Swallowing profiles of food polysaccharide gels in relation to bolus rheology

Swallowing profiles of food polysaccharide gels were investigated in relation to bolus rheology. Polysaccharide gel from either gellan gum or a mixture of gellan gum and psyllium seed gum was used as a model food. Acoustic analysis and sensory evaluation were carried out to investigate the swallowing profiles using the same human subjects. Model bolus was prepared through instrumental mastication using a mechanical simulator to mimic the action of the human jaw in the presence or absence of artificial saliva and was subjected to dynamic viscoelasticity measurements to investigate the rheological properties. Bolus from the binary gel was shorter in time required to transfer through the pharyngeal phase due to mass flow and was scored higher in sensory perceived cohesiveness (bolus forming) than that from gellan gum gel. Model bolus from the binary gel showed a rheologically weak gel (or structured fluid) behavior and was higher in structural homogeneity than that from gellan gum gel. Also, dynamic viscoelasticity parameters of the binary gel were less dependent on the addition level of saliva. Results indicate that the viscoelasticity balance is a key for texture design of dysphagia foods in relation to the saliva miscibility.     

Effect of high pressure homogenization (HPH) on the rheological properties of a fruit juice serum model

High pressure homogenization (HPH) is a non-thermal technology that has been widely studied as a partial or total substitute for thermal food processing. The present work evaluated the effect of HPH on the rheological properties of a fruit juice serum model, designed to be similar to tomato juice serum. Product viscosity decreased due to the increase in homogenization pressure, and could be modelled well using two functions (power-sigmoidal and exponential; R² > 0.98). The serum model processed at 200 MPa showed a viscosity decrease of 20% when compared to the original. Since fruit juice rheology is defined by the interactions occurring between the dispersed phase (suspended particles) and the solution (serum), the expected fruit juice behaviour was then discussed.     

红烧肉咀嚼过程中唾液分泌对食团特性和吞咽动作的影响

本实验选用12名感官品评员,分别咀嚼红烧肉的脂肪层和瘦肉层,收集不同咀嚼阶段食团并记录感官品评员的咀嚼次数,测定食团水分含量,跟踪分析品评员在咀嚼过程中的咀嚼参数、唾液分泌量以及不同部位红烧肉食团水分含量的动态变化规律。结果表明:在咀嚼过程中,品评员的咀嚼次数显著升高(p<0.05),咀嚼频率相对稳定(p>0.05);品评员的唾液分泌量显著升高(p<0.05),唾液流速显著下降(p<0.05)并趋于稳定;食团湿基和干基水分含量均显著上升(p<0.05)。在同一咀嚼阶段,品评员咀嚼脂肪层的唾液分泌量和唾液流速均显著低于瘦肉层(p<0.05);脂肪层食团的水分含量显著低于瘦肉层食团(p<0.05)。对于红烧肉同一部位,每名感官品评员的个性咀嚼行为和唾液分泌导致食团在吞咽点时的水分含量差异显著(p<0.05),但相对集中,其中脂肪层的食团水分含量大约在25%~30%之间,瘦肉层大约在60%~65%之间。由此可见:食团水分含量是触发吞咽的重要标志之一。      

Effect of high pressure homogenization (HPH) on the rheological properties of tomato juice: Time-dependent and steady-state shear

High pressure homogenization (HPH) is a non-thermal technology that has been widely studied as a partial or total substitute for the thermal processing of food. Although microbial inactivation has been widely studied, there are only a few works in the literature reporting the physicochemical changes caused in fruit products due to HPH, especially those regarding the rheological properties. The present work evaluated the effect of HPH (up to 150 MPa) on the time-dependent and steady-state shear rheological properties of tomato juice. HPH reduced the mean particle diameter and particle size distribution (PSD), and increased its consistency and thixotropy. The rheological results were in accordance with the PSD observed. The rheological properties of the juice were evaluated by the Herschel–Bulkley and Falguera–Ibarz models (steady-state shear) and Figoni–Shoemaker and Weltman models (time-dependent). The parameters of these equations were modelled as a function of the homogenization pressure. The models obtained described the experimental values well, and contributed to future studies on product and process development.     

