Lara Matia-Merino

Effects of low-methoxyl amidated pectin and ionic calcium on rheology and microstructure of acid-induced sodium caseinate gels

Abstract The influence of low-methoxyl amidated pectin on the rheological and microstructural properties of sodium caseinate gels (2%, w/v), made by acidifying with glucono-δ-lactone, has been investigated at 25 °C. In the absence of calcium ions, a substantial reduction in the time-dependent storage modulus was detected at pectin concentrations as low as 0.01–0.02% (w/v), and a significant increase in gelation time at pectin concentrations ≥0.05% (w/v). Complete inhibition of acid-induced caseinate gelation was noted at ≥0.8% (w/v) pectin. Confocal microscopy has confirmed that the presence of an increasing content of pectin prevents aggregation of caseinate particles into a coherent network. Consistent with the sensitivity of both these biopolymers to calcium ions, the addition of calcium chloride (2 mol Ca 2+ /mol caseinate) has a major influence on the interactions in the caseinate+pectin system. Whereas for low pectin content the modulus was reduced (as for the calcium-free system), there was found to be a large enhancement of the time-dependent modulus at higher pectin contents (≥0.2%, w/v). The combination of a gradual release of calcium ions from caseinate aggregates as the pH is lowered and the electrostatic adsorption of pectin onto the casein particles influences the balance of casein–casein, pectin–pectin and casein–pectin interactions in the final gel structure. Strong syneresis was clearly evident in calcium-containing systems with 0.2–0.6% (w/v) pectin. Microscopy confirmed the total absence of the characteristic acid–casein gel network connections at high pectin content (0.8%, w/v).

Characterization of gold kiwifruit pectin from fruit of different maturities and extraction methods

Studies on gold kiwifruit pectins are limited. In this work, the characterization of pectin isolated from two different stages of maturity of gold kiwifruit, namely early harvested fruit (EHF) and main harvested fruit (MHF) isolated by three methods (acid, water, enzymatic) was carried out. Pectins isolated from MHF were higher in galacturonic acid content (52-59% w/w) and weight-average molecular weights (Mw, 1.7-3.8 × 10(6)g/mol) compared with EHF pectins (29-49% w/w and 0.2-1.7 × 10(6)g/mol respectively). Enzymatic treatment gave the highest yield but lowest in Mw, viscosity and mechanical spectra for both maturities. The pectin of both maturities was classified as high-methoxyl pectin with the degree of esterification ranged from 82% to 90%. Water-extracted MHF pectin molecules had the highest RMS radius (182.7 nm) and Mw (3.75 × 10(6)g/mol). The water extraction method appeared to retain the native state of pectin molecules compared with acid and enzymatic extraction methods based on the Mw and viscosity data.

Extraction and characterisation of pomace pectin from gold kiwifruit (Actinidia chinensis)

Gold kiwifruit pomace extracted using citric acid, water and enzyme (Celluclast 1.5L) were studied in terms of pectin yield, protein, ash, non-starch polysaccharide, galacturonic acid (GalA), neutral sugar composition, molar mass (Mw), viscosity and degree of branching. Water-extracted pectin was considered closest to its native form. Enzyme extracted pectin showed the highest yield (∼ 4.5%w/w) as compared with the acid and water extraction methods (∼ 3.6-3.8%w/w). Pectin obtained from different extraction methods showed different degree of branching. The Mw and root mean square (RMS) radius varied with the extraction methods with values of 8.4 × 10(5) g/mol and 92 nm, 8.5 × 10(5)g/mol and 102 nm, 6.7 × 10(5) g/mol and 52 nm for acid, water and enzymatic extraction methods, respectively. Similar trend was observed for pectin viscosity, with water-extracted pectin giving a slightly higher viscosity followed by acid and enzyme-extracted pectin. This study showed that gold kiwifruit pomace pectin has potential application in food products.

Effect of Celluclast 1.5L on the physicochemical characterization of gold kiwifruit pectin.

The effects of Celluclast 1.5L concentration on the physicochemical characterization of gold kiwifruit pectin was evaluated. Varying the enzyme concentration affected the pectin yield and pectin physicochemical properties. The viscosity of extracted pectin was largely dependent on the enzyme concentration. Celluclast 1.5L with medium concentration exhibited the highest viscosity. Varying the enzyme concentration also influenced the molecular weight distribution. High molecular weight (Mw) pectin (1.65 × 106 g/mol) was obtained when the medium concentration was used. Overall, the study clearly reflects the importance of taking into consideration the amount of cellulytic enzyme added in order to determine the final quality of pectin.

Probing hydrogen bond interactions in a shear thickening polysaccharide using nonlinear shear and extensional rheology.

