Compression behaviour of jute–polypropylene blended needle-punched nonwoven under wet conditions

The subject of this paper is the compression behaviour of jute–polypropylene blended needle-punched nonwoven under wet conditions. It is essential to know the compression behaviour of the needle-punched fabrics under wet conditions because of its various applications like geotextiles and carpets. Needle-punched fabric samples were prepared based on the three-factor three-level Box–Behnken design of experiment to study the individual as well as interaction effects of process parameters of fabric weight, needling density and blend proportion of jute and polypropylene fibre blend on compression properties under wet conditions. Initial thickness, percentage compression, percentage thickness loss and percentage compression resilience are the compression properties considered. The compression properties under wet conditions were compared with their respective dry conditions. This study reveals that most of the wet samples show a slightly higher value of initial thickness, percentage compression and thickness loss than dry samples, irrespective of processing variables, though for compression resilience value it is vice versa. The effect of blend does not have much influence on percentage compression in wet conditions. There is optimum level of needling density (around 250 punches/cm²) and blend proportions (around 75% polypropylene) for minimum percentage thickness loss of wet fabric under higher fabric weight. The compression resilience increases with increase in the content of polypropylene in the blend of polypropylene and jute. Optimum compression properties (highest percentage compression and compression resilience with minimum percentage thickness loss) can be achieved at fabric weight of 450 g/m² with the combination of around 250 punches/cm² needling density and around 75% polypropylene content.     

Influence of shearing on the physical characteristics and rheological behaviour of an aqueous whey protein isolate–κappa-carrageenan mixture

The incompatibility of whey protein isolate (WPI) and κappa-carrageenan (κ-car) in aqueous mixtures has been extensively studied under quiescent conditions; however, the effect of shear on segregative phase separation is still not fully understood. The present work reports for the first time quantitatively the effect of shearing on the segregative phase separation behaviour of these two polymers. Demixing was observed at pH 7.0 and 22 °C, determining the phase diagram and rheological properties of the mixtures. Phase diagrams were derived after heating and cooling mixes at a constant shear rate (28 s⁻¹). The phase behaviour was compared to that of the same mixtures under quiescent conditions. The shearing process affects segregative phase separation, causing a shift in the position of the binodal towards lower concentrations of WPI. The bottom layer contained a higher ratio of WPI while the upper layer was enriched in κ-car. The addition of κ-car to WPI solutions led to a much stiffer heat-induced gel than that prepared with WPI heated in isolation. The height of the plateau of the final elastic modulus G′_∞(t) depends on the position of the system on the phase diagram. Using a selected tie line, the viscosity of different systems measured at 80 °C was more influenced by the amount of WPI, than by the κ-car concentration. Shear treatment of segregative phase separating systems offer a way to modulate the functional properties of the ingredients and the texture of the final product.     

Protein–polysaccharide interactions: Phase behaviour of pectin–soy flour mixture

Biopolymers mixed systems have been widely studied in the past two decades, resulting in advances in knowledge of the key parameters involved in macromolecules–macromolecules interactions. Sound understanding and control of these parameters should enable food scientists to design coating or film with desired functional properties. In this study the phase behaviour of high methoxyl pectin and soy flour at pH 4.6 was investigated. The aim was to investigate the effect of different concentrations of pectin (P) and soy flour (SF) solution and different P/SF ratios on mixture phase behaviour. Pectin suspensions at 16 mg ml⁻¹ and 8 mg ml⁻¹ concentrations and soy flour suspensions at 13 mg ml⁻¹ and 6.5 mg ml⁻¹ concentrations were prepared and mixed together in different ratios (10/90, 25/75, 50/50, 75/25, 90/10). Turbidity and rheological measurements were performed to obtain information on pectin–soy flour interaction in electrostatic compatibility conditions. The experimental data show that soy flour solution is a non-stable system in which complexes may be formed during aging. It becomes insoluble and settles to the bottom of the suspension. By blending charged soy flour, at high concentration, with anionic pectin an associative interaction between biopolymers occurs which stabilizes the protein in solution. The best pectin and soy flour suspension for forming film with a continuous network was at concentrations of 16 mg ml⁻¹ and 13 mg ml⁻¹.     

