Macromolecular Changes in Extruded Starch‐Films Plasticized with Glycerol,Water and Stearic Acid

Native corn starch, plasticized with water, glycerol and stearic acid, was extruded in a conical twin‐screw extruder and sheeted into 0.4–0.6 mm thick films. The effects of extrusion and plasticizers on gelatinization, as well as the molecular and structural changes, in thermoplastic starch were analyzed. The onset and peak gelatinization temperatures of extruded starch varied from 42–46°C and 52.9–56.9°C, respectively, depending on the glycerol content. The enthalpy of gelatinization of extruded thermoplastic starch in excess water varied from 3.6–7.6 J/g, which also increased with plasticizer content. Amylose‐lipid complexes were formed during extrusion, and their enthalpies depended on the initial stearic acid and moisture contents. High‐performance size‐exclusion chromatography (HPSEC) data revealed that the starch underwent fragmentation during extrusion even under highly plasticized conditions, but the degradation was not severe as compared to previous findings. The relative percentages of amylopectin and amylose in native starch were 76.9 and 23.1%, respectively, which were changed to 71.3–76.6% and 23.4–28.7% in the extrudates. The average molecular weights of amylopectin and amylose in the extrudates ranged from 1.55×10⁷–2.07×10⁷ and 4.35×10⁵–7.39×10⁵, respectively. On the other hand, the molecular weights of amylopectin and amylose in native corn starch were observed as 2.27×10⁷ and 4.68×10⁵, respectively. Cross‐polarization magical angle spinning (CP/MAS) and high‐power decoupling (HP‐DEC) nuclear magnetic resonance (NMR) spectra of thermoplastic starch revealed the characteristics of amylomaize starch, confirming HPSEC results that the amylopectin macromolecules underwent fragmentation into amylose‐like fractions. In the extrudates, glycerol was found to be less mobile and entrained within the starch network.     

Developing Biodegradable Mulch Films from Starch‐Based Polymers

This paper examines the development of starch‐based plastics for use as biodegradable mulch film. A variety of starch‐based polymers are blended with high performance biodegradable polyester polymers in order to determine the applicability of films to be processed on a film blowing line and to perform well in mulch film field trials. The process of material formulation, film blowing processing and scale‐up and performance properties are highlighted for a successful material. Insights into future developments of starch‐derived biodegradable polymers are given.     

Aging Effects on Sorbitol‐ and Non‐Crystallizing Sorbitol‐Plasticized Tapioca Starch Films

The effect of aging on the properties of tapioca starch films plasticized with either sorbitol (S) or non‐crystallizing sorbitol (NCS) was investigated in this study. Tapioca starch, plasticizer and deionized water were mixed, heated, cast on high‐density polyethylene plates and dried at ambient conditions. The results showed that S was more effective in plasticizing fresh starch film than NCS. However, sorbitol crystallization was observed in S‐plasticized starch film after one month of storage, while there was no crystallization observed in NCS‐plasticized starch film after two months of storage. Mechanical properties of both S‐ and NCS‐plasticized starch films changed significantly with time, but with less change in the NCS‐plasticized films. Tensile strength, elastic modulus and toughness increased over time; conversely, elongation decreased. Additionally, the water vapor transmission rate decreased as storage time increased. The fact that mechanical properties of both S‐ and NCS‐plasticized films changed is likely due to an increase in crystallinity of the starch in the films with time.     

