Richard Ashby - Academia.edu (original) (raw)

Papers by Richard Ashby

Food Science and Biotechnology, 2006

INFORM International News on Fats, Oils, and Related Materials, 2021

Household detergents have undergone many formulation updates to improve the cleaning power of sur... more Household detergents have undergone many formulation updates to improve the cleaning power of surfactants and to adapt formulations to specific applications. This paper focuses on more recent developments in the use of surfactants for household as well as industrial use. Specific examples include the use of enzymes derived from moderately thermophilic bacteria as laundry detergent additives, the use of surfactants and surfactant additives in the manufacture of warm mix asphalt, and the use of foaming agents in chemical enhanced oil recovery.

Progress in Organic Coatings, 2020

Abstract Epoxy resins are one class of important reactive pre-polymers used in the coating indust... more Abstract Epoxy resins are one class of important reactive pre-polymers used in the coating industry. To manufacture epoxy resins with antimicrobial properties, active quaternary ammonium groups are often introduced into the polymeric backbones following resin polymerization reactions for structure modification. However, these complicated approaches associated with these types of reactions make the commercialization of the antimicrobial epoxy polymers uneconomical, impractical and inconvenient. Besides, quaternary ammonium groups are undesirable because the hydrophilicity of the groups makes the resins less water-resistant. In order to simplify the development of antimicrobial epoxy polymers, we prepared an amide by reacting novel bio-based phenolic-branched fatty acids with ethylenediamine. The resulting amide was cured into a commercial epoxy resin -- diglycidyl ether of bisphenol A (DGEBA), which was solution-cast into epoxy polymer films. The antimicrobial activities of the resulting epoxy polymer films were investigated. The crude phenolic branched fatty acid amides (PBC-FAAs) as curing agents were separated and characterized by thin-layer chromatography, proton nuclear magnetic resonance (1H-NMR), gas chromatography-mass spectrometry (GC MS), liquid chromatography-mass spectrometry (LC/MS) and Fourier-transform infrared spectroscopy (FT-IR). The thermal and mechanical properties of the polymer films were also investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Cured epoxy films prepared from purified PBC-FAA exhibited antimicrobial activity against Listeria innocua. However, the crude, unpurified PBC-FAA-cured epoxy film showed much more promising antimicrobial activity against both Listeria innocua (Gram positive) and Escherichia coli (Gram negative).

Starch - Stärke, 2016

The rheological properties of waxy starch‐γ‐polygutamic acid (PGA) graft copolymers were investig... more The rheological properties of waxy starch‐γ‐polygutamic acid (PGA) graft copolymers were investigated. Grafting was confirmed by FTIR spectroscopy. The starch–PGA copolymers absorbed water and formed gels, which exhibited concentration‐dependent viscoelastic solid properties. Higher starch–PGA concentrations resulted in stronger viscoelastic properties. The analysis for moduli of different concentrations indicated that the starch–PGA graft copolymer gels were physical gels, meaning the cross‐links between the molecules were physical junctions. However, stress relaxation measurements showed that the starch–PGA graft copolymer gels had long relaxation times, which result from the presence of the chemical cross‐links that were evident in the FTIR spectra. The non‐linear steady shearing rheological properties studies indicated that starch–PGA gels exhibited shear thinning behavior, which can be well fitted with the power law constitutive equation. The function and behavior of the starch–PGA graft copolymer gels suggest that this kind of starch‐based biomaterial could be a potential candidate for applications in cosmetic gels, skin wound care materials, and agricultural products.

Journal of Biobased Materials and Bioenergy, 2009

ABSTRACT Cast gelatin films were plasticized with a biodiesel coproduct stream (BCS). Films were ... more ABSTRACT Cast gelatin films were plasticized with a biodiesel coproduct stream (BCS). Films were well formed and appeared homogeneous by visual inspection. There is no deterioration in mechanical properties when BCS replaces glycerol as plasticizer. A BCS content of 18-34% resulted in elongations of 35-182%, with corresponding tensile strengths of 45-6 MPa and elastic moduli of 1330-38 MPa. Factor analysis indicated that replacing glycerol with BCS increases elongation but has little effect on tensile strength or modulus. The use of BCS as a plasticizer for biopolymers would increase the value of BCS, increase the value of agricultural fats and oils from which biodiesel is synthesized, and increase the feasibility of fuel production in a biorefinery. The use of low-cost BCS may also increase the feasibility of producing thermoplastics from gelatin and from other biopolymers now more expensive than starch.

