Milk Model Systems Research Articles

Heating affects protein digestion of skimmed goat milk proteins with different casein:whey ratios under simulated infant conditions

This research compared effects of heating on the digestion of goat milk proteins in skimmed goat milk model systems with different casein-to-whey protein ratios. The digestion was evaluated both the supernatant and gastric clot part of the digesta. Whey protein concentrates were added in skimmed goat milk (80% casein, C80 sample) to make a 40% casein sample (C40 sample). Heating at 65 °C showed limited influence on digestibility of proteins in supernatant and clot of both model systems. In the supernatant, the C80 sample had a higher soluble protein concentration after 85 °C heating, compared to the C40 sample. After heating at 85 °C for 30 min, the digestibility of proteins in the supernatant of C40 and C80 samples was increased. This heating also increased the casein digestibility of the gastric clot of C80 sample, but resulted in more undigested whey protein aggregates in C40 sample. For the difference between C80 and C40 sample, the proteins in the supernatant of C80 samples showed a higher digestibility than those in the supernatant of C40 samples, both in non-heated and in 85 °C heated samples. The clots of C40 sample showed a relatively higher digestion rate than C80 sample clots, which may be due to their higher water content and looser microstructure. Overall, this study showed that heating induced different digestion kinetics of goat milk model systems with different casein-to-whey ratios.

Lycium barbarum and Delphinium denudatum for Hastened Lipid Oxidation and Microbial Stability of Heat-Desiccated Milk Model System

Lycium barbarum and Delphinium denudatum for Hastened Lipid Oxidation and Microbial Stability of Heat-Desiccated Milk Model System

Antioxidant potential of Lycium barbarum and Delphinium denudatum to improve shelf life of acid-coagulated milk model system

The value-added channa was optimized for its processing with the incorporation of 3% Lycium barbarum and 0.25% Delphinium denudatum. The value added channa was optimized and standardized for its processing and subjected to an in vitro antioxidant profile analysis of total phenols, total flavonoids content, DPPH, ABTS and FRAP assays and product storage profile. The value-added channa prepared with 3% Lycium barbarum and 0.25% Delphinium denudatum was having a shelf life of more than three weeks stored at refrigeration temperature. Thus, functional channa can be prepared with the fortification of 3% Lycium barbarum and 0.25% Delphinium denudatum with enhanced shelf-life.

In situ SAXS study of non-fat milk model systems during heat treatment and acidification

Small-angle X-ray scattering (SAXS) was used to monitor structural changes induced by heat treatment and acid gelation in milk matrices with added whey protein concentrates (WPCs) and nano-particulated whey protein (NWP). In general, heat treatment was found to mainly affect whey protein components while pure casein micelles remained largely unaffected. Conversely, acidification mainly affected caseins while leaving pure whey protein components intact. In mixed systems, the overall behaviour could be understood as a combination of the above effects, however, the type of the added whey protein components influenced the resulting structure formation and dynamics. NWP led to formation of larger structures compared to WPC components during heat treatment, although the latter showed faster aggregation dynamics. During acidification the NWP containing samples exhibited structural changes at slightly higher pH values than the WPC samples. The modeling of pure liquid whey protein (LWPC) samples showed that the heat induced denaturation and resulting aggregation of individual whey proteins is mainly a surface effect leaving the overall protein shape and dimensions unaffected. Schematic diagrams based on the current SAXS data and previous studies were constructed to illustrate the suggested interaction mechanisms between casein and whey proteins during both heating and acidification.

Interaction between added whey protein ingredients and native milk components in non-fat acidified model systems

Non-fat acidified milk model systems were constructed from frozen casein and whey protein concentrates produced from skim milk using membrane filtration, and combined with commercial whey protein ingredients, i.e. nano-particulated whey protein (NWP), micro-particulated whey protein (MWP), and whey protein concentrate (WPC). Model systems were characterised in terms of particle size distribution and fractionation, surface hydrophobicity and accessible thiol groups, rheological behaviour, water holding capacity and graininess. Samples containing NWP exhibited higher surface hydrophobicity and increase in accessible thiol groups, shorter gelation time, higher gelation pH and G′, but increasing particle size and number of grains, when compared with addition of MWP and WPC. Addition of MWP resulted in weak gels with a less connected protein network and decreased number of grains. Mixtures of NWP and MWP (1:1) had rheological properties closer to those seen for MWP. Systems with WPC differentiated themselves with a large quantity of small aggregates.

