Relationships between rheological properties, texture and structure of apple (Granny Smith var.) affected by blanching and/or osmotic dehydration

The objective of this work was to evaluate and correlate rheological properties (small-scale dynamic oscillatory and creep/recovery measurements and large-scale compression force-deformation testing), texture (sensory evaluation by trained panel) and structure (optical and transmission electronic microscopy observations) of apples osmotically dehydrated to water activity (a _w) 0.97 with glucose, with or without previous blanching. All apple samples showed a solid behavior (G′?>?G″) dominating the viscoelastic response, but both dynamic moduli were reduced due to processing. The instantaneous elastic compliance (J ₀) and the retarded compliances (J ₁ and J ₂) increased for treated tissues and the steady-state viscosity (η _N) was approximately 15% to 29% of the value of fresh apple. In general, compression parameters decreased for all treated tissues. Changes in structural features were mainly evidenced in heated samples. Partial least squares regression analysis regression models revealed that texture could be well predicted by rheological properties (compression and creep parameters). Juiciness, crispness and sensory hardness were negatively correlated to J ₀, J ₁ and J ₂, and η _N was negatively correlated to sensory fracturability. Some mechanical parameters (fracturability, hardness 2, area 2, modulus of deformability and cohesiveness) were positively related to sensory fracturability, crispness and sensory hardness; and juiciness was negatively correlated to hardness. Compression and creep parameters showed ability to evidence structure differences (rupture of membranes, swelling of cells and degradation of cell walls) and to explain texture of treated apples.     

Viscoelasticity, texture and ultrastructure of cut apple as affected by sequential anti-browning and ultraviolet-C light treatments

The aim of this work was to analyze the effect of UV-C radiation (fluence: 11.2 kJ/m²), with or without an anti-browning pretreatment containing 1% (w/v) ascorbic acid plus 0.1% (w/v) calcium chloride, on the linear viscoelastic properties (oscillatory shear and creep/recovery), instrumental texture (TPA), sensory texture and ultrastructure (ESEM, TEM) of cut apple. Changes in structural features and viscoelastic parameters were mainly evidenced after refrigerated storage. All samples showed a viscoelastic solid behavior with the storage modulus (G′) dominating the viscoelastic response. Overall, both dynamic moduli decreased, and instantaneous compliance (J₀), decay compliances (J₁ and J₂) and fluidity significantly increased after treatments and storage at 5 °C, while retardation times were in general constant. Fracture properties proved to be the most highly correlated with sensory texture. The test panel only significantly differentiated stored untreated apple from the other samples regarding fracturability and juiciness. Mechanical spectra and creep parameters showed ability to evidence ultrastructural differences (rupture of membranes, swelling of cells, alteration of cell walls) in the surface of cut apples subjected to the different treatments.     

Sensory,physical, chemical and microbiological changes in aquacultured meagre (Argyrosomus regius) fillets during ice storage

Commercial-sized meagre fillets were stored on ice at 4 °C for 18 days, in order to evaluate the loss of quality and freshness that occurs over this period of time. Physicochemical (pH, thiobarbituric acid (TBA), total volatile basic nitrogen (TVBN), trimethylamine (TMA), water activity, water-holding capacity, colour, texture and fatty acid profile), sensory and microbiological analyses were carried out at 0, 4, 7, 11, 14 and 18 days of storage. As part of the sensory analysis, attributes associated with fillet appearance, odour and texture were examined. Variations in pH, TBA, TVBN and TMA were observed throughout the storage period, although only TBA displayed a significant correlation with time (r = 0.96). L^∗ and b^∗ values increased, and the chroma and hue values decreased, reflecting the colour changes experienced by the fillets over time. With regards to the texture profile, hardness was significantly correlated with time (−0.68). All the sensory analysis attributes exhibited significant variations and correlations close to 1.00 with storage time, which is a reflection of the fillets’ loss of freshness. The correlation coefficients between aerobic mesophilic and psychrophilic bacteria, enterobacteria and coliform counts on the one hand and storage time on the other were also very high (0.99–1.00). A regression analysis using the acceptability limit set by the ICMSF standard (1986) for total aerobic mesophilic counts (7 log cfu/g) yielded a shelf-life for meagre fillets of 9 days. The TBA, sensory and microbiological analyses displayed very strong correlations with storage time, and they may be considered suitable indicators for evaluating meagre fillet spoilage during refrigerated storage.     