卡拉胶的流变性能

本文重点对卡拉胶的流变学性能进行说明。包括卡拉胶溶液浓度、温度、恒温时间、转速、搅拌时间、pH值、离子等对卡拉胶溶液粘度、凝胶强度等的影响;卡拉胶的流变特性;卡拉胶与其他高分子物质的相互作用。     

The role of characteristic times in rheological description of structure forming food additives

The work is focused on the interpretation of flow curves obtained at two different temperatures for water solutions of xanthan and guar gum, and pastes of oxidized corn starch and starch phosphate. Based on exponential state equations for shear thinning and shear thickening systems characteristic times distributions were estimated using Tikhonov regularization method. Values of time constants and their intensities were strongly associated with the composition of the examined mixtures. Food thickeners such as GG or XG form solutions of very high viscosity. Characteristic times determined from De Kee equation take large values (0.1–1 s). This could be connected with a predominance of viscous behavior during shear. Starch pastes with GG or XG show very complex rheological behavior resulting from synergistic effects. This is reflected in the form of distributions of time constants, which have two peaks. One of them is specific to the non-starch hydrocolloid and corresponds to the characteristic time of approximately 1 s. Global maximum is located at the time of 0.001 s and is associated with the presence of starch and its gel structure. The differences in rheological characteristic times for various structure forming agents reflect their technological functions.     

Adaption of a vane tool for the viscosity determination of flavoured yoghurt

In order to determine the viscosity of flavoured yoghurt with incorporated fruit pieces, a four-bladed vane tool fitted to a stress-controlled rheometer was calibrated against a conventional cup-and-bob system in steady shear measurements using several Newtonian and non-Newtonian fluids. The angular velocities obtained with both systems were compared at particular shear stress values, resulting in a conversion factor valid for angular velocities between 10^–4 and 10⁰ rad s^–1. After checking the validity of the vane tool on carboxymethylcellulose solutions with embedded perspex beads, viscosity measurements were carried out on commercial stirred yoghurt without and with spherical fruit pieces. As flow curves were successfully fitted to the Cross model, the vane tool can be considered to be a suitable method for measuring the flow properties of food systems with large solid particles.     

Both a higher number of sips and a longer oral transit time reduce ad libitum intake

BackgroundA higher eating rate leads to a higher food intake, possibly through shorter orosensory exposure to food. The transit time in the oral cavity and the number of bites or sips per gram (inversely related to bite or sip size) are main contributors that affect eating rate. The separate role of these two aspects on satiation and on orosensory exposure needs further clarification.ObjectiveThe objective of the first study was to investigate contributions of the number of sips per gram (sips/g) and oral transit time per gram (s/g) on ad libitum intake. The objective of the second study was to investigate both aspects on the total magnitude of orosensory exposure per gram food.MethodsIn study 1, 56 healthy male subjects consumed soup where the number of sips and oral transit time differed by a factor three respectively: 6.7 vs. 20 sips/100 g, and 20 vs. 60 s/100 g (2 × 2 cross-over design). Eating rate of 60 g/min was kept constant. In study 2, the effects of number of sips and oral transit time (equal as in study 1) on the total magnitude of orosensory exposure per gram soup were measured by time intensity functions by 22 different healthy subjects.ResultsHigher number of sips and longer oral transit time reduced ad libitum intake by respectively ∼22% (F(1, 157) = 55.9, P < 0.001) and ∼8% (F(1, 157) = 7.4, P = 0.007). Higher number of sips led to faster increase in fullness per gram food (F(1, 157) = 24.1, P < 0.001) (study 1). Higher number of sips and longer oral transit time both increased the orosensory exposure per gram food (F(1, 63) = 23.8, P < 0.001) and (F(1, 63) = 19.0, P < 0.001), respectively (study 2).ConclusionHigher number of sips and longer oral transit time reduced food intake, possibly through the increased the orosensory exposure per gram food. Designing foods that will be consumed with small sips or bites and long oral transit time may be effective in reducing energy intake.     

