Headspace analysis of natural yoghurt using headspace solid phase microextraction : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Food Technology at Massey University (Turitea Campus), Palmerston North, New Zealand

The Solid Phase Microextraction (SPME) method was originally developed to extract volatile and semivolatile compounds from wastewater samples but has since been applied to flavour compounds in foods and beverages. Research using the HS-SPME in related areas such as cheese and skim milk powder has been carried out but, to date, no work has been done on yoghurt flavours. The main objective of this study was to devise a methodology for the Headspace Solid Phase Microextraction (HS-SPME) technique to investigate and quantify six flavour analytes in natural, set yoghurts made from recombined milk. The relevant literature was reviewed and from it, a research proposal for this work on yoghurts was drawn. The first step in analysing and quantifying the yoghurt volatiles was to set up a working methodology for the HS-SPME method. The 100 μm polydimethylsiloxane (PDMS) fibre was chosen along with 20 minutes being the optimum fibre adsorption time. General equipment, materials and methods used throughout this thesis are also detailed. The external standard (ES) method was used to calibrate the GC and quantify the analyte concentrations in this study. The internal standard (IS) method was not used as a quantitative tool in this study. Once the HS-SPME methodology had been set up for the analysis of yoghurts, the classical Static Headspace (SH) method was compared with the HS-SPME method for extraction efficiency. The results suggested that the two methods were complementary in that the SH method extracted the more volatile compounds (acetaldehyde, acetone and 2-butanone) whereas, the HS-SPME method extracted the semi- to non-volatile compounds (ethanol, diacetyl and acetoin) more readily. However, the HS-SPME was found to be the more sensitive and effective method of the two techniques tested. The next step in the thesis was to investigate the presence of the six analytes in milk and cultured yoghurt. The effects of the sample matrix, fat levels and incubation on the volatile concentrations were also examined. The results suggested that the six analytes were inherently present in milks but at low concentrations. No conclusive effects were found for the sample matrix, fat levels and incubation. However, it was evident that fermentation of the milks using bacterial starter cultures resulted in a large increase in some of the volatiles being investigated. Following this, the effects of fat levels, storage time and storage temperature on the six volatiles in yoghurts were examined. The results indicated that significant fat level effects were only seen for diacetyl and acetoin, while temperature effects were only observed for ethanol. In both trials, only general trends for the analytes concentrations were drawn because the data varied from day to day. The results suggested that most of the compounds decreased with time except for diacetyl, which seemed to increase. The final part of this study looked at applying the devised HS-SPME methodology to a series of commercial yoghurts as a preliminary trial, with a view to investigating a potential application for the HS-SPME method. Fourteen commercial yoghurts were analysed and the six analytes quantified. The data obtained was analysed using Principle Component Analysis (PCA), which divided the yoghurts into groups based on their analyte concentrations. From these groupings, eight yoghurts were selected and fresh samples were analysed using HS-SPME and PCA. This was carried out parallel with an untrained consumer panel, which had to distinguish differences between the yoghurts in a series of triangle tests by smelling the headspace on opening the yoghurt containers. The conclusions drawn were that, unlike the HS-SPME method with PCA, the average consumer could not differentiate the yoghurts based on smell alone. PCA also showed that the HS-SPME results obtained were fairly reproducible. In conclusion, the HS-SPME method was shown to be a useful analytical technique, which can be used to analyse and quantify flavour compounds in natural, set yoghurts. This area of investigation has a lot of scope, with the results from this study providing a basis or starting point for further investigations in this area. Future studies may lead to potential applications for the HS-SPME method, one of which may be quality control where correlation of sensory data with HS-SPME analytical data is required

Honey volatiles as a fingerprint for botanical origin: a review on their occurrence on monofloral honeys

