Effect of pH(24), NaCl content and proteolysis index on the relationship between water content and texture parameters in biceps femoris and semimembranosus muscles in dry-cured ham

The aim of the present study was to determine the effect of pH level and NaCl content on the relationship between water content and texture parameters in semimembranosus and biceps femoris muscles in dry-cured ham. The experiment was undertaken using 18 hams, selected in a commercial slaughterhouse. Half of the hams had a pH<5.7 and the rest a pH>6.2, measured in the semimembranosus muscle at 24-h post mortem (pH(SM24)). The hams were treated with 20, 50 or 80g of NaCl per kg of ham. At the end of the aging process nine samples from semimembranosus and biceps femoris muscles were dried to different levels of water content covering the range from 22.4% to 58.5%. At the end of the drying period, a Texture Profile Analysis was used to determine textural parameters. Samples from biceps femoris muscle and samples from hams with low pH(SM24) showed a higher proteolysis index (100×non-protein nitrogen/total nitrogen) than samples from semimembranosus muscle and samples from hams with high pH(SM24), respectively. The proteolysis index decreased when the added NaCl amount increased. The proteolysis index was the parameter that best explained the modifications in the relationship between water content and the texture parameters (hardness, cohesiveness and springiness) of dry-cured ham muscles and it would be considered in order to predict the texture in dry-cured ham at different drying levels. Dry-cured hams with a lower proteolysis index were more prone to present harder texture at low water contents, which is typical of hams with crustiness problems.     

Time course of peptide fingerprints in semimembranosus and biceps femoris muscles during Bayonne ham processing

The aim of this work was to define reliable markers of muscle and processing time in dry-cured ham using a rapid, precise semi quantitative method for the protein fraction soluble in low ionic strength buffer. For this purpose protein labchip Agilent was used to separate proteins and peptides and accurately determine their molecular weights and concentrations electrophoretically. In this way the protein fingerprinting of dry-cured ham at different process times was characterised, together with targets and products of proteolysis. In addition, the comparison of all the electrophoregrams indicated muscle and dry-curing process markers.     

Lipolysis in dry-cured ham maturation

Thirty light Parma hams were tested for muscle lipolytic activity (acid and neutral lipase activity) and free fatty acid (FFA) amounts in M. semimembranosus and biceps femoris, during progressive phases (0, 3, 6, 10 months) of dry-cured ham manufacturing. No correlation was found between the activities of acid and neutral lipases in fresh M. semimembranosus, while during processing the activities were positively related (p<0.1), probably due to effects of muscle composition changes on lipolytic activities. In each processing step tested, acid lipase activities were higher in the M. semimembranosus than in the M. biceps femoris, and FFA amounts varied accordingly, the only exception being for the very dehydrated 10-month old M. semimembranosus, which yielded lower FFA than in the corresponding M. biceps femoris. FFAs in the end product correlated positively with acid and neutral lipase activities of green ham, suggesting that FFA production could be influenced by both raw meat properties and muscle composition during processing.     

RELATIONSHIPS BETWEEN MUSCLE TISSUE CHARACTERISTICS AND SENSORY QUALITIES OF DRY-CURED HAM

Forty dry-cured hams were identified at the end of 9 months processing. The Biceps femoris was analyzed for dry matter, pH, protein, lipids, acid value, hydroxyproline, Cl^-, pigment, glycogen, lactic acid and protein fractions, and average diameter and metabolic type of fibers. Sensory analysis involved color scoring on a whole slice of ham; assessment (by sniffing) of the acceptability on the semimembranosus of all 40 hams; and evaluation of odor, texture, taste and aroma on the biceps femoris of 26 hams. Among the traits under study, dry matter, glycogen, lactic acid, Cl^- and pH appeared as the most important determinants of sensory qualities of dry-cured ham. High levels of glycogen, lactic acid and Cl^- and low pH were associated with dry texture and high intensity of dry ham and cured meat aroma. The other components studied revealed scarce and generally low correlations with sensory traits.     