Sweetness and texture perception in mixed pectin gels with 30% sugar and a designed rheology

Pure low-methoxyl (LM) pectin and mixtures of LM and high-methoxyl (HM) pectin in different ratios were used to produce gels with control over the rheological parameter storage modulus (G′). The gels either had similar pectin concentrations and different G′ values, or different pectin concentrations and similar G′ values. All gels were prepared with 30 g/100 g sugar, in the presence of 0.1 g/100 g CaCl₂, at pH 3.5; these are conditions that favour gel formation of both LM and HM pectin.The gels were compared for their sensory characteristics; specifically sweetness, sourness, thickness, and glueyness. Sweetness was found to increase with increasing storage modulus (G′) in pectin gels of similar pectin concentration, but different G′ values. Gels with higher proportions of LM pectin were perceived as sweeter than those with low LM pectin ratios. These gels also had increasing loss modulus (G″), and increasing differences between G′ and G″, which indicates that diffusion has a bearing on the perception of sweetness in pectin gels. Thickness and glueyness were mostly determined by total pectin concentration. Thickness also increased with increasing LM pectin concentration while glueyness increased with increasing HM pectin concentration.     

Role of the bolus degree of structure on the protein digestibility during in vitro digestion of a pea protein-fortified sponge cake chewed by elderly

This study investigated the digestibility of proteins in a pea protein-fortified sponge cake, as well as the impact of the degree of structure of the bolus produced by elderly subjects on the digestibility of proteins by combining ex vivo and in vitro approaches via the standardized protocol INFOGEST. The sponge cakes were consumed by a group of 20 elderly subjects with contrasting physiology, their boli were recovered just before swallowing, and their apparent viscosity was measured to delineate the bolus degree of structure. According to this criterion, two pools were formed with boli from subjects selected at the extremes: low viscosity and high viscosity, with apparent viscosity values (at 120 s⁻¹) of 124 ± 18 and 208 ± 19 Pa s, respectively. The sponge cakes and the two pools underwent in vitro digestion. Protein hydrolysis kinetics was followed by measuring the released primary amino groups (NH₂) and by sodium-dodecyl-sulfate polyacrylamide gel electrophoresis at different time points. For all samples, the representative bands of pea proteins disappear gradually during digestion, accompanied by the appearance of bands indicating the presence of proteins with M_W < 15 kDa. In addition, the NH₂ concentrations increase over time and do not differ between sponge cake and pea protein isolate. Moreover, the degree of structure of the food bolus has no significant effect on the concentration of NH₂ released. These results showed that pea proteins in a fortified sponge cake are bioaccessible under standardized conditions and that the degree of structure of the bolus did not influence protein digestibility for these foods.     

Prediction of Adulteration in Honey Using Rheological Parameters

Honey is a sweet substance that can be adulterated easily with inexpensive sweeteners by making syrup. Water being the second major constituent of honey, makes its flow behavior one of the important parameter for quality determination. In the present study, the rheological characteristics of honey samples adulterated with different concentrations of jaggery syrup were studied using rotational rheometer with parallel plate geometry. The viscosity of honey and adulterated honey samples was determined by varying temperature and percentage of jaggery concentration. All the adulterated honey samples behaved as non-Newtonian fluid. The viscosity increased linearly with increase in concentration of adulteration and varied from 2.48–4.80 Pa s as adulteration increased from 5 to 30%. Oscillatory tests were performed to find the possible effect of storage time on different honey samples. It was found that adulteration decreased the shelf life of honey, thus rheology can be considered one of the important parameters to determine adulteration of honey.     

Solid–liquid transitions in the rheology of a structured yeast extract paste, Marmite™

The rheology of Marmite™, a popular yeast extract spread, was studied using a range of techniques. Steady-state data indicated a structured, thixotropic material at ambient temperature; the extent of breakdown and restructuring exhibited a dependence on both stress and strain. At higher temperatures the extent of thixotropy decreased and behaviour approached Newtonian. Non-steady-state data indicated a period of shear-thickening at shear rates below those at which shear-thinning occurs. Creep tests indicated a transition between solid and liquid regimes at a critical stress that is a strong function of the solids content of the sample. A ‘true’ yield stress was not found although this may be related to the limits of the region which could be accessed experimentally.     

