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.     

Effect of autoclave–cooling cycles combined pullulanase on the physicochemical and structural properties of resistant starch from black Tartary buckwheat

A starch-rich portion is produced as a by-product of black Tartary buckwheat processing. The effect of enzymatic combined with autoclaving–cooling cycles (one, two, or three times) on the physicochemical and structural properties of black Tartary buckwheat type 3 resistant starch (BRS) was evaluated. The autoclaving–cooling cycles enhanced solubility and reduced swelling, with the BRS content increasing from 14.12% to 25.18%. The high crystallinity of the BRS reflected a high molecular order. However, increasing the number of autoclaving–cooling cycles did not result in higher BRS content. The highest BRS yield in the autoclaved starch samples was 25.18% after double-autoclaving–cooling cycles. Furthermore, the autoclaving–cooling cycles altered the crystalline structure of black Tartary buckwheat, and the subsequent crystallinity changed from 36.33% to 42.05% to 38.27%. Fourier-transform infrared spectroscopy shows that the number of cycles results in more efficient double-helical packing within the crystalline lamella. Principal component analysis showed that the autoclaving–cooling cycle treatment leads to significant changes in the molecular structure of resistant starch (RS). These results indicated that autoclaving–cooling cycles might be a feasible way for producing RS from black Tartary buckwheat starch with better structural stability to expand their application range.     

Nutrient composition and physicochemical properties of Indian medicinal rice – Njavara

Njavara, a medicinal rice, was assessed for its nutrient composition and physicochemical properties, in order to understand its therapeutic properties. Dehusked Njavara rice consisted of 73% carbohydrates, 9.5% protein, 2.5% fat, 1.4% ash and 1628 kJ per 100 g of energy. Physicochemical properties and nutritive components of dehusked rice of Njavara were evaluated and compared with two commonly consumed non-medicinal rice varieties – Jyothi (red coloured) and IR 64 (brown coloured). The carbohydrates, fats, apparent amylose equivalent, fatty acid profile and triglycerides of Njavara were comparable to Jyothi and IR 64. However, Njavara rice had 16.5% higher protein, and contained higher amounts of thiamine (27–32%), riboflavin (4–25%) and niacin (2–36%) compared to the other two rice varieties. The total dietary fibre content in Njavara was found to be 34–44% higher than that of Jyothi and IR 64. Significantly higher phosphorus, potassium, magnesium, sodium and calcium levels were found in Njavara rice, compared to the other two varieties. The cooking time of dehusked Jyothi and IR 64 varieties were found to be 30 min, while Njavara needed longer time to cook, (38 min). The cooked rice of Njavara was slimy in nature, probably due to the presence of non-starch polysaccharides.     

Influence of α-tocopherol on physicochemical properties of chitosan-based films

Chitosan has been exploited as a material for the development of edible films, and additionally can be used as a carrier of functional compounds such as α-tocopherol. The aim of this work was to evaluate the effects of the incorporation of α-tocopherol in chitosan-based films. FTIR and thermal analyses were performed and showed that the incorporation of α-tocopherol affects the chemical structure of chitosan-based films with the establishment of new chemical bonds and the decrease of crystallinity. Results also showed that the increase of α-tocopherol concentration promotes a decrease of water content (from 12.6 to 11.4%) of the films. The addition of α-tocopherol to chitosan films leads to a significant reduction (p < 0.05) of tensile strength from 34.06 to 16.24 MPa, and elongation-at-break from 53.84 to 23.12%. Film opacity values (ranging from 4.74 to 7.83%) increased when α-tocopherol was incorporated into the film. Antioxidant capacity of chitosan-based films was evaluated and was enhanced when α-tocopherol was present in the film matrix. Results showed that α-tocopherol can be successfully added to the chitosan films enhancing the final quality and shelf-life extension of food products.     

Effect of γ-irradiation on the physicochemical and sensory properties of cashew nuts (Anacardium occidentale L.)

