Case Of Mixtures Research Articles

An innovative method for fractionating the milk fat globule membrane and the major buttermilk proteins

Buttermilk (BM) is a by-product of butter manufacturing that shares a similar composition to skim milk but contains a higher concentration of phospholipids due to milk fat globule membrane (MFGM) fragments released during cream churning. Despite its high added-value components, MFGM is underutilized mainly due to the challenge in separating its components from the other constituents of buttermilk. Our work has focused on the use of calcium phosphate particles, called hydroxyapatite (HA), to extract and separate the different components from buttermilk. This study investigated the impact of various physicochemical parameters (temperature, ionic strength, and pH) on the adsorption of a mixture of micellar casein (CM), whey proteins, and MFGM from BM onto HA surfaces. A box-Behnken design was utilized to predict optimal physicochemical conditions for selectively separating components in buttermilk. Ionic strength (IS) played a crucial role, with low IS having a minimal positive influence and high IS negatively influencing adsorption. pH influenced adsorption by altering protein and HA surface charges. The optimal conditions for adsorption were an IS of 100 mM for a pH of 7, for 90 % of CM, 37 % of β-lactoglobulin, 11 % of α-lactalbumin and 7 % of MFGM. Desorption experiments using citrate and alkaline pH showed promising results for CM recovery, with citrate efficiently releasing the adsorbed CM. Additionally, MFGM were separated from whey proteins through selective precipitation at a pH of 4.0, allowing sedimentation of MFGM (100 %) while keeping whey proteins soluble. The presence of β-lactoglobulin in the protein fraction of MFGM (31 %) and CM (37 %) was attributed to pasteurization, which denatured a portion of β-lactoglobulin and led to its attachment to MFGM surfaces and interaction with CM. This protocol produces a nearly pure fraction of MFGM with a simple method which is suitable for industrial production, representing significant valorization for the dairy sector.

Curcumin‐loaded nanoparticles developed from sodium caseinate and OSA starch and the in vitro semi‐dynamic elderly digestion behaviour of fortified yogurt

SummaryCurcumin is a bioactive substance, while poor stability and low bioavailability limit its effective utilisation. Curcumin‐loaded nanoparticles were prepared using the wall materials containing OSA starch alone (HI), sodium caseinate alone (SC), and a mixture of OSA starch and sodium caseinate (HS). Compared to HI and SC, HS had obvious network structure and smaller particle size, with the loading capacity higher than 20%. The storage stability at 4 °C were higher in HS and SC, FTIR and XRD results showed that all nanoparticles encapsulated curcumin through hydrogen bonding. When nanoparticles were added to yogurt, HI showed slower curcumin release during in vitro semi‐dynamic elderly digestion, whereas SC and HS can better accelerate the digestion rate of proteins in yogurt, leading to a decrease in the apparent viscosity of digestive emptying products. This study provided a reference for curcumin delivery wall materials and pushed forward development of functional foods for elderly.

Effect of natural agents on the mechanical and flame retardant properties of cotton fabrics – finishing technique

The current study carefully examines the antibacterial finished cotton fabric materials in terms of enhanced flame-retardant capability by eco-friendly herbal extracts to cotton fabrics while concurrently analysing their tensile strength qualities. Because active compounds have been incorporated into the fabric’s structure, the treated fabrics’ tensile strength has changed less over time than untreated fabrics. The plain weave cotton fabric with a specification of 140 g/m2 and a 15% finished concentration had a tensile strength of 238.92 kg/cm2, while cotton fabrics with specifications of 240 g/m2, terry weave with a 15% finished concentration, had a tensile strength of 294.43 kg/cm2. The finishing process has betterment in comparison to the untreated cotton fabrics had tensile strengths of of 140 g/m2 plain and 240 g/m2 terry weaves fabric which has 238.38 kg/cm2 and 288.47 kg/cm2, indicating that the ashwagandha-finished cotton fabrics performed better. The burning period increases from 35 sec for untreated 140 g/m2 plain cotton fabric, according to the flame reaction studies. According to tests on flame reaction, fabrics treated with a combination of banana peels and casein have a burning time rise from 35 s for untreated 140 g/m2 plain cotton fabric to 100 s, and up to 60 s for Ashwaganda and Ginger completed fabrics. The findings of the Limited Oxygen Index (LOI) test revealed that the completed fabrics made from a mixture of banana peels and casein had significantly higher LOI values of 23 than the other treated samples, which had an average LOI of 19 and 20, compared to the untreated cotton fabrics’ LOI of 18.

