Sajid Alavi

Recent Advances in Biopolymers and Biopolymer-Based Nanocomposites for Food Packaging Materials

Plastic packaging for food and non-food applications is non-biodegradable, and also uses up valuable and scarce non-renewable resources like petroleum. With the current focus on exploring alternatives to petroleum and emphasis on reduced environmental impact, research is increasingly being directed at development of biodegradable food packaging from biopolymer-based materials. The proposed paper will present a review of recent developments in biopolymer-based food packaging materials including natural biopolymers (such as starches and proteins), synthetic biopolymers (such as poly lactic acid), biopolymer blends, and nanocomposites based on natural and synthetic biopolymers. The paper will discuss the various techniques that have been used for developing cost-effective biodegradable packaging materials with optimum mechanical strength and oxygen and moisture barrier properties. This is a timely review as there has been a recent renewed interest in research studies, both in the industry and academia, towards development of a new generation of biopolymer-based food packaging materials with possible applications in other areas.

Thermo-mechanical extrusion pretreatment for conversion of soybean hulls to fermentable sugars.

Thermo-mechanical extrusion pretreatment for lignocellulosic biomass was investigated using soybean hulls as the substrate. The enzyme cocktail used to hydrolyze pretreated soybean hulls to fermentable sugars was optimized using response surface methodology (RSM). Structural changes in substrate and sugar yields from thermo-mechanical processing were compared with two traditional pretreatment methods that utilized dilute acid (1% sulfuric acid) and alkali (1% sodium hydroxide). Extrusion processing parameters (barrel temperature, in-barrel moisture, screw speed) and processing aids (starch, ethylene glycol) were studied with respect to reducing sugar and glucose yields. The conditions resulting in the highest cellulose to glucose conversion (95%) were screw speed 350rpm, maximum barrel temperature 80°C and in-barrel moisture content 40%wb. Compared with untreated soybean hulls, glucose yield from enzymatic hydrolysis of soybean hulls increased by 69.6%, 128.7% and 132.2%, respectively, when pretreated with dilute acid, alkali and extrusion.

Structural properties of protein-stabilized starch-based supercritical fluid extrudates

Abstract Supercritical fluid extrusion, a low temperature and low shear process, was used to produce pre-gelatinized corn and potato starch-based extrudates, containing 4–10% thermosetting egg white (EW) or whey protein concentrate (WPC-34), and dried at 22–100°C. Addition of proteins reduced shrinkage of high-moisture extrudates, as indicated by increases in expansion ratio by up to 140 and 341% when the drying temperatures were 22 and 100°C, respectively. Products containing 7% EW or WPC-34 and dried at 85°C expanded best while maintaining an intact structure, with expansion ratio (∼12) and bulk density (∼0.10 g/cm3) comparable to steam extrudates. The products had a unique composite and uniform microcellular structure, with average cell sizes in the range of 50-250 μm and cell density of the order of 106 cells/cm3. The classical nucleation theory and a qualitative model for cell growth and shrinkage based on glass transition temperature were used to explain the microcellular structure.

Barrier and Mechanical Properties of Starch-Clay Nanocomposite Films

ABSTRACT The poor barrier and mechanical properties of biopolymer-based food packaging can potentially be enhanced by the use of layered silicates (nanoclay) to produce nanocomposites. In this study, starch-clay nanocomposites were synthesized by a melt extrusion method. Natural (MMT) and organically modified (I30E) montmorillonite clays were chosen for the nanocomposite preparation. The structures of the hybrids were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Films were made through casting using granulate produced by a twin-screw extruder. Starch/MMT composite films showed higher tensile strength and better water vapor barrier properties than films from starch/I30E composites, as well as pristine starch, due to formation of intercalated nanostructure. To find the best combinations of raw materials, the effects of clay content (0–21 wt% MMT), starch sources (corn, wheat, and potato), and amylose content (≈0, 28, 55, 70, 100%) on barrier and mechanical properties ...

Effect of Type and Content of Modified Montmorillonite on the Structure and Properties of Bio-Nanocomposite Films Based on Soy Protein Isolate and Montmorillonite

The nonbiodegradable and nonrenewable nature of plastic packaging has led to a renewed interest in packaging materials based on bio-nanocomposites (biopolymer matrix reinforced with nanoparticles such as layered silicates). Bio-nanocomposite films based on soy protein isolate (SPI) and modified montmorillonite (MMT) were prepared using melt extrusion. The effect of different type (Cloisite 20A and Cloisite 30B) and content (0% to 15%) of modified MMT on the structure (degree of intercalation and exfoliation) and properties (color, mechanical, dynamic mechanical, thermal stability, and water vapor permeability) of SPI-MMT bio-nanocomposite films were investigated. Extrusion of SPI and modified MMTs resulted in bio-nanocomposites with exfoliated structures at lower MMT content (5%). At higher MMT content (15%), the structure of bio-nanocomposites ranged from intercalated for Cloisite 20A to disordered intercalated for Cloisite 30B. At an MMT content of 5%, bio-nanocomposite films based on modified MMTs (Cloisite 20A and Cloisite 30B) had better mechanical (tensile strength and percent elongation at break), dynamic mechanical (glass transition temperature and storage modulus), and water barrier properties as compared to those based on natural MMT (Cloisite Na(+)). Bio-nanocomposite films based on 10% Cloisite 30B had mechanical properties comparable to those of some of the plastics that are currently used in food packaging applications. However, much higher WVP values of these films as compared to those of existing plastics might limit the application of these films to packaging of high moisture foods such as fresh fruits and vegetables.

Development and validation of a dynamic growth model for Listeria monocytogenes in fluid whole milk.

