High pH Group Research Articles

Effect of delay time before chilling on toughness in pork with high or low initial pH

Paired M. longissimus dorsi muscles from 56 carcasses of Danish Landrace and Yorkshire breeds, slaughtered at approximately 90 kg live weight, were utilized to study the potential of cold induced toughness in pork. Based upon the pH value 45 min post stunning, the carcasses were divided in two groups: a low (5·7 ≤ pH < 6·1) and a high one (6·1 ≤ pH ≤ 6·5). The effects on Warner-Bratzler shear force, sarcomere length and myofibril fragmentation of inserting a delay time of 0, 2 and 4 h before carcasses entered the chilling tunnel (operating at −28°C to −22°C) were investigated on early excised muscles as well as on muscles removed 30 h post stunning. The left LD muscle from each carcass served as a control while all right sides were used for treatments. pH and temperature measurements obtained from LD muscles left on carcasses during chilling showed that LD muscles belonging to the high pH group involve a risk of cold shortening even when a 2 h delay was used before passing in to the chilling tunnel. Comparing pH groups, however, sarcomere lengths did not differ in control sides whereas the Warner-Bratzler shear force values were significantly higher in LD muscles taken from the high pH group. Early excision of the LD muscle resulted in shorter sarcomere lengths and increased WB shear force only for carcasses belonging to the high pH group, which, however, could be avoided by introducing a 4 h delay time before rapid chilling. The effect of delay time on tenderness from muscles excised from the carcass 30 h post stunning was much less but a 4 h delay did significantly (P < 0·05) improve tenderness in carcasses with high initial pH. Coefficient of correlation between Warner-Bratzler shear force and sarcomere length was −0·12 and nonsignificant in the low pH group, whereas it was −0·57 and highly significant in the high pH group.

Post-mortem processing of export beef in Costa Rica

Eighteen intact male beef animals of 2 1 2 to 3 years of age, weighing 400–425 kg and fed entirely on rangelands grass, were slaughtered in a Costa Rican export plant. Six animals each were assigned to: low-voltage stimulation (75V), high-voltage stimulation (350V) and control. Hot-boning coupled with various chilling rates was also investigated. Mean muscle pH values for all treatment groups were above 6·4 at 1 1 2 h after slaughter, which may be related to the fact the animals were intact males which had been exposed to stressful conditions prior to slaughter. Palatability traits measured were tenderness, juiciness, flavor and overall desirability. With the exception of tenderness, there were no significant differences among electrical stimulation or chill treatments, and there were no interactions. The low-voltage electrical-stimulation treatment produced less tender meat ( P<0·05) than the high-voltage treatment, but there was no significant difference compared to the control. In an attempt to explain the finding that electrical stimulation had little or no effect on tenderness, the data were inspected in regard to ultimate pH. The panel score for samples with an ultimate pH less than 6 was 3·27, and for samples with a pH higher than 6 it was 5·70. A possible explanation is to suggest that the high-pH group underwent appreciable neutral proteolytic enzyme activity compared to the low-pH group.

The pH of Cervical Mucus and the Postcoital Test

In this study, 25 women with 28-day cycles were considered for a total of 44 menstrual cycles. The women were subjected to the Sims-Huhner postcoital test at 6.2 hours after intercourse during the periovulatory period. Each couple was instructed to abstain from sexual intercourse for 4 days prior to the test. Samples of cervical mucus were obtained and evaluated for quantity, viscosity, elasticity, ferning, cellularity, pH, and the postcoital status of the spermatozoa (percentage motility and grade). The pH measurements were made by the use of phenaphthazine paper. After the establishment of the pH measurements the patients were divided into two groups (low and high pH) and statistically compared on the basis of the spermatozoal postcoital test results. The results obtained revealed significant differences (P < 0.01) between the low pH (less than or equal to 6.0) and high pH (greater than or equal to 6.1) groups with respect to percentage motility and grade of recovered spermatozoa. Ejaculate characteristics of the males corresponding to the two different pH groups showed no significant differences (P > 0.05).

Proton equilibria in the binding of Zn2+ and of methylmercuric iodide to papain.

The proton liberation on the binding of zinc chloride and methylmercuric iodide to the (essential) thiol group of papain has been examined as a function of pH. This was carried out by (a) direct titration of the protons on the addition of the metal compound to active papain and (b) measurement of the extent of inhibition of enzyme activity by the metal compound as a function of pH. It was found that in the neutral pH range the thiol group or the neighbouring imidazole group in the free enzyme carries one proton, at low pH both groups do so, whereas at high pH neither group carries a proton. The pK values of the free enzyme that govern the proton release, 4.2 and 8.5, correspond to those that govern overall activity. Both from the experiments with methylmercuric iodide and from fluorescence measurements of methylmercuric papain, it was established that the imidazole group in the latter compound exhibits a pK of 5.4. Taking recent data into account, it was considered that the ion pair of thiolate anion and imidazolium cation, proposed by Polgar, is the best approximation to describe the charge distribution in the active centre and to explain the reaction mechanism.