Salted hides and soaked hides treated with certain antibacterial agents, may still contain differ... more Salted hides and soaked hides treated with certain antibacterial agents, may still contain different proteolytic and lipolytic Gram-positive and Gram-negative bacteria that affect the quality of leather adversely. The prevalence of bacteria resistant to antimicrobial agents in the leather industry has drawn attention of scientists to search new and effective antimicrobial agents. Examination of antimicrobial glycolipids such as sophorolipids for their effectiveness against proteolytic and lipolytic hidedegrading microorganisms, may offer important information. Hence, we describe a research that evaluates the susceptibility of various hide-degrading bacteria to sophorolipids. These extracellular glycolipids were produced by fermentation using Candida bombicola ATCC 22214. Palmitic acid, stearic acid, and oleic acid were used respectively to produce SL-p, SL-s, and SL-o. The minimal inhibitory concentrations (MICs) of SL-p, SL-s, and SL-o against Gram-positive endospore-forming bacter...

Biobased Surfactants, 2019

Abstract Sophorolipids (SLs) are glycolipids produced by many yeast species. They are amphiphilic... more Abstract Sophorolipids (SLs) are glycolipids produced by many yeast species. They are amphiphilic molecules and therefore possess the attributes of surfactants. Research has shown that they additionally possess various other useful biological and physicochemical properties that add value to SLs in certain applications. This chapter surveys the various natural yeast species known to produce SLs and documents the structural varieties of the products. The genetic engineering of the producing organisms and the resultant SLs being generated are described along with the advances in process development, that is, fermentation and purification together with the important process parameters such as productivity, yield, titers, and product types. Finally, the chapter concludes by surveying the all-important biological activities of SLs, such as antimicrobial, antiviral, antifungal, and anticancer properties, and demonstrates the emulsifying and taste sensory properties of SLs, useful in potential applications in the food industry.

Journal of Surfactants and Detergents, 2019

Sophorolipids (SL) are typically produced and secreted by select nonpathogenic yeast species (i.e... more Sophorolipids (SL) are typically produced and secreted by select nonpathogenic yeast species (i.e., Candida) from renewable substrates. They are currently being used by industry on a limited basis in formulations for cleaning solutions as well as laundry and dishwashing detergents. Due to the nature of their chemical structure, it was hypothesized that SL would demonstrate taste‐sensory properties. In this study, SL were produced via fermentation on a mixed substrate platform with glucose and either palmitic acid, stearic acid, or oleic acid using Candida (currently reclassified as Starmerella) bombicola ATCC 22214. The taste properties of SL were determined using a single‐cell manual calcium imaging technique on cultured human fungiform taste papillae (HBO) cells. The results of those studies demonstrated that sweetener‐responsive HBO cells also respond to SL, and these responses are mediated by the type 1 taste receptors 3 (T1R3), because they were blocked by lactisole (a T1R3 rec...

Journal of the American Oil Chemists' Society, 2015

estolides, the plasticity and elongation improved validating that these unique SL-derived estolid... more estolides, the plasticity and elongation improved validating that these unique SL-derived estolides can be effectively used as plasticizers in P3HB films.

