Volatile compounds produced in cheese by Enterobacteriaceae strains of dairy origin

The formation of volatile compounds in fresh cheese by 10 Enterobacteriaceae strains of dairy origin (4 Hafnia alvei, 2 Serratia liquefaciens, 1 Enterobacter cloacae, 1 Enterobacter sakazakii, and 2 Escherichia coli strains) was investigated. Small cheeses were made from pasteurized cow's milk separately inoculated with 1-3 x 10(3) CFU/ml of each of the Enterobacteriaceae strains, with glucono-8-lactone added to achieve a pH value of 5.2 in the curds. All strains reached counts close to 10(8) CFU/g in 1-day-old cheeses and survived well from day 1 to day 8. Cheeses were analyzed for volatile compounds by gas chromatography-mass spectroscopy, after extraction by dynamic headspace using a purge and trap apparatus. Sixty-one volatile compounds were determined in cheeses, 31 of which were further investigated. Significant increases of aldehydes, sulfur compounds, and aromatic compounds were recorded from 2-h curd to 1-day-old cheese, and of ketones, alcohols, and acids from 2-h curd to 8-day-old cheese. Acetaldehyde, 2-methyl propanal, and 3-methyl butanal predominated among aldehydes; 2,3-butanedione, 2,3-pentanedione, and 3-hydroxy 2-butanone among ketones; ethanol, 2-methyl propanol, and 3-methyl butanol among alcohols; and ethyl acetate among esters. Hierarchical cluster analysis of strains using the data of 31 volatile compounds separated clearly the strain of E. sakazakii, which produced high amounts of volatile compounds, from the other Enterobacteriaceae strains.     

Occurrence of volatile chiral compounds in dairy products, especially cheese – A review

The current review lists a total of 126 chiral compounds described in the literature for at least 21 different cheese varieties: 30 alcohols, 8 ketones, 2 aldehydes, 20 esters, 20 lactones, 27 carboxylic acids, 13 hydrocarbons (8 terpenes), 4 furanones, and 2 amines. Of these only a few authentic reference compounds are commercially available. All these data are compiled in seven tables.     

Analyzing volatile compounds in dairy products

Volatile compounds give the first indication of the flavor in a dairy product. Volatiles are isolated from the sample matrix and then analyzed by chromatography, sensory methods or an electronic nose. Isolation may be performed by solvent extraction or headspace analysis, and gas chromatography is often employed with various detectors to identify odorants. The human nose is also used as a detector, and electronic noses are being developed to qualitate and quantitate volatiles. A reliable technique for analyzing odorants in dairy products has not yet been invented. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Production of volatile organic compounds by apples

There is great variation in the rate at which different apple cultivars produce volatiles. The rate of production of volatiles, in terms of loss of carbon, is some 0.3–1.0% of the loss of CO₂; depending on conditions of storage, some 50–95% of the carbon lost as volatiles is accounted for by ethylene. Increase in concentration of CO₂ in the storage atmosphere reduces the rate of production of volatiles. Reduction of the oxygen concentration to a low level has the same effect, and ethylene production ceases in the complete absence of oxygen. The peel of the fruit is more active in production of ethylene than is the pulp; the rate of production is greater for small apples than for large. When the volatiles are removed from the storage atmosphere, the rate of production increases. The incidence of superficial scald, and the shape of the time/rate graph for ethylene are related. This could be due to an effect of climate during the growing period, affecting the porosity of the peel.     

Production of volatile organic compounds by pears

There is considerable variation between the rates of production of volatile organic compounds by different cultivars of pears, as has been shown for apples; the rates are lower in controlled atmosphere (C.A. ) storage than in air. When pears which have been cold stored, in air or in C.A. are ripened at a higher temperature, the rate of evolution of ethylene rises rapidly to a high value, but subsequently declines as the pears develop overripe symptoms.     

Growth Conditions Affecting Proteolytic Enzyme and Extracellular Vesicle Production by Pseudomonas fragi ATCC 4973

Pseudomonas fragi ATCC 4973 was grown in liquid culture (trypticase soy broth) and on a solid surface (tryticase soy broth + 1.5% agar). Pseudomonas fragi grown in liquid culture started extracellular proteolytic enzyme production at 24 hr, during the late exponential early stationary growth phase. Pseudomonas fragi, grown on solid surfaces, initiated proteinase production at 4 hr, 20 hr earlier than in liquid medium. Proteinase production was greatest during periods when the cells were not actively growing. Electron micrographs of P. fragi grown on solid surfaces revealed extracellular vesicles ca. 20 nm in diameter “blebbing” off the surface of the cells. The greatest number of vesicles coincided with maximum proteinase production. These vesicles were absent from the surface of P. fragi cells grown in liquid culture.     

