Changes in flavour volatiles of whole pasteurized milk as affected by packaging material and storage time

Changes in volatile profiles of whole pasteurized milk stored under fluorescent light at 4 °C, packaged in different containers were monitored for a period of 7 days in a study designed to differentiate between light-induced oxidative and purely autoxidative effects related to packaging material. Changes in volatiles were measured using solid-phase microextraction–gas chromatography/mass spectroscopy, while microbiological and sensory analyses were used to assess milk quality. Two distinct patterns of milk flavour deterioration were observed. In light-exposed samples, a light-induced oxidation mechanism prevailed while in light-protected samples, an autoxidation mechanism was apparent. Under both conditions, the concentration of selected odorous compounds increased with storage time. Microbiological data correlated poorly with both sensory and GC/MS data. Sensory data correlated well with selected volatile compounds pointing to dimethyl disulphide, pentanal, hexanal and heptanal as potential markers of fresh milk quality. Based on sensory analysis, the optimal shelf life of the whole pasteurized milk used in this study was approximately 5 days.     

Volatile profile of human milk subjected to high-pressure thermal processing

High pressure thermal (HPT) treatments consist of a combination of high pressure (500–900 MPa) and temperature (70–120 °C) over a short holding time. The rapid temperature increase during compression and temperature decrease in the product upon decompression could help to reduce the hardness of thermal effects encountered in conventional thermal technologies. The objective of this study was to evaluate the effect of HPT processing (300, 600 and 900 MPa combined with 50, 65 and 80 °C) on the profile of volatile compounds in breast milk. A total of 50 volatiles, belonging to 6 different chemical groups, were detected in milk samples. In general, HPT processing increased aldehydes, ketones, furans and pyrans, as well as alcohols, however, it did not modify the levels of carboxylic acids, and reduced the content of aliphatic hydrocarbons present in the non-treated human milk samples. HPT processing enhanced the total area content of volatile compounds derived from Maillard and lipid oxidation reactions, these changes being subjected to the intensity of pressure and temperature applied. Given that the levels of volatiles were significantly modified after the application of HPT processing, we can conclude that the range of the intensity of the treatments selected was not adequate to preserve the original profile of volatile compounds in breast milk.     

Flavour profiles and survival of starter cultures of yoghurt produced from high-pressure homogenized milk

Volatile carbonyl compounds, organic acids and yoghurt bacteria counts were investigated in yoghurts made from ultra-high pressure homogenized milk. Yoghurts were manufactured from milk treated using ultra-high pressure homogenization at 200 or 300 MPa and at 30 °C or 40 °C, and compared with those produced from heat-treated milk with 3% added skim milk powder. To study the evolution of these parameters, samples were analysed after days 1, 14 and 28 of storage. Yoghurts from milk heat-treated or treated at 300 MPa had very similar profiles of organic acids and volatile compounds, as well as similar bacterial counts of both starter cultures. In comparison, yoghurts from milk treated at 200 MPa at either 30 °C or 40 °C gave different profiles, together with a sharp decrease in counts of lactobacilli. During storage, only slight differences in flavour compounds and yoghurt bacteria counts were detected, except in those samples from milk treated at 200 MPa.     

Optimisation of HS-SPME to study representativeness of partially baked bread odorant extracts

Head-space solid phase microextraction (HS-SPME) has been successfully applied to extract partially baked bread volatile compounds. During this study, three HS-SPME parameters (extraction time, extraction temperature, SPME fibre) were optimised on volatile compounds extraction thanks to a representativeness analysis. Results displayed that a CAR/PDMS or a CAR/PDMS/DVB fibre associated with a time of 30 min or 60 min and a temperature of 35 °C allowed obtaining odorant extracts representative of the bread odour. A flash profile was then carried out to highlight the different flavour perceptions which could exist between these four extracts even if they were close to the same bread odour. Completed by the analysis of their qualitative composition, the study revealed that there were some analytical differences in odour perceptions. These differences may be linked to synergic effects caused by the presence of characteristic volatile compounds in the extracts.     

