Identification of odour-active compounds in ewes' raw milk commercial cheeses with sensory defects

The aim of this work was to identify key odorant compounds associated with main off-flavours (acid, rancid and faecal) and one defect related to the internal appearance (big irregular eyes) in ewes' raw milk commercial cheeses. Cheese samples were submitted to solvent assisted flavour evaporation (SAFE) and odorant compounds were detected by gas chromatography–olfactometry (GC–O). Odour-active compounds detected by GC–O were identified and quantified by gas chromatography–mass spectrometry (GC–MS). Partial least square regression was performed to determine relationships between relative abundances of the odour-active compounds and sensory defects of commercial cheeses. An imbalance in the concentration of short-chain free fatty acids, predominant compounds in all cheese samples, was associated with acid and rancid off-flavour, whereas faecal off-flavour was related to minor compounds such as 4-methylphenol and 3-methyl-1-butanol. No volatile compound could be related to the defect of big irregular eyes.     

Further studies on lipid composition of bovine milk in relation to spontaneous oxidised flavour

Milk samples from five commercial dairy herds having severe problems with spontaneous oxidised flavour (SOF) and milk samples from five herds without such problems were analysed for parameters connected with SOF in milk. The study was directed towards analysing parameters which primarily are influenced by feeding. The fatty acid compositions of both neutral lipids and phospholipids were determined as well as the concentrations of α-tocopherol, β-carotene and copper in the milk. The samples were also analysed by dynamic headspace GC to determine volatile oxidation products. The results showed that the reasons for the occurrence of SOF in a specific herd are still obscure, since the only consistent result found for the five control herds, when compared with the corresponding experimental herd, was a higher proportion of the 18:1 trans fatty acid. However, within the affected herds, the difference between cows giving milk with off-flavour and cows giving milk without off-flavour was quite clear. In four out of five herds the ratio between antioxidants and fatty acid unsaturation was lower in milk with off-flavour, and in the fifth herd an extremely high proportion of 18: 2 in the phospholipids seemed to have been the reason for the off-flavour that developed. One of the herds also had a higher copper content in milk showing SOF. The data showed differences in importance of α-tocopherol and β-carotene, in different herds. Also the unsaturation in fatty acids of both neutral lipids and phospholipids had different importance for the flavour stability in different herds. © 1998 SCI.     

Determination of trimethylamine in milk using an MS based electronic Nose

A simple, rapid, reliable and highly automated analytical method has been developed to determine trimethylamine (TMA) in milk using an MS based electronic nose (SMart Nose). A set of Swedish milk samples with and without naturally occurring TMA was used to compare this new method with sensory analysis and dynamic headspace (DHS) gas chromatography with flame ionisation detection (GC-FID). The results show good agreement between these three analytical methods. A lower detection limit (0.5 mg kg^-1) and better repeatability were achieved with this new method compared to both sensory and DHS GC-FID analyses (1-2 mg kg^-1). The user-friendly multivariate analysis software provided with the SMart Nose system was used for TMA determination via a numerical PCA. Using Excel, peak intensity, correlated with TMA concentration via a second order equation, gave similar results. Thus, this is an up to date method of choice for the quantitative determination of TMA in milk. It is also able to give further qualitative information on the milk analysed using the PCA analysis supplied with this equipment.     

迷迭香提取物对白鲢鱼肉腥味的影响及其脱腥条件优化

选用迷迭香提取物对白鲢鱼肉进行浸泡脱腥处理,以硫代巴比妥酸(thiobarbituric acid,TBA)值、三甲胺(trimethylamine,TMA)值和感官腥味值作为评价指标,在单因素试验的基础上运用响应面模型优化脱腥条件,通过顶空固相微萃取-气相色谱-质谱联用技术评价脱腥前后鱼肉挥发性成分的变化。结果表明,最优脱腥条件为迷迭香提取物浸泡液质量浓度1.7 g/L,料液比1∶3.40(g∶mL),浸泡时间41 min,在此条件下脱腥后,TBA值为(0.35±0.02)mg MDA/kg(MDA:丙二醛,malondialdehyde),TMA值为(1.55±0.06)mg/kg,腥味值为1.81±0.07,验证结果与优化结果之间的误差均小于1.00%。此外,白鲢鱼肉脱腥前后分别检测出24种和14种挥发性成分,挥发性成分含量均显著降低。脱腥后,对腥味贡献较大的己醛和1-辛烯-3-醇含量分别下降了100%和79.97%,同时庚醛、辛醛、壬醛和癸醛的含量分别下降了100%、70.37%、51.43%和42.11%,这一结果与TBA值、TMA值和腥味值的评价结果一致。因此,迷迭香提取物在脱除白鲢鱼肉腥味和改善白鲢加工产品的风味方面具有良好的应用前景。     