Colonization of Beef Muscle Surfaces by Pseudomonas fluorescens and Pseudomonas fragi

Attached and unattached cell densities were determined for Pseudomonas fluorescens and Pseudomonas fragi growing on the surface of beef muscle stored at 4 and 25°C, in presence of NaCl, KCl, and CaCl₂. A mechanical rinsing procedure was developed for this purpose. Both species colonized the surface at both temperatures and were enhanced at low (4°C) temperature. Attached cells represented up to 90% of the total until a density of 10⁵-10⁶ CFU cm^?2 was reached. At that point, a proportion of attached cells to unattached cells declined but colonization of the surface continued. In presence of CaCl₂, ratios of attached to unattached cells did not decline, suggesting a significant role for the calcium ion in colonization. Ability to colonize meat surfaces may be a significant competitive advantage for meat spoilage bacteria such as Pseudomonas fragi and Pseudomonas fluorescens.     

一种硬质蒙古干酪成分组成和风味化合物分析研究

对蒙古干酪的成分和风味化合物进行了系统研究。结果表明,蒙古干酪的水分含量为24.13%,脂肪含量为10.24%,粗蛋白质含量为52.45%,pH值为3.57,符合其低水分含量、低脂、高蛋白、偏酸性的特点。通过固相微萃取-色谱-质谱联用(SPME-GC-MS)方法对蒙古干酪中的风味化合物进行分析,共检出15种风味化合物,包括4种羧酸类、3种醇类、7种酯类和1种其他类化合物。其中,羧酸类相对含量最高。     

Production of volatile compounds by Muskmelon,Cucumis melo

The volatile constituents of ‘PMR 45’, ‘Top Mark’, ‘Honeydew’ and ‘Crenshaw’ cultivars of Muskmelon were examined by trapping the essence on Porapak Q and analysing the eluted compounds on wall coated open-tubular glass capillary columns. The relative concentrations of forty-three compounds were determined. Also, by direct sampling of gas from the fruit cavity of ‘PMR 45’ and ‘Top Mark’ cantaloupe cultivars, the relative concentrations of fifteen compounds were measured daily over a period of eight days. Computer-constructed arrays of chromatograms revealed trends in the progressive changes of volatile compounds produced by the ripening fruits. The volatile constituents measured in this study could be fitted into groups, depending on the pattern exhibited by the production of that compound. One group showed a continuously accelerating rate of production (e.g. ethyl esters, acetaldehyde, ethanol) and another increased rapidly and then plateaued (e.g. acetate esters).     

Production of volatile aroma compounds by kefir starter cultures

Production of carbonyl compounds by single-strain cultures, kefir starter (Lactobacillus delbrueckii subsp. bulgaricus HP1+Lb. helveticus MP12+Lactococcus lactis subsp. lactis C15+Streptococcus thermophilus T15+Saccharomyces cerevisiae A13) and kefir grains during fermentation and storage of kefir was studied. The content of carbonyl compounds produced by kefir starter was greater than that produced by kefir grains. The maximum acetaldehyde concentration (18.3 μg g⁻¹) in kefir with starter culture was mainly due to the metabolic activity of Lb. delbrueckii subsp. bulgaricus HP1 isolated from kefir grains. The highest diacetyl production activity was recorded in the starter culture (1.87 μg g⁻¹) and the single-strain culture St. thermophilus T15 (1.62 μg g⁻¹), followed by Lb. helveticus MP12 (0.85 μg g⁻¹) and Lc. lactis subsp. lactis C15 (0.42 μg g⁻¹). The lactobacilli Lb. delbrueckii subsp. bulgaricus HP1 and Lb. helveticus MP12 produced acetone, which was not found in the cocci cultures. The presence of 2-butanone was related to the production ability of Lb. helveticus MP12. In comparison, Lc. lactis subsp. lactis C15 synthesized ethyl acetate more actively than the other single-strain cultures included in the starter. S. cerevisiae A13 produced ethanol and CO₂ in amounts (3975 μg g⁻¹; 1.80 g L⁻¹) that lent cultured kefir distinctive flavour and aroma characteristic of authentic kefir.     

酸凝干酪成熟过程中挥发性风味物质的分析

就酸凝干酪成熟10,30,50 d时的主要挥发性化合物作了分离、鉴定,并对各种风味化合物的可能来源以及对酸凝干酪风味的贡献大小进行了讨论.结果表明:酸凝干酪在成熟的各个时期所含的挥发性风味化合物不同,成熟10 d时以烷烃类、酸类和其他类中的柠檬油精等为主.成熟30 d时酮类、酸类和其他类中的吡咯、吡啶等含氮化合物成为主要的挥发性的风味化合物.成熟50 d时主要以酮类、酸类和酚类为主.     