Proteomic profile of dry-cured ham relative to PRKAG3 or CAST genotype, level of salt and pastiness

Two-dimensional electrophoresis was used to compare dry-cured biceps femoris insoluble protein fraction according to genotype (PRKAG3Ile199Val and CASTLys249Arg/Ser638Arg) as well as salt and pastiness level. The PRKAG3 affected mainly muscle metabolic enzymes, indicating its possible influence on muscle metabolism with heterozygotes Ile/Val appearing different from both homozygous genotypes. The effect of CAST was smaller, affecting the quantity of one actin fragment. Dry-cured ham salt and pastiness level affected a wide variety of protein spots including metabolic enzymes, plasma proteins, chaperones and myofibrillar proteins, including protein fragments, indicating the connection with proteolysis. Pastiness was associated with salt content, reflected also by the fact that many spots were affected by both factors. Despite the absence of extreme pastiness (or low salt samples), some protein spots (actin, MHC fragment, desmin fragment) exhibited important differences in intensity according to pastiness (and salt level) suggesting they could be used as potential quality markers.     

云南干腌火腿加工过程中肌肉组织理化特性和氧化稳定性研究

云腿是我国一类重要的传统肉制品。研究通过对加工过程中的云腿肌肉组织进行理化指标测定,初步确定了云腿的理化特性和氧化稳定性。结果显示随着加工工艺的进行,云腿肌肉组织中pH缓慢上升,aw值逐渐下降。股二头肌和半膜肌中的食盐含量分别增加到7.94%和6.75%。水分含量到了平衡期之后快速下降,蛋白质和脂肪含量相对增加。肌内脂肪和蛋白质氧化持续进行,但是总体上处于较低的氧化水平。TBARS值先增加后降低,半膜肌中的蛋白质氧化程度强于股二头肌。     

复合精油涂层对干腌火腿挥发性风味品质的影响研究

采用电子鼻法分析复合精油涂层对火腿风味品质的影响,并通过气相色谱-质谱联用技术研究其对火腿半膜肌及股二头肌中挥发性风味物质组成的影响。电子鼻结果表明,复合精油涂层能提高火腿半膜肌中芳香类、烷烃类、萜烯类化合物的风味特征,且能降低含氮类、有机硫化物类化合物的风味特征,而股二头肌中风味特征无明显变化。GC-MS分析结果表明,在半膜肌中,除酮类风味物质外,涂层组的风味物质数量均高于未涂层组,而多出的风味物质种类分别为烃类5种、醇类2种、酯类1种、酸类3种、醛类1种、其他类2种;增加诸如1-辛烯-3醇、2-甲基-1-丁醇、3-甲基丁醛、2-辛烯醛等特征性风味物质的相对含量;复合精油涂层对火腿股二头肌中挥发性风味化合物种类数量及相对含量均无显著(p>0.05)影响,这是由于涂层中的植物精油无法渗透至股二头肌,从而无法对股二头肌的风味产生影响。因此复合精油涂层对提高火腿半膜肌风味品质有明显的促进作用,可以用于干腌火腿的风干成熟中。     

CHEMICAL, COOKING AND TEXTURAL PROPERTIES OF SEMIMEMBRANOSUS, SEMITENDINOSUS AND BICEPS FEMORIS MUSCLES OF PORK

The chemical, cooking and physical properties of semimembranosus, semitendinosus and biceps femoris of ham were determined. Significant differences in fat content of muscle and force required to penetrate the ham samples from the three muscles were found. No significant differences among three muscles in other properties were noted. A statistically significant correlation (r=-0.54) existed between the fat content of muscle and force required to penetrate the ham sample. Expressible juice from the muscles was significantly related to the cook loss and yield of hams. The moisture content of hams was also negatively related to the expressible juice. The possible mechanisms for these correlations are related to the ability of porcine muscles to chemically bind moisture during the cooking processes.     

Proteomic analysis of water soluble and myofibrillar protein changes occurring in dry-cured hams

