Textural,histological and biochemical changes in cucumber (Cucumis sativus L) due to immersion and variations in turgor pressure

Textural, histological and biochemical characteristics of cucumber (Cucumis sativus L) under different tissue turgor pressures were studied after equilibration of mesocarp tissue cylinders in various polyethylene glycol 400 (PEG) solutions. Tissue swelling was observed for all hypotonic solutions. Cell membrane vitality was detected in all cucumber tissues where significant values of initial firmness (f_i) and residual relaxation force (F_R) were found. Good turgor status was also associated with higher values of these parameters, observing higher values of the textural parameters for higher turgor. Cell wall integrity was observed through Calcofluor fluorescence assay in tissue equilibrated in hypotonic, isotonic and hypertonic solutions, although a lower fluorescence intensity was observed in tissue equilibrated with 0 mol m^?3 PEG solution, probably owing to some cell bursting. Calcium bridges between pectic polymers were proven to be responsible for cell–cell adhesion and tissue integrity of cucumber mesocarp tissue. Compression curves obtained for raw tissue showed a stage of fracture, and its loss after immersion might be attributed to cell–cell adhesion weakness due to immersion in calcium‐free PEG solutions. Peroxidase and polygalacturonase increased after cucumber equilibration in the solutions, probably expressing tissue injury. Cucumber textural behaviour was very much affected by immersion in calcium‐free solutions, determining the loss of fracture stage and a great influence of turgor pressure on the textural response of soaked tissue. © 2003 Society of Chemical Industry     

Proteolysis and texture changes of a Spanish soft cheese (‘Torta del Casar’) manufactured with raw ewe milk and vegetable rennet during ripening

Proteolysis and textural changes of the Spanish ewe raw milk soft cheese of the Protected Designation of Origin Torta del Casar were studied in four different stages of ripening, with 1, 30, 60 and 90 days. In general, proteolysis in Torta del Casar cheese was weak at 1 and 30 days and it was more intense between the 30–60 days of ripening. Soluble nitrogen non‐protein nitrogen, polypeptide N and free amino acids values significantly increased during cheese ripening. Protein and casein nitrogen decreased significantly after 60 days of ripening resulting in the increase of the other nitrogen fractions measured. Caseins changes determined by capillary zone electrophoresis showed that proteolysis of β‐casein occurred faster than αs1‐casein but the latter suffered higher proteolytic degradation at the end of ripening (day 90). This pattern of degradation of caseins is reversed in other cheeses made with animal rennet. Texture analysis showed that firmness and consistency decreased along ripening while adhesiveness increased. Highly significant correlations were found between textural parameters, residual caseins levels and nitrogen fractions during maturation, which shows the importance of proteolytic changes for an optimal texture formation.     

The effect of supplementing goats milk with whey protein concentrate on textural properties of set-type yoghurt

Yoghurt was manufactured from goat's milk and supplemented with 30 g L^?1 of whey protein concentrate (WPC). The textural properties of the yoghurt were evaluated during the shelf‐life of the product and the textural characteristics of yoghurt made from cow's milk were used as a reference. The instrumental analyses used were the puncture test, stress relaxation test and texture profile analysis. The addition of WPC to goat's milk enhanced the textural characteristics of yoghurt. These advantageous attributes included increased firmness, hardness and adhesiveness. These attributes were quantitatively similar (P > 0.05) to those obtained from yoghurt made from cow's milk. In addition, the textural properties were maintained constant throughout the shelf‐life of the product.     

Physical properties and microstructural changes during soaking of individual corn and quinoa breakfast flakes

The importance of breakfast cereal flakes (BCF) in Western diets deserves an understanding of changes in their mechanical properties and microstructure that occur during soaking in a liquid (that is, milk or water) prior to consumption. The maximum rupture force (RF) of 2 types of breakfast flaked products (BFP)--corn flakes (CF) and quinoa flakes (QF)--were measured directly while immersed in milk with 2% of fat content (milk 2%) or distilled water for different periods of time between 5 and 300 s. Under similar soaking conditions, QF presented higher RF values than CF. Soaked flakes were freeze-dried and their cross section and surface examined by scanning electron microscopy. Three consecutive periods (fast, gradual, and slow reduction of RF) were associated with changes in the microstructure of flakes. These changes were more pronounced in distilled water than in milk 2%, probably because the fat and other solids in milk become deposited on the flakes' surface hindering liquid infiltration. Structural and textural modifications were primarily ascribable to the plasticizing effect of water that softened the carbohydrate/protein matrix, inducing partial collapse of the porous structure and eventually disintegration of the whole piece through deep cracks.     

