Although nonpathogenic in nature, spores of Geobacillus are able to attach to surfaces, germinate... more Although nonpathogenic in nature, spores of Geobacillus are able to attach to surfaces, germinate, and form biofilms, allowing rapid multiplication and persistence within milk powder processing plants, causing final product contamination, and eventually leading to a loss of revenue in terms of downgraded product quality. As a result, Geobacillus spp. have been found to be common contaminants of milk powder worldwide. Genotyping methods can help in gaining insight into the ecology and transmission of these thermophilic bacteria within and between dairy processing plants. The objective of this study was to use the assembled draft genomes of two Geobacillus spp. to identify and test new hypervariable genotyping targets for differentiating closely related dairy Geobacillus isolates. The two Geobacillus spp. strains obtained from high spore count powders were obtained in 2010 (isolate 7E) and in 1995 (isolate 126) and were previously shown to be of same genotype based on a variable number tandem repeat genotyping method. Significant nucleotide sequence variation was found in genes encoding pili and flagella, which were further investigated as suitable loci for a new high-resolution melt analysis (HRMA)-based genotyping method. Three genes encoding pulG (containing prepilin-type N-terminal cleavage domain), pilT (pili retraction protein), and fliW (flagellar assembly protein) were selected as targets for the new pili/flagella gene (PilFla) HRMA genotyping method. The threegene-based PilFla-HRMA genotyping method differentiated 35 milk powder Geobacillus spp. isolates into 19 different genotype groups (D ~0.93), which compared favorably to the previous method (which used four variable number tandem repeat loci) that generated 16 different genotype groups (D ~0.90). In conclusion, through comparative genomics of two closely related dairy Geobacillus strains, we have identified new hypervariable regions that prove to be useful targets for highly discriminatory genotyping.
Australian Journal of Dairy Technology, Nov 1, 2008
Many chemical changes take place in UHT milk during storage. In this work UHT milk was stored at ... more Many chemical changes take place in UHT milk during storage. In this work UHT milk was stored at different temperatures (5°C, 20°C, 37°C and 45°C) for 12 weeks and assessed for pH, browning, proteolysis and protein changes by HPLC, PAGE and lysinoalanine determination. There was a greater decrease in pH and increase in browning, due to Maillard reactions, and proteolysis in samples stored at 37°C and 45°C than in samples stored at 5°C and 20°C; these changes were positively related to both time and temperature of storage. The RP-HPLC chromatogram of the proteins in the UHT milk samples stored at 45°C changed considerably during storage and at the end of 12 weeks' storage was completely different from that of a sample stored at 5°C, indicating that considerable change takes place in the proteins of samples stored at elevated temperature. Lysinoalanine concentration, an indicator of covalent, non-disulfide cross-linking of proteins, increased with storage temperature and time. The cross-linking was also observed by reduced SDS-PAGE from which the percentages of cross-linked milk proteins were estimated to be 1.1%, 1.3%, 7.0% and 36.8% after 12 weeks' storage at 5°C, 20°C, 37°C and 45°C, respectively.
Milk proteins are susceptible to chemical changes during processing and storage. We used proteomi... more Milk proteins are susceptible to chemical changes during processing and storage. We used proteomic tools to analyse bovine a S1 -casein in UHT milk. 2-D gels of freshly processed milk a S1 -casein was presented as five or more spots due to genetic polymorphism and variable phosphorylation. MS analysis after phosphopeptide enrichment allowed discrimination between phosphorylation states and genetic variants. We identified a new alternatively-spliced isoform with a deletion of exon 17, producing a new C-terminal sequence, K 164 SQVNSEGLHSYGL 177 , with a novel phosphorylation site at S 174 . Storage of UHT milk at elevated temperatures produced additional, more acidic a S1 -casein spots on the gels and decreased the resolution of minor forms. MS analysis indicated that non-enzymatic deamidation and loss of the N-terminal dipeptide were the major contributors to the changing spot pattern. These results highlight the important role of storage temperature in the stability of milk proteins and the utility of proteomic techniques for analysis of proteins in food.
