Monitoring of warmed-over flavour in pork using the electronic nose – correlation to sensory attributes and secondary lipid oxidation products

Sensory analysis of meatballs was carried out to monitor the warmed-over flavour (WOF) development in cooked, cold-stored (at 4 °C for 0, 2 and 4 days) and reheated meatballs derived from M. longissimus dorsi (LD) and M. semimembranosus (SM) of pigs fed a standard diet supplemented with either 3% of rapeseed oil or 3% of palm oil. This was performed in combination with measurement of volatile compounds using a solid-state-based gas sensor array system (electronic nose) and gas chromatography/mass spectrometry together with measurement of thiobarbitoric acid reactive substances (TBARS). Subsequently, to elucidate the relations and predictability between the obtained data, the gas sensor responses were correlated with chemical (volatile and non-volatile secondary lipid oxidation products) and sensory data (flavour and odour attributes), using partial least squares regression modelling (PLSR). The TBARS, hexanal, pentanal, pentanol and nonanal all correlated to the sensory attributes associated to WOF formation. Moreover, the responses from eight of the MOS (metal oxide semiconductor) sensors within the electronic nose proved to be significantly related to WOF characteristics detected by both sensory and chemical analysis, while six of the MOSFET (metal oxide semiconductor field effect transistor) sensors were related to freshly cooked meat attributes determined by sensory analysis. The obtained results show the potential of the present gas sensor technology to monitor WOF formation in pork.     

Rapid identification of pork for halal authentication using the electronic nose and gas chromatography mass spectrometer with headspace analyzer

The volatile compounds of pork, other meats and meat products were studied using an electronic nose and gas chromatography mass spectrometer with headspace analyzer (GCMS-HS) for halal verification. The zNose™ was successfully employed for identification and differentiation of pork and pork sausages from beef, mutton and chicken meats and sausages which were achieved using a visual odor pattern called VaporPrint™, derived from the frequency of the surface acoustic wave (SAW) detector of the electronic nose. GCMS-HS was employed to separate and analyze the headspace gasses from samples into peaks corresponding to individual compounds for the purpose of identification. Principal component analysis (PCA) was applied for data interpretation. Analysis by PCA was able to cluster and discriminate pork from other types of meats and sausages. It was shown that PCA could provide a good separation of the samples with 67% of the total variance accounted by PC1.     

Sensory based quality control utilising an electronic nose and GC-MS analyses to predict end-product quality from raw materials

The objective of the present study was to investigate if an electronic nose, comprising six metal oxide sensors (MOS) could predict the sensory quality of porcine meat loaf, based on measuring the volatiles in either the raw materials or the meat loaf produced from those raw materials. A multivariate data analysis strategy involving analysis of variance partial least squares regression (APLSR) and principal component analysis (PCA) was used to determine causal and predictive relationships between the raw material and meat loaf samples, sensory analysis, electronic nose, and GC-MS measurements. The results showed that the six MOS sensors in the Danish odour sensor system (DOSS) could detect the raw materials that led to unacceptable products, as determined by sensory profiling and in-house sensory quality control (QC), and separate those raw materials from each other, based on the volatile composition, as determined by GC-MS. However, the electronic nose was unable to detect all the sensory unacceptable meat loaf samples themselves due to changes in the volatile composition after cooking. Analysis of the GC-MS compounds identified from raw materials and meat loaf samples indicate that two MOS sensors mainly responded to alcohols and to a lesser degree to aldehydes and alkanes, whereas two other sensors most likely responded to low molecular weight sulphur compounds. Thus, the results indicate that measuring volatiles with the MOS sensors in the DOSS system, on raw materials for processed meat products, may be a feasible strategy in sensory based quality control, and may also have potential in predicting the sensory quality of the end product.     