Honeys have specific organoleptic characteristics, with nutritional and health benefits, being highly appreciated by consumers, not only in food but also in the pharmaceutical and cosmetic industries. Honey composition varies between regions according to the surrounding flora, enabling its characterization by source or type. Monofloral honeys may reach higher market values than multifloral ones. Honey's aroma is very specific, resulting from the combination of volatile compounds present in low concentrations. The authentication of honey's complex matrix, according to its botanical and/or geographical origin, represents a challenge nowadays, due to the different sorts of adulteration that may occur, leading to the search for reliable marker compounds for the different monofloral honeys. The existing information on the volatiles of monofloral honeys is scarce and disperse. In this review, twenty monofloral honeys and honeydews, from acacia, buckwheat, chestnut, clover, cotton, dandelion, eucalyptus, fir tree, heather, lavender, lime tree, orange, pine, rape, raspberry, rhododendron, rosemary, strawberry tree, sunflower and thyme, were selected for volatile comparison purposes. Taking into consideration the country of origin, the technique of isolation and analysis, the five main volatiles from each of the honeys are compared. Whereas some compounds were found in several types of monofloral honey, and thus not considered good volatile markers, some monofloral honeys revealed characteristic volatile compounds independently of their provenance.Funding: SFRH/BD/117013/2016, UID/AGR/00690/2019, UID/AMB/50017/2019, MED (UIDB/05183/2020), FEDER, PT2020 PACompete 2020info:eu-repo/semantics/publishedVersio

Characterization of craft beer through flavour component analysis by GC-MS and multivariate statistical tools

Beer is a rather popular drink and represents the most widely consumed alcoholic beverage in the world.The present research aims at characterizing the flavour profile of lager pilsner, the category of low fermentation beers most common in Europe. The largest portion of the global market is dominated by a few multinational companies, but in the last years the number of independent craft breweries has increased very rapidly also in countries where there weren’t an established craft brewing tradition. According to the Italian Brewers Association, in Italy there are eight brewing companies which operate 14 industrial breweries, which in the years have standardized the product to increase their slice of market. The craft-beer sector represents a niche market, about 3% of total production (1% in 2011) [EU Report, 2016]. Italy has a relatively young craft brewing tradition, but the data together with the new ways of consumption, can be considered promising for the sector development. In 2016, the “craft beer” has been defined for the first time in Italy with DDL 1328-B (art.35). Legislation does not consider the quality of the raw materials, but only the manufacturing processes: the artisanal beer-making is a beer obtained without microfiltration and pasteurization steps, unlike industrial products. In this contest, the aim of the study was to characterize the beers (all lager style) purchased on the market through the analysis of the aromatic profile of samples produced under different processes (craft methods or industrial processes). In fact, in addition to smaller production scale and independent, the main characteristic of craft beer is to put the emphasis on flavour and brewing techniques. Flavour, consisting of a large number of volatile compounds, has a great influence on consumer acceptability and, when safety and nutritional value are guaranteed, sensory parameters become the discriminating factor in the product quality assessment which determines the differentiation on the market. The identification of specific compounds, which confer a particular aroma, suitable to be used as potential quality/process markers in order to discriminate beer samples according to their production method. A headspace solid-phase microextraction coupled to gas chromatography-mass spectrometry (HS-SPME-GC-MS) was performed to evaluate the beer samples fingerprint. Multivariate statistical methods were then applied to the collected profiles to built model which could allow differentiating craft beers from all the others. Hence, the proposed method may represent an interesting tool to authenticate craft beer by verification of the compliance with their label description which, at the same time, can entail brand protection

Potentialities of two solventless extraction approaches—Stir bar sorptive extraction and headspace solid-phase microextraction for determination of higher alcohol acetates, isoamyl esters and ethyl esters in wines

