The physicochemical characteristics of nonfat set yoghurt containing some hydrocolloids

The effect of incorporating the hydrocolloids carrageenan (0.10%, 0.30%), xanthan gum (0.15%, 0.35%) and alginate (0.05%, 0.15%) in nonfat set yoghurt was examined in respect of instrumental texture profile and water‐holding capacity (WHC) of the yoghurt. The yoghurts which exhibited the similar behaviour of commercial yoghurts in terms of WHC, firmness and consistency, low adhesiveness and gumminess were analysed by difference‐from‐control sensory test. Carrageenan increased firmness, adhesiveness, gumminess and WHC at the highest concentration tested. The sensory tests did not show any significant difference between the formulations tested.     

Influence of fortification with sodium–calcium caseinate and whey protein concentrate on microbiological,textural and sensory properties of set‐type yoghurt

The effect of fortification of yoghurt with sodium–calcium caseinate (SCC) and whey protein concentrate (WPC) on some properties of set‐type yoghurt were investigated. The addition of WPC enhanced the viability of Lactobacillus delbrueckii subsp. bulgaricus more than SCC. The highest firmness values were obtained from SCC‐fortified yoghurts, whereas yoghurts fortified with WPC had the highest water‐holding capacity during storage. The yoghurts fortified with 4% w/w SCC or 4% w/w WPC had the highest viscosity. Yoghurts fortified with 2% w/w SMP, SCC or WPC showed similar taste and overall acceptability scores; however, samples containing 4% w/w SCC or 4% w/w WPC had the lowest scores.     

Texture of nonfat yoghurt as influenced by whey protein concentrate and Gum Tragacanth as fat replacers

Seven batches of nonfat yoghurt stabilized with different concentrations of whey protein concentrate (WPC) and Gum Tragacanth (GT) were produced to study the effects of WPC and GT as fat replacers on the rheological properties of yoghurt. By increasing the WPC up to 15 g/L, storage modulus (G'), loss modulus (G") and complex dynamic viscosity (η*) values were increased and sensory impressions of texture and appearance were improved when compared with the control nonfat yoghurt. Addition of gum above 0.5 g/L led the decrease of G', G", η* and resulted in lower scores for sensory attributes than control nonfat yoghurt.     

Effect of pullulan on the physicochemical properties of yoghurt

The effects of pullulan (PUL) addition (0, 1.0 and 2.0% w/ v) on the physicochemical properties of yoghurts stored at 4 °C for 28 days were investigated. Fortification of the yoghurt with 1% PUL had a weakening effect on the gel network structure, leading to a decrease in initial viscosity and an extreme increase in syneresis, when compared to control. The addition of 2% PUL largely improved product stability by increasing gel firmness and adhesiveness, showing higher viscosity and consistency index values as well as displaying the lowest syneresis. Storage time increased yoghurt gel firmness and susceptibility to serum separation.     

Physical properties of yoghurt manufactured with milk whey and transglutaminase

The effect of milk protein polymerization prior to the yoghurt fermentation process was evaluated by enzymatic reaction with microbial transglutaminase (Streptoverticillium mobaraense). Yoghurt samples were manufactured with 100% milk or by substituting milk with 20 or 30% of liquid milk whey, aimed at determining the use of natural milk whey in dairy products. Transglutaminase was added at a protein ratio of 0.5 U g⁻¹ to all samples and evaluated regarding rheological behavior, syneresis index and texture profile. The addition of enzyme transglutaminase contributed to syneresis prevention and increased the consistency index in yoghurt samples manufactured with milk whey. Yoghurt manufactured from 70% milk plus 20% milk whey, followed by enzymatic treatment, presented similar characteristics to traditionally manufactured yoghurt (C 100), with no alteration in the syneresis of the samples (p > 0.05) and presented texture parameters similar to the control yoghurt (C 100).     

