Effect of high hydrostatic pressure on bovine α-lactalbumin functional properties

Impact of high-pressure processing on the bioactive compounds of milk - A comprehensive review

High-pressure processing (HPP) is a promising alternative to thermal pasteurization. Recent studies highlighted the effectivity of HPP (400-600 MPa and exposure times of 1-5 min) in reducing pathogenic microflora for up to 5 logs. Analysis of modern scientific sources has shown that pressure affects the main components of milk including fat globules, lactose, casein micelles. The behavior of whey proteins under HPP is very important for milk and dairy products. HPP can cause significant changes in the quaternary (> 150 MPa) and tertiary (> 200 MPa) protein structures. At pressures > 400 MPa, they dissolve in the following order: αs2-casein, αs1-casein, k-casein, and β-casein. A similar trend is observed in the processing of whey proteins. HPP can affect the rate of milk fat adhering as cream with increased results at 100-250 MPa with time dependency while decreasing up to 70% at 400-600 MPa. Some studies indicated the lactose influencing casein on HP, with 10% lactose addition in case in suspension before exposing it to 400 MPa for 40 min prevents the formation of large casein micelles. Number of researches has shown that moderate pressures (up to 400 MPa) and mild heating can activate or stabilize milk enzymes. Pressures of 350-400 MPa for 100 min can boost the activity of milk enzymes by up to 140%. This comprehensive and critical review will benefit scientific researchers and industrial experts in the field of HPP treatment of milk and its effect on milk components.

Graphical abstract

Physical treatment synergized with natural surfactant for improving gas-water interfacial behavior and foam characteristics of α-lactalbumin

The purpose of this study was to investigate effect of physical treatment (ultrasound, U/high pressure homogenization, H/combined treatment, UH or HU) and surfactant (Mogroside V, Mog) on air/water interface adsorption and foaming properties of α-lactalbumin (ALa). Firstly, the binding of Mog and all physical-treated ALa was a static quenching process. Mog had the greatest binding affinity for HU-ALa among all treated samples. U or H treatment could change surface hydrophobicity of ALa/Mog complex. Secondly, at the molar ratio (ALa:Mog) of 1:50, foaming ability (FA) of all ALa samples got the maximum. The sequence of FA in ALa and ALa/Mog complex was listed as follow: HU > U > H > UH. Moreover, foaming stability (FS) of HU-ALa was the highest, followed by H-ALa, U-ALa and UH-ALa. Meanwhile, low concentration Mog increased FS of ALa or UH-ALa, but it reduced FS of H-ALa, U-ALa and HU-ALa. Quartz crystal microbalance with dissipation monitoring (QCM-D) experiment indicated that ALa/Mog complex after U or H treatment was quickly absorbed at air/water interface, compared with the treated ALa, and HU-ALa/Mog had the largest frequency shift. In addition, HU-ALa had the thickest bubble membrane and the highest dissipation shift in all samples, indicating that the absorbed membrane thickness and viscoelasticity of samples was correlated with foam stability. Therefore, U and H treatment synergism with Mog was an effective approach to enhance foam properties of ALa, which indicated that HU-treated ALa/Mog complex could be viewed as the safe and efficient foaming agent applied in food processing.

Effect of high hydrostatic pressure processing on the structure, functionality, and nutritional properties of food proteins: A review

Proteins are important food ingredients that possess both functional and nutritional properties. High hydrostatic pressure (HHP) is an emerging nonthermal food processing technology that has been subject to great advancements in the last two decades. It is well established that pressure can induce changes in protein folding and oligomerization, and consequently, HHP has the potential to modify the desired protein properties. In this review article, the research progress over the last 15 years regarding the effect of HHP on protein structures, as well as the applications of HHP in modifying protein functionalities (i.e., solubility, water/oil holding capacity, emulsification, foaming and gelation) and nutritional properties (i.e., digestibility and bioactivity) are systematically discussed. Protein unfolding generally occurs during HHP treatment, which can result in increased conformational flexibility and the exposure of interior residues. Through the optimization of HHP and environmental conditions, a balance in protein hydrophobicity and hydrophilicity may be obtained, and therefore, the desired protein functionality can be improved. Moreover, after HHP treatment, there might be greater accessibility of the interior residues to digestive enzymes or the altered conformation of specific active sites, which may lead to modified nutritional properties. However, the practical applications of HHP in developing functional protein ingredients are underutilized and require more research concerning the impact of other food components or additives during HHP treatment. Furthermore, possible negative impacts on nutritional properties of proteins and other compounds must be also considered.