The present study evaluated cashew nuts' quality as a function of γ-irradiation dose in order to determine dose levels causing minimal undesirable changes to the product. Physicochemical (colour, peroxide value, hexanal content, fatty acid composition, volatile compounds) and sensory (colour, texture, odor, taste) properties of cashew nuts were determined after irradiation at doses up to 7 kGy. Results showed a five-fold increase in peroxide value (PV) and a two-fold increase in hexanal content after irradiation at a dose of 7 kGy. Of the fatty acids determined, stearic acid concentration increased while oleic acid decreased with irradiation dose. PUFA were unaffected by irradiation. Volatile compounds such as aldehydes, ketones and alcohols increased after irradiation indicating enhanced lipid oxidation. Colour parameter a∗ increased (p < 0.05) at doses >3 kGy while colour parameters L∗ and b∗ remained unaffected by irradiation. Sensory analysis showed that cashew nuts remained organoleptically acceptable at doses <3 kGy.     

Fabrication and evaluation of physicochemical properties of probiotic edible film based on pectin–alginate–casein composite

The objective of this study was to develop a casein-based edible film for the entrapment of probiotic Enterococcus faecium Rp1. Casein, pectin, sodium alginate and glycerol were used to prepare the film. In this study, the physicochemical and morphological properties of casein-based edible film and its impact on the stability of probiotic were evaluated. Surface morphology and properties of the film were tested using a scanning electron microscope, fluorescence microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Probiotic-incorporated casein-based edible film showed significant improvement in the antimicrobial and antioxidant properties and enhanced the structural, optical and thermal properties. Furthermore, the film was found to be desirable to carry probiotics, with the viability of 10⁷ CFU mL⁻¹ rate up to 30 days of storage at 4 °C. Hence, the current study suggests a probiotic-incorporated casein-based edible film for active packaging of food products.     

Effect of γ-polyglutamate on the rheological properties and microstructure of tofu

The effects of γ-polyglutamates with different concentrations (0.1%, 0.15%, 0.2%) and molecular weights (high, medium, low) addition on the rheological properties, microstructure, and syneresis of tofu were studied. The addition of γ-polyglutamate increased the gelation time, and decreased the storage modulus (G′) and the loss modulus (G″) of tofu. The molecular weight and concentration of γ-polyglutamate effectively changed the rheological properties of tofu. The network of tofu without γ-polyglutamate addition was constructed by fine strands in a dense arrangement as seen by using scanning electron microscope. However, the addition of γ-polyglutamate reduced the thickness of the strands in tofu network. Tofu syneresis was also reduced by the addition of γ-polyglutamate. Increase the concentration of γ-polyglutamate significantly decreased the syneresis of tofu. This trend was more evident on the tofu with high molecular weight γ-polyglutamate.     

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.     

Ultrasonic effect on physicochemical and functional properties of α-lactalbumin

Ultrasound is the sound whose frequency is too high for humans to hear which is within the frequency range of 20 Hz-20 kHz, and the frequency of ultrasound is above 20 kHz. The aim of this study was to observe the effect of ultrasound and sonication on α-lactalbumin (α-LA) with a view to improving its physicochemical and functional properties. In this work both low-intensity ultrasound (500 kHz bath) and the high-intensity ultrasound (20 kHz probe and 40 kHz bath) were used. Ten per cent wt (g g⁻¹ dry matter) protein model suspensions of α-lactalbumin (α-LA) were treated with ultrasound probe (20 kHz for 15 and 30 min) and ultrasound baths (40 kHz and 500 kHz for 15 and 30 min).Changes in pH values, electrical conductivity, solubility measurements, foaming properties, as well as rheological and freezing-thawing properties have been examined. The protein fractions of α-lactalbumin were analyzed before and after ultrasound treatment by SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis).The result showed that pH did not change significantly upon ultrasound however conductivities increased significantly after 20 kHz sonication. Electrical conductivity decreased significantly for ultrasound treatments in baths at 40 kHz and 500 kHz for all samples. Solubility increased significantly for all samples at 20 kHz. Foam capacities and foam stabilities were improved after ultrasound treatments for both 20 kHz and 40 kHz treatments. Foaming properties were not improved for protein model suspensions for 500 kHz treatments. The molecular weight of the protein decreased significantly after ultrasound treatments both using a 20 kHz probe and 40 kHz bath. The flow behaviour of α-lactalbumin was observed to be shear-thickening after all treatments. Apparent viscosity data calculated with power law equation (R² = 0.983-0.999) have not been changed significantly after all treatments. A remarkable decrease of initial freezing point was obtained after 20 kHz treatments.     