Mamaku gum is a polysaccharide extracted from the fronds of the black tree fern found in New Zealand. The cooked pith has traditionally been used for various medicinal purposes and as a food source by the Maori people of New Zealand. It has potential applications as a thickener in the food industry and as a palliative for patients with dysphagia. Studies on the shear rheology of Mamaku gum have revealed that the gum exhibits shear thickening at a critical shear rate due to a transition from intra- to inter-molecular chain interactions upon shear-induced chain elongation. In this paper, we demonstrate that these interactions are primarily due to hydrogen bonding. We perform extensional rheology on mixtures of Mamaku gum and urea (a known disruptor of hydrogen bonds) to quantify the nature of these interactions. Capillary Breakup Extensional Rheometry (CaBER) performed on the pure Mamaku gum solutions yield plateau values of the Trouton ratio as high as ∼10(4), showing that the viscoelasticity of the gum in uniaxial elongation is much higher than in shear. For all Mamaku concentrations tested, the extensional viscosity decreases upon increasing urea concentration. Furthermore, the relaxation time decreases exponentially with increasing urea concentration. This exponential relationship is independent of the Mamaku concentration, and is identical to the relationships between urea concentration and characteristic timescales measured in nonlinear shear rheology. We show using the sticky reptation model for polymers with multiple sticker groups along the backbone how such a relationship is consistent with a linear decrease in the free energy for hydrogen bond dissociation. We then demonstrate that a time-concentration superposition principle can be used to collapse the viscoelastic properties of the Mamaku-gum/urea mixtures.

Assessing the iron chelation capacity of goat casein digest isolates

We isolated goat phosphopeptides via calcium and ethanol precipitation from a caseinate digest and investigated their feasibility as an iron-fortification ingredient in nutritional foods. Goat tryptic-digested phosphopeptides could bind 54.37 ± 0.50 mg of Fe/g of protein compared with goat milk, which could bind 3.83 ± 0.01 mg of Fe/g of protein, indicating that isolation did increase iron binding. However, the >13-fold increase in iron binding was only partly explained by the increased concentration of phosphoserine-rich residues in the isolated fraction: we observed a 77% increase in serine residue content and a 5.9-fold increase in phosphorus in the goat peptide isolate compared with the starting caseinate material. We investigated the effect of potential industrial processing conditions (including heating, cooling, holding time, and processing order) on iron binding by the tryptic-digested phosphopeptides. In addition, we tested the effect of ionic strength and the addition of peptides to a milk system to understand how food formulations could affect iron binding.

Use of viscous fibres in beverages for appetite control: a review of studies

Abstract Dietary fibres, particularly viscous fibres appear to be more effective for appetite control (reduce subjective appetite, energy intake and/or body weight). Three types of viscous fibres, pectin, alginate and cereal beta-glucan, were identified as potential satiety-enhancing ingredients. The aim of this review was to collect evidence from human intervention studies evaluating pectins, alginates and beta-glucans in beverages, liquid preloads and liquid test meals for their satiety effects. Our focused, narrative review of several satiety studies shows an overall consistent result on the effectiveness of pectin, alginate and beta-glucan for appetite control. Beverages or liquid test meals are probably the better delivery mode for these fibres, as their effect on satiety is affected by their physico–chemical properties. Most, if not all, of these reviewed studies gave little or no consideration to the potential effects of common food processing (e.g. pasteurisation, ultra-high temperature process) on the physico–chemical properties of these fibre-containing beverages. This is one of the research gaps we have identified warranting further work, which is likely to be of significance from the industry and consumer perspective.

The cation-controlled and hydrogen bond-mediated shear-thickening behaviour of a tree-fern isolated polysaccharide.

The shear-thickening rheological behaviour (between 5 and 20s(-1)) of a 5% (w/w) viscoelastic gum extracted from the fronds of the native New Zealand black tree fern or mamaku in Māori was further explored by manipulating the salt content. The freeze-dried mamaku gum contained a high mineral content and sugars which upon removal via dialysis, resulted in the loss of shear thickening. However, this loss was reversible by the addition of salts to the dialysed dispersion. The mechanism of shear-thickening behaviour was therefore hypothesised to be due to shear-induced transition of intra- to intermolecular hydrogen bonding, promoted by the screening effect of cations. Mono-, di- and trivalent salts, i.e. Na(+), K(+), N(CH3)4(+), Ca(2+), Mg(2+), Al(3+) and La(3+) at concentrations between 0.001 and 1.0M were tested to support the hypothesis as well as to demonstrate the sensitivity of the biopolymer to cation valency and concentrations. The cation valency and concentration were crucial factors in determining: (i) zero-shear viscosity, (ii) critical shear rate, γ˙c (or shear rate at the onset of shear-thickening) and (iii) the extent of shear-thickening of the solution. For mono- and divalent cations these parameters were similar at equivalent ionic strengths and fairly independent of the cation type. Trivalent cations (La(3+)) however caused precipitation of the gum in the concentration range of 0.005-0.05 M but clear dispersions were obtained above 0.05 M.

Time- and shear history-dependence of the rheological properties of a water-soluble extract from the fronds of the black tree fern, Cyathea medullaris

A shear-thickening polysaccharide extracted from the New Zealand black tree fern was characterized for its time-dependent rheology and the effects of shear-history. The material exhibited antithixotropic behavior at shear rates between 4 and 10 s−1. The parallel growth of normal stresses with time at these shear rates indicated the development of an elastic network under shear. The formation of association structures is proposed to take place via cooperative zipping of stretched chains where associative groups are exposed only on shearing. Hysteresis effects were also observed at shear rates between 4 and 10 s−1. This was probably caused by rapid structure formation at these shear rates, which cannot be easily disrupted at subsequent lower shear rates (<10 s−1). Preshearing at high shear rates (∼1000 s−1) fully stretched out and aligned the polysaccharide chains, exposing all sites for intermolecular association at appropriate lower shear rates.