Hsian-tsao Leaf Research Articles

Effect of Tapioca Starch/Decolorized Hsian-tsao Leaf Gum-Based Active Coatings on the Qualities of Fresh-Cut Apples

The effect of tapioca starch/decolorized hsian-tsao leaf gum (dHG)-based edible coatings with various food additives (including ascorbic acid, calcium chloride, and cinnamon oil) on the qualities and shelf life of fresh-cut “Fuji” apple pieces was investigated during the refrigerated storage. The initial respiration rate, headspace gas composition, color, texture, microbial quality, peroxidase activity, and sensory qualities were analyzed. The results were also compared to those for samples submerged in distilled water and the samples treated with 120-ppm chlorine solution widely used in the industry. It was found that ascorbic acid and cinnamon oil delayed the browning of fresh-cut apples effectively when being applied in the starch/dHG-based edible coating solutions. In combination with calcium chloride, starch/dHG coated fresh-cut apples retained satisfactory firmness. Incorporation of cinnamon oil in starch/dHG coatings significantly reduced the growth of microorganisms, respiration rate, CO2, and ethylene production of fresh-cut apples, but these apple pieces received lower scores in overall preference during sensory evaluation. Among the starch/dHG-based active coatings studied, starch/dHG coatings with ascorbic acid and calcium chloride are suggested for fresh-cut apples, as they could enhance qualities in terms of color and firmness, and prolong the shelf life up to 5–7 days by providing reasonable microbial quality.

Development of Tapioca Starch/Decolorized Hsian-Tsao Leaf Gum-Based Antimicrobial Films: Physical Characterization and Evaluation Against Listeria monocytogenes

The physical properties and antimicrobial activities against Listeria monocytogenes of the tapioca starch/decolorized hsian-tsao leaf gum (the polysaccharide gum extracted from hsian-tsao herb followed by removing the color matters, abbreviated as dHG hereafter)-based films incorporated with potassium sorbate (KS) or the ethanolic extract of thyme (TH) were investigated. It was found that the cross-sectional microstructure of starch/dHG films with KS showed some rough texture, and films with TH showed a relatively smooth microstructure with dispersed microparticles. The equilibrium moisture content and water vapor permeability of starch/dHG films with 20 % KS (based on the weight of starch/dHG) was higher than the others tested, possibly due to the plasticizing effect of KS. In general, the tensile strength and tensile modulus decreased with increasing antibacterial concentration. As compared with the KS solutions, the TH solutions showed a pronounced antimicrobial activity against L. monocytogenes as determined by the inhibition zone test. However, the antimicrobial migration of both KS and TH in the starch/dHG matrix was limited to a certain extent, as evidenced by the significantly lower antimicrobial activity in the film system. When applying the starch/dHG films with antimicrobials to the fresh beef slices, all samples showed detectable improvement against the growth of L. monocytogenes, implying that starch/dHG films incorporated with TH or KS were effective against L. monocytogenes in conjunction with some modification of the physical properties due to the interactions between the antimicrobials and the components of film matrix.

Effects of Tapioca Starch/Decolorized Hsian-Tsao Leaf Gum-Based Active Coatings on the Quality of Minimally Processed Carrots

Edible coatings made from tapioca starch/decolorized hsian-tsao leaf gum (dHG) containing cinnamon essential oil or grape seed extract (GSE) were developed and applied to minimally processed carrots. Coatings based on 0.3% dHG and 1.7% tapioca starch were prepared and incorporated with 0.1–0.3% cinnamon oil or 0.3–0.6% GSE as antimicrobial agents. Fresh-cut carrots were immersed into coating solutions, placed in expanded polystyrene trays, and sealed in polypropylene bag. Changes in the initial respiration rate, the headspace atmosphere, color, microbial growth, and sensory evaluation were then measured. During refrigeration, the initial respiration rates for carrots with various coating treatments slightly increased as compared to the control group carrots, and the coatings with cinnamon oil showed the highest rates. Headspace analysis revealed that coated samples also had higher CO2 and lower O2 concentrations, which were consistent with the initial respiration rate results. Though samples coated with the antimicrobial solutions (cinnamon oil or GSE) did not show advantages in reducing microbial growth as compared to the control group carrots, they presented better acceptance during the sensory evaluations. The use of edible coatings successfully maintained the surface appearance and retarded the formation of “white blush” on the surface of carrots during refrigeration. While the visual appearance quality of minimally processed carrots was significantly improved by the coating treatments, the microbial growth was the same or even worse in some cases. Based on the pronounced improvements of the carrots’ appearance and the comparable microbial control, the plain starch/dHG coating without cinnamon oil or GSE was recommended for extending the shelf life of minimally processed carrots.

