Water–water and water–macromolecule interactions in food dehydration and the effects of the pore structures of food on the energetics of the interactions

A molecular dynamics (MD) modeling and simulations approach has been rationally built and developed to study porous food systems constructed with amylose and dextran chains. The findings from our MD studies indicate that the presence of food macromolecules decreases the energetics of the water–water interactions for the nearby water molecules in the pore space, but provides additional water–macromolecule interactions that can significantly outweigh the partial loss of water–water interactions to make the adjacent water molecules strongly bound to the food macromolecules so that the water activity and water removal rate are decreased as dehydration proceeds and, thus, the dehydration energy requirement would be increased. The effects of pore structures are greater in systems with higher densities of food macromolecules, smaller in size pores, and stronger water–macromolecule interactions. Dehydration of food materials can thus be reasonably expected to start from the largest pores and from the middle of the pores, and to have non-uniform water removal rates and non-planar water–vapor interfaces inside individual pores as well as across sections of the food materials. The food porous structures are found to have good pore connectivity for water molecules. As dehydration proceeds, water content and the support from water–water and water–macromolecule interactions both decrease, causing the food porous structures to adopt more compact conformations and their main body to decrease in size. Dehydration in general also reduces pore sizes and the number of pore openings, increases the water–macromolecule interactions, and leads to the reduction of the overall thermal conductivity of the system, so that more energy (heat), longer times, and/or greater temperature gradients are needed in order to further dehydrate the porous materials. Our thermodynamic analysis also shows that the average minimum entropy requirement for food dehydration is greater when the water–macromolecule interactions are stronger and the food macromolecular density is higher. The importance of the physicochemical affinity of food molecules for water and of the compatibility of the resultant porous structures with water configurational structures in determining food properties and food processing through the water–macromolecule interactions, is clearly and fundamentally verified by the results and discussion presented in this work.     

Denaturation of soy proteins in solution and at the oil–water interface: A fluorescence study

Structural changes ensuing from denaturation of soy proteins in solution or occurring at the oil–water interface were studied by fluorescence spectroscopy. Studies were carried out on solutions and emulsions stabilized with β-conglycinin or glycinin. Tryptophan fluorescence spectroscopy was used to evaluate tertiary structural changes. The binding of fluorescent dyes and the accessibility of reactive cysteine thiols were also used to better identify structural changes of these proteins in solution. Protein conformational changes after interaction with the hydrophobic oil surface were compared with those ensuing from physical (temperature) or chemical denaturation (chaotropes). Results from solution denaturation experiments indicate that structural changes of β-conglycinin by both temperature and chaotropes are reversible under appropriate conditions, and result in a rearrangement of the supramacromolecular assembly of the protein structure. On the other hand, glycinin treated under the same conditions undergoes irreversible denaturation in solution at temperatures well below 90 °C. Both proteins undergo partial denaturation after adsorption on the lipid surface, and no further denaturation occurs upon heating of the emulsions prepared with either protein.     

Effect of alcohol on adsorption of casein at the oil—water interface

We report on the effect of added ethanol on time-dependent interfacial tensions and surface shear viscosities at 25°C for adsorbed films of sodium caseinate at the interface between n-hexadecane and an aqueous solution (pH 7, ionic strength 0.005 M) containing from 10⁻⁴ wt% to 10⁻¹ wt% protein. Addition of 10 wt% ethanol causes changes in interfacial tension which vary from ~15 mN/m at short times to just 2–3 mN/m under steady-state conditions. The presence of 1 wt% ethanol inhibits the formation of a film with measurable surface viscosity. Experiments in which ethanol is added to the sub-phase below an aged protein film are explained in terms of a rapid displacement step, followed by slow accumulation of ethanol-aggregated protein in secondary layers if the bulk protein concentration is high enough.     