A stir bar sorptive extraction with liquid desorption followed by large volume injection coupled to gas chromatography–quadrupole mass spectrometry (SBSE-LD/LVI-GC–qMS) was evaluated for the simultaneous determination of higher alcohol acetates (HAA), isoamyl esters (IsoE) and ethyl esters (EE) of fatty acids. The method performance was assessed and compared with other solventless technique, the solid-phase microextraction (SPME) in headspace mode (HS). For both techniques, influential experimental parameters were optimised to provide sensitive and robust methods. The SBSE-LD/LVI methodology was previously optimised in terms of extraction time, influence of ethanol in the matrix, liquid desorption (LD) conditions and instrumental settings. Higher extraction efficiency was obtained using 60 min of extraction time, 10% ethanol content, n-pentane as desorption solvent, 15 min for the back-extraction period, 10 mL min−1 for the solvent vent flow rate and 10 °C for the inlet temperature. For HS-SPME, the fibre coated with 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) afforded highest extraction efficiency, providing the best sensitivity for the target volatiles, particularly when the samples were extracted at 25 °C for 60 min under continuous stirring in the presence of sodium chloride (10% (w/v)). Both methodologies showed good linearity over the concentration range tested, with correlation coefficients higher than 0.984 for HS-SPME and 0.982 for SBES-LD approach, for all analytes. A good reproducibility was attained and low detection limits were achieved using both SBSE-LD (0.03–28.96 μg L−1) and HS-SPME (0.02–20.29 μg L−1) methodologies. The quantification limits for SBSE-LD approach ranging from 0.11 to 96.56 μg L−and from 0.06 to 67.63 μg L−1 for HS-SPME. Using the HS-SPME approach an average recovery of about 70% was obtained whilst by using SBSE-LD obtained average recovery were close to 80%. The analytical and procedural advantages and disadvantages of these two methods have been compared. Both analytical methods were used to determine the HAA, IsoE and EE fatty acids content in “Terras Madeirenses” table wines. A total of 16 esters were identified and quantified from the wine extracts by HS-SPME whereas by SBSE-LD technique were found 25 esters which include 2 higher alcohol acetates, 4 isoamyl esters and 19 ethyl esters of fatty acids. Generally SBSE-LD provided higher sensitivity with decreased analysis time

Use of headspace solid-phase microextraction for the analysis and characterisation of volatile compounds in rumen contents : a thesis presented in partial fulfillment of the requirements for the degree of Masterate of Science in Chemistry at Massey University

Appendix 2&3 removed due to copyright restrictions. Please consult print copy in Library.Volatile fatty acids (VFAs), alkyl phenols and indolic compounds are produced by rumen microbes during the fermentation of forages in ruminants. In this study, ruminal fluid obtained from sheep was examined by headspace solid-phase microextraction (SPME) sampling followed by GC-MS analysis. This technique provides a non-invasive, clean and selective method to characterize the volatiles in ruminal fluid from an in vitro fermentation system. The factors which can influence the extraction efficiency were studied and include the SPME fibre, sample volume, pH of sample matrix (rumen fluid) and extraction time by the fibre in the headspace. The optimum experimental conditions for the analytes in question included: polyacrylate fibre to perform the headspace SPME above 20 mL of rumen fluid in a 68 mL vial for 5 min, followed by immediate GC-MS analysis. The pH of the rumen fluid sample greatly influenced VFA extraction efficiency. Quantitative analysis of p-cresol, m-cresol, indole and skatolc with SPME were compared with steam distillation simultaneous extraction. This comparison showed that the HS-SPME method was semi-quantitative. The optimum in vitro system (16 mL of rumen fluid and 4 mL of artificial saliva in a 68 mL vial incubated at 39°C) was utilised to study production of indole, skatolc and p-cresol from the anaerobic fermentation of tryptophan and tyrosine. Spirulina is an abundant source of dietary protein. Therefore, ¹³C labelled spirulina was used to study the metabolism of protein and formation of analytes derived from ruminal metabolism of protein. A series of labelled end products, including toluene, acetic acid, propanoic acid, iso-butyric acid, n-butyric acid, iso-valeric acid, n-valeric acid, p-cresol, indole, skatole, dimethyldisulfide and dimethyltrisulfide were detected by GC-MS. This result indicates that these compounds are the products of ruminal metabolism of spirulina. When applied to the in vitro rumen system the headspace SPME technique provides a fast approach to study metabolism of target compounds and allows the researcher to follow proposed pathways with labelled substrate

A chromatographic approach to distinguish Gram-positive from Gram-negative bacteria using exogenous volatile organic compound metabolites