Effects of wall materials on the physicochemical properties of spray-dried bitter gourd (Momordica charantia L.) powders

Bitter gourd has numerous health-promoting effects on the human body. However, its use has been greatly limited due to its poor acceptance by consumers, resulting from its strong bitterness. This study investigated the effects of five wall materials, namely, soybean protein isolate, gum arabic, maltodextrin, resistant starch, and a soybean lecithin calcium caseinate mixture, on the physicochemical properties of spray-dried bitter gourd powders. The results showed that all five wall materials reduced the moisture content, water activity, browning degree, agglomeration, and bitterness of the spray-dried bitter gourd powder. Maltodextrin was found to be the most effective at reducing water activity, while soybean protein isolate was best at protecting the colour, and the soybean lecithin calcium caseinate mixture was best at reducing hygroscopicity and masking bitterness. Additionally, all five wall materials improved the preservation of flavonoids, saponins, and vitamin C, with soybean protein isolate being the most effective in improving the total flavonoid retention ratio and the soybean lecithin calcium caseinate mixture being the best in improving the retention ratios of total saponins and vitamin C. The spray-dried bitter gourd powder prepared with soybean protein isolate had the highest antioxidant activity and α-glucosidase inhibitory activity. These results are significant for understanding the relationship between wall materials and the physicochemical properties of spray-dried powder. Additionally, these materials provide bitter gourd product manufacturers with useful guidance for producing high-quality products. Furthermore, the results could provide useful insights for processing fruits with similar product characteristics, thus contributing to the enrichment of food processing knowledge.

Acid-induced gels from mixtures of micellar casein and pea protein: Effect of protein ratio and preheating route

Enhancing the sustainability of dairy products through the partial substitution of dairy proteins with plant proteins requires exploring formulation and processing strategies. This study investigates the gluconic-δ-lactone (GDL)-induced hybrid gels from commercial micellar casein isolate (M) and pea protein isolate (P) dispersions (5% w/w protein content). Variations in the M/P ratios (3:1, 2:2, and 1:3) and preheating routes (Route 1: preheating M and P dispersions together; Route 2: preheating them separately) impacted the physical/conformational properties of protein dispersions as well as the rheological/structural features of resulting gels. Small and large amplitude oscillatory shear (SAOS and LAOS) tests revealed that lower M/P ratio led to earlier gelling points and increased the stiffness and elasticity of hybrid gels in the linear viscoelastic (LVE) region. All gels transitioned from elastic to plastic behavior in the non-linear viscoelastic (NLVE) region, with lower M/P ratio showing reduced stretchability and faster structural breakdown. Regardless of routes, the preheating step (95 °C, 30 min) disintegrated inherent aggregates/agglomerates in these commercial protein ingredients, leading to smaller particle size, but higher protein solubility, surface hydrophobicity, and |ζ-potential|. Pea proteins formed soluble aggregates during preheating, but the presence of micellar caseins (Route 1) hindered this process. Consequently, mixtures with lower M/P ratio and from preheating route 2, possessed higher quantities of pea protein soluble aggregates, forming a compact gel network with low water mobility, as observed by CLSM, STED, and LF-NMR. These findings show the potential for using pea proteins in acid-induced gel foods like yogurt and paneer-type cheeses.

Development of cross‐linked polyvinyl alcohol/sodium caseinate/silver nanoparticle electrospun mats for antibacterial wound dressing