Fish meal and egg taint

A ‘fishy’ or ‘crabby’ taint in brown eggs from commercial flocks was associated with the use of capelin meal as a protein supplement and was reproduced under controlled conditions. Analysis of eggs and samples of the meal established that trimethylamine (TMA) was responsible for the taint and that the meal may contain rich sources of TMA in the form of TMA oxide and choline. Only certain hens were affected and their ability to metabolise TMA was very low as indicated by the oxidation of an intravenous dose of ¹⁴C-TMA and the activity of hepatic TMA oxidase. Oxidation of the ¹⁴C-TMA was further depressed by feeding the meal or injecting non-radioactive TMA. Experiments with hens and chickens which had been bred for sensitivity to the inhibition of TMA oxidation by thionamides (and rapeseed meal) gave no indication that the meal supplied a potent inhibitor of this kind. It was concluded that the tainting is caused by overloading hens with TMA and that these hens have a genetic defect which impairs their synthesis of TMA oxidase and consequently their ability to metabolise TMA. The removal of this defect from commercial flocks by selective breeding would probably prevent tainting by both fish and rapeseed meals.     

Survey of the occurrence of Aflatoxin M1 in ovine milk by HPLC and its confirmation by MS

During the period of October-July 2000, 240 samples of dairy ewes milk, obtained from farms of Enna (Sicily, Italy), were checked for Aflatoxin M(1) (AFM(1)) by HPLC using a fluorimetric detector. The limit of detection and the limit of quantification were 250 ng/L for AFM(1). All the positive milk samples for AFM(1) were confirmed by LC-MS. AFM(1) was detected in 81% of milk samples, ranging from 2 to 108 ng/L. Three samples were over the legal limits (50 ng/L). Mean contamination of samples obtained from stabulated ewes was higher than that from grazing ewes (35.27 vs. 12.47 ng/L). Furthermore, samples collected in the period September-October showed higher contamination than samples collected during the other months (42.68 vs. 10.55 ng/L). Both differences are related to the administration of compound feed. Based on current toxicological knowledge we concluded that the AFM(1) contamination levels recorded in ewe milk did not present a serious human health hazard. However, as ewe milk is exclusively used to produce cheese due to its higher protein content, and also considering the preferential binding of AFM(1) to casein during coagulation of milk, a potentially high concentration effect could occur, thus the surveillance of contamination levels should be more continuous and widespread.     

利用Flash E-Nose方法探究漂洗处理对鲶鱼鱼糜的脱腥效果

目的：探索不同漂洗方法对鲶鱼碎肉的脱腥效果。方法：测定不同漂洗处理（未漂洗、调配液漂洗和清水漂洗）的鲶鱼碎肉的营养成分,并利用超快速电子鼻（Flash E-Nose）检测在冷藏过程中的挥发性气味物质变化,测定的时间点为pH值的起始点、极限pH值点和鱼肉腐败点,通过对所获数据进行主成分分析,来判断不同漂洗处理对鲶鱼肉的脱腥效果。结果：漂洗后的碎肉蛋白质含量,水分含量均比对照组高,而脂肪含量明显减少,调配液漂洗效果更佳;Flash E-Nose可以将不同漂洗处理的鱼肉样品中的挥发性气味物质很好地分离开来,未漂洗的鲶鱼肉检出醛类、烃类、醇类、呋喃类、三甲胺等成分,它们的协同作用构成了鲶鱼肉的土腥味,而经过漂洗处理能够有效地去除三甲胺。结论：调配液漂洗能够提高鱼肉品质;并且鲶鱼鱼肉中含有较多的腥味成分如2-甲基戊醛、3-甲基-3-磺酰基-1-羟基丁醇和三甲胺等,通过漂洗处理后前2 种成分的相对含量明显减少,三甲胺能够被完全去除。所以漂洗能够有效地达到脱腥的效果,调配液漂洗的效果更佳。     

