Wenceslao Canet

Purification and characterisation of two pectinmethylesterase from persimmon (Diospyros kaki)

Two pectinmethylesterase isoforms, PME I and PME II, have been separated and purified from persimmon using chromatography techniques. Both isoforms presented differences in molecular weight (PME I: 51 kDa, PME II: 30 kDa), isoelectric point (PME I: 8.4, PME II: 6.9) and K m values (PME I: 54 μg ml -1 , PME II: 31 μg ml -1 ). They differed in their optimum pH and thermal stability, PME being the more thermostable isoform. Both isoforms exhibited similar behaviour with respect to Ca 2+ and Na + concentrations and were strongly inhibited by CaCl 2 concentrations of over 80 mM and by NaCI concentrations of over 500 mM. Both isoforms were activated by low concentrations of polygalacturonic acid and were competitively inhibited by D-galacturonic acid and high concentrations of polygalacturonic acid.

Effect of various thermal pre-treatments on the texture of frozen cherries (Prunus avium L.). Related enzyme activities

ZusammenfassungEs wird die Wirkung verschiedener Wärmebehandlungen (50, 60 und 70 °C) während 3, 6, 9 und 12 min vor dem Einfrieren sowie nach 3 und 6 Monaten Lagerung in gefrorenem Zustand auf das Gewebe von Kirschen untersucht. Gleichzeitig wurden dabei die Veränderungen der enzymatischen Aktivität der Zellwand analysiert, und zwar mit objektiven Messungen der Festigkeit der Früchte mittels mechanischen Eindringungsversuchen, mit Schnitt- und Kramer-Shear-Cell-Messungen (K.S.C.) sowie Messungen der Pectin-Esterasen- und der Polygalakturonase-Aktivitäten durchgeführt. Es wurden Korrelationen zwischen den Ergebnissen der technischen Tests und der Aktivität der Pectin-Esterasen der Kirschen aufgestellt, wobei bedeutsame Korrelationen gefunden wurden. Die Anwendung der Wärmebehandlung bei niedriger Temperatur (70 °C) vor dem Einfrieren verbessert die Textur des Produkts bedeutend.AbstractThe effect produced on the texture of cherries by heating at 50, 60 and 70° C for 3, 6, 9, and 12 mins before freezing followed by 3 and 6 months of frozen storage was studied. Variations in cell-wall enzyme activity were also analysed. To this end, objective measurements were carried out on the firmness of the cherries, by means of mechanical penetration, shear and Kramer Shear Cell tests. Pectinesterase and polygalacturonase activity were also measured. Correlations were established between the mechanical test results and pectinesterase activity in cherries subjected to different treatments. Significant correlations were found between this activity and the final firmness of the frozen fruit. Low-temperature heating (70° C) prior of freezing significantly improves the final texture of the product.

Optimisation of freezing process with pressure steaming of potato tissues (cv Monalisa)

Response surface methodology (RSM) was used for determining optimum conditions of the freezing process on pectinesterase (PE) activity, rheological parameters and textural properties in potato tissues. In the process of production of frozen potatoes, the second step of the stepwise blanching prior to freezing was considered as a fixed factor and performed at 97 °C for 2 min as well as the freezing rate in the freezing step itself, which was carried out at -2 °C min -1 . The effects of variation in levels of temperature (57.93-72.07°C) and time (15.86-44.14 min) in the first blanching step on the PE activity were studied using a central composite rotatable design. A Box-Behnken factorial design was used to investigate the effects of simultaneous variation of temperature (60-70 °C) and time (20-40min) in the first blanching step and steaming temperature (112-122°C) and time (1-3 min) on rheological parameters and textural properties. Blanching temperature was the independent variable that most influenced either enzymatic activity or rheological parameters. Stationary points showing maximum PE activity had critical temperature and time values of 64.22°C and 29.37min before freezing and 64.39°C and 28.02min after freezing and steaming of the tissues, and these values were very close to those obtained for some creep compliance parameters. Results show a high correlation between increases in PE activity and tissue firmness below optimum experimental freezing conditions, proving the role of the enzyme as one of the main contributors to the firmness which determines the textural quality of frozen potato tissues.

Sensory and texture properties of mashed potato incorporated with inulin and olive oil blends

The effect of adding different ratios of inulin and extra virgin olive oil blends, formulated without (MPA) and with cryoprotectants (MPB), on texture properties of fresh mashed potatoes and frozen/thawed mashed potatoes was studied. Inulin and extra virgin olive oil behaved like soft fillers, but inulin was associated with increased fibrousness and extra virgin olive oil with increased creaminess. In the total dataset and frozen mashed potatoes, frozen/thawed mashed potatoes, and MPA subgroups, component 1 was a contrast between mechanical and surface textural attributes, whereas in MPB samples component 1 was determined by geometrical attributes. Addition of inulin at 30 g/kg and extra virgin olive oil at 45 g/kg is recommended.

Effects of Pressure, Temperature, Treatment Time, and Storage on Rheological, Textural, and Structural Properties of Heat-Induced Chickpea Gels

Pressure-induced gelatinization of chickpea flour (CF) was studied in combination with subsequent temperature-induced gelatinization. CF slurries (with 1:5 flour-to-water ratio) and CF in powder form were treated with high hydrostatic pressure (HHP), temperature (T), and treatment time (t) at three levels (200, 400, 600 MPa; 10, 25, 50 °C; 5, 15, 25 min). In order to investigate the effect of storage (S), half of the HHP-treated CF slurries were immediately analyzed for changes in oscillatory rheological properties under isothermal heating at 75 °C for 15 min followed by cooling to 25 °C. The other half of the HHP-treated CF slurries were refrigerated (at 4 °C) for one week and subsequently analyzed for changes in oscillatory properties under the same heating conditions as the unrefrigerated samples. HHP-treated CF in powder form was analyzed for changes in textural properties of heat-induced CF gels under isothermal heating at 90 °C for 5 min and subsequent cooling to 25 °C. Structural changes during gelatinization were investigated using microscopy. Pressure had a more significant effect on rheological and textural properties, followed by T and treatment t (in that order). Gel aging in HHP-treated CF slurries during storage was supported by rheological measurements.