Dynamic rheological and thermal study of the heat-induced gelation of tomato-seed proteins

The structural aspects of proteins prepared from tomato seeds were studied by dynamic rheology, modulated differential scanning calorimetry (MDSC) and Fourier transform infrared (FTIR) spectroscopy. The critical gel point was determined from storage (G’) and loss (G”) moduli as functions of time and frequency. The findings indicate that tomato-seed proteins can create gels during heat treatment at 90–95 °C. Mechanical spectra of the tomato-seed protein gels were classified as weak gels based on the frequency sweep, complex viscosity (η∗) and tan δ results. Moreover, G’ and G” changes were found to be dependent on both concentration and frequency. MDSC showed two peaks, with gelation temperatures (T_d) of 70 and 87 °C, which we attribute to starch and globular protein fractions, respectively. The FTIR spectra show an increase in the absorbance of amides I and II after increasing the solid content from 1 to 10% w/w, indicating mostly β-sheet and α-helical conformations.     

Some properties of corn starches II: Physicochemical,gelatinization, retrogradation,pasting and gel textural properties

The physicochemical, thermal, pasting and gel textural properties of corn starches from different corn varieties (African Tall, Ageti, Early Composite, Girja, Navjot, Parbhat, Partap, Pb Sathi and Vijay) were studied. Amylose content and swelling power of corn starches ranged from 16.9% to 21.3% and 13.7 to 20.7 g/g, respectively. The enthalpy of gelatinization (ΔH_gel) and percentage of retrogradation (%R) for various corn starches ranged from 11.2 to 12.7 J/g and 37.6% to 56.5%, respectively. The range for peak viscosity among different varieties was between 804 and 1252 cP. The hardness of starch gels ranged from 21.5 to 32.3 g. African Tall and Early Composite showed higher swelling power, peak, trough, breakdown, final and setback viscosity, and lower ΔH_gel and range of gelatinization. Pearson correlations among various properties of starches were observed. Gelatinization onset temperature (T_o) was negatively correlated to peak-, breakdown-, final- and setback viscosity (r = −0.809, −0.774, −0.721 and −0.686, respectively, p < 0.01) and positively correlated to pasting temperature (r = 0.657, p < 0.01). ΔH_gel was observed to be positively correlated with T_o, peak gelatinization temperature and (T_p) and gelatinization conclusion temperature T_c (r = 0.900, 0.902 and 0.828, respectively, p < 0.01) whereas, it was negatively correlated to peak- and breakdown- (r = −0.743 and −0.733, respectively, p < 0.01), final- and setback viscosity (r = −0.623 and −0.611, respectively, p < 0.05). Amylose was positively correlated to hardness (r = 0.511, p < 0.05) and gumminess (r = 0.792, p < 0.01) of starch gels.     

Effect of varying the gas headspace to meat ratio on the quality and shelf-life of beef steaks packaged in high oxygen modified atmosphere packs

Beef steaks (M. longissimus dorsi) were stored in modified atmosphere packs (MAP) (80% O₂:20% CO₂) with gas headspace to meat ratios of 2:1, 1:1 and 0.5:1 for 14 days at 4 °C. The pH, surface colour, texture and microbiology of beef steaks were unaffected (P > 0.05) by varying the gas headspace to meat ratio. APLSR (ANOVA-partial least squares regression) and jack-knife uncertainty testing indicated that lipid oxidation (TBARS) was significantly positively correlated with days 10 (P < 0.05) and 14 (P < 0.001) of storage. Chemical and sensory detection of lipid oxidation in beef steaks were in agreement on day 14 of storage. The sensory quality and acceptability of beef steaks were similar in gas headspace to meat ratios of 2:1 or 1:1 and unacceptable in 0.5:1. Results indicate that pack size and gas volume can be reduced without negatively affecting fresh beef quality and shelf-life.     