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.     

Effect of homogenization conditions on properties of gelatin–olive oil composite films

Gelatin–olive oil composite films were prepared through emulsification to improve water barrier ability of gelatin-based films. The effects of homogenization conditions of film-forming dispersions (FFD) on lipid droplets distributions in the FFD and films were evaluated and compared. Some selected physical properties, e.g., water vapor permeability (WVP), microstructure of the films were also evaluated. The rotor–stator homogenizer provided a lower energy input and so the largest particles were observed in the related FFD and films. These films exhibited excellent water barrier ability, but poor mechanical resistance, extensibility and transparency. The microfluidizer provided the FFD with lower and narrower particle size distributions, promoting mechanical resistance, extensibility and transparency of the films. The physical properties of the emulsified films were dependent on the special microfluidization pressure or cycle used, e.g., the WVP of the films decreased upon increasing microfluidization pressure or cycle. The present results indicated that the microfluidizer can be used to modulate lipid droplets in the FFD, thus films’ properties.     

Effects of oxidative treatment on the physicochemical,rheological and functional properties of oat β-glucan

The objective of this work was promote oxidation of β-glucan from oat bran with hydrogen peroxide at different concentration levels (0.3%, 0.6% and 0.9% H₂O₂) and reaction times (30 and 60 min), and evaluate the physicochemical and functional properties of isedoxidised β-glucan with in-vitro tests. An increase in carbonyl and carboxyl groups and alterations in swelling power were verified in the oxidised β-glucan. The cholic acid binding capacity increased in the oxidised β-glucan; however, the fat binding capacity was not affected. After chemical digestion, the available glucose of the oxidised β-glucan was increased. Oxidation with hydrogen peroxide decreased the viscosity, hardness, adhesiveness and gumminess of the β-glucan gels. More studies are necessary to determine the effect of the oxidative treatment of β-glucan on its technological properties in food products, and biological properties should be examined with in-vivo studies.     

Effect of underwater high-current discharge on the properties of low-concentration β-lactoglobulin solutions

Solutions of 0.5–2 mg/ml β-lactoglobulin (β-LG) at pH 7.0 were treated with underwater high-current discharges (UHCD) using a bench top system constructed in our laboratory. The short time duration of the UHCD (less than 3 μs) and the high energy delivered to the discharge (∼800 J) produced strong shock waves, in a microsecond time scale, as well as a powerful flash of light with a broad spectrum, ranging from soft X-rays to IR. Structural changes in β-LG were evaluated using hydrophobicity fluorescence of the β-LG molecule, differential scanning calorimetry, reactivity of the free thiol group to Ellman's reagent, small angle X-ray scattering (SAXS) and circular dichroism (CD). The results indicated that the application of the UHCD to β-LG leads to the increase of its surface hydrophobicity by approximately 40%. The enthalpy (ΔH_UHCD) of UHCD treated samples decreased as much as 40% compared to the enthalpy (ΔH_native) of native untreated proteins, indicating extensive but incomplete unfolding of the protein structure with no aggregation. It was found that no refolding occurred after the UHCD treatment. Also, it was shown that the reactivity of the free thiol group of UHCD treated samples increased 10-fold. Tryptophan residues in β-LG were markedly modified, as observed by UV absorption, indicating a change in its position. CD spectra indicated slight modifications in both secondary and tertiary structure.     