Synthesis and Preparation of Crosslinked Allylglycidyl Ether‐Modified Starch‐Wood Fibre Composites

Native potato starch has been modified with allylglycidyl ether (AGE) under various reaction conditions including different sodium hydroxide and AGE concentrations, reaction temperatures and times. ¹H‐NMR and FT‐IR were used to analyze the products. AGE‐modified starch, with two degrees of substitution (DS), namely DS = 1.3 and DS = 2.3, was synthesized and used for preparation of a new family of crosslinked composites reinforced with various amounts of bleached softwood fibres. Composite premixes of modified starch, wood fibres and ethylene glycol dimethacrylate (EGDA) were cured in a hot press using 2% (w/w) of benzoyl peroxide at 150°C under high pressure for 10 min. The matrix with high degree of substitution exhibited good processability and was easily processed even for the highest fibre contents, up to 70% (w/w). In addition, scanning electron micrographs showed good dispersion and adhesion between the starch matrix with high degree of substitution and fibre. The original poor mechanical properties of the cured modified starch were markedly improved by the addition of wood fibres. In the extractions tests cured high‐DS and low‐DS composite samples showed weight losses in the range of 1 and 15% (w/w), respectively. No unreacted crosslinker ethylene glycol dimethacrylate was detected in the solutes as determined by NMR.     

Response Surface Methodology for the Optimization and Characterization of Cassava Starch‐graft‐Poly(acrylamide)

Response surface methodology (RSM) was employed for the synthesis of cassava starch‐graft‐poly(acrylamide) using ceric ammonium nitrate as free radical initiator. Concentration of acrylamide, concentration of ceric ammonium nitrate, reaction temperature and duration of reaction were optimized using a 4‐factor 3‐level Box‐Behnken design. The dependent variables were percentage grafting (%G) and grafting efficiency (GE). Second order polynomial relationships were obtained for %G and GE, which explained the main, quadratic and interaction effects of factors. The highest%G and GE obtained were 174.8% and 90.7%, respectively. The optimum values of parameters predicted through RSM were 20 g acrylamide/10 g dry starch, 3.3 g/L ceric ammonium nitrate, 180 min reaction duration and 45ºC temperature with a %G of 190.0. For GE, the predicted levels of factors for the optimum value of 90.8% were 17.5 g acrylamide/10 g dry starch, 4.1 g/L ceric ammonium nitrate, 180 min reaction duration and 55ºC temperature. The graft reaction was confirmed by FTIR analysis, where the absorption bands corresponding to the C=O stretching and N‐H bending of the –CONH₂ group were observed. Scanning electron microscopic studies on grafted starches revealed that the granular structure of the starch was affected by the reaction. X‐ray diffraction analysis showed that the crystallinity of starch was decreased as a result of grafting and the reduction was higher for the grafted starches with higher percentage grafting.     

Thermal and Molecular Characterization of Aspergillus awamori Glucoamylase Catalytic and Starch‐Binding Domains

Aspergillus awamori glucoamylase catalytic domain, linker, and starch‐binding domain, the first and third expressed from yeast, have molecular masses of 56.2, 12.6 and 12.9 kDa, respectively, as determined by MALDI‐TOF mass spectroscopy, and have 10.2, 73.2 and 7.0 % (w/w) carbohydrate, respectively, showing overglycosylation by yeast. Unfolding of the starch‐binding domain monitored by circular dichroism is reversible at pH 6.0—8.0, with the unfolding T_m and ΔH increasing from 49.7 to 58.5 °C and from 284 to 351 kJ/mol, respectively, as pH decreases from 8.0 to 6.0. The catalytic domain unfolds irreversibly at pH 7.5, producing a single asymmetric endotherm by differential scanning calorimetry, with T_m and ΔH at a 1 °C/min heating rate being 60.9 °C and 1720 kJ/mol, but with both increasing as the heating rate increases. This suggests that unfolding is partially under kinetic control, while various tests show that it does not follow a simple two‐state irreversible model. Values of ΔH from calculated solvent‐accessible surface areas of unglycosylated catalytic and starch‐binding domains are about 100 kJ/mol lower than experimentally determined ΔH values of the corresponding glycosylated domains, showing the effect of glycosylation on unfolding enthalpies.     