The myofibrillar fraction of raw ham muscles and dry-cured hams with different ripening times was extracted in denaturing and reducing conditions and subjected to two-dimensional gel electrophoresis. The two-dimensional maps gave overall pictures of the already noted progressive disappearance of actin, tropomyosin and myosin light chains during ripening. In addition, two fragments from Myosin Heavy Chain proteolysis, marked as myosin chain fragments MCF1 and MCF2, were identified by immunodetection and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). Furthermore, a new form of actin on two-dimensional gel was identified by MALDI-TOF peptide mapping. In 12-month-old dry-cured ham, most myofibrillar proteins were completely hydrolyzed. At this stage of ripening, in fact, in some Parma and S. Daniele dry-cured ham samples, myosin heavy chain fragments and other unidentified neo-formed spots were found. Some of the sarcoplasmic proteins in water extracts from pork meat markedly decreased in amount or disappeared totally, during ripening. Surprisingly, two-dimensional gel electrophoresis maps of the water soluble protein fraction from dry-cured ham showed the presence of two spots identified as tropomyosin α- and β-chain. This result suggests that some of the saline soluble myofibrillar proteins can disappear from this fraction because of salt solubilization and not due to complete enzyme action. Two-dimensional gel electrophoresis (2-DGE) has proved a powerful tool to evaluate the enzymatic susceptibility of meat proteins and the evolution of protein map fragmentation throughout ripening process as well as a means of obtaining a standard fingerprinting map characterizing the final product.     

Contribution of a selected fungal population to proteolysis on dry-cured ham

The proteolytic changes taking place in dry-cured hams lead to increases in free amino acids. Such free amino acids not only contribute to flavour, but also serve as precursors of volatile compounds. Several months of ripening time are required to allow the particular flavour to develop. The fungal population allowed to grow on the surface of some types of dry-cured could play a key role on proteolysis, as it has been shown for dry-cured sausages. The purpose of this work was to study the possible contribution of fungi to proteolysis in dry-cured ham. For this, a strain each of non-toxigenic Penicillium chrysogenum (Pg222) and Debaryomyces hansenii (Dh345), selected for their proteolytic activity on myofibrillar proteins, were inoculated as starter cultures. Changes in the high ionic strength-soluble proteins of an external muscle (adductor) revealed in only 6 months higher proteolysis in the inoculated hams when compared to non-inoculated control hams. Proteolytic strains among the wild fungal population on non-inoculated control hams prevented from obtaining similar differences at the end of processing. However, inoculation with Pg222 and Dh345 led to higher levels for most free amino acids at the external muscle in fully dry-cured hams. In addition, the concentration for some of the more polar free amino acids (i.e. Asp, Glu, Ser and Gln) in inoculated hams was higher at external than at internal (biceps femoris) muscles. These promising results deserve further studies to know the impact of a selected fungal population on the volatile compounds and sensory properties of dry-cured ham.     

现代滚揉腌制工艺对低盐火腿风干成熟中品质变化的影响

本研究以猪后腿为原料,采用现代滚揉腌制及风干成熟工艺加工低盐火腿,并分析滚揉腌制对火腿半膜肌及股二头肌品质的影响。结果表明,现代滚揉腌制对火腿理化品质有显著的影响(p<0.05),具体表现为半膜肌中水分含量显著高于对照组(p<0.05),股二头肌中实验组水分含量显著低于对照组(p<0.05),食盐含量显著高于对照组(p<0.05),半膜肌和股二头肌中水分及盐分含量差异较小,在火腿风干成熟过程中,滚揉腌制对火腿色差L*、a*、b*变化趋势影响较小;与对照组相比,滚揉腌制能显著降低半膜肌和股二头肌的硬度(p<0.05),显著改善了火腿的质构特性。并且对半膜肌和股二头肌中游离脂肪酸重量、蛋白质水解指数及感官品质无显著影响(p>0.05)。因此,现代滚揉腌制能平衡火腿半膜肌及股二头肌的理化品质,促进产品的内外部位品质的稳定性。      

干腌火腿现代滚揉腌制工艺研究

通过干腌火腿现代滚揉腌制成套技术装备进行滚揉腌制工艺正交试验,研究用盐量、腌制时间、上盐次数等试验因素对腌制效果的影响。结果表明:采用滚揉腌制能有效提高腌腿表层盐分和内部水分传质渗透速度,腌制25d股二头肌NaCl含量达到传统工艺35d水平,且用盐量比传统工艺降低30%,均匀性提高10%;回归试验因数的相关分析结果表明:NaCl含量与腌制时间呈极显著正相关(p<0.01),与用盐量也呈显著正相关(p<0.05)。滚揉腌制工艺优化结果为:6%用盐量-25d腌制时间-4次上盐滚揉处理组合。     