Functional implications of bound phenolic compounds and phenolics–food interaction: A review

Sizeable scientific evidence indicates the health benefits related to phenolic compounds and dietary fiber. Various phenolic compounds-rich foods or ingredients are also rich in dietary fiber, and these two health components may interrelate via noncovalent (reversible) and covalent (mostly irreversible) interactions. Notwithstanding, these interactions are responsible for the carrier effect ascribed to fiber toward the digestive system and can modulate the bioaccessibility of phenolics, thus shaping health-promoting effects in vivo. On this basis, the present review focuses on the nature, occurrence, and implications of the interactions between phenolics and food components. Covalent and noncovalent interactions are presented, their occurrence discussed, and the effect of food processing introduced. Once reaching the large intestine, fiber-bound phenolics undergo an intense transformation by the microbial community therein, encompassing reactions such as deglycosylation, dehydroxylation, α- and β-oxidation, dehydrogenation, demethylation, decarboxylation, C-ring fission, and cleavage to lower molecular weight phenolics. Comparatively less information is still available on the consequences on gut microbiota. So far, the very most of the information on the ability of bound phenolics to modulate gut microbiota relates to in vitro models and single strains in culture medium. Despite offering promising information, such models provide limited information about the effect on gut microbes, and future research is deemed in this field.     

Sodium caseinate/carboxymethylcellulose interactions at oil–water interface: Relationship to emulsion stability

The effect of carboxymethylcellulose (CMC) on the properties of oil-in-water emulsions prepared with sodium caseinate (CN) was studied at different pHs (4–7). At pH 7, the surface protein coverage increased gradually with increasing CMC concentration, followed by a preferential adsorption of β-casein. While at pH 4, a sharp decrease in surface protein coverage was noted between 0 and 0.3 wt.% CMC, and no obvious difference in protein composition was observed. ζ-Potential measurements indicated that CMC adsorbed onto the CN-coated droplets at pH 4–5, but not at pH 6–7. As a result, the excess of non-adsorbed CMC induced depletion flocculation in the neutral emulsions. However, the acidic emulsions containing high levels of CMC (>0.3 wt.%) remained stable after 60 days of storage due to the formation of multilayer structures. At pH 4, CMC desorbed from the droplet surfaces at high NaCl concentrations, leading to lower emulsion stability.     

Disappearance of intermolecular beta-sheets upon adsorption of beta-lactoglobulin aggregates at the oil–water interfaces of emulsions

Native proteins usually undergo structural modification upon adsorption at interface. Heat treatments are commonly applied at the industrial scale and lead to aggregation of proteins. We characterized nanometric aggregates of β-lactoglobulin by infrared spectroscopy in solutions, in hexadecane oil-in-water emulsions and at the air–water interface at low and high (0.1 M) ionic strengths and at pH 7. In solutions, on the contrary to native β-lactoglobulin, all aggregates prepared with or without salt possessed intermolecular β-sheets evidenced by two strong absorption bands at 1614 cm⁻¹ and 1682 cm⁻¹. In emulsions, at low ionic strength, they lose their intermolecular β-sheets once they are adsorbed at the oil–water interface. At high ionic strength, most of aggregates are localized at the interfaces where they lose their intermolecular β-sheets in direct contact with the surface and only partially when they are farther from the interface. The loss of intermolecular β-sheets was similarly observed at the air–liquid interface.     

Sodium caseinate/xanthan gum interactions in aqueous solution: Effect on protein adsorption at the oil–water interface

In this work, the phase behaviour of 1.0 wt% sodium caseinate (CN) in admixture with different amounts of xanthan gum (XG) in aqueous solution was investigated under different pH and ionic strength. XG concentration, pH and ionic strength showed a significant impact on biopolymer interactions. Considering the strong effects of pH on the net charge around CN, pH dependence of CN/XG interactions was investigated by zeta potential, viscometry techniques, and confocal laser scanning microscopy (CLSM). The results indicated that CN/XG interactions may take place in solution, both at neutral and acidic environments. Then, a close relationship was obtained between CN/XG interactions in the aqueous phase and CN adsorption at the oil–water interface. It showed that the complex formed at acidic pH revealed a significant influence on the dynamic characteristics of CN adsorbed films. At short adsorption time, the diffusion rate (k_diff) of CN to the interface was increased due to the interactions with XG in the aqueous phase which could accelerate protein availability for the adsorption. Moreover, XG could also lead to an increase in the rates of penetration (k_P) and rearrangement (k_R) of CN at the interface at long adsorption time, which was quite different from the adsorption behaviour of CN/XG mixtures prepared at neutral pH.     

