Costas G. Biliaderis

Cereal arabinoxylans: advances in structure and physicochemical properties

Abstract Arabinoxylans constitute a major fraction of cereal cell wall polysaccharides. They consist of a linear β-(1 → 4) linked xylan backbone to which α- l -arabinofuranose units are attached as side residues via α-(1 → 3) and/or α-(1 → 2) linkages. Several structural models have been put forward based on enzymic degradation studies and structure elucidation of oligosaccharides by NMR, methylation, and periodate oxidation techniques. These tentative models present different substitution patterns of arabinoses along the xylan chain. Cereal arabinoxylans exhibit a great deal of structural heterogeneity with respect to ratio of Ara f Xyl p , substitution pattern of arabinoses, content of feruloyl groups and molecular size. The conformation and physicochemical properties (viscosity, gelation potential, intermolecular association) of arabinoxylans in aqueous solutions are dependent on the molecular features of these polysaccharides; specific structure-property relationships have been established in model and actual food systems. Wheat and rye arabinoxylans are important functional ingredients in baked products affecting the mechanical properties of dough, as well as the texture and other end-product quality characteristics.

Thermal behavior of amylose-lipid complexes

Abstract Melting and crystallization phenomena of amylose-lipid complexes, crystallized either from dilute solution or concentrated amylose ‘melts’ under various conditions, were studied using differential scanning calorimetry (DSC). The melting enthalpies (complex/H 2 O: 0·1–0·5 w/w) of the solution-grown crystalline complexes were 20·4±0·8 J g −1 for amylosemonopalmitin (AM-1-C16), 26·5±1·5 J g −1 for amylose-lysolecithin (AM-lys/in) and 26·6±1·6 J g −1 for amylose-lauric acid (AM-C12). While melting of the AM-lys/in complex showed a single transition for all concentrations studied, the melting behavior of the AM-1-C16 and the AM-C12 was rather complex at low or intermediate water contents. At a heating rate of 10°C min −1 two endothermic transitions with an intermediate exothermic peak were observed, indicative of non-equilibrium melting. A process of partial melting, followed by recrystallization and final melting, is suggested to explain such multiple-melting characteristics. These phenomena become less prominent with increasing water content; presumably due to the depression of the glass transition (T g ) and the melting temperatures (T m ). The annealing behavior of AM-1-C16 further suggested that the development of new structural order upon heating takes place primarily after partial melting of the initial crystalline structure. Overall, the DSC data are typical of those for semicrystalline polymers and consistent with a lamellar type of molecular organization in the crystalline regions of these materials.

Crystallization behavior of amylose-V complexes: Structure-property relationships

Abstract The effect of temperature on the crystallization behavior of amylose-lipid complexes from dilute solution has been investigated by differential scanning calorimetry, X-ray diffraction, and structural analysis using alpha amylase etching-gel permeation chromatography, as well as birefringence, density, and dynamic rheological measurements. For any given monoglyceride used as a complexing ligand (monomyristin, monopalmitin, or monostearin), two thermally distinct forms of the complex were identified, namely, I (low T m ) and II (high T m ), depending on the crystallization temperature (T c ); complex I predominated at low T c , while II was the preferred form at high T c . Minor differences between the two forms in the size distribution of chain segments constituting the ordered regions are inadequate to explain the lack of a well defined V-pattern for form I. Instead, explanations of a number of thermal and physicochemical properties can be provided if it is postulated that form I is a separate thermodynamic state, with internal energy and entropy intermediate between those of a melt and of a classical crystalline system, such as form II. Form I is assumed to be formed when rapid nucleation occurs, and is morphologically described by a random distribution of the basic structural elements ( i.e. helical segments), having little crystallographic register. A prerequisite for the conversion I→II is the partial melting of its structure, which appears to foster crystallite formation and thickening by chain diffusion. Annealing effects on form II of the crystals of V were also found typical of metastable semicrystalline polymers.

