Physical properties and antioxidant capacity of starch–sodium caseinate films containing lipids

Biodegradable films based on starch, sodium caseinate, glycerol and lipids (oleic acid and/or α-tocopherol) were obtained and evaluated in terms of microstructure, mechanical behaviour, barrier and optical properties and antioxidant capacity. The effect of film storage time on these properties was also analysed. The lipid incorporation provoked phase separation due to the different interaction between each polymer and lipids, although structural rearrangement of components during storage could be deduced from the change in mechanical behaviour. After storage, all films showed similar mechanical properties, but lipid containing films were more stretchable. Lipid addition did not induce a notable decreased in water vapour permeability of the films, but oxygen permeability highly increased when they contained oleic acid. All films were highly transparent, with very small differences among formulations, although their gloss values increased when lipids were added. The incorporation of α-tocopherol greatly increased the antioxidant capacity of the films which affected oxygen permeability.     

Rheological behaviors,structural properties and freeze–thaw stability of normal and waxy genotypes of barley starch: a comparative study with mung bean,potato, and corn starches

Food Science and Biotechnology - The rheological behaviors, structural properties and freeze-thaw stability of starch isolated from Tetonia barley (Normal genotype, Reg. No. CV-334, PI 646199) and...     

Time-dependent flow properties of starch–milk–sugar pastes

The time-dependent flow properties of starch–milk–sugar (SMS) pastes have been studied. The flow properties were assessed from the measurement of the shear stress versus time of shearing at constant shear rate. Corn and wheat starches were used in this study, while the sugars were glucose, sucrose, and fructose. The Weltman model was used to evaluate the flow properties of SMS pastes prepared under different conditions. SMS pastes heated at 95 and 85 °C exhibited a thixotropic behavior, while pastes heated at 75 °C behaved like a rheopectic fluid. It was noted that the thixotropy occurred at high shear stress (above 50 Pa), and the rheopexy occurred at low shear stress (below 45 Pa). The degree of thixotropy, as assessed by the Weltman model parameters, increased significantly with starch concentration, and with less pronounced effect with sugar concentration. The effect of sugar type on the degree of thixotropy of SMS pastes heated at 95 °C decreased in the following order: fructose>sucrose>glucose. The type of starch played a role in the time-dependent flow properties of the SMS paste, with a general conclusion that wheat starch had a greater degree of thixotropy than corn starch.     

Glycosylation of κ-casein: Genetic and nongenetic variation and effects on rennet coagulation properties of milk

The aims of this study were to investigate genetic and nongenetic variation in the degree of glycosylation of κ-casein (κ-CN) and to estimate the effects of glycosylated (G-κCN) and unglycosylated (U-κCN) κ-CN contents on milk coagulation properties of Simmental cows. Measures of contents of the main casein fractions, G-κCN, and U-κCN, and assessment of genotypes at CSN2, CSN3, and BLG were obtained by reversed-phase HPLC analysis of 2,015 individual milk samples. Content of total κ-CN (κ-CNtot, g/L) was the sum of G-κCN and U-κCN, and the glycosylation degree of κ-CN (GD) was measured as the ratio of G-κCN to κ-CNtot. Rennet coagulation time (RCT) and curd firmness were measured by using a computerized renneting meter. Measures of curd firmness were adjusted for RCT before statistical analysis. Variance components of κ-CNtot, G-κCN, U-κCN, and GD were estimated by Bayesian procedures and univariate linear models that included the class effects of the herd-test-day, parity, days in milk, genotypes at milk protein genes, and animal. These class effects, those of G-κCN, U-κCN, and content of other caseins, and the linear effect of milk pH were accounted for by models investigating the influence of κ-CN glycosylation on coagulation properties. The GD ranged from 22 to 76%, indicating that variation in G-κCN depends on the variation both in κ-CNtot and in the efficiency of κ-CN glycosylation. Genotype CSN3 BB exhibited high G-κCN and U-κCN relative to that of CSN3 AA. Heritability of G-κCN, U-κCN, and GD was high and ranged from 0.46 to 0.56. A large proportion of the additive genetic variation in G-κCN and U-κCN was attributable to influence of CSN and BLG, but these genes did not affect variation in GD, and across-genotypes differences in the trait were small or trivial. Average RCT of the milk class having the highest G-κCN was, on average, 2 min (standard deviation 0.5) shorter than that of the lowest class. Conversely, U-κCN and content of other caseins were not associated with any effect on RCT, except for a slight delay in coagulation when U-κCN was very high. Curd firmness increased when the contents of both κ-CN fractions and other caseins increased. This study provides evidence that the positive association between RCT and κ-CN content is exclusively attributable to the glycosylated fraction of the protein. Because exploitable additive genetic variation in G-κCN exists, improvement of κ-CN composition through selective breeding might be an effective way to enhance milk coagulation properties.     