Physicochemical,textural and sensory properties of white soft cheese made from buffalo and cow milk mixtures

The physicochemical, textural and sensory properties of white soft cheeses made from three different buffalo and cow milk mixtures (100:0, 70:30 and 30:70) during 3‐month storage were studied. The increase in buffalo milk concentration resulted in increasing total cheese yield, dry matter (DM) and fat retention and fat in DM content. However, it caused reductions in moisture content, salt intake, hardness, chewiness, elasticity, sensory hardness and sensory cohesiveness of the samples. The percentage of water‐soluble nitrogen to total nitrogen increased during storage resulting in decreased fracturability, hardness (textural and sensory), cohesiveness (textural and sensory), springiness, chewiness and elasticity. The panellists evaluated the white soft cheese made with buffalo milk as the most acceptable.     

Effect of milk fat and total solids concentration on the kinetics of moisture uptake by ready-to-eat breakfast cereal

Summary When immersed in milk, breakfast cereal easily take up moisture, lose their brittle texture and become soggy. Earlier comparative analysis of the moisture sorption by breakfast cereal immersed in water and milk indicated that milk solids might play an important role on the sorption kinetics. In this work, the moisture uptake by ready-to-eat corn breakfast cereal immersed in milk solutions, reconstituted from whole and skimmed milk powder, was measured under isothermal conditions at 5, 30 and 55 °C. Dilutions between 0.25 and 1.5 were tested, with the factor of dilution 1 corresponding to the standard recommended by the milk powder manufacturer. The Weibull probabilistic model adequately fitted the experimental data by appropriate choice of its variable parameters. The dependence of the model parameters on temperature and total solids concentration was assessed for both skimmed and whole milk. Fat was found to play a major role on the process mechanism, which was attributed to the deposition of a fat layer at the solid matrix surface, hindering water and solids uptake. Yet, for short times, moisture uptake proceeded at a similar rate both in skimmed and whole milk.     

Effect of pretreatments and freezing rate on the firmness of potato tissue after a freeze–thaw cycle

The texture of potato tissue after a freeze–thaw process using different freezing rates and different pretreatments was analysed, in order to select the best strategy for optimum preservation of the textural characteristics of pre‐frozen potato. Ten blanching conditions were tested and a two‐step blanching process with calcium chloride (0.07 g mL^?1) proved the most effective in protecting the tissue after a freeze–thaw process (maximum load force around 10–55% of the raw tissue, depending on potato batch, for air‐blast freezing and 20–60% for immersion freezing). Vacuum impregnation at 100 and 400 mbar, even when followed by different pre‐drying treatments to remove excess water, was very detrimental to resistance to a freeze–thaw process (maximum load force below 10% of the raw tissue for air‐blast freezing and below 20% for immersion freezing). Microstructure analysis confirmed better tissue integrity retention with ethyleneglycol immersion freezing instead of air‐freezing. Differences were found between batches with a 6‐month difference in storage time, indicating that the fresher batch was more suitable for freezing.     

The advantage of using extrusion processing for increasing dietary fibre level in gluten-free products

Gluten-free products generally are not enriched/fortified and frequently are made from refined flour and/or starch. Such products have been found to provide lower amounts of total dietary fibre than their enriched/fortified gluten-containing counterparts.The objective of this study was to increase the level of total dietary fibre in gluten-free products by using extrusion technology and by incorporating a number of different fruits and vegetables, such as apple, beetroot, carrot, cranberry and gluten-free Teff flour cereal. The materials were added at the level of 30% into the gluten-free balanced formulation (control) made from rice flour, potato starch, corn starch, milk powder and soya flour. Different process conditions, such as water feed rate 12%, solid feed rate 15–25 kg/h, screw speed 200–350 rpm, barrel temperatures: 80 °C at feed entry and 80–150 °C at die exit were used. Pressure, material temperature and torque were monitored during extrusion runs. The relationships and interactions between raw ingredients, extrusion processing parameters and resulting extrudate nutritional and textural properties were investigated.The results of this study clearly show that extrusion technology has the potential to increase the levels of total dietary fibre in gluten-free products made from vegetables, fruits and gluten-free cereals.     