Mashed potatoes enriched with soy protein isolate and inulin: chemical, rheological and structural basis

Soy protein isolate is typical vegetable protein with health-enhancing activities. Inulin, a prebiotic no digestible carbohydrate, has functional properties. A mashed potato serving of 200 g with added soy protein isolate and/or inulin concentrations of 15–60 g/kg provides from 3 to 12 g of soy protein isolate and/or inulin, respectively. Currently, no information is available about the possible texture-modifying effect of this non-ionizable polar carbohydrate in different soy-based food systems. In this study, the effect of the addition of soy protein isolate and inulin blends at different soy protein isolate: inulin ratios on the degree of inulin polymerization and the rheological and structural properties of fresh mashed and frozen/thawed mashed potatoes were evaluated. The inulin chemical structure remained intact throughout the various treatments, and soy protein isolate did not affect inulin composition being a protein compatible with this fructan. Small-strain rheology showed that both ingredients behaved like soft fillers. In the frozen/thawed mashed potatoes samples, addition of 30 : 30 and 15 : 60 blend ratios significantly increased elasticity (G′ value) compared with 0 : 0 control, consequently reducing the freeze/thaw stability conferred by the cryoprotectants. Inulin crystallites caused a significant strengthening effect on soy protein isolate gel. Micrographs revealed that soy protein isolate supports the inulin structure by building up a second fine-stranded network. Thereby, possibility of using soy protein isolate and inulin in combination with mashed potatoes to provide a highly nutritious and healthy product is promising.

Comparative Characterization of Dietary Fibre-Enriched Frozen/Thawed Mashed Potatoes

The potential use of commercial fibres (pea fibre, inulin, and their blends), as fibre-enriching agents in frozen/thawed mashed potatoes was reported. Pea fibre and inulin supplementations conferred hardness and softness to the product, respectively. Differences were attributed to the relationship of the fibre with the potato starch matrix. The association of pea fibre at low concentration (<15 g/kg mashed potatoes) and inulin at high concentration (>45 g/kg) is strongly encouraged to fortify the diet without promoting negative effects on textural and rheological properties of frozen/thawed mashed potatoes or colour and overall acceptability of the resulting products.

Corn starch and egg white enriched gluten-free chickpea flour batters: Rheological and structural properties

ABSTRACT Ten batter formulations were made with different chickpea flour:corn starch (CF:CS) ratios (0:0, 100:0, 75:25, 50:50, and 25:75), with or without partial replacement of whole egg with egg white (EW). EW in control gluten batter (0:0 ratio) and batters made with CS resulted in weaker structured systems. CF-based batters had more viscous behaviour than gluten ones. All batters showed time-dependence which was reduced after shearing. Batter with CF alone (100:0 ratio) without EW had the highest d43, d90, and span values. The 100:0 ratio batters were much more complex structured systems than gluten batters because of their higher protein content.

Rheometric Non-Isothermal Gelatinization Kinetics of Chickpea Flour-Based Gluten-Free Muffin Batters with Added Biopolymers

An attempt was made to analyze the elastic modulus (G′) of chickpea flour (CF)-based muffin batters made with CF alone and with added biopolymers (whey protein (WP), xanthan gum (XG), inulin (INL), and their blends) in order to evaluate their suitability to be a wheat flour (WF) substitute in muffins, and to model the heat-induced gelatinization of batters under non-isothermal heating condition from 25 °C to 90 °C. A rheological approach is proposed to determine the kinetic parameters (reaction order (n), frequency factor (k0), and activation energy (Ea)) using linearly-increasing temperature. Zero-order reaction kinetics adequately described batter gelatinization process, therefore assuming a constant rate independent of the initial G′ value. The change of the derivative of G′ with respect to time (dG′/dt) versus temperature is described by one exponential function with activation energies ranging from 118 to 180 kJ·mol−1. Control wheat gluten batter, with higher and lower starch and protein contents, respectively, than CF-based batters, exhibited the highest Ea value. Formulation of CF-based gluten-free batters with starch and protein contents closer to the levels of WF-based batter could be a strategy to decrease differences in kinetic parameters of muffin batters and, therefore, in technological characteristics of baked muffins.

Characterization of commercial Spanish hummus formulation: Nutritional composition, rheology, and structure

ABSTRACT Nutritional composition, rheological behavior, and structure of a commercial Spanish hummus were analyzed. The hummus is “high in fiber,” and Fe (1.9 ± 0.02 mg/100 g), Ca (65.7 ± 10.9 mg/100 g), Mg (66.8 ± 1.0 mg/100 g), P (164.9 ± 4.6 mg/100 g), and especially, K (250.7 ± 11.6 mg/100 g) are present in it. The hummus, with dispersion index of 4.14, behaved like a weak gel and exhibited hysteresis loops, and the Herschel-Bulkley model described its steady time-independent flow behavior. Complex viscosity and apparent viscosity at similar frequency and shear rate failed to follow the Cox-Merz rule.