Listeria monocytogenes, a psychrotrophic microorganism, has been the cause of several food-borne illness outbreaks, including those traced back to pasteurized fluid milk and milk products. This microorganism is especially important because it can grow at storage temperatures recommended for milk (< or =7 degrees C). Growth of L. monocytogenes in fluid milk depends to a large extent on the varying temperatures it is exposed to in the postpasteurization phase, i.e., during in-plant storage, transportation, and storage at retail stores. Growth data for L. monocytogenes in sterilized whole milk were collected at 4, 6, 8, 10, 15, 20, 25, 30, and 35 degrees C. Specific growth rate and maximum population density were calculated at each temperature using these data. The data for growth rates versus temperature were fitted to the Zwietering square root model. This equation was used to develop a dynamic growth model (i.e., the Baranyi dynamic growth model or BDGM) for L. monocytogenes based on a system of equations which had an intrinsic parameter for simulating the lag phase. Results from validation of the BDGM for a rapidly fluctuating temperature profile showed that although the exponential growth phase of the culture under dynamic temperature conditions was modeled accurately, the lag phase duration was overestimated. For an alpha0 (initial physiological state parameter) value of 0.137, which corresponded to the mean temperature of 15 degrees C, the population densities were underpredicted, although the experimental data fell within the narrow band calculated for extreme values of alpha0. The maximum relative error between the experimental data and the curve based on an average alpha0 value was 10.42%, and the root mean square error was 0.28 log CFU/ml.

Structure and physical properties of starch/poly vinyl alcohol/sodium montmorillonite nanocomposite films.

Nanocomposites of starch, poly vinyl alcohol (PVOH), and sodium montmorillonite (Na(+)MMT) were produced by solution mixing and cast into films. Tensile strength (TS) and elongation at the break (E%) of the films ranged from 11.60 to 22.35 MPa and 28.93-211.40%, respectively, while water vapor permeability (WVP) ranged from 0.718 to 1.430 g·mm/kPa·h·m(2). In general, an increase in Na(+)MMT content (0-20%) enhanced TS and decreased E% and WVP. Use of higher molecular weight PVOH increased both TS and E% and also decreased WVP. Mechanical properties were negatively affected, but water vapor barrier properties improved with increasing starch content (0-80%). X-ray diffraction and transmission electron microscopy were used to analyze the nanostructure, and molecular conformations and interactions in the multicomponent nanocomposites were inferred from glass transition behavior. Interactions between starch and PVOH were strongest, followed by polymer/clay interactions. On the basis of this insight, a conceptual model was presented to explain the phenomena of intercalation and exfoliation in the starch/PVOH/Na(+)MMT nanocomposites.

Sorghum proteins: the concentration, isolation, modification, and food applications of kafirins.

Celiac disease is a serious condition affecting millions of individuals. Those afflicted with this illness are resigned to a lifelong avoidance of products containing the storage prolamin proteins found in cereal grains wheat, rye, and barley. Since many food products are based on these cereals, especially wheat, celiac patients have very limited food choices, and those that are available to them are generally poor in quality, often nutritionally deficient, and expensive. Furthermore, this condition also indirectly affects their families and friends with whom they share meals. Thus, a burgeoning need exists to develop nutritious, palatable, and affordable foods, especially staples like bread and pasta, for these individuals and their families and friends who are accustomed to wheat based products. Grain sorghum and its proteins are safe for celiac patients and individuals with varying levels of gluten intolerances. However, the main sorghum proteins, kafirins, are resistant to digestion. They are also difficult to extract and modify in an industrial-scale process and with food-compatible chemicals, thus limiting their use in foods. This review describes studies on kafirin extraction and methods for modifying sorghum proteins for improved nutrition and functionality, as well as food applications. Armed with this knowledge, scientists and technologists will be in a better position to identify opportunities that will further enhance the nutritional and functional value of sorghum proteins.

Process dynamics of starch-based microcellular foams produced by supercritical fluid extrusion. I: model development

Abstract Supercritical fluid extrusion (SCFX) has been used successfully to produce biopolymeric foams with bubble size in the range of 50–200 microns, and bubble density to the order of 106 per cm3. Final bubble size and expansion ratio of extrudates depend on process and material parameters like CO2 injection rate, nozzle temperature, oven temperature, melt viscosity, melt yield stress, etc. The objective of this study was to describe SCFX process dynamics and post-extrusion drying mechanism by using a mathematical model for bubble growth at the microscopic level in conjunction with a macroscopic model for flow of starch melt through the extruder nozzle, bulk diffusion of CO2 and water to the atmosphere and heat transfer in the extrudate. The model was written in Visual Basic. The model provided the basis for a good understanding of the mechanisms of bubble growth and collapse, post-extrusion drying and open cell formation during SCFX processing, and is the only such one developed so far for extrusion puffed products. Simulation results and comparison with experimental data are presented in Part II of this paper.

Structure and Physical Properties of Starch/Poly Vinyl Alcohol/Laponite RD Nanocomposite Films

Nanocomposites of starch, poly vinyl alcohol (PVOH), and laponite RD (LRD) were produced by solution mixing and cast into films. In general, an increase in LRD content (0-20%) enhanced tensile strength and decreased water vapor permeability, irrespective of the relative humidity (50% and 75% RH). Tensile strength (TS) of starch/PVOH/LRD films ranged from 6.51 to 13.3 MPa. At 75% RH, TS was up to 65% higher as compared to films with sodium montmorillonite as filler. The most striking results were obtained with respect to elongation at break (E%), which ranged from 144% to 312%. Contrary to other polymer/clay nanocomposites, E% increased on addition of 5-20% LRD and was up to 175% higher than the control without clay. Nanocomposite structure and interactions were investigated using X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. Results indicated that LRD was a compatibilizer and cross-linking agent between polymers, and has the potential for use in biodegradable packaging films with good mechanical performance even in high humidity conditions.