José V. Carbonell

Physical and structural properties of barley (1 → 3),(1 →4)-β-d-glucan. Part I. Determination of molecular weight and macromolecular radius by light scattering

Abstract (1 → 3),(1 → 4)-β- d -Glucan purified from the 65 °C water extract of barley flour, commercial β-glucans and samples obtained by controlled depolymerisation of the former, covering a range from 9 × 103 to 6 × 105 dalton, were characterised by size exclusion chromatography and light scattering. The on-line measurement of molecular weight with a multiangle laser-light scattering photometer gave reproducible and consistent values according to: (a) the process followed in sample preparation; (b) their Chromatographic elution in terms of hydrodynamic volume; and (c) the kinetics of depolymerization. However, batch light scattering measurements of β-glucan molecular weights did not give concordant and reproducible results. These last data, together with the study of the very early stages of enzymatic degradation of high molecular weight β-glucans by barley endo-β-glucanases as monitored by the Calcofluor-F.I.A. method, seem to suggest the formation of very labile molecular aggregates.

Physical and structural properties of barley (1 → 3),(1 → 4)-β-d-glucan. Part II. Viscosity, chain stiffness and macromolecular dimensions

Intrinsic viscosities and molecular weights of (1 → 3),(1 → 4)-β-d-glucan samples, covering a range of 9 × 103–6 × 105 daltons, have been used to determine their conformational parameters and molecular dimensions. The chain of β-glucan is satisfactorily modelled by a partially stiff worm-like cylinder, with persistence length 3.5–3.8nm and cross-section diameter 0.45 nm. This corresponds to an average of about four β(1 → 3) links per statistical segments. The characteristic ratio, C∞, calculated from this worm-like description of the macromolecule, gave a value of 13–14, in good agreement with the theoretical calculations.

The dehydration of paprika with ambient and heated air and the kinetics of colour degradation during storage

Abstract The hygroscopic behaviour of dried red pepper is characterized by means of water vapour adsorption isotherms at 5, 20 and 35°C; from the GAB equation, a monolayer water content of 0·0816 kg H 2 O per kg dry matter has been deduced. The effect of temperature on the drying rate of pepper is considered and yields are compared when the drying is carried out with ambient air and with different loading densities (10–40 kg m −2 ). The kinetics of paprika colour degradation during storage at different temperatures and with a moisture content corresponding to the monolayer have been studied. A sharp change in the rate of colour loss is observed at 15°C: the value Q 10 (°C) changes from 1·62 to 2·82 when the temperature rises above 15°C.

Physical and structural properties of barley (1→3),(1→4)-β-D-glucan—III. Formation of aggregates analysed through its viscoelastic and flow behaviour

Abstract The Theological properties (flow and viscoelastic) of barley β-glucan in aqueous solution have been studied. The results shed light on the association behaviour of these macromolecules and even on the formation of network-like structures under certain circumstances. The concentrations used for this study were both in the dilute and in the semidilute regime, close to the critical value where overlap of macromolecular coils sets in. However, the association behaviour detected in such a regime and together with the present experimental techniques, agrees with previous results obtained with other techniques such as capillary viscometry and light scattering, which operate in the dilute solution regime, where no overlapping of the chains is expected. The influence of the molecular weight of the samples, the temperature and the ionic strength on the flow and oscillatory shear measurements has been studied. The preparation of samples and their thermal history have proved to be important factors in the development of associated structures, both affecting the results.

Effects of Heat Treatment Conditions on Fresh Taste and on Pectinmethylesterase Activity of Chilled Mandarin and Orange Juices

Juices from oranges, mandarins and hybrids were thermally treated in a plate exchanger at different conditions to evaluate the effects of treatment on fresh taste and on residual pectinmethylesterase (PME) activity. Freshness was significantly higher in fresh juices than in samples treated at 70°C or higher temperatures for 10 seconds of retention time, whereas no differences were found among samples heated at temperatures from 70 to 90°C for the same time, however at 95°C fresh taste decreased again. Residual PME activity was about 20% in samples treated at 70°C for 5, 10 and 20 seconds and in those heated at 80°C for 5 and 10 seconds, decreasing to 15%, also at 80°C, when retention time increased to 20 seconds. A drastic reduction to about 3% of residual activity was observed at 85°C for 10 seconds. Minimum activities of 0-1% corresponded to samples treated at 95°C. Considering the results of sensory and residual enzyme analyses, the treatment at 85°C for 10 seconds can be considered suitable. In these conditions fresh taste did not differ from that of juices treated at lower temperatures but residual enzyme activity was clearly smaller and acceptable for chilled juices, products of high quality but short shelf life. On the other hand, a deeper reduction of PME activity increasing the temperature to 95°C does not seem advisable since fresh taste decreases. Mandarin juices pasteurised at 85°C for 10 seconds and pasteurised again at the same conditions did not show a further decrease of fresh taste. Two heat treatments were usually applied when packing plants receive the juice from other factories.

