Microstructure and viscoelastic properties of low-fat yoghurt structured by monoglyceride gels

Three monoglyceride gels (MG gels) made up by 5 g of monopalmitin/monostearin blends in ratios of 0.10:0.87, 0.30:0.65 and 0.43:0.50, and 0.05 g of an anionic co-surfactant per 100 mL of water were prepared. Differential Scanning Calorimetry (DSC) results indicated that when cooled below the Krafft temperature (T_krafft) the three MG gels were predominantly in the α-gel phase, and were used under this condition to prepare three low-fat yoghurt variations (Y_0.1MP,0.87MS, Y_0.3MP,0.65MS, and Y_{0.43MP,0.50MS}). Scanning electron micrographs showed that Y_0.1MP,0.87MS and Y_0.3MP,0.65MS structure was characterized by aggregated fused casein micelles, which had attached to their surface MG gels, with comparatively smaller interspaced voids than those showed by the control full-fat yoghurt (Y₁₀₀). Y_0.1MP,0.87MS and Y_0.3MP,0.65MS exhibited higher viscoelastic parameters over the whole frequency experimental sweep than Y₁₀₀, Y_{0.43MP,0.50MS}, and low-fat control yoghurt (Y₅₀).     

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).     

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.     

Rheological quality and stability of yog-ice cream with added inulin

Research was conducted to examine the effect of inulin on the rheological and textural characteristics of yog-ice cream desserts in relation to their sensory attributes. Addition of inulin to yog-ice cream was shown to increase viscosity of the yogurt-ice cream mix and increase hardness of the resulting yog-ice cream. Meltdown characteristics of the yog-ice creams demonstrated a clear relationship between increased oligosaccharide levels and improved melting properties.     

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.     

Physicochemical properties of cell wall materials from apple, kiwifruit and tomato

Cell wall materials (CWMs) were isolated from the fruit of ripe apple, kiwifruit and tomato using methods of isolation which maximised the water retaining capacity and viscosity generating properties of the CWMs. Aqueous suspensions of all three CWMs were able to form a gel-like matrix at a concentration of 1%. There was a dramatic enhancement in gel firmness of kiwifruit and tomato following a high shear treatment, but no such effect was apparent with apple CWM. Confocal microscopy showed that the shear-induced increase in viscosity was accompanied by fragmentation of the CWMs of kiwifruit and tomato which increased the available surface area for particle–particle and/or particle–solvent interaction. The viscosity of kiwifruit and tomato CWM dispersions was reduced in the presence of electrolytes indicating an important role for the double electrical layer in the gelling properties of the CWMs. The viscosifying properties of apple CWM were however independent of both shear and added electrolyte. This was attributed to the fact that CWM from apple resisted breakup under high shear. The greater connective integrity of the apple cell walls compared to that of kiwifruit and tomato is discussed in relation to differences in ripening induced changes to the pectic polysaccharides of the cell walls.     

Enrichment of yogurt with carrot soluble dietary fiber prepared by three physical modified treatments: Microstructure,rheology and storage stability

Three modified soluble dietary fibers including microwave (M-SDF), ultrasonic (U-SDF) and high-pressure cooking (H-SDF) and SDF without treatment (W-SDF) were prepared, then these SDF were supplemented in yogurt. U-SDF and M-SDF showed rougher structure than others. U-SDF and W-SDF possessed higher Mw (Molecular weight), water-holding, cholesterol absorption capacities, with more reddish and yellowish colour. Moreover, addition of SDF into yogurt resulted in stabilizing of structure, increasing of viscosity, consistency index, pH, and decreasing of flow index, titratable acidity, syneresis percent. U-SDF and W-SDF supplemented yogurts exhibited greater stability compared with others. Overall, our data demonstrated that U-SDF and W-SDF would be better choices to be incorporated in yogurt for improving its quality. This study could provide scientific evidence supporting SDF as potential reinforcing ingredients in production of fiber-supplemented yogurt and offer a new insight into design of novel dairy products with functional properties.     

