Characterization of eQTLs associated with androstenone by RNA sequencing in porcine testis.

Characterization of genetic variants affecting genome-wide gene expression levels (expression quantitative trait loci or eQTLs) in pig testes may improve our understanding of genetic architecture of boar taint (an animal welfare trait) and helps in genome-assisted or genomic selection programs. The aims of this study were to identify eQTLs associated with androstenone, to find candidate eQTLs for low androstenone, and to validate the top eQTL by reverse transcriptase quantitative PCR (RT-qPCR). Gene expression profiles were obtained by RNA sequencing in testis from Danish cross-bred pigs and genotype data by 80K single nucleotide polymorphism panel. A total of 262 eQTLs [false discovery rate (FDR) < 0.05] were identified by using two software packages: Matrix eQTL and Krux eQTL. Of these, 149 cis-acting eQTLs were significantly associated with androstenone concentrations and gene expression (FDR < 0.05). The eQTLs were associated with several genes of boar taint relevance including CYP1A2, CYB5D1, and SPHK2. One eQTL gene, AMPH, was differentially expressed (FDR < 0.05) and affected by chicory. Five candidate eQTLs associated with low androstenone concentrations were discovered, including the top eQTL associated with CYP1A2. RT-qPCR confirmed target gene expression to be significantly (P < 0.05) different based on eQTL genotypes. Furthermore, eQTLs were enriched as QTLs for 15 boar taint related traits from the PigQTLdb. This is the first study to report eQTLs in testes of commercial crossbred pigs used in pork production and to reveal genetic architecture of boar taint. Potential applications include development of a DNA test and in advanced genomic selection models for boar taint.

Which product characteristics are preferred by Chinese consumers when choosing pork? A conjoint analysis on perceived quality of selected pork attributes.

Due to the economic growth achieved by China over the past 20 years, Chinese consumers have changed their purchasing behavior regarding meat. Instead of buying locally produced pork, they are increasingly willing to purchase imported pork. A conjoint analysis investigated how intrinsic pork attributes (fat content and processing) and extrinsic pork attributes (origin, price, and packaging) relate to the perceived quality of pork and the choices made by Chinese consumers. A questionnaire distributed among a sample of Chinese consumers (n = 81) revealed that processing (fresh/frozen) is the most important determinant of pork choice (36%), followed by fat content (27%), origin (18%), price (12%), and packaging (6.6%). Estimates of utility showed that Chinese consumers value fresh pork highly (0.147), followed by lean pork (0.111) and pork imported from countries other than China (0.073). The findings indicate that Chinese consumer's value both intrinsic and extrinsic attributes, and these results may help the meat industry improve China's competitive meat market by developing new and more products that are tailored to the needs of the consumer.

Meat flavour in pork and beef - From animal to meal.

An intense meat flavour is greatly appreciated by consumers. Meat flavour is generated during the cooking process through a complex series of chemical reactions between precursors, intermediate reaction products and degradation products. The content and nature of the precursors present in the meat are affected by several factors including genetics, feed, handling of the live animals and subsequent handling of the meat. The fatty acid composition can easily be altered though feeding, especially in monogastric animals, while the carbohydrate content is more closely related to genetics (pigs), feeding in the last days before slaughter and handling at slaughter (both ante and post mortem). Ageing of the meat is not particularly important for the flavour, unless the meat is dry-aged. In comparison, cooking is crucial for the development of flavour.

Distribution of skatole and androstenone in the pig carcass correlated to sensory characteristics.

Reliable sorting and optimised use of boar-tainted pig carcasses are dependent on knowledge of the distribution of skatole and androstenone and the corresponding sensory characteristics. In this study, skatole and androstenone were measured in the neck fat and in six different meat cuts from 14 entire male pigs. There was a strong correlation between the content of skatole in the neck fat and in the meat cuts, though the concentration of skatole in the meat cuts was much lower than in the neck fat. Furthermore, clear correlations were found between the intensity of boar taint flavours and the concentration of skatole in both the neck fat and the meat. The concentration of androstenone was below the limit of quantification (LOQ) in a large number of meat cuts, and a correlation could therefore not be established. Despite low concentrations of skatole and/or androstenone in the meat cuts, distinct boar taint flavours were detected in the cooked lean meat.

Application of hydrolyzed proteins of animal origin in processed meat.

With increasing consumer interest in functional foods, proteins from slaughterhouse side streams can offer interesting application opportunities in this respect. Worldwide, increasing numbers of people are suffering from hypertension and protein deficiency. Hydrolyzed proteins of animal origin may show ACE-inhibitory activity, which is central to the treatment of hypertension. Furthermore, the protein content of, for example, meat products increases markedly through the addition of hydrolyzed proteins, and these protein-rich products are of interest to those suffering from protein deficiency. Through a series of analyses, six selected hydrolysates were analyzed for their application potential in the Danish meat product saveloy. Hydrolyzed pig rectum and bovine diaphragm showed the highest ACE-inhibitory activities, and these activities were maintained in the processed saveloys. The ACE-inhibitory activities could not readily be explained by the amino acid profile. The content of N-compounds in the saveloys increased with increasing addition of hydrolysate, with little difference between the added hydrolysates. A sensory panel assessed the saveloys with added porcine rectum (8%), bovine diaphragm (8%), and bovine heart (4% and 8%) as having the strongest off-flavors (chemical flavor). No increase in salty taste resulting from the addition of hydrolysates was detected in the saveloys. Finally, the consumers found the saveloys too mild in flavor and recommended the addition of more spices.