The effects of addition of polysaccharides with different ionic charge on rheology, microstructur... more The effects of addition of polysaccharides with different ionic charge on rheology, microstructure, texture and water holding capacity (WHC) of acid milk gels were studied and compared to that of gelatin addition. Similar to gelatin, starch (neutral) and xanthan gum (anionic) did not prevent milk gelation in the first 30 min of the acidification stage, even at high concentrations, and the typical casein network in acid milk gels could still be seen from electron micrographs; gelling and melting of these hydrocolloids were observed during the cooling and heating stages at specific concentrations. On the other hand, two neutral polysaccharides, guar gum (≥0.05%) and locust bean gum [LBG] (≥0.1%) inhibited milk gelation from the beginning of the acidification stage; the microstructure of the gel was modified greatly and no gelling/melting was observed during the cooling or heating stages. Another anionic polysaccharide, carrageenan, induced earlier milk gelation at low concentration (≤ 0.05%), but inhibited gelation entirely at high concentration (0.2%); inflections at ~27 °C and 21 °C were also observed during the cooling and heating stages at 0.05% concentration. The gel microstructure was not changed greatly, but showed smaller particle size at a carrageenan concentration of 0.05% than control sample. None of the polysaccharides showed as much improvement in WHC of the milk gels as gelatin did. Hence, xanthan and starch were found to be closer to gelatin in their effect on acid milk gels compared to guar gum, LBG and carrageenan.
This chapter discusses understanding the contribution of milk constituents to the texture of dair... more This chapter discusses understanding the contribution of milk constituents to the texture of dairy products, specifically focusing on liquid milk products. It starts by examining the viscosity of milk, reviewing flow behaviour models and the effect of milk composition and temperature on milk viscosity. The chapter moves on to discuss the viscosity of concentrated milks and examines the composition and temperature of these milks and the role of whey proteins and minerals. The effect of preheating concentrated milks on viscosity is also discussed. A section on ultra-high-temperature milk texture is also provided, which is then followed by a section on the texture of fat-containing products. The chapter also discusses the perceived texture of milk and the effects of non-thermal technologies on milk and dairy products.
During heating of goat milk at 60, 65, 70, 75, 80, 85, 90 and 95°C for 10 min, non-casein nitroge... more During heating of goat milk at 60, 65, 70, 75, 80, 85, 90 and 95°C for 10 min, non-casein nitrogen (NCN) generally decreased with increasing temperature of heating (except at 70°C). The effect of pH (6, 6.2, 6.4, 6.6, 6.8, 7) on interactions between milk proteins depended on the temperature of heating. During heating at 75 °C for 10 min, the NCN increased gradually with increasing pH, while during heating at 95 °C it decreased with increasing pH. In general, association of proteins with the MFGM increased with increasing temperature and increasing pH.
A liquid chromatographic method has been developed for the determination of free fatty acids in b... more A liquid chromatographic method has been developed for the determination of free fatty acids in butter. The fatty acids are converted to the p-bromophenacyl esters, via a crown ether-catalyzed reaction, without separation from the other butter components. The esters are separated on a C18-bonded silica column by using an acetonitrile-water solvent gradient and quantitated using the ester of heptadecanoic acid as internal standard. C16 and C18:1 co-elute in the acetonitrile-water system but are separated using an isocratic methanol-acetonitrile-water system. Limits of detection range from 7 ng for butyric acid to 45 ng for linoleic acid. The average coefficient of variation (n = 10) for 10 free fatty acids from a butter was 5.83%.
ABSTRACT After high-pressure processing, pulsed electric field technology and ultrasonication hav... more ABSTRACT After high-pressure processing, pulsed electric field technology and ultrasonication have attracted most attention by researchers in recent years. Pulsed electric field technology has been investigated largely as a possible replacement for thermal ‘pasteurization’ and for extending the shelf life of liquid products. It reduces the number of bacteria, including pathogens, in liquid products and has gained FDA approval for ‘pasteurization’ of fruit juices. However, it has not been adopted commercially by the food industry in general or the dairy industry in particular. It shows considerable potential for use in liquid foods, including milk, but more research is required to better define and optimize the many factors that influence its efficacy. Ultrasonication has some effect on microorganisms, but is generally considered unlikely to be a suitable alternative to thermal treatments for producing pasteurized or extended-shelf life products. It has a synergistic effect with heat at elevated temperatures, with or without mild pressure, and reduces the heat resistance of both vegetative cells and spores. Ultrasound is also capable of physically altering milk components, particularly milk fat globules, that are effectively homogenized, and whey proteins whose functional properties such as solubility, foaming capacity, and heat stability can be enhanced. These applications are now the major focus for this technology.
