• Saturation Mutagenesis of Lysine 12 Leads to the Identification of Derivatives of Nisin A with Enhanced Antimicrobial Activity

      Molloy, Evelyn M.; Field, Des; O'Connor, Paula M.; Cotter, Paul D.; Hill, Colin; Ross, R Paul; Irish Research Council for Science, Engineering and Technology; Enterprise Ireland; Science Foundation Ireland (PLOS, 11/03/2013)
      It is becoming increasingly apparent that innovations from the “golden age” of antibiotics are becoming ineffective, resulting in a pressing need for novel therapeutics. The bacteriocin family of antimicrobial peptides has attracted much attention in recent years as a source of potential alternatives. The most intensively studied bacteriocin is nisin, a broad spectrum lantibiotic that inhibits Gram-positive bacteria including important food pathogens and clinically relevant antibiotic resistant bacteria. Nisin is gene-encoded and, as such, is amenable to peptide bioengineering, facilitating the generation of novel derivatives that can be screened for desirable properties. It was to this end that we used a site-saturation mutagenesis approach to create a bank of producers of nisin A derivatives that differ with respect to the identity of residue 12 (normally lysine; K12). A number of these producers exhibited enhanced bioactivity and the nisin A K12A producer was deemed of greatest interest. Subsequent investigations with the purified antimicrobial highlighted the enhanced specific activity of this modified nisin against representative target strains from the genera Streptococcus, Bacillus, Lactococcus, Enterococcus and Staphylococcus.
    • Second generation GM foods: perspectives on likely future acceptance by Irish consumers

      O'Connor, Elaine; Cowan, Cathal; Williams, Gwilym; O'Connell, John; Boland, Maurice; Downey, Gerard; Teagasc Walsh Fellowship Programme; Safefood; Safefood (Teagasc, 2005-07)
      Two hypothetical second-generation genetically-modified (GM) products, a yogurt and a dairy spread, were evaluated by consumers. Second-generation GM food products offer specific consumer benefits - in the case of this study, health benefits.
    • Second Generation GM Foods: Perspectives on Likely Future Acceptance by Irish Consumers

      O'Connor, Elaine; Cowan, Cathal; Williams, Gwilym; O'Connell, John; Boland, Maurice; Downey, Gerard (Teagasc, 01/07/2005)
      Two hypothetical second-generation genetically-modified (GM) products, a yogurt and a dairy spread, were evaluated by consumers. Second-generation GM food products offer specific consumer benefits - in the case of this study, health benefits.
    • Selective enrichment of dairy phospholipids in a buttermilk substrate through investigation of enzymatic hydrolysis of milk proteins in conjunction with ultrafiltration

      Barry, Kate M.; Dinan, Timothy G.; Kelly, Philip M.; Department of Agriculture, Food and the Marine, Ireland; Teagasc Walsh Fellowship Programme; 10RD/TMFRC/709 (Elsevier, 04/02/2017)
      Extensive enzymatic hydrolysis of milk proteins in reconstituted buttermilk powder was combined with ultrafiltration to generate a phospholipid (PL) enriched fraction with maximum permeation of hydrolysed peptides. Buttermilk, naturally high in PLs, is the ideal substrate for enrichment of these bio- and techno-functionally active compounds. A 7.8 fold increase in PL was achieved in the 50 kDa retentate; 6.16 ± 0.02% total PL compared with 0.79 ± 0.01% in the starting substrate, an increase considerably greater than previously reported. Total lipid content (% dry matter) increased 6.3 fold in the retentate, 43.43 ± 0.61%, from the starting substrate, 6.84 ± 0.17%. This combined strategic approach enabled maximum enrichment of PLs with no transmission of lipid material into the permeate, 0.09 ± 0.02% total lipid, and non-detectable levels of PLs recovered in the permeate, 0.00 ± 0.01% total PL.
    • Semi-supervised linear discriminant analysis