Analytical methods for the determination of the geographic origin of Emmental cheese: volatile compounds by GC/MS-FID and electronic nose

The volatile compounds of Emmental cheese of different origins were investigated to check their suitability as markers of geographic origin. A total of 20 Emmental cheese samples from Switzerland, Allgäu (D), Bretagne (F), Savoie (F), Vorarlberg (A) and Finland (produced in winter with a ripening time according to that sold in the corresponding regions) were analysed using dynamic headspace gas chromatography followed by flame ionisation and mass spectrometry. All regions were easily differentiated by using compounds occurring only in the corresponding region or by combining a few compounds by principal component analysis (PCA). Further analyses were carried out using a mass spectrometry-based electronic nose. PCA achieved 90 and 91% of correct classifications for the Emmental from Switzerland and other regions, respectively.     

Effect of wild strains used as starter cultures and adjunct cultures on the volatile compounds of the Pecorino Siciliano cheese

The effect of six wild strains on the volatile profile of the PS cheese was investigated and compared to that generated from industrial starters generally used to produce PS cheese. All cheeses were subjected to microbiological, physicochemical, and volatile compounds analyses. The DGGE of the 16S rDNA analysis was also applied. The volatile compounds generated during ripening were studied through the SPME and the GC-MS methods. No difference was detected between the experimental and control cheeses throughout chemical and microbiological analyses, while the DGGE results showed the presence of Streptococcus thermophilus in all cheeses, and the dominance of Enterococcus durans, Lactobacillus rhamnosus, and Lactobacillus casei in most of the experimental cheeses. Moreover, the presence of Lactococcus lactis species as in the control and in the experimental P2 and P4 cheeses was also revealed. The SPME results showed more pronounced volatile compounds in the experimental cheese samples than in the control ones.     

Comparison of volatile compounds produced in model cheese medium deacidified by Debaryomyces hansenii or Kluyveromyces marxianus

The aroma of a deacidified cheese medium is the result of the overall perception of a large number of molecules belonging to different classes. The volatile compound composition of (60%) cheese medium (pH 5.8) deacidified by Debaryomyces hansenii (DCM(Dh)) was compared with the one deacidified by Kluyveromyces marxianus (DCM(Km)). It was determined by dynamic headspace extraction, followed by gas chromatography separation and quantification as well as by mass spectrometry identification. Whatever the media tested, a first class of volatile compounds can be represented by the ones not produced by any of the yeasts, but some of them are affected by K. marxianus or by D. hansenii. A second class of volatile compounds can be represented by the ones produced by K. marxianus, which were essentially esters. Their concentrations were generally higher than their thresholds, explaining the DCM(Km) global fruity odor. A third class can be represented by the ones generated by D. hansenii, which were essentially methyl ketones with fruity, floral (rose), moldy, cheesy, or wine odor plus 2-phenylethanol with a faded-rose odor. The impact of methyl ketones on the DCMDh global flavor was lower than the impact of 2-phenylethanol and even negligible. Therefore, the global faded-rose odor of D. hansenii DCM can be explained by a high concentration of 2-phenylethanol.     

Impact of processing steps on the composition of volatile compounds in cheese powders

Changes in the composition of volatile compounds during processing of cheese powders, made from Emmental and Danbo cheese were analysed by dynamic headspace gas chromatography–mass spectrometry. Samples comprised cheese, melted cheese slurry, the slurry heat treated using three different time and temperature combinations, and the spray‐dried cheese powder. About 100 volatile compounds were identified. During melting of the cheese the level of some volatile compounds increased significantly; heat treatment mainly leads to a loss of compounds and spray drying leads to a substantial reduction of volatile compounds, with the exception of a range of aldehydes that increased. The final cheese powders could, however, be distinguished according to cheese type.     

Physicochemical and textural characteristics and volatile compounds of semihard goat cheese as affected by starter cultures