Glass transition and physical properties of polyol-plasticised pullulan–starch blends at low moisture

The effects of water and polyols, at low weight fractions, on water sorption behaviour, thermal and mechanical properties, and gas permeability of blends of pullulan and gelatinised corn starch (ps), prepared by either hot pressing or casting aqueous solutions, were studied. Incorporation of sorbitol or xylose in the ps blends resulted in lower equilibrium moisture contents in the low to medium aw range, and much higher moisture contents at aw . 0.75; the Guggenheim‐Anderson‐DeBoer isotherm model adequately described the sorption data up to the aw of 0.9. Water and polyols exerted a strong plasticising action, lowering the Tg of the blends and allowing enthalpy relaxation events to occur during aging of the amorphous specimens. At the low polyol levels examined (10 and 20% dry basis), a single glass transition temperature for the polymeric constituents was identified in all samples by DSC and DMTA; apparent activation energies of 226‐ 296 kJ mol 21 for the a-relaxation were estimated from multifrequency mechanical measurements. Large deformation mechanical tests demonstrated sharp decreases in Young’s moduli with increasing levels of polyol and water, typical of the glass‐rubber transition of amorphous polymers; the relationship of flexural modulus and moisture content was quantified using the Fermi’s model. The relationship between maximum stress (s max) and water content showed an increase in stiffness of the blends from 7 to 11% moisture, and a strong softening effect when the water content exceeded this range. The Arrhenius plots of O2 and CO2 permeability data showed distinct changes in slope in the glass transition region of the blends. Analysis of viscoelastic data with the time‐temperature superposition principle and treatment of gas permeability data with the Williams‐Landel‐Ferry equation suggested that application of this model is meaningful if the coefficients,C1 and C2, are allowed to vary instead of assuming their ‘universal’ values. q 1999 Elsevier Science Ltd. All rights reserved.

Amylolytic enzymes and products derived from starch: A review

This review provides current information on starch and its molecular composition, common and potential sources, and manufacturing processes. It also deals with the five groups of enzymes involved in the hydrolysis of starch: the endo- and exoamylases, which act primarily on the alpha-1,4 linkages; the debranching enzymes, which act on the alpha-1,6 linkages; the isomerases which convert glucose to fructose; and the cyclodextrin glycosyltransferases which degrade starch by catalyzing cyclization and disproportionation reactions. This work mainly discusses the enzymatic processes for the manufacture of maltodextrins and corn syrup solids, including the production, both batch and continuous, of glucose syrup, and the processes to obtain sweeteners, such as maltose and 42, 55, and 90% high-fructose corn syrups. It highlights the novel production of Schardingers dextrins: the alpha-, beta-, and gamma-cyclodextrins, consisting of six, seven, and eight glucose monomers, respectively. New products are emerging on the market that can serve as fat and oil substitutes, moisture-retention compounds, crystal-formation controllers, stabilizers for volatile materials like flavors and spices, or products for the pharmaceutical industry. As a result, particular attention is given to functional properties and applications of the above-cited compounds.

Physico-chemical properties of whey protein isolate films containing oregano oil and their antimicrobial action against spoilage flora of fresh beef

Antimicrobial films were prepared by incorporating different levels of oregano oil (0.5%, 1.0%, and 1.5% w/w in the film forming solution) into sorbitol-plasticized whey protein isolate (WPI) films. The moisture uptake behavior and the water vapor permeability (WVP) were not affected by the addition of oregano oil at any of the concentrations used. A reduction of the glass transition temperature (∼10-20°C), as determined by dynamic mechanical thermal analysis (DMTA), was caused by addition of oil into the protein matrix. A decrease of Young modulus (E) and maximum tensile strength (σ(max)) accompanied with an increase in elongation at break (%EB) was observed with increasing oil concentration up to a level of 1.0% (w/w). Wrapping of beef cuts with the antimicrobial films resulted in smaller changes in total color difference (ΔΕ) and saturation difference (Δ(chroma)) during refrigeration (5°C, 12days). The maximum specific growth rate (μ(max)) of total flora (total viable count, TVC) and pseudomonads were significantly reduced (P<0.05) by a factor of two with the use of antimicrobial films (1.5% w/w oil in the film forming solution), while the growth of lactic acid bacteria was completely inhibited. These results pointed to the effectiveness of oregano oil containing whey protein films to increase the shelf life of fresh beef.