      Toher, Deirdre; Downey, Gerard; Murphy, Thomas Brendan (Wiley, 02/07/2012)
      Fisher's linear discriminant analysis is one of the most commonly used and studied classification methods in chemometrics. The method finds a projection of multivariate data into a lower dimensional space so that the groups in the data are well separated. The resulting projected values are subsequently used to classify unlabeled observations into the groups. A semi-supervised version of Fisher's linear discriminant analysis is developed, so that the unlabeled observations are also used in the model fitting procedure. This approach is advantageous when few labeled and many unlabeled observations are available. The semi-supervised linear discriminant analysis method is demonstrated on a number of data sets where it is shown to yield better separation of the groups and improved classification over Fisher's linear discriminant analysis.
    • Sequencing of the Cheese Microbiome and Its Relevance to Industry

      Yeluri Jonnala, Bhagya. R.; McSweeney, Paul L. H.; Sheehan, Jeremiah J.; Cotter, Paul D.; Teagasc Walsh Fellowship Programme (Frontiers, 2018-05-23)
      The microbiota of cheese plays a key role in determining its organoleptic and other physico-chemical properties. It is essential to understand the various contributions, positive or negative, of these microbial components in order to promote the growth of desirable taxa and, thus, characteristics. The recent application of high throughput DNA sequencing (HTS) facilitates an even more accurate identification of these microbes, and their functional properties, and has the potential to reveal those microbes, and associated pathways, responsible for favorable or unfavorable characteristics. This technology also facilitates a detailed analysis of the composition and functional potential of the microbiota of milk, curd, whey, mixed starters, processing environments, and how these contribute to the final cheese microbiota, and associated characteristics. Ultimately, this information can be harnessed by producers to optimize the quality, safety, and commercial value of their products. In this review we highlight a number of key studies in which HTS was employed to study the cheese microbiota, and pay particular attention to those of greatest relevance to industry.
    • Sequencing of the Cheese Microbiome and Its Relevance to Industry

      Yeluri Jonnala, Bhagya R.; McSweeney, Paul L. H.; Sheehan, Jeremiah J.; Cotter, Paul D.; Teagasc Walsh Fellowship Programme (Frontiers, 2018-05-23)
      The microbiota of cheese plays a key role in determining its organoleptic and other physico-chemical properties. It is essential to understand the various contributions, positive or negative, of these microbial components in order to promote the growth of desirable taxa and, thus, characteristics. The recent application of high throughput DNA sequencing (HTS) facilitates an even more accurate identification of these microbes, and their functional properties, and has the potential to reveal those microbes, and associated pathways, responsible for favorable or unfavorable characteristics. This technology also facilitates a detailed analysis of the composition and functional potential of the microbiota of milk, curd, whey, mixed starters, processing environments, and how these contribute to the final cheese microbiota, and associated characteristics. Ultimately, this information can be harnessed by producers to optimize the quality, safety, and commercial value of their products. In this review we highlight a number of key studies in which HTS was employed to study the cheese microbiota, and pay particular attention to those of greatest relevance to industry.
    • Sequencing-Based Analysis of the Bacterial and Fungal Composition of Kefir Grains and Milks from Multiple Sources

      Marsh, Alan J.; O'Sullivan, Orla; Hill, Colin; Ross, R Paul; Cotter, Paul D.; Science Foundation Ireland; 07/CE/B1368 (PLOS, 19/07/2013)
      Kefir is a fermented milk-based beverage to which a number of health-promoting properties have been attributed. The microbes responsible for the fermentation of milk to produce kefir consist of a complex association of bacteria and yeasts, bound within a polysaccharide matrix, known as the kefir grain. The consistency of this microbial population, and that present in the resultant beverage, has been the subject of a number of previous, almost exclusively culture-based, studies which have indicated differences depending on geographical location and culture conditions. However, culture-based identification studies are limited by virtue of only detecting species with the ability to grow on the specific medium used and thus culture-independent, molecular-based techniques offer the potential for a more comprehensive analysis of such communities. Here we describe a detailed investigation of the microbial population, both bacterial and fungal, of kefir, using high-throughput sequencing to analyse 25 kefir milks and associated grains sourced from 8 geographically distinct regions. This is the first occasion that this technology has been employed to investigate the fungal component of these populations or to reveal the microbial composition of such an extensive number of kefir grains or milks. As a result several genera and species not previously identified in kefir were revealed. Our analysis shows that the bacterial populations in kefir are dominated by 2 phyla, the Firmicutes and the Proteobacteria. It was also established that the fungal populations of kefir were dominated by the genera Kazachstania, Kluyveromyces and Naumovozyma, but that a variable sub-dominant population also exists.
    • Short Communication: The effect of dry period duration and dietary energy density on the rennet gelation properties of milk in early lactation