Antioxidant capacity of hydrolyzed porcine tissues.

The antioxidative capacity of seven different porcine tissue hydrolysates (colon, appendix, rectum, pancreas, heart, liver, and lung) were tested by four different assays, including iron chelation, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, 2,2-Diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl (DPPH) radical scavenging, and inhibition of lipid oxidation. All hydrolyzed tissues displayed antioxidant capacity in all four assays, with colon, liver, and appendix as the three most potent inhibitors of lipid oxidation (47, 29, and 27 mmol/L trolox equivalent antioxidant capacity [TEAC], respectively) and liver, colon, pancreas, and appendix as the four most potent iron chelators (92% ± 1.1, 79.3% ± 3.2, 77.1% ± 1.8, and 77% ± 2.3, respectively). Furthermore, colon and appendix showed good radical scavenging capacities with ABTS scavenging of 86.4% ± 2.1 and 84.4% ± 2.9 and DPPH scavenging of 17.6% ± 0.3 and 17.1% ± 0.2, respectively. Our results provide new knowledge about the antioxidant capacity of a variety of animal by-products, which can be transformed into antioxidant hydrolysates, thereby creating added value.

Content of heterocyclic amines and polycyclic aromatic hydrocarbons in pork, beef and chicken barbecued at home by Danish consumers.

It is a well-known fact that, when meat is barbecued, several harmful components, including heterocyclic amines (HCA) and polycyclic aromatic hydrocarbons (PAH), may be formed. The aim of this study was to determine the HCA and PAH content in meat (pork, chicken and beef) when barbecued at home by Danish consumers according to their normal practice. With regard to HCA, beef contained the highest concentrations of 9H-pyrido[3,4-b]indole (norharman) and 2-methyl-ß-carboline (harman), while chicken contained more 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) than pork and beef. The analysis of PAH showed a markedly higher concentration of PAH in beef compared with pork and chicken. In general, a correlation between the HCA content and the surface colour of the meat was found, the darker the colour the higher the HCA concentrations.

Consuming pork proteins at breakfast reduces the feeling of hunger before lunch.

This study investigated the effect of pork proteins consumed at breakfast on the subsequent feeling of hunger until the evening meal. The study involved 136 students at a local boarding school, which meant that the study could be carried out in the test persons' normal environment. All students consumed the control breakfast on one of the two test days, and then half the students consumed the medium-protein breakfast and the other half the high-protein breakfast on the other test day, thereby acting as his/her own control. It was clearly shown that consuming a medium- or high-protein breakfast decreased the hunger ratings until lunch (4 h) compared with a control breakfast. A dose-response relationship related to the amount of proteins consumed at breakfast was observed, the high-protein breakfast leading to feelings of being less hungry compared with consuming a medium-protein breakfast. However, there was no direct link between hunger ratings and actual energy intake at lunch. The self-reported snacking during the whole day showed no clear relationship with the type of breakfast consumed.

Flavour development in pork. Influence of flavour precursor concentrations in longissimus dorsi from pigs with different raw meat qualities.

Flavour development and overall eating quality of pan-fried pork chops of longissimus dorsi from eight different raw meat qualities aged for 4 and 15 days were assessed by a trained sensory panel. The raw meat qualities were obtained through combinations of strategic feeding/fasting (control vs. low glycogen concentration), slaughter live-weight (84kg vs. 110kg), and gender (female vs. castrate). The flavour development was investigated for possible correlation with the concentrations of selected individual flavour precursors present in the raw meat: monosaccharides, IMP and degradation products, fatty acids, lactate and thiamine. Differences in precursor concentrations between the raw meat qualities were observed with feeding/fasting and ageing as the main factors with the largest influence of all experimental factors. However, the concentrations of the precursors could not explain the differences in sensory perception of the pan-fried pork chops. Overall, the differences were small.

Comparison of glucose, glucose 6-phosphate, ribose, and mannose as flavour precursors in pork; the effect of monosaccharide addition on flavour generation.