Dynamic viscoelastic behaviour of high pressure treated gluten–soy mixtures

Hydrated gluten and soy mixtures with concentrations of gluten–soy=20:80, 40:60, 60:40 and 80:20% were subjected to high pressure treatment at 700 MPa for 50 min at 20 and 60 °C. The treated samples were subsequently analysed for viscoelastic properties and electrophoretic patterns. A quadratic canonical polynomial model was used for the mixture design. Following high pressure treatment, the samples formed solid-like gel structures. In general, in the gels having high concentrations of gluten, both storage and loss moduli tended to increase with increasing pressure and temperature whereas, in the gels having high concentrations of soy, both moduli appeared to increase only slightly with increasing severity of the treatments. These results meant that the combined effect of temperature and pressure was much greater on the large complex gluten molecule than on the smaller soy globulins.     

Glass-transition behaviour of plasticized starch biopolymer system – A modified Gordon–Taylor approach

Two plasticizers namely, glycerol and xylitol, based on their similar molecular size (˜6.3 Å) but different molecular weights (Glycerol-92; Xylitol-152) were selected for studying the glass-transition behaviour (rubber like behaviour) in multi-plasticized starch biopolymer with about 70% amylopectin structure. In the calorimetry measurements, glass-transition temperatures (onset temperature for bulk viscous flow) of plasticized samples were higher than non-plasticized samples at low water activities, thus showing typical antiplasticization behaviour. However, when plasticizer concentration was increased up to 15% and 20% wt, all plasticized samples showed significant reduction in glass-transition temperature. We used a modified Gordon–Taylor model to understand the competitive plasticization of glycerol and xylitol in presence of water, and suggest that competitive plasticization exists and occurs at a threshold amount of matrix free water content, due to strong three-way interactions: starch–plasticizer, plasticizer–plasticizer/water and starch–water. This competitive interaction is significant in determining the onset temperature for viscous flow behaviour; at higher matrix water content, the Gordon–Taylor constant was relatively unaffected by the plasticizer amount, and water was the dominant plasticizer. A new interaction parameter that separates the starch–plasticizer interaction in a starch–plasticizer–water system is also discussed.     

Stress–strain behavior of polyamide 6 staple fibers of punch-needled press felts under simulated wet-pressing conditions

This study evaluates the specific stress (tenacity) and strain (elongation) of polyamide 6 staple fibers, which were virgin, punch-needled on the press felt, and worn on the press felt under simulated wet-pressing conditions. The staple fibers were distinguished by molecular weights. The fiber deformation and defects were microscopically characterized after the felt preparation and aging. We discovered that the tensile breaking force and elongation of the polyamide 6 staple fibers decreased markedly during the felt preparation and aging. The mechanical reduction of staple fibers reflected their tenacity, work, and modulus values. Surprisingly, the linear density of staple fibers remained unchanged – although fibers strongly deformed and lost their mechanical properties after the felt aging. The results indicate that an increase in molecular weight improves the mechanical durability of staple fibers, the preparation of the press felt (punch-needling) decreases the tenacity and elongation of staple fibers, and humidity provokes their degradation.     

Hydrolysis of β-lactoglobulin by trypsin under acidic pH and analysis of the hydrolysates with MALDI–TOF–MS/MS