Biocatalysis and Agricultural Biotechnology, 2015

Sophorolipid (SL) purified from fermentation broth of Candida bombicola grown on oleic acid and g... more Sophorolipid (SL) purified from fermentation broth of Candida bombicola grown on oleic acid and glucose substrates was embedded at 0, 9, 17, and 29% (%-total weight of final product) in solvent-cast films of poly(L-lactic acid) (PLLA), poly(ε-caprolactone), and poly(hydroxybutyrate) (PHB). Growth-inhibition activity of the SL-biopolymers against Propionibacterium acnes, a causative agent of acne vulgaris skin condition, is dependent on the SL contents of the films; the degree of inhibition as determined from the width of the zone of inhibition in agar-plate assays follows the order of SL-PCL > SL-PLLA > SL-PHB. The release of SL from the films into aqueous medium after a 4-d shaking at 25°C showed that SL-PLLA (30.1 ± 1.7 wt-% SL released) most readily released the embedded SL, followed by SL-PHB (11.4 ± 4.3 wt-%) and SL-PCL (4.3 ± 1.4 wt-%). Thermal properties as determined by differential scanning calorimetry showed that SL decreases the heat of fusion (ΔH) and the melting temperature (T m) of the biopolymers, indicating for the first time its usefulness as a plasticizer to prevent crystallization. In summary, the study shows the feasibility of controlling the release of antimicrobial SL by varying the type of biopolymer used, with the added advantage of SL functioning as a plasticizer to improve the physical properties of the film in term of lower crystallinity. Future research could benefit the agricultural sector via new developments as varied as antimicrobial food packaging and algal bloom mitigation.

Journal of the American Oil Chemists' Society, 2011

One refined and two crude glycerol (from biodiesel production) samples were utilized to produce p... more One refined and two crude glycerol (from biodiesel production) samples were utilized to produce poly(3-hydroxybutyrate) (PHB) by Pseudomonas oleovorans NRRL B-14682. A batch culture fermentation protocol including 1% glycerol and an aeration rate of 3 standard liters per minute proved best for PHB synthesis (av. yield = 1.0 ± 0.2 g/L at 48 h) and efficient glycerol utilization. PHB molecular weights decreased as MeOH concentration increased. Refined glycerol resulted in PHB polymers with number average molecular weights (M n) of 314,000 g/mol which decreased by 17 and 90% as MeOH media concentrations increased to \0.005 and 0.85%, respectively. Proton (1 H) NMR demonstrated the presence of glycerol-and methoxy-based end-capping, which was confirmed by 1 H diffusion experiments (DOSY analyses). NMR diffusion analyses of the PHB polymers established their diffusivities, and confirmed that their relative molecular sizes were dependent on the impurities in the glycerol. In addition, DOSY analyses indicated that each end-capped PHB polymer and the glycerol or methoxy groups bound to it had the same diffusion constants, demonstrating that they migrated together as covalent complexes. Non-covalent complexation was eliminated by physically mixing free glycerol with PHB synthesized from oleic acid; their respective diffusivities were notably faster.

Biotechnology Letters, 2010

Candida bombicola, a known producer of sophorolipids (SLs; glycolipid surfactants), was grown on ... more Candida bombicola, a known producer of sophorolipids (SLs; glycolipid surfactants), was grown on glycerol and oleic acid with up to 1.5% (v/v) methanol in the fermentation growth media to assess the effects of methanol presence on SL synthesis and structural distribution. Increasing methanol concentrations had little effect on the growth of the organism resulting in average cell dry weights (CDW; after SL separation) of 20.8 ± 0.7 g/l between 0 and 1.5% methanol. However, increasing methanol concentrations decreased SL production by 56% (from 12.7 to 5.6 g/l at 1.5% methanol) which translated to SL yields on a cellular basis of between 0.60 g SL/g cells (in the absence of methanol) to 0.27 g SL/g cells (in the presence of 1.5% methanol). LC/MS revealed that increased methanol concentrations also resulted in larger concentrations (up to 20 mol%) of free acid SLs but had little effect on the ratios of diacetylated SL lactones synthesized with palmitic acid (4 mol%), linoleic acid (3 mol%), oleic acid (80 mol%), and stearic acid (13 mol%) as the hydrophobic moieties.