This paper utilized L-alanine aminopeptidase activity as a useful approach to distinguish between Gram-negative and Gram-positive bacteria. This was done using two enzyme substrates, specifically 2-amino-N-phenylpropanamide and 2-amino-N-(4-methylphenyl)propanamide which liberated the volatile compounds aniline and p-toluidine, respectively. Two complementary analytical techniques have been used to identify and quantify the VOCs, specifically static headspace multicapillary column gas chromatography ion mobility spectrometry (SHS-MCC-GC-IMS) and headspace solid phase microextraction gas chromatography mass spectrometry (HS-SPME-GC-MS). Superior limits of detection were obtained using HS-SPME-GC-MS, typically by a factor of x6 such that the LOD for aniline was 0.02 μg/mL and 0.01 μg/mL for p-toluidine. In addition, it was also possible to determine indole interference-free by HS-SPME-GC-MS at an LOD of 0.01 μg/mL. The approach was applied to a range of selected bacteria: 15 Gram-negative and 7 Gram-positive bacteria. Use of pattern recognition, in the form of Principal Component Analysis, confirmed that it is possible to differentiate between Gram-positive and Gram-negative bacteria using the enzyme generated VOCs, aniline and p-toluidine. The exception was Stenotrophomonas maltophilia which showed negligible VOC concentrations for both aniline and p-toluidine, irrespective of the analytical techniques used and hence was not characteristic of the other Gram-negative bacteria investigated. The developed methodology has the potential to be applied for clinical and food applications

Comparison of two extraction methods for evaluation of volatile constituents patterns in commercial whiskeys: Elucidation of the main odour-active compounds

An analytical procedure based on manual dynamic headspace solid-phase microextraction (HS-SPME) method and the conventional extraction method by liquid–liquid extraction (LLE), were compared for their effectiveness in the extraction and quantification of volatile compounds from commercial whiskey samples. Seven extraction solvents covering a wide range of polarities and two SPME fibres coatings, has been evaluated. The highest amounts extracted, were achieved using dichloromethane (CH2Cl2) by LLE method (LLECH2Cl2)(LLECH2Cl2) and using a CAR/PDMS fibre (SPMECAR/PDMS) in HS-SPME. Each method was used to determine the responses of 25 analytes from whiskeys and calibration standards, in order to provide sensitivity comparisons between the two methods. Calibration curves were established in a synthetic whiskey and linear correlation coefficient (r ) were greater than 0.9929 for LLECH2Cl2LLECH2Cl2 and 0.9935 for SPMECAR/PDMS, for all target compounds. Recoveries greater than 80% were achieved. For most compounds, precision (expressed by relative standard deviation, R.S.D.) are very good, with R.S.D. values lower than 14.78% for HS-SPME method and than 19.42% for LLE method. The detection limits ranged from 0.13 to 19.03 μg L−1 for SPME procedure and from 0.50 to 12.48 μg L−1 for LLE. A tentative study to estimate the contribution of a specific compound to the aroma of a whiskey, on the basis of their odour activity values (OAV) was made. Ethyl octanoate followed by isoamyl acetate and isobutyl alcohol, were found the most potent odour-active compounds

Comparative study on freeze-dried lactic cheese starters and ripening cultures for the production of camembert cheese : a thesis submitted in partial fulfillment of the requirements for the degree of Master of Food Technology, Massy [i.e. Massey] University, Albany, New Zealand.

