School of Chemistry - Research Publications
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ItemNo Preview AvailableIncorporating whey protein aggregates produced with heat and ultrasound treatment into rennet gels and model non-fat cheese systems(Elsevier, 2020-12-01)Native whey proteins (WP) are expulsed from cheese coagulation during syneresis. Although incorporating denatured WP aggregates into cheese gels has been previously proposed to improve the overall cheese yield, the effects of WP aggregate properties on gelation kinetics and protein retention are not yet fully understood. In this study, heat and power ultrasound were used to produce denatured whey protein aggregates with a wide range of sizes. The effects of size and hydrophobicity differences in WP aggregates produced by heat and heat coupled with ultrasound were investigated in relation to the kinetics of rennet gelation and protein retention in model non-fat cheddar cheeses. Rheological measurements showed that sufficiently large, denatured WP aggregates could avoid impairment of rennet gelation caused by native WP, irrespective of changes in the soluble calcium concentration or the surface hydrophobicity of the aggregates. WP aggregates formed by the combined heat and ultrasound treatment were more hydrophobic than the larger heat-treated aggregates and were better retained in the cheese. However, inclusion of sufficiently large aggregates in cheese milk conferred an openness to the cheese microstructure and showed promise in improving the otherwise rigid non-fat cheese.
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ItemProtein fortification of model cheese matrices using whey protein-enriched double emulsions(Elsevier, 2023-02)Whey proteins represent 20% of the protein content of milk and are an underutilised by-product of cheese manufacturing. This study was aimed at encapsulating whey proteins in the fat content of cheese using double emulsions. A two-stage power ultrasound (20 kHz) emulsification process was used to produce double emulsions with an internal aqueous phase enriched with high concentrations of whey proteins contained within droplets of sunflower oil. Primary water-in-oil (W1/O) nanoemulsions were successfully formed at an applied ultrasonic power of 1.35 W/mL, using 20% w/w and 30% w/w whey protein concentrate (WPC) solutions in the internal phase. The inner water droplets were stabilised by a combination of food grade lipophilic emulsifiers included in the sunflower oil at minimum concentrations of 1% w/w lecithin and 3% w/w PGPR. The secondary oil emulsions were formed by emulsifying the primary W1/O emulsions in 5% w/w WPC solutions, with the whey proteins serving as the emulsifying agent. The encapsulation loading rate of whey proteins within the double emulsion droplets was investigated in relation to ultrasound parameters and formulation loading rates. A very high encapsulation loading rate of ∼45 gwhey protein/Ldouble emulsion was achieved using 0.81 W/mL of ultrasound, with oil droplets of comparable diameter to native milk fat globules (∼10 μm). These double emulsions were successfully incorporated into renneted and cooked curd systems to enable the retention of whey protein in cheese matrices. This study demonstrates the potential of ultrasound emulsification to form whey protein-enriched double emulsions with minimum food-grade emulsifiers to fortify the protein content of cheese and other food products.
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ItemNo Preview AvailableTurbulence-dependent reversible liquid-gel transition of micellar casein-stabilised emulsions(ELSEVIER SCI LTD, 2022-10)
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ItemUltrasound-induced protein restructuring and ordered aggregation to form amyloid crystals(SPRINGER, 2022-07)Amyloid crystals, a form of ordered protein aggregates documented relatively recently, have not been studied as extensively as amyloid fibres. This study investigates the formation of amyloid crystals with low frequency ultrasound (20 kHz) using β-lactoglobulin, as a model protein for amyloid synthesis. Acoustic cavitation generates localised zones of intense shear, with extreme heat and pressure that could potentially drive the formation of amyloid structures at ambient bulk fluid temperatures (20 ± 1 °C). Thioflavin T fluorescence and electron microscopy showed that low-frequency ultrasound at 20 W/cm3 input power induced β-stacking to produce amyloid crystals in the mesoscopic size range, with a mean length of approximately 22 µm. FTIR spectroscopy indicated a shift towards increased intermolecular antiparallel β-sheet content. An increase in sonication time (0-60 min) and input power (4-24 W/cm3) increased the mean crystal length, but this increase was not linearly proportional to sonication time and input power due to the delayed onset of crystal growth. We propose that acoustic cavitation causes protein unfolding and aggregation and imparts energy to aggregates to cross the torsion barrier, to achieve their lowest energy state as amyloid crystals. The study contributes to a further understanding of protein chemistry relating to the energy landscape of folding and aggregation. Ultrasound presents opportunities for practical applications of amyloid structures, presenting a more adaptable and scalable approach for synthesis.