Influence of storage temperature and duration on lipid and protein oxidation and flavour changes in frozen pork dumpling filler

This study was conducted to evaluate the effect of storage temperature and duration on oxidation and flavour changes in frozen pork dumpling filler. Freshly prepared dumplings were stored for 0, 30, 60, 90, and 180 d at − 7 °C, − 18 °C, and an oscillation between − 7 °C and − 18 °C. The samples stored at − 7 °C for 180 d had significantly higher levels of TBARS and protein carbonyls than those stored at − 18 °C and the fluctuating − 7 °C/− 18 °C (P < 0.05). The percentage of unsaturated fatty acids in total lipids decreased with extended storage times. The volatile compounds with pleasant odours decreased with time, while the compounds with pungent tastes and smells increased (P < 0.05). The sensory results showed that the dumplings stored at higher frozen temperatures for long periods of time had significantly lower acceptability scores (P < 0.05). The results suggest that oxidation is a primary cause of quality deterioration in pork dumpling filler during frozen storage.     

A comparison of warmed-over flavour in pork by sensory analysis, GC/MS and the electronic nose

Pork muscle samples (M. longissimus dorsi and M. psoas major) were obtained from pigs given one of 4 dietary treatments, (i) control diet, (ii) supplemental iron (300 mg iron (II) sulphate/kg feed), (iii) supplemental vitamin E (200 mg dl-α-tocopheryl acetate/kg of feed) and (iv) supplemental vitamin E+supplemental iron. Warmed-over flavour (WOF) was evaluated by a trained sensory panel (n=8) for the four treatments cooked and refrigerated at 4?°C for up to 5 days. Gas chromatography mass spectrometry (GC/MS) and Electronic nose analysis was performed on a subset of the full design which included samples of M. longissimus dorsi, treatments (ii) and (iii) and M. psoas major with treatment (i) for 0 days of WOF development. Day 5 of WOF development was included in the subset and represented by samples of M. longissimus dorsi, treatment (iv) and M. psoas major, treatments (ii) and (iii). Bi-linear modeling was used to determine the correlation of GC/MS and electronic nose data to sensory data. Also, the reproducibility and reliability of electronic nose data was evaluated by repeating the analysis of samples in a different laboratory and with a time difference of approximately 11 months. Mean-centring was used to normalise the data from these two different electronic noise data sets. GC/MS data correlated to sensory data with specific compounds (e.g., pentanal, 2-pentylfuran, octanal, nonanal, 1-octen-3-ol and hexanal), proving to be good indices of oxidation in cooked samples of M. longissimus dorsi and M. psoas major. Electronic nose data correlated to sensory data and separated the sensory variation. The reproducibility of this data was high with the second set of samples being predictive of the first set.     

Effect of antioxidant on the fatty acid composition and lipid oxidation of intramuscular lipid in pressurized pork

To investigate the effect of antioxidants on lipid oxidation and fatty acid composition in pressurized pork, minced pork with or without 1% Na(2)EDTA was pressurized at 500MPa before 7days storage at 4°C. TBARS value, lipid content and fatty acid composition in untreated and high-pressure (HP) treated samples were analyzed. HP treatment induced marked increases in TBARS values and lipolysis of partial phospholipids causing an increase of free fatty acid content. Preferential hydrolysis for polyunsaturated fatty acids (PUFA) in phospholipids resulted in the percentage of PUFA in phospholipids decreasing markedly and thereby that in free fatty acids increasing significantly. Addition of 1% Na(2)EDTA to minced pork before HP significantly decreased the TBARS values in pressurized samples, but did not inhibit the lipolysis of phospholipids, causing the fatty acid composition of phospholipids and free fatty acids to change similarly to those samples without Na(2)EDTA.     