The effect of glucose, glucose 6-phosphate, mannose and ribose on the generation of aroma volatiles in pork was investigated. The monosaccharides were added individually to minced pork prior to heat treatment (160°C for 10min) in the following concentrations: glucose (27.5µmol/g), ribose (1.2µmol/g), mannose (8.3µmol/g) and glucose 6-phosphate (0.5µmol/g). The natural concentrations of the monosaccharides in the pork used were found to be 4.0µmol/g for glucose, 0.1µmol/g for ribose, 0.3µmol/g for mannose and 2.6µmol/g for glucose 6-phosphate. The major aroma compounds identified in the headspace of the heated samples were pyrazines, aldehydes (Strecker and lipid-derived), ketones, and sulphides. Glucose generated the highest amounts of volatiles followed by glucose 6-phosphate. However, when related to the added concentration of glucose 6-phosphate, this phosphorylated monosaccharide showed the highest aroma generating potential. The addition of ribose did not increase the concentration of volatiles compared with pork without the added monosaccharide. The fates of ribose 5-phosphate and ribose in pork were studied over time. The concentrations of ribose and ribose 5-phosphate clearly decreased during 2h equilibration, which may be due to enzymatic activities. These precursors may, therefore, be less important pork flavour precursors than glucose and glucose 6-phosphate.

Flavour formation in pork semimembranosus: Combination of pan-temperature and raw meat quality.

Flavour development and overall eating quality of pork semimembranosus were investigated with regard to different raw meat qualities (feeding/fasting strategy; control/low glycogen level, gender; castrate/female, slaughter live-weight; 84kg/110kg) combined with frying temperature (150°C/240°C). It was further investigated whether the precursor levels of glycogen, IMP, inosine, and hypoxanthine in the raw meat were correlated to the raw meat quality and fried/grilled attributes. Pork schnitzels were fried on a pan (155°C) or grill-pan (240-250°C) to a core temperature of 70°C. Frying temperature was the one factor with greatest influence on the sensory attributes, and pan-grilled schnitzels had significantly higher scores in fried/grilled attributes regardless of meat quality compared to pan-fried schnitzels. Texture was not appreciably influenced by any treatment. There was no correlation between precursor levels and raw meat qualities or fried sensory attributes. Gender and slaughter live-weight had no pronounced influence on flavour and overall eating quality.

Eating quality of pork from pure breeds and DLY studied by focus group research and meat quality analyses.

The eating quality of pan-fried pork chops from the pure breeds of Duroc, Hampshire, Black spotted and Wild pigs, and of the cross-breed of Duroc, Landrace and Yorkshire (DLY) was investigated by focus group research in combination with analyses of raw meat quality. The three focus groups, all consisting of young consumers, generally agreed in their description of the eating quality of the five breeds. The focus group methodology was found to be an informative method for the sensory evaluation of pork chops. Chemical and physical analyses of raw meat quality were performed in parallel with the focus group research, and this combination proved useful. The chemical and physical analyses generally supported the focus group evaluation, and differences between the breeds could be explained. Duroc was the breed with the overall best eating quality, while Hampshire had the lowest overall eating quality. DLY, Black spotted, and Wild pigs were intermediate, though not similar.

Chemical and sensory characterisation of pan-fried pork flavour: Interactions between raw meat quality, ageing and frying temperature.

The effect of raw meat quality and cooking temperature on flavour generation in pork was investigated. The semimembranosus muscle was varied through genetics (carrier (HLY) and non-carrier (DLY) of the RN(-) allele) and ageing at 2°C (2, 15, and 22 days), whereas the pan-frying temperatures were 150°C and 250°C. HLY gave more pronounced 'fried' and 'burnt' notes than DLY after frying. This could partly be explained by a significantly higher concentration of glucose and glucose 6-phosphate in HLY after 22 days of ageing. HLY was generally perceived as more sour, which correlated well with the measured pH of HLY, but not to the l-lactate concentration. HLY was furthermore perceived as more tender and juicier than DLY, both attributes increased during ageing. Lipid-derived aroma volatiles dominated the samples fried at 150°C, while those from Maillard reactions mostly prevailed in the aroma profile at 250°C.

Development of inosine monophosphate and its degradation products during aging of pork of different qualities in relation to basic taste and retronasal flavor perception of the meat.

Inosine monophosphate (IMP) and its degradation products, ribose and hypoxanthine, are all considered to be important constituents in meat flavor formation and development. The present study explored the fate of IMP during the aging of two qualities of pork (pH >5.7 and 5.5 < pH < 5.6) and the potential relationship between IMP, hypoxanthine, and sensory attributes of pork registered both as retronasal and basic taste responses in whole meat, meat juice, and the remaining meat residue. During aging the concentration of IMP decreased with a simultaneous increase in the concentrations of inosine, hypoxanthine, and ribose. The rates at which IMP was degraded to inosine and inosine to hypoxanthine during aging were found to be in agreement with the known rate constants of the dephosphorylation of IMP and the hydrolysis of inosine, respectively. Moreover, high-pH pork resulted in a significantly higher concentration of hypoxanthine throughout storage compared with low-pH pork due to an initially higher concentration of IMP in high-pH meat. The sensory analysis showed increasing intensity in bitterness and saltiness of pork as a function of aging, with the intensity being most pronounced in the meat juice. The increasing bitterness of the pork as a function of aging coincided with the higher content of hypoxanthine in these samples, thereby suggesting that degradation of IMP to hypoxanthine might influence pork flavor. In contrast, IMP was associated with nonaged meat and the sensory attributes meaty and brothy.