Production and Properties of Spin‐Coated Cassava‐Starch‐Glycerol‐Beeswax Films

Cassava‐starch based polymer films containing glycerol as a plasticizer (1.0‐2.5‐5.0%, w/w) and different lipids as additives (paraffin, stearyl alcohol, and beeswax – 0.25‐0.5‐1.0%, w/w) were produced. Control films were produced by heating a mixture of glycerol, starch, and water, while treated films were produced by the addition of lipids/ ethanol solutions. The solutions were kept at around 70ºC during amalgamation, and once congealed, were placed in a vacuum oven for 1 h at 90ºC. The solutions were then spun on 7‐inch diameter non‐stick disks, allowed to dry, and conditioned at 23ºC and 50% RH before testing. Cassava starch‐glycerol‐beeswax films were successfully produced with a stable film structure at glycerol concentration equal or below 5% (w/w). Addition of glycerol and beeswax did not visually change the color of the films. Increasing glycerol content improved elongation while decreasing tensile strength. Increasing the glycerol concentration from 1.0 to 5.0% increased the water vapor permeability by 150% and addition of beeswax further increased these values by 250%.     

Viscoelastic, Thermal, and Microstructural Characterization of Soy Protein Isolate Films

ABSTRACT: Viscoelastic, thermal, and microstructural properties of plasticized soy protein isolate (SPI) films processed by thermal compaction are discussed. Thermogravimetric analysis indicates that protein films exhibit substantial thermal degradation at temperatures above 180 °C and that the processing temperature limit is about 150 °C. Dynamic mechanical analysis indicates the existence of multiple glass transition temperatures associated with glycerol- and protein-rich phases. Scanning electron micrographs of the cross-sections of films containing 30 and 40 wt% glycerol indicate the presence of ridges and valleys resulting from an extensive local deformation of the "protein matrix," which explains the large flexibility of these films as compared to those containing only 20 wt% plasticizer.     

Development and Characterization of Edible Films Based on Fruit and Vegetable Residues

Edible films were developed from the solid residue of the processing of whole fruits and vegetables. The solid residue, processed into flour (FVR flour) was chemically and structurally characterized by microstructure, elemental composition, structural links, and moisture sorption isotherm. Films were prepared by casting using aqueous extracts of 8% and 10% of flour (w/w) and characterized in terms of thickness, water solubility, mechanical properties, water vapor permeability, and Fourier transform infrared (FTIR). The analysis of microstructure and elemental composition, performed on flour (mean particle size 350 μm), showed an essentially granular aspect, with the presence of fibrous particles having potassium as one of the most abundant elements. FTIR results showed similarity between the characteristic bands of other raw materials used in edible films. The sorption isotherm of FVR flour showed a typical profile of foods rich in soluble components, such as sugars. Dried films presented an average thickness of 0.263 ± 0.003 mm, a homogenous aspect, bright yellow color, pronounced fruit flavor, and high water solubility. The FTIR spectra of the edible films revealed that addition of potato skin flour did not change the molecular conformation. Moreover, the films presented low tensile strength at break when compared with fruit starch‐based films.     

Physical Properties of Gelatin Films Plasticized by Blends of Glycerol and Sorbitol

ABSTRACT: The addition of plasticizers increases the flexibility and workability of films based on biopolymers. However, the use of some plasticizers cause undesirable results, such as the migration of these additives out the film or crystallization during shelf life. Thus, the aim of this study was to evaluate the effect of blends with different ratios of sorbitol and glycerol, at 2 plasticizer concentrations, on mechanical, viscoelastic, and water vapor barrier properties of films based on gelatin. The films were prepared with 2 g gelatin/100 mL of water and with 25 or 55 g plasticizer/100 g gelatin. The ratio, glycerol to sorbitol, was studied as 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0. The increase of plasticizer concentration from 25 to 55 g plasticizer/100 g gelatin caused an increase of flexibility and reduction of resistance and water vapor barrier as expected. In relation to the effect of the mixture, the increase in the proportion of glycerol caused a reduction of the puncture force, tensile strength, modulus of elasticity, and an increase of the puncture deformation, elongation at break, and water vapor permeability due to the higher plasticizing effect of glycerol. This behavior was explained in terms of molecular weight of the plasticizers, which demonstrated that the studied properties could be considered as functions of the number of molecules of plasticizers in the films.     