AbstractIn this study, nanofibers were produced by the electrospinning method by adding 1%, 3%, 5%, and 7% silver nanoparticles (Ag NPs) into the polyvinyl alcohol/sodium caseinate (60/40, w/w) mixture. Electrospun materials were cross‐linked by immersion in a glutaraldehyde bath. Thus, antibacterial wound dressings that could be used on exuding wounds were developed. According to the scanning electron microscopy images of nanofibers, the cross‐linking process by immersion method did not cause negative effects such as breakage or adhesion on the surface of fibers. The cross‐linking of nanofibers was demonstrated by the presence of acetal linkages by Fourier‐transform infrared spectroscopy analysis. The cross‐linking process significantly improved the thermal properties of the nanofibers. The lowest crystallinity calculated in the differential scanning calorimeter was observed in the 3% Ag NP‐added nanofiber with a value of 1.83%. It exhibited the lowest total soluble matter content with a value of 11.98% owing to its high cross‐linking density. In addition, the 3% Ag NP‐added nanofiber, which had the highest toughness and ductility, displayed the highest tensile stress with 3.5 MPa and the highest tensile strain with 7.53%. Moreover, it showed 78.11% cell viability on the L929 fibroblast cell line at the end of the 24th hour. It was indicated that although the electrospun mats maintained 100% antibacterial effectiveness, they could not be used as a wound dressing for 48 h. It was reported that only 3% Ag NP‐added nanofiber could be used as a 100% effective antibacterial wound dressing for both Escherichia coli and Staphylococcus aureus provided that it was renewed every 24 h. Consequently, it was notified that cross‐linking by the immersion method can be used in biomedical applications.Highlights The antibacterial effects of Ag NP‐doped PVA/NaCAS electrospun mats were significant. The cross‐linking process did not induce toxic effects some of the nanofibers. High cross‐linking density was observed in the nanofibers. The swelling property of nanofibers is a good feature required in an ideal wound dressing.

Influence of Soy Lecithin and Sodium Caseinate on The Stability and in vitro Bioaccessibility of Lycopene Nanodispersion.

Various approaches have been used to present functional lipids including lycopene in a palatable food form to consumers. However, being highly hydrophobic, lycopene is insoluble in aqueous systems and has a limited bioavailability in the body. Lycopene nanodispersion is expected to improve the properties of lycopene, but its stability and bioaccessibility are also affected by emulsifier type and environmental conditions such as pH, ionic strength and temperature. The influence of soy lecithin, sodium caseinate and soy lecithin/sodium caseinate at 1:1 ratio on the physicochemical properties and stability of lycopene nanodispersion prepared using the emulsification-evaporation methods before and after treatment at different pH, ionic strength and temperature were investigated. The in vitro bioaccessibility of the nanodispersions was also studied. Under neutral pH conditions, nanodispersion stabilized with soy lecithin had the highest physical stability and the smallest particle size (78 nm), the lowest polydispersity index (PDI) value (0.180) and highest zeta potential (-64 mV) but the lowest lycopene concentration (1.826 mg/100 mL). Conversely, nanodispersion stabilized with sodium caseinate had the lowest physical stability. Combining the soy lecithin with sodium caseinate at 1:1 ratio resulted in a physically stable lycopene nanodispersion with the highest lycopene concentration (2.656 mg/100 mL). The lycopene nanodispersion produced by soy lecithin also had high physical stability under different pH range (pH=2-8) where the particle size, PDI and zeta potential remained fairly consistent. The nanodispersion containing sodium caseinate was unstable and droplet aggregation occurred when the pH was reduced close to the isoelectric point of sodium caseinate (pH=4-5). The particle size and PDI value of nanodispersion stabilized with soy lecithin and sodium caseinate mixture increased sharply when the NaCl concentration increased above 100 mM, while the soy lecithin and sodium caseinate counterparts were more stable. All of the nanodispersions showed good stability with respect to temperature changes (30-100 °C) except for the one stabilized by sodium caseinate, which exhibited an increased particle size when heated to above 60 °C. The combination of soy lecithin and sodium caseinate was found to increase the bioaccessibility of the lycopene nanodispersion. The physicochemical properties, stability and extent of the lycopene nanodispersion digestion highly depend on the emulsifier type. Producing a nanodispersion is considered one of the best ways to overcome the poor water solubility, stability and bioavailability issues of lycopene. Currently, studies related to lycopene-fortified delivery systems, particularly in the form of nanodispersion, are still limited. The information obtained on the physicochemical properties, stability and bioaccessibility of lycopene nanodispersion is useful for the development of an effective delivery system for various functional lipids.

