Structural and thermal properties of nanofibrillated whey protein isolate in the glassy state

Ultrasonication modifies the structural, thermal and functional properties of pumpkin seed protein isolate (PSPI)

Protein isolates from pumpkin seeds were prepared and then treated with high-intensity ultrasound (HIUS) using a probe-based method. The impact of ultrasonication on the physicochemical, molecular, and thermal properties of these isolates were analyzed and compared to untreated controls. Results showed significant improvements (p ≤ 0.05) in color (L*, a*, b* values), solubility, emulsification capacity, and stability, as well as a reduction in molecular weight, indicating enhanced functionality of the pumpkin seed protein isolates (PSPIs) after HIUS treatment. However, HIUS treatment decreased the denaturation temperature (Td), denaturation enthalpy (ΔH), thermal stability, and particle size of the isolates. With treatment durations ranging from 5 to 20 min, Td dropped from 67.31 °C to 56.38 °C, and ΔH declined from 45.78 to 35.43 J/g, likely due to structural and conformational modifications from ultrasonic-induced molecular bond disruptions. The greatest reduction in particle size, from 117.46 μm to 85.26 μm, was observed after 20 min of ultrasonication. X-ray diffraction (XRD) analysis showed two distinct diffraction peaks at 2θ = 10° and 2θ = 20°, indicating altered crystallite sizes post-ultrasound treatment. Ultrasonication induced structural and conformational changes in the pumpkin seed protein isolates, as confirmed by SDS-PAGE and weight loss analyses. Alterations in the SDS-PAGE profile and reduced weight loss were associated with improved solubility and enhanced thermal and functional properties in the treated pumpkin seed protein isolates. This emphasizes the potential of PSPI to increase their value-added potential through ultrasonication.

Acid-induced hydrogels of edible Chlorella pyrenoidosa protein with composite biopolymers network

This study aimed to prepare Glucono-δ-lactone (GDL)-induced Chlorella pyrenoidosa protein (CPP) hydrogel and further investigate the effect of polysaccharides on the mechanical properties and stability enhancement of the composite hydrogels. Polysaccharides composed of different ratios of low acyl gellan gum (GE) and guar gum (GU) imparted dense honeycomb-like networks and adjustable textural properties to the composite hydrogels induced by CaCl2. In particular, the hardness of hydrogels increased significantly from 14 to 833 g. Scanning electron microscopy results revealed that CPP-GE/GU composite hydrogels had better stable spatial porous structures. Moreover, fourier transform infrared spectroscopy (FTIR) indicated hydrogen bonding interaction between CPP and GE/GU. The composite network showed improved viscoelasticity, increased thermal stability, and self-healing ability of hydrogels. The composite hydrogels also showed high water holding (89-98%) and swelling (747-862%) properties compared to the pure CPP hydrogel. These findings further expand CPP hydrogel products and broaden application in plant protein-based food.

Characterization and kinetics of whey protein isolate amyloid fibril aggregates under moderate electric fields

Food proteins solutions enable the controlled flow of electrical current when subjected to a Moderate electric field (MEF). This application results in internal heat generation, known as ohmic heating, accompanied by electrochemical reactions. These effects play a significant role in influencing the formation of protein amyloid fibril aggregates (AFA), which have broad applications in food and biomedical fields, ranging from improving food texture to biomedical applications such as drug delivery and disease treatment. This study focused on investigating the formation of β-Lactoglobulin (β-lg) AFA under MEF conditions using WPI as protein source and various characterization techniques (e.g., Thioflavin T fluorescence, circular dichroism, and electron microscopy). The results indicated that MEF prolonged the lag phase of AFA formation. Furthermore, nucleation and fibril growth showed higher activation coefficients and cooperativity level (n > 2) compared to conventional heating method. MEF treatment resulted in unique fibril clustering and the presence of unexpected higher-order AFA networks confirmed by electron microscopy. These findings highlight the significant role of MEF in influencing the aggregation kinetics of β-lg AFA. Exploring further into the electrochemical and thermal effects during protein aggregation processes holds the key to unlocking deeper insights into fibril formation process.

