Inhibition of Brevibacterium linens by Probiotics from Dairy Products

Brevibacterium linens is an important species in dairy products rendering a specific taste and aroma to numerous smear ripened and blue veined cheeses due to proteolysis. However, the presence of the species in South African blue veined cheeses is undesirable and consumers demand the product void of the species. Accordingly, numerous methods including microbial inhibition using fungi and bacterial probiotic cultures with possible inhibitory effects were applied in an attempt to inhibit the species. None of the fungi, however, proved to be successful, whereas Lactobacillus rhamnosus and Bifidobacterium lactis, two typical probiotic species applied in dairy products, showed inhibitory effects against B. linens when tested using the spot-on-lawn assay

Hlapljivi organski spojevi u mlijeku dobivenom prirodnom fermentacijom i fermentacijom s pomoću pojedinačnih ili mješovitih kultura kvasaca i mliječno-kiselih bakterija

The volatile organic compounds present in 18 Zimbabwean naturally fermented milk (amasi) samples and those produced by various yeasts, lactic acid bacteria (LAB) and yeast/ LAB combinations were determined using headspace gas chromatography. The yeast strains used were: Candida kefyr 23, C. lipolytica 57, Saccharomyces cerevisiae 71, C. lusitaniae 68, C. tropicalis 78, C. lusitaniae 63, C. colliculosa 41, S. dairenensis 32, and Dekkera bruxellensis 43, and were coded Y1 to Y9, respectively. The LAB strains used were Lactococcus lactis subsp. lactis Lc39, L. lactis subsp. lactis Lc261, Lactobacillus paracasei Lb11, and L. lactis subsp. lactis biovar. diacetylactis C1, and were coded B1 to B4, respectively. Some of the volatile organic compounds found in amasi were acetaldehyde, ethanol, acetone, 2-methyl propanal, 2-methyl-1-propanol and 3-methyl-1-butanol. However, the levels of volatile organic compounds in the naturally fermented milk (NFM) samples varied from one sample to another, with acetaldehyde ranging from 0.1–18.4 ppm, 3-methyl butanal from <0.1–0.47 ppm and ethanol from 39.3–656 ppm. The LAB/C. kefyr 23 (B/Y1) co-cultures produced significantly (p<0.05) higher levels of acetaldehyde and ethanol than the levels found in the NFM. The acetaldehyde levels in the B/Y1 samples ranged from 26.7–87.7 ppm, with L. lactis subsp. lactis biovar. diacetylactis C1 (B4) producing the highest level of acetaldehyde in combination with C. kefyr 23 (Y1). Using principal component analysis (PCA), most of the NFM samples were grouped together with single and co-cultures of Lc261, Lb11 and the non-lactose fermenting yeasts, mainly because of the low levels of ethanol and similar levels of 3-methyl butanal. Chromatograms of amasi showed prominent peak of methyl aldehydes and their alcohols including 3-methyl-butanal and 3-methyl-butanol, suggesting that these compounds are important attributes of Zimbabwean naturally fermented milk.Hlapljivi organski proizvodi, u 18 uzoraka prirodno fermentiranog mlijeka iz Zimbabvea (amasi) i mlijeka dobivenog fermentacijom s pomoću kvasaca, mliječno-kiselih bakterija (LAB) i kombinacijom kvasaca i mliječno-kiselih bakterija određeni su plinskom kromatografijom na čvrstoj fazi. Upotrijebljeni su ovi sojevi kvasaca: Candida kefyr 23, C. lipolytica 57, Saccharomyces cerevisiae 71, C. lusitaniae 68, C. tropicalis 78, C. lusitaniae 63, C. colliculosa 41, S. dairenensis 32 i Dekkera bruxellensis 43, te su označeni s Y1 do Y9. Od LAB korišteni su sojevi Lactococcus lactis subsp. lactis Lc39, L. lactis subsp. lactis Lc261, Lactobacillus paracasei Lb11 i L. lactis subsp. lactis biovar. diacetylactis C1, označeni s B1 do B4. Acetaldehid, etanol, aceton, 2-metilpropanal, 2-metil-1-propanol i 3-metil-1-butanol su neki hlapljivi organskih spojevi pronađeni u prirodno fermentiranom mlijeku amasi. Količina hlapljivih organskih spojeva u prirodno fermentiranom mlijeku (naturally fermented milk – NFM) razlikovala se od uzorka do uzorka, te je iznosila 0,1-18,4 ppm acetaldehida, <0,1-0,47 ppm 3-metilbutanala i 39,3-656 ppm etanola. Upotrebom kulture LAB/C. kefyr 23 (B/Y1) proizvedena je kudikamo veća (p<0,05) količina acetaldehida i etanola nego u NFM. Količina acetaldehida u uzorcima B/Y1 iznosila je 26,7-87,7 ppm, a najviše acetaldehida dobiveno je fermentacijom s pomoću L. lactis subsp. lactis biovar. diacetylactis C1 (B4) u kombinaciji s C. kefyr 23 (Y1). Metodom glavnih komponenata (principal component analysis – PCA) svrstana je većina NFM uzoraka s pojedinačnim i mješovitim kulturama Lc261, Lb11 i kvascima koji ne fermentiraju laktozu, prema malim količinama etanola i sličnom udjelu 3-metilbutanala. Kromatogram prirodno fermentiranog mlijeka amasi pokazuje visok pik metilaldehida i njihovih alkohola, uključujući 3-metilbutanal i 3-metilbutanol, čime je dokazano da su ti spojevi značajni za mlijeko amasi