Effects of dietary soybean oil on lipid and protein oxidation in pork patties during chill storage

The effect of dietary soybean oil on lipid and protein oxidation in low and high fat pork patties made from quadriceps femoris during chill storage in a high oxygen atmosphere packaging (80% O(2)/20% CO(2)) in the dark for 7 days was investigated. Pigs were fed either a standard diet or a diet added 2% soybean oil. After slaughter high fat pork patties were prepared for both feeding regimes by addition of back fat from pigs fed the same diet whereas low fat pork patties were prepared without addition of back fat. The 2% soybean diet increased the amount of unsaturated fat in the pork. Secondary lipid oxidation products determined as thiobarbituric acid reactive substances (TBARS) were found to increase in the pork patties with increased unsaturated fat. Increased unsaturated fat in the pork patties had no effect on protein oxidation determined as free protein thiol content and protein carbonyl content. A small, but significant increase in protein oxidation was found in the high fat pork patties independent on dietary fat. In conclusion, protein oxidation is unaffected by dietary fat in pork patties during chill storage for periods normally used in retail trade, and lipid and protein oxidation are not coupled under these conditions.     

The effect of free fatty acids on the odour of pork investigated by sensory profiling and GC-O-MS

The precursors for fried flavour in pork include fatty acids, carbohydrates and amino acids. The aim of this study was to investigate the effect of free fatty acids on the odour of a pork model system and to identify important aroma compounds detected by GC-O. The odour of heat-treated minced pork to which a free fatty acid had been added was assessed by a sensory panel. The following fatty acids were compared with a control meat sample: C18:1, C18:2ω6, C18:3ω3, C18:3ω6, C20:4ω6 and C22:6ω3. The fatty acids were added at either 40 or 100 times the natural level present in the minced pork. The addition of fatty acids reduced the intensity of the meaty odour. C18:2ω6 resulted in an oily odour, while C18:3ω3 and C22:6ω3 resulted in a fishy odour. The effect of C18:1, C18:3ω6 and C20:4ω6 on the odour was smaller. An aroma analysis was performed by GC-O-MS, using eight panellists, on a control meat sample and on meat samples after addition of C18:2ω6, C18:3ω3 and C22:6ω3. Sixty-two odour-active areas were detected. An underlying compound was identified in 38 areas. A large number of long-chain aldehydes, alcohols and ketones were detected in the sample to which C18:2ω6 had been added, and this might explain the oily odour of these samples. Especially 1-penten-3-ol was detected in the samples to which C18:3ω3 and C22:6ω3 had been added, and this might explain the fishy odour of these samples.     

Aroma features of honey measured by sensory evaluation,gas chromatography-mass spectrometry,and electronic nose

To study the aroma features of different varieties of honey, five honey samples from different botanical origins were characterized by sensory evaluation, gas chromatography-mass spectrometry and electronic nose analysis. The sensory evaluation results gave a good reflection of the honey’s different aroma characteristics. A total of 55 volatile compounds were identified by headspace solid-phase micro-extraction followed by gas chromatography-mass spectrometry, and among these compounds, 13 were found in all of the honey samples. A number of differences were observed in the composition of volatile components from the five types of honey. Twenty-two compounds were selected as typical odor-active compounds which co-varied well with the five sensory attributes by partial least squares regression. The correlation results between the sensory profiles and electronic nose data showed that the electronic nose could give comparable results in predicting the sensory attributes of honey. In conclusion, the combination of sensory evaluation, gas chromatography-mass spectrometry analysis of volatile compounds, and electronic nose data with partial least squares regression analysis could be applicable for the overall analysis of aroma features for honey.     

Purification of glutathione S-transferase from lean pork muscle and its reactivity with some lipid oxidation products

Soluble glutathione S-transferase was isolated from lean pork meat by S-hexylglutathione Sepharose 6B. A single form of the enzyme with a subunit molecular weight of 24 800, a pH optimum of 6.2 and an isoelectric point of 7.6 accounted for the majority of the transferase activity. The pure enzyme is stable upon storage at pH 6, and has a relatively low K_m (87 μM) for glutathione. Substrate specificity suggests membership of class Pi. Glutathione S-transferase was able to reduce certain primary products of lipid oxidation. Linoleic acid hydroperoxides, for example, were converted to their corresponding hydroxides (specific activity = 260 nmol min^?1 mg^?1). The transferase could also inactivate secondary products of lipid oxidation. Trans,trans-2, 4-decadienal, which results from breakdown of lipid hydroperoxides, was chosen as an example of this class. A high specific activity (1400 nmol min^?1 mg^?1) was found for conjugation of the dienal with glutathione. It is suggested that endogenous glutathione S-transferase functions as an antioxidant in stored muscle food by removing some of the reactive products that propagate the oxidation of lipids.     