      Butler, Stephen T.; de Feu, M.A.; O'Brien, Bernadette; Guinee, Timothy P.; Murphy, J.J.; National Development Plan (Dublin, Ireland) (American Dairy Science Association and Elsevier Inc., 2010-02)
      This study was carried out to examine the effects of decreasing dry period duration (DP) and altering the energy density of the diet during early lactation on the rheological characteristics of milk. Forty mature Holstein-Friesian cows were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Cows were randomly assigned to one of two dry period treatments and one of two nutritional treatments. The dry period treatments were continuous milking (CM) or an 8-week standard dry period (SDP), and the nutritional treatments were a standard energy diet (SE) or a high energy diet (HE). Actual dry period lengths were 6.3 ± 1.7 days and 62.1 ± 1.9 days for cows for the CM and SDP treatments, respectively. Milk samples were collected at 2, 6 and 10 weeks postpartum. The concentration of fat, protein and lactose was determined in each sample. The rennet gelation properties were measured at 31 ° C using dynamic low-amplitude strain oscillatory rheometry. The following parameters were obtained from the resultant elastic shear modulus (G′): gelation time (GT), maximum curd firming rate (CFRmax) and gel strength (GS). Reducing dry period duration from 62 to 6 days resulted in increases in milk protein concentration (31.8 vs. 34.7 g/kg; P < 0.001), CFRmax (2.58 vs. 3.60 Pa/min; P < 0.001) and GS (69.4 vs. 90.5 Pa; P = 0.003). Raising the dietary energy density decreased percentage milk fat (43.1 vs. 37.7 g/kg; P < 0.001) but otherwise had no effect. GS was correlated with CFRmax (r = 0.98; P < 0.001), and both variables were correlated with milk protein concentration (r = 0.71; P < 0.001, and r = 0.73; P < 0.001, respectively). The results indicate that decreasing the duration of DP increased milk protein concentration and improved the rennet gelation properties of milk, but that dietary energy density had little effect.
    • A Simple Method for the Purification of Nisin

      Gough, Ronan; Gomez-Sala, Beatriz; O'Connor, Paula M.; Rea, Mary C.; Miao, Song; Hill, Colin; Brodkorb, Andre (Springer, 29/05/2017)
      Nisin, an antimicrobial peptide showing activity against a broad range of Gram-positive bacteria, is widely used as a food preservative and has potential as a therapeutic for a range of infectious diseases. Here, we present a simple purification method, based on a salting-out approach, which can produce a powder containing ∼33% nisin, from a nisin-producing culture in a whey permeate-based medium. This process removes over 99% of the lactic acid, NaCl, lactose and non-nisin proteins from the cell-free culture supernatant. The approach can also enrich a commonly used commercial nisin preparation over 30-fold to a purity of ∼58%. These are higher purities than comparable published methods. The simplicity of this approach facilitates its use in research and also its scale-up.
    • Simulated gastrointestinal digestion of nisin and interaction between nisin and bile