Characterization of Soluble Glandless Cottonseed Meal Proteins Based on Electrophoresis, Functional Properties, and Microscopic Structure

This investigation aimed to extract and characterize the GCSM proteins, determine their solubility potential at two different temperatures and different solvents, and explore their functional properties. During the extraction, no water- or ethanol-soluble protein was found. Most of the protein was extracted with KOH solution. GCSM showed major protein bands between 13,273 and 56,564 Da with an isoelectric point of 5.1. The results showed that extraction temperature and solvent affected the amount of protein extracted from GCSM. The highest protein yield (63.4%) was obtained with KOH at 55 °C. Fat content negatively affected the protein solubility. The highest protein purity (99.9%) was obtained with 6% of fat content and the lowest one with 19% of fat content. GCSM has a high glutamic acid content, followed by arginine and aspartic acid compared to the other amino acids. The essential amino acids make up about 30.0% of the total amino acid concentration in KOH-soluble fractions. The results showed a denaturation temperature of GCSM protein ranging from 61.4 to 63.6 °C. Scanning electron microscopy reveals a microglobular protein structure. GCSM protein isolate showed lower (P < 0.05) water-holding and oil-holding capacity but similar gelation properties as soy protein. GCSM protein shows a high foaming capacity at high pH values and high emulsion stability. PRACTICAL APPLICATION: The results of this investigation have a direct impact on the plant protein processing industry. This paper presents a new source of plant protein with a high foaming capacity in alkaline conditions with potential applications for human consumption and feed for aquaculture and animals. The results of this research may impact the cotton producers who can increase their income, and the aquaculture industry will have a cheaper source of protein that can partially substitute the expensive fishmeal. Cottonseed protein can be used to develop high protein extruded snacks and other functional foods, such as plant protein-based food products.

Chemical Lipophilization of Bovine α-Lactalbumin with Saturated Fatty Acyl Residues: Effect on Structure and Functional Properties

Bovine α-lactalbumin (α-LA) was chemically modified by the covalent attachment of fatty acid residues of different length (lauroyl, palmitoyl, and stearoyl) to modify its functional and antioxidant properties. Structural changes, functional properties, and antioxidant capacity in the pH interval between 3 and 10 were analyzed. Surface properties were improved. The esterification increased the hydrophobic interactions leading to a reduction in the solubility dependent on the incorporation ratio of the fatty acid residues. Improvement in emulsifying, foaming, and antioxidant properties were observed when the length of the fatty acid chains was short and mostly at a basic pH. With these results in mind, experiments could be conducted for the technological applications of these derivatives in the food, pharmaceutical, and cosmetic industries.

High pressure effects on the structural functionality of condensed globular-protein matrices

High pressure technology is the outcome of consumer demand for better quality control of processed foods. There is great potential to apply HPP to condensed systems of globular proteins for the generation of industry-relevant biomaterials with advanced techno- and biofunctionality. To this end, research demonstrates that application of high hydrostatic pressure generates a coherent structure and preserves the native conformation in condensed globular proteins, which is an entirely unexpected but interesting outcome on both scientific and technological grounds. In microbiological challenge tests, high pressure at conventional commercial conditions, demonstrated to effectively reduce the concentration of typical Gram negative or Gram positive foodborne pathogens, and proteolytic enzymes in high-solid protein samples. This may have industrial significance in relation to the formulation and stabilisation of "functional food" products as well as in protein ingredients and concentrates by replacing spray dried powders with condensed HPP-treated pastes that maintain structure and bioactivity. Fundamental concepts and structural functionality of condensed matrices of globular proteins are the primary interest in this mini-review, which may lead to opportunities for industrial exploitation, but earlier work on low-solid systems is also summarised presently to put recent developments in context of this rapidly growing field.

High pressure control of protein structure and functionality

Purpose

– This article aims to consider the use of high pressure processing in order to gain functional advantages through proteins structure control. High pressure processing has been used to produce high-quality food with extended shelf life and could also be used to modify foods functionality.