Instrumental and sensory characterisation of industrially processed applesauces

BACKGROUND: In the context of fruit consumption promotion, applesauce is an interesting ready‐to‐eat product. However, little information has been gathered on its sensory properties. Yet, the processing involved easily triggers rheological and structural changes, possibly modifying these sensory properties. The aim of this study was thus to provide a global approach for applesauce characterisation by studying instrumental and sensory properties, with knowledge of the processing conditions applied. Four applesauce samples processed under controlled parameters were therefore compared with seven purchased applesauces. RESULTS: The four studied samples were characterised by their high creaminess and low graininess. These products were homogeneous and presented a small average particle size (332–354 µm). Their flow properties were best described with the Hershel–Bulkey model. The products were shear‐thinning with low yield stress. Interestingly, significant differences in textural and flow properties were also found among these four manufactured samples. CONCLUSION: Sensory characterisation revealed aromatic and textural diversity even though applesauce is considered as a common product. Differences found among the samples of interest might be related to postharvest maturity of fruits and consequent pectic degradation from cell walls. Finally, the candied odour and flavour that distinguished these products could be related to the extensive heating applied during processing. Copyright © 2009 Society of Chemical Industry     

The Use of High-pressure Processing in the Production of Queso Fresco Cheese

ABSTRACT: Three varieties of Queso Fresco cheese were produced: a control cheese made from raw milk, cheese made from pressure-treated milk, and cheese treated with high pressure after production. Sensory attributes, texture profile analysis, and composition were compared following 1 and 8 d of storage time. High-pressure treatment of cheese (400 MPa, 20 min, 20 °C) did not impart major textural and compositional changes; however, cheese made from pressure-treated milk contained more moisture and was less firm, less crumbly, and more sticky than the control and decreased in firmness during storage. High-pressure processing treatment of cheese can provide an alternative method for producing Queso Fresco-style cheese with acceptable textural attributes.     

Application of proteomics to the areas of milk production,processing and quality control – A review

Milk contains a complex mixture of proteins that undergo several qualitative and quantitative changes during processing and storage. Elucidation of these changes is important to optimise milk processing and storage parameters. Proteomics has become widely used in the field of research on milk proteins due to improvements in the tools and diversified ways in which the methodologies of protein analysis have been developed. This review describes the use of proteomics in studies on milk proteins in relation to species–species differences, post‐translational modification, effect of lactation, mastitis, changes in heated milk and during cheese ripening, and the detection of milk adulteration.     

USE of PHYTOGLYCOGEN EXTRACTED FROM CORN to INCREASE the BOWL-LIFE of BREAKFAST CEREAL

Phytoglycogen was extracted from frozen corn using water and ethanol. the phytoglycogen powder was dissolved in distilled water, sprayed onto ready‐to‐eat breakfast cereal, and dried. the coated cereal was soaked in milk for three minutes and compared to control samples. the coated cereal showed a significant improvement in texture over control samples after soaking in milk. Peak force for control samples dropped by almost 40% after soaking, while the peak force for samples coated with phytoglycogen dropped by less than 20%. Coated samples were also found to absorb less milk than did uncoated samples. Therefore, use of a corn phytoglycogen coating could potentially be used to increase the bowl‐life of some breakfast cereals.     

Serum Protein Aggregates in the High-Heated Milk and Their Gelation Properties in Rennet-Induced Milk Gel

The influence of different heat treatments on the protein aggregates and changes in gelation properties of rennet-induced milk gels were investigated. In the heated milk, a visible difference in milk serum proteins was found resulting from the formation of protein aggregates. Meanwhile, the size of protein aggregates increased from 25 to 170 nm with increasing the intensity of heat treatment. Furthermore, the differences in textural variables of rennet gels were found among the heat treatments using the principal component analysis. The water holding capacity and cheese curd yield of rennet gels obtained from the heated milk were significantly greater than those of raw milk (p < 0.05). It was also found heat treatments above 80°C could endow rennet-induced milk gels with novel textural properties.     

Effects of various whey proteins on the physicochemical and textural properties of set type nonfat yoghurt

In this study, the changes during storage in the physicochemical, textural and sensory properties of nonfat yoghurts fortified with whey proteins, namely whey protein concentrates (WPC), whey protein isolates and whey protein hydrolysates, were investigated. Enrichment of nonfat yoghurt with the whey protein additives (1% w/v) had a noticeable effect on pH, titratable acidity, syneresis, water‐holding capacity, protein contents and colour values on the 14th day of storage (P < 0.01). The addition of whey proteins to the yoghurt milk led to increases in the hardness, cohesiveness and elasticity values, resulting in improved textural properties. The addition of WPC improved the texture of set‐type nonfat yoghurt with greater sizes in the gel network as well as lower syneresis and higher water holding capacity. This study suggests that the addition of whey protein additives used for fortification of yoghurt gave the best textural and sensory properties that were maintained constant during the shelf life.     