Formation and Physicochemical Properties of Freeze-Dried Amyloid-Like Fibrils From Pinto Bean Protein: Amyloid-Like Fibrils From Pinto Bean Protein

Amyloid nanofibrils are long and thin strands with cross β structures associated by hydrogen bonds. These structures can be formed under suitable conditions commonly at low pH and high temperatures. Fibrillated pinto bean protein isolate (FPBPI) was made by heating pinto bean protein at 85°C in an acidic condition while gently stirring at initial protein solution concentrations of 4 mg/mL, 13 mg/mL, and 21 mg/mL. Freeze-dried FPBPI's physicochemical, structural, and thermal characteristics were assessed, and they were compared with a native pinto bean protein isolate (PBPI) as a control. An increase in Congo red spectral absorption at 544 nm was observed following the fibril formation process. The largest concentration of freeze-dried fibrillated protein exhibited the highest Congo red spectral absorption. Fibrillar proteins' Fourier transform infrared (FTIR) spectrograms with lower wave numbers were seen than the native protein. For native PBPI, transmission electron microscopy (TEM) images were globular in shape, but they changed to long and curly morphologies in fibrillated proteins. FPBPI has a lower melting enthalpy than native protein when measured by differential scanning calorimetry (DSC). With the rising initial protein content, the enthalpy rose. Concurrently, semicrystalline structure for native and fibrillated pinto bean proteins was revealed by X-ray diffraction (XRD) findings. As the original protein concentration grew, so did the crystallinity intensity. Water-holding capacity (WHC) and oil-holding capacity (OHC) of freeze-dried FPBPI were higher than those of native protein. So, fibrillation of pinto bean protein helped it to serve as a good thickener in food industries.

Using silver nanoparticle-decorated whey protein isolate amyloid fibrils to modify the electrode surface used for electrochemical detection of para-nitrophenol

Due to their organized structures, remarkable stiffness, and nice biocompatibility and biodegradability, amyloid fibrils serve as building blocks for versatile sustainable materials. Silver nanoparticles (AgNPs) are commonly used as the nano-catalysts for various electrochemical reactions. Given their large specific surface area and high surface energy, AgNPs exhibit high aggregation propensity, which hampers their electrocatalytic performance. Food protein wastes have been identified to be associated with climate change and environmental impacts, and a surplus of whey proteins in dairy industries causes high biological and chemical demands, and greenhouse gas emissions. This study is aimed at constructing sustainable electrode surface modifiers using AgNP-deposited whey protein amyloid fibrils (AgNP/WPI-AFs). AgNP/WPI-AFs were synthesized and characterized via spectroscopic techniques, electron microscopy, and X-ray diffraction. Next, the electrocatalytic performance of AgNP/WPI-AF modified electrode was assessed via para-nitrophenol (p-NP) reduction combined with various electrochemical analyses. Moreover, the reaction mechanism of p-NP electrocatalysis on the surface of AgNP/WPI-AF modified electrode was investigated. The detection range, limit of detection, sensitivity, and selectivity of the AgNP/WPI-AF modified electrode were evaluated accordingly. This work not only demonstrates an alternative for whey valorization but also highlights the feasibility of using amyloid-based hybrid materials as the electrode surface modifier for electrochemical sensing purposes.

From Fundamental Amyloid Protein Self-Assembly to Development of Bioplastics

Proteins can self-assemble into a range of nanostructures as a result of molecular interactions. Amyloid nanofibrils, as one of them, were first discovered with regard to the relevance of neurodegenerative diseases but now have been exploited as building blocks to generate multiscale materials with designed functions for versatile applications. This review interconnects the mechanism of amyloid fibrillation, the current approaches to synthesizing amyloid protein-based materials, and the application in bioplastic development. We focus on the fundamental structures of self-assembled amyloid fibrils and how external factors can affect protein aggregation to optimize the process. Protein self-assembly is essentially the autonomous congregation of smaller protein units into larger, organized structures. Since the properties of the self-assembly can be manipulated by changing intrinsic factors and external conditions, protein self-assembly serves as an excellent building block for bioplastic development. Building on these principles, general processing methods and pathways from raw protein sources to mature state materials are proposed, providing a guide for the development of large-scale production. Additionally, this review discusses the diverse properties of protein-based amyloid nanofibrils and how they can be utilized as bioplastics. The economic feasibility of the protein bioplastics is also compared to conventional plastics in large-scale production scenarios, supporting their potential as sustainable bioplastics for future applications.

