Transfers of small analytes in a multiphasic stirred fruit yoghurt model (original) (raw)
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Rheological and Biochemical Properties of Acidified Milk / Pectin Co-Gels
The influence of pH and Low Methoxyl Pectin (LMP) on the stability and properties of acid milk gel was studied by measuring rheology, ζ potential, particle size, micelle hydration and buffering properties. Glucono-delta-lactone (gdl) addition decreased rapidly the pH and stabilized it at ~ 4.6. During acidification stiffness (K) increased while the gel point decreased. The presence of pectin on milk reconstituted with or without gdl increased significantly the stiffness and the particle size compared with a non treated sample. On the other land lowering pH from the initial pH to pH 5.9-5.8 decreased significantly the micelle hydration of acidified milk treated with or without pectin and storage at 4°C.
Food Hydrocolloids, 2010
Doogh is a traditional Iranian drink prepared by fragmentation and dilution of yogurt, with addition of salt and flavouring. In the present work, we have used viscometry, microscopy, particle-size analysis and measurements of serum separation to explore the effect of very low concentrations of gellan gum (0.01, 0.03 and 0.05 wt %), alone or in combination with 0.25 wt % high-methoxy pectin (HMP), on its structure and stability. HMP is known to prevent association of casein particles in acidic milk drinks by steric stabilisation, forming a protective layer bound electrostatically to the surface of the particles. Doogh incorporating 0.25 wt % HMP alone showed satisfactory stability on storage for w10 days at 5 C, but after 15 days there was obvious separation into a dense sediment and a much clearer upper layer that occupied more than 80% of the total volume, which we attribute to progressive sedimentation of individual sterically-stabilised particles. Samples incorporating gellan (with or without HMP), by contrast, showed rapid development of a clear serum phase, with little further separation at longer times (up to w1 month), suggesting expression of fluid by contraction of a gel network (i.e. syneresis rather than sedimentation). Particle size increased dramatically (more than 10-fold) with increasing concentration of gellan, and at the highest concentration studied (0.05 wt %) a continuous network of casein-rich strands was observed by phase-contrast microscopy. The concentration of NaCl used in the doogh samples (0.5 wt % z 85 mM) is known to be sufficient to maintain gellan in its ordered (double-helix) conformation, which has higher charge density than individual molecules of HMP. We suggest that network structure is formed by electrostatic attachment of gellan to fragments of acid-casein gel, thus increasing particle size and inhibiting surface-coverage by HMP, with weaker associations between gellan helices allowing the samples to flow. Observed decrease in serum volume with increasing concentration of gellan is attributed to formation of progressively stronger coupled networks with greater resistance to syneresis. Stabilisation of doogh with 0.05 wt % gellan in combination with 0.25 wt % HMP had no adverse effect on organoleptic acceptability, and reduced serum volume on protracted storage to w10% (in comparison with over 80% for the same concentration of HMP alone), suggesting that gellan could be of practical value in extending the shelf-life of doogh (and related acidic milk drinks).
Flavour release at gas/matrix interfaces of stirred yoghurt models
International Dairy Journal, 2006
Release of strawberry flavour compounds at vapour/matrix interfaces was studied in model food systems simulating a yoghurt with a fruit preparation syrup. The effect of different parameters including physicochemical characteristics of the flavour compound, the structure and composition of the matrix and the temperature (4 and 101C) on the release of the flavour compounds were investigated. There was an effect of the composition and structure of the matrix upon the partition of the flavour compounds. In the dairy gel, retention of flavour compounds was caused by the physicochemical interactions with the proteins and the solubilisation in dispersed fat. The addition of syrup to the low-fat dairy gel slightly increased the retention of the flavour compounds; this was attributed to physicochemical interactions with pectin and sucrose. In the presence of fat (5%), the flavour compounds were solubilised in the fat and their release was not affected by the composition of the dispersing medium. As expected, temperature affected the release; an increase from 4 to 10 1C resulted in an increase in the overall amount of flavour released. r
Electrostatic complexes of whey protein and pectin as foaming and emulsifying agents
International Journal of Food Properties, 2017
Five types of electrostatic complex (macromolecular complexes, core-shell particles, and mixed homogeneous particles) were formed between whey protein (whey protein concentrate [WPC]) and pectin. By controlling the thermal treatment, composition, and order of mixing, it was possible to produce complexes that for the same biopolymer concentration gave differing functional properties. All protein-pectin complexes showed higher foaming ability and stability than native or heated WPC without pectin. Native WPC had higher emulsifying ability than protein-pectin complexes but exhibited the lowest emulsion stability. Ingredients based on such ideas might offer the food manufacturer greater control over food structure, stability, and organoleptic properties.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007
Combining total carbon (TC) and total nitrogen (TN) measurements, the solubility of both protein and pectin in mixtures of 0.5% whey protein isolate and non-amidated high methoxyl sugar beet pectin was determined at pH 4.0, as well as pH 5.5. The experimental results indicated that insoluble complexes with a protein to pectin ratio of 3.84 ± 0.88 were formed at pH 4.0 at protein to pectin ratios ranging from 5 to 0.5. At pH 5.5, the protein solubility was independent from the amount of pectin added, indicating that at these pH conditions, located above the whey protein's iso-electric point, either soluble complex formation or cosolubility occurred. Light microscopic analysis of the corresponding emulsions revealed that the large droplet sizes at a protein-pectin ratio of 5 at pH 4.0 were due to the low amount of soluble protein left due to complexation with pectin. Comparing the residual dissolved protein and pectin concentrations in the absence and presence of oil droplets indicated that not only the protein, but also the pectin was accumulated at the O/W interface both below and above the protein's iso-electric point. Electrophoretic mobility measurements clearly indicated that pectin adsorption to the whey proteins induced a charge reversal at pH 4.0 at higher pectin concentrations, giving rise to smaller droplet sizes. At pH 5.5, on the other hand, the electrophoretic mobility of the whey protein stabilised emulsion droplets became gradually more negative upon pectin addition, which not only resulted in a smaller droplet size, but also in a significant increase of the creaming stability. From the experimental results, it follows that pectin has an emulsion stabilising effect on protein stabilised emulsions both below and above the protein's iso-electric point, provided that electrostatic protein precipitation is prevented.