PН-sensitive edible films based on the sodium caseinate/agaragar biocomposite

In the modern world, shelf life extension of foods with a possibility of controlling their freshness and quality in real time is gaining increasing importance. To solve this task, the development of pH-sensitive films based on edible biopolymers with addition of anthocyans as a color indicator can be proposed. For this experiment, sodium caseinate/ agar-agar biocomposite films with different content of anthocyans from black carrot (Scorconera hispanica) in a range of 0 to 15 mass% in increments of 5 mass% were prepared. It was established that the anthocyan content did not affect the thickness and moisture content of the films; however, it significantly reduced their moisture absorption and transparence. Water vapor permeability of the biocomposite films increased with an increase in the content of the aqueous extract of anthocyans from black carrot, which can be linked with the formation of pores and microcracks in the biocomposite matrix. All films with anthocyans showed changes in color depending on the environmental pH, which intensities depended on the anthocyan content. Edible films based on the mixture of sodium caseinate and agar-agar can potentially be used in the food industry to determine freshness of foods, which spoilage results in pH changes.

Impact of glucose syrup and antioxidants on properties and oxidative stability of microcapsules loaded with skipjack tuna eyeball oil

Effects of glucose syrup (GS) at different ratios as wall materials on encapsulation efficiency (EE) and properties of micro-encapsulated skipjack tuna eyeball oil (ME-STEO) were determined. Highest EE (90.45-90.61%) was obtained when the mixtures of fish gelatin (FG), sodium caseinate (SC) and GS at ratios of 1:1:1 and 1:1:2 (w/w/w) were used. Moisture content, water activity and lightness (L*) of ME-STEO were declined when the amount of GS was augmented, but redness (a*), yellowness (b*), total difference in color (∆E*) and surface shrinkage of ME-STEO were increased. When α-tocopherol (AT) in combination of ascorbyl palmitate (AP) were incorporated in STEO, lower peroxide and thiobarbituric acid substances were found in ME-STEO than others (P < 0.05). Mixtures of wall material (FG:SC:GS=1:1:2) and the addition of 200 ppm AT in combination with 200 ppm AP yielded STEO as a core with higher oxidative stability during 30 days of storage at room temperature.

Characterization of microbial communities in anaerobic acidification reactors fed with casein and/or lactose

Protein-rich agro-industrial waste streams are high in organic load and represent a major environmental problem. Anaerobic digestion is an established technology to treat these streams; however, retardation of protein degradation is frequently observed when carbohydrates are present. This study investigated the mechanism of the retardation by manipulating the carbon source fed to a complex anaerobic microbiota and linking the reactor performance to the variation of the microbial community. Two anaerobic acidification reactors were first acclimated either to casein (CAS reactor) or lactose (LAC reactor), and then fed with mixtures of casein and lactose. Results showed that when lactose was present, the microbial community acclimated to casein shifted from mainly Chloroflexi to Proteobacteria and Firmicutes, the degree of deamination in the CAS reactor decreased from 77 to 15%, and the VFA production decreased from 75 to 34% of the effluent COD. A decrease of 75% in protease activity and 90% in deamination activity of the microbiota was also observed. The microorganisms that can ferment both proteins and carbohydrates were predominant in the microbial community, and from a thermodynamical point of view, they consumed carbohydrates prior to proteins. The frequently observed negative effect of carbohydrates on protein degradation can be mainly attributed to the substrate preference of these populations.Keypoints• The presence of lactose shifted the microbial community and retarded anaerobic protein degradation.• Facultative genera were dominant in the presence and absence of lactose.• Substrate-preference caused retardation of anaerobic protein degradation.

Caffeic acid phenethyl ester loaded in a targeted delivery system based on a solid-in-oil-in-water multilayer emulsion: Characterization, stability, and fate of the emulsion during in vivo digestion