Production and functional evaluation of nonfat dry milk with whey proteins as fibrils

Commercial manufacturing of dairy products involves the addition of dairy ingredients (such as nonfat dry milk and milk protein concentrates), as well as nondairy additives (such as gums, stabilizers, emulsifiers, and texture modifiers) to get the best product appearance, maintain the product quality, and extend shelf life. Though these nondairy additives are not harmful, consumers do not prefer them in dairy food formulations. Therefore, the dairy industry is working on improving the inherent functionality of dairy ingredients using different processes. Recently, fibrillation emerged as a new technique to convert globular proteins such as whey proteins into fibrils, which provide enhanced viscosity, foaming, and emulsification capacity. Therefore, skim milk was subjected to microfiltration followed by ultrafiltration of microfiltration permeate to fractionate whey proteins. Then, whey proteins were selectively fibrillated and mixed back with other streams of microfiltration and ultrafiltration to get fibrillated skim milk. Fibrillated skim milk was spray-dried to get fibrillated nonfat dry milk (NDM). Visible whey protein fibrils were observed in reconstituted fibrillated NDM, which showed survival of fibrils in fibrillated NDM. Fibrillated NDM showed significantly higher viscosity than control NDM. Fibrillated NDM also showed higher emulsification capacity, foaming capacity, and stability than the control NDM but lower gel strength. Considering the improved functionality of fibrillated NDM, they can be used in product formulations such as ice cream mix, where the thickening of a solution, good emulsification, and foaming properties are required.

Fabrication of high strength cold-set sodium alginate/whey protein nanofiber double network hydrogels and their interaction with curcumin

Enhancing the bio-based hydrogels strength is fundamental to extend their engineering applications. In this study, high strength cold-set sodium alginate/whey protein nanofiber (SA/WPN) double network hydrogels were prepared and their interaction with curcumin (Cur) was studied. Our results indicated that the rheological and textural properties of SA/WPN double network hydrogels were enhanced with increasing WPN by forming SA-COO^--Ca²⁺-^-OOC-WPN bridge through electrostatic interactions. The storage modulus (768.2 Pa), hardness (273.3 g), adhesiveness (318.7 g·sec) and cohesiveness (0.464) of SA/WPN50 (WPN concentration of 50 mg/mL) double network hydrogels were 3.75, 2.26, 3.76 and 2.19 times higher than those of SA hydrogels, respectively. Cur was combined with SA/WPN hydrogels through hydrogen bonding, van der Waals forces and hydrophobic interactions with an encapsulation efficiency of 91.6 ± 0.8 %, and the crystalline state was changed after binding. In conclusion, SA/WPN double network hydrogels can be enhanced by the addition of WPN and have potential as carriers for hydrophobic bioactive substances.

Whey Protein Films for Sustainable Food Packaging: Effect of Incorporated Ascorbic Acid and Environmental Assessment

The management of food waste and by-products has become a challenge for the agri-food sector and an example are whey by-products produced in dairy industries. Seeking other whey valorisation alternatives and applications, whey protein films for food packaging applications were developed in this study. Films containing different amounts (0, 5, 10, and 15 wt%) of ascorbic acid were manufactured via compression-moulding and their physicochemical, thermal, barrier, optical, and mechanical properties were analysed and related to the film structure. Additionally, the environmental assessment of the films was carried out to analyse the impact of film manufacture. Regarding physicochemical properties, both FTIR and water uptake analyses showed the presence of non-covalent interactions, such as hydrogen bonding, between whey protein and ascorbic acid as band shifts at the 1500-1700 cm^-1 region as well as a water absorption decrease from 380% down to 240% were observed. The addition of ascorbic acid notably improved the UV-Vis light absorbance capacity of whey protein films up to 500 nm, a relevant enhancement for protecting foods susceptible to UV-Vis light-induced lipid oxidation. In relation to the environmental assessment, it was concluded that scaling up film manufacture could lead to a reduction in the environmental impacts, mainly electricity consumption.