Comparison of meat quality between eland (Taurotragus oryx) and cattle (Bos taurus) raised under similar conditions

Physical, chemical and sensory characteristics of meat were compared between non-domestic eland (Taurotragus oryx) bulls (n = 6) and domestic Fleckvieh (Bos taurus) bulls (n = 6) which were finished under controlled conditions of feeding and management. Musculus longissimus lumborum from eland were darker and less yellow in colour, with a higher pH₂₄ and lower contents of intramuscular fat and total collagen, compared to cattle. Contents (mg/100 g muscle tissue) and proportions (g/100 g of FA determined) of SFA and MUFA were higher (P < 0.01) in cattle. Although the proportion of total PUFA were higher (P < 0.001) in eland, contents of PUFA were similar between species. Meat from cattle was consistently scored higher (P < 0.05) for sensory texture characteristics, juiciness, flavour, and overall acceptance. We concluded that bulls of eland provided low-fat meat with a beneficial fatty acid composition from a human nutrition perspective, but with lower sensory scores, compared to bull beef.     

Effect of microbial transglutaminase on the rheological and textural characteristics of black soybean packed tofu coagulating with Agar

The objective of this study was to investigate the effects of microbial transglutaminase (MTGase) on the rheological and textural characteristics of black soybean packed tofu containing agar as the coagulant. Results showed that the addition of MTGase increased the gelation temperature of soymilk, and produced a firmer and more elastic packed tofu with low cooking loss. Dynamic rheological and textural parameters of the tofu were significantly affected by enzyme concentration, incubation temperature and time. Both G′ and η∗ were positively correlated to the hardness, gumminess and adhesiveness of packed tofu, thus the rheological parameters (G′ and η∗) were good indicators of the texture of the packed tofu. Results suggested that good quality packed tofu could be produced by mixing 90 g black soymilk solid and 2 g agar powder in 1 L of water and incubating with 10 g MTGase for 30 min at 55 °C.     

Color improvement by titanium dioxide and its effect on gelation and texture of proteins recovered from whole fish using isoelectric solubilization/precipitation

Whiteness is a critical attribute for restructured fish products such as surimi seafood. However, the whiteness of gels made from proteins recovered from fish processing by-products or whole fish using isoelectric solubilization/precipitation is poor. The by-products and whole fish contain bones, scales, skin, etc. that affect gel color. Therefore, whiteness needs to be improved if marketable products are to be developed from recovered proteins. The objectives of this study were to determine effects of titanium dioxide (TiO₂) on: (1) color; (2) texture; and (3) viscoelasticity (G′) of gels made from isolated carp proteins and Alaska pollock surimi. Carp proteins were recovered with isoelectric solubilization/precipitation. TiO₂ was added to carp proteins at 0-0.5 g/100 g. TiO₂ was not added to surimi. Due to much higher (P < 0.05) yellowness (b^∗) and lower (P < 0.05) lightness (L^∗), the whiteness of carp gels without TiO₂ was lower (P < 0.05) than surimi gels. TiO₂ at ≥ 0.2 g/100 g resulted in better (P < 0.05) whiteness of carp gels than surimi gels without chalky and artificially white appearance. TiO₂ did not affect texture or viscoelasticity. This research demonstrates that whiteness of restructured fish products based on proteins recovered from whole fish via isoelectric solubilization/precipitation can be similar to the whiteness of surimi seafood.     

Effects of tea polyphenol coating combined with ozone water washing on the storage quality of black sea bream (Sparus macrocephalus)

The present research evaluated the effects of tea polyphenol (TP) combined with ozone water (O₃) on the quality of black sea bream (Sparus macrocephalus) over a period of 15 days storage at 4 °C. A solution of TP (0.2%, w/v) was used to coat the fish after washing with ozone water (1 mg/L). Fish physicochemical (pH, K value, peroxide value, thiobarbituric acid, total volatile basic nitrogen, trimethylamine, texture, and colour), sensory, and bacteriological characteristics were all analysed. TP + O₃ treatment effectively reduced nucleotide breakdown, lipid oxidation, protein decomposition, and microbial growth, and maintained better characteristics of texture, colour, and sensory compared with the control. The efficiency of TP + O₃ treatment was also better than that of TP treatment or O₃ treatment alone. Therefore, tea polyphenol coating combined with ozone water prewashing may be a promising method of maintaining the storage quality of black sea bream and of extending fish post-mortem shelf-life during 4 °C storage.     

