Curtis L. Weller

Soy protein isolate–dialdehyde starch films

Abstract This study was conducted to determine the effect of dialdehyde starch (DAS) on selected physical properties of cast soy protein isolate (SPI) films. Films were cast from heated (70°C for 20 min) alkaline (pH 10) aqueous solutions of SPI at 5 g/100 ml water, glycerin (50%, w/w, of SPI), and DAS at 0, 5, 10, 15, or 20% (w/w) of SPI. For all types of films, Hunter color values (L, a, and b), tensile strength (TS), percentage elongation at break (E), water vapor permeability (WVP), moisture content (MC) after conditioning at 50% RH and 25°C for 48 h, and total soluble matter (TSM) after immersion in water at 25°C for 24 h were measured. DAS addition increased (P 0.05) affected by DAS. Small increases (P

Mechanical and Barrier Properties of Edible Corn and Wheat Protein Films

ABSTRACTPublished methods for production of homogeneous edible films from com and wheat proteins were adapted. Barrier and mechanical properties of the edible films were evaluated with procedures commonly used on polymeric films. Mechanical property data included thickness, elongation, tensile strength, tear strength, and burst strength measurements. Barrier property data included water vapor, oxygen, and carbon dioxide gas transmission rate measurements. Homogeneous com and wheat protein films were found to have low tensile strengths, far less than cellophane. Com films were brittle while wheat films were elastic in comparison to cellophane. All three types of film had low permeabilities for dry gases but relatively high water vapor permeabilities.

Heat Curing of Soy Protein Films

Modification of soy protein film properties by heat-curing was studied. Glycerin-plasticized films were cast from alkaline aqueous solutions of soy protein isolate. Films were heated at 80 or 95°C for 2, 6, 14, or 24 h. Tensile strength (TS), elongation at break (E), moisture content (MC), water solubility (WS), water vapor permeability (WVP), and color of heated and control films were measured. Heated films had increased TS and +b (yellowness) Hunter color values and reduced E, MC, WS, and WVP values. These effects were enhanced as heating time and temperature increased.

Water Vapor Permeability and Mechanical Properties of Grain Protein-based Films as Affected by Mixtures of Polyethylene Glycol and Glycerin Plasticizers

Grain protein-based films containing mixtures of glycerin and polyethylene glycol (PEG) as plasticizers were prepared and evaluated for water vapor permeability (WVP), tensile strength (TS), and elongation (E). Changes in mechanical properties during storage were also studied. The PEG produced opposite trends in E of wheat gluten and corn-zein films. The TS of wheat gluten films increased and E of the films decreased as the ratio of glycerin/PEG decreased. Corn-zein films containing only glycerin were very brittle (E of 4%), and E of the films improved to 94% when the ratio of mL PEG/g protein was 0.39. The WVP of both films decreased as the ratio of glycerin/PEG was decreased. Also, WVP of both films increased as the total amount of plasticizer added to the films increased. Mixtures of glycerin and PEG as plasticizer are less fugitive than glycerin alone in grain protein-based films and can reduce the deterioration of mechanical properties during storage.

Property Modification of Edible Wheat, Gluten-based Films

Procedures were developed to produce edible wheat, gluten-based films. A film was produced as a standard. Five additional films were then produced by modifying the initial film-forming solution. Modifications included changing the plasticizer, partially substituting wheat gluten with soy protein isolate and corn zein, and incorporating two acetylated monoglyceride products. All films were characterized by measuring selected mechanical properties, and permeabilities to water vapor and to oxygen. Comparison of the films, in terms of their measured properties, indicates ways to improve the overall performance of the standard film as a potential packaging material. A main limitation of all of the films was their poor water vapor barrier characteristics. On the other hand, they were very good oxygen barriers. All modified films were stronger than the standard in terms of tensile and bursting strength. The film containing soy protein was the strongest and the most uniform. Significant differences in measured properties were observed when the plasticizer was changed from glycerin to triethylene glycol.

Cast Films from Soy Protein Isolates and Fractions

ABSTRACT Glycerol-plasticized soy protein films were cast from alkaline aqueous film-forming solutions of laboratory-prepared 7S, 11S, and soy isolate (LSI) fractions and from commercial soy isolate (CSI). Tensile strength (TS), elongation at break (E), water vapor permeability (WVP), total soluble matter (TSM), protein solubility (PS), and Hunter L, a, and b color values of these films were determined. The 11S films had greater TS than 7S films (P 0.05). The 7S films had higher TSM and PS values than 11S films (P < 0.05). CSI films were significantly darker (lower L value) and more yellow (greater positive b value) than LSI films (P < 0.05).