Regular and decaffeinated espresso coffee capsules: Unravelling the bioaccessibility of phenolic compounds and their antioxidant properties in milk model system upon in vitro digestion

Coffee is the most consumed beverage in the US and several other countries such as Brazil and Colombia. Coffee has been recognized for a myriad of health benefits including those arising from its antioxidant properties. However, to the best of our knowledge, there is no literature addressing the fate of phenolic compounds from espresso capsules considering the role of caffeine as well as the interaction with milk upon in vitro digestion. In this study, regardless of the sample (regular or decaffeinated espresso coffee capsule), oral and gastric digested samples showed lower contents of caffeine and phenolic acids than their undigested counterparts. In contrast, with recovery of up to 48%, only caffeic acid was present in the intestinal phase. Regular coffee samples showed a prooxidative action during the intestinal phase. In contrast, decaffeinated coffee prevented milk lipid peroxidation during the gastric and intestinal phases. A significant positive correlation existed between the caffeine concentration and the milk lipid peroxidation during the gastrointestinal phase. Thus, under the experimental conditions employed, decaffeinated coffee from commercial espresso capsules was considered the best choice in terms of prevention of the potential exposure of the gastrointestinal tract to products of milk lipid peroxidation.

Phytochemical-Rich Antioxidant Extracts of Vaccinium Vitis-idaea L. Leaves Inhibit the Formation of Toxic Maillard Reaction Products in Food Models.

Thermal treatment of proteinaceous foods generates heat-induced Maillard reaction substances including toxic advanced glycation end products (AGEs) and heterocyclic amines (HAs). It is known that plant phenolic compounds may influence Maillard reaction. This study investigated the impact of lingonberry leaf extracts on the formation of Nε -(carboxymethyl)lysine (CML) and Nε -(2-furoylmethyl)-L-lysine (furosine) in milk model system and HAs in meat-protein and meat model systems. In addition, lingonberry leaf extracts obtained by different solvents were characterized by radical scavenging, Folin-Ciocalteu assays and ultrahigh pressure liquid chromatography quadruple-time-of flight mass spectrometry (UPLC-qTOF-MS). Water extract (WE) stronger suppressed CML than furosine formation in milk model system: CML levels were reduced by nearly 40%. Moreover, quinic acid and catechin, which were abundant in WE, were effective in inhibiting CML and furosine formation. WE and acetone extract (AE) at 10 mg/mL significantly inhibited HAs formation in both model systems. However, higher suppressing effect on HAs formation showed AE, which had lower antioxidant capacity and total phenolic content values than WE. WE contained higher amounts of hydroxycinnamic acids, proanthocyanidins and flavonols, while AE was richer in flavan-3-ols and arbutin derivatives. It indicates that the composition of phenolics might be a major factor for explaining different effect of extracts from the same plant on HAs formation. In general, the results suggest that lingonberry leaves is a promising source of phytochemicals for inhibiting toxic Maillard reaction products and enriching foods with plant bioactive compounds. PRACTICAL APPLICATION: The increased consumption in processed foods has been linked with the increased risks of various diseases, while thermal food processing is required to develop flavor, insure safety, and extend shelf life. Therefore, developing effective technological means for inhibiting the formation of heat-induced toxic substances is an important task. This study showed a potential of lingonberry leaf extracts containing health beneficial phytochemicals to suppress the formation of toxic Maillard reaction products during heating of milk and meat.

Inhibition of the double-edged effect of curcumin on Maillard reaction in a milk model system by a nanocapsule strategy

In this work, the double-edged effect of curcumin (Cur) on Maillard reaction (MR) in model milk pasteurization process was demonstrated for the first time, where Cur inhibits MR at low concentrations (<5 μg/mL), while promotes it at high concentrations (>5 μg/mL). A nanocapsule strategy was introduced to resolve the disadvantages of Cur on MR at high temperature. In vitro experiments confirmed that curcumin @ polyvinylpyrrolidone nanocapsules (Cur@PVP NCs) synthesized by a one-pot method can control the continuous and slow release of Cur and exert inhibitory effect on MR by competing with lactose for casein, trapping the reactive dicarbonyl compounds and scavenging ROS, which might provide a new strategy for the application of functional food ingredients in the control of MR during food heat processing, including milk pasteurization.