      Gough, Ronan; O'Connor, Paula M.; Rea, Mary C.; Gomez-Sal, Beatriz; Miao, Song; Hill, Colin; Brodkorb, Andre; Department of Agriculture, Food and the Marine; Teagasc Walsh Fellowship Programme; 10/RD/TMFRC/701; 2012221 (Elsevier, 14/08/2017)
      Nisin, an antimicrobial peptide showing activity against many Gram positive bacteria, is widely used as a food preservative. The simulated gastrointestinal digestion of nisin (variant A) was studied using the in vitro INFOGEST digestion method. Following oral, gastric and small intestinal digestion, there was no intact nisin in the system and the nisin was primarily digested by pancreatin. After digestion, six nisin fragments (1–11, 1–12, 1–20, 1–21, 1–29 and 1–32) were identified by reversed phase high performance liquid chromatography and mass spectroscopy and four of these nisin fragments (1–20, 1–21, 1–29 and 1–32) demonstrated low antibacterial activity against Lactococcus lactis HP in agar diffusion activity assays. Additionally, it was observed that bile salts form a complex with nisin. This was examined by atomic force microscopy, turbidity and dynamic light scattering, which showed that this interaction resulted in significantly larger bile salt micelles. The presence of bile salts at physiological levels significantly altered the relative amounts of the nisin fragments 1–12, 1–20 and 1–29 produced during an in vitro digestion. This study highlights the importance of including bile in simulated digestions of antimicrobial peptides in order to obtain a more accurate simulation of the in vivo digestion products and their activity.
    • Sinapinic and protocatechuic acids found in rapeseed: isolation, characterisation and potential benefits for human health as functional food ingredients

      Quinn, Leah; Gray, Stephen G.; Meaney, Steven; Finn, Stephen; Kenny, Owen; Hayes, Maria (Teagasc (Agriculture and Food Development Authority), Ireland, 13/12/2017)
      Rapeseed is one of the world’s major oilseeds, and rapeseed oil is produced by pressing of the seeds. This process results in the production of a low-economic-value by-product, rapeseed meal, which is commonly used as animal feed. Rapeseed meal is rich in bioactive phenolic compounds, including sinapinic acid (SA) and protocatechuic acid (PCA). Isolation of these bioactive compounds from a by-product of rapeseed oil production is largely in agreement with the current concept of the circular economy and total utilisation of crop harvest using a biorefinery approach. In this review, current information concerning traditional and novel methods to isolate phenolic compounds – including SA and PCA – from rapeseed meal, along with in vitro and in vivo studies concerning the bioactivity of SA and PCA and their associated health effects, is collated. These health effects include anti-inflammatory, anti-cancer, anti-diabetes activities, along with histone deacetylase inhibition and protective cardiovascular, neurological and hepatic effects. The traditional extraction methods include use of solvents and/or enzymes. However, a need for simpler, more efficient methodologies has led to the development of novel extraction processes, including microwave-assisted, ultrasound-assisted, pulsed electric field and high-voltage electrical discharge extraction processes.
    • Single nucleotide polymorphisms in the insulin-like growth factor 1 (IGF-1) gene are associated with performance in Holstein-Friesian dairy cattle

      Mullen, Michael Paul; Berry, Donagh P.; Howard, Dawn J.; Diskin, Michael G.; Lynch, Ciaran O.; Giblin, Linda; Kenny, David A.; Magee, David A; Meade, Kieran G; Waters, Sinead M.; Science Foundation Ireland; Department of Agriculture, Food and the Marine; 07/SRC/B1156; RSF-06-0353; RSF-06-0409; Irish Dairy Levy Research Trust (Frontiers Media SA, 16/02/2011)
      Insulin-like growth factor 1 (IGF-1) has been shown to be associated with fertility, growth, and development in cattle. The aim of this study was to (1) identify novel single nucleotide polymorphisms (SNPs) in the bovine IGF-1 gene and alongside previously identified SNPs (2) determine their association with traits of economic importance in Holstein-Friesian dairy cattle. Nine novel SNPs were identified across a panel of 22 beef and dairy cattle by sequence analysis of the 5′ promoter, intronic, and 3′ regulatory regions, encompassing ∼5 kb of IGF-1. Genotyping and associations with daughter performance for milk production, fertility, survival, and measures of body size were undertaken on 848 Holstein-Friesian AI sires. Using multiple regression analysis nominal associations (P < 0.05) were identified between six SNPs (four novel and two previously identified) and milk composition, survival, body condition score, and body size. The C allele of AF017143 a previously published SNP (C-512T) in the promoter region of IGF-1 predicted to introduce binding sites for transcription factors HSF1 and ZNF217 was associated (P < 0.05) with increased cow carcass weight (i.e., an indicator of mature cow size). Novel SNPs were identified in the 3′ region of IGF-1 were associated (P < 0.05) with functional survival and chest width. The remaining four SNPs, all located within introns of IGF-1 were associated (P < 0.05) with milk protein yield, milk fat yield, milk fat concentration, somatic cell score, carcass conformation, and carcass fat. Results of this study further demonstrate the multifaceted influences of IGF-1 on milk production and growth related traits in cattle.
    • SNP variation in the promoter of the PRKAG3 gene and association with meat quality traits in pig