To investigate the abilities of various probiotic bacteria to produce volatile sulfur compounds (... more To investigate the abilities of various probiotic bacteria to produce volatile sulfur compounds (VSCs) relevant to food flavour and aroma. Probiotic strains (Lactobacillus acidophilus NCFM, Lactobacillus plantarum 299v, Lactobacillus rhamnosus GG, Lactobacillus reuteri ATCC55730 and L. reuteri BR11), Lactobacillus delbrueckii ATCC4797, L. plantarum ATCC14917 and Lactococcus lactis MG1363 were incubated with either cysteine or methionine. Volatile compounds were captured, identified and quantified using a sensitive solid-phase microextraction (SPME) technique combined with gas chromatography coupled to a pulsed flame photometric detector (SPME/GC/PFPD). Several VSCs were identified including H(2)S, methanethiol, dimethyldisulfide and dimethyltrisulfide. The VSC profiles varied substantially for different strains of L. plantarum and L. reuteri and it was found that L. reuteri ATCC55730 and L. lactis MG1363 produced the lowest levels of VSCs (P < 0.05). Levels of VSCs generated by bacteria were found to be equivalent to, or higher than, that found in commercial cheeses. Several probiotic strains are able to generate considerable levels of VSCs and substantial variations in VSC generating potential exists between different strains from the same species. This study demonstrates that probiotic bacteria are able to efficiently generate important flavour and aroma compounds and therefore has implications for the development of probiotic containing foods.
The application of high-pressure processing to foods has attracted considerable research and comm... more The application of high-pressure processing to foods has attracted considerable research and commercial interest in recent years. High pressure disrupts non-covalent bonds in macromolecules, such as proteins and polysaccharides, causing denaturation, aggregation and gelling, but has little or no effect on small molecules responsible for the flavour, colour and nutritive value of foods. Vegetative micro-organisms and, under certain conditions, bacterial spores, are destroyed without accompanying detrimental chemical changes caused by heat. High-pressure treatment of milk at similar to 600 MPa destroys most vegetative micro-organisms and greatly increases its shelf-life. Through changes in the milk proteins, it also affects other characteristics of the milk, and the yield and nature of products such as cheese produced from it. The process has been in commercial use since 1990, with yogurt being the major dairy product treated. The unique physical and sensory properties of pressure-processed foods offers new opportunities for new product development in the dairy industry. This paper reviews the principles, equipment, effects and applications of high-pressure processing of foods, with particular emphasis on milk and dairy products.
Abstract This chapter first defines the term “whey proteins” as it pertains to the contents of th... more Abstract This chapter first defines the term “whey proteins” as it pertains to the contents of this book. We define whey proteins as the proteins not associated with the casein micelle or other milk particles such as membrane structures and somatic and microbial cells. This chapter divides the whey proteins into two categories of major and minor whey proteins. The major whey proteins discussed here are β-lactoglobulin, α-lactalbumin, serum albumin, and immunoglobulins. Several characteristics of these proteins are discussed including their abundance in milk of various species, amino acid composition and molecular structure, genetic polymorphism, biological and technological function as well as their significance. The minor whey proteins included in this chapter are lactoferrin, proteose peptone 3, osteopontin, glycomacropeptide, lactoperoxidase, lysozyme, cathepsin D, acid phosphatase, and ribonucleases. In addition to discussing the abundance, characteristics and significance of these minor whey proteins, this chapter summarizes their important features in several useful tables.
International Journal of Dairy Technology, Dec 15, 2014
Calcium in milk is significant for both its nutritive value and its key role in many functional p... more Calcium in milk is significant for both its nutritive value and its key role in many functional properties of milk and milk products. Manipulating its concentration, particularly of the ionic form, alters the properties of the products and facilitates or hinders certain processing operations. Stability to thermal treatment is the major property affected, but several others such as gelation, coagulation and foaming are influenced by either adding or removing calcium. This article reviews the manipulation of the calcium content of several products and its practical consequences for dairy processing.