Potential interactions among phenolic compounds and probiotics for mutual boosting of their health-promoting properties and food functionalities – A review

Several foods are rich sources of phenolic compounds (PC) and their beneficial effects on human health may be increased through the action of probiotics. Additionally, probiotics may use PC as substrates, increasing their survival and functionality. This review presents available studies on the effects of PC on probiotics, including their physiological functionalities, interactions and capability of surviving during exposure to gastrointestinal conditions and when incorporated into food matrices. Studies have shown that PC can improve the adhesion capacity and survival of probiotics during exposure to conditions that mimic the gastrointestinal tract. There is strong evidence that PC can modulate the composition of the gut microbiota in hosts, improving a variety of biochemical markers and risk factors for chronic diseases. Available literature also indicates that metabolites of PC formed by intestinal microorganisms, including probiotics, exert a variety of benefits on host health. These metabolites are typically more active than parental dietary PC. The presence of PC commonly enhances probiotic survival in different foods. Finally, further clinical studies need to be developed to confirm in vitro and experimental findings concerning the beneficial interactions among different PC and probiotics.     

Secondary adsorption of milk proteins from the continuous phase to the oil–water interface in dairy emulsions

Low protein surface concentration emulsions are susceptible to secondary protein adsorption where protein moves from the continuous phase to the existing, oil–water interface. The resulting increase in protein surface concentration can greatly alter emulsion properties. Butteroil was emulsified with whey proteins and the emulsion was combined with a solution of dissolved skim milk powder (SMP), producing mixes with fat and protein levels representative of ice cream. The primary adsorbed layer was modified by heating the whey protein solution prior to emulsion formation (70°C, 80°C, 90°C), by heating the emulsion (70°C, 80°C, 90°C) or by pH adjustment of the emulsion (6–8). Modifications of the SMP solution included heat treatment (80°C, 95°C) or sugar addition with or without κ-carrageenan. The effect of addition of SMP solution on the protein surface concentration and shear stability of the diluted emulsions was determined. Addition of untreated solution to the control, heated or pH adjusted emulsions greatly reduced shear destabilization and increased the protein surface concentration. Addition of heat treated or sugar containing SMP solution to the control emulsion produced the same result. However, sugar and carrageenan in the mix maintained the susceptibility to partial coalescence and reduced the secondary adsorption of caseins and whey proteins.     

A review of the structure,function, and application of plant-based protein–phenolic conjugates and complexes

Interactions between plant-based proteins (PP) and phenolic compounds (PC) occur naturally in many food products. Recently, special attention has been paid to the fabrication of PP–PC conjugates or complexes in model systems with a focus on their effects on their structure, functionality, and health benefits. Conjugates are held together by covalent bonds, whereas complexes are held together by noncovalent ones. This review highlights the nature of protein–phenolic interactions involving PP. The interactions of these PC with the PP in model systems are discussed, as well as their impact on the structural, functional, and health-promoting properties of PP. The PP in conjugates and complexes tend to be more unfolded than in their native state, which often improves their functional attributes. PP–PC conjugates and complexes often exhibit improved in vitro digestibility, antioxidant activity, and potential allergy-reducing activities. Consequently, they may be used as antioxidant emulsifiers, edible film additives, nanoparticles, and hydrogels in the food industry. However, studies focusing on the application of PP–PC conjugates and complexes in real foods are still scarce. Further research is therefore required to determine the structure–function relationships of PP–PC conjugates and complexes that may influence their application as functional ingredients in the food industry.     