Sensory stability and oxidation of fish oil enriched milk is affected by milk storage temperature and oil quality

The experiments evaluated the influence of fish oil quality and cold storage temperature on the oxidative stability of milk emulsions containing 1.0% w/w milk fat and 0.5% w/w of either a pure fish oil or a fish oil:rapeseed oil mixture. The results showed that it was possible to produce a pasteurised milk product enriched with the important n-3 PUFA from fish oil with acceptable sensory characteristics if (1) the emulsions were based on a mixture of fish oil and rapeseed oil and (2) the initial peroxide value (PV) of the added oil blend was below 0.5 meq kg⁻¹. The sensory analysis showed a clear distinction between emulsions based on oil with PV 0.1 and 0.5 meq kg⁻¹, whereas the PV and the gas chromatographic (GC) analysis of volatile oxidation products were not sensitive enough to reveal these differences clearly. The GC analyses showed that the onset of formation of the volatiles was earlier with increased storage temperature in the range of 2–9 °C.     

Microbiological and physicochemical stability of raw,pasteurised or pulsed electric field-treated milk

Pulsed electric field (PEF) processing was investigated as an alternative dairy preservation technology that would not compromise quality yet maintain safety. PEF processing of raw whole milk (4% fat) was conducted at two processing conditions (30 kV/cm, 22 μs, at either 53 or 63 °C outlet temperature) and compared with two thermal treatments (15 s, at either 63 or 72 °C) and a raw milk control and replicated twice. Milk bottles (2 L) from each treatment were incubated for two weeks, at 4 and 8 °C, and assessed for total plate count, pH, colour, rennetability, plasmin activity and lipid oxidation. The microbial quality of the thermal (72 °C/15 s) and PEF (63 °C) were similar. A drop in pH occurred after a change in counts was observed. Rennetability was not different between the treatments. Short chain acids dominated the volatile profile of the milk samples. Concentration of volatiles derived from microbial activity, namely 2,3-butanedione, acetic acid and other milk lipid derived short chain free fatty acids (e.g. butanoic and hexanoic acids), followed the trend of microbial activity in milk samples.Industrial relevanceResearch on the application of PEF to control spoilage and pathogenic microorganisms and enzyme systems in milk spans a wide array of processing equipment and reaction conditions. While industrial scale PEF processing of liquid milk for preservation and improved quality seems generally possible, substantiation of lower thermal damage under safe and scalable PEF conditions is required to enable economic feasibility.     

Contribution of coagulant and native microflora to the volatile-free fatty acid profile of an artisanal cheese

The contributions of the coagulant Cynara cardunculus and of the microflora of raw milk to the volatile-free fatty acid profile of Serra da Estrela cheese were evaluated. The experimental design included both a model system and, dual cheeses. The study in the model system showed that isovaleric acid was the predominant volatile compound after 7 d of ripening. The systems inoculated with Enterococcus faecium produced the highest amount of this volatile (ca. 135.8 mg kg⁻¹ curd), while those inoculated with Lactobacillus plantarum produced the least (21.4 mg kg⁻¹ curd); Lactococcus lactis produced moderate amounts (ca. 34.2 mg kg⁻¹ curd) but a total amount of volatile-free fatty acids similar to those found in control samples. This is considered advantageous since this volatile fatty acid confers a harsh, piquant, mature flavour to cheese, coupled with the realisation that excess volatiles may result in off-flavours. The addition of cultures in experimental cheeses helped reduce ripening time to about one half. Inclusion of Lb. plantarum led to cheeses containing the highest amounts of volatiles, and exhibiting an aroma closest to that of typical Serra da Estrela cheese.     