An assay of relative cell wall porosity in Saccharomyces cerevisiae, Kluyveromyces lactis and Schizosaccharomyces pombe

We have developed a new assay to determine relative cell wall porosity in yeasts, which is based on polycation-induced leakage of UV-absorbing compounds. Polycations with a small hydrodynamic radius as measured by gel filtration (poly-L-lysine) caused cell leakage independent of cell wall porosity whereas polycations with a large hydrodynamic radius (DEAE-dextrans) caused only limited cell leakage due to limited passage through the cell wall. This allowed the ratio between DEAE-dextran- and poly-L-lysine-induced cell leakage to be used as a measure of cell wall porosity in Saccharomyces cerevisiae, Kluyveromyces lactis and Schizosaccharomyces pombe. Using this assay, we found that the composition of the growth medium affected cell wall porosity in S. cerevisiae. In addition, we could show that cell wall porosity is limited by the number of disulphide bridges in the wall and is dependent on cell turgor. It is argued that earlier methods to estimate cell wall porosity in S. cerevisiae resulted in large underestimations.     

Yield and composition of cell wall residues isolated from various feedstuffs used for non-ruminant farm animals

The contents of cell wall residue were measured in 14 common feedstuffs used for non-ruminant farm animals by utilising a technique involving pronase and α-amylase treatments. Comparison with the contents of neutral detergent fibre (NDF) revealed that the NDF procedure underestimated cell wall contents in the dicotyledonous plant materials. The losses of cell wall material due to the neutral detergent solution were correlated (r=0.931, P<0.01) with the amount of pectic substances present in the cell wall residues of the dicotyledonous plant materials. Cell wall residues were analysed for starch, crude protein, polysaccharides, condensed tannins, sulphuric acid lignin, acetyl bromide lignin, and ash. Condensed tannins in the cell wall residues of sorghum, rapeseed meal and field bean resulted in a large protein contamination (11.3–26.6%) of these residues and to an overestimation of their lignin content. Compositions of polysaccharides are discussed from chemical and nutritonal viewpoints.     

Effect of micronised oat bran by ultrafine grinding on dietary fibre,texture and rheological characteristic of soft cheese

The purpose of this research was to study the effect of micronised oat bran on dietary fibre, textural and rheological of soft cheese. The soft cheese was processed by using the different particle size oat bran as fibre supplement, and its dietary fibre content, rheological and textural properties were determined. The results show that the micronised oat bran with 5–30 μm particle size was prepared by ultrafine grinding and passed through 60–400 mesh sieves. The soluble dietary fibre content in micronised oat bran soft cheeses was higher than that of the control (untreated oat bran soft cheeses; P < 0.05), with a maximum of 2.65 g per 100 g cheeses when oat bran was ultrafine crushed and passed through 300 mesh sieves, while the content of insoluble dietary fibre was lower than that of the control (P < 0.05). The micronised oat bran soft cheese in fermentation is a typical non-newtonian fluid. G′, G″ and apparent viscosity of soft cheeses were increased with the reduction of oat bran particle size. The chewiness and springiness of micronised soft cheeses were increased with the reduction of oat bran particle size, and were higher than that of the control (P < 0.05). The hardness and cohesiveness of micronised soft cheese were decreased with the reduction of oat bran particle size, the hardness was lower, but the cohesiveness of micronised soft cheese was higher than that of the control (P < 0.05). The 1% micronised oat bran can obtain better processing characteristics and overall acceptability for cheese products.     

The effect of postharvest calcium application on tissue calcium concentration, quality attributes, incidence of flesh browning and cell wall physicochemical aspects of peach fruits

The effects of postharvest calcium applications on cell wall properties and quality attributes of peach fruits (Prunus persica L. Batsch, cv. ‘Andross’) after harvest or cold storage up to 4 weeks were determined. The fruits were immersed in deionised water or in different calcium sources (calcium chloride, calcium lactate and calcium propionate) at two calcium concentrations (62.5 and 187.5 mM Ca). Calcium concentration profiles in fruits (peel and flesh), in cell wall and in pectin fractions were determined. The calcium content in the peel increased up to 2.7-fold, whereas flesh calcium increased up to 74%, 1 day after immersion. The increase of flesh calcium was accompanied by increase of cell wall calcium, which corresponded to a significant increase of calcium in the water-insoluble pectin fraction. However, calcium became saturated in the water-insoluble, but not water-soluble, pectin fraction with 62.5 mM Ca treatment. Treatment with 62.5 mM Ca salts was as effective as higher concentrations of calcium chloride maintaining tissue firmness during storage. Inversely, calcium lactate and calcium propionate at high concentrations (187.5 mM Ca) caused toxicity symptoms on the fruit surface, expressed as skin discoloration and superficial pitting, leading to additional chemical changes and reduced tissue firmness. Postharvest calcium applications limited the intense of chilling injury symptoms, expressed as flesh browning after 4 weeks cold storage. Peach fruits with severe flesh browning symptoms were characterized by reduced ethylene production, and reduced activities of the pectin modifying enzymes poly-galacturonase and pectin-methyl-esterase.     