Antimicrobial activities of tapioca starch/decolorized hsian-tsao leaf gum coatings containing green tea extracts in fruit-based salads, romaine hearts and pork slices

The antimicrobial activities of edible coatings based on a tapioca starch/decolorized hsian-tsao leaf gum (dHG) matrix with various green tea extracts (GTEs) were evaluated. Its effect on the shelf-life extension of fruit-based salads, romaine hearts, and pork slices were investigated as well. Three types of GTEs from hot water (80 °C) (W), 40% (E4) and 80% (E8) ethanol were prepared. It was found that all GTEs showed pronounced inhibition on Gram positive bacteria in agar media, including Staphylococcus aureus BCRC 10781, Bacillus cereus BCRC 11778 and Listeria monocytogenes BCRC 14848, but not on Gram negative bacteria, such as Escherichia coli DH10β and Salmonella enteria BCRC 10747. The antimicrobial activities increased with increasing GTEs concentration (1, 2 and 5%), but did not differentiate significantly in terms of the effect of extraction solvents. When various GTEs (1%) were added to an edible coating formulation based on 1.35% tapioca starch + 0.15% dHG + 0.225% glycerol, pronounced antimicrobial activity on Gram positive bacteria was also observed as evaluated by using cylinder diffusion and antimicrobial migration tests. It was believed that the active compounds in green tea extracts could leave the coating matrix and migrate to increase the non-growth area. When being sprayed on various real food models, all tapioca starch/dHG coatings containing GTEs could successfully reduce the aerobic counting and growth of yeasts/molds by 1 to 2 log cycles in fruit-based salads, as compared to the control sample. Furthermore, during refrigerated storage of romaine hearts and pork slices for 48 h, tapioca starch/dHG coatings with E4 extracts demonstrated pronounced antimicrobial activity against Gram positive bacteria (4–6 log cycles reduction), followed by W extracts and E8 extracts in a decreasing order. Such results implied the high efficacy of antimicrobial migration of tapioca starch/dHG coatings containing GTEs and their application potentials on foods.

Water barrier and physical properties of starch/decolorized hsian-tsao leaf gum films: Impact of surfactant lamination

The moisture barrier and physical properties of bilayer films prepared by lamination of starch/decolorized hsian-tsao leaf gum (dHG) and surfactant layers were investigated. It was found that the water vapor permeability (WVP) of tapioca starch/dHG film (1.31 × 10 −10 g/m s Pa) pronouncedly decreased by the aid of a surfactant layer lamination (1.36–5.25 × 10 −12 g/m s Pa). The WVP of bilayer film increased with increasing the concentration of starch/dHG in the surfactant layer, but was not significantly influenced when it was thickened. The sorption isotherms of both monolayer and bilayer films made from starch/dHG showed typical behavior of water-vapor-sensitive hydrophilic biopolymers. However, the equilibrium moisture content of the monolayer film was significantly higher than that of bilayer films when water activity ( a w) reaches 0.33. Both the tensile and puncture force of starch/dHG films did not vary significantly by laminating a surfactant layer, indicating the mechanical strength of surfactant layer is relatively weak, and this surfactant layer mainly served as a barrier for moisture. When compared to emulsion-based starch/dHG films with surfactant, the surfactant laminated starch/dHG films showed higher water barrier property, mechanical strength, and transparency.

Rheological and physical characterization of film-forming solutions and edible films from tapioca starch/decolorized hsian-tsao leaf gum

Rheological properties of the film-forming solutions of tapioca starch/decolorized hsian-tsao leaf gum (dHG) as well as the structural properties and viscoelasticity of the resulting films were characterized as a function of dHG and glycerol concentrations. As compared to film-forming solutions with tapioca starch alone, the apparent viscosity, storage modulus and loss modulus of starch/dHG film-forming solutions increased, and tan δ decreased with increasing dHG. After casting of the film-forming solutions, all starch/dHG films showed relatively low opacity values. SEM and X-ray diffraction analysis revealed that all starch/dHG films exhibited homogeneous and highly amorphous structure. The extensional creep compliance of starch/dHG films increased with increasing glycerol concentration, implying weaker mechanical strength and higher mobility of polymer chains by the plasticizing effect of glycerol. However, addition of dHG pronouncedly increased the mechanical and elastic properties of tapioca starch films as evidenced by a decrease in extensional creep compliance and retardation time. Such results implied that dHG may possibly modify the network structure of tapioca starch film.