Although nonpathogenic in nature, spores of Geobacillus are able to attach to surfaces, germinate... more Although nonpathogenic in nature, spores of Geobacillus are able to attach to surfaces, germinate, and form biofilms, allowing rapid multiplication and persistence within milk powder processing plants, causing final product contamination, and eventually leading to a loss of revenue in terms of downgraded product quality. As a result, Geobacillus spp. have been found to be common contaminants of milk powder worldwide. Genotyping methods can help in gaining insight into the ecology and transmission of these thermophilic bacteria within and between dairy processing plants. The objective of this study was to use the assembled draft genomes of two Geobacillus spp. to identify and test new hypervariable genotyping targets for differentiating closely related dairy Geobacillus isolates. The two Geobacillus spp. strains obtained from high spore count powders were obtained in 2010 (isolate 7E) and in 1995 (isolate 126) and were previously shown to be of same genotype based on a variable number tandem repeat genotyping method. Significant nucleotide sequence variation was found in genes encoding pili and flagella, which were further investigated as suitable loci for a new high-resolution melt analysis (HRMA)-based genotyping method. Three genes encoding pulG (containing prepilin-type N-terminal cleavage domain), pilT (pili retraction protein), and fliW (flagellar assembly protein) were selected as targets for the new pili/flagella gene (PilFla) HRMA genotyping method. The threegene-based PilFla-HRMA genotyping method differentiated 35 milk powder Geobacillus spp. isolates into 19 different genotype groups (D ~0.93), which compared favorably to the previous method (which used four variable number tandem repeat loci) that generated 16 different genotype groups (D ~0.90). In conclusion, through comparative genomics of two closely related dairy Geobacillus strains, we have identified new hypervariable regions that prove to be useful targets for highly discriminatory genotyping.
Australian Journal of Dairy Technology, Nov 1, 2008
Many chemical changes take place in UHT milk during storage. In this work UHT milk was stored at ... more Many chemical changes take place in UHT milk during storage. In this work UHT milk was stored at different temperatures (5°C, 20°C, 37°C and 45°C) for 12 weeks and assessed for pH, browning, proteolysis and protein changes by HPLC, PAGE and lysinoalanine determination. There was a greater decrease in pH and increase in browning, due to Maillard reactions, and proteolysis in samples stored at 37°C and 45°C than in samples stored at 5°C and 20°C; these changes were positively related to both time and temperature of storage. The RP-HPLC chromatogram of the proteins in the UHT milk samples stored at 45°C changed considerably during storage and at the end of 12 weeks' storage was completely different from that of a sample stored at 5°C, indicating that considerable change takes place in the proteins of samples stored at elevated temperature. Lysinoalanine concentration, an indicator of covalent, non-disulfide cross-linking of proteins, increased with storage temperature and time. The cross-linking was also observed by reduced SDS-PAGE from which the percentages of cross-linked milk proteins were estimated to be 1.1%, 1.3%, 7.0% and 36.8% after 12 weeks' storage at 5°C, 20°C, 37°C and 45°C, respectively.
Milk proteins are susceptible to chemical changes during processing and storage. We used proteomi... more Milk proteins are susceptible to chemical changes during processing and storage. We used proteomic tools to analyse bovine a S1 -casein in UHT milk. 2-D gels of freshly processed milk a S1 -casein was presented as five or more spots due to genetic polymorphism and variable phosphorylation. MS analysis after phosphopeptide enrichment allowed discrimination between phosphorylation states and genetic variants. We identified a new alternatively-spliced isoform with a deletion of exon 17, producing a new C-terminal sequence, K 164 SQVNSEGLHSYGL 177 , with a novel phosphorylation site at S 174 . Storage of UHT milk at elevated temperatures produced additional, more acidic a S1 -casein spots on the gels and decreased the resolution of minor forms. MS analysis indicated that non-enzymatic deamidation and loss of the N-terminal dipeptide were the major contributors to the changing spot pattern. These results highlight the important role of storage temperature in the stability of milk proteins and the utility of proteomic techniques for analysis of proteins in food.