Sodium dodecyl sulfate treatment improves properties of cast films from soy protein isolate

The manufacture of edible/biodegradable films or coatings can potentially add value to soy protein. This study was conducted to determine the effect of sodium dodecyl sulfate (SDS) on selected physical properties of glycerin-plasticized soy protein isolate (SPI) films. Films were cast from heated (70 °C for 20 min), alkaline (pH 10) aqueous solutions of SPI (5 g/100 ml water), glycerin (50% w/w of SPI), and SDS (0, 5, 10, 20, 30, or 40% w/w of SPI). Tensile strength (TS), elongation at break (E), moisture content (MC), total soluble matter (TSM), water vapor permeability (WVP), and color values (L, a, and b) were determined after conditioning film specimens at 25 °C and 50% relative humidity (RH) for 2 days. SDS reduced (P < 0.05) film TS by as much as 43% for films with 40% SDS (6.2 vs. 10.9 MPa for control SPI films). In con trast, film E increased ( P < 0.05) notably with addition of SDS even at 5%. Films with SDS had smaller (P < 0.05) MC and larger (P < 0.05) TSM values than control SPI films. Films contain ing 10% or more SDS had lower WVP values than control SPI films by as much as 50%. In creased yellowness, evidenced by greater (P < 0.05) + b color values, was noted for films with high amounts (20, 30, or 40%) of SDS. Changes in tensile, solubility, and water vapor barrier properties of SPI films due to the addition of SDS were largely attributed to disruption of hy drophobic associations among neighboring protein molecules as the non-polar portions of the SDS molecules attached onto hydrophobic amino acid residues within the film structure. It was demonstrated that adding anionic surfactant SDS to film-forming solutions prior to casting could greatly modify the properties of SPI films. In particular, SDS improved the water vapor barrier ability and the extendibility of SPI films, both desirable attributes when assessing the potential of such films for packaging applications.

Ultrasound-Assisted Osmotic Dehydration of Strawberries: Effect of Pretreatment Time and Ultrasonic Frequency

Pretreatment of fruits prior to drying has shown success in reducing drying time and costs. In this work, ultrasound-assisted osmotic dehydration has been implemented as a method to increase water diffusivity and reduce drying time in strawberries. Strawberry halves were immersed in distilled water and in two different concentrations of sucrose solutions while pretreatment time and ultrasonic frequency levels were varied to determine their effect on drying time, water loss, and soluble solids gain. A microscopic analysis was carried out to evaluate the formation of microchannels and other changes to the fruit tissue structure. Greater sucrose concentration used in ultrasound-assisted osmotic dehydration resulted in greater water loss with greatest loss observed for the strawberry halves pretreated for 45 min in a 50% w/w sucrose solution. The pretreatment carried out for 30 min employing an osmotic solution of 50% w/w of sucrose resulted in the highest drying rate among the pretreatments. Osmotic dehydration used alone during pretreatment increased total processing time, whereas osmotic dehydration combined with ultrasonic energy during pretreatment reduced total processing time and increased effective water diffusivity. Cell distortion and breakdown were observed not only in pretreatments employing ultrasound-assisted osmotic dehydration but in conventional osmotic dehydration. Formation of microchannels through ultrasonic application and effects of osmotic pressure differential were considered to be largely responsible for reducing drying time for strawberry halves.

Relative Humidity and Temperature Effects on Tensile Strength of Edible Protein and Cellulose Ether Films

The effect of relative humidity and temperature on tensile strength of two types of protein-based [corn zein (CZ) and wheat gluten (WG)] and two types of cellulosic [methylcellulose (MC) and hydroxypropyl cellulose (HPC)] hydrophilic edible films was investigated. A central composite response surface design was used. Studied ranges of relative humidity and temperature were 23 to 75% and 5 to 45° C, respectively. For all four types of films, tensile strength (TS) decreased with relative humidity and increased with temperature. Ranges of mean tensile strength values among the nine different combinations of the two variables were 5.7 to 23.6 MPa, 2.7 to 21.4 MPa, 61.9 to 104.4 MPa, and 11.1 to 35.0 MPa for CZ, WG, MC, and HPC, respectively. A second-order polynomial model was fitted to the data with least squares regression. A regression model linear in relative humidity and quadratic in temperature showed a very good fit to tensile strength data of CZ (R2 = 0.93) and MC (R2 = 0.98) films. A regression equation linear with respect to both relative humidity and temperature satisfactorily fitted (R2 = 0.75) TS data of HPC films. A best fitted model for TS data of WG films, that included relative humidity and temperature, the square of temperature, and the cross-product of the two variables, had a poor fit (R2 = 0.67).

Moisture Adsorption by Grain Protein Films

Grain protein films plasticized with glycerol were prepared from corn zein (CZ), wheat gluten (WG), and a 2.3:1 mixture of wheat gluten and soy protein isolate (WG/SPI). Moisture adsorption curves of the three types of protein films at 25° C and within an approximate water activity range of 0.11 to 0.84 were obtained using a static gravimetric method. The Smith, Oswin, Halsey, and Guggenheim-Anderson-de Boer (GAB) models were applied to collected data. For all protein films, the GAB model showed the best fit over the entire studied water activity range yielding mean deviation modulus values (P) of 4.69, 3.44, and 7.95 for WG, WG/SPI, and CZ films, respectively. The Smith and Halsey models fitted well the high water activity (0.53 to 0.84) portion of the isotherms with P values ranging between 2.55 and 6.74. Moisture adsorption behavior by the protein films at the low water activity range (0.11 to 0.58) was reasonably well described by the Oswin model (P values of 6.68, 5.25, and 5.24 for WG, WG/SPI, and CZ films, respectively).