Effects of Acylation on the Functional Properties and In Vitro Trypsin Digestibility of Red Kidney Bean (Phaseolus vulgaris L.) Protein Isolate

ABSTRACT:  The effects of succinylation and acetylation on some functional properties and the  in vitro  trypsin digestibility of kidney bean protein isolate (KPI) were investigated. The extent of succinylation or acetylation progressively increased from 0% to 96% to 97%, as the anhydride-to-protein ratio increased from 0 to 1 g/g. Polyacrylamide gel electrophoresis (PAGE) and zeta potential analyses indicated that acylation, especially succinylation, considerably increased the net charge and hydrodynamic radius of the proteins in KPI, especially vicilin. Acylation treatment at various anhydride-to-protein ratios (0.05 to 1 g/g) remarkably improved the protein solubility (PS) and emulsifying activity index (EAI) at neutral pH, but the improvement by succinylation was much better than that by acetylation. Succinylation resulted in a marked decrease in mechanical moduli of heat-induced gels of KPI, while the mechanical moduli were, on the contrary, increased by acetylation. Additionally,  in vitro  trypsin digestibility was improved by the acylation in an anhydride-type and level-dependent manner. The results suggest that the functional properties of KPI could be modulated by the chemical acylation treatment, using succinic or acetic anhydride at appropriate anhydride-to-protein ratios.     

Effects of high hydrostatic pressure on the conformational structure and the functional properties of bovine serum albumin

Non-thermal technologies, such as High Hydrostatic Pressure (HHP), are able to induce extensive changes in the structure of biological macromolecules, namely proteins. HHP treatments disrupt the electrostatic interactions, which stabilize the quaternary and the tertiary structure of the proteins, and activate the reactions of sulfhydryl-disulfide bond exchange. These structural changes result in the dissociation and refolding of proteins during HHP treatments, and consequently in the modification of protein functional properties, namely physicochemical properties (solubility, binding and surfactant properties, water and oil absorption capacity, emulsifying and foaming properties). The technological behavior of the proteins in food preparation, processing, storage, as well as their contribution to determine quality perception of foods mainly depends on these functional properties.This work aims at investigating the effects of HHP treatments on the conformational (quaternary, tertiary and secondary) structure and the functional properties of a globular water soluble protein, the Bovine Serum Albumin (BSA). BSA (50–100 mg/mL) solutions in Sodium Phosphate Buffer were processed at different pressure levels (100–500 MPa) and treatment times (15, 25 min). BSA unfolding and refolding were analyzed in terms of free sulfhydryl (SH) groups, changes of secondary structure, foaming and emulsifying properties.Analyzing the experimental data it can be concluded that the unfolding of BSA samples with a concentration of 50 mg/mL occurred in the pressure range between 100 and 400 MPa. In fact an increased number of the free SH groups as well as an improved foaming and emulsifying ability were detected in the treated samples. Pressure levels above 400 MPa promoted the interactions between adjacent polypeptide chains and the formation of soluble high molecular mass aggregates. The concentration of the protein in the samples, also, controlled the occurrence of unfolding and aggregation. Extensive changes in BSA secondary structure were observed at pressure level above 300 MPa, for longer processing times and higher protein concentrations. In these processing conditions β-sheet aggregates were likely to replace the initial α-helixes.Industrial relevanceThe paper consists in the study of the Effects of High Hydrostatic Pressure processing (HHP) on the conformational structure and the functional properties of Bovine Serum Albumin.he work proposes an innovative technology for Food Industries that can be widely used for food conservation and to induce protein modifications in the same time. For this reason the technology represents a good tool for the production of hypoallergenic compounds especially in the field of dairy products and infant formula companies.     

Physicochemical, functional and structural properties of vicilin-rich protein isolates from three Phaseolus legumes: Effect of heat treatment

The physicochemical, functional and structural properties of vicilin-rich protein isolates from kidney, red and mung beans (KPI, RPI and MPI) were investigated, and the influences of heating (at 95 °C for 30 min) were also evaluated and compared. In the untreated samples, the thermal stability, free SH contents and surface hydrophobicity were different. The differences seemed to be closely related to the differences in extent of aggregation and/or tertiary and secondary conformational structures among proteins. The heating resulted in extensive denaturation of the protein, significant decreases in free SH groups and increases in surface hydrophobicity, but to a varying extent, depending on the type of protein isolates. The protein solubility and emulsifying activities were significantly improved by the heating. The tertiary and secondary structures of these proteins were also to a various extent affected. The conformational structures of proteins in RPI were most flexible, and susceptible to the heating, while the proteins in KPI were most heat-stable in structures. The results clearly indicated close relationships between functional properties of these vicilin-rich protein isolates and their conformational structures.     