Background and Methodology The key to success in producing cheeses is the performance of the starter cultures (Parente and Cogan, 2004). Storage of freeze-dried cheese cultures at refrigeration and ambient temperature or higher provides convenience to culture handling and transportation, as well as reduce cost. This study investigated the effects of 4 storage temperatures: -18°C, 4°C, 20°C and 37°C on the stability of mesophilic lactic cheese starters and ripening cultures intended for Camembert production. In phase one, a 22 randomized complete block design (RCBD) was used to determine the potential of 14 commercial freeze-dried direct-vat-set (DVS) mixed cultures to produce Camembert after 5 months storage at the 4 temperatures. The cultures used were: O-type: Lactococcus (L.) lactis subsp. lactis, L. lactis subsp. cremoris; LD-type: L. lactis subsp. lactis, L. lactis subsp. cremoris, L. lactis subsp. lactis biovar. diacetylactis and Leuconostoc species (Leuconostoc (Leuc.) lactis and Leuc. mesenteroides subsp. cremoris) and a mould, Penicillum (P.) camemberti. During storage, the cultures were analysed for cell viability, acid production, colour and species composition. The characterised cultures were screened to select the most stable cultures with good potential for Camembert production. In phase two, a 23 RCBD design was used to study the potential of the cultures to produce prototype Camembert cheese using I-Make® Limited domestic cheese kits. The prepared cheeses were characterised for acidity, viable cell counts content, texture, volatile aromatic compounds and proteolysis using standard procedures. Results and Discussion Viable cell counts and acidification potential of cultures decreased (P<0.05) during storage at selected temperatures for 5 months. Cultures stored at 37°C were the most affected. Proportion of citrate-fermenting lactic acid bacteria (LAB) in LD-type starters also decreased in a similar pattern. Cell inactivation at high temperature was probably attributed to high oxidation, browning reactions, lactose crystallization, changes in glass transition temperature (Tg) of culture-lactose matrix and loss of β-galactosidase enzyme activity, which were possibly also affected by water activity (aw) of the culture during storage (Higl et al., 2007; Kurtmann et al., 2009c). Viability and activities of cultures stored at 4 and 20°C after 5 months were comparable to those of -18°C cultures and levels normally used in industry. Thus, the cultures demonstrated good potential for Camembert cheese production. Similar patterns of microbial growth (LAB and P. camemberti) and acidification were observed in both cheeses (O- and LD-types) during cheese fermentation. However, cheeses fermented with O-type starters had better growth and acidification activity (P<0.05), which may be attributed to compositional differences of culture, leading to variable metabolic patterns (Mcsweeney and Fox, 2004). Cheeses produced with cultures stored at 4 and 20°C had lower levels of cell growth and acidity (P<0.05), suggesting that the microorganisms could have been affected by prolonged storage at relatively high temperatures. During cheese ripening, changes in microbial content, acidity, proteolysis, texture and aroma compounds, were similar, and significantly changed (P<0.05) with ripening time. Viable cell counts of LAB reduced, while pH and P. camemberti counts increased. Increase of pH may result from lactate metabolism by P. camemberti creating an alkaline environment due to the deamination activity of the mould (Spinnler and Gripon, 2004). Proteolysis of cheeses was correlated (P<0.05) with LAB and P. camemberti activity as well as the pH of Background and Methodology The key to success in producing cheeses is the performance of the starter cultures (Parente and Cogan, 2004). Storage of freeze-dried cheese cultures at refrigeration and ambient temperature or higher provides convenience to culture handling and transportation, as well as reduce cost. This study investigated the effects of 4 storage temperatures: -18°C, 4°C, 20°C and 37°C on the stability of mesophilic lactic cheese starters and ripening cultures intended for Camembert production. In phase one, a 22 randomized complete block design (RCBD) was used to determine the potential of 14 commercial freeze-dried direct-vat-set (DVS) mixed cultures to produce Camembert after 5 months storage at the 4 temperatures. The cultures used were: O-type: Lactococcus (L.) lactis subsp. lactis, L. lactis subsp. cremoris; LD-type: L. lactis subsp. lactis, L. lactis subsp. cremoris, L. lactis subsp. lactis biovar. diacetylactis and Leuconostoc species (Leuconostoc (Leuc.) lactis and Leuc. mesenteroides subsp. cremoris) and a mould, Penicillum (P.) camemberti. During storage, the cultures were analysed for cell viability, acid production, colour and species composition. The characterised cultures were screened to select the most stable cultures with good potential for Camembert production. In phase two, a 23 RCBD design was used to study the potential of the cultures to produce prototype Camembert cheese using I-Make® Limited domestic cheese kits. The prepared cheeses were characterised for acidity, viable cell counts content, texture, volatile aromatic compounds and proteolysis using standard procedures. Results