      Ryan, Marion T; Hamill, Ruth M; O’Halloran, Aisling M; Davey, Grace C; McBryan, Jean; Mullen, Anne Maria; McGee, Chris; Gispert, Marina; Southwood, Olwen I; Sweeney, Torres; Department of Agriculture, Food and the Marine, Ireland (Biomed Central, 25/07/2012)
      Background: The PRKAG3 gene encodes the γ3 subunit of adenosine monophosphate activated protein kinase (AMPK), a protein that plays a key role in energy metabolism in skeletal muscle. Non-synonymous single nucleotide polymorphisms (SNPs) in this gene such as I199V are associated with important pork quality traits. The objective of this study was to investigate the relationship between gene expression of the PRKAG3 gene, SNP variation in the PRKAG3 promoter and meat quality phenotypes in pork. Results: PRKAG3 gene expression was found to correlate with a number of traits relating to glycolytic potential (GP) and intramuscular fat (IMF) in three phenotypically diverse F1 crosses comprising of 31 Large White, 23 Duroc and 32 Pietrain sire breeds. The majority of associations were observed in the Large White cross. There was a significant association between genotype at the g.-311A>G locus and PRKAG3 gene expression in the Large White cross. In the same population, ten novel SNPs were identified within a 1.3 kb region spanning the promoter and from this three major haplotypes were inferred. Two tagging SNPs (g.-995A>G and g.-311A>G) characterised the haplotypes within the promoter region being studied. These two SNPs were subsequently genotyped in larger populations consisting of Large White (n = 98), Duroc (n = 99) and Pietrain (n = 98) purebreds. Four major haplotypes including promoter SNP’s g.-995A>G and g.-311A>G and I199V were inferred. In the Large White breed, HAP1 was associated with IMF% in the M. longissmus thoracis et lumborum (LTL) and driploss%. HAP2 was associated with IMFL% GP-influenced traits pH at 24 hr in LTL (pHULT), pH at 45 min in LTL (pH45LT) and pH at 45 min in the M. semimembranosus muscle (pH45SM). HAP3 was associated with driploss%, pHULT pH45LT and b* Minolta. In the Duroc breed, associations were observed between HAP1 and driploss% and pHUSM. No associations were observed with the remaining haplotypes (HAP2, HAP3 and HAP4) in the Duroc breed. The Pietrain breed was monomorphic in the promoter region. The I199V locus was associated with several GP-influenced traits across all three breeds and IMF% in the Large White and Pietrain breed. No significant difference in promoter function was observed for the three main promoter haplotypes when tested in vitro. Conclusion: Gene expression levels of the porcine PRKAG3 are associated with meat quality phenotypes relating to glycolytic potential and IMF% in the Large White breed, while SNP variation in the promoter region of the gene is associated with PRKAG3 gene expression and meat quality phenotypes.
    • Spread of brain and spinal cord material during beef slaughter

      Daly, Dyan J.; Prendergast, Deirdre M.; Sheridan, James J. (Teagasc, 2002-04)
      Emboli of brain tissue in the lungs have been reported in cases following severe head injury (McMillan 1956) and birth trauma in people (Hauck e t al 1990) and in cattle following stunning (Bauer 1996; Garland 1996). This has important implications for food safety if the brain tissue of stunned cattle is infected with the prion responsible for bovine spongiform encephalopathy (BSE), (Prusiner 1991). BSE emerged following changes in the rendering process in the early 1980s which allowed the aetiologic agent to survive, contaminate protein feed supplement and infect cattle (Brown e t al. 2001). Within a short period of time after the first case of BSE, concerns were expressed regarding the transmission of BSE to humans and the likelihood of infection from consumption of beef and beef products. This has become increasingly significant with the discovery of the link between BSE in cattle and variant Creutzfeldt-Jakob disease (vCJD) in man (Bruce e t al 1997).
    • Stabilising effect of α-lactalbumin on concentrated infant milk formula emulsions heat treated pre- or post-homogenisation