Early post-mortem sarcoplasmic proteome of porcine muscle related to lipid oxidation in aged and cooked meat

In order to identify specific markers of lipid oxidation generated in meat during refrigerated storage and cooking an analysis was conducted to investigate the relationships between the early post-mortem sarcoplasmic proteome, which contains the majority of enzymes involved in the oxidative process, and the level of lipid oxidation. This study was performed in Longissimus lumborum pig muscle. Proteome was analysed by 2-D electrophoresis in combination with liquid chromatography–tandem mass spectrometry (LC–MS/MS) and lipid oxidation was estimated by the TBA reactive substances (TBA-RS) measurement. Many markers of lipid oxidation were identified, but no single marker covered the oxidative process in its entirety. The role of five protein groups (albumin, redoxins, annexins, lipid transporters and enzymes of aerobic respiration), from which a link with lipid oxidation can be established, is discussed. This study, which completes a precedent work focused on protein oxidation, clearly demonstrates that a combination of several markers is needed to assess the sensitivity of meat to oxidation during both ageing and cooking.     

The effects of brined onion extracts on lipid oxidation and sensory quality in refrigerated cooked turkey breast rolls during storage

The effects of brined onion extracts on selected aspects of quality in cooked encased turkey breast rolls were evaluated during refrigerated storage over 7 days. Using the thiobarbituric acid (TBA) assay, a 50% strength juice gave a significant reduction (P < 0.0001) in lipid oxidation in both 100 g and 1 kg rolls relative to controls. Quercetin, the main onion juice antioxidant, was reduced by 65% in freshly cooked 1 kg rolls compared with raw rolls but changed little thereafter in storage. Cook yields were significantly higher for rolls containing added onion extracts than for controls (P < 0.05) but no colour differences were detected using Hunter Lab values (P ? 0.05). A 30-member untrained sensory panel expressed no preference for freshly opened 4 day-stored control or onion extract-supplemented rolls packed in plastic casings but there was a significant preference (P < 0.05) for the onion extract product when 4 mm thick meat slices were stored in air for an additional 24 h.     

Effect of an active packaging with citrus extract on lipid oxidation and sensory quality of cooked turkey meat

An antioxidant active packaging was prepared by coating a citrus extract, consisting of a mixture of carboxylic acids and flavanones, on polyethylene terephthalate trays. The effect of the packaging in reducing lipid oxidation in cooked turkey meat and on meat pH, colour characteristics and sensorial parameters was investigated. An untrained sensory panel evaluated the odour, taste, tenderness, juiciness and overall acceptability of the meat, using triangle, paired preference and quantitative response scale tests. A comparison between the antioxidant effects of the different components of the extract was also carried out. The packaging led to a significant reduction in lipid oxidation. After 2 days of refrigerated storage the sensory panel detected differences in odour and, after 4 days, rated the meat stored in the active packaging higher for tenderness and overall acceptability. Citric acid appeared to be the most important component of the extract with regard to its antioxidant potency.     

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.     

