School of Chemistry - Research Publications
Permanent URI for this collection
Search Results
1 - 8 of 8
-
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.
-
ItemNo Preview Available
-
ItemNo Preview AvailableTurbulence-dependent reversible liquid-gel transition of micellar casein-stabilised emulsions(ELSEVIER SCI LTD, 2022-10)
-
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.
-
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.
-
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.
-
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.
-
ItemFormation of Cheddar cheese analogues using canola oil and ultrasonication – a comparison between single and double emulsion systems(Elsevier BV, 2020-06)Cheddar cheese analogues were produced from skim milk in which canola oil was emulsified using ultrasound to form either single (O/W) or double emulsions (W1/O/W2). The double emulsion cheese analogues (DECH) had a distinct microstructure and retained small skim milk droplets, dispersed in the fat phase, for more than 7 months of aging at 4 °C. The single emulsion cheese analogues (SECH), prepared with the same fat content as control cheeses, produced comparable yields of cheese and whey, with similar composition, although the fat droplets were more spherical and showed greater coalescence. The DECH cheese with skim milk encapsulated in the oil droplets was harder, melted less and showed more free fatty acid development over 7 months of aging than the control cheeses. The SECH cheeses were softer than the control and also melted less effectively but did not show greater free fatty acid development.