Effect of homogenisation in formation of thermally induced aggregates in a non- and low- fat milk model system with microparticulated whey proteins.

The objective of the research presented in this paper was to investigate how different characteristics of whey protein microparticles (MWP) added to milk as fat replacers influence intermolecular interactions occurring with other milk proteins during homogenisation and heating. These interactions are responsible for the formation of heat-induced aggregates that influence the texture and sensory characteristics of the final product. The formation of heat-induced complexes was studied in non- and low-fat milk model systems, where microparticulated whey protein (MWP) was used as fat replacer. Five MWP types with different particle characteristics were utilised and three heat treatments used: 85 °C for 15 min, 90 °C for 5 min and 95 °C for 2 min. Surface characteristics of the protein aggregates were expressed as the number of available thiol groups and the surface net charge. Intermolecular interactions involved in the formation of protein aggregates were studied by polyacrylamide gel electrophoresis and the final complexes visualised by darkfield microscopy. Homogenisation of non-fat milk systems led to partial adsorption of caseins onto microparticles, independently of the type of microparticle. On the contrary, homogenisation of low-fat milk resulted in preferential adsorption of caseins onto fat globules, rather than onto microparticles. Further heating of the milk, led to the formation of heat induced complexes with different sizes and characteristics depending on the type of MWP and the presence or not of fat. The results highlight the importance of controlling homogenisation and heat processing in yoghurt manufacture in order to induce desired changes in the surface reactivity of the microparticles and thereby promote effective protein interactions.

Interactions in heated milk model systems with different ratios of nanoparticulated whey protein at varying pH

To better understand the interactions between nanoparticulated whey protein (NWP) and other milk proteins during acidification, milk model systems were diluted to 0.5% protein concentration and adjusted to pH of 6.0–4.5 following homogenisation and heat treatment. The diluted systems with different concentrations of NWP (0–0.5%) were characterised in terms of particle size, viscosity, surface charge and hydrophobicity. When pH was adjusted to 5.5, aggregation was initiated at levels of NWP (0.25–0.5%) leading to significant increase in particle size and viscosity. Pure NWP (0.5%) showed largest initial surface charge (−27 mv) and higher surface hydrophobicity than the other systems. The results indicated that NWP could self-associate above pH 5.5 and not only the decrease of electrostatic repulsion but also other interactions, such as hydrophobic interaction, play an important role in contributing to the early self-association of NWP.

Study of the browning and gelation kinetics in a concentrated sheep milk and sucrose system

Browning and gelation kinetics of a sheep milk and sucrose model system with 70% total solids (simulating dulce de leche) and the influence of temperature and sucrose content on this process were studied. The Kubelka–Munk index and subjective heat stability tests were used to monitor nonenzymatic browning and to determine gelation time. Browning and gelation processes showed different kinetics where gelation was shown to occur much faster than browning. Both independent variables (temperature and sucrose content) had a significant influence in both processes, where temperature had the higher impact.

Effects of added whey protein aggregates on textural and microstructural properties of acidified milk model systems

Non-fat milk model systems containing 5% total protein were investigated with addition of micro- or nanoparticulated whey protein at two levels of casein (2.5% and 3.5%, w/w). The systems were subjected to homogenisation (20 MPa), heat treatment (90 °C for 5 min) and chemical (glucono-delta-lactone) acidification to pH 4.6 and characterised in terms of denaturation degree of whey protein, particle size, textural properties, rheology and microstructure. The model systems with nanoparticulated whey protein exhibited significant larger particle size after heating and provided acid gels with higher firmness and viscosity, faster gelation and lower syneresis and a denser microstructure. In contrast, microparticulated whey protein appeared to only weakly interact with other proteins present and resulted in a protein network with low connectivity in the resulting gels. Increasing the casein/whey protein ratio did not decrease the gel strength in the acidified milk model systems with added whey protein aggregates.