Effect of oral calcium bolus supplementation on early-lactation health and milk yield in commercial dairy herds

The objective of this study was to evaluate the effect of supplementation with oral Ca boluses after calving on early-lactation health and milk yield. Cows in their second lactation or greater (n = 927) from 2 large dairies in Wisconsin were enrolled during the summer of 2010. Both herds were fed supplemental anions during the prefresh period and less than 1% of fresh cows were treated for clinical milk fever. Cows were scored before calving for lameness and body condition, and then randomly assigned to either a control group or an oral Ca bolus-supplemented group. Control cows received no oral Ca boluses around calving. Cows in the oral Ca bolus group received 2 oral Ca boluses (Bovikalc, Boehringer Ingelheim, St. Joseph, MO), one bolus 0 to 2 h after calving and the second 8 to 35 h after calving. The oral Ca bolus administration schedule allowed fresh cows to be restrained in headlocks only once daily. Whole-blood samples were collected immediately before the second oral Ca bolus was given and were analyzed for ionized Ca (Ca²⁺) concentration. Early-lactation health events were recorded and summed for each cow. Only 6 cases (0.6% of calvings) of clinical milk fever occurred during the trial, and only 14% of cows tested were hypocalcemic (Ca²⁺ less than 1.0 mmol/L) at 8 to 35 h after calving. Mean Ca²⁺ concentrations were not different between the control and oral Ca bolus-supplemented groups. Blood samples from the cows given oral Ca boluses were collected an average of 20.6 h after administration of the first bolus. Subpopulations of cows with significant responses to oral Ca bolus supplementation were identified based on significant interactions between oral Ca bolus supplementation and covariates in mixed multiple regression models. Lame cows supplemented with oral Ca boluses averaged 0.34 fewer health events in the first 30 d in milk compared with lame cows that were not supplemented with oral Ca boluses. Cows with a higher previous lactation mature-equivalent milk production (greater than 105% of herd rank) and supplemented with oral Ca boluses produced 2.9 kg more milk at their first test after calving compared with cows with higher previous lactation milk yields that were not supplemented. Results of this study indicate that lame cows and higher producing cows responded favorably to supplementation with oral Ca boluses. Supplementing targeted subpopulations of cows with oral Ca boluses was beneficial even for dairies with a very low incidence of hypocalcemia.     

Influence of gliadins on rheology of methylcellulose in 70% (v/v) aqueous ethanol

Rheological properties of methylcellulose in 70% (v/v) aqueous ethanol with and without 100 g L⁻¹ gliadins were studied as a function of methylcellulose concentration C from 0 g L⁻¹ to 20 g L⁻¹. The overlapping concentration of methylcellulose is 7.5 g L⁻¹ in the absence of gliadins while methylcellulose is in the semidilute region at C ≤ 20 g L⁻¹ in the presence of gliadins. The presence of gliadins weakens the shear thinning under strain rate sweep. However, dynamic stress sweep reveals that gliadins may enhance the stress thinning and the solutions at C > 7.5 g L⁻¹ exhibit two Newtonian plateaus which are not observed in the absence of gliadins. The results suggest that the mutual interaction between methylcellulose and gliadin leads to the appearance of two Newtonian plateaus. The methylcellulose solutions in the absence of gliadins do not gel upon heating. On the other hand, gliadins in the solution facilitate the hydrophobic association of methylcellulose molecules upon heating, which leads to the thermal gelation of the solution at C = 20 g L⁻¹.     

Dynamic testing rheology and fluorescence spectroscopy investigations of surface to centre differences in ripened soft cheeses

The viscoelastic properties and the matrix structures of three different retailed soft cheeses (M1, M2 and M3), for which the manufacturing process was varied, were studied from the surface to the centre of the cheese using dynamic rheology and front-face fluorescence spectroscopy. The storage modulus (G′) and the loss modulus (G″) values of the samples increased from the surface to the inner part of the cheeses, while strain and tan δ decreased. Protein tryptophan (excitation: 290 nm; emission: 305–400 nm) and vitamin A (emission: 410 nm; excitation: 250–350 nm) spectra were recorded at 20°C in samples cut from the surface to the centre. For each cheese, the data sets containing fluorescence spectra and rheology data were evaluated using multidimensional statistical methods. In addition, the three cheeses were well discriminated by their spectra by applying factorial discriminant analysis. From the tryptophan fluorescence data sets, 94% and 87.7% good classifications were observed for calibration and validation groups, respectively. A better classification (100% and 96% for principal and test samples) was obtained from the vitamin A spectra. Canonical correlation analysis was performed on the rheology and tryptophan fluorescence spectral data sets, and on the rheology and vitamin A fluorescence spectra data sets. The two groups of variables were found to be highly correlated since the squared canonical coefficients for canonical variates 1, 2, 3, 4 were higher than 0.98. These high correlations indicate that cheese rheology is a reflection of its structure at the molecular level.     