Influence of size distribution of proteins,thiol and disulfide content in whole wheat flour on rheological and chapati texture of Indian wheat varieties

The influence of protein composition, as measured by size-exclusion high performance liquid chromatography (SE-HPLC), on rheological properties and chapati texture was investigated in the whole wheat flours of eight Indian wheat cultivars grown at a single location. Proteins were extracted using two-step procedure: extraction with buffer containing 0.5% SDS (SDS buffer), followed by sonication. The results showed that SDS buffer extracted 72–90% of the total flour protein in different varieties and 7–11% protein was extracted from the remaining residues by sonication. The proteins extracted were fractionated by SE-HPLC into large polymeric proteins (>130 kDa), small polymeric proteins (80–130 kDa) and monomeric proteins (10–80 kDa). Total polymeric protein content in the flour protein showed a significant positive correlation with dough hardness (r = 0.71, p < 0.05) and positive correlation with chapati texture (r = 0.58, p < 0.05). Of the SDS extractable polymeric proteins, large polymeric protein in flour protein had significant positive correlation to dough hardness (r = 0.89, p < 0.05) and chapati cutting force, which reflects the chapati texture (r = 0.70, p < 0.05). Protein disulfide content showed positive correlation to dough hardness (r = 0.66, p < 0.05) and texture of chapati (r = 0.58, p < 0.05) while protein thiol content showed significant negative correlation to chapati texture (r = −0.77, p < 0.05). Thus, the results indicate that high proportion of SDS extractable large polymeric protein in flour protein increases the toughness of chapati texture while flours having high thiol content decrease the toughness of chapati.     

Microstructure of highly concentrated tomato suspensions on homogenisation and subsequent shearing

The changes in the microstructure of tomato paste suspensions have been investigated during homogenisation and subsequent shearing in suspensions with similar composition, at three tomato paste concentrations 10, 30 and 40%. The suspensions were characterised by the particle size distribution (PSD), volume fraction (ø), and dynamic rheological properties (G′, G″). All suspensions exhibit a solid-like behaviour with G′ > G″. Micrographs indicate that the process of homogenisation creates a smooth network of finer particles, that is easily disrupted by prolonged shearing, giving rise to the formation of densely packed flocs that become clearly oriented in the direction of the shearing. At high concentrations, these changes in the microstructure on homogenisation and subsequent shearing were better reflected by differences in ø than in G′. The rheological behaviour of the suspensions exhibits a power-law dependence on ø, over a large range of PSD and for 0.05 < ø < 0.55. Finally, an experimental equation, including ø and the size of the coarse particles in the surface-weighted PSD, is found to accurately estimate G′ (R² > 99.3%, p < 0.001).     

Sensory,microbiological and chemical assessment of the freshness of red mullet (Mullus barbatus) and goldband goatfish (Upeneus moluccensis) during storage in ice

The shelf life of red mullet and goldband goatfish during ice storage were studied in terms of sensory, microbiological and chemical changes. The sensory acceptability limit was 8 days for goldband goatfish (Upeneus moluccensis) and 11 days for red mullet (Mullus barbatus) stored in ice. The TVC level was correlated with sensory assessment. The TVC exceeded 7 log cfu g⁻¹ after 8 days for goldband goatfish, and 11 days for red mullet. At the end of storage period, pH, TVB-N, TBA, FFA and PV for red mullet were 7.84, 47.19 mg/100 g, 0.69 mg MA kg⁻¹, 1.17% oleic acid and 1.58 meq O₂/kg and for goldband goatfish they were 7.53, 43.97 mg/100 g, 0.74 mg MA kg⁻¹, 1.62% oleic acid and 1.68 meq O₂/kg, respectively. In red mullet, agmatine, serotonin, histamine and dopamine became the dominant amines, reaching 7.30, 5.97, 2.52 and 2.31 mg/100 g, respectively. Also the dominant amines for goldband goatfish were 4.37, 3.88, 3.38 and 2.00 mg/100 g for histamine, agmatine, dopamine and putrescine, respectively.     