Odour and flavour perception in flavoured model systems: Influence of sodium chloride,umami compounds and serving temperature

The effects of salt (0% or 0.5% of NaCl) and umami compounds (0% or 0.3% of monosodium glutamate (MSG) + 0.15% of disodium salts of ribonucleotides) on odour and flavour attributes of beef broth model systems (BG) were studied at two serving temperatures (25 and 50 °C). Flavoured BG samples were prepared using 1-octen-3-ol (35 mg l^?1) and 2,6-dimethylpyrazine (100 mg l^?1) alone (BGO and BGD) or in combination (BGOD). A noticeable odour and flavour potentiator effect of NaCl on flavour intensities (overall, broth-like and saltiness in all samples; mushroom flavour in BGO and BGOD samples; nutty and cocoa flavour in BGD and BGOD samples), partly related to a “salting out” phenomenon, was found. Compared to 2,6-dimethylpyrazine, 1-octen-3-ol provided a less congruent flavour, which could explain the absence of a potentiator effect of umami compounds on mushroom flavour intensity. Cocoa and nutty flavour intensities increased with serving temperature in both BGD and BGOD model systems. However, mushroom odour and flavour increased in BGOD model systems but not in BGO samples, as a result of the likely enhancement effect displayed by the presence of 2,6-dimethylpyrazine. Salting-out phenomenon on particular aroma-active volatile compounds was established using sensory analysis. The potentiator flavour effect of MSG and NaCl was dependent on the characteristics of the model systems.     

Properties of oregano (Origanum vulgare L.), citronella (Cymbopogon nardus G.) and marjoram (Majorana hortensis L.) flavors encapsulated into milk protein-based matrices

Encapsulating properties of skimmed milk powder (SMP) and whey protein concentrate (WPC) for the coating of the essential oil (EO) of oregano (Origanum vulgare L.) and aroma extracts (AE) of citronella (Cymbopogon nardus G.) and sweet marjoram (Majorana hortensis L.) by spray-drying were evaluated. The efficiency of microencapsulation expressed as a percentage of flavoring entrapped into the microcapsules varied from 54.3% (marjoram in WPC) to 80.2% (oregano in SMP). The content of flavoring remaining on the surface of encapsulated oregano EO was remarkably lower (1.1% and 1.4%) as compared with citronella (11.2% and 15.2%) and marjoram (16.7% and 22.1%) AEs encapsulated in SMP and WPC matrixes, respectively. Consequently, the changes in the composition of individual flavor compounds during encapsulation were considerably smaller for oregano EO as compared with citronella and marjoram AEs. The release of aroma compounds from the encapsulated products was assessed by solid phase microextraction (SPME) of headspace volatiles and their analysis by gas chromatography; some differences were observed between the analysed products. However, the effect of SPME fiber polarity was another important factor affecting the amount of extracted aroma compounds from encapsulated flavors. The percentages of nonpolar aliphatic terpenes were higher in the extracts obtained by nonpolar polydimethylsiloxane or bipolar polydimethylsiloxane–divinylbenzene fibers, while the content of oxygenated constituents in most cases was higher on the polar polyacrylate fiber. The latter extracted lower amounts of volatiles during 10 min exposure. The scanning electron microscopy and particle size analysis revealed that microcapsules were well-formed spherically shaped particles; however, SMP coated products had smoother surface as compared to WPC, containing more dents and wrinkles on the capsule surface. Particle size varied from 6 to 280 μm for SMP and from 2 to 556 μm for WPC microencapsulated products.     

Method for the static headspace analysis of carrot volatiles

A static headspace analysis/gas chromatography/mass spectrometry (SHA/GC/MS) method was developed to analyse the volatile composition of raw (seven different varieties), stored and cooked carrot samples. A total of 35 different volatile compounds were identified in carrots. Of these, trans-ocimene, 2,5-dimethyl styrene, camphor, borneol, α-santalene, α-selinene, γ-elemene and α-zingiberene in raw carrots and propanol in stored carrots were identified for the first time. Major volatile compounds identified in raw carrots were α-pinene, sabinene, myrcene, limonene, γ-terpinene, terpinolene, β-caryophyllene and γ-bisabolene. Mono-and sesquiterpenes accounted for about 97% of the total volatiles identified. Sizeable varietal differences (p<0.01) were observed. Carrot volatiles did not change appreciably during the 28 day storage period at 5, 25 and 35°C, except propanol that showed exponential increases at higher temperatures. No propanol was detected in fresh raw carrots. Cooking resulted in 88.6, 93.0 and 95.5% loss in total volatiles after cooking times of 10, 20 and 30 min, respectively.     