Trypsin (EC 3.4.21.4) hydrolysis of food proteins are done at the optimum pH (7.8) and temperature (37 °C). Little information is available on the effect of sub-optimal conditions on hydrolysis. Bovine β-lactoglobulin (β-Lg) was hydrolysed by trypsin under acidic pH (pH 4–7) between 20 and 60 °C and the substrate concentration from 2.5% to 15% (w/v) and compared with hydrolysis at pH 7.8 and 37 °C. Aliquots were taken at different times (t = 0 up to 10 min). Samples were analysed using matrix-assisted laser desorption/ionisation time-of-flight tandem mass spectrometry (MALDI–TOF–MS/MS) with α-cyano-4-hydroxycinnamic acid (HCCA) and 2,5-dihydroxyacetophenone (DHAP) matrices. Hydrolysis patterns of β-Lg were generally similar at pH 7.8, 7, 6 and 5 while at pH 4 fewer peptides were detected except a unique fragment f(136–141). The different cleavage sites of β-Lg showed low resistance to trypsin at optimum conditions and pH 7 while being random and simultaneous. At lower pH, some cleavage sites showed increased resistance, while hydrolysis was relatively slow and ordered. Initial attack by trypsin occurred at Arg⁴⁰–Val⁴¹, Lys¹⁴¹–Ala¹⁴² and Arg¹⁴⁸–Leu¹⁴⁹ resistance was at Lys⁶⁰–Trp⁶¹, Arg¹²⁴–Thr¹²⁵ and Lys¹³⁵–Phe¹³⁶. Five domains were identified based on β-Lg resistance to trypsin in the order f(1–40) < f(41–75) < f(76–91) > f(92–138) > f(139–162). Results suggest that hydrolysis away from trypsin optimum offer better hydrolysis process control and different peptides. This strategy may be used to protect target bioactive or precursor peptides, or avoid the production of unwanted peptides.     

Effects of fatty acid chain length on properties of potato starch–fatty acid complexes under partially gelatinization

A series of starch–fatty acid samples were prepared using potato starch and four fatty acids differing in their chain length, including lauric (C12), myristic (C14), palmitic (C16), and stearic (C18) acids. The results indicated that the fatty-acid chain length played a significant role in altering the properties of potato starch–fatty acid complexes. The complexing index of potato starch–fatty acid complexes decreased from 0.38 to 0.18 with increasing carbon-chain length. V-type crystalline polymorphs were formed between starch and four fatty acids, with shorter chain fatty acids preserving more crystalline structure. X-ray diffraction studies revealed that the degree of crystallinity exhibited by the starch samples was dependent on the fatty-acid chain length. In the Fourier transformed infrared spectrum of the samples, the new spikes at 2917, 2850, 1018, and 720 cm^?1 were assumed to be related to the presence of fatty long chains. The formation of amylose–fatty acid complex inhibited granule swelling of potato starch, w\ith longer chain fatty acids showing greater inhibition. Scanning electron microscopy microscopic examination indicated that amylose–fatty acid interactions taken place during starch gelatinization retarded the destruction of the granules.     

Mechanical spectra and calorimetric evaluation of gelatin–xanthan gum systems with high levels of co-solutes in the glassy state

Mechanical properties of gelatin–xanthan gum (XG) mixtures with high levels of co-solutes were examined by dynamic mechanical analysis (DMA). The mechanical spectra of the samples were modeled according to the Williams–Landel–Ferry (WLF) equation/free-volume theory, which requires an entropic lightly cross-linked network. For the α dispersion, E′ and E′′ superposed with the horizontal shift factor a_T, which was temperature-dependent according to the WLF equation; no other secondary dispersion mechanism was detected. The addition of XG to gelatin networks with high levels of co-solutes changed the glass transition temperature (T_g) and kinetics of glass transition and glassy states. In the glassy state, the WLF equation was unable to follow progress in the mechanical properties, which were better described by the Andrade equation. The calorimetric measurements of the gelatin–XG systems were made using a modulated temperature differential scanning calorimetry (MTDSC) to improve the determination of T_g. The samples were exposed to two cooling and heating cycles to provide a controlled recent thermal history in the temperature range of 40 °C to −70 °C. The T_g values of the samples were determined from the second heating cycle in the reversing heat signal. The calorimetric T_g values increased with increasing glucose syrup:sucrose ratio due to increased crosslinking, whereas mechanical T_g decreased with increased XG content due to network formation.     

Mechanical properties and water vapour permeability of hydrolysed collagen–cocoa butter edible films plasticised with sucrose