Functional and textural properties of vegetable‐fibre enriched yoghurt

In this study, different vegetable‐fibre enriched yoghurts namely control (C), pumpkin (PY), carrot (CY), green pea (GY) and zucchini (ZY), were produced. It was observed that Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus counts were higher in yoghurts supplemented with vegetable purees, in accordance with the enhanced growth of lactic acid bacteria due to the fibres, phenolic compounds and organic acids present in the vegetables. Furthermore, vegetable puree supplementation affected the pH, titratable acidity, syneresis, colour (L*, a*, b*, ΔE values), texture (firmness, cohesiveness, consistency and viscosity index) and sensorial properties of the yoghurts. Firmness, consistency and viscosity indices were higher in the yoghurt produced with carrot puree, whereas the highest antioxidant capacity was detected in the pumpkin yoghurt, which corresponded to the highest total phenolic, ascorbic acid and total carotenoid contents. The results of the present study could lead to an innovative approach in the functional dairy product market for the development of dairy products enriched with vegetables that have nutritional and potential therapeutic characteristics.     

Structural properties of stirred yoghurt as influenced by whey proteins

The effect of whey protein addition on structural properties of stirred yoghurt systems at different protein and fat content was studied using laser diffraction spectroscopy, rheology and confocal laser scanning microscopy (CLSM). The composition of heated milk systems affected micro- and macroscopic properties of yoghurt gels. Particle size increased as a function of increasing whey protein content and decreased as a function of increased fat level. Firmness (elastic modulus) and apparent viscosity of manufactured yoghurt samples increased as a function of increased interparticle interactions, mainly caused by self-aggregation of whey proteins or aggregated whey protein-coated fat globules, respectively. The resistance towards shear-induced disruption of yoghurt gels increased with an increasing proportion of casein protein in the protein mixture, whereas products with high whey protein level revealed lower resistance behaviour towards shear-forces. CLSM images illustrated that the presence of large whey protein aggregates and lower number of fat globules lead to the formation of an interrupted and coarse gel microstructure characterised by large interstitial spaces. The higher the casein fraction and/or the fat level, the less interspaced voids in the network were observed. However, it is evident that the addition of whey proteins reinforces firmness properties of low-fat yoghurts comparable to characteristics of full-fat yoghurt.     

The effect of heat treatment of ovine milk on the compositional and sensory properties of set yoghurt

The aim of this study was to investigate the effect of heat treatment of ovine milk at 60 °C/5 min and 90 °C/5 min (control group) on the compositional and sensory properties of set yoghurt (n = 40). The concentration of apparent casein and total whey protein were significantly higher while sensory properties (except consistency) were not significantly different from the yoghurts in control group (P < 0.05). The results showed that ovine set yoghurt produced by heat treatment at low temperature possessed higher amount of preserved inherent functional and nutritional properties of milk than yoghurt produced by heat treatment at high temperature.     

Enhancing the rheological,technological, textural and microstructural characteristics of set yoghurt using certain nano-stabilisers

The purpose of this study was to investigate the impact of adding nano-stabilisers on some properties of yoghurt. Carboxymethyl cellulose (CMC), sodium alginate (SA) and kappa-carrageenan (K-C) were used at 0.2%, 0.2% and 0.02% in their original forms and 0.15%, 0.15% and 0.015% in nano-form, respectively. The effects of these additives on yoghurt pH, titratable acidity, viscosity, syneresis, texture, colour, starter culture bacterial count, mould and yeast count, coagulation time and microstructure were studied. The use of nano-stabilisers increased viscosity, hardness and coagulation time; reduced syneresis and Streptococcus thermophilus count; and improved colour. Results indicated that nano-stabilisers improved the rheological and technological characteristics of yoghurt.     

The influence of transglutaminase treatment on functional properties of set yoghurt

The objective of this study was to investigate the effect of transglutaminase (Tgase) on the functional properties of set yoghurt, due to enzymatic cross-linking of the milk proteins. Yoghurt samples were prepared from three formulations: reconstituted skim milk, and whole milk containing two different solid-non-fat (SNF) content, with four enzyme treatments: Control (no enzyme) and three microbial Tgase treatments: Pre-incubated 90 min, Pre-incubated and inactivated after 90 min, Not pre-incubated. The modifications which were caused by Tgase were found to be more clear when Tgase was active in set type yoghurts. It was found that nonfat yoghurt sample with lower SNF content can be produced with improved textural properties using Tgase.     