Effect of surfactants on water barrier and physical properties of tapioca starch/decolorized hsian-tsao leaf gum films

The objective of this research is to enhance the water barrier properties of tapioca starch/dHG edible films by incorporating sucrose ester surfactants with different HLB values. The moisture sorption isotherms, mechanical properties, microstructure and optical character of the resulting films were examined as well. It was found that the water barrier property of starch/dHG films is promoted significantly by surfactants, alongside a decreasing tendency in tensile strength and tensile strain at break. Scanning electron micrographs of the starch/dHG/surfactant composite films revealed the folded (multi-layer) microstructure in contrast to the homogeneous matrix of the control films. Starch/dHG/surfactant composite films show low opacity values. With increasing HLB value of the surfactant, the water vapor permeability and tensile strength of starch/dHG/surfactant composite films decrease. Moreover, the water vapor permeability, tensile strength, strain at break, and equilibrium moisture content of starch/dHG/surfactant composite films decrease when the surfactant content is increased, accompanied by an increasing tendency in opacity value. On the other hand, starch/dHG composite film with an emulsion of surfactant and beeswax shows a lower mechanical strength and significantly higher opacity value with less improvement in water vapor permeability.

Mechanical and water vapor barrier properties of tapioca starch/decolorized hsian-tsao leaf gum films in the presence of plasticizer

The objectives of this research were to examine the mechanical and water vapor barrier properties of the starch/decolorized hsian-tsao leaf gum (dHG) films as a function of dHG and glycerol concentration. Edible film-forming solutions were prepared by mixing tapioca starch with dHG at different starch/dHG ratios to make a total solid content of 2%. In total, 15–40% glycerol was then added based on the dry film matter. Starch/dHG films were obtained by casting. It was found that the puncture strength, tensile strength, and modulus as well as the inverse of relaxation coefficient of starch/dHG films pronouncedly increased with increasing dHG, accompanied with a decreasing tendency in puncture deformation and tensile strain at break. Such results implied that starch interacted with dHG synergistically, resulting in the formation of a new network to improve the mechanical properties of tapioca starch/dHG films. Mechanical strengths of starch/dHG films decreased and water vapor permeability (WVP) at 75% RH increased with increasing glycerol concentration. However, the plasticizing effect of glycerol became less significant at high dHG concentration, particularly for the puncture deformation and tensile strain at break of the films. Water sorption isotherm results indicated that significant water sorption would only occur at high water activity (about 0.75), and generally became more pronounced with increasing glycerol and dHG concentration, but to a lesser extent for the latter. Dynamic mechanical analysis revealed that the major glass transition of starch/dHG films occurred at about −50 °C.

Rheology of decolorized hsian-tsao leaf gum in the dilute domain

The polysaccharide extract of hsian-tsao leaves was treated with active carbon. Decolorized hsian-tsao leaf gum (dHG) solutions were then evaluated for their rheological properties as a function of concentration, ionic strength and ion types by using a glass capillary viscometer and dynamic rheometer. It was found that the weight average molecular weight of dHG in 0.1 M sodium chloride solution was about 550,000, with a Mark–Houwink constant and exponent of 9.32×10 −6 ml/ g and 0.29, respectively, indicating a less extended conformation. The specific viscosity of dHG exhibited a power-law dependence on concentration. The exponent b ranged from 0.78 to 0.80 in the dilute domain and from 1.67 to 1.71 in the semi-dilute domain. The coil overlap parameter of the dHG was found to be in the range of 13.32–13.42. The hydrodynamic behavior of dHG was strongly affected by ion types and ionic strength. The chain stiffness parameter of dHG was lower than that of several polysaccharides, indicating the stiff backbone of dHG. Dynamic rheological results indicated that the storage and loss modulus of dHG decreased with increasing sodium, potassium or magnesium ion concentrations, but increased with increasing calcium ion concentrations. The dHG solutions can be classified rheologically as those of dilute or concentrated solutions or weak gels, depending on the types and concentrations of ions presented.

Studies on the antioxidative activities of Hsian-tsao (Mesona procumbens Hemsl) leaf gum.