Many studies have shown that caffeic acid phenethyl ester (CAPE) has various functions, such as antioxidant, anti-inflammatory and anticancer activity, but its low bioavailability and stability limit its application. In this study, the colorectal targeted delivery system for CAPE based on a solid-in-oil-in-water (S/O/W) multilayer emulsion was prepared using CAPE-loaded nanoparticles as the solid phase, coconut oil as the oil phase, and a mixture of lecithin and sodium caseinate as the aqueous phase. The stability of the O/W interfacial layer was improved by using a sodium casein-lecithin mixture as the aqueous surface layer in the preparation. This S/O/W emulsion is a spherical droplet with an S/O/W trilayer structure with a particle size of 155.5 ± 0.72 nm and a polydispersity index (PDI) of 0.24 ± 0.01. The Fourier transform infrared (FTIR) results confirmed that CAPE was successfully loaded into the S/O/W emulsion. This S/O/W emulsion was able to maintain a stable liquid state at pH 6.00–7.4 or cholate concentration of 0–50 mg/mL but showed a gel state at pH 2.0–3.0. The storage experiments demonstrated that the S/O/W emulsion was stable for 15 days at 4 °C, but was prone to agglomeration and emulsion breakage at 25 °C. The in vivo digestion process indicated that the S/O/W emulsion was gradually digested in the digestive tract and released solid phase nanoparticles in the large intestine. Therefore, this newly developed targeted delivery system can effectively deliver CAPE to the colorectum and achieve a 12-hour delayed release, which improved the bioavailability and activity of CAPE.

Sodium caseinate and OSA‐modified starch as carriers for the encapsulation of lutein using spray drying to improve its water solubility and stability

SummaryLutein is a fat‐soluble substance with plentiful unsaturated carbon–carbon double bonds in the chemical structure. Spray‐drying formulations of lutein emulsions stabilised by a mixture of sodium caseinate (CS) and octenyl succinic anhydride‐modified starch (OS) yield lutein microcapsules. The yield (19.3–65.8%), encapsulation efficiency (74.7–82.9%), moisture (0.92–3.50%), wettability (226.8–392.4 s) and solubility (65.3–95.7%) were obtained in this study. The formulations with CS:OS (7:3) presented the excellent encapsulation efficiency (82.9%), glass transition temperatures (126.77 °C) and retention rate at 50 °C (80.51%), 25 °C (82.49%), and 4 °C (90.68%), and in UV light (75.44%) and lightness (80.40%) after 15 days. Based on the study, encapsulation would be an alternative for generating high value‐added products and could promote lutein's use as a functional ingredient with a ‘clean label’.

Mechanical and biodeterioration behaviours of a clayey soil strengthened with combined carrageenan and casein

In the last decade, biopolymers have been used as organic soil binders in ground improvement and earthen construction material modification. Although biopolymer-treated soils have substantially enhanced mechanical strength, the deformation characteristics under external loads and material durability (e.g. biodeterioration due to microbial activity) have not yet been fully understood, which limits the in situ practical application of the biopolymer-based soil treatment technology. This study investigated the efficiency of combined carrageenan and casein in strengthening a clayey soil with the biodeterioration consideration. Both mechanical tests (e.g. unconfined compressive strength and one-dimensional consolidation) and biological tests (e.g. high throughput sequencing and rating of mould growth) were conducted. Results indicated that the usage of the carrageenan–casein mixture induced a higher soil compressive strength compared with either carrageen or casein, due to the formation of a three-dimensional gel network. In addition, carrageenan–casein mixture and casein decreased the compressibility of the clayey soil, which might be attributed to the casein’s peculiarity of self-associating into micelles, leading to minimal interactions with water molecules. Carrageenan, due to its affinity for water, increased the soil compressibility. Under the impact of microbial activity, the biopolymer-treated soils underwent deterioration in both surface appearance (i.e. coloured stains and patches caused by mould growth) and compressive strength. A linear relationship was proposed, in which a reduction in compressive strength by approximately 11% is expected while the rating of mould growth is increased by one in a five-rating system. The current research demonstrates that the soil reinforcement with combined carrageenan and casein is able to improve both soil strength and deformation behaviours. It is also suggested to take into account the biodeterioration considerations in the design and implementation of biopolymer-based soil reinforcement practices.

Sodium caseinate enhances the effect of konjac flour on delaying gastric emptying based on a dynamic in vitro human stomach-IV (DIVHS-IV) system.