Microstructure and elastic modulus of phase-separated gelatin–starch hydrogels containing dispersed oil droplets

The microstructure and elastic modulus (G′) of phase-separated gelatin + hydroxypropyl starch gels containing emulsified olive oil were investigated. Either droplet-type or bicontinuous gel morphologies were obtained depending on the initial placement (gelatin or starch) and proportion of added oil as well as the presence of polysorbate 20 dispersed in the oil. A gradual increase in oil content generally led to an increase in the volume fraction and microstructural interconnectivity of the oil-containing phase. However, addition of polysorbate 20 increased the tendency of the dispersed oil droplets to reside at the gelatin–starch periphery and potentially relocate to the phase initially lacking any oil. Compared to the control phase-separated gelatin–starch system, the largest increase in G′ was seen upon addition of oil to the gelatin phase of the phase-separated systems whereas the smallest rise occurred with polysorbate 20-containing oil added to the starch phase. This strongly indicated that the dispersed oil phase acted as an active filler within the phase-separated gel matrix. As each microstructure imparted its own rheological properties, these observations demonstrated the possibility of creating a diverse group of phase-separated emulsion gel microstructures with user-defined G′ values, depending on the proportion and initial location of the emulsified oil within the gel as well as the presence of a surfactant.     

Influence of vegetable and animal rennet on proteolysis during ripening in ewes’ milk cheese

The renewed interest in using enzymes from thistles of the genus Cynara in the making of traditional ewes’ milk cheese prompted us to investigate the effect of vegetable and animal rennet on proteolysis during ripening of Los Pedroches cheese. Casein hydrolysis was found to be much more extensive and faster in cheese made by using vegetable rennet (the amount of soluble nitrogen at 60, 80 and 100 days of ripening was more than 28% greater than that in cheese produced using animal rennet). The levels of insoluble Tyr and Trp were higher in cheese produced with vegetable rennet. PAGE, using gels containing 7 M urea, revealed decreased contents in residual α_s-CN and β-CN, as well as markedly increased levels of the more mobile components in cheese produced from vegetable rennet at the end of ripening. On the other hand, the degree of proteolysis in terms of NPN or its main components (peptides, amino acids and ammonia) was similar in cheese produced using animal or vegetable rennet.     

Thermal,mechanical and water adsorption properties of corn starch–carboxymethylcellulose/methylcellulose biodegradable films

The objective of this study was to investigate the effect of the addition of methylcellulose and carboxymethylcellulose on the thermal, mechanical and water adsorption properties of starch-based films plasticized with glycerol or polyethylene glycol (PEG). Mechanical tests showed that as the methylcellulose and carboxymethylcellulose proportion increased, starch films became more resistant to break, resulting in higher TS values. Besides there has been a positive effect on the elasticity of starch films realized by a considerable increase in E% values. Depending on the plasticizer type, either single or dual glass transitions were seen in DSC thermograms. One glass transition temperature was observed for films plasticized with glycerol, on the contrary, dual glass transitions were detected for PEG plasticized films. This behavior was attributed to the phase separation of the PEG. In addition, the presence of an endothermic peak in the thermograms of PEG plasticized films was taken as another indicator of the phase separation. As a result, it was suggested that PEG was not as compatible as glycerol with the composite polysaccharide matrix and plasticizer type was the main factor that shaped the thermal profiles of the film samples. Water adsorption isotherm data showed that samples displayed nonlinear sorption profile which is typical for hydrophilic films. In all films tested, equilibrium moisture contents, increased almost linearly up to a a_w of 0.65–0.85, beyond where a sharp increase was noted. Adsorption data was adequately fitted by BET and GAB models. Eventually, it can be concluded that film forming properties of starch can be improved by incorporation of methylcellulose and carboxymethylcellulose to the polymer matrix.     