Rheological,thermal and structural behavior of poly(ε-caprolactone) and nanoclay blended films

Poly(ε-caprolactone)/nanoclay composite (PCLNC) films were prepared by solvent casting method using a wide range of layered silicate (2.5–10%) and were characterized by different techniques. Nanofiller dispersions in PCL matrix were studied by wide-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM), and results indicated the formation of some intercalated nanostructure of PCLNC. Rheological and thermal properties of PCLNC were measured by parallel-plate oscillatory rheometry and differential scanning calorimetry (DSC), respectively. Rheological study indicated that the predominating liquid-like properties (viscous modulus, G″ > elastic modulus, G′) of neat PCL gradually transformed to solid-like (G′ > G″) behavior after incorporation of clay in the temperature range of 90–120 °C. A plot of G′ vs. G″ provide information on intercalation and microstructure of nanocomposite. Applicability of time–temperature superposition (TTS) principle and van Gurp–Palmen plot (phase angle vs. absolute complex modulus) on rheological data of clay incorporated PCL were employed and found that the results failed to follow the rules. Incorporation of the nanoclay into PCL matrix increased the crystallization temperature (T_c) and melting temperature (T_m) of neat PCL from 28.7 to 32.3 °C and 56.3 to 59.2 °C, respectively due to the nucleating effect, but the glass transition temperature (T_g) (≈−65 °C) was remained unaffected. The decrease in crystallinity with increase in clay concentration was confirmed by both XRD and DSC data.     

Effect of temperature on dynamic and steady-state shear rheological properties of siriguela (Spondias purpurea L.) pulp

The present work has evaluated the dynamic and steady-state shear rheological properties of siriguela (Spondias purpurea) pulp as function of temperature (0-80 °C), as well as the applicability of the Cox-Merz rule. The product flow behavior could be well described by the Herschel-Bulkley’s model (R² > 0.98), whose parameters were modeled as function of temperature (R² > 0.91). The product has shown a weak gel behavior, with storage modulus higher than loss modulus in the evaluated frequency range. The storage and loss modules could be well described by a power function of the oscillatory frequency (R² > 0.93), whose parameters were modeled as function of temperature (R² > 0.97). Moreover, a power modified Cox-Merz rule could describe the rheological properties of S. purpurea pulp (R² > 0.96). The obtained data are potentially useful for future studies on food properties and process design.     

Influence of yeast and frozen storage on rheological, structural and microbial quality of frozen sweet dough

The aim of the present study was to investigate the effect of yeast content and frozen storage (9 weeks at −40 °C) on the structural and rheological parameters, and fermentative activity of frozen sweet dough. Two types of dough were studied (to estimate dough shelf life): simple yeasted dough (SY) and double yeasted dough (DY). Fermentative activity (yeast viability, gassing power, and dough volume), rheological and textural parameters were assessed for frozen sweet doughs.These effects were explored by different and complementary methods: Fourier transform infrared (FTIR), dynamic rheology, texture profile analysis (TPA) and differential scanning calorimetry (DSC).The data showed that the longer the frozen storage time at −40 °C, the higher the decreased of frozen sweet dough quality. The rheological attributes such as hardness, ΔS, springiness, tan δ and yeast activity declined significantly during frozen storage. This modification led to lower specific volume of frozen sweet dough during proofing.The observed changes of the frozen sweet doughs rheological properties after thawing may be attributed to the damage on the gluten cross-linking, mainly produced by the ice crystallization during frozen storage. The storage effect was particularly concentrated in the first 27 days of storage.     