      Buggy, Aoife K.; McManus, Jenifer J.; Brodkorb, Andre; McCarthy, Noel; Fenelon, Mark A.; Department of Agriculture, Food and the Marine; Teagasc Walsh Fellowship Programme; 11/F/037 (Springer, 22/11/2016)
      Protein type and/or heat treatment pre- or post-homogenisation can affect the physical stability of infant formulations during manufacture. Previous research has described the use of α-lactalbumin addition in infant formulae, but has not demonstrated the effect of heating pre- or post-emulsion formulation during processing. The objective of this study was to evaluate the effect of both of these parameters. Three batches of model 1st-stage infant formula containing differing whey protein ratios (60:40 whey: casein with α-lactalbumin content 12, 30 or 48% of total protein) were prepared. Each batch was split; one half receiving heat treatment pre-homogenisation and the second half homogenised and then heat treated. Emulsion stability was determined by size exclusion chromatography, SDS-PAGE, particle size and viscosity measurements. There was a significant (P < 0.05) reduction in the formation of large soluble aggregates upon increasing α-lac concentration in emulsions heat treated either before or after homogenisation. Heat treatment of formulations post-homogenisation resulted in a higher (P < 0.05) D.v09 within the particle size distribution; increasing α-lactalbumin concentration to 30 or 48% significantly (P < 0.05) reduced the D.v09 within the particle size distribution in these emulsions. The viscosity of concentrates (55 % total solids) containing the 12% α-lactalbumin, heat treated post-homogenisation, was significantly greater (P < 0.05) than the equivalent emulsion heat treated pre-homogenisation; increasing the α-lactalbumin concentration to 30 or 48% significantly (P < 0.05) reduced viscosity. When the α-lactalbumin content was increased to 48% as a percentage of the total protein, heating before or after emulsion formation had no effect on concentrate viscosity. The findings demonstrate the importance of thermal denaturation/aggregation of whey proteins (and in particular, the ratio of α-lactalbumin to β-lactoglobulin) prior to homogenisation of infant formula emulsions.
    • Strategies to improve the bacteriocin protection provided by lactic acid bacteria

      O'Shea, Eileen F.; Cotter, Paul D.; Ross, R Paul; Hill, Colin; Department of Agriculture, Food and the Marine; Science Foundation Ireland; 04R and DC; 07/CE/B1368 (Elsevier, 18/01/2013)
      Lactic acid bacteria (LAB) produce a wide variety of antimicrobial peptides (bacteriocins) which contribute to the safety and preservation of fermented foods. This review discusses strategies that have been or could be employed to further enhance the commercial application of bacteriocins and/or bacteriocin-producing LAB for for food use.
    • Streptococcus thermophilus APC151 Strain Is Suitable for the Manufacture of Naturally GABA-Enriched Bioactive Yogurt

      Linares, Daniel M.; O'Callaghan, Tom F.; O'Connor, Paula M.; Ross, R Paul; Stanton, Catherine; Science Foundation Ireland (Frontiers, 23/11/2016)
      Consumer interest in health-promoting food products is a major driving force for the increasing global demand of functional (probiotic) dairy foods. Yogurt is considered the ideal medium for delivery of beneficial functional ingredients. Gamma-amino-butyric acid has potential as a bioactive ingredient in functional foods due to its health-promoting properties as an anti-stress, anti-hypertensive, and anti-diabetic agent. Here, we report the use of a novel Streptococcus thermophilus strain, isolated from the digestive tract of fish, for production of yogurt naturally enriched with 2 mg/ml of gamma-aminobutyric acid (200 mg in a standard yogurt volume of 100 ml), a dose in the same range as that provided by some commercially available gamma-amino-butyric acid supplements. The biotechnological suitability of this strain for industrial production of yogurt was demonstrated by comparison with the reference yogurt inoculated with the commercial CH1 starter (Chr. Hansen) widely used in the dairy industry. Both yogurts showed comparable pH curves [1pH/1t D 0.31􀀀0.33 h􀀀1], viscosity [0.49 Pa-s], water holding capacity [72–73%], and chemical composition [moisture (87– 88%), protein (5.05–5.65%), fat (0.12–0.15%), sugar (4.8–5.8%), and ash (0.74–1.2%)]. Gamma-amino-butyric acid was not detected in the control yogurt. In conclusion, the S. thermophilus APC151 strain reported here provides a natural means for fortification of yogurt with gamma-amino-butyric acid.
    • Structural mechanism and kinetics of in vitro gastric digestion are affected by process-induced changes in bovine milk