Rheological and textural studies of fresh and freeze-thawed native sago starch–sugar gels. II. Comparisons with other starch sources and reheating effects

The viscoelastic and textural properties of freshly prepared and freeze-thawed sago starch–sugar gels were studied in comparison with other native starches from corn, wheat, tapioca, and potato. The gelatinisation and retrogradation properties of starches were studied using a DSC while the pasting properties of starch–sugar mixtures during the cooking period were studied using a starch pasting cell. The freeze-thaw stability of gels was evaluated by gravimetric measurements of the water of syneresis. The different starches gave properties which varied following to their botanical sources. High-amylose cereal starches (wheat and corn) produced harder gels, while low-amylose root starch (tapioca) produced softer gels. Sago and potato gels showed close similarities in their viscoelastic and textural characteristics. Although the freeze-thaw cycle greatly increased the viscoelasticity and hardness of these two gels, reheating at high temperature significantly reduced these negative effects and resulted in partial recovery of the gel structures. Sago starch produced gels with very low syneresis and high cohesiveness, implying its potential use as a gelling agent in the frozen food industries.     

Rheological properties of patatin gels compared with β-lactoglobulin, ovalbumin, and glycinin

BACKGROUND: The thermal unfolding and rheological properties of patatin gels were compared with those of commonly used proteins (β‐lactoglobulin, ovalbumin, glycinin). RESULTS: A significant difference between these proteins was observed in both the denaturation temperature (59 °C for patatin; about 20 °C lower than the other proteins) and the onset temperature of gel formation (50–60 °C, compared to 70–85 °C for the other proteins). At low ionic strength the minimal concentration was only 6% (w/v) for patatin, compared to 8–11% for the other proteins. This effect was attributed to the relatively high exposed hydrophobicity of patatin as determined by hydrophobic interaction chromatography. For gels compared at ‘iso‐strength’, the frequency dependence was found to be close to identical, while small differences were observed in the strain at fracture. CONCLUSIONS: Patatin was found to form gels with comparable small‐deformational rheological properties as typical food proteins. In addition, at concentrations where the elastic modulus was similar for all proteins, the frequency and strain dependence were also comparable. From this it is concluded that patatin is a promising protein to be used in food applications as a gelling agent. Copyright © 2010 Society of Chemical Industry     

Effect of the type of emulsifying salt on microstructure and rheological properties of "requeijão cremoso" processed cheese spreads

Abstract: The role of different types of emulsifying salts—sodium citrate (TSC), sodium hexametaphosphate (SHMP), sodium tripolyphosphate (STPP) and tetrasodium pyrophosphate (TSPP)—on microstructure and rheology of “requeijão cremoso” processed cheese was determined. The cheeses manufactured with TSC, TSPP, and STPP behaved like concentrated solutions, while the cheese manufactured with SHMP exhibited weak gel behavior and the lowest values for the phase angle (G”/G’). This means that SHMP cheese had the protein network with the largest amount of molecular interactions, which can be explained by its highest degree of fat emulsification. Rotational viscometry indicated that all the spreadable cheeses behaved like pseudoplastic fluids. The cheeses made with SHMP and TSPP presented low values for the flow behavior index, meaning that viscosity was more dependent on shear rate. Regarding the consistency index, TSPP cheese showed the highest value, which could be attributed to the combined effect of its high pH and homogeneous fat particle size distribution.     

Viscoelastic behavior and microstructure of aqueous mixtures of cross-linked waxy maize starch,whey protein isolate and κ-carrageenan

The viscoelasticity and microstructure of mixtures of cross-linked waxy maize starch (CH10), whey protein isolate (WPI) and κ-carrageenan (κC) at pH 7.0 with 100 mM NaCl were investigated by oscillatory rheometry and confocal laser scanning microscopy (CLSM). Mixtures were heated to 90 °C (1.5 °C/min), held for 10 min at this temperature and cooled. Within the range of concentrations studied, CH10 swollen granules reinforced WPI and κC networks. The mechanical behavior of the three-component mixtures was modified by different WPI concentrations, but κC governed the overall response due to its gelling ability. CLSM images of three-component mixtures showed particulate systems in which swollen starch granules are surrounded by κC and WPI. CH10 granules were immersed in a single phase and a separate phase of κC and WPI, for low and high concentrations of these components, respectively. Therefore, it is possible to obtain two- and three-phase mixtures.     

