Véronique Santé-Lhoutellier

Effect of Meat Cooking on Physicochemical State and in Vitro Digestibility of Myofibrillar Proteins

The effect of meat cooking was measured on myofibrillar proteins from bovine M. Rectus abdominis. The heating treatment involved two temperatures (100 degrees C during 5, 15, 30, and 45 min and 270 degrees C during 1 min). Protein oxidation induced by cooking was evaluated by the level of carbonyl and free thiol groups. Structural modifications of proteins were assessed by the measurement of their surface hydrophobicity and by their aggregation state. With the aim of evaluating the impact of heat treatment on the digestive process, myofibrillar proteins were then exposed to proteases of the digestive tract (pepsin, trypsin, and alpha-chymotrypsin) in conditions of pH and temperature that simulate stomach and duodenal digestion. Meat cooking affected myofibrillar protein susceptibility to proteases, with increased or decreased rates, depending on the nature of the protease and the time/temperature parameters. Results showed a direct and quantitative relationship between protein carbonylation (p<0.01) and aggregation (p<0.05) induced by cooking and proteolytic susceptibility to pepsin. However, no such correlations have been observed with trypsin and alpha-chymotrypsin.

Variations in chicken breast meat quality: implications of struggle and muscle glycogen content at death.

1. Pectoralis major (P. major) muscle pH and meat quality traits were studied in relation to bird response to ante-mortem stress in three chicken lines: a fast-growing standard line (FGL), a slow-growing French ‘Label Rouge’ line (SGL) and a heavy line (HL). Ninety-nine birds of the three genetic types were slaughtered at their usual marketing age (6, 12 and 6 weeks for FGL, SGL and HL birds, respectively) on the same day. The birds of each line were divided into three different ante-mortem treatment groups: minimum stress (shackling for 10 s) (C), shackling for 2 min (SH) and acute heat plus shackling stress (exposure to 35°C for 3·5 h and shackling for 2 min before stunning) (H + SH). 2. Regardless of chicken line, wing flapping duration (WFD) between hanging and stunning was strongly negatively related to P. major muscle pH at 15 min post-mortem. It was also moderately negatively related to P. major muscle glycolytic potential (GP), which represents glycogen level at death. Increasing WFD induced an increased ultimate pH (pHu) only in HL. The consequences of increased WFD for breast meat traits were dependent on the chicken line: it induced lower L* and b* and higher a* and drip loss in SGL while it only increased breast a* in HL birds. By contrast, WFD variations did not alter breast meat quality traits of FGL birds. Regardless of the chicken line, increased GP was associated with lower pHu and higher L* and drip loss. In SGL, it also increased b* and decreased curing–cooking yield of breast meat. 3. Struggling activity on the shackle line and muscle glycogen content at death could partly explain line and pre-slaughter variations in breast meat pH and quality traits. The water holding capacity of the raw and cooked meat was impaired by long shackling in the case of SGL birds while it was barely affected by ante-mortem conditions in the two standard lines. In conditions which minimised bird struggling (C), SGL and FGL birds had meat with a better water holding ability than that of broilers from the heavy line. However, when broilers were subjected to SH or H + SH conditions, the breast meat water holding capacity of SGL birds was lowered to the same level as that of the heavy line birds.

Technical note: A simplified procedure for myofibril hydrophobicity determination.

A simple and reliable method for the determination of surface hydrophobicity of nonsolubilized myofibrils (from pig M. longissimus dorsi) was developed and validated. This method is based on the interaction of the hydrophobic chromophore bromophenol blue (BPB) with myofibrillar proteins and the separation of free and bound BPB by centrifugation. The titration of bound BPB is performed by absorption spectroscopy, and the amount of bound BPB is considered as an index of protein hydrophobicity. Heating, which is known to increase protein hydrophobicity, was performed in order to validate this method. Fixation of BPB to myofibrils increased with heating time and temperature, strongly suggesting that it may be closely related to protein hydrophobicity.