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ItemTurbulence-induced formation of emulsion gels(ELSEVIER, 2021-12)Emulsion gels have a wide range of applications. We report on a facile and versatile method to produce stable emulsion gels with tunable rheological properties. Gel formation is triggered by subjecting a mixture containing aqueous colloidal particle (CP) suspensions and water-immiscible liquids to intense turbulence, generated by low frequency (20 kHz) ultrasound or high-pressure homogenization. Through systematic investigations, requisite gel formation criteria are established with respect to both formulation and processing, including ratio/type of liquid pairs, CP properties, and turbulence conditions. Based on the emulsion microstructure and rheological properties, inter-droplet bridging and CP void-filling are proposed as universal stabilization mechanisms. These mechanisms are further linked to droplet-size scaling and sphere close-packing theory, distinctive from existing gel-conferring models. The study thereby provides the foundation for advancing the production of emulsion gels that can be tailored to a wide range of current and emerging applications in the formulation and processing of food, cosmetics or pharmaceutical gels, and in material science.
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ItemInnovative Technologies for Extraction and Microencapsulation of Bioactives from Plant-Based Food Waste and Their Applications in Functional Food Development(MDPI, 2021-02)The by-products generated from the processing of fruits and vegetables (F&V) largely are underutilized and discarded as organic waste. These organic wastes that include seeds, pulp, skin, rinds, etc., are potential sources of bioactive compounds that have health imparting benefits. The recovery of bioactive compounds from agro-waste by recycling them to generate functional food products is of increasing interest. However, the sensitivity of these compounds to external factors restricts their utility and bioavailability. In this regard, the current review analyses various emerging technologies for the extraction of bioactives from organic wastes. The review mainly aims to discuss the basic principle of extraction for extraction techniques viz. supercritical fluid extraction, subcritical water extraction, ultrasonic-assisted extraction, microwave-assisted extraction, and pulsed electric field extraction. It provides insights into the strengths of microencapsulation techniques adopted for protecting sensitive compounds. Additionally, it outlines the possible functional food products that could be developed by utilizing components of agricultural by-products. The valorization of wastes can be an effective driver for accomplishing food security goals.
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ItemThe effect of high-intensity ultrasound on cell disruption and lipid extraction from high-solids viscous slurries of Nannochloropsis sp biomass(ELSEVIER SCIENCE BV, 2018-11-01)The effect of ultrasonication on the cell rupture of marine microalgae Nannochloropsis sp. was studied as a function of the slurry solids concentration and treatment time. The concentrated viscous wet-biomass (~12 to 25% solids concentration) was subjected to ultrasonication (20 kHz) at 3.8 W/mL for up to 5 min. Compared to extraction without cell rupture, sonication led to a significant increase in lipid yield from ~11% to about 70% within 5 min of sonication. The extraction yield was found to decrease with increased solids concentration, with a large decrease between 20% to 25% solids. This is attributed to the increase in viscosity and decrease in speed of sound with increase in solids. The ultrasound attenuation coefficient increased 320-fold as the solids increased from 20 to 25%. Such a large attenuation of ultrasound places a limit of 20% solids to be used for cell rupture by ultrasound. The specific energy requirements per unit mass of extracted lipid were lowest at 20% solids. At lower concentrations energy was wasted heating water, at higher concentrations the lipid yields were reduced due to ultrasound attenuation.
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ItemEffect of Bulk Viscosity and Emulsion Droplet Size on the Separation Efficiency of Model Mineral Oil-in-Water (O/W) Emulsions under Ultrasonic Standing Wave Fields: A Theoretical and Experimental Investigation(American Chemical Society (ACS), 2020-04-22)Ultrasound standing waves can be used to separate emulsions. So far, they have been applied to oil-in-water emulsions with low continuous phase viscosity. This technique has the potential to be used for novel applications such as separating lipids from algal biomass; however, this requires the methodology to be optimized to process viscous emulsions. We have addressed this issue by studying the effects of bulk phase viscosity (1–23 mPa·s), emulsion droplet size (4.5–20 μm), power (10–54 W/L), and frequency (1 and 2 MHz) of ultrasound on the separation efficiency of model mineral oil-in-water–glycerol-mixture emulsions. For the small droplet size (4.5 μm) emulsion in water, the maximum separation achieved increased from 36 to 79% when ultrasound power increased from 10 to 54 W/L. However, for the large droplet size (11 μm) emulsion, the maximum separation was greater than 95% and was independent of ultrasound power. The maximum separation efficiency for small droplet size (4.5–6 μm) emulsions decreased from 80 to 14% when the viscosity increased from 1 to 23 mPa·s. However, for the large droplet size (11–20 μm) emulsion, the maximum separation efficiency decreased from 98 to 62% when the viscosity of the bulk phase was increased from 1 to 23 mPa·s. The experimental results were then interpreted using analytical and numerical simulations by calculating the time required for the emulsion droplets to migrate to the nearest pressure antinodal plane under the influence of ultrasound standing waves. Further experiments showed that increasing the ultrasound frequency from 1 to 2 MHz increased the maximum separation from 36 to 86% for fine emulsions and water as the continuous phase.