Effects of milk supplementation with skim milk powder, whey protein concentrate and sodium caseinate on acidification kinetics, rheological properties and structure of nonfat stirred yogurt

Milk supplementation with milk proteins in four different levels was used to investigate the effect on acidification and textural properties of yogurt. Commercial skim milk powder was diluted in distilled water, and the supplements were added to give different enriched-milk bases; these were heat treated at 90 °C for 5 min. These mixtures were incubated with the bacterial cultures for fermentation in a water bath, at 42 °C, until pH 4.50 was reached. Chemical changes during fermentation were followed by measuring the pH. Protein concentration measurements, microbial counts of Lactobacillus bulgaricus and Streptococcus thermophilus, and textural properties (G′, G″, yield stress and firmness) were determined after 24 h of storage at 4 °C. Yogurt made with milk supplemented with sodium caseinate resulted in significant properties changes, which were decrease in fermentation time, and increase in yield stress, storage modulus, and firmness, with increases in supplement level. Microstructure also differed from that of yogurt produced with milk supplemented with skim milk powder or sodium caseinate.     

Effect of enzymatic cross-linking of milk proteins on functional properties of set-style yoghurt

This paper presents research on the effect of enzymatic cross-linking of milk proteins on the properties of yoghurt. Whole milk was incubated with transglutaminase (TG) prior to fermentation (2 h, 40°C, E/S ratio 1/2000). Enzyme action was stopped by heating (1 min, 80°C). Skim-milk was treated by simultaneous use of TG and thermophilic yoghurt starter culture without inactivation of the enzyme. A TG treatment of milk prior to fermentation led to prolonged fermentation, while the concomitant use of TG and culture had no influence on fermentation time. Post acidification of yoghurt during storage was lower for products from enzyme-treated milk. This applies both for products cross-linked prior to fermentation with enzyme inactivation, and for simultaneous use of culture and TG without inactivation of the enzyme. Scanning electron microscopic studies revealed that a TG treatment of milk led to reduced mesh sizes of the protein network, and a more regular distribution of the proteins in the yoghurt gel. As a result, yoghurt products from enzyme-treated milk showed increased gel strength and less syneresis, especially when the enzyme was not inactivated. Sensory studies revealed that odour and consistency properties of products from TG-treated milk were assessed as less 'yoghurt specific'. On the other hand, products from enzyme-treated milk were described as being more creamy, indicating that a TG treatment may simulate fat in fermented milk products.     

Effects of sunflower honey on the physicochemical,microbiological and sensory characteristics in set type yoghurt during refrigerated storage

The primary purpose of this research was to monitor the influence of sunflower honey addition (2%, 4% and 6% w/v) to yoghurt milk on survival of the microbial flora of yoghurt and the physicochemical and sensory characteristics during refrigerated storage for 4 weeks. The water activity decreased according to the addition of honey with higher concentrations in the storage period (4°C). At the end of fermentation, pH values of yoghurt samples ranged between 4.33 (without honey) and 4.52 (addition of honey with 6%). The highest water holding capacity, consistency and the lowest brightness values were determined in the groups produced with 6% honey addition. The water holding capacity and a* (redness) values of the honey incorporated yoghurt samples increased during storage. Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus values of the yoghurt with honey increased compared with the control group samples (P < 0.01). Addition of honey to yoghurt milk has affected the vitality of the characteristics starters in the incubation and storage time of the yoghurt samples (P < 0.01). Optimum sweetness was obtained with the samples containing 4% honey level.     

Effects of tea polyphenols on physicochemical and antioxidative properties of whey protein coating

Food Science and Biotechnology - Effects of tea polyphenols (TP) incorporation on physicochemical and antioxidative properties of whey protein isolate (WPI) coating were studied. Two WPI coating...     

Functional and technological aspects of whey powder and whey protein products

Commercial whey powder, whey protein concentrates and whey protein isolates (WPIs) were evaluated for certain functional properties and for their application in full‐fat and nonfat yoghurts. The functional properties of whey products varied, and the highest functionality was recorded in samples with high protein levels. Whey powder had the lowest foaming performance and emulsifying capacity, while WPIs possessed the best functional properties of all the other samples. Curd tension (CT), viscosity and syneresis were improved in yoghurts made using fortified cow's milk or reconstituted skim milk with any whey products, while whey powder had no impact on CT.     