Chicken meat quality: genetic variability and relationship with growth and muscle characteristics

BackgroundThe qualitative properties of the meat are of major importance for poultry breeding, since meat is now widely consumed as cuts or as processed products. The aim of this study was to evaluate the genetic parameters of several breast meat quality traits and their genetic relationships with muscle characteristics in a heavy commercial line of broilers.ResultsSignificant levels of heritability (averaging 0.3) were obtained for breast meat quality traits such as pH at 15 min post-slaughter, ultimate pH (pHu), color assessed by lightness L*, redness a* and yellowness b*, drip loss, thawing-cooking loss and shear-force. The rate of decrease in pH early post-mortem and the final pH of the meat were shown to be key factors of chicken meat quality. In particular, a decrease in the final pH led to paler, more exudative and tougher breast meat. The level of glycogen stored in breast muscle estimated by the Glycolytic Potential (GP) at slaughter time was shown to be highly heritable (h2 0.43). There was a very strong negative genetic correlation (rg) with ultimate meat pH (rg -0.97), suggesting a common genetic control for GP and pHu. While breast muscle weight was genetically positively correlated with fiber size (rg 0.76), it was negatively correlated with the level of glycogen stored in the muscle (rg -0.58), and as a consequence it was positively correlated with the final pH of the meat (rg 0.84).ConclusionThis genetic study confirmed that selection should be useful to improve meat characteristics of meat-type chickens without impairing profitability because no genetic conflict was detected between meat quality and meat quantity. Moreover, the results suggested relevant selection criteria such as ultimate pH, which is strongly related to color, water-holding capacity and texture of the meat in this heavy chicken line.

Proteome changes during pork meat ageing following use of two different pre-slaughter handling procedures.

The influence of postmortem storage time and pre-slaughter conditions (transport the day before slaughter or immediately before slaughter) on proteome changes of pork meat was investigated over a 72 h ageing period. Intensities of 37 spots varied significantly (p<0.05) with ageing time. Changes indicated proteolysis of troponin T, actin, α-crystallin, myokinase, creatine kinase and mitochondrial ATPase, but also of proteins constitutive of the Z-lines, namely cypher proteins and myozenin. Other modifications were the intensity increase of a full-length protein of the sarcoplasmic reticulum, which may be linked to its increased extractibility after membrane disruption, and a gradual shift in pHi towards alkaline values of some forms of myosin light chains (MLC) 2 and 3. The pre-slaughter conditions affected significantly (p<0.05) 8 spots. Mitochondrial ATPase was over-expressed in the group transported immediately before slaughter, also characterised by a faster pH fall, and the shift in pHi of MLC 2 was more pronounced. The pre-slaughter conditions had no significant effect on the above proteolytic events.

Behavioural and physiological responses of three chicken breeds to pre-slaughter shackling and acute heat stress.

1. The aim of this study was to compare the behavioural and physiological responses to hanging and acute heat stress in three different chicken breeds. Chicks were obtained from a slow-growing French ‘Label Rouge’ line (SGL), a fast-growing standard line (FGL) and a heavy line (HL). The SGL, FGL and HL birds were slaughtered at their respective market ages of 12, 6 and 6 weeks, in an attempt to achieve similar body weights. Before stunning, birds were either shackled by their legs on the moving line for 2 min (shackling stress: SH) or placed in a room at 35°C and 60% of humidity for 3·5 h and then shackled for 2 min (acute heat stress plus shackling: H + SH) or subjected to minimal stress by shackling for 10 s before stunning (control group: C). 2. Bird physiological responses to the three pre-slaughter treatments were estimated by measuring blood corticosterone, glycaemia, creatine kinase activity, acid–base status and electrolyte concentration as well as lactate content and glycolytic potential in the breast (Pectoralis major) and thigh (Ilio tibialis) muscles. Behavioural responses to shackling stress were evaluated by measuring wing flapping duration, straightening up attempts and vocalisations. 3. Blood corticosterone was higher in SH and H + SH groups than in the C group, regardless of genotype. The struggling activity on the shackle line differed among chicken breeds. It was more intense and occurred more rapidly after hanging in the SGL birds than in both other breeds. Furthermore, SGL struggling activity was not affected by hanging duration while it increased with hanging duration in FGL and HL birds. 4. Wing flapping duration was negatively correlated with blood pH, bicarbonate concentration and positively correlated with breast muscle lactate content, indicating that struggling stimulated ante-mortem glycolysis activity in breast muscle. Acute heat stress affected blood Ca2+ and Na+ concentration and increased glycaemia and glycolytic potential of thigh muscle. 5. Both acute heat stress and shackling before slaughter were experienced as stressful events by all types of birds.

