Thermally driven interactions between β-lactoglobulin and retinol acetate investigated by fluorescence spectroscopy and molecular modeling methods

International audienceAbstractWhey proteins have important functional properties as it can bind a wide range of bioactive molecules. In this study, the complexation of β-lactoglobulin with retinol at alkaline pH was investigated. The fluorescence spectroscopy was used to determine the temperature dependent behavior of the β-lactoglobulin-retinol acetate (βLG-RET) ensemble. The pattern of protein unfolding in the temperature range of 25–85 °C was followed mainly considering the exposure of tryptophan (Trp) residues. The βLG-RET complex appeared rather stable in the 25–60 °C range, while further increase of the temperature caused partial unfolding. The anisotropy measurements indicated a more flexible conformation at temperature increase up to 80 °C. In addition, the in silico approach was used to complement the experimental results. Important changes in the interaction surface were observed after performing molecular dynamics simulations. The temperature increase caused important rearrangements of the amino acids of the EF loop involved in the interaction with the retinol molecule, which got twisted. These atomic level events induced a significant increase of the affinity between βLG and retinol. This study offers useful information on the potential use of βLG as a carrier for biologically active compounds in order to obtain food products with desired functionalities

Microencapsulation of Red Grape Juice by Freeze Drying and Application in Jelly Formulation

Svrha je ovoga rada bila proizvesti nove prehrambene proizvode obogaćene bioaktivnim sastojcima iz koncentriranog soka od crvenog grožđa, mikroinkapsuliranog pomoću sušenja zamrzavanjem u otopini izolata proteina sirutke i kitozana. Dobiven je prah s učinkovitošću enkapsulacije od (86,1±4,0) %, masenih udjela antocijana (izraženih kao ekvivalenti cijanidin-3-O-glukozida) od (1,4±0,2) mg/g, ukupnih polifenola (izraženih kao ekvivalenti galne kiseline) od (3,3±0,6) mg/g i flavonoida (izraženih kao ekvivalenti katehina) od (1,6±0,5) mg/g. Konfokalnom laserskom mikroskopijom otkriveno je da su flavonoidni pigmenti bili umotani u matriks, dok su antocijani tvorili velike i kompaktne nakupine. Mikroinkapsulirani prah je zatim upotrijebljen za proizvodnju želea. Novi prehrambeni proizvodi imali su zadovoljavajući maseni udjel antocijana, i to od (0,03±0,01) do (0,12±0,02) mg/g, dok se udjel flavonoida nije bitno promijenio. Svi želei su imali znatnu antioksidacijsku aktivnost. Rezultati ispitivanja probavljivosti in vitro potvrdili su je da tijekom simulirane probave došlo do polaganog otpuštanja antocijana iz hrane u želucu, a zatim znatnog otpuštanja bioaktivnih sastojaka u crijevima. Dodatak mikroinkapsuliranog praha znatno je smanjio tvrdoću, kohezivnost i elastičnost želea, što je dovelo do destabilizacije strukture gela i smanjenja privlačnih sila između komponenata matriksa. Sensorska analiza pokazala je da su panelisti preferirali uzorak želea pripremljen od grožđanog soka.The aim of this work is to obtain new food products enriched with bioactive compounds from concentrated grape juice microencapsulated by freeze drying using a whey protein isolate- chitosan system. The obtained powder showed an encapsulation efficiency of (86.1±4.0) %, with an anthocyanin mass fraction (expressed as cyanidin-3-O-glucoside equivalent) of (1.4±0.2) mg/g, while the total polyphenolic (expressed as gallic acid equivalents) and flavonoid (expressed as catechin equivalents) mass fractions were (3.3±0.6) and (1.6±0.5) mg/g, respectively. The confocal laser microscopy revealed the presence of the flavonoid pigments wrapped inside the matrix, whereas the anthocyanins were grouped into large and compact clusters. The microencapsulated powder was used for jelly formulation. The new food formulations have a satisfactory anthocyanin mass fraction ranging from (0.03±0.01) to (0.12±0.02) mg/g, while no significant differences were observed in flavonoid content. All the value-added jelly showed appreciable antioxidant activity. The in vitro digestibility results confirm a slow release of anthocyanins from the food matrices during simulated gastric digestion and a significant release of the bioactive compounds into the gut. The addition of microencapsulated powder caused a significant decrease in firmness, cohesiveness and springiness, leading to the destabilization of the gel structure, while reducing the attraction forces between the matrix components. The sensorial analysis indicated that the panellists preferred the sample with grape juice the most

Extraction Optimization and Valorization of the Cornelian Cherry Fruits Extracts: Evidence on Antioxidant Activity and Food Applications

In this work, the optimization of two extraction methods, conventional CE and ultrasound-assisted UAE, to obtain extracts from cornelian cherry fruit with high antioxidant activity, which can be used to produce healthier jelly candies, is presented. In the CE process, the effects of temperature (30–50 °C), time (15–45 min), and hydroalcoholic mixtures (60–100% ethanol, v/v) were studied. The highest antioxidant activity (29.83 ± 0.85 mg TE/g dw) was found in the extracts obtained using 60% ethanol at 40 °C for 15 min. The UAE process led to comparable values of 26.60 ± 0.53 mg TE/g dw at 40% amplitude and pulsed sonication (5 s on and 5 s off) for 12.5 min. Under these experimental conditions, the specific energy consumed was 1.91 kJ/g. The vitamin C content and its inhibitory activity against metabolic enzymes were evaluated in extracts with different antioxidant activity. A significant inhibitory effect against carbohydrate-metabolism-associated enzymes was identified for all the tested extracts, with an inhibitory effect against α-glucosidase higher than 75%, but with a lower effect against α-amylase. The extract obtained by CE (60% ethanol, 40 °C, 15 min) provided the highest vitamin C content of 39.9 ± 1.2 mg ascorbic acid/100 g dw. Four variants of the healthier jelly candies were formulated, with a vitamin C content of 0.34 mg ascorbic acid/100 g dw in samples with agar-agar and 0.70 mg ascorbic acid/100 g dw in samples with gelatin.Romanian Ministry of Research and Innovation, CNCS-UEFISCDI, project numbers PN-III-P1-1.1-MC-2019-1905 and PN-III-P1-1.1-MC-2019-1908, within PNCDI III. The APC was funded by M.T.S. The authors are also grateful to Junta de Castilla y León (Spain) and ERDF for the financial support of project BU050P20. The Ó. Benito–Román post-doctoral contract was funded by Junta de Castilla y León (Spain) and ERDF through project BU050P20 and by Agencia Estatal de Investigación through project PID2020-116716RJ-I00/AEI/10.13039/501100011033