International Dairy Journal, 2009
The influence of a CO 2-acidification cycle on the acid (glucono-d-lactone, GDL) gelation properties of skim milk with and without added low-methoxyl pectin (LM-pectin) was assessed. Ionic calcium level, zeta potential, particle size, buffering properties and small amplitude oscillatory rheology moduli were monitored. The presence of LM-pectin in milk had an impact on the average size of the casein micelles and a large and dominant influence on its rheological behaviour during GDL acidification. The application of a CO 2-pH cycle (pH target 4.9) as a milk pretreatment induced during GDL acidification a stabilization of the colloidal system in wide pH range (pH 6.0-5.1) with modifications of the structure of the casein micelles before the onset of gelation. These modifications induced a significant improvement on its acid gelation behaviour. The measurements of Ca 2þ level during GDL acidification showed that an important and significant part of the Ca 2þ released during the CO 2-pH cycling was electrostatistically trapped by pectin molecules in the serum.
Formation of a Protein Aggregate Layer at a Milk/Acidified Gel Interface
International Dairy Journal, 1998
In bilayer systems consisting of acidified sweetened agar gels and milk, mass transfer between the two layers led to the formation of a milk protein aggregate layer at the boundary, so called 'hard layer'. The aim of this work was to understand main mechanisms involved in the formation of that 'hard layer'. The kinetics of growth of the hard layer was followed using an experimetal set up described here, and in situ pH profile was determined by a microelectrode. The boundary of the hard layer with milk was found to coincide with pH 4.9. Increased acid concentration in the agar gel and preacidication of the milk increased the rate of formation of the 'hard layer'. Increased sucrose concentration in the agar gel increased the rate of formation at longer contact times. This effect of sucrose was explained by a modification of water activity in the milk phase brought by mutual sucrose-water migration. It was concluded that the hard layer was induced by a pH drop of milk in contact of acidifed agar gels, below the gelation pH of milk in the boundary region. That pH drop was caused by acid and sugar migration from the agar gel into the milk phase.
Food Hydrocolloids, 2019
Protein and fiber, especially pectin, can form complexes at acidic pH. Studies on these complexes under actual food conditions are scarce. The aim of this work was to study interactions between whey proteins and blueberry puree, in particular its pectin, and to evaluate the impact on the functionality of the puree alone or incorporated into a model beverage. After the addition of a whey protein isolate (WPI) into purees at pH 3.5 or 6.5, the soluble pectin and protein contents and the viscosity of the resulting mixtures were determined. The decrease in the solubility of pectin (80%) and proteins (94%) indicated the formation of protein-pectin complexes by electrostatic interactions at pH 3.5, contributing to increase the mixture viscosity. The amount of soluble pectin in blueberry limited the formation of complexes when more WPI was added (5%). Heating the puree prior to the WPI addition solubilized pectin, which limited the formation of insoluble complexes and reduced the viscosity increase. The solubility of the blueberry polyphenols did not decrease after WPI addition. Finally, the non-heated puree enriched in WPI was used to prepare smoothies. This time, the protein-pectin complexation, probably reinforced by the final pasteurization of the smoothies, contributed to reduce the smoothie viscosity and can be explained in particular by particles of smaller sizes. Although the smoothie stability can be improved, the interactions between blueberry pectin in a puree and whey proteins allowed to design a novel functional ingredient that may be helpful in formulating beverages rich in fiber and protein.
Citrus Pectin: Structure and Application in Acid Dairy Drinks
Pectin, a plant cell wall polysaccharide, is mainly used in food industries for its gelling and stabilizing properties. In industrial applications, pectin is usually widely extracted from citrus peels, and in some intances, apple pomace is also used. Lime and lemon are the preferred citrus species used in the extraction of pectin, while orange and grapefruit are used less often. In the food industry, pectin is widely employed in the production of jams and jellies, confectionary products and bakery fillings. The fine structure of pectin is affected by many parameters, such as the origin of raw material and extraction conditions. This structural variability impacts greatly on pectin functional properties. The other major use of pectin concerns the stabilization of acidified milk drinks and yogurts. With their refreshing natural taste and high nutritional value, acidified milk drinks enjoy great popularity. A large selection of different sour milk drinks, which vary according to the manufacturing process, ingredients and consistency, is available to meet the needs of every consumer. In all cases, protein flocculation and whey separation occur in the absence of stabilizers in acidified milk drinks. To prevent this behaviour and to stabilize milk drinks, citrus pectin can be added as a protecting colloid. This review presents the structure of citrus pectin and functionality, with a special emphasis on acid dairy drinks.