Development of Yeast Populations during Processing and Ripening of Blue Veined Cheese

Varieties of blue veined cheese were analyzed regularly during different stages of manufacturing and ripening to determine the origin of contaminating the yeasts present in them, their population diversity and development until the end of the storage. Yeast diversity and development in the inner and outer core of the cheeses during ripening were also compared. Air samples revealed few if any yeasts whereas the samples in contact with the equipment and the surroundings revealed high number of yeasts, implicating it as the possible main source of post-pasteurization contamination, as very few yeasts were isolated from the milk and cheese making process itself. Samples from the inner and outer core of the maturing cheeses had typical survival curves. The number of yeasts on the outer core was about a 100-fold more than of those in the inner core. The most abundant yeasts isolated from the environment and ripening cheeses were identified as Debaryomyces hansenii, Saccharomyces cerevisiae, Torulaspora delbrueckii, Trichosporon beigelii, Candida versatilis and Cryptococcus albidus, while the yeasts Candida zeylanoides and Dekkera anomala were additionally isolated from the environment. Yeasts were present in high number, making their occurrence in blue-veined cheeses meaningful

Volatile Organic Compounds in Naturally Fermented Milk and Milk Fermented Using Yeasts, Lactic Acid Bacteria and Their Combinations As Starter Cultures

The volatile organic compounds present in 18 Zimbabwean naturally fermented milk (amasi) samples and those produced by various yeasts, lactic acid bacteria (LAB) and yeast/ LAB combinations were determined using headspace gas chromatography. The yeast strains used were: Candida kefyr 23, C. lipolytica 57, Saccharomyces cerevisiae 71, C. lusitaniae 68, C. tropicalis 78, C. lusitaniae 63, C. colliculosa 41, S. dairenensis 32, and Dekkera bruxellensis 43, and were coded Y1 to Y9, respectively. The LAB strains used were Lactococcus lactis subsp. lactis Lc39, L. lactis subsp. lactis Lc261, Lactobacillus paracasei Lb11, and L. lactis subsp. lactis biovar. diacetylactis C1, and were coded B1 to B4, respectively. Some of the volatile organic compounds found in amasi were acetaldehyde, ethanol, acetone, 2-methyl propanal, 2-methyl-1-propanol and 3-methyl-1-butanol. However, the levels of volatile organic compounds in the naturally fermented milk (NFM) samples varied from one sample to another, with acetaldehyde ranging from 0.1–18.4 ppm, 3-methyl butanal from <0.1–0.47 ppm and ethanol from 39.3–656 ppm. The LAB/C. kefyr 23 (B/Y1) co-cultures produced significantly (p<0.05) higher levels of acetaldehyde and ethanol than the levels found in the NFM. The acetaldehyde levels in the B/Y1 samples ranged from 26.7–87.7 ppm, with L. lactis subsp. lactis biovar. diacetylactis C1 (B4) producing the highest level of acetaldehyde in combination with C. kefyr 23 (Y1). Using principal component analysis (PCA), most of the NFM samples were grouped together with single and co-cultures of Lc261, Lb11 and the non-lactose fermenting yeasts, mainly because of the low levels of ethanol and similar levels of 3-methyl butanal. Chromatograms of amasi showed prominent peak of methyl aldehydes and their alcohols including 3-methyl-butanal and 3-methyl-butanol, suggesting that these compounds are important attributes of Zimbabwean naturally fermented milk

The Effect of Incubation Temperature on the Survival and Growth of Yeasts in Sethemi, South African Naturally Fermented Milk

The effect of temperature on the growth of yeasts during the production of Sethemi, South African naturally fermented milk (NFM), was studied by incubating raw milk and milk inoculated with selected yeast strains at 7, 15, 25 and 37 °C. The different temperatures were selected to represent the average ambient temperatures around Bloemfontein, South Africa, during winter, spring, summer, and in the human body, respectively. The yeast strains used had previously been isolated from Sethemi and identified as Kluyveromyces marxianus, Saccharomyces cerevisiae, Candida albicans and Debaryomyces hansenii. The yeast strains were inoculated into raw milk separately and also as a mixture of the four strains. The yeast counts, lactic acid bacteria counts and pH were monitored over a period of 20 days. It was observed that although all the yeast strains grew in the milk at all temperatures, the fastest growth was at 37 °C but there was a prolonged lag phase at 7 and 15 °C. The highest yeast counts of 8.30 log (CFU/mL) were obtained at 25 °C in the milk inoculated with K. marxianus. At all temperatures, the initial yeast count in the control was significantly (p<0.05) lower than the counts in the inoculated milk. Lactic acid bacteria also grew to high numbers both with added yeast and in the control. The highest LAB counts of about 11.59 log (CFU/mL) were obtained in the presence of S. cerevisiae after about 4 days of incubation at 25 °C. The addition of different yeast strains did not affect significantly the growth of LAB at all temperatures. After 3 days, the LAB counts decreased rapidly at 37 °C, while from day 2 to day 5 the LAB numbers remained stable at 25 °C. There was a rapid decrease in pH at higher temperatures than at 7 or 15 °C, corresponding to the LAB growth. A temperature of 25 °C was found to be ideal for producing fermented milk with high LAB counts, low pH and a visually acceptable coagulum