Effects of Kudoa spores,endogenous protease activity and frozen storage on cooked texture of minced Pacific hake (Merluccius productus)

The effects of Kudoa infection of Pacific hake (Merluccius productus) on endogenous protease activity and on cooked mince texture were investigated. Texture was significantly (p < 0.05) negatively correlated with spore counts as well as protease activity. Soft texture (maximum force <150 g) was observed in fish with 10⁴–10⁶Kudoa thyrsites spores g⁻¹ mince, compared to 10⁵–10⁸K. paniformis spores g⁻¹ mince, suggesting that especially for fish having lower infection levels, K. thyrsites may have a greater impact than K. paniformis on Pacific hake quality. Pre-incubation for 15 min at 52 °C prior to cooking resulted in softer texture in some samples due to endogenous proteolytic action. This pre-incubation effect was not consistently observed in fish held 6 months or longer at −25 °C or after freeze-thaw cycling, which may be explained by an opposing toughening effect attributed to protein denaturation and aggregation during prolonged or abusive frozen storage.     

Decreased gelling and emulsifying properties of myofibrillar protein from repeatedly frozen-thawed porcine longissimus muscle are due to protein denaturation and susceptibility to aggregation

The effects of freeze–thaw cycles (FT, 0, 1, 3 and 5 times) on protein functional properties of porcine longissimus muscle were investigated. FT increased gapping between muscle fibres and tore muscle fiber bundles. Myofibrillar protein (MP) isolated from FT muscle showed an increased hydrophobicity (P < 0.05), reduced thermal transition temperatures (T_max) and enthalpy of denaturation (ΔH) (P < 0.05), and enhanced susceptibility to thermal aggregation. These structural changes resulted in major losses in protein functionalities, e.g., 41–43% reductions (P < 0.05) in MP emulsifying capacity and emulsion stability after five FT cycles. The ability of MP to form a viscoelastic gel network, as analyzed by small-strain oscillatory rheological testing, also attenuated with FT cycles. The FT process lowered (P < 0.05) water-holding capacity (WHC), whiteness, and texture (hardness, springiness, chewiness and cohesiveness) of MP gels. Overall, repeated FT had a detrimental effect on the general functionality of porcine MP, and protein denaturation and aggregation were implicated in the functionality losses.     

Evaluation of monosodium glutamate,disodium inosinate and guanylate umami taste by an electronic tongue

An electronic tongue (e-Tongue) was used to evaluate umami taste and compare different flavor enhancers (concentration and manufacture). Monosodium glutamate and three kinds of disodium inosinate and guanylate (I + G) were analyzed. The obtained data were analyzed by principal component analysis (PCA). The first principal component represented the intensity of umami taste. Based on Euclidean distance between ‘I + G’ samples and MSG (0.5%) on the PCA score plot, the umami intensity of all samples was ranked. The ‘I + G’ samples produced by three manufactures were successfully discriminated on the second principal component with a high discrimination index (82.26). Besides, the drift phenomenon of sensor was discussed and finishing sensor analyses in a continuous time could help avoid the drift. This study showed that e-Tongue was useful in analyzing the umami taste and might be a complementary tool in evaluation of flavor enhancer.     

Effects of potassium lactate and high pressure on transglutaminase restructured dry-cured hams with reduced salt content

Ten raw hams (from 5 carcasses) were boned and salted either with salt reduction (15 g/kg NaCl) or salt reduction with addition of potassium lactate (15 g/kg NaCl and 39.74 g/kg of a 60% K-lactate solution). Subsequently, the ham pieces were assembled together with transglutaminase, vacuum packed into water-permeable plastic bags and kept at 3 °C and 85% RH until reaching above 30% weight losses. The effects of K-lactate addition and the high-pressure (HP) treatment at 600 MPa on the physicochemical, instrumental colour and texture (Tensile test) and sensory characteristics of the biceps femoris (BF) muscle were evaluated. The addition of K-lactate did not have a negative effect on colour, flavour or texture of restructured dry-cured hams. The HP treatment increased significantly the pH, L^∗, a^∗ and b^∗ values and the breaking stress, and decreased the water-holding capacity and elasticity (apparent Young’s modulus) of BF muscle. The HP treatment also affected significantly the flavour (increasing saltiness, umami and sweetness) and the sensory texture attributes (increasing muscle binding, hardness, gumminess and fibrousness and decreasing adhesiveness and pastiness), as well as slice appearance (increasing brightness and iridescence and decreasing colour homogeneity).