Microwave‐accelerated Synthesis and Characterization of Potato Starch‐g‐poly(acrylamide)

Using a very low concentration of potassium persulfate as initiator, acrylamide could be efficiently grafted onto potato starch under microwave irradiation and for the grafting O₂ removal from the reaction vessel was not required. Under optimal conditions, grafting and efficiency observed were 160% and 89%, respectively. Grafted starch was characterized by using Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA). It was observed that the microwave irradiation could significantly accelerate the synthesis of starch‐graft‐poly(acrylamide), because under identical conditions no grafting was observed in a conventional procedure. Viscosity, shear stability and water/saline solution retention of the microwave‐synthesized grafted starch were studied and compared with that of the parent starch.     

Inverse Emulsion of Starch‐graft‐Polyacrylamide

An inverse emulsion of cationic starch‐graft‐polyacrylamide was prepared by inverse emulsion polymerization and a subsequent Mannich reaction. The copolymerization was carried out using potassium persulfate as initiator. The reaction conditions and factors affecting emulsion stability were studied. Experiments showed that a high solids content, a high cationic degree and a stable latex can be obtained under the following condition: A molar ratio starch/acrylamide/formaldehyde/dimethylamine of 0.11:1:1:1.2; a stable inverse emulsion system; graft copolymerization of starch and acrylamide for 2‐3 h at 50 °C; pre‐formation of an aldehyde‐amine adduct, which is subsequently dropped into an inverse emulsion of starch‐graft‐polyacrylamide. The reaction temperature was 45 °C, the reaction time was 3‐4 h, and the pH was 5.5.     

Development and Characterization of Edible Films from Cranberry Pomace Extracts

The feasibility of using cranberry pomace extract as a new film‐forming material was studied. Cranberry pomaces were extracted using hot water. Low methoxyl pectin (LMP) or high methoxyl pectin (HMP) at a concentration of 0.50% or 0.75% (w/w) and 0.25% (w/w) sorbitol or glycerol was incorporated into film‐forming solutions (FFSs) for improving film functionality. Proximate compositions of cranberry pomace and its extract were determined. The pH and total soluble solid content (SSC) of FFSs, physical and mechanical properties, water vapor permeability, and microstructure of dried films were analyzed. About 1.4% (w/w) of solids was obtained from cranberry pomace water extracts, of which about 93% was carbohydrate. Dried films had bright red color and strong cranberry flavor. Films plasticized with sorbitol were denser in matrix structure and had higher color intensity than those of glycerol plasticized films. In general, LMP and sorbitol incorporated films had higher tensile strength and lower elongation at break and lower water vapor permeability than other films. The higher (0.75%) pectin concentration resulted in increased tensile strength, but decreased elongation at break. Scanning electron microscopy images revealed that sorbitol added films had more regular and compact cross‐section structure than those of glycerol added films. This study demonstrated that it is feasible to create natural colorful and fruit flavor edible films from fruit pomace water extracts. Depending on specific applications of the films, targeted film functionality can be achieved by incorporating proper pectin type and concentration and plasticizer into pomace extracts.     