An overview of bovine α-lactalbumin structure and functionality

α-Lactalbumin is the second major protein in bovine milk (2-5% of the total protein in bovine milk). The human variant has several physiologic functions in the neonatal period. In the mammary gland, itparticipates in lactose synthesis and facilitates milk production and secretion. α-Lactalbumin binds divalent cations (Ca2+, Zn2+) and may facilitate the absorption of essential minerals. Also, it provides awell-balanced supply of essential amino acids for the growing infant. During its digestion, peptides with antibacterial and imunostimulatory properties are formed, thereby possibly helping in the protection against infection. The protein fractions enriched with α-lactalbumin may be added to infant formula to provide some of the benefits of this protein. This article reviews a number of studies which may contribute to a more coherent understanding of the structure and some functional properties of α-lactalbumin

Encapsulation of Anthocyanins from Cornelian Cherry Fruits Using Heated or Non-Heated Soy Proteins

In the current study, the effect of temperature on the potential of soy proteins to ensure the encapsulation and gastric stability of bioactives, such as anthocyanins from cornelian cherry fruits, was investigated. The powders obtained after freeze-drying were analyzed in relation to flow properties, encapsulation retention and efficiency, stability in simulated gastrointestinal medium, color, and morphology. Preheating the soy proteins generated a powder with low density. Powders obtained with native soy proteins allowed the highest encapsulation efficiency and the lowest was obtained when using preheated soy proteins. The heat treatment of the mixture of soy proteins and cornelian cherry fruits prior to encapsulation generated powders with the highest lightness and the lowest intensity of red shades among all samples. The in vitro experiments revealed that the highest protection in simulated gastric environment was provided when protein was heat treated either alone or in combination with bioactives to be encapsulated. The morphological analysis highlighted that powders consisted of large and rigid structures

A spectroscopic study on the heat induced changes of glucose oxidase at acidic pH values

The heat induced conformational and structural changes of glucose oxidase from Aspergillus niger at pH 5.0 and 4.0 were investigated using fluorescence spectroscopy. Experimental studies were conducted in buffer solution in the 25°C-70°C temperature range at constant time. At both pH values, the phase diagram was linear, indicating the presence of two molecular species induced by thermal treatment. When thermally treating the glucose oxidase at pH 4.0, the denaturation process was faster than the one at pH 5.0, probably due to the release of cofactor FAD and molten globule formation. The quenching experiments using acrylamide and iodide revealed a more flexible conformation of glucose oxidase at higher temperatures, especially at pH 4.0

Spectroscopic and Molecular Modeling Investigation on the Interaction between Folic Acid and Bovine Lactoferrin from Encapsulation Perspectives

The impact of thermal treatment on the ability of lactoferrin (FL) to bind folic acid (FA) was investigated by employing fluorescence spectroscopy, molecular dynamics and docking tests. The structural and conformational particularities of LF upon heating at 80 °C and 100 °C were first estimated based on the intrinsic fluorescence changes in respect to the native protein. The emission spectra indicated gradual unfolding events accompanied by Trp exposure with increasing temperature. In agreement with the experimental results, molecular modeling investigations showed that the secondary and tertiary structure of LF are slightly affected by the thermal treatment. Some minor unfolding events related particularly to the α-helical regions of LF were observed when the temperature increased to 100 °C. The LF fluorescence quenching upon FA addition indicated that a static mechanism stands behind LF-FA complex formation. Regardless of the simulated temperature, the hydrogen bonds played an important role in regulating the interaction between the protein and ligand. FA binding to LF equilibrated at different temperatures occurred spontaneously, and all complexes displayed good thermodynamic stability. The obtained results support the suitability of LF as biocompatible material, for obtaining micro- and nanoparticles for delivery of dietary supplements or for enhancing the functionality of target delivery systems

Journal of Food Quality Thermal Degradation of Plum Anthocyanins: Comparison of Kinetics from Simple to Natural Systems

The stability of anthocyanin was assessed over a temperature range of 50–120°C in different simulated plum juices in order to compare the thermal behavior in the presence of certain compounds. The results were correlated with the antioxidant activity and intrinsic fluorescence spectra. The results suggested significant changes, especially at higher temperature; hence, increase in the fluorescence intensity and some bathochromic and hypsochromic shifts were observed. Anthocyanins in natural matrices presented the highest rate for degradation, followed by the anthocyanins in juices with sugars. Values of the activation energies were 42.40 ± 6.87 kJ/mol for the degradation in water, 40.70 ± 4.25 kJ/mol for the juices with citric acid, 23.03 ± 3.53 kJ/mol for the juices containing sugars, 35.99 ± 3.60 kJ/mol for simulated juices with mixture, and 14.19 ± 2.39 kJ/mol for natural juices. A protective effect of sugars was evidenced, whereas in natural matrices, the degradation rate constant showed lower temperature dependence