Effects of disulphide bonds between added whey protein aggregates and other milk components on the rheological properties of acidified milk model systems

Micro- and nanoparticulated whey protein (MWP, NWP) were added to non-fat milk model systems and processed into chemically (glucono-delta-lactone) acidified milk gels. Model systems contained 5% protein in total and were made at two levels of casein (2.5% and 3.5%, w/w) with and without the thiol-blocking agent N-ethylmaleimide. The systems were characterised in terms of thiol groups, gel electrophoresis, particle size, and rheology during processing (homogenisation, heat treatment and acidification). The results showed that the formation of disulphide-linked structures in milk model systems was closely related to the increased particle size and rheological behaviour of the gels. MWP enriched systems produced, upon acidification, weak protein networks and required the addition of whey protein isolate (WPI) to increase gel strength. However, systems containing NWP exhibited pronounced increase in particle size and higher firmness of acidified gels through both covalent and non-covalent interactions.

Effects of beetroot (Beta vulgaris) preparations on the Maillard reaction products in milk and meat-protein model systems

The effects of beetroots (Beta vulgaris) on the formation of Maillard reaction (MR) products possessing health, nutritional and sensory implications were studied. The effect of dried beetroot juice on the formation of Nε-(carboxymethyl)lysine (CML) and Nε-(2-furoylmethyl)-L-lysine (furosine) was determined in a milk model system. Beetroot juice reduced furosine formation more than CML, inferring that betalain compounds present in the juice are more effective in reducing the formation of MR products in the early stage than in the advanced stage of MR. Beetroot water extract was fractionated on Sephadex LH20 and obtained three beetroot fractions were used to assess their effect on the formation of heterocyclic amines in a meat-protein model system. Beetroot fraction possessing the highest antioxidant capacity and containing the highest betalain content reduced the amounts of 2-amino-1-methyl-6-phenylimidazo-[4,5-b]-pyridine (PhIP), 2-amino-3,8-dimethyl-imidazo-[4,5-f]-quinoxaline (MeIQx), and 2-amino-3-methylimidazo-[4,5-f]-quinoline (IQ) by approximately 60, 77 and 87%, respectively. Beetroot preparations were characterized by ultra performance liquid chromatography quadrupole time of flight mass spectrometry (UPLC–Q-TOF–MS/MS). The antioxidant activities of beetroot preparations were also evaluated by 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS+) scavenging capacity, oxygen radical absorbance capacity (ORAC) and total phenolic compound assays. Our findings could be useful for creating novel source of functional ingredients exerting anti-carcenogenic and antiglycation activities.

Structure and Antioxidant Activity of Milk Model Systems after Microwave Heating

Structure and Antioxidant Activity of Milk Model Systems after Microwave Heating

Stability and quality of herb (Pueraria Tuberosa)-milk model system.

The medicinal benefits of herbs could be conveyed via certain foods as carriers. Milk is one of the important carrier which has been effectively used to deliver phytochemicals presents in herbs (mainly polyphenols) for targeted health benefits in the traditional Indian system of medical science. The present study was conducted to evaluate the effect of herb components (Pueraria tuberosa) on properties of Pueraria tuberosa-milk model system. The herb was added into cow milk on the basis of sensory evaluation (0.4%) by using 9-point hedonic scale. The physical and chemical changes were evaluated after various processing treatments viz. pasteurization (72°C, 15s), sterilization (121°C, 15min), separation etc. These changes were determined using viscosity, hydroxy methyl furfural (HMF) value, ethanol stability, colour characteristics and trolox equivalent antioxidant capacity (TEAC). It was observed that addition of Pueraria tuberosa to milk resulted in decreased HMF content, ethanol stability and lightness whereas antioxidant activity, redness and yellowness increased as compared to control. It can be concluded that addition of Pueraria tuberosa to milk at 0.4% concentration altered the functional properties of milk and Pueraira tuberosa could be suitable for preparation of low heat treated functional dairy food products.

Rheological performance of pectin-enriched products isolated from red beet ( Beta vulgaris L. var. conditiva) through alkaline and enzymatic treatments