Effects of ultrasound pretreatment on functional property, antioxidant activity, and digestibility of soy protein isolate nanofibrils

Nanofibrils, an effective method to modulate the functional properties of proteins, can be promoted by ultrasound pretreatment. This study investigated the effect of ultrasound pretreatment on the structure, functional property, antioxidant activity and digestibility of soy protein isolate (SPI) nanofibrils. The results showed that high amplitude ultrasound had a significant effect on structure of SPI nanofibrils. SPI nanofibrils pretreated by 80% amplitude ultrasound showed a blueshift of the amide II band in Fourier transform infrared spectroscopy (FTIR), resulted in more tryptophan residues being buried and increased the crystallinity. Low amplitude ultrasound (20%) pretreatment significantly improved the solubility, emulsifying activity index (EAI) and water absorption capacity (WAC) of SPI nanofibrils, but 80% amplitude ultrasound pretreatment of SPI nanofibrils reduced emulsifying stability index (ESI). High amplitude ultrasound (60% and 80%) pretreatment of SPI nanofibrils improved the foaming capacity and foaming stability and decreased denaturation temperature. DPPH radical scavenging activity of SPI nanofibrils were significantly improved by ultrasound pretreatment. 20% amplitude ultrasound pretreatment improved DPPH, ABTS radical scavenging activity and ferric reducing antioxidant power of SPI nanofibrils. The digestion rate of 80% amplitude ultrasound-pretreated nanofibrils were consistently higher, and SPI nanofibrils pretreated by ultrasound were more fragmented and shorter after simulating gastrointestinal digestion. This study would expand the application of food-grade protein nanofibrils in the food industry.

Homogeneous nuclei-induced, secondary nuclei-induced, and spontaneous whey protein concentrate nanofibril formation through different pathways

The addition of homogeneous nuclei (HN) or secondary nuclei (SN) could lead to different kinetics and thermodynamics as the nucleation energy barrier decreases and the lag time is shortened to different degrees compared with spontaneous fibrillation. To explain these differences, we monitored the formation and depletion of HN during fibril formation and found that both SN-induced fibrils and HN-induced fibrils follow the same nucleated growth pathway as spontaneously formed WPC fibrils. Moreover, there were also other paths, which were confirmed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The surfaces of the SN could recruit monomers and resulted in stronger intersheet stacking and a larger fibril height and periodicity. The HN incorporation led to a propensity for hydrogen-bonding interactions and a longer fibril. Fibrillation by the addition HN and SN followed both common and distinct pathways, as spontaneous fibrillation and led to different capacities to induce fibrillation.

Whey Protein Isolate Microgel Properties Tuned by Crosslinking with Organic Acids to Achieve Stabilization of Pickering Emulsions

Whey protein isolate (WPI) can be used effectively to produce food-grade particles for stabilizing Pickering emulsions. In the present study, crosslinking of WPI microgels using organic acids (tannic and citric acids) is proposed to improve their functionality in emulsions containing roasted coffee oil. It was demonstrated that crosslinking of WPI by organic acids reduces the microgels’ size from ≈1850 nm to 185 nm and increases their contact angle compared to conventional WPI microgels, achieving values as high as 60°. This led to the higher physical stability of Pickering emulsions: the higher contact angle and smaller particle size of acid-crosslinked microgels contribute to the formation of a thinner layer of particles on the oil/water (O/W) interface that is located mostly in the water phase, thus forming an effective barrier against droplet coalescence. Particularly, emulsions stabilized by tannic acid-crosslinked WPI microgels presented neither creaming nor sedimentation up to 7 days of storage. The present work demonstrates that the functionality of these crosslinked WPI microgels can be tweaked considerably, which is an asset compared to other food-grade particles that mostly need to be used as such to comply with the clean-label policy. In addition, the applications of these particles for an emulsion are much more diverse as of the starting material.