Physicochemical and Microstructural Characterization of Corn Starch Edible Films Obtained by a Combination of Extrusion Technology and Casting Technique

Starch edible films (EFs) have been widely studied due to their potential in food preservation; however, their application is limited because of their poor mechanical and barrier properties. Because of that, the aim of this work was to use the extrusion technology (E_xT) as a pretreatment of casting technique to change the starch structure in order to obtain EFs with improved physicochemical properties. To this, corn starch and a mixture of plasticizers (sorbitol and glycerol, in different ratios) were processed in a twin screw extruder to generate the starch modification and subsequently casting technique was used for EFs formation. The best conditions of the E_xT and plasticizers concentration were obtained using response surface methodology. All the response variables evaluated, were affected significatively by the Plasticizers Ratio (Sorbitol:Glycerol) (PR (S:G)) and Extrusion Temperature (ET), while the Screw Speed (SS) did not show significant effect on any of these variables. The optimization study showed that the appropriate conditions to obtain EFs with the best mechanical and barrier properties were ET = 89 °C, SS = 66 rpm and PR (S:G) = 79.7:20.3. Once the best conditions were obtained, the optimal treatment was characterized according to its microstructural properties (X‐ray diffraction, Scanning Electron Microscopy and Atomic Force Microscopy) to determine the damage caused in the starch during E_xT and casting technique. In conclusion, with the combination of E_xT and casting technique were obtained EFs with greater breaking strength and deformation, as well as lower water vapor permeability than those reported in the literature.     

Development and Characterization of Edible Films Based on Mucilage of Opuntia ficus-indica (L.)

Abstract: Mucilage of Opuntia ficus-indica (OFI) was extracted and characterized by its composition and molecular weight distribution. Mucilage film-forming dispersions were prepared under different pHs (3, 4, 5.6, 7, and 8) and calcium concentration (0% and 30% of CaCl₂, with respect to mucilage's weight), and their particle size determined. Mucilage films with and without calcium (MFCa and MF, respectively) were prepared. The effect of calcium and pH on mucilage films was evaluated determining thickness, color, water vapor permeability (WVP), tensile strength (TS), and percentage of elongation (%E). The average molecular weight of the different fractions of mucilage was: 3.4 × 10⁶ (0.73%), 1 × 10⁵ (1.46%), 1.1 × 10³ (45.79%), and 2.4 × 10² Da (52.03%). Aqueous mucilage dispersions with no calcium presented particles with an average size d(0.5) of 15.4 μm, greater than the dispersions with calcium, 13.2 μm. MFCa films showed more thickness (0.13 mm) than the MF films (0.10 mm). The addition of calcium increased the WVP of the films from 109.94 to 130.45 gmm/m²dkPa. Calcium and pH affected the mechanical properties of the films; the largest TS was observed on MF films, whereas the highest %E was observed on MFCa films. The highest differences among MF and MFCa films were observed at pHs 5.6 and 7 for TS and at pHs 4 and 8 for %E. No effect of pH and calcium was observed on luminosity and hue angle. Chroma values were higher for MF when compared with MFCa, and increased as pH of the films increased. Practical Application: In this study mucilage from nopal was extracted and characterized by its ability to form edible films under different pHs, and with or without the addition of calcium. Opuntia ficus-indica mucilage had the ability to form edible films. In general, it can be considered that mucilage films without modification of pH and without the addition of calcium have the best water vapor barrier properties and tensile strength. Mucilage from nopal could represent a good option for the development of edible films in countries where nopal is highly produced at low cost, constituting a processing alternative for nopal.     

Starch properties of various potato (Solanum tuberosum L) Cultivars susceptible and resistant to low-temperature sweetening

Properties of starch granules isolated from different varieties and selections of potato (which vary in their degree of chill sweetening) were examined. Differential scanning calorimetry (DSC) showed an increase in resistance to gelatinisation of isolated starch granules which correlated (r = 0.911) with higher chip scores following storage at 4°C and 12°C. Varying water level content during DSC studies resulted in significantly lower water content required to produce two endotherms for starch isolated from varieties resistant to chill sweetening. These data strongly suggest that starch granule composition might be a factor differentiating the low temperature sweetening sensitive from resistant cultivars, and may provide a screening method for predicting chip colour of potatoes out of storage.     