In the context of the increasing prevalence of overweight and obesity worldwide, satiety-enhancing foods may help people control their energy intake and weight. In this study, an advanced near-real human gastric simulator equipped with a dynamic in vitro human stomach-IV (DIVHS-IV) system was used to determine the gastric digestion and gastric retention ratio of konjac flour (KF)/sodium caseinate (SC) mixtures with different ratios. The apparent viscosity, viscoelastic properties, confocal laser scanning microscopy (CLSM) of the digested products were collected and analyzed to further study the effect of SC on the physical properties of KF during digestion. The results showed that the addition of SC could enhance the effect of KF on delaying gastric emptying in vitro. Besides, the addition of SC was shown to weaken the effect of gastric juice on the dilution of gastric contents by forming SC gel blocks in the acid environment. In particular, the synergistic gastric emptying delaying effect was the strongest in the KF/SC mixture containing 1% KF and 8% SC, and obvious massive aggregates were observed. The combination of 1% KF and 8% SC was shown to synergistically delay gastric emptying and potentially enhance the sense of fullness. © 2022 Society of Chemical Industry.

Controlled release and antibacterial properties of PEO/casein nanofibers loaded with Thymol/β-cyclodextrin inclusion complexes in beef preservation

There are still many limitations in the application of natural active compounds in meat preservation. Herein, thymol was first inserted into the cavity of β-cyclodextrin (β-CD) to form a stable inclusion complex (THY/β-CD-IC). The computational investigation showed that the optimized complexation energy for THY/β-CD-IC was −12.95 kcal mol−1. It contributed to the improvement of the thermal stability of thymol in the inclusion compound. Furthermore, the functionalized nanofibers (THY/β-CD-IC-NFs) loaded with THY/β-CD-IC were successfully fabricated by electrospinning of the mixture of casein and polyethylene oxide. When dealing with protease-producing bacteria, controllable release of thymol from THY/β-CD-IC-NFs was achieved through the response of casein to the hydrolysis of bacterial protease. The application results indicated that the prepared THY/β-CD-IC-NFs had a long-term antimicrobial activity for chilled beef preservation during 7-days storage. The information from this study presents a feasible strategy for the development of natural extracts for use in meat preservation.

PROTEASE ACTIVITY OF THERMOPHILIC BACTERIA FROM LEJJA HOT SPRINGS IN SOPPENG SOUTH SULAWESI

This research aimed to observe quantitatively the effect of temperature and pH on protease activities from thermophilic bacteria collected from Lejja—Hot springs. Spectrophotometry on the casein substrate was used to test the proteolytic activity of the crude protease. Mixtures of enzyme and casein were incubated at various temperatures and pH for 20 minutes. The absorbance of tyrosine from protein hydrolysis was determined by spectrophotometry on λ 280 nm. Temperature and pH impacted on protease activity were determined at temperature (60; 65; 70; 75; 80; 85 and 90oC) and pH (6.0; 6.5; 7.0; 7.5; 8, 0; 8,5 and 9,0). Results showed that treatment of temperature variations and pH had a significant effect on protease activity. Crude extract of Bacillus licheniformis protease showed that the highest activity at 80oC and pH 7.5 was 0.1303 unit/ml/minute. Bacillus stearoformis showed the highest enzymatic activity of the protease at 85oC, and pH 7.5 was 0.1226 Unit/ ml/minute. In comparison, Bacillus coagulans reached optimum activity at 75oC, and pH 7.5 was 0.2052 Unit/ml/minute. Isolates of Bacillus licheniformis, B. coagulans and B. stearoformis are bacteria that produce thermostable protease enzymes that can be developed as a source of genes and as a producer of the enzyme itself.

PROTEASE ACTIVITY OF THERMOPHILIC BACTERIA FROM LEJJA HOT SPRINGS IN SOPPENG SOUTH SULAWESI

This research aimed to observe quantitatively the effect of temperature and pH on protease activities from thermophilic bacteria collected from Lejja—Hot springs.  Spectrophotometry on the casein substrate was used to test the proteolytic activity of the crude protease.  Mixtures of enzyme and casein were incubated at various temperatures and pH for 20 minutes. The absorbance of tyrosine from protein hydrolysis was determined by spectrophotometry on λ 280 nm. Temperature and pH impacted on protease activity were determined at temperature (60; 65; 70; 75; 80; 85 and 90oC) and pH (6.0; 6.5; 7.0; 7.5; 8, 0; 8,5 and 9,0). Results showed that treatment of temperature variations and pH had a significant effect on protease activity. Crude extract of Bacillus licheniformis protease showed that the highest activity at 80oC and pH 7.5 was 0.1303 unit/ml/minute. Bacillus stearoformis showed the highest enzymatic activity of the protease at 85oC, and pH 7.5 was 0.1226 Unit/ ml/minute. In comparison, Bacillus coagulans reached optimum activity at 75oC, and pH 7.5 was 0.2052 Unit/ml/minute. Isolates of Bacillus licheniformis, B. coagulans and B. stearoformis are bacteria that produce thermostable protease enzymes that can be developed as a source of genes and as a producer of the enzyme itself.