Acid-induced gelation of whey protein polymers: effects of pH and calcium concentration during polymerization

Heating whey protein dispersions (90°C for 15 min) at low ionic strength and pH values far from isoelectric point (pH>6.5) induced the formation of soluble polymers. The effect of mineral environment during heating on the hydrodynamic characteristics and acid-induced gelation properties of polymers was studied. Whey protein dispersions (80 g/l) were denatured at different pH (6.5–8.5) and calcium concentrations (0–4 mm) according to a factorial design. At pH 6.5, the hydrodynamic radius of protein polymers increased with increasing calcium concentration, while the opposite trend was observed at pH 8.5. Intrinsic viscosity results suggested that heating conditions altered the shape of protein polymers. Whey protein polymers were acidified to pH 4.6 with glucono-δ-lactone and formed opaque particulate gels. The storage modulus and firmness of gels were both affected by conditions used to prepare protein polymers. As a general trend, polymers with high intrinsic viscosity produced stronger gels, suggesting a relationship between polymer shape and gel strength.Acid gelation properties of whey protein polymers makes them suitable ingredients for yoghurt applications. Using whey protein polymers to standardize protein content increased yoghurt viscosity to 813 Pa.s while using skim milk powder at same protein concentration increased yoghurt viscosity to 393 Pa.s. Water holding capacity of protein polymers in yoghurt was 19.8 ml/g compared to 7.2 ml/g for skim milk powder protein. Acid gelation properties of whey protein polymers are modulated by calcium concentration and heating pH and offers new alternatives to control the texture of fermented dairy products.     

The physicochemical parameters during dry heating strongly influence the gelling properties of whey proteins

In this study we determined the composition (proportion of native proteins, soluble and insoluble aggregates) and quantified the gelling properties (gel strength and water holding capacity) of pre-texturized whey proteins by dry heating under controlled physicochemical conditions. For this purpose, a commercial whey protein isolate was dry heated at 80 °C (up to 6 days), 100 °C (up to 24 h) and 120 °C (up to 3 h) under controlled pH (2.5, 4.5 or 6.5) and water activity (0.23, 0.32, or 0.52). Gelling properties were quantified on heat-set gels prepared from reconstituted pre-texturized proteins at 10% and pH 7.0. The formation of dry-heat soluble aggregates enhanced the gelling properties of whey proteins. The maximal gelling properties was achieved earlier by increasing pH and water activity of powders subjected to dry heating. An optimized combination of the dry heating parameters will help to achieve better gelling properties for dry heated whey proteins.     

发酵剂的筛选及其对搅拌型酸奶理化特性的影响

通过调查单菌株发酵特性、球菌/杆菌比例的选择、菌株复配后的性能,得到了4组优化的发酵剂配方。在不添加任何增稠剂的条件下,其发酵的酸奶在28d货架期内质构、后酸化程度表现优异且稳定。此外,为了预测酸奶货架期后酸化程度的强弱,比较了15组28d储存期实验与加速实验中所得的pH值及其变化趋势。结果表明,加速试验中趋于定值时的pH值可以作为判断后酸化程度强弱的先行指标。     

Influence of tribomechanical micronization on the physical and functional properties of whey proteins

Because of their high nutritional value and commercially important functional properties, whey proteins are of high interest nowadays. Whey protein concentrates (WPCs) containing 60% and 80% proteins (WPC-60 and WPC-80, respectively) were treated using laboratory equipment for tribomechanical micronization and activation (TMA) with three different rotor speeds: 16 000, 20 000 and 22 000 r.p.m. The results showed that the TMA treatment causes a significant decrease (  P < 0.05) in particle size, a change in particle size distribution and an increase in specific area of WPC. As a consequence of the TMA process, rupturing of protein globules and the appearance of a greater number of protein fragments occurred. The solubility, dispersibility, foaming and emulsifying properties of tribomechanically treated whey protein concentrates (TWPCs) were also modified. The results of particle analysis confirmed that a decrease in particle size correlates with an improvement of the foaming properties. These changes in the treated materials depend on the type of the WPCs used and the rotor speed of the TMA equipment. The most obvious changes were observed in samples treated at the maximum rotor speed of the TMA equipment.