Antimicrobial Activity of Nisin and Natamycin Incorporated Sodium Caseinate Extrusion‐Blown Films: A Comparative Study with Heat‐Pressed/Solution Cast Films

Antimicrobial edible films based on sodium caseinate, glycerol, and 2 food preservatives (nisin or natamycin) were prepared by classical thermomechanical processes. Food preservatives were compounded (at 65 °C for 2.5 min) with sodium caseinate in a twin‐screw extruder. Anti‐Listeria activity assays revealed a partial inactivation of nisin following compounding. Thermoplastic pellets containing food preservatives were then used to manufacture films either by blown‐film extrusion process or by heat‐press. After 24 h of incubation on agar plates, the diameters of K. rhizophila growth inhibition zones around nisin‐incorporated films prepared by solution casting (control), extrusion blowing or heat pressing at 80 °C for 7 min of nisin‐containing pellets were 15.5 ± 0.9, 9.8 ± 0.2, and 8.6 ± 1.0 mm, respectively. Since heat‐pressing for 7 min at 80 °C of nisin‐incorporated pellets did not further inactivate nisin, this indicates that nisin inactivation during extrusion‐blowing was limited. Moreover, the lower diameter of the K. rhizophila growth inhibition zone around films prepared with nisin‐containing pellets compared to that observed around films directly prepared by solution casting confirms that nisin inactivation mainly occurred during the compounding step. Natamycin‐containing thermoplastic films inhibited Aspergillus niger growth; however, by contrast with nisin‐containing films, heat‐pressed films had higher inhibition zone diameters than blown films, therefore suggesting a partial inactivation of natamycin during extrusion‐blowing.     

Effects of Water-Glycerol and Water-Sorbitol Interactions on the Physical Properties of Konjac Glucomannan Films

Konjac glucomannan (KGM)‐edible films were prepared with different amounts of glycerol or sorbitol as a plasticizer. Films were characterized by moisture sorption isotherm, and following conditioning at different relative humidities, by differential scanning calorimetry and tensile tests. Moisture and polyols (sorbitol and glycerol) were found to plasticize KGM‐based films with respect to their tensile properties. However, thermal properties and water sorption capacity (WSC) of polyolplasticized KGM films were found to vary with water activity (a_w), namely at low a_w (< 0.6), WSC and melting enthalpy were decreased with increasing in polyol content and the opposite was true at higher a_w (>0.6). This was attributed to extensive interactions between plasticizer and KGM that reduced the available active site (‐OH groups) for water adsorption. The presence of polyols at low a_w appeared to suppress crystalline structures due probably to restricted molecular mobility. These effects were diminished when the moisture content was >20%.     

Effect of Hydrothermal Treatment on Formation and Structural Characteristics of Slowly Digestible Non‐pasted Granular Sweet Potato Starch

The formation and structural characteristics of slowly digestible non‐pasted granular starch in sweet potato starch were investigated under various hydrothermal treatment conditions. The moisture content of the sweet potato starch was adjusted to 20, 50 or 90%, and the starch was heated at 40, 55 or 100°C for 12 h in a dry oven. The relative crystallinity of the hydrothermally treated samples was decreased with increasing temperature, and the X‐ray diffraction patterns of the samples were altered from C_b‐type to A‐type. Microscopic observations did not reveal any changes in the starch granules of any samples except those with moisture contents of 50 and 90% that were heated at 100°C. When gelatinization parameters were examined, samples with moisture contents of 50 and 90% that were heated at 55°C and samples of all moisture contents that were heated at 100°C had peak temperatures higher than that of raw starch but gelatinization enthalpies lower than that of raw starch. The swelling factor of the samples heated at 40°C did not change significantly, whereas that of samples heated at 55 and 100°C was decreased at increased moisture levels. The sweet potato starch with 50% moisture content that was heated at 55°C had the highest content of granular slowly digestible starch, about 200% that of raw starch, although our study did not involve further hydrothermal treatment conditions. Further study is required to complete a process for more efficient production of heat stable and slowly digestible starch.