Instrumental evaluation of defective texture in dry-cured hams

In the first experiment, the effect of the stress relaxation time on texture evaluation of biceps femoris (BF) muscle from dry-cured hams was studied. The specimens were compressed to 25% of their original height and the crosshead speed was 5mm/s. The force decay versus time was recorded and Peleg's model was fitted with different relaxation times. Whatever relaxation time was used, Peleg's model did not describe simultaneously the initial fall of force and the asymptotic tendency of force decay correctly. The initial force and force decay at 2s and at 90s are proposed to assess texture in dry-cured ham. In the second experiment, stress relaxation (SR) and texture profile analysis (TPA) tests were performed on BF and semimembranosus (SM) muscles of 10 hams with abnormal softness and 10 hams with normal texture, at different assay conditions: sample temperature (4°C or 20°C); compression crosshead speed (1mm/s or 10mm/s). The instrumental texture test and the assay conditions that detected defective textures better depended on the muscle considered: for BF muscle the SR test at 4°C and at 1mm/s and for SM muscle the TPA test at 10mm/s at both 4°C or 20°C.     

FAT CONTENT AND SENSORY ANALYSIS OF SELECTED PORK MUSCLES TAKEN FROM CARCASSES WITH VARIOUS BACKFAT LEVELS

Sixteen carcasses from each of four last-rib backfat thicknesses (1.8, 2.3, 2.8 and 3.3 cm) were evaluated. Crude fat, moisture and protein contents were completed on the following muscles: triceps brachii, longissimus, psoas major, gluteus medius, semimembranosus, biceps femoris and semitendinosus. Boneless rib chops and fresh ham (top) steaks were broiled to 77°C and evaluated for crude fat, moisture and protein contents and for sensory attributes. In the raw state, the intramuscular crude fat content of the boneless rib chop (longissimus muscle) from the least backfat class averaged 2.9%, and when averaged over backfat, six of the seven muscles contained crude fat contents of 4.3% or below. Broiled boneless rib chops (longissimus) and fresh ham (top) steaks (semimem-branosus) averaged 4.3 and 3.5% crude fat, respectively, when averaged over backfat. Generally, sensory scores for juiciness of the boneless rib chop increased as backfat level increased. Both juiciness and tenderness of the fresh ham (top) steak increased as backfat level increased.     

Characterization of traditional Istrian dry-cured ham by means of physical and chemical analyses and volatile compounds

The aroma-active compounds of Istrian dry-cured ham were investigated by using headspace-solid phase microextraction and gas chromatography-mass spectrometry (GC-MS). Samples of biceps femoris were also evaluated by measuring physical and chemical characteristics: moisture, protein, fat, ash and NaCl content, a(w) value; colour: L*, a*, b* and oxidation of fat: TBARS test. About 50 volatile compounds were identified and quantified which belonged to several classes of chemical: 5 alcohols, 8 aldehydes, 7 alkanes, 1 ketone, 2 esters, 9 monoterpenes and 15 sesquiterpenes. Except volatile compounds derived from lipolysis and proteolysis the most abundant constituents were terpenes (62.97; 41.43%) that originate from spices added in the salting phase of the production process.     

Evaluation of protein degradation and flavor compounds during the processing of Xuan'en ham

Protein degradation occurs during the processing of dry-cured ham, which has important influences on the flavor and quality of products. The aim of this work was to study the degradation kinetics of myofibrillar proteins (MPs) and sarcoplasmic proteins (SPs) extracted from the biceps femoris muscle during the processing of Xuan'en ham. A relationship between protein degradation and the flavor formation was found. During the processing of Xuan'en ham, MPs and SPs were mainly degraded in the salting stage and incipient fermentation. Accompanied by protein degradation, the content of carbonyl group in SPs increased gradually, but in MPs, it first increased and then decreased. Interconversion between sulfhydryl and disulfide bonds was investigated during this processing. Oxidation, degradation, and thermal effects significantly affected the surface hydrophobicity of proteins. More than one hundred volatile compounds have been identified at each stage of ham preparation. Among them, organic acids were the predominant group, followed by hydrocarbons, aldehydes, alcohols, ketones, and esters.     