水发条件对海参(Acaudina molpadioidea)质构特性及微观结构的影响研究

利用TPA质构分析法和Masson三色染色法研究水发条件对东海海参微观结构和质构特性的影响,比较不同水发条件下体系组织结构和质构特性的差异。研究表明,不同水发条件所得的海参质构参数差异显著,水煮温度对海参的硬度、黏附性、弹性、凝聚性和回复性有显著影响,保温温度则对海参的硬度、黏附性、咀嚼性、凝聚性和回复性有显著影响,而且海参硬度和黏附性两个质构参数还受水煮温度和保温温度间交互作用的极显著影响。与之相对应,在不同的水发条件下,海参的组织结构存在明显的差异。此外,水发海参的各项质构参数间,黏附性与硬度、咀嚼性、弹性、凝聚性之间均呈现负相关,硬度与咀嚼性之间以及凝聚性与回复性之间分别呈现很好的正相关性。     

Fat-free fermented concentrated milk products as milk protein-based microgel dispersions: Particle characteristics as key drivers of textural properties

The popularity of fat-free fermented concentrated milk products, such as fresh cheeses and high-protein yogurt, has increased over the recent years, attributed to greater availability and improvements in taste and texture. These improvements have been achieved through modifications and new developments in processing technologies, for example, higher heat treatment intensities and incorporating different membrane filtration technologies. Though numerous processing parameters are discussed in the literature, as well as reasons behind the developments, detailed examinations of how process modifications affect the final textural attributes of these products are lacking. To draw links between processing parameters and texture, we review the literature on fat-free fermented concentrated milk products from the perspective of fermented milk protein-based microgel particles as the basic structural unit. At each main processing step, relationships between process parameters, micro- and macrostructural and sensory (textural) properties are discussed.An overview of particle characteristics that drive structural changes at each processing step is developed in relation to textural characteristics. Using this approach of assessing relationships between structural characteristics of concentrated dispersions of fat-free fermented milk protein-based microgel particles and processing parameters provides a basic context for the selection of optimal parameters to achieve a desired texture.     

NATURAL CHEDDAR CHEESE TEXTURE VARIATION AS A RESULT OF MILK SEASONALITY

A set of standard testing conditions using the TA-XT2 Texture Analyser were established to monitor cheddar cheese texture variation. Cheddar cheese was produced in the standard commercial practice and sampled at monthly intervals throughout the milk production season (August - June), and monitored for textural and compositional changes occurring during ripening. The composition, based on fat and protein levels, of the cheese was relatively constant during the period, which was expected as the commercial process aims for that outcome. A reduction in the force and degree of compression at fracture with time, indicative of a reduction in cheese firmness and an increase in cheese crumbliness, was recorded as the milk production season progressed. The degree of proteolysis and changes in milk fat in late season milk are primarily responsible for the changes recorded in cheese texture. The differences observed between cheeses produced at different times during the season indicate that the current fat and protein standardization employed by cheese-makers is not adequate to provide cheddar cheese with consistent textural characteristics year round.     

Effects of enzymatic modification of milk proteins on flavour and textural qualities of set yoghurt

Milk proteins were enzymatically modified, using neutrase and trypsin immobilised on CM‐Sephadex C‐50, to the extent of 3, 4 and 5% degrees of hydrolysis. The neutrase‐treated milk and the trypsin‐treated milk were used separately to prepare set yoghurt. The set yoghurt prepared from neutrase‐treated milk showed an improvement in body, texture and flavour, a faster rate of acid development and a reduction in setting time compared with the control. However, the set yoghurt prepared from trypsin‐treated milk showed either a small or no improvement in textural and sensory properties. © 2000 Society of Chemical Industry     

Chemical and biochemical changes of pumpkin (Cucumis moschata,Duch) tissue in relation to osmotic stress

Chemical and biochemical changes of pumpkin (Cucumis moschata, Duch) tissue in relation to osmotic stress were studied and related to tissue textural behavior. Turgor pressure of raw tissue was adjusted by immersion in hypotonic (0.0 mol m^?3), isotonic (250 mol m^?3) and plasmolyzing (1050 mol m^?3) buffered (20 mol m^?3 potassium phosphate, pH 6.8) solutions of poly(ethylene glycol) 400 (PEG). It was found that a substantial proportion of polysaccharides located in the cell wall (CW)–middle lamellae (ML) of studied tissue was water extractable. This proportion decreased when CW‐stretch increased. Ionically bound peroxidase (POX) presented an increased activity in swollen and isotonic tissue, probably associated to oxidative cross‐linking of extensin located in the CW of this tissue, as a response to stress promoted by cut, immersion and turgor pressure change. The resistance of CW to elongation when equilibrated in hypotonic medium, might be ascribed to reinforcement of the CW by the oxidative cross‐linking of extensin, with simultaneous formation of pectin‐in‐extensin entanglements. Plasmolyzed tissue where CW is relaxed, showed pectin–rhamnogalacturonan degradation. The water‐soluble fraction (WSF) was shown to be a negative function of CW stretching and infinite force of relaxation. Copyright © 2005 Society of Chemical Industry