The effect of freeze–thaw cycles on microstructure and physicochemical properties of four starch gels

The effect of repeated freeze–thaw (FT) cycles (up to seven) on microstructure, thermal and textural properties of four starch gels from various botanical origins (gingko, Chinese water chestnut, potato and rice) was investigated and compared by scanning electronic microscope, differential scanning calorimetry and texture analyzer. The chemical composition and molecular structure of four starches were also examined. The Chinese water chestnut, potato and rice starch gels formed a honey-comb structure after 7 FT cycles, while gingko starch gel exhibited lamellar structure. The 7 FT cycles decreased the transition temperatures and enthalpies of four starches in comparison with each native starch, and the retrogradation percentage followed the order: rice > gingko > Chinese water chestnut > potato. The 7 FT cycles increased the hardness of all the evaluated starch gels and decreased springiness and cohesiveness. Results showed that the molecular structure of starches caused notable differences to the microstructure and textural properties of starch gels. The higher amount of longer branch chain (degree of polymerization (DP) > 18) might benefit the formation of the lamellar structure of gingko starch. The percentage of branch chains (DP 18–23) was negatively related with the springiness and cohesiveness of native starch gels, while the percentage of medium chains (DP 12–17) was positively related to the springiness of starch gels after 7 FT cycles.     

Effect of the incorporation of antioxidants on physicochemical and antioxidant properties of wheat starch–chitosan films

Blend edible films were prepared from wheat starch (WS) and chitosan (CH) with glycerol as plasticizer. Four active ingredients (antioxidants) were added, namely basil essential oil, thyme essential oil, citric acid and α-tocopherol. The starch:antioxidant mass ratio was 1:0.1. Prior to characterisation, the films were conditioned at 25 °C–53%RH as to their structural, mechanical, optical and barrier properties. The antioxidant capacity of the active ingredients was determined by means of a spectrophotometric method. The incorporation of antioxidants led to a heterogeneous film microstructure, mainly in those containing α-tocopherol, which affected the surface roughness. Yellowness was induced in films when α-tocopherol was added and no notable colour changes were observed in the other cases, although all the antioxidants increased the transparency of the films. Despite of the fact that the mechanical properties were barely affected by the incorporation of antioxidants, citric acid promoted an increase in the elastic modulus but a decrease in film stretchability. The water vapour barrier properties of the films were only slightly improved when citric acid and α-tocopherol were added, whereas the oxygen barrier properties were significantly improved in all cases. The greatest antioxidant capacity of the films was reported for films containing α-tocopherol, which exhibited the highest antioxidant power.     

Characteristics of wheat starch–pectin hydrolysate complexes by dry heat treatment

Food Science and Biotechnology - The objective of this study was to characterize dry heat-induced wheat starch–pectin hydrolysate (WST/PH) complexes to develop the retrogradation-retarded...     

Effects of heat moisture treatment on the structural,physicochemical and digestibility properties of potato starch–soybean peptide complexes

In this study, potato starch (PS) was complexed with soybean peptides (SPTs) with different molecular weights under heat moisture treatment (HMT) at different moisture contents. The results showed that PSSPT complexes formed under HMT were characterised by weaker and fuzzier polarised cross patterns, and more agglomerates. After HMT, higher gelatinisation temperatures and lower enthalpies were observed for PSSPT complexes. In particular, higher gelatinisation temperatures were observed when moisture levels were higher during HMT. Compared with physically mixed counterparts, the PSSPT complexes under HMT displayed higher pasting temperatures and lower swelling power, and peak viscosity. Higher moisture content during HMT led to a less thermodynamically stable B-polymorphic structure converting to a more stable A-type polymorph. Higher SDS content was found in the PSSPT complexes subjected to HMT with lower moisture content, while relatively higher RS content was associated with higher moisture content of HMT. These results could be attributed to restructuring of the amylose/amylopectin chains, the physical barrier of SPT and interactions between the negatively charged groups in PS and the side chains in SPT. This study will advance our understanding of food multicomponent interactions, as well as guidance for the application development of low-glycaemic index foods containing SDS and RS in the field of fine food processing.