The rheological performance of pectin-enriched products extracted from red beet ( Beta vulgaris L. var. conditiva) root by-products was evaluated in the present work. They were extracted through an alkaline pre-treatment with or without a subsequent enzymatic (hemicellulase or cellulase) hydrolysis at pH 5.2. Flow assays performed with 2.00% w/v-pectin aqueous systems showed pseudoplastic (flow index, n ≈ 0.4 or 0.8) or Newtonian ( n = 1.0) behaviour after fitting of experimental data to Ostwald’s law, also showing poor thickening effect. When Ca 2+ was added to water with the same pectin concentration, true gels developed as confirmed by the mechanical spectra obtained through dynamic assays. Junction zones of homogalacturonan (HG) side chains mediated by Ca 2+ were able to build up rigid networks in water. Isolated pectins (2.00% w/v) were also used to constitute milk model systems. Whole and skimmed milk were used at two different concentrations. Milk systems showed more transient and weaker gel networks when compared to Ca 2+-aqueous systems, and were associated to the formation of a [κ-casein⋯calcium cross linked low methoxyl pectin] complex dampened by the included milk fat globules. Relaxation spectra of pectin–milk systems were in general extended to large relaxation times (10 4 s) for all isolated fractions studied, which is typical of structured systems. Since all pectin fractions showed very similar chemical composition and molecular weight (average value and distribution), it was suggested that some differences in the rheological performance of each pectin product came from the different length of arabinans and distribution of rhamnose kinks (RG-I, random coil) as well as from the length of demethylated HG chains (semi-flexible coils). The results of this research show that the pectin-enriched fractions isolated from red beet root wastes are useful as additives in food formulation.

Stability of antioxidants in an apple polyphenol–milk model system

The stability of antioxidants in an apple polyphenol–milk model system was examined. The model system consisted of skim milk fortified with pH-neutralised apple polyphenols (AP, 0–200mg per 100ml milk), with or without ascorbic acid (100mg per 100ml milk). Physical and chemical changes were evaluated after thermal treatment (120°C, 5min) and oxidative storage (20°C and 38°C, up to 12 weeks). Antioxidant capacity was determined using both oxygen radical absorbance capacity (ORAC) assay and ferric reducing antioxidant power (FRAP) assay. Significant antioxidant capacity was detected in the presence of milk. Antioxidant capacity was retained during thermal treatment but decreased slowly during storage.The concentration of ascorbic acid decreased rapidly, and was close to zero after 2-week storage at 38°C or 10-week storage at 20°C. The brownness of the polyphenol–milk system increased over storage duration of 0–12 weeks; this effect was retarded by the addition of ascorbic acid. This high polyphenol–milk has demonstrated good physical stability.

Investigation of the Retronasal Perception of Strawberry Aroma Aftersmell Depending on Matrix Composition

The development of strawberry aroma aftersmell after consumption in aqueous and milk model systems was followed. A recently developed sensory approach was used to seize the qualitative, quantitative, and temporal aspects of aroma profile development. The results obtained from sensory evaluation were then correlated to analytical data, obtained by means of intraoral aroma detection using the buccal odor screening system (BOSS). A clear correlation was found between the sensory persistence of single odor impressions and the intraoral detectability of odorants by BOSS. For the strawberry aroma mixture it could be shown that BOSS is capable of selecting those odorants of a complex aroma mixture that elicit a certain aftersmell impression developing after a certain period of time in the oral cavity. Also, the changes in in vivo odorant persistence depending on changes in food matrix composition could be directly followed by means of BOSS.

Effect of lipid source on probiotic bacteria and conjugated linoleic acid formation in milk model systems

AbstractThe objective of this research was to study the effects of probiotic bacteria, lipid source, and fermentation time on the CLA content of a milk model system. The evaluation of 11 probiotic bacteria showed that they were able to produce CLA from linoleic acid in a model system containing hydrolyzed soy oil (1%) emulsified in milk, but not in model systems of unhydrolyzed oil (1%) emulsified in milk or 1% fat milk. Propionibacterium freudenreichii subsp. shermanii 56, P. freudenreichii subsp. shermanii 51, and P. freudenreichii subsp. freudenreichii 23 demonstrated the greatest increase in CLA content. Propionibacterium freudenreichii subsp. shermanii 51, produced the highest cis‐9,trans‐11 CLA content and also produced the greatest increase in trans‐10,cis‐12 CLA content as fermentation time was increased from 24 to 48 h. The fermentation of probiotic bacteria for 24 h was often most effective in increasing the CLA content. Viable counts of probiotic bacteria increased significantly from 0 to 24 h. These results demonstrated that the content of CLA during fermentation was primarily dependent on the strain of probiotic bacteria and the lipid source in the milk model system. This research suggests an efficient approach to produce CLA‐enriched cultured dairy products.