      Mulet-Cabero, Ana Isabel; Mackie, Alan R.; Wilde, Peter J.; Fenelon, Mark A.; Brodkorb, Andre; Irish Dairy Levy Research Trust; Teagasc Walsh Fellowship Programme; BBSRC; 2014029; BB/J004545/1 (Elsevier, 2018-03-20)
      Bovine milk is commonly exposed to processing, which can alter the structure, biochemical composition, physico-chemical properties and sensory quality. While many of these changes have been studied extensively, little is known about their effect on digestive behaviour. In this study, heat treatments of pasteurisation at 72 °C for 15 s or Ultra-High-Temperature (UHT) treatment at 140 °C for 3 s and homogenisation at pilot-plant scale were applied to whole milk. The gastric behaviour was investigated using a recently developed semi-dynamic adult in vitro model. The emptied digesta were analysed to assess the nutrient delivery kinetics, changes in microstructure and protein digestion. All samples showed protein aggregation and coagulum formation within the first 15 min of gastric digestion at which time the pH ranged from 5.5 to 6. Homogenised samples creamed regardless of heat treatment, whereas all non-homogenised samples exhibited sedimentation. The consistency of the coagulum of the heated samples was more fragmented compared to those of the non-heated samples. Rheological analysis showed that the higher the temperature of the heat treatment, the softer the obtained coagulum and the higher the protein hydrolysis at the end of digestion. The study also confirmed that gastric emptying of caseins from milk is delayed due to coagulation in the stomach, while β-lactoglobulin was emptied throughout the gastric phase, except for UHT-treated milk. The gastric behaviour also had an impact on the lipid and protein content of the emptied chyme. The homogenised samples seemed to release more nutrients at the end of gastric digestion.
    • Structure and antioxidant activity of Maillard reaction products from α-lactalbumin and β-lactoglobulin with ribose in an aqueous model system

      Jiang, Zhanmei; Brodkorb, Andre; Innovative Research Team of Higher Education of Heilongjiang Province; Program for New Century Excellent Talents in Heilongjiang Province University (Elsevier, 11/02/2012)
      Maillard reaction products (MRPs) were prepared from aqueous model mixtures containing 3% (w/w) ribose and 3% (w/w) of the dairy proteins α-lactalbumin (α-LA) or β-lactoglobulin (β-LG), heated at 95 °C, for up to 5 h. The pH of MRPs decreased significantly during heat treatment of α-LA-Ribose and β-LG-Ribose mixtures from 8.4 to 5.3. The amino group content in MRPs, derived from the α-LA-Ribose and β-LG-Ribose model system, was decreased noticeably during the first hour and did not change thereafter. The loss of free ribose in MRPs was higher for β-LG-Ribose than for α-LA-Ribose. During the Maillard reaction, the concentration of native and non-native α-LA, or β-LG, decreased and the formation of aggregates was observed. Fluorescence intensity of the β-LG-Ribose MRPs reached maximum within 1 h, compared to 2 h for α-LA-Ribose MRPs. Meanwhile, modification of the UV/vis absorption spectra for α-LA and β-LG was mainly due to a condensation reaction with ribose. Dynamic light scattering showed a significant increase in the particle size of the MRPs. Size exclusion chromatography of MRPs revealed the production of both high and low molecular weight material. Electrophoresis of MRPs indicated polymerization of α-LA and β-LG monomers via inter-molecular disulfide bridge, but also via other covelant bonds. MRPs from α-LA-Ribose and β-LG-Ribose exhibited increased antioxidant activities, therefore theses MRPs may be used as natural antioxidants in food products.