and Discussion Viable cell counts and acidification potential of cultures decreased (P<0.05) during storage at selected temperatures for 5 months. Cultures stored at 37°C were the most affected. Proportion of citrate-fermenting lactic acid bacteria (LAB) in LD-type starters also decreased in a similar pattern. Cell inactivation at high temperature was probably attributed to high oxidation, browning reactions, lactose crystallization, changes in glass transition temperature (Tg) of culture-lactose matrix and loss of β-galactosidase enzyme activity, which were possibly also affected by water activity (aw) of the culture during storage (Higl et al., 2007; Kurtmann et al., 2009c). Viability and activities of cultures stored at 4 and 20°C after 5 months were comparable to those of -18°C cultures and levels normally used in industry. Thus, the cultures demonstrated good potential for Camembert cheese production. Similar patterns of microbial growth (LAB and P. camemberti) and acidification were observed in both cheeses (O- and LD-types) during cheese fermentation. However, cheeses fermented with O-type starters had better growth and acidification activity (P<0.05), which may be attributed to compositional differences of culture, leading to variable metabolic patterns (Mcsweeney and Fox, 2004). Cheeses produced with cultures stored at 4 and 20°C had lower levels of cell growth and acidity (P<0.05), suggesting that the microorganisms could have been affected by prolonged storage at relatively high temperatures. During cheese ripening, changes in microbial content, acidity, proteolysis, texture and aroma compounds, were similar, and significantly changed (P<0.05) with ripening time. Viable cell counts of LAB reduced, while pH and P. camemberti counts increased. Increase of pH may result from lactate metabolism by P. camemberti creating an alkaline environment due to the deamination activity of the mould (Spinnler and Gripon, 2004). Proteolysis of cheeses was correlated (P<0.05) with LAB and P. camemberti activity as well as the pH ofBackground and Methodology The key to success in producing cheeses is the performance of the starter cultures (Parente and Cogan, 2004). Storage of freeze-dried cheese cultures at refrigeration and ambient temperature or higher provides convenience to culture handling and transportation, as well as reduce cost. This study investigated the effects of 4 storage temperatures: -18°C, 4°C, 20°C and 37°C on the stability of mesophilic lactic cheese starters and ripening cultures intended for Camembert production. In phase one, a 22 randomized complete block design (RCBD) was used to determine the potential of 14 commercial freeze-dried direct-vat-set (DVS) mixed cultures to produce Camembert after 5 months storage at the 4 temperatures. The cultures used were: O-type: Lactococcus (L.) lactis subsp. lactis, L. lactis subsp. cremoris; LD-type: L. lactis subsp. lactis, L. lactis subsp. cremoris, L. lactis subsp. lactis biovar. diacetylactis and Leuconostoc species (Leuconostoc (Leuc.) lactis and Leuc. mesenteroides subsp. cremoris) and a mould, Penicillum (P.) camemberti. During storage, the cultures were analysed for cell viability, acid production, colour and species composition. The characterised cultures were screened to select the most stable cultures with good potential for Camembert production. In phase two, a 23 RCBD design was used to study the potential of the cultures to produce prototype Camembert cheese using I-Make® Limited domestic cheese kits. The prepared cheeses were characterised for acidity, viable cell counts content, texture, volatile aromatic compounds and proteolysis using standard procedures. Results and Discussion Viable cell counts and acidification potential of cultures decreased (P<0.05) during storage at selected temperatures for 5 months. Cultures stored at 37°C were the most affected. Proportion of citrate-fermenting lactic acid bacteria (LAB) in LD-type starters also decreased in a similar pattern. Cell inactivation at high temperature was probably attributed to high oxidation, browning reactions, lactose crystallization, changes in glass transition temperature (Tg) of culture-lactose matrix and loss of β-galactosidase enzyme activity, which were possibly also affected by water activity (aw) of the culture during storage (Higl et al., 2007; Kurtmann et al., 2009c). Viability and activities of cultures stored at 4 and 20°C after 5 months were comparable to those of -18°C cultures and levels normally used in industry. Thus, the cultures demonstrated good potential for Camembert cheese production. Similar patterns of microbial growth (LAB and P. camemberti) and acidification were observed in both cheeses (O- and LD-types) during cheese fermentation. However, cheeses fermented with O-type starters had better growth and acidification activity (P<0.05), which may be attributed to compositional differences of culture, leading to variable metabolic patterns (Mcsweeney and Fox, 2004). Cheeses produced with cultures stored at 4 and 20°C had lower levels of cell growth and acidity (P<0.05), suggesting that the microorganisms could have been affected by prolonged storage at relatively high temperatures. During cheese ripening, changes in microbial content, acidity, proteolysis, texture and aroma compounds, were