This study aimed at evaluating the antioxidative activity of crude hsian-tsao leaf gum extracted by sodium bicarbonate solutions and precipitated by 70% ethanol. The antioxidative activities, including the radical-scavenging effects, Fe(2+)-chelating ability, and reducing power as well as the inhibition of FeSO(4)-H(2)O(2)-induced malondialdehyde formation in rat tissue homogenate were studied in vitro. It was found that the antioxidative effect provided by hsian-tsao leaf gum was strongly concentration dependent. In general, the antioxidative activity increased with increasing gum concentration, to a certain extent, and then leveled off with further increase in gum concentration. A concentrtaion-dependent kinetics for the rate of change in antioxidative activity was proposed. The antioxidative activity constant (k) and the half-inhibition concentration (IC(50)) for each antioxidative reaction studied were calculated. From a comparison of the IC(50) values for different antioxidative reactions, it seemed that hsian-tsao leaf gum was more effective in scavenging superoxide radicals than chelating Fe(2+) or scavenging alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) radicals. As compared to the commercial antioxidants, hsian-tsao leaf gum showed less scavenging effect on the DPPH radical and reducing power but better superoxide radical-scavenging effect and Fe(2+)-chelating ability than alpha-tocopherol and BHT.

Effects of Salts on the Thermal Reversibility of Starch and Hsian-tsao (Mesona procumbens Hemsl) Leaf Gum Mixed System

ABSTRACT: Two-cycle rapid-visco analysis was performed on the admixture of 1% hsian-tsao leaf gum and 2% wheat starch as a function of salt types and concentrations. The salt concentrations (Cs) studied were 5 to 75 mM for sodium and potassium chloride, and 3.4 to 8.5 mM for calcium and magnesium chloride. The gelling temperature, gelling rate and gel viscosity of the mixed system increased with increasing Cs. In addition, the melting temperature increased, but melting rate and percentage of viscosity loss decreased with increasing Cs. These results indicated the presence of appropriate amount of salts could facilitate and reinforce the formation of junction zones, and provided a more pronounced thermal resistance.

A DSC study on the gel-sol transition of a starch and hsian-tsao leaf gum mixed system.

Differential scanning calorimetric analysis was performed on the admixture of 4% hsian-tsao leaf gum and 8% wheat starch as a function of salt types and concentrations. The salt concentrations (C(s)) studied were 5-100 mM for sodium and potassium chloride, and 3.4-34 mM for calcium and magnesium chloride. It was found that hsian-tsao leaf gum or starch alone did not present a readily recognizable exothermic peak or endothermic peak during cooling or heating in DSC. However, mixing these two polymers promoted the intermolecular binding and subsequent gelation of the mixtures as evidenced by the DSC exothermic and endothermic peaks during cooling and heating, respectively. The setting and melting temperatures of such a mixed system shifted progressively to higher temperatures with increasing concentrations of added salts. It was considered that the aggregated mixed polymers formed thermally stable junction zones with higher binding energies. The thermal behavior change was more remarkable by the addition of K(+) than by Na(+), and by Ca(2+) than by Mg(2+). For monovalent cations, the DSC heating and cooling curves showed a single endothermic and exothermic peak. For divalent cations at low concentration, the DSC curves showed a single peak. However, with sufficient divalent cations, the DSC curves eventually developed a bimodal character. A mixed system with sufficient Ca(2+) could form firm gel that was difficult to remelt completely upon heating to 130 degrees C, indicating the possibility of the formation of ionic bonds through cross-links with the carboxyl groups in hsian-tsao leaf gum.

Solution properties of hsian-tsao ( Mesona procumbens Hemsl) leaf gum

In order to characterize the coil overlap parameters of hsian-tsao leaf gum, the specific viscosity of the hsian-tsao leaf gum was measured as a function of pretreatment and concentration using a glass capillary viscometer. It was found that the onset of molecular entanglements varied with pretreatment, which occurred at a concentration around 1.0 g/dl for hsian-tsao leaf gum extracted from fresh or frozen hsian-tsao leaf, and around 3.5 g/dl for hsian-tsao leaf gum extracted from dehydrated hsian-tsao leaf. The specific viscosity of hsian-tsao leaf gum exhibited a power-law dependence on concentration. The exponent b ranged from 1.25 to 1.43 in the dilute domain and from 2.21 to 2.93 in the semi-dilute domain, depending on the pretreatment. The coil overlap parameter of the hsian-tsao leaf gum was found to be in the range of 1.79–2.17, which was closer to that of a rod-like polymer. The effects of ionic strength and ion types on the viscosity of the hsian-tsao leaf gum in the dilute regime were also measured. The extent of the ionic strength dependence of intrinsic viscosity was used to characterize the salt tolerance and chain stiffness parameters. It was found that the chain stiffness parameter of the hsian-tsao leaf gum was in the range of 0.026–0.03, which was lower than that of several polysaccharides, indicating the stiff backbone of the hsian-tsao leaf gum.