Interactions between tea polyphenol and two kinds of typical egg white proteins—ovalbumin and lysozyme: Effect on the gastrointestinal digestion of both proteins in vitro

The promotion or inhibition of gastrointestinal digestion of tea polyphenol (TP) towards the two typical proteins from egg white (ovalbumin (OVA) and lysozyme (LYZ)) was examined. The results showed that TP made OVA/LYZ easier for digestion in the pepsin solution at pH 1.2 and inhibited OVA/LYZ digestion in pancreatin solution at pH 7.5. Non-covalent interactions between OVA/LYZ and TP and the secondary structure of OVA/LYZ were studied by using Fluorescence spectroscopy and Fourier transform infrared spectroscopy (FTIR), respectively. Results suggested that stronger conformational change occurred at pH 1.2 compared with that of pH 7.5 affected by TP in both proteins. Non-covalent interactions between OVA/LYZ and TP at pH 1.2 increased random and β-sheet structures in both proteins at the expense of α-helix, which resulted in the proteins with looser structures. At pH 7.5, an opposite second structural change of both proteins caused by the non-covalent interactions between OVA/LYZ and TP. The conformational and second structural change of proteins (substrate) might be a reason for promoting and inhibiting digestion of OVA/LYZ affected by TP.     

Effect of succinylation on physicochemical and functional properties of milk protein concentrate

Milk protein concentrate (MPC) is a complete dairy protein ingredient (containing both caseins and whey proteins) available with protein concentrations ranging from 40 to 90%. However, MPC powders are poorly soluble which thus, restricts their potential use for food application. Succinylation involves chemical derivatisation of ϵ-amino group of lysine in proteins and enhances solubility of less soluble proteins. In the present investigation, highest degree of succinylation was achieved at the level of 4 mol of succinic anhydride/mole of lysine in MPC. Findings from intrinsic tryptophan intensities stated that succinylation of milk proteins showed structural modification and increase in hydrophobicity. Further, the effects of succinylation on the functional properties (solubility, water- and oil-binding capacities, viscosity, foaming capacity and stability, emulsion activity and stability) of MPC were evaluated. Succinylation of proteins significantly (P < 0.05) increased solubility as a result of altered charge on protein and reduced particle size of native MPC, which in turn improved other functional properties of native MPC. The microstructure of succinylated MPC at different degrees of succinylation by scanning electron microscopy revealed that the size and number of white patch like structures present on protein increased with degree of succinylation.     

Rheological characterization of acylated and dextran conjugated African yam bean (Sphenostylis stenocarpa Hochst. Ex A. Rich.) proteins

The molecular weight distribution and rheological properties of acetylated, succinylated and dextran conjugated African yam bean (Sphenostylis stenocarpa) proteins dispersion were studied. Succinylation of the protein showed the three prominent electrophoretic bands of the unmodified protein but all the bands disappeared with acetylation. Immobile band characterized dextran conjugated S. stenocarpa electrophoregram. The flow behavior indices (n) of these modified S. stenocarpa protein dispersions were in the range 0.03–0.22. This is an indication that they were pseudoplastic in nature. This pseudoplastic nature was maintained in ionic media 0.05–0.5 mol dm^?3, pH 3–8 and temperature range of 27–75 °C. The yield stresses were 0.270, 0.302 and 0.320 Pa for acetylated, succinylated and dextran conjugated protein respectively. Activation energy of acetylated and succinylated protein were in the range 6.2–8.2 and 2–5.4 J mol^?1 respectively. Thus acetylation of S. stenocarpa protein made its dispersion viscosity more susceptible to temperature change than succinylation. These results suggest that acylation and dextran conjugation of African yam bean (S. stenocarpa) protein produce protein species with different rheological properties.     

Physicochemical and functional properties of cowpea protