Loong-Tak Lim

Poly(lactic acid) : synthesis, structures, properties, processing, and applications

This book describes the synthesis, properties, and processing methods of poly(lactic acid) (PLA), an important family of degradable plastics. As the need for environmentally-friendly packaging materials increases, consumers and companies are in search for new materials that are largely produced from renewable resources, and are recyclable. To that end, an overall theme of the book is the biodegradability, recycling, and sustainability benefits of PLA. The chapters, from a base of international expert contributors, describe specific processing methods, spectroscopy techniques for PLA analysis, and and applications in medical items, packaging, and environmental use.

Electrospun Zein Fibers as Carriers to Stabilize (−)-Epigallocatechin Gallate

In this study, a method was developed for continuous electrospinning of ultrafine corn zein protein fibers with diameters ranging from 150 to 600 nm. Fiber-forming solutions with various zein concentrations (10% to 30%, w/w) and aqueous ethanol concentrations (60% to 90%, w/w) were electrospun at 15 and 20 kV. Scanning electron microscopy results showed that the morphology of zein fibers was affected by aqueous ethanol concentration, zein concentration, and the applied voltage. The optimal condition for forming bead-less fibers was found to be 20% protein, 70% alcohol, and 15 kV. The zein fibers resisted solubilization in water, although swelling and plasticization were apparent after the water treatment. The efficacy of zein fibers was tested for stabilization of a green tea polyphenol, (-)-epigallocatechin gallate (EGCG), by incorporating the EGCG in zein fiber-forming solutions. Freshly spun fibers were less effective at immobilizing the EGCG upon immersion in water (82% recovery) as compared to fibers that were aged at 0% relative humidity for at least 1 d (>98% recovery) before water immersion. Fourier transform infrared spectroscopy studies demonstrated that hydrogen bonding, hydrophobic interactions, and physical encapsulation are the major contributors to the stabilization of EGCG in zein fibers in water.

Sorption and transport of water vapor in nylon 6,6 film

The sorption and transport of water in nylon 6,6 films as functions of the relative humidity (RH) and temperature were studied. Moisture-sorption isotherms determined gravimetrically at 25, 35, and 45°C were described accurately by the GAB equation. Water-vapor transmission rates were enhanced above ≈ 60–70% RH, primarily due to the transition of the polymer from glassy to rubbery states. The glass transition temperatures (Tgs) of nylon 6,6 were measured at various moisture contents using differential scanning calorimetry. The results showed that the sorbed water acted as an effective plasticizer in depressing the Tg of the polyamide. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the interaction of water and the nylon. Evidence from FTIR suggested that the interaction of water with nylon 6,6 took place at the amide groups. Based on the frequency shift of the peak maxima, moisture sorption appeared to reduce the average hydrogen-bond strength of the NH groups. However, an increase was seen for the CO groups.

Electrospinning of Sodium Alginate-Pectin Ultrafine Fibers

In this study, we investigated the electrospinning process of sodium alginate-pectin fibers intended to be used as a carrier for stabilizing folic acid. Fiber-forming solutions containing 0.01% (w/w) folic acid were prepared by blending low- or medium-viscosity sodium alginate with pectin in a 70 : 30 ratio to form LSAP and MSAP solutions, respectively. Similar to other polysaccharide polymers reported previously, these solutions could not be electrospun. However, the incorporation of poly(ethylene oxide) (PEO) effectively enabled the electrospinning process. Electrospun fibers of different morphologies, ranging from fiber to fiber-bead, were obtained, depending on the blend ratio, concentration, and viscosity of the polymer-PEO solution used. Fibers electrospun from 3% MSAP/PEO (80%/20% w/w) had the smallest diameter (about 40 nm), whereas fibers containing higher PEO contents were larger in diameter. Bead-free fibers were formed when 4% LSAP/PEO (50/50) and 5% LSAP/PEO (80/20 to 50/50) were electrospun. The electrical conductivity and surface tension lowering effects of PEO on the polymer solution were likely the contributing factors for the observed electrospinning behaviors. By adjusting the formulation of the polymer solution, fibers of various morphologies may be obtained to suit different end-use applications. A study is currently ongoing to investigate the effectiveness of these fibers for stabilizing folic acid.

Feasibility study on chemometric discrimination of roasted Arabica coffees by solvent extraction and Fourier transform infrared spectroscopy.

In this feasibility study, Fourier transform infrared (FTIR) spectroscopy and chemometric analysis were adopted to discriminate coffees from different geographical origins and of different roasting degrees. Roasted coffee grounds were extracted using two methods: (1) solvent alone (dichloromethane, ethyl acetate, hexane, acetone, ethanol, or acetic acid) and (2) coextraction using a mixture of equal volume of the solvent and water. Experiment results showed that the coextraction method resulted in cleaner extract and provided a greater amount of spectral information, which was important for sample discrimination. Principal component analysis of infrared spectra of ethyl acetate extracts for dark and medium roast coffees showed separated clusters according to their geographical origins and roast degrees. Classification models based on soft independent modeling of class analogy analysis were used to classify different coffee samples. Coffees from four different countries, which were roasted to dark, were 100% correctly classified when ethyl acetate was used as a solvent. The FTIR-chemometric technique developed here may serve as a rapid tool for discriminating geographical origin of roasted coffees. Future studies involving green coffee beans and the use of larger sample size are needed to further validate the robustness of this technique.

Activation of lactoperoxidase system in milk by glucose oxidase immobilized in electrospun polylactide microfibers.