The aim of this study was to develop and characterise edible films produced from hydrolysed collagen and cocoa butter and plasticised with sucrose. The mechanical properties, water vapour permeability, opacity and morphology of the films were characterised. The film composition that yielded the best results was used to produce a coating for application in chocolate panned products. A water-based coating with desirable barrier properties that could replace shellac is important for the environment as well as health, and also because chocolate products have great appeal among children. The films obtained were easily manageable and flexible. Sucrose reduced tensile strength (TS), while hydrolysed collagen at concentrations above 15% increased it. Cocoa butter resulted in less-resistant films. The elongation at break values (EAB%) were higher for films containing higher sucrose concentrations. The water vapour permeability (WVP) ranged from 0.32 to 0.63 g mm m⁻² h⁻¹ kPa⁻¹. For the same concentration of cocoa butter, the WVP was directly affected by the thickness of the film, i.e., the greater the thickness, the higher the WVP. Cocoa butter increased film opacity, while sucrose decreased it, particularly at concentrations above 17.5%. High concentrations of hydrolysed collagen produced films with more homogeneous surfaces. The brightness of the product with the coating developed in this study was attractive; however the brightness of the product with shellac was considered more intense. The properties of these films indicate that they are promising systems for coating chocolate panned products.     

Monitoring of physical–chemical and microbiological changes in fresh pork meat under cold storage by means of a potentiometric electronic tongue

This work describes the correlation found along 10 days between potentiometric measurements obtained by using an electronic tongue and the variation in certain physicochemical, microbial and biochemical parameters measured on a whole piece of pork loin stored under refrigeration. The electronic tongue consists of a set of six electrodes made of Au, Ag, Cu, Pb, Zn and C, and a reference electrode. Through the use of various multivariate analysis techniques, such as: PCA and two types of artificial neural networks (i.e. multilayer perceptron (MLP) and fuzzy ARTMAP) it was found that it is possible to determine the time elapsed in relation to the degradation of the loin by using simple potentiometric measurements. Additionally, in the same pork sample used to measure redox potentials with the electronic tongue, the following parameters were also determined; pH, microbial count, concentrations of inosine 5′-monophosphate (IMP), inosine (Ino) and hypoxanthine (Hx). Through the use of PLS analysis, it was found a rather good correlation between pH and the potentiometric data. Also a remarkable correlation was observed between the measures carried out with the electronic tongue and the so-called K-index that simultaneously measures the variation in the adenosine triphosphate (ATP) degradation products. These results suggest that this simple, or a similar electronic tongue, could be useful for the undemanding qualitative or semi-quantitative evaluation of freshness in meat samples in a wide range of situations.     

Mechanical and physical properties of thermally modified Scots pine wood in high pressure reactor under saturated steam at 120, 150 and 180 °C

Scots pine sapwood and heartwood were thermally modified under saturated steam at 120, 150 and 180 °C in a high pressure reactor. Mechanical properties such as dynamic and static modulus of elasticity (MOE), static modulus of rupture (MOR), Brinell hardness and impact toughness were evaluated. The static MOE for sapwood did not decrease substantially (approximately 1 %), not even with a high mass loss of more than 12 %, when the wood was modified at 180 °C. Static MOE of the wood increased approximately 14 %, when modified at 150 °C. Surprisingly, MOR increased by 15 %, when modified at 150 °C with mass loss of 2.3 %. Whereas impact strength and hardness decreased somewhat, when modified at 180 °C. Moreover, high anti-swelling efficiency values were obtained (60 % for sapwood and 52 % for heartwood) when modified at 180 °C.     

The wettability and bonding performance of densified VTC beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) bonded with phenol–formaldehyde adhesive and liquefied wood

The influence of viscoelastic thermal compression (VTC) on surface wettability and bonding performance of wood was evaluated. Low quality beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) were densified with the VTC process to different degrees of densification. Control and densified strips were bonded with phenol–formaldehyde (PF) adhesive and liquefied wood (LW). Shear strength of bonded assemblies was determined after 1 week of conditioning at 20 °C and relative humidity of 65 %. Wettability was determined on the basis of the contact angle of water, PF adhesive, and LW using the Wilhelmy method. Results showed that densification of beech and spruce wood did not significantly affect the shear strength of specimens bonded with PF adhesive. In beech assemblies bonded with LW shear strength decreased significantly with increased density, whereas in bonded spruce specimens decrease of shear strength was not significant. It was found that degree of densification and bonding process used in the study were not appropriately chosen for spruce wood specimens, since major deformations after the bonding process occurred. Wettability changed significantly after densification. Contact angle of water and LW increased after densification, whereas contact angle of PF showed inverse trend and decreased after VTC process. Furthermore, the degree of densification had a minor effect on the wettability.