Utjecaj temperature inkubacije na preživljavanje i rast kvasca u južnoafričkom prirodno fermentiranom mlijeku Sethemi

The effect of temperature on the growth of yeasts during the production of Sethemi, South African naturally fermented milk (NFM), was studied by incubating raw milk and milk inoculated with selected yeast strains at 7, 15, 25 and 37 °C. The different temperatures were selected to represent the average ambient temperatures around Bloemfontein, South Africa, during winter, spring, summer, and in the human body, respectively. The yeast strains used had previously been isolated from Sethemi and identified as Kluyveromyces marxianus, Saccharomyces cerevisiae, Candida albicans and Debaryomyces hansenii. The yeast strains were inoculated into raw milk separately and also as a mixture of the four strains. The yeast counts, lactic acid bacteria counts and pH were monitored over a period of 20 days. It was observed that although all the yeast strains grew in the milk at all temperatures, the fastest growth was at 37 °C but there was a prolonged lag phase at 7 and 15 °C. The highest yeast counts of 8.30 log (CFU/mL) were obtained at 25 °C in the milk inoculated with K. marxianus. At all temperatures, the initial yeast count in the control was significantly (p<0.05) lower than the counts in the inoculated milk. Lactic acid bacteria also grew to high numbers both with added yeast and in the control. The highest LAB counts of about 11.59 log (CFU/mL) were obtained in the presence of S. cerevisiae after about 4 days of incubation at 25 °C. The addition of different yeast strains did not affect significantly the growth of LAB at all temperatures. After 3 days, the LAB counts decreased rapidly at 37 °C, while from day 2 to day 5 the LAB numbers remained stable at 25 °C. There was a rapid decrease in pH at higher temperatures than at 7 or 15 °C, corresponding to the LAB growth. A temperature of 25 °C was found to be ideal for producing fermented milk with high LAB counts, low pH and a visually acceptable coagulum.Inkubacijom svježeg mlijeka i mlijeka inokuliranog odabranim sojevima kvasca na 7, 15, 25 i 37 °C istražen je utjecaj temperature na rast kvasca pri dobivanju južnoafričkog prirodno fermentiranog mlijeka (naturally fermented milk – NFM) Sethemi. Odabrane su različite temperature fermentacije koje predstavljaju prosječnu zimsku, ljetnu i proljetnu temperaturu zraka u okolici grada Bloemfontein (Južna Afrika), te prosječnu temperaturu ljudskoga tijela. Upotrijebljeni su sojevi kvasca Kluyveromyces marxianus, Saccharomyces cerevisiae, Candida albicans i Debaryomyces hansenii izolirani iz mlijeka Sethemi. Sojevi su inokulirani zasebno i kao mješovita kultura u svježe mlijeko. Tijekom 20 dana praćen je broj kvasaca i mliječno-kiselih bakterija te pH-vrijednost. Iako je primijećen rast sojeva kvasca pri svim vrijednostima temperature korištenim u istraživanju, najbrže su rasli pri temperaturi od 37 °C, a na 7 i 15 °C došlo je do produljenja lag faze. Najveći broj kvasaca, i to od 8,30 log (CFU/mL), postignut je u mlijeku inokuliranom s K. marxianus pri temperaturi od 25 °C. Početni broj kvasaca u kontrolnom uzorku bio je značajno (p<0,05) niži nego u inokuliranom mlijeku pri svim temperaturnim vrijednostima. Porastao je i broj mliječno-kiselih bakterija (LAB) u kontrolnom i inokuliranom uzorku. Najveći broj LAB (11,59 log (CFU/mL)) postignut je u prisutnosti S. cerevisiae nakon 4 dana inkubacije na 25 °C. Dodatak različitih sojeva kvasca nije značajno utjecao na rast LAB bez obzira na temperaturnu vrijednost. Nakon 3 dana na 37 °C drastično je smanjen broj LAB, dok je nakon 2-5 dana pri 25 °C ostao nepromijenjen. Pri temperaturama višim od 7 i 15 °C uvelike se snizio pH zbog povećanja broja LAB. Temperatura od 25 °C ocijenjena je idealnom za proizvodnju fermentiranog mlijeka zbog velikog broja LAB, niske pH-vrijednosti i prihvatljivog izgleda koaguluma