Theoretical and practical considerations in electrostatic depositioning of charged polymers

An interfacial engineering technology, based on the electrostatic deposition of charged polyelectrolytes onto surfaces of oppositely charged templates is reviewed with an emphasis on practical applications in the food, pharmaceutical and personal care industries. On interfaces of disperse systems consecutively deposited polymers provide major advantages in terms of physical and chemical stability of dispersions against superimposed stresses (pH, temperature, ionic strength, freezing, chilling, dehydration, lipid oxidation). The controlled deposition of multiple layers allows for a controlled and triggered release of incorporated functional components. This review highlights the basic principles of the layer‐by‐layer (LbL) electrostatic deposition method as well as some major advantages and drawbacks of this approach. An overview of several systems that can be used as templates for the deposition including emulsion droplets, liposomal vehicles, colloidal aggregates, and planar surfaces is given. Suitable substrates for the deposition are presented with a focus on charged biopolymers such as proteins or polysaccharides since they play an essential role in the formulation and stabilization of food, pharmaceutical and personal care applications. Issues and difficulties associated with implementing the technology on a larger, industrial scale are discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40099.     

An investigation of the hole machining processes on woven carbon-fiber reinforced polymers (CFRPs) using abrasive waterjets

An investigation of the hole cutting and drilling processes on woven carbon-fiber reinforced polymer sheets using abrasive waterjet (AWJ) is presented. The drilling process uses a stationary AWJ to impinge a target material to make a hole, while the cutting process requires an AWJ to penetrate the workpiece before moving in a circular path to cut a hole. It is found that the holes machined by both the processes exhibit similar geometrical features, where the diameter at the top is greater than at the bottom. It is further found that the holes from the drilling process have a better roundness than those from cutting process primarily due to the jet instability during cutting movement. Plausible trends of the hole characteristics (e.g., diameter and wall inclination) and defects (e.g., delamination) with respect to the process parameters are discussed. It is shown that water pressure is the major parameter affecting hole defects. The hole drilling process yields more severe defects than the cutting process because of the initial impact of the jet. Predictive models for machined hole diameter in both processes are developed. The model predictions are in good agreement with the experimental data under the corresponding conditions.     

Effect of reducing agents on physicochemical properties and gel-forming ability of surimi produced from frozen fish

Effects of different reducing agents (cysteine, ascorbic acid and sodium bisulfite) at various levels on physicochemical properties of protein, transglutaminase activity and gel properties of surimi produced from frozen croaker, lizardfish, threadfin bream and bigeye snapper were studied. Addition of cysteine resulted in the highest increase in the breaking force and the deformation of surimi gels, compared with other reducing agents. The optimum levels of cysteine were 0.05, 0.1, 0.05 and 0.1% (w/w) for surimi from frozen croaker, lizardfish, threadfin bream and bigeye snapper, respectively. Surimi from frozen croaker with cysteine added showed a similar breaking force and deformation to that produced from fresh fish. With addition of cysteine, an increase in sulfhydryl content with a concomitant decrease in disulfide bond content was generally observed. Ca²⁺ ATPase activity also increased, indicating the renaturation of the myosin molecule. T_max of peak 1 (myosin peak) of all surimi sols in the presence of cysteine was shifted to higher temperature. The increased transglutaminase activity was observed with addition of cysteine. Therefore, reducing agents, especially cysteine, recovered the denatured muscle proteins and activated the transglutaminase in the muscle, leading to the increased gel-forming ability of surimi produced from frozen fish.     

Using hydrocolloids to decrease oil absorption in banana chips

The aim of this research was to investigate the influence of hydrocolloids (alginate, CMC and pectin) on the oil absorption in fried banana chips. The control banana chips (no hydrocolloid treatment) had oil content as high as 40 g/100 g sample, whereas the sample blanched in 0.5 g CaCl₂/100 ml water and following with immersion in 1 g alginate/100 ml water exhibited a small decrease of oil uptake (p ≤ 0.05) to 38 g/100 g sample. The others which treated with 0.5 g CaCl₂/100 ml and 1 g pectin/100 ml water, and with 0.25 g CaCl₂/100 ml water and 1 g CMC/100 ml water absorbed much less oil (p ≤ 0.05), approximately 23 g/100 g sample. Besides, pectin-treated chips had higher sensory scores in all attributed than CMC-treated sample. These resulted showed that pectin was the most effective hydrocolloid for low fat fried banana chip production. Scanning electron microscope photographs indicted that coating banana chips with pectin was effective in protecting the cellular structure of the banana tissue from damage during deep-fat frying.     

Initial Droplet Size Impacts pH‐Induced Structural Changes in Phase‐Separated Polymer Dispersions

The effect of pH change on the morphology of whey protein isolate (WPI)–pectin dispersions obtained from phase‐separated systems after mild shear was studied. The purpose of this study was to examine the impact of mixing speed on the initial particle size of biopolymer complexes and their structure morphology after sequentially changing the pH. Therefore, solutions of WPI and pectin were combined at pH 6.1, allowed to phase separate and were then mildly homogenized at 50, 100, and 150 rpm, respectively, to form a dispersion containing differently sized WPI droplets in a surrounding pectin‐rich phase. Each dispersion was then subjected to a pH change, such as 6.1 to 5.2 and 3.2, by slowly adding hydrochloric acid. The systems morphology, size, appearance, rheology, and storage stability was then characterized by optical microscopy, static light scattering, visual inspections, and steady shear rheometry to gain insights into the structural rearrangements. Results indicated substantial changes in the structure of the dispersion when the pH was changed. Formation of core‐shell structures from the WPI droplets was observed at an intermediate pH. There, initial droplet size was found to affect structures formed, that is, core‐shell type particles would only form if droplets were large (>1.5 μm) prior to pH change. Insights gained may be of importance to food manufacturers intending to create new structures from mixtures of proteins and carbohydrates.