Partition of selected food preservatives in fish oil–water systems

The partition coefficients (K_ow) of benzoic acid and sorbic acid in systems of fish oil (sand eel)–water, fish oil–buffer solution, rape oil–water and olive oil–water were experimentally determined in a temperature range from 5 to 43 °C and pH from 4.5 to 6.5 °C. The dimerization of benzoic acid in fish oil–water system was observed at 25 °C. Two modifications have been made to the Nordic Food Analysis Standard for the determination of sorbic acid by HPLC. The experimental results show that the K_ow of benzoic acid and sorbic acid in fish oil–buffer system is ca. 100 times lower than that in fish oil–water system. The K_ow values of benzoic acid and sorbic acid in fish oil and water system decrease with increasing system pH values. The partition coefficients of plant origin and fish origin oils are in the same order of magnitude even though their molecular structures are very different.     

Dynamic surface pressure and dilatational viscoelasticity of sodium caseinate/xanthan gum mixtures at the oil–water interface

The effect of xanthan gum (XG) on the surface dynamic properties (dynamic surface pressure and surface dilatational properties) of the sodium caseinate (CN) adsorbed film at the oil–water interface has been studied in this paper. The measurements were performed as a function of bulk protein concentration in the range of 0.001–1.0 wt% using an automatic pendant drop tensiometer. The XG concentration (0.05 wt%), temperature (25 °C), pH (7.0) were maintained constants. The results revealed a significant effect of XG on dynamic characteristics of CN adsorbed films. At short adsorption time, the diffusion (k_diff) of CN to the interface decreased due to the interactions with XG in the aqueous phase which could limit protein availability for the adsorption. The presence of XG led to a decrease in the rates of penetration (k_P) and rearrangement (k_R) of CN at the interface at long adsorption times. High concentrations of CN in the bulk solutions showed significant impact on the dilatational viscosity close to the interface, due either to diffusional relaxation or to rearrangement of the adsorbed primary layer and multilayers of protein molecules. Moreover, CN/XG mixtures presented higher dilatational elasticity at the bulk concentration of CN beyond 0.001 wt%.     

Brewster angle microscopy of adsorbed protein films at air–water and oil–water interfaces after compression,expansion and heat processing

Recent Brewster angle microscopy (BAM) observations of adsorbed films of proteins at the air-water (A–W) and oil–water (O–W) interfaces are reviewed and compared. At the A–W interface β-lactoglobulin (β-L) and ovalbumin (OA) were studied at pH 7 and 5. At the O–W interface β-L, α_s1-, β- and κ-caseins were studied at pH 7. The adsorbed films were periodically subjected to compression and expansion cycles such that the film area was typically varied between 125% and 50% of the original film area. At the A–W interface, little structure was observable on compression or expansion or aging, especially at pH 7. For ovalbumin at pH 5, some cracks and ridges in the films appeared. But, for both β-L and OA, such features became much more obvious on addition to the interface of a low area fraction (<0.01%) of 20 μm polystyrene latex (PS) particles. With particles present the structuring was also more obvious at pH 5 (closer to the protein isoelectric point) than at pH 7, and for greater adsorption times and/or higher bulk protein concentration (C_b). Particle addition was not necessary to highlight folding and ridges that occurred at the O–W interface for β-L. After heating to 80 and 90 °C, β-L films adsorbed from low C_b (0.005 wt%) even greater film structuring was evident. However, β-L films adsorbed from higher C_b (≥0.05 wt%) showed fewer, but more pronounced ridges and cracks. The caseins at the O–W interface showed comparatively little evidence of structuring, either before or after heating. A measure of the dilatational elastic modulus of the films correlated with the observed variations in the structural integrity of the films. Clearly, protein films subjected to these types of thermal and mechanical perturbations can become highly inhomogeneous, depending on the type of protein and the bulk solution conditions, with implications for the stability of the corresponding foams and emulsions. This is in agreement with earlier computer simulations. Protein films at the O–W interface (particularly after heating) appear to be more resilient and less aggregated than films at the A–W interface.     