Today, cheese is valued because of its high nutritional value and unique characteristics. Improving the texture and flavor of cheese by selecting suitable starter cultures is an important way to promote the development of cheese industry. The effect of starter cultures on the physicochemical and textural properties and volatile compounds during the ripening of semihard goat cheese were investigated in this work. Different starter cultures—mesophilic (M) and thermophilic starters (T), Lactobacillus plantarum ssp. plantarum ATCC 14917 (Lp), a mix of the M and T starters (M1), and mix of the M, T, and Lp starters (M2)—were used in the production of the goat cheeses. Volatile compounds were determined by a solid-phase microextraction/gas chromatography-mass spectrometric (SPME/GC-MS) method. The results showed that the moisture content of cheeses produced with the 5 kinds of starter cultures decreased after maturation, whereas ash content increased. The pH values of goat cheeses decreased first and then increased during maturity, and the pH value of M2 cheese was the lowest among the cheeses. The hardness and chewiness of the cheeses increased with increasing maturity, whereas cohesiveness, springiness, and resilience showed the opposite tendency. The 60-d-old cheese made with Lp had the highest chewiness, cohesiveness, springiness, and resilience, whereas the 60-d-old cheese made with M2 had the highest hardness. A total of 53 volatile components were identified by SPME/GC-MS, and carboxylic acids, alcohols, ketones, and esters were the 4 major contributors to the characteristic flavors of the cheeses. Volatile components and their contents differed greatly among the produced cheeses. The M2 cheese contained the highest relative content of the main volatile compounds (90.10%), especially butanoic acid and acetoin. Through a comprehensive comparison of the results, we concluded that M2 cheese had a dense texture and milky flavor, and M2 is a potential starter culture candidate for the production of goat cheese.     

芳樟醇对三文鱼源莓实假单胞菌的抑菌机理

本研究应用高通量测序技术分析不同贮藏期三文鱼的菌相变化,并分离、纯化、鉴定出1 株4 ℃贮藏环境下三文鱼的优势腐败菌——莓实假单胞菌MS 02（Pseudomonas fragi MS 02）。再以分离出的莓实假单胞菌MS 02为靶标菌,深入探究芳樟醇对其抑菌性能及其抑菌机理。结果表明：4 ℃贮藏三文鱼的菌相呈现动态变化的趋势,其中发光杆菌属、假单胞菌属、青枯菌属和不动杆菌属细菌在三文鱼贮藏中占主要地位。随着贮藏时间的延长,假单胞菌属的相对丰度逐渐增大,而莓实假单胞菌是三文鱼在贮藏期间增长速率最快的菌种。以分离鉴定出的莓实假单胞菌MS 02为研究对象,发现芳樟醇对其具有良好的抑菌效果,扫描电子显微镜观察结果表明芳樟醇能使细菌细胞膜产生凹陷褶皱,而电导率、OD260 nm、二乙酸荧光素荧光强度和碱性磷酸酶（alkaline phosphatase,AKP）、钠钾ATP酶活力测定结果证明芳樟醇能破坏莓实假单胞菌的细胞膜和细胞壁的通透性和完整性,进而影响细菌细胞正常能量代谢,最终导致菌体死亡。     

Production of bacteriocin-like inhibitory compounds by human fecal Bifidobacterium strains

Acid- and bile-resistant Bifidobacterium strains were isolated from human feces and identified by genus-specific PCR and randomly amplified polymorphic DNA PCR. Twenty-four different strains were screened for possible production of proteinaceous antimicrobial compounds by assaying the inhibitory effects of their neutralized culture supernatants. Six Bifidobacterium strains (BIR-0304, BIR-0307, BIR-0312, BIR-0324, BIR-0326, and BIR-0349) were selected on the basis of their broad inhibitory spectra. These strains were active against gram-positive and gram-negative bacteria and yeasts relevant to food safety and human health. The antagonistic effects of the six selected Bifidobacterium strains were related to bacteriocin-like compounds, which were active at pH values between 3 and 10, stable at 100 degrees C for 10 min, resistant to alpha-amylase and lipase A, but sensitive to proteinases (trypsin, proteinase K, protease A, pepsin, and cathepsin B). The molecular masses of the antimicrobial compounds produced by Bifidobacterium BIR-0312 and BIR-0324 were in the range of 10 to 30 kDa, and those of the compounds produced by Bifidobacterium BIR-0304, BIR-0307, BIR-0326, and BIR-0349 were less than 10 kDa. All Bifidobacterium strains produced maximum antimicrobial activities in the late logarithmic phase of growth and in the presence of Tween 80. These results confirm that the synthesis of bacteriocin-like inhibitory compounds is a key factor in the in vitro inhibition of pathogen and spoilage bacteria by Bifidobacterium strains.     

不同部位奶公犊小白牛肉挥发性风味物质分析

取120d奶公犊不同部位小白牛肉(牛腩、牛柳、牛霖),利用顶空固相微萃取技术(SPME)采集风味物质,采用气相色谱和质谱联用法(GC—MS)对风味物质进行定性分析和峰面积相对含量测定。结果表明:同一类化合物在不同部位小白牛肉所占比例不同。其中牛腩的醛类含量最低,只有32.181%,牛腩的烃类含量最高,是牛柳、牛霖的2倍之多,牛霖的酮类含量最低,只有2.928%。不同部位挥发性风味物质种类及占总风味含量的比例不同,牛腩中的挥发性风味物质种类64种、牛柳48种、牛霖34种。