Generation of volatile compounds in Brazilian low-sodium dry fermented sausages containing blends of NaC1, KC1, and CaC12 during processing and storage

Brazilian dry fermented sausages with different salt contents were manufactured: control (2.5% NaCl), 50% salt reduced (1.25% NaCl, F1), 50% replaced by KCl (1.25% NaCl and 1.25% KCl, F2), 50% replaced by CaCl₂ (1.25% NaCl and 1.25% CaCl₂, F3), and 50% replaced by KCl and CaCl₂ (1.25% NaCl, 0.625% KCl and 0.625% CaCl₂, F4). Changes in the composition of volatile compounds were studied during processing (0, 7, and 19 days) and storage (30, 60, and 90 days). Neither reduction nor replacement of NaCl by KCI affected the volatile compounds produced during the manufacturing process, and both increased the volatile compounds from carbohydrate fermentation and amino acid degradation during storage. The addition of CaCl₂ improved the generation of hexanal and (E)-hept-2-enal and other volatiles from lipid oxidation during processing and storage. After 90 days of storage, the control sample showed an increase in the generation of volatile compounds from lipid oxidation.     

Evaluation of pre-rigor injection of beef with proteases on cooked meat volatile profile after 1 day and 21 days post-mortem storage

This research was carried out to determine the effects of pre-rigor injection of beef semimembranosus muscle with nine proteases from plant and microbial sources, on the volatile profile of cooked beef after 1 day and 21 days post-mortem (PM) storage using Solid-phase microextraction gas chromatography mass spectrometry analysis. A total of 23 aldehydes, 5 ketones, 3 furans, 8 nitrogen and sulphur compounds, 4 alkanes, 7 alcohols and 6 terpenes were detected. Eleven volatile compounds characteristic of ginger flavour were detected in zingibain-treated meat. Benzaldehyde significantly increased (p < 0.05) only in kiwifruit juice (KJ), fungal 31 protease and Asparagus protease (ASP) treated samples from 1 day to 21 days PM storage. A significant increase (p < 0.05) in 3-methylbutanal was observed in KJ, bacterial and fungal protease treated samples at 21 days PM storage. Treatments with bromelain, papain, ASP, actinidin, and KJ (except KJ 21 days) proteases resulted in flavour profiles closer to that of the control beef sample.     

Inhibition of the decrease of volatile esters and terpenes during storage of a white wine and a model wine medium by caffeic acid and gallic acid

Caffeic acid and gallic acid were tested as inhibitors of the decrease of volatile acetate esters, ethyl esters and terpenes during storage of a white wine and a model wine medium. Wine and model wine samples were analysed by SPME along with GC–MS. At t = 0, no effect on the concentration of any volatile was observed as a result of adding each phenolic acid in any of wine or model wine samples. Many esters, such as isoamyl acetate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, and linalool decreased during storage of Debina-white wine for up to 20 months. Caffeic acid and gallic acid at 60 mg/L inhibited the decrease of these volatiles. Isoamyl acetate, ethyl hexanoate and linalool decreased during storage of the model wine medium containing 0, 20 or 40 mg/L SO₂. Caffeic acid and gallic acid inhibited the decrease of three volatiles; SO₂ inhibited the decrease of isoamyl acetate and ethyl hexanoate. In some cases, SO₂ increased the inhibitory action of two phenolic acids. The inhibitory action of caffeic acid and gallic acid was dose dependent in the range 0–60 mg/L. Caffeic acid was active at 7.5 mg/L while gallic acid at 15 mg/L.Present results indicate that caffeic acid and gallic acid may be taken into account as potent inhibitors of the disappearance of aromatic volatile esters and terpenes in wines at concentrations similar to those existing in wines.     