Cognitive dissonance in food and nutrition–A review

The study of cognitive dissonance in food and nutrition has been relatively under-developed. This review paper looks at food and/or food-related studies that have utilized cognitive dissonance as a primary construct in a priori theorization and hypothesis-formulation, examining the ways in which the dissonance construct has been used and its corresponding effects on various food-related outcomes in those studies. Current gaps and critical issues underlying cognitive dissonance investigation in food and nutrition research are also identified and discussed.     

Use of ultrasounds in the food industry–Methods and effects on quality,safety, and organoleptic characteristics of foods: A review

The use of ultrasounds has recently gained significant interest in the food industry mainly due to the new trends of consumers toward functional foods. Offering several advantages, this form of energy can be applied for the improvement of qualitative characteristics of high-quality foods as well as for assuring safety of a vast variety of foodstuffs, and at the same time minimizing any negative effects of the sensory characteristics of foods. Furthermore, the non-destructive nature of this technology offers several opportunities for the compositional analysis of foods. However, further research is required for the improvement of related techniques and the reduction of application costs in order to render this technology efficient for industrial use. This review paper covers the main applications of ultrasounds as well as several advantages of the use of the technology in combination with conventional techniques. The effects of ultrasounds on the characteristics, microbial safety, and quality of several foods are also detailed     

Hydroxypropylmethylcellulose–β-lactoglobulin mixtures at the oil–water interface. Bulk,interfacial and emulsification behavior as affected by pH

In this work we have studied the bulk, interfacial and emulsification behavior of a surface-active polysaccharide, hydroxypropylmethylcelulose (HPMC) and β-lactoglobulin (βlg) mixtures at two pHs, 3 and 6.     

Stability of oil–water primary emulsions stabilised with varying levels of casein and whey proteins affected by high-intensity ultrasound

This study evaluates physical and chemical stability of ultrasound-assisted grape seed oil primary emulsions stabilised by varying compositions of caseins to whey proteins (80:20, 60:40, 50:50 and 40:60) at different sono-operating conditions (81.9 and 117.0 J mL⁻¹). Physical and chemical stabilities were influenced by both sonication energy densities and milk protein compositions. Emulsions prepared at 81.9 J mL⁻¹ energy density with ≥40% whey protein fraction (60:40, 50:50, 40:60 and WPI) showed greater physical stability than the emulsions sonicated at 117.0 J mL⁻¹ which exhibited physical instability due to the depletion flocculation mechanism at the critical casein concentration (≥40%). The emulsion oxidative stability was found to be affected by sonication conditions as 117.0 J mL⁻¹ induced the oxidation reactions once the whey concentration exceeds 40%. Therefore, ultrasound prepared emulsions with casein to whey ratios of 60:40, 50:50, 40:60 and WPI at 81.9 J mL⁻¹ energy density was found to be stable for 10 days at 4 °C.     

Effect of the structure of monoglyceride–oil–water gels on aroma partition

The aim of the present research was to study the aroma partition properties of saturated monoglyceride–oil–water gels. To this purpose, gels added with lemon oil were prepared mixing water, sunflower oil and commercial saturated monoglycerides. Three mixtures containing different ratios between the ingredients were considered. The gel characteristics were studied by synchrotron X-ray diffraction (XRD), calorimetry, polarized light microscopy and rheological measurements. The aroma partition was studied by using HSGC analysis.The gel structure is made of a multilamellar crystalline network, in which monoglycerides form shells encapsulating oil. Depending on the ratio between ingredients, the gel shows different rheological behaviour. The structured multilamellar phases greatly affect the partition of aroma evidencing the capability to entrap lipophilic compounds within the monoglyceride/oil shells. Since the aroma entrapping capacity showed by monoglyceride structures could greatly affect the perceived aroma intensity of the final product, this effect should be carefully taken into account during the development of new formulations.