Clinical role of lipid transfer proteins in food allergy

Lipid transfer proteins are widespread plant food allergens, highly resistant to food processing and to the gastrointestinal environment, which have recently been described as true food allergens in the Mediterranean area, where they have been associated with severe allergic reactions to foods in patients without pollen allergy. In this review we analyze their molecular structure, biological function, and clinical relevance in food allergy.     

Measuring eating capability,liking and difficulty perception of older adults: A textural consideration

Malnutrition in older adults is partly attributable to decreasing muscle strength leading to inadequate intakes. It is therefore important to investigate ways of identifying eating capability both through objective measures of strength and subjective measures of perceived difficulty and liking. In addition, food texture design might affect the oral processing and the difficulty perceived. Therefore the present study sets out to examine the relationship between various quantitative measures of eating capability (EC) and perceived difficulty of processing foods and gels varying in hardness in older adults. Tests were conducted on 30 participants (mean age 79 ± 9.4 years) using non-invasive techniques (hand gripping force, tongue pressure, biting force, and hand dexterity) in conjunction with frame-by-frame video recording analysis of chewing and swallowing of food stimuli and ratings of eating difficulty. The EC scores were computed to grade the population into three different groups. Stimuli were classified into two categories: food products and flavourless hydrocolloid gels with different inhomogeneity (textures). The EC parameters did not correspond to oral residence time, or the difficulty perceived. Bite force differed by EC group, and was significantly different by dental status [F(3,4.26) = 3.842, p = 0.022], and influenced both liking and number of chews. The food hardness (r = 0.915, p = 0.01) was significantly correlated with the number of chews. Gel heterogeneity influenced food oral processing behaviour. Oral residence time was significantly correlated with number of chews, liking and difficulty perceived. In summary, dental status and bite force of older adults are determining EC parameters to design optimized food-texture.     

Oral tolerance induction does not resolve gastrointestinal inflammation in a mouse model of food allergy

Scope : Oral immunotherapy (OIT) involving continuous oral administration of allergenic foods has gained attention as a therapy for food allergies. To study the influence of oral administration of allergenic foods on gastrointestinal symptoms including inflammation, we established a mouse model of food‐induced intestinal allergy. Methods and results : BALB/c mice were fed an egg white (EW) diet containing ovalbumin (OVA, a major EW allergen) after intraperitoneal sensitisation with OVA and Alum. The mice on the EW diet for one wk presented gastrointestinal symptoms (i.e. weight loss and soft stools) and inflammation in the small intestines (i.e. duodenum, jejunum and ileum). Further continuous EW diet resolved the weight loss but not the soft stools. Splenic CD4⁺ T‐cells of EW diet‐fed mice on the continuous diet showed less proliferation and cytokine production compared with those of control mice, suggesting tolerance induction by the diet. The continuous EW diet reduced levels of OVA‐specific IgE antibodies, but significantly aggravated the inflammation in the jejunum. Conclusion : Our mouse model would be useful to investigate inflammatory and regulatory mechanisms in food‐induced intestinal allergies. Our results suggest potential gastrointestinal inflammation in patients undergoing OIT as continuous administration of allergenic foods, even though the therapy may induce clinical tolerance.     

Evaluation of four types of resistant starch in muffin baking performance and relationship with batter rheology

The influence of wheat flour partial replacement with different types of resistant starch (RS) in muffin batter rheological properties and in baked muffin height, volume and number of air bubbles was investigated. The type of RS affected the above-described properties differently. In comparison to the control batter (without RS), replacement with RS type 3 (Novelose 330 and C*Actistar) increased viscosity and viscoelasticity, at both 20 and 80 °C. On the contrary, RS type 2 (Hi-maize 260 and Novelose 240) decreased them. These differences in viscosity and viscoelasticity were related to different baking performance. The RS3 type muffins had higher height, volume and number of air bubbles than the RS2 type muffins. An increase in viscosity and elasticity of the raw batter and during the heating process favours bubble retention and stability, thus favours baking performance. However, despite the improvement provided by the RS type 3, the baking performance was still lower than in the control muffins. One feature that may contribute to the baking differences is the delay in all the RS batters in the starch gelatinization temperature.