In this study, glucose oxidase (GOX) was immobilized in polylactide (PLA) fibers that were used to activate the lactoperoxidase (LP) system in milk. The GOX-containing microfibers were electrospun from emulsions prepared by dispersing aqueous GOX in PLA dissolved in a chloroform and N,N-dimethylformamide blend, using sorbitan monopalmitate as an emulsifier. The enzymatic activity of GOX-in-PLA fibers (1100 +/- 400 nm diameter) was more than 19 times higher than that of the GOX-in-PLA membrane formed by direct casting, due to the larger surface area of the electrospun fibers. The activation of LP in model solutions using GOX-in-PLA fibers provided a more sustained generation of antimicrobial OSCN(-) than direct activation using H(2)O(2). Preliminary evaluation on milk samples showed that the electrospun GOX-in-PLA microfibers are capable of activating the naturally present LP system, indicating that they may be promising for active food packaging applications to extend the shelf life of milk.

Fourier transform infrared and physicochemical analyses of roasted coffee.

In this study, Brazilian coffee beans processed to different stages of roast at 210, 220, 230, and 240 °C were analyzed for pH value, titratable acidity, moisture content, and color lightness. Fourier transform infrared (FTIR) spectroscopy, in conjunction with principal component analysis, was conducted to study the effects of process time and temperature on the IR-active components of the acetyl acetate extract of the roasted coffee. The results showed that high-temperature-short-time resulted in higher moisture content, higher pH value, and higher titratable acidity when the beans were roasted beyond the start-of-second-crack stage, as compare to low-temperature-long-time process (LTLT). The LTLT process also resulted in greater IR absorbance for aldehydes, ketones, aliphatic acids, aromatic acids, and caffeine carbonyl bands on the FTIR spectra. Clusters for principal component score plots were well separated, indicating that the changes IR-active components in the coffee extracts, due to the different roasting treatments, can be discriminated by the FTIR technique. On the basis of the loading plots of principal components, changes of IR-active compounds in the coffee extract at various stages of roasting were discussed.

Encapsulation of folic acid and its stability in sodium alginate-pectin-poly(ethylene oxide) electrospun fibres

In this study, we investigated the effect of alginate-pectin-poly(ethylene oxide) (PEO) electrospun fibres on the stability of folic acid. Fibre-forming solutions containing folic acid were prepared by blending low- or medium-viscosity alginate with pectin. PEO was added to make the electrospinning process possible. Folic acid encapsulated in electrospun fibres achieved close to 100% retention when stored in the dark at pH 3 after 41 days of storage. By contrast, recovery of unencapsulated folic acid was 0% and 8% within the first day when stored at pH 3 in the presence and the absence of light, respectively. Electrospun fibres produced from the combination of alginate-pectin resulted in higher retention of folic acid compared to that of alginate alone. Nucleic magnetic resonance and FTIR results show that folic acid has been encapsulated in electrospun fibres through physical entrapment.

The Impact of Anthocyanin‐Rich Red Raspberry Extract (ARRE) on the Properties of Edible Soy Protein Isolate (SPI) Films

UNLABELLED To modify the properties of edible soy protein isolate (SPI) films, 0.5% anthocyanin-rich red raspberry (Rubus strigosus) extract (ARRE) (0.5 g raspberry powder in 95% ethyl alcohol/water/85% lactic acid [80:19:1. v/v/v]) was incorporated into film-forming solutions. ARRE resulted in an SPI film having significantly enhanced tensile strength (P < 0.05) and % elongation at break (P < 0.05), as well as increased water swelling ratio (P < 0.05) and in vitro pepsin digestibility (P < 0.05). The resultant films also showed significantly decreased water solubility and water vapor permeability (P < 0.05). In addition, ARRE increased darkness, redness, and yellowness film appearance as evidenced by a lower L* (P < 0.05), greater positive a* (P < 0.05), and a higher b* (P < 0.05) than the control film. Scanning electron microscopy images revealed that extract-added films had denser and more compact cross-section microstructure. Fourier transform infrared spectra illustrated that ARRE-created hydrogen bonding involved conformational changes of soy protein without destroying its backbone structure. SDS-PAGE electrophoretograms revealed that the extract induced intermolecular interaction of the soy protein monomers. Natural plant extracts would be a promising ingredient to make SPI films with different physicochemical properties and applications. PRACTICAL APPLICATION This study characterizes the potential physicochemical changes of SPI film with incorporated raspberry extract. Upon the above modification, the resultant film was found to enhance the applications of pure SPI film in food packaging. For example, SPI-ARRE film could prolong the usage life of SPI film due to increased strength, or could be useful as a desiccant (drying agent) such as a water-absorbing sheet for preserving dried foods due to its increased hydrophilic surface and water-swelling ratio. SPI-ARRE film could also be alternately used as a food wrap with unique color.

Effects of single and dual physical modifications on pinhão starch

Pinhão starch was modified by annealing (ANN), heat-moisture (HMT) or sonication (SNT) treatments. The starch was also modified by a combination of these treatments (ANN-HMT, ANN-SNT, HMT-ANN, HMT-SNT, SNT-ANN, SNT-HMT). Whole starch and debranched starch fractions were analyzed by gel-permeation chromatography. Moreover, crystallinity, morphology, swelling power, solubility, pasting and gelatinization characteristics were evaluated. Native and single ANN and SNT-treated starches exhibited a CA-type crystalline structure while other modified starches showed an A-type structure. The relative crystallinity increased in ANN-treated starches and decreased in single HMT- and SNT-treated starches. The ANN, HMT and SNT did not provide visible cracks, notches or grooves to pinhão starch granule. SNT applied as second treatment was able to increase the peak viscosity of single ANN- and HMT-treated starches. HMT used alone or in dual modifications promoted the strongest effect on gelatinization temperatures and enthalpy.