi muscle taken from live pigs under anesthesia was 7.0; in muscle taken immediately after slaughter it was 6.3. When the neuromuscular blocking agent, curare, was given intramuscularly before slaughter the initial pH was raised to 6.8. The gastrocnemius muscle was stimulated to contract via the sciatic nerve in vivo and the pattern of pH change compared with that of the unstimulated muscle in the other side of the animal. Stimulation caused a fall in initial pH and an acceleration in the subsequent rate of pH fall in the excised muscle under nitrogen at 37°. It was concluded that neural stimuli entering the muscle at the time of death were the major factors involved in the rapid postmortem glycolysis observed in the pigs studied.