Differential scanning calorimetry in food research—A review☆

Abstract Differential scanning calorimetry (DSC) has gained remarkable popularity in thermal studies of foods and their components following the development of instrumentation of sufficient sensitivity. DSC is rapid, facile and capable of supplying both thermodynamic (heat capacity, enthalpy and entropy) and kinetic data (reaction rate and activation energy) on protein denaturation. Calorimetric studies have also provided a better insight into the order-disorder transition processes of granular starch and other gelling polysaccharides. DSC can be used to characterise mixtures of polymorphic forms of fats as well as to evaluate hydrogenation and various tempering regimes for their effectiveness in bringing about desired polymorphic changes. Calorimetry has also been employed to examine the physical state and properties of water in foodstuffs.

Effect of arabinoxylans on bread-making quality of wheat flours

Two highly purified arabinoxylan preparations of different molecular weight (HMW, [η] = 5.48 dl/g and LMW, [η] = 3.69 dl/g) were used to study the effect of these water-soluble polysaccharides on the bread-making quality of two wheat flours: a Canada western red spring (CWRS) composite sample and a Canada prairie spring (CPS), cv. HY 368. Both preparations significantly increased the farinograph water absorption and the dough development time for the two flours; the HMW arabinoxylans exerted significantly (P < 0.01) greater effects than the LMW preparation. The HMW arabinoxylans maximally improved the loaf volume of CWRS and CPS breads at a level of 0.5% (w/w) supplementation. The LMW arabinoxylans maximally increased the loaf volume of CWRS and CPS breads at 0.7 and 1.1% (w/w), respectively. Breads containing HMW arabinoxylans retained significantly (P < 0.01) more water than the breads with LMW polymers at 0.5-0.9% (w/w) supplementation levels. Because of their higher moisture content the arabinoxylan-fortified breads exhibited a greater rate of starch retrogradation as assessed by calorimetry. Nevertheless, these breads had softer breadcrumbs than the controls; breads fortified (0.3-0.9% w/w) with HMW arabinoxylans were significantly (P < 0.01) less firm than those with LMW polymers over the 7-day storage period.

Physical properties of polyol-plasticized edible films made from sodium caseinate and soluble starch blends

Abstract Aqueous blends of sodium caseinate and soluble starch, plasticized with polyols, were prepared by casting or by extrusion and hot pressing. The mechanical, thermal, gas and water permeation properties of these blends were studied after their conditioning at various relative humidities. With increasing plasticizer (water, polyols) content there was a progressive decrease of Tg of the blends. The plasticized blends also showed increased percentage elongation, whereas their flexural modulus and tensile strength exhibited a substantial drop. The gas permeability-temperature plots revealed Arrhenius-type relationships with an inflection in the glass transition temperature region.

Oxidative gelation studies of water-soluble pentosans from wheat

The gel formation potential of purified wheat water-soluble pentosans and their fractions, arabinoxylan and arabinogalactan, in the presence of H 2 O 2 /peroxidase was investigated by small amplitude oscillatory rheological measurements. Gelation proceeded in two stages: a rapid increase in gel rigidity ( G ´) during the first hour, followed by a much lower rate of gel development thereafter. Disappearance of feruloyl groups coincided with the first stage of the gelation process. Gel permeation chromatography on 8epharose CL-4B and Sephacryl 8-300 revealed that only arabinoxylan actively participated in the network. The rate and extent of gel rigidity development was dependent on polymer and oxidant concentration. Temperature had a negative effect on the gelation process. Gel network development with FeCl 3 was similar to that with H 2 O 2 /peroxidase, while (NH 4 ) 2 S 2 O 8 induced gelation at a much lower rate. The cross-linked pentosans and arabinoxylan held up to 100 g of H 2 O per g of polymer.