Experimental simulation of solar drying of garlic using an adsorbent energy storage bed

Abstract Solar drying of garlic with energy storage in silica gel is experimentally simulated in a closed system in which the air is continuously circulated between food and adsorbent. Kinetics of the drying process are studied and equilibrium data are predicted by a mathematical model developed from the experimental results. By comparing the end points of drying with equilibrium values the length of the drying process can be established. From sorption data, a garlic surface area of 63–188 m 2 g −1 and a heat of adsorption in the first layer of 2548–2691 kJ kg −1 have been calculated. A value of 746 kJ kg −1 has been deduced for the activation energy for water removal.

Effect of Thermal Treatment on Enzymatic Activity and Rheological and Sensory Properties of Strawberry Purees

The behavior of strawberry purees submitted to processes of mild pasteurization (75 °C — 15 s) and severe pasteurization (90 °C — 20 s), using as references fresh and hot-filled purees, was studied. Purees thermally treated were stored at +3 °C during 2 months. Pectin methylesterase activity, rheological behavior, and taste quality were analyzed. The results showed how the pectin methylesterase activity of strawberry puree (0.385nanokatal/mL) was reduced to 25.5% by the mild heat treatment, to 5.4% by the severe one and to undetectable levels in the hot-filled puree. A significant increase in the viscosity was detected as a consequence of the severe thermal treatments, although in any case it decreased with storage time. Taste quality, evaluated by simple ranking tests of samples, was superior in the fresh puree, without significant differences among the three samples thermally treated. The assessors pointed out the greater aromatic intensity of the fresh puree and the lack of cooked flavors in all samples. All treated samples maintained their sensory quality during 2 months of storage at 3 °C. The taste quality of hot-filled purees stored 1 or 2 months at room temperature (21 °C) was significantly lower than the respective chilled samples. From this point of view, the hot-filled treatment and chilling storage will be recommended for this product.

Occurrence of 20S RNA and 23S RNA replicons in industrial yeast strains and their variation under nutritional stress conditions.

We have characterized industrial yeast strains used in the brewing, baking, and winemaking industries for the presence or absence of cytoplasmic single‐stranded 20S and 23S RNAs. Furthermore, the variation of intracellular concentrations of these replicons in brewing and laboratory strains under nutritional stress conditions was determined. Our results show a correlation between the relative abundance of these replicons and exposure of yeast to nutritionally stressful conditions, indicating that these RNAs could be employed as molecular probes to evaluate the exposure of 20S+ and/or 23S+ yeast strains to stress situations during industrial manipulation. During this study, several 20S−23S+ Saccharomyces cerevisiae strains were isolated and identified. This is the first time that a yeast strain containing only 23S RNA has been reported, demonstrating that 20S RNA is not required for 23S RNA replication. Copyright

Determination of the Depolymerisation Kinetics of Amylose, Amylopectin and Maltodextrin by Aspergillus niger Glucoamylase Using a 2-p-toluidinylnaphthalene-6-sulfonate/Flow-injection Analysis System with Fluorimetric Detection

This work describes the determination of depolymerisation kinetics of amylose, amylopectin and maltodextrin by Aspergillus niger glucoamylase using a flow-injection analysis system with fluorimetric detection and 2-p-toluidinylnaphthalene-2-sulfonate as the fluorescent probe. Experimental data corresponding to the time evolution of the concentration of detectable substrate were fitted to a single exponential decay curve in the case of amylose (linear substrate) and to a double exponential decay curve in the case of amylopectin and maltodextrin (ramified substrates). For all the substrates assayed, the depolymerisation rates at time zero correlated well with the initial substrate and enzyme concentrations through the Michaelis-Menten hyperbola. Therefore, this methodology allowed the determination of glucoamylase activity using any of these substrates. The determined value of the enzymic constant K m was lower for amylose than for amylopectin and maltodextrin, thus reflecting the higher difficulty of glucoamylase to hydrolyse the (1,6) when compared to the (1,4) linkages. In contrast, the values obtained for the rate constant k 3 were very similar for all the substrates assayed.

Time evolution of exposed hydrophobicity of water-soluble proteins during their depolymerisation by endo-proteases

During the depolymerisation of a water-soluble protein by an endo-protease, the exposed hydrophobicity of the substrate, that is the hydrophobicity that is accessible to hydrophobic probes, changes with the progress of the reaction. This work describes the depolymerisation of bovine serum albumin, α-casein and β-lactoglobulin using the proteases Alcalase, Flavourzyme, α-chymotrypsin, mercuripapain and trypsin. Time evolution of substrate hydrophobicity was monitored by a flow-injection analysis (FIA) system with fluorescence detection and an aqueous eluant containing p-toluidinylnaphthalene-6-sulfonate (2,6-TNS) as the fluorescent probe. In all cases, the time evolution of the substrate hydrophobicity was fitted using a derived mathematical function containing two adjustable rate constants and two constant parameters. This methodology allowed the determination of protease activities, as well as online monitoring of the depolymerisation process, when using water-soluble proteins as substrate.