similar, and significantly changed (P<0.05) with ripening time. Viable cell counts of LAB reduced, while pH and P. camemberti counts increased. Increase of pH may result from lactate metabolism by P. camemberti creating an alkaline environment due to the deamination activity of the mould (Spinnler and Gripon, 2004). Proteolysis of cheeses was correlated (P<0.05) with LAB and P. camemberti activity as well as the pH of samples. Softening of cheese was associated with increased proteolysis and pH due to the growth of P. camemberti (Spinnler and Gripon, 2004). A range of volatile organic compounds, dominated by fatty acids, alcohols and aldehydes were identified in cheese samples as reported in other studies (Sable and Cottenceau, 1999). Changes in 3-methylbutanal and 3-methylbutanol profiles of samples reflected the degradation of leucine,, synthesis of the aldehyde and its degradation to branched alcohols as a consequence of peptidolytic activity of LAB (Yvon and Rijene, 2001) and enzymatic activity of P. camemberti (Molimard and Spinnler, 1996). Increased concentrations of 2-heptanone, 2-nonanone and butyric acid in cheese samples suggested lipolytic activity in all samples (Molimard and Spinnler, 1996). The activity of P. camemberti involved in β-oxidation pathway for producing methyl ketones was also demonstrated confirmed by identified metabolites. Higher proteolysis and softness in LD-cheeses than O-type, suggested a higher degree of cheese ripening (Ardö, 1999), which may be attributed to proteolytic and peptidolytic activity of LD-starters (Tzanetaki et al., 1993). Higher proteolysis may be also associated with higher pH of cheese curd at draining, which facilitated higher syneresis. Increased whey content of curd may retain higher concentration of coagulant enzyme in the curd (Guinee and Wilkinson, 1992) and effectively stimulate the growth of P. camemberti, thus probably allowing proteolysis to occur more readily (Grappin et al., 1985). A relatively higher concentration of 3-methylbutanal was found in O-type cheeses than in LD-type. This suggests that LAB in O-type starters may exhibit higher activity in degrading leucine to 3-methylbutanal than LD-type starters (Yvon and Rijene, 2001). 2,3-butandione was suspected in LD-type cheeses but not in O-type samples, demonstrating the active role of citrate-fermenting bacteria of LD-starters (Mcsweeney and Fox, 2004). Results indicate that storage temperature of cultures had a significant (P<0.05) impact on viable cell counts and acidity of samples. In spite of reduced cell counts, proteolysis, texture and aroma of the prototype cheese samples were not affected (P<0.05). Although there were no differences between the Camembert cheeses, 4 and 20°C cultures used in cheese-making may enhance the ripening process (Ardö, 1999) than -18°C cultures, as indicated by relatively higher proteolysis and degree of softening. Lower levels of 3-methylbutanal in samples containing 4 and 20°C cultures was probably due to the reduced aminotransferases activity of LAB (Yvon and Rijene, 2001) after prolonged storage at the two temperatures. The slightly higher levels of 2-heptanone, 2-nonanone and butyric acids in samples with 4 and 20°C cultures were probably due to increased lipolytic activity of enhanced growth of P. camemberti (Molimard and Spinnler, 1996) during cheese ripening. Conclusion LAB starter cultures and P. camemberti can be stored for 5 months at 4 and 20°C without affecting their activities and the quality of prototype Camembert produced. Camembert cheese samples produced in this study had typical characteristics of this type of cheese. Cheese fermented with LD-type starters showed extra flavour enhancement potential and the products had higher degree of softening due pronounced proteolysis. Cultures stored at 37°C for 5 months were characterised by poor viable cells and capability to the produce acid, therefore, they were not suitable for Camembert cheese production

Chromatography of beer

The objectives of the review are the collection, concise description and evaluation of the various chromatographic techniques used for the separation and quantitative determination of macro- and microcomponents present in beers

A headspace solid-phase microextraction method of use in monitoring hexanal and pentane during storage: Application to liquid infant foods and powdered infant formulas

The determination of two secondary lipid oxidation compounds (hexanal and pentane) in liquid infant foods using a headspace solid-phase microextraction gas chromatographic (HS-SPME-GC) method has been developed and validated. The HS-SPME analytical conditions (fibre position, equilibration and sampling times) were selected. The analytical parameters of the method (linearity: hexanal from 2.48 to 84.78 ng/g, pentane from 6.21 to 79.55 ng/g; precision: hexanal 2.87%, pentane 2.343.46%; recovery: hexanal 106.60%, pentane 95.39%; detection limit: hexanal 3.63 ng and pentane 4.2 ng) demonstrate the usefulness of the method. Once optimized, the method was applied to liquid infant foods based on milk and cereals, and to powdered adapted and follow-up milk-based infant formulas (IF), stored for four and seven months. In all cases the hexanal content was higher in IF than in milk-cereal based infant foods. No pentane was found in IF