Comparison between novel and standard methods for analysis of free fatty acids in milk – Including relation to rancid flavour

A range of analytic methods for quantifying free fatty acids (FFAs) in milk were compared and further correlated to rancid flavour detected by sensory analysis. Proton transfer reaction–mass spectrometry (PTR–MS) and ¹H nuclear magnetic resonance (NMR) spectrometry were introduced as novel methods for quantifying individual short chain FFAs. Gas chromatography–mass spectrometry (GC–MS) combined with in-solution derivatisation was used for quantifying all individual FFAs, and Bureau of dairy industries (BDI), acyl-CoA-synthetase–acyl-CoA oxidase (ACS–ACOD) assay, Fourier transform infrared spectroscopy were used to estimate the total FFA concentration in 28 milk samples. High correlations (r between 0.76 and 0.86) to rancid off-flavour were found for all analytical methods, and all the individual FFAs were quantitatively inter-correlated. Furthermore, a high correlation was found between PTR–MS and GC–MS quantification of hexanoic acid. For the BDI method, the sensory thresholds rancid off-flavour in farm bulk milk were 1.95 mmol 100 g⁻¹ fat.     

Dynamic changes in the volatiles and sensory properties of chilled milk during exposure to light

Exposure of milk to light causes photo-oxidation and off-flavour generation. To characterise these reactions, semi-skimmed (1.5% fat) and whole (3.8% fat) extended shelf-life cows' milk were exposed to light for 20–48 h at 4 °C and volatiles in the milk headspace were measured on-line using proton-transfer-reaction mass spectrometry (PTR-MS). The flavour of the whole-milk was assessed by aroma profile analysis on both orthonasal/retronasal odour and taste after 0, 0.25, 1, 6 and 24 h light-exposure. Sensory changes perceived in milk exposed to light for up to 6 h varied in intensity and between replicates, most notably a transient sensory defect being detectable after 0.25 h exposure, but these changes did not correspond to any volatile organic compound (VOC) generation detected by PTR-MS. After 24 h, several compounds showed enhanced release profiles. Principal components analysis related these VOCs to changes in the sensory properties of the milk, described as oxidised/rancid/hay-like.     

Gas chromatographic method for the determination of volatile amines in seafoods

A method of quantitative analysis of trimethylamine (TMA) and dimethylamine (DMA) in seafoods by gas chromatography (GC) was developed. The amines are separated by using a precolumn of Chromosorb 103 with a main column of Carbopack coated with Carbowax 20M and KOH: a flame ionization detector (FID) and a nitrogen-phosphorous-specific flame ionization detector (NPFID) were used. The effectiveness of the procedure was demonstrated on selected seafood samples.     

Characterization of fish sauce aroma-impact compounds using GC-MS, SPME-Osme-GCO, and Stevens' power law exponents

ABSTRACT:  The objectives of this study were to characterize volatile compounds and to determine the characteristic aromas associated with impact compounds in 4 fish sauces using solid-phase micro-extraction, gas chromatography-mass spectrometry, Osme, and gas chromatography olfactometry (SPME-Osme-GCO) coupled with Stevens' Power Law. Compounds were separated using GCMS and GCO and were identified with the mass spectral database, aroma perceived at the sniffing port, retention indices, and verification of compounds by authentic standards in the GCMS and GCO. Aromas that were isolated and present in all 4 fish sauce samples at all concentrations included fishy (trimethylamine), pungent and dirty socks (combination of butanoic, pentanoic, hexanoic, and heptanoic acids), cooked rice and buttery popcorn (2,6-dimethyl pyrazine), and sweet and cotton candy (benzaldehyde). All fish sauces contained the same aromas as determined by GCO and GCMS (verified using authentic standard compounds), but the odor intensity associated with each compound or group of compounds was variable for different fish sauce samples. Stevens' Power Law exponents were also determined using this analytical technique, but exponents were not consistent for the same compounds that were found in all fish sauces. Stevens' Power Law exponents ranged from 0.14 to 0.37, 0.24 to 0.34, 0.09 to 0.21, and 0.10 to 0.35 for dirty socks, fishy, buttery popcorn, and sweet aromas, respectively. This demonstrates that there is variability in Stevens' Power Law exponents for odorants within fish sauce samples.     