Development and Characterization of Functional Starch-Based Films Incorporating Free or Microencapsulated Spent Black Tea Extract.

Antioxidant polyphenols in black tea residue are an underused source of bioactive compounds. Microencapsulation can turn them into a valuable functional ingredient for different food applications. This study investigated the potential of using spent black tea extract (SBT) as an active ingredient in food packaging. Free or microencapsulated forms of SBT, using a pectin–sodium caseinate mixture as a wall material, were incorporated in a cassava starch matrix and films developed by casting. The effect of incorporating SBT at different polyphenol contents (0.17% and 0.34%) on the structural, physical, and antioxidant properties of the films, the migration of active compounds into different food simulants and their performance at preventing lipid oxidation were evaluated. The results showed that adding free SBT modified the film structure by forming hydrogen bonds with starch, creating a less elastic film with antioxidant activity (173 and 587 µg(GAE)/g film). Incorporating microencapsulated SBT improved the mechanical properties of active films and preserved their antioxidant activity (276 and 627 µg(GAE)/g film). Encapsulates significantly enhanced the release of antioxidant polyphenols into both aqueous and fatty food simulants. Both types of active film exhibited better barrier properties against UV light and water vapour than the control starch film and delayed lipid oxidation up to 35 d. This study revealed that starch film incorporating microencapsulated SBT can be used as a functional food packaging to protect fatty foods from oxidation.

A quantitative calcium phosphate nanocluster model of the casein micelle: the average size, size distribution and surface properties.

Caseins (αS1, αS2, β and κ) are the main protein fraction of bovine milk. Together with nanoclusters of amorphous calcium phosphate (CaP) and divalent cations, they combine to form a polydisperse distribution of particles called casein micelles. A casein micelle model is proposed which is consistent with the way in which intrinsically disordered proteins interact through predominantly polar, short, linear, motifs. Using the model, an expression is derived for the size distribution of casein micelles formed when caseins bind to the CaP nanoclusters and the complexes further associate with each other and the remaining mixture of free caseins. The result is a refined coat-core model in which the core is formed mainly by the nanocluster complexes and the coat is formed exclusively by the free caseins. Example calculations of the size distribution and surface composition of an average bovine milk are compared with experiment. The average size, size distribution and surface composition of the micelles is shown to depend on the affinity of the nanocluster complexes for each other in competition with their affinity for free caseins, and on the concentrations of free caseins, calcium ions and other salts in the continuous phase.

The production of volatile compounds in model casein systems with varying fat levels as affected by low‐frequency ultrasound

SummaryThe effects of low‐frequency ultrasound on the production of volatile compounds in model casein protein systems containing various fat concentrations of 2%, 4% and 6% (w/w) were investigated. Ultrasound application was performed at 20 kHz for up to 10 min which corresponded to energy densities ranging from 9.54 to 190.8 J mL−1. Similar volatile compounds were detected both in pure fat and mixtures of casein and fat (CF) systems. These volatiles belonged to the groups of aldehydes, ketones, esters, alcohols and hydrocarbons, which were the products of oxidation of lipids or protein degradation due to acoustic cavitation. The amount of fat in the casein systems had minor effects on the production of volatiles, whereas the production of volatile compounds was significantly affected by the ultrasound treatment. Short sonication times &lt;5 min generated similar volatile profiles to the untreated samples. In contrast, prolonged sonication for 5 and 10 min considerably increased the production of volatile compounds and the amounts of fatty acids. Thus, the application of low–frequency ultrasound for short periods should be considered to minimise the production of volatile compounds which can ultimately affect the taste.