Design/methodology/approach

– The effect of high pressure on protein structure and functionality is looked at and comparisons are made with heat effect in places. β-lactoglobulin and whey proteins are mainly taken as examples.

Findings

– A controlled partial protein unfolding through mild high pressure processing could lead to a range of intermediate molecular structures. These are distinct from the native and completely unfolded structure and have been referred to as molten globules. The partly unfolded molecular states, hence, are postulated to have increased functionality and could be interesting for the food industry.

Originality/value

– The opportunity and challenges represented by these theoretical elements are discussed. In particular, the effect of protein concentration and aggregation is emphasised.

Functional properties of Ditaxis heterantha proteins

Ditaxis heterantha is a plant of the Euphorbiaceae family that grows in semiarid regions of Mexico. It produces yellow pigmented seeds that are used for coloring of foods. The seeds contain about 20% of proteins. Proteins of D. heterantha were extracted and fractionated on the basis of solubility. Three main protein fractions were obtained: glutelins, 488 ± 0.5; albumins, 229 ± 2; and total globulins, 160 ± 1 g/kg. The amino acid profile was evaluated for each fraction and protein isolated, where the protein isolate contains essential amino acids such as Val, Phe, Tyr, and Leu. A calorimetric study showed that globulins and glutelins have a high denaturing temperature between 100 and 106°C, while albumins showed a denaturing temperature at 76°C. The protein isolate and its fractions exhibited functional properties: the isolated protein demonstrated good oil‐holding capacity of 40.7 g/kg. Foam capacity (FC) and foam stability (FS) were observed principally in glutelins and globulins where FC maximum was 330% and the FS was 28 min. The emulsifying capacity was observed in the same fractions of glutelins and globulins, followed by albumins. However, the glutelin fraction in particular was the only fraction that exhibited emulsifying stability at pH 5, 6, and 7. Gelling capacity was observed in albumins and globulins. This study indicated that protein isolated from D. heterantha could be used in food formulations due to its essential amino acid profile. Glutelin could be used as an emulsifying additive. Additionally, glutelin and globulin were stable at temperatures above 100°C; this is an important factor in food industry, principally in heat processes.

Effect of different treatments on the ability of α-lactalbumin to form nanoparticles

Nanoparticles of bovine α-lactalbumin (α-LA) prepared by desolvation and glutaraldehyde crosslinking are promising carriers for bioactive compounds in foods. The objective of this work was to study the effect of changes in hydrophobic interactions by using different desolvating agents (acetone, ethanol, or isopropanol) and the use of a heat or high-pressure treatment step before the desolvation process on the size, structure, and properties of α-LA nanoparticles. In all cases, a high average particle yield of 99.63% was obtained. Smaller sizes (152.3 nm) can be obtained with the use of acetone as the desolvating agent and without any pretreatment. This is the first time that α-LA nanoparticles in the size range of 100 to 200 nm have been obtained. These nanoparticles, with an isoelectric point of 3.61, are very stable at pH values >4.8, based on their ζ-potential, although their antioxidant activity is weak. The use of the desolvating agent with the smallest polarity index (isopropanol) produced the largest particles (293.4 to 324.9 nm) in all cases. These results support the idea that controlling hydrophobic interactions is a means to control the size of α-LA nanoparticles. No effect of pretreatment on nanoparticle size could be detected. All types of nanoparticles were easily degraded by the proteolytic enzymes assayed.

Effects of high hydrostatic pressure on the structure of bovine alpha-lactalbumin

The effects of high hydrostatic pressure (HHP) processing (at 200 to 600 MPa, 25 to 55 degrees C, and from 5 to 15 min) on some structural properties of alpha-lactalbumin was studied in a pH range of 3.0 to 9.0. The range of HHP processes produced a variety of molten globules with differences in their surface hydrophobicity and secondary and tertiary structures. At pH values of 3 and 5, there was a decrease in the alpha-helix content concomitant with an increase in beta-strand content as the pressure increased. No changes in molecular size due to HHP-induced aggregation were detected by sodium dodecyl sulfate-PAGE. All samples showed higher thermostability as the severity of the treatment increased, indicating the formation of a less labile structure related to the HHP treatment.