Effect of high pressure homogenization (HPH) on the rheological properties of tomato juice: Viscoelastic properties and the Cox–Merz rule

High pressure homogenization (HPH) is a non-thermal technology which has been widely studied as a partial or total substitute for the thermal processing of food. Although microbial inactivation has been widely studied, there are only a few papers in the literature reporting on physicochemical changes in fruit products due to HPH, especially regarding their rheological properties. The present work evaluated the effect of HPH (up to 150 MPa) on the viscoelastic properties of tomato juice. HPH increased the tomato juice storage (G′) and loss (G″) moduli. The parameters G′ and G″ were modelled as a power function of the oscillatory frequency (ω), and then evaluated as a function of homogenization pressure. It was observed that HPH processing improved tomato juice consistency more than it modified its nature/behaviour. The changes observed in the viscoelastic properties were attributed to disruption of the suspended particles during processing. Moreover, two modified Cox–Merz rules were used to correlate the products steady-state shear properties with viscoelasticity. The results obtained indicated that this process could be used to improve both product elastic and viscous behaviour, highlighting possible applications of the HPH process as a valuable tool to promote physical property changes in food products.     

Effect of frozen storage and freeze–thaw cycles on the rheological and baking properties of frozen doughs

The effects of prolonged frozen storage and repeated partial freeze–thaw cycles on the rheological and baking properties of nine commercial wheat cultivars were evaluated. The gluten strength of the cultivars ranged from medium to high, whereas the starch swelling characteristics were similar for most cultivars, except Parshall, which exhibited exceptionally high swelling properties. The doughs were subjected to frozen storage for 4–12 weeks, with and without freeze–thaw cycles. The enthalpy of freezable water was significantly affected by initial freezing, whereas, the rheological properties of the doughs were more susceptible to freeze–thaw cycles. After baking, all cultivars produced bread of acceptable quality, although cv. Parshall exhibited the highest crumb softness, irrespective of the frozen treatment. Results indicate that flours with high starch swelling characteristics, along with moderately high gluten strength, may be most ideal for producing optimum quality frozen doughs, with good shelf life and baking properties.     

Effects of pH on the stress–strain properties of wool fabric

In wool dyeing and finishing processes, fabric is often treated under conditions of different pHs and is subjected to a variety of physical and chemical environments. This work investigates fabric tensile properties at three different fabric pHs. Wool fabric extensibility under a 5 N/cm load was observed to be greatest at the wool isoelectric point of pH 4.8 and lower at both pH 2.1 and pH 7.2. The impact of pH on fabric extensibility was found to be similar to the variation in fabric hygral expansion previously observed. Fabric stress–strain curves at different pHs showed that for a given fabric extension level, the work required to stretch a fabric was less at pH 2.1 than at pH 4.8. These results suggest that the strength of wool fabric is at maximum when the pH of the fibres is close to the wool isoelectric point and that for consistency, the pH of fabric should be adjusted before standard strength tests are carried out.     

Effect of Premna microphylla turcz leaves’ extract addition on physicochemical and antioxidant properties of packed tofu by lactic fermentation

In the present study, Premna microphylla turcz leaves (PMTLs) containing rich pectin and isoflavones were introduced to prepare packed tofu coagulated by lactic fermentation, in order to promote its physicochemical and functional properties. Results showed that the final storage (G′) moduli of packed tofu added with PMTL extracts range from 195.2 ± 5.6 Pa to 420.6 ± 10.3 Pa, which were significantly higher (P < 0.05) than the control (PMTL-free, 99.5 ± 8.3 Pa). The hardness, gumminess and chewiness of packed tofu added with 0.8% (w/w) PMTL extracts were 1.43–1.49 times higher than the control without decreasing its water-holding capacity and exhibited the highest scores of overall acceptability, which was recommended as the most acceptable concentration. The total phenolic and flavonoid contents of 0.8%-PMTL supplementation in packed tofu were 1.20 and 1.65 times higher than the control and showed enhanced antioxidant properties in DPPH radical-scavenging capacity, FRAP and RP.