Characterization of p‐coumarate accumulation,p‐coumaroyl transferase,and cell wall changes during the development of corn stems

BACKGROUND: Developmental changes occur in corn (Zea mays L.) stems from cell initiation to fully mature cell types. During cell wall maturation the lignin is acylated with p‐coumarates (pCA). This work describes characterization studies of the p‐coumaroylation process in relation to corn stem development. RESULTS: Corn plants from three locations were harvested and tissues were analyzed from all nodes and even‐numbered internodes above soil line. Changes in carbohydrates reflect a shift to lignification at the expense of structural polysaccharide synthesis. Accumulation of pCA paralleled the incorporation of lignin while ferulate (FA) remained relatively constant as a proportion of the cell wall (5–7 g kg^?1 CW). The p‐coumaroyl transferase (pCAT), which is responsible for attaching pCA to lignin monomers, displayed maximum levels of activity in the middle region of the stem (internodes 10–12, 2–3 nmol L^?1 min^?1 mg^?1). The syringyl content as a proportion of the total lignin did not change significantly with cell wall maturation although there was a trend towards increased amounts of syringyl units in the more mature cell walls. CONCLUSIONS: Incorporation of pCA into corn cell walls not only mirrored lignification but the pCAT activity as well. Levels of pCAT activity may be an indicator of rapid lignification specifically for syringyl type lignin. Copyright © 2008 Society of Chemical Industry     

Traditional and industrial oven-dry processing of olive fruits: influence on textural properties,cell wall polysaccharide composition,and enzymatic activity

The preparation of table olives according to the Italian traditional “Ferrandina” method (Fer) includes an initial blanching step of black Cassanese olives, followed by salting and oven-drying. Its industrial implementation, also called the “Sybaris” method (Syb), replaces the blanching procedure by cutting the olives followed by immersion in water. The measurement of tensile properties showed that the Fer processing increased the weakness, softness, and deformability of the skin and the flesh of olive fruits, while the flesh of the Syb fruits became stronger and stiffer. These differences are probably correlated to the degradation and/or reorganisation of cell wall polysaccharides in the fruits. The degradation of pectic and hemicellulosic polysaccharides in the Fer olives was inferred by their increased solubility in aqueous solutions. Contrarily, retention of pectic polysaccharides was observed in Syb olives. As no correlation was found between cell wall degrading enzymatic activities and cell wall polysaccharides extractability, it is probable that these modifications were driven by heat.     

Impact of magnesium and mannose in the cultivation media on the magnesium biosorption, the biomass yield and on the cell wall structure of Candida utilis yeast

Binding capacity of Mg²⁺ ions, the biomass yield and the cell wall structure of Candida utilis ATCC 9950 cultivated in the media containing magnesium and mannose were evaluated in the study. Mannose has been added to two types of culture media: not enriched and enriched with Mg²⁺ ions. The YPD medium was used as a control while the experimental media (without or with Mg²⁺ ions) have been prepared by replacing glucose in the YPD medium by 1% (YPDM) or 2% (YPM) of mannose. The highest content of magnesium (5.39 and 5.42 mg/g_d.w.) as well as the highest biomass yield (15.22 and 14.03 g_d.w./L) were observed after 24 h of cultivation in the media enriched with magnesium and supplemented with mannose. The yeast cultivated for 48 h in those media were also characterized by thicker cell walls (74.3 and 67.7 nm). Introduction of mannose to the cultivation media was the factor that has influenced biosorption of magnesium ions as the result of twofold thickening of the mannoprotein layer of the cell wall of Candida utilis ATCC 9950 yeast.