Cooking temperature is a key determinant of in vitro meat protein digestion rate: investigation of underlying mechanisms.

The present study aimed to evaluate the digestion rate and nutritional quality of pig muscle proteins in relation to different meat processes (aging, mincing, and cooking). Under our experimental conditions, aging and mincing had little impact on protein digestion. Heat treatments had different temperature-dependent effects on the meat protein digestion rate and degradation potential. At 70 °C, the proteins underwent denaturation that enhanced the speed of pepsin digestion by increasing enzyme accessibility to protein cleavage sites. Above 100 °C, oxidation-related protein aggregation slowed pepsin digestion but improved meat protein overall digestibility. The digestion parameters defined here open new insights on the dynamics governing the in vitro digestion of meat protein. However, the effect of cooking temperature on protein digestion observed in vitro needs to be confirmed in vivo.

EFFECT OF ANIMAL (LAMB) DIET AND MEAT STORAGE ON MYOFIBRILLAR PROTEIN OXIDATION AND IN VITRO DIGESTIBILITY

Effect of pasture- or concentrate-diet on myofibrillar protein oxidation and in vitro digestibility was measured in lamb meat (M. longissimus dorsi) during a refrigerated storage of 7days under gas permeable film. Protein oxidation was measured by the carbonyl content determined chemically using 2,4-dinitrophenylhydrazine (DNPH) and specific targets of oxidation were identified by immunoblotting. Carbonyl content significantly increased during storage and diet affected protein oxidation where animals fed concentrate showed higher carbonyl group levels than animals fed pasture. To evaluate effect of diet and storage time on protein digestibility, myofibrillar proteins were exposed to proteases of the digestive tract (pepsin, and a mixture of trypsin and α-chymotrypsin) in conditions of pH and temperature which mimic digestive process. The myofibrillar protein digestibility was not influenced by the diet. Storage time had no significant effect on myofibrillar protein susceptibility to pepsin while an important increase in digestibility by trypsin and α-chymotrypsin was detected during storage.

Extraction, fractionation and functional properties of proteins from the microalgae Chlorella vulgaris

This paper deals with the extraction and emulsifying properties of proteins from Chlorella vulgaris. Solubilisation of proteins has been achieved using high pressure cell disrupter under pH=7 or pH=12. The higher solubilisation yield (52±3%w/w) was obtained using a combination of alkaline conditions and mechanical treatments (2.7kbar). After solubilisation, proteins were recovered by two procedures: precipitation in acid media and concentration/fractionation by tangential ultrafiltration. Proteins were analysed for their molecular weights, isoelectric points and amino acids compositions and their emulsifying properties were quantified and compared to those of commercial ingredients. In spite of lower yield, better emulsifying capacity was obtained when protein solubilisation takes place at pH=7 and when using proteins from permeate of tangential ultrafiltration. In all cases, emulsifying capacity (1780±20 and 3090±50mLoil/g protein) and stability (72±1% and 79±1%) of microalgae proteins remained comparable or higher than the commercial ingredients such as sodium caseinate.

Pig Longissimus lumborum proteome: Part II: Relationships between protein content and meat quality

Gender, rearing environment and breed of sire influenced 50.5% of the matched protein spots of the soluble fraction and some meat quality traits [Kwasiborski, A., Sayd, T., Chambon, C., Santé-Lhoutellier, V., Rocha, D., & Terlouw, C. (2008). Muscle proteome in pigs: Part I: Effects of genetic background, rearing environment and gender. Meat Science]. Multiple regression analyses determined that 1 or 2 proteins explained between 24% and 85% of variability in Longissimus meat quality. Regression models differed between treatment groups, but relationships between proteins and meat quality traits seemed to be related to common underlying mechanisms. Thus, proteins retained in models for ultimate pH, lightness, drip, thawing and cooking loss were related to the glycolytic pathway, phosphate transfer, or fibre type composition. Another model for thawing loss retained proteins related to denaturation of myofibrils or lipid content. The models for redness involved proteins related to post-mortem oxidative activity. Thus, proteins correlated with meat quality traits were related to biochemical mechanisms known to be involved in meat quality. Relative contributions of these mechanisms may vary according to gender, sire breed or rearing environment.