The effects of addition of polysaccharides with different ionic charge on rheology, microstructur... more The effects of addition of polysaccharides with different ionic charge on rheology, microstructure, texture and water holding capacity (WHC) of acid milk gels were studied and compared to that of gelatin addition. Similar to gelatin, starch (neutral) and xanthan gum (anionic) did not prevent milk gelation in the first 30 min of the acidification stage, even at high concentrations, and the typical casein network in acid milk gels could still be seen from electron micrographs; gelling and melting of these hydrocolloids were observed during the cooling and heating stages at specific concentrations. On the other hand, two neutral polysaccharides, guar gum (≥0.05%) and locust bean gum [LBG] (≥0.1%) inhibited milk gelation from the beginning of the acidification stage; the microstructure of the gel was modified greatly and no gelling/melting was observed during the cooling or heating stages. Another anionic polysaccharide, carrageenan, induced earlier milk gelation at low concentration (≤ 0.05%), but inhibited gelation entirely at high concentration (0.2%); inflections at ~27 °C and 21 °C were also observed during the cooling and heating stages at 0.05% concentration. The gel microstructure was not changed greatly, but showed smaller particle size at a carrageenan concentration of 0.05% than control sample. None of the polysaccharides showed as much improvement in WHC of the milk gels as gelatin did. Hence, xanthan and starch were found to be closer to gelatin in their effect on acid milk gels compared to guar gum, LBG and carrageenan.
This chapter discusses understanding the contribution of milk constituents to the texture of dair... more This chapter discusses understanding the contribution of milk constituents to the texture of dairy products, specifically focusing on liquid milk products. It starts by examining the viscosity of milk, reviewing flow behaviour models and the effect of milk composition and temperature on milk viscosity. The chapter moves on to discuss the viscosity of concentrated milks and examines the composition and temperature of these milks and the role of whey proteins and minerals. The effect of preheating concentrated milks on viscosity is also discussed. A section on ultra-high-temperature milk texture is also provided, which is then followed by a section on the texture of fat-containing products. The chapter also discusses the perceived texture of milk and the effects of non-thermal technologies on milk and dairy products.
During heating of goat milk at 60, 65, 70, 75, 80, 85, 90 and 95°C for 10 min, non-casein nitroge... more During heating of goat milk at 60, 65, 70, 75, 80, 85, 90 and 95°C for 10 min, non-casein nitrogen (NCN) generally decreased with increasing temperature of heating (except at 70°C). The effect of pH (6, 6.2, 6.4, 6.6, 6.8, 7) on interactions between milk proteins depended on the temperature of heating. During heating at 75 °C for 10 min, the NCN increased gradually with increasing pH, while during heating at 95 °C it decreased with increasing pH. In general, association of proteins with the MFGM increased with increasing temperature and increasing pH.
A liquid chromatographic method has been developed for the determination of free fatty acids in b... more A liquid chromatographic method has been developed for the determination of free fatty acids in butter. The fatty acids are converted to the p-bromophenacyl esters, via a crown ether-catalyzed reaction, without separation from the other butter components. The esters are separated on a C18-bonded silica column by using an acetonitrile-water solvent gradient and quantitated using the ester of heptadecanoic acid as internal standard. C16 and C18:1 co-elute in the acetonitrile-water system but are separated using an isocratic methanol-acetonitrile-water system. Limits of detection range from 7 ng for butyric acid to 45 ng for linoleic acid. The average coefficient of variation (n = 10) for 10 free fatty acids from a butter was 5.83%.
ABSTRACT After high-pressure processing, pulsed electric field technology and ultrasonication hav... more ABSTRACT After high-pressure processing, pulsed electric field technology and ultrasonication have attracted most attention by researchers in recent years. Pulsed electric field technology has been investigated largely as a possible replacement for thermal ‘pasteurization’ and for extending the shelf life of liquid products. It reduces the number of bacteria, including pathogens, in liquid products and has gained FDA approval for ‘pasteurization’ of fruit juices. However, it has not been adopted commercially by the food industry in general or the dairy industry in particular. It shows considerable potential for use in liquid foods, including milk, but more research is required to better define and optimize the many factors that influence its efficacy. Ultrasonication has some effect on microorganisms, but is generally considered unlikely to be a suitable alternative to thermal treatments for producing pasteurized or extended-shelf life products. It has a synergistic effect with heat at elevated temperatures, with or without mild pressure, and reduces the heat resistance of both vegetative cells and spores. Ultrasound is also capable of physically altering milk components, particularly milk fat globules, that are effectively homogenized, and whey proteins whose functional properties such as solubility, foaming capacity, and heat stability can be enhanced. These applications are now the major focus for this technology.