Extracts of olive polyphenols improve lipid stability in cooked beef and pork: Contribution of individual phenolics to the antioxidant activity of the extract

Crude polyphenol extracts (50 or 100 mg gallic acid equivalents (GAE)/kg meat) from the waste waters of olive oil pomace reduced the formation of 2-thiobarbituric reactive substances (TBARS) in pre-cooked beef (63–83%) and pork (47–66%). When compared with other antioxidants, the ranking of activities were: tea ? olive > wine. The olive extract contained hydroxy-tyrosol (70.6%), tyrosol (17.5%), caffeic acid (9.5%), p-coumaric acid (1.9%) and vanillic acid (0.3%). Relationship between polyphenol composition and antioxidant activity of a blend containing oleuropein, tyrosol, hydroxy-tyrosol, quercetin, rutin and caffeic, vanillic and coumaric acids was described by a first order polynomial model. Quercetin, hydroxy-tyrosol, caffeic acid and oleuropein had the highest contributions to the linear term followed by rutin and tyrosol. We detected the strongest positive synergism between tyrosol and quercetin, hydroxy-tyrosol, oleuropein and to a lesser degree with caffeic acid whilst the effect of vanillic and coumaric acids were not significant.     

Antioxidant properties of plum concentrates and powder in precooked roast beef to reduce lipid oxidation

Boneless beef roasts (Semimembranosus + Adductor) were injected (20%) with a brine containing (1) no plum ingredient (control), (2) 2.5 or 5% fresh plum juice concentrate (FP), (3) 2.5 or 5% dried plum juice concentrate (DP), or (4) 2.5 or 5% spray dried plum powder (PP). Whole roasts were cooked, vacuum-packaged and stored at <4.0 °C for 10 wk. At 2 wk intervals, evaluations were performed on sliced product to determine vacuum-packaged purge, Allo-Kramer shear force, lipid oxidation (TBARS), color space values, and sensory attributes. All plum ingredients reduced TBARS values and had minimal effects on tenderness, sensory characteristics, color and appearance. Small changes in purge, color values, TBARS and some sensory properties were found during storage. These results indicate that 2.5% FP or DP could be incorporated into precooked beef roasts to reduce lipid oxidation and potentially, warmed-over flavor (WOF).     

Use of electronic nose and trained sensory panel in the evaluation of tomato quality

In this paper the performances of an electronic nose based on metalloporphyrin‐coated quartz microbalance sensors and of an experienced panel of seven human assessors in the evaluation of gases derived from degradation reactions in tomatoes are presented and discussed. The performances are measured in terms of the capability of both systems to distinguish between samples of different quality coming from conventional and organic production systems. The study deals with the application of pattern recognition techniques based on either multivariate statistical methods (PCA, GPA) or artificial neural networks using a self‐organising map (SOM). The response pattern of the sensor array and the sensory data are analysed and compared using these methods. Similarities in the classification of the data by electronic nose and human sensory profiling are found. © 2000 Society of Chemical Industry     

Measurement of lipid oxidation and porphyrins in high oxygen modified atmosphere and vacuum-packed minced turkey and pork meat by fluorescence spectra and images

This paper illustrates that fluorescence spectroscopy and imaging can be used to measure the extent and distribution of lipid oxidation in meat. Minced turkey thighs and pork semimembranosus muscles were stored for 7 and 12 days at 4°C in high oxygen (O(2)) modified atmosphere packages and vacuum. Turkey meat packed in high O(2) atmosphere was oxidised already after 7 days of storage. The sensory rancid odour score was 4.7 (on a scale from 1 to 9) and the TBARS value was 1.86mg MDA/kg. There was also an increase in fluorescence emission intensity in the 410-550nm region, which arises from lipid oxidation products. The combination of unsaturated fatty acids and access to O(2) resulted in lipid oxidation gradients in the turkey meat samples, and these gradients were clearly visualised by fluorescence images. In comparison, pork meat was more stable against lipid oxidation, with TBARS values <0.2mg MDA/kg and no development of fluorescent lipid oxidation products was detected. The fluorescence spectra measured in the present experiment suggest that turkey thighs and pork semimembranosus muscle in addition to protoporphyrin also have a natural content of Zn protoporphyrin. The porphyrin content was higher in pork meat than in turkey meat. It increased during storage time when the meat was packed in vacuum, and it decreased with O(2) availability. The distribution of porphyrins in the meat was visualised by fluorescence imaging.