Chemical and structural changes in dry-cured hams (Bayonne hams) during processing and effects of the dehairing technique

Pigs of similar genetic backgrounds and feeding regimes were slaughtered in two abattoirs, one carrying out dehairing by scalding and the other by singeing. One ham from each of 80 carcasses was retained. Sixteen fresh hams (8 from each dehairing technique) were used for analysis while 64 hams were processed into dry-cured ham. Sixteen hams (8 from each dehairing technique) were taken for analysis at end of salting (day 14), end of rest (day 78), mid-processing (day 127) and end of processing (day 251). During processing, the water content of all muscles decreased while the salt content increased. The salt concentration in muscle water tended to equalize in all muscles. The nitrogen content of desalted dry matter (i.e. dry muscle tissue) decreased in both Biceps femoris and Semimembranosus. The content of every free amino acid increased with time, except for taurine and glutamine. Electrophoresis of the low ionic strength-soluble fractions showed all protein bands decreased during processing. Electrophoresis of the myofibrillar fractions indicated changes in all bands except actin (42kDa). These changes were more marked in the Semimembranosus than the Biceps femoris in the earlier processing steps. Ultrastructural changes were more marked in Semimembranosus than Biceps femoris. Hardness and chewiness increased in both muscles during the first half of processing then returned to values close to the initial ones in Semimembranosus but changed little in Biceps femoris. The scalded hams lost more weight than the singed ones during processing. The salt content was higher in scalded hams. Water-soluble nitrogen and NPN were higher in singed hams at the end of processing. The scalded hams were saltier and pungent. They had more pronounced aromas of dry ham, rancidity and hazelnut, and less aroma of fresh meat. Their texture was drier and less mellow.     

Pyridinoline in ovine intramuscular collagen

Pyridinoline, a mature crosslink of collagen, was measured in intramuscular connective tissue isolated from ovine semimembranosus, a muscle noted for its highly insoluble collagen. Concentration ranged between 0·25 and 0·59 mol/mol of collagen, on the high side of concentrations reported in the literature for this and other muscles in various species. Pyridinoline concentration was inversely related to collagen solubility in muscle homogenates (P < 0·0). In a comparison between semimembranosus, biceps femoris and gluteus medius, pyridinoline concentration was again inversely related to collage solubility. For all these muscles, pyridinoline remained insoluble in a heat-dependent solubility test, but it is argued that pyridinoline does not explain all the solubility properties of ovine intramuscular collagen. Pyridinoline concentration was not significantly correlated with sensory or shear properties of cooked semimembranosus, confirming the importance of other heat-stable crosslinks.     

COMPOSITION,WATER-HOLDING CAPACITY AND pH OF MUSCLES FROM PIGS SUPPLEMENTED WITH PORCINE SOMATOTROPIN (pSt)1

Eighteen pigs were injected with one of three levels of recombinant porcine somatotropin (pSt) and received no more injections 7 days before slaughter. Excised triceps brachii, psoas major, semimembranosus, semitendinosus and biceps femoris muscles were analyzed for crude fat, moisture and protein contents, pH and water-holding capacity, Generally, raw muscles from somatotropin-supplemented pigs contained less crude fat than did muscles from control animals. The crude fat content of the broiled triceps brachii and roasted biceps femoris decreased in response to somatotropin supplementation. Muscles from supplemented and unsupplemented pigs did not differ in cooked muscle moisture or protein contents, raw or cooked pH or raw muscle water holding capacity.     

Proteolysis in biceps femoris during Jinhua ham processing

Sixty experimental Jinhua hams were processed by a traditional method. The nitrogen fractions and free amino acids in biceps femoris were analyzed. Intense proteolysis was found in ham muscle and totally more than 10% of muscle proteins were degraded during the course of Jinhua ham processing. The proteolytic index of Jinhua ham was between 14 and 20. Both insoluble and soluble proteins were degraded to some degree and the later showed more intense degradation. In the soluble fraction, the percentage of non-protein nitrogen (NPN) increased gradually whereas that of protein nitrogen decreased during processing (P<0.05). However, very small amount of peptides larger than 1kDa was accumulated during the whole course of processing, which proved that intense degradation reactions were also happened to them, especially at the post ripening stage when dramatic decrease of nitrogen fraction from all the peptides larger than 1kDa was found. As a result, more than 90% of the NPN products from muscle proteolysis were free amino acids and peptides of MW less than 1kDa that might make important contribution to Jinhua ham taste and provide precursors for the generation of volatile flavor compounds in ham muscle. The pattern of muscle proteolysis coincided with the reported changes of muscle proteolytic enzymes during processing, seemingly indicating that the enzymes could have played important roles in ham muscle proteolysis.