To investigate the abilities of various probiotic bacteria to produce volatile sulfur compounds (... more To investigate the abilities of various probiotic bacteria to produce volatile sulfur compounds (VSCs) relevant to food flavour and aroma. Probiotic strains (Lactobacillus acidophilus NCFM, Lactobacillus plantarum 299v, Lactobacillus rhamnosus GG, Lactobacillus reuteri ATCC55730 and L. reuteri BR11), Lactobacillus delbrueckii ATCC4797, L. plantarum ATCC14917 and Lactococcus lactis MG1363 were incubated with either cysteine or methionine. Volatile compounds were captured, identified and quantified using a sensitive solid-phase microextraction (SPME) technique combined with gas chromatography coupled to a pulsed flame photometric detector (SPME/GC/PFPD). Several VSCs were identified including H(2)S, methanethiol, dimethyldisulfide and dimethyltrisulfide. The VSC profiles varied substantially for different strains of L. plantarum and L. reuteri and it was found that L. reuteri ATCC55730 and L. lactis MG1363 produced the lowest levels of VSCs (P < 0.05). Levels of VSCs generated by bacteria were found to be equivalent to, or higher than, that found in commercial cheeses. Several probiotic strains are able to generate considerable levels of VSCs and substantial variations in VSC generating potential exists between different strains from the same species. This study demonstrates that probiotic bacteria are able to efficiently generate important flavour and aroma compounds and therefore has implications for the development of probiotic containing foods.
The application of high-pressure processing to foods has attracted considerable research and comm... more The application of high-pressure processing to foods has attracted considerable research and commercial interest in recent years. High pressure disrupts non-covalent bonds in macromolecules, such as proteins and polysaccharides, causing denaturation, aggregation and gelling, but has little or no effect on small molecules responsible for the flavour, colour and nutritive value of foods. Vegetative micro-organisms and, under certain conditions, bacterial spores, are destroyed without accompanying detrimental chemical changes caused by heat. High-pressure treatment of milk at similar to 600 MPa destroys most vegetative micro-organisms and greatly increases its shelf-life. Through changes in the milk proteins, it also affects other characteristics of the milk, and the yield and nature of products such as cheese produced from it. The process has been in commercial use since 1990, with yogurt being the major dairy product treated. The unique physical and sensory properties of pressure-processed foods offers new opportunities for new product development in the dairy industry. This paper reviews the principles, equipment, effects and applications of high-pressure processing of foods, with particular emphasis on milk and dairy products.
Abstract This chapter first defines the term “whey proteins” as it pertains to the contents of th... more Abstract This chapter first defines the term “whey proteins” as it pertains to the contents of this book. We define whey proteins as the proteins not associated with the casein micelle or other milk particles such as membrane structures and somatic and microbial cells. This chapter divides the whey proteins into two categories of major and minor whey proteins. The major whey proteins discussed here are β-lactoglobulin, α-lactalbumin, serum albumin, and immunoglobulins. Several characteristics of these proteins are discussed including their abundance in milk of various species, amino acid composition and molecular structure, genetic polymorphism, biological and technological function as well as their significance. The minor whey proteins included in this chapter are lactoferrin, proteose peptone 3, osteopontin, glycomacropeptide, lactoperoxidase, lysozyme, cathepsin D, acid phosphatase, and ribonucleases. In addition to discussing the abundance, characteristics and significance of these minor whey proteins, this chapter summarizes their important features in several useful tables.
International Journal of Dairy Technology, Dec 15, 2014
Calcium in milk is significant for both its nutritive value and its key role in many functional p... more Calcium in milk is significant for both its nutritive value and its key role in many functional properties of milk and milk products. Manipulating its concentration, particularly of the ionic form, alters the properties of the products and facilitates or hinders certain processing operations. Stability to thermal treatment is the major property affected, but several others such as gelation, coagulation and foaming are influenced by either adding or removing calcium. This article reviews the manipulation of the calcium content of several products and its practical consequences for dairy processing.
Uploads
Papers by Hilton Deeth