Extrusion parameters and consumer acceptability of a peanut-based meat analogue

Despite its high protein content and low cost, defatted peanut flour (DPF) remains underutilised in human foods. The objectives of this study were to: (1) determine the best extrusion parameters for a peanut-based textured meat analogue (TMA); (2) develop new TMA products from DPF and (3) evaluate their consumer acceptability. Preliminary runs using a wide range of extrusion parameters were conducted. A central composite RSM design was used to determine the optimal extrusion conditions within the best ranges revealed by the preliminary runs. Three levels of moisture, screw-speed and barrel temperature were used in 31 runs. Expansion ratio, bulk density, texture profile, water absorption/solubility indexes of the extrudates were determined and used as indicators of product quality. Peanut-based TMAs produced at optimal extrusion conditions were flavoured with beef flavour and evaluated by a 60-member sensory panel for flavour, texture, and overall liking, using a 9-point hedonic scale. Optimisation studies revealed that the most important extrusion conditions are in descending order: protein content, temperature, moisture and screw-speed. Extrusion conditions that produced the best TMA were 60–65% protein, 50–55% moisture, 160–165 °C and 80–90 r.p.m. Sensory acceptability of snacks incorporating peanut-based TMAs was similar or better than those containing soya-based TMAs in terms of flavour, texture, off-flavour and overall liking. TMA produced from inexpensive DPF has the potential to compete with commercial meat analogues, thereby adding value to the peanut industry.     

海带、椰汁复合饮料的研制

以椰汁、海带为主要原料,经科学调配,研制成一种饮料。同时研究了海带浸提条件和脱腥方法。     

Determination of polycyclic aromatic hydrocarbons in Italian milk by HPLC with fluorescence detection

The presence of polycyclic aromatic hydrocarbons (PAHs) in Italian commercial milk samples is reported. The study was carried out on lactating (cow and goat) and plant (rice, soya, oat) milk. The quantitative determination involved liquid–liquid extraction of PAHs, a pre-concentration and determination by HPLC using a fluorescence detector. The recovery of analytes was in the range of 70–115%. The precision of the method was found to be between 6% and 24%. The detection limit ranged from 0.66 to 33.3 µg l^–1 corresponding to 0.03–1.66 µg kg^–1 milk (wet weight), at a signal-to-noise ratio of 3, depending on the compound. By this procedure, the levels of more volatile PAHs (two to three aromatic rings) were confirmed in 34 commercial milk and three plant milk samples, whereas benzo[a]pyrene was found only in five pasteurised milk samples at a mean concentration of 0.17 µg kg^–1 milk. These results provide evidence that PAH levels are influenced by heat treatments and skimming processes of milk production.     

Effect of bleeding on lipid oxidation and quality changes of Asian seabass (Lates calcarifer) muscle during iced storage

Lipid oxidation, microbial load and fishy odour development in the slices of bled and un-bled Asian seabass during 15 days of iced storage were comparatively investigated. Bled samples showed the lower peroxide value (PV) and thiobarbituric acid-reactive substances (TBARS) throughout the storage period (P < 0.05). Bleeding effectively lowered the total haem and non-haem iron contents in Asian seabass slices. The release of non-haem iron was pronounced in the un-bled samples during the storage. Solid phase micro-extraction coupled with gas chromatography and mass spectrometric (SPME-GCMS) analysis revealed that the bled samples stored in ice for 15 days contained the lower amount of volatile compounds. Heptanal, the major volatile compound detected in the un-bled samples, was four-fold higher than that of bled counterparts. The contents of aldehydic compounds, including hexanal, octanal, nonanal and nonenal were also higher in the former. Bled samples had the lower fishy odour, compared with the un-bled counterparts during storage (P < 0.05). The lower total viable counts (TVC) and psychrophilic bacterial counts (PBC) were observed in the bled samples, in comparison with the un-bled ones (P < 0.05). Thus, bleeding was a potential means in retarding lipid oxidation, fishy odour development, and microbial growth of Asian seabass slices during storage in ice.     