Effect of plant extracts on the oxidative stability of sunflower oil and emulsion

The antioxidative activities of six plant extracts (catnip, hyssop, lemon balm, oregano, sage and thyme) were evaluated in sunflower oil and its 20% oil-in-water emulsion in the dark at 60°C. The oxidation process was followed by measuring the formation of primary (conjugated diene hydroperoxides) and secondary (volatile compounds) oxidation products. Sage extracts (600 and 1200 ppm) effectively inhibited the formation of conjugated dienes and volatile compounds (hexanal and pentanal) in oil and emulsion and showed the highest antioxidative activity compared with 300 ppm BHT. Thyme and lemon balm extracts inhibited hexanal generation more than formation of conjugated dienes in both oil and emulsion. Oregano extract was more active in oil than in emulsion. Catnip and hyssop extracts (600 ppm) showed prooxidative action to sunflower oil at 60°C. These two extracts increased the formation of conjugated dienes compared with the control oil. In emulsions, catnip extract (600 ppm) was active and significantly inhibited the formation of conjugated dienes more than BHT (300 ppm) during additional incubation.     

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.     

A novel approach to monitor the oxidation process of different types of heated oils by using chemometric tools

The oxidative stability of seven oils with different fatty acid profiles was assessed. Oxidation at 0, 2 and 4 h at 180 °C was monitored by measuring the absorbance of thiobarbituric acid reactive substances (TBARS) along the absorption spectrum (300–600 nm), the volatile aldehydes (HS-SPME–GC–MS) and the fatty acid profile (FID-GC).TBARS absorption spectrum behavior depended on the lipid composition of heated oils. Higher absorbance increments during heating were noticed at 390 nm compared to 532 nm (from 2 to 21 fold higher depending on the oil), pointing to its better sensitivity to detect oxidation. Furthermore, a close relationship between ABS₃₉₀, the loss of polyunsaturated fatty acids and their corresponding oxidation compounds (volatile aldehydes) was revealed by Principal Component Analysis.Multiparametric equations allowed predicting the formation of volatile aldehydes of heated oils by measuring only two parameters: TBARS₃₉₀ during their heating, and the lipid profile in unheated oils (MUFA, ω-3 and ω-6). Results pointed out the interest of choosing ABS₃₉₀ when the oxidative evolution of vegetable oils under heating is assessed by the TBARS test.     

The use of sedimentation field-flow fractionation in the size characterization of bovine milk fat globules as affected by heat treatment

Size distribution of fat globules affects the appearance, taste and stability of milk and milk-based products. Full-fat, semi-fat and chocolate bovine milk were subjected to heat treatment within a temperature range of 50–125 °C for 1 h. Sedimentation field-flow fractionation was employed to determine the changes in mean particle diameter of milk fat globules as affected by heat treatment. The mean particle diameter of fat droplets increased with increasing heating temperature for most samples. The particle size of fat globules increased on average 40 nm (4.65%) for full-fat and 72 nm (8.52%) for semi-fat milk following the heat treatment (50–125 °C). Chocolate milk exhibited considerable increase in particle size (104 nm, 12.53%) within a certain temperature range (50–110 °C), followed by a decrease in particle size when heated at 125 °C for 1 h. Heat-induced flocculation due to attractive interactions between hydrophobic sites on denatured protein molecules on different droplets was assumed to be mainly responsible for the increases in particle size observed in this study. Extensive heat-induced denaturation of milk proteins was also indicated by Native PAGE. Sedimentation field-flow fractionation proved to be a useful technique for adequately monitoring heat-induced changes in particle size distributions in milk.