Express Polymer Letters, 2009

In order to explore the possibility of substituting an unrefined biodiesel coproduct stream (BCS)... more In order to explore the possibility of substituting an unrefined biodiesel coproduct stream (BCS) for refined glycerol as a polymer plasticizer we have prepared cast gelatin films plasticized with a simulated BCS, i.e., mixtures of glycerol and some of the typical components found in BCS (methyl linoleate, methyl oleate, linoleic acid, and oleic acid). We measured the tensile properties as a function of plasticizer composition, and analyzed the specific effect of each individual component on tensile properties. We found that it is the unrecovered alkyl esters that largely determine the tensile properties, and that BCS can be successfully used to plasticize cast gelatin films as long as the BCS contains 11 parts by weight, or less, of unrecovered alkyl esters per 100 parts glycerol.

Journal of the American Oil Chemists' Society, 2012

ABSTRACT In this study, the stability of oil-in-water (O/W) emulsions prepared with structured li... more ABSTRACT In this study, the stability of oil-in-water (O/W) emulsions prepared with structured lipid (SL) were evaluated in which the SL was produced through lipase-catalyzed interesterification between soybean oil and rice bran oil. After interesterification, the major TAG species in the SL were PLP (22.5 %), PLL/OOLn (21.8 %), LPL (16.1 %), and LLS/PLO (16.1 %), and the total amount of tocopherol and tocotrienol was 20.9 mg/100 g of SL. Sophorolipid was used as an emulsifier for preparing SL-based O/W emulsions, and the effect of pH (pH 5.8, 7 and 7.2) on stability was studied by analyzing the fat globule size. From the results, SL-based O/W emulsions showed similar stabilities to those prepared with Tween 20 at the neutral environment. In the oxidation study, any antioxidant addition of propyl gallate (PG), ascorbic acid 6-palmitate (AP) or quercetin hydrate (Que) distinctively prevented peroxide formation on the SL-based O/W emulsion throughout the 23 days of storage while AP was less effective to lower TBARS values than PG and Que.

Journal of Surfactants and Detergents

Journal of Polymers and the Environment

Frontiers in microbiology, 2016

Food contaminated with human pathogens, such as Salmonella spp. and Listeria monocytogenes, frequ... more Food contaminated with human pathogens, such as Salmonella spp. and Listeria monocytogenes, frequently causes outbreaks of foodborne illness. Consumer concern over the use of synthesized antimicrobials to enhance microbial food safety has led to a search of natural alternatives. The objectives of this study were to evaluate the antimicrobial activity of various types of sophorolipids (SLs) and thiamine dilauryl sulfate (TDS) against pathogenic Salmonella spp. and Listeria spp. Both free and lactonic forms of SLs were synthesized from Candida bombicola using palmitic, stearic, and oleic acids as co-feedstocks. TDS and purified SLs were used to treat cocktails of Salmonella spp. and Listeria spp. Results showed that lactonic SLs had higher antimicrobial activity than the free-acid form, and Gram-positive Listeria spp. were more susceptible to SLs and TDS than Gram-negative Salmonella spp. Listeria populations were reduced from an initial concentration of 7.2 log CFU/mL to a non-detect...

Journal of microbiological methods, May 1, 2017

Sophorolipid (SL) is a class of glycolipid biosurfactant produced by yeast and has potent antimic... more Sophorolipid (SL) is a class of glycolipid biosurfactant produced by yeast and has potent antimicrobial activity against many microorganisms. In this paper, a microplate-based method was developed to characterize the growth inhibition by SL on five representative species of caries-causing oral bacteria. Bacterial growth on microplate in the absence and presence of varying concentrations of SL was continuously monitored by recording the absorbance at 600nm of the cultures using a microplate reader. The results showed that SL completely inhibited the growth of the Lactobacilli at ≥1mg/ml and the Streptococci at much lower concentrations of ≥50μg/ml. More importantly, we further defined the mechanism of antimicrobial activity of SL by analyzing the pattern of the cell growth curves. SL at sublethal concentrations (<1mg/ml) is bactericidal towards the Lactobacilli; it lengthens the apparent cell-doubling time (Td) and decreases the final cell density (as indicated by A600nm) in a con...