Evaluation of processed cheese fortified with fish oil emulsion

Processed cheese fortified with fish oil is an excellent food for the delivery of omega-3 long-chain polyunsaturated fatty acids (omega-3 LC PUFA). However, oxidation and the “fishy” flavour of fish oil limit the level of fortification. The physical properties, lipid oxidation, and sensory perception of model processed cheese slices fortified with a fish oil emulsion (encapsulated fish oil) were examined and were compared with those of samples fortified with straight fish oil. Peroxide values, the results of thiobarbituric acid reactive substances (TBARS) tests, and propanal values showed that cheese samples fortified with fish oil emulsion had lower levels of oxidation than cheese samples fortified with non-encapsulated fish oil. A sensory panel detected a “fishy” flavour at a higher level of fish oil addition in the samples fortified with fish oil emulsion. This suggests that a fish oil emulsion made with a milk protein complex is a useful carrier for elevating the fortification level of omega-3 LC PUFA in processed cheese products.     

PAHs concentration in heat-treated milk samples

In this study the presence of residual levels of Polycyclic Aromatic Hydrocarbons (PAHs) in milk samples from Calabria was evaluated. A comparative analysis of PAHs concentrations was conducted on raw, pasteurized, UHT semi-skimmed and whole milk.Quantitative determination of PAHs was performed by HPLC using a fluorescence detector and analysis in HPLC-MS was conducted to confirm the presence of these compounds.Residual levels of PAHs were found in all milk samples analyzed, showing higher concentrations in pasteurized and UHT milk than in raw milk samples.The results obtained demonstrate that PAHs presence also in raw milk is dependent from environmental pollution but pasteurization and UHT treatments of milk can influence PAHs formation; the differences found between whole and semi-skimmed samples can be due to different fat content of milk.     

Quantification of Lactulose and Epilactose in the Presence of Lactose in Milk using a dual HPLC analysis

The valuable lactose derivatives lactulose and epilactose can be derived from lactose either by the Lobry de Bruyn-Alberda van Ekenstein transformation during heat treatments or by enzymatic conversion using cellobiose 2-epimerases (EC 5.1.3.11). The chromatographic determination of lactose, lactulose, and epilactose in milk is challenging, due to the variable ratio of the three saccharides and their similar retention properties. In this work, a dual high-performance liquid chromatography (HPLC) analysis for the quantification of lactose, lactulose, and epilactose in milk samples was developed and validated. The samples originated from an enzymatic lactose conversion using the cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus. Application of this enzyme led to the formation of high lactulose concentrations (28.0 g/L) in milk. The dual HPLC analysis utilized a combination of two chromatographic separation techniques, configured in two parallel systems. After precolumn derivatization, the samples were analyzed as follows: Method 1 determined the concentration of lactose and epilactose using a C₁₈ column with an ion-pair reagent as eluent, coupled with a UV detector. Method 2 determined the concentration of lactulose using a trimodal stationary phase (hydrophilic interaction, anion- and cation-exchange properties) with acetonitrile/ammonium formiate buffer as eluent, coupled with an evaporative light scattering detector. Both methods were validated in terms of linearity, precision and recovery. The revealing detection limits in the milk samples were 3.32 mg/L for lactose, 4.73 mg/L for epilactose and 139 mg/L for lactulose. The dual HPLC analysis presented allows accurate lactose, lactulose, and epilactose separation in complex food matrices such as milk.     

Recent observations on the occurrence of fishy flavour in bacon

An examination of reject bacon samples supplied directly from a factory showed that some samples described by a sensory panel as oily and fishy contained significantly higher levels of long chain polyunsaturated fatty acids (PUFA) in their fat than normal samples. When bacon samples obtained from retail outlets were similarly analysed and then subjected to sensory assessment, those found to contain long chain PUFA were given significantly higher scores for oily and fishy flavour. Observations on the fatty acid composition of fishy bacon samples as compared to non-fishy ones and further investigation into the diets of pigs producing suspect carcasses led to the conclusion that too high a content of fish products in the diet was the main cause of the problem. Contrary to what had been believed, fresh non-fishy bacon samples did not develop fishy flavour after storage at ?20°C for 15 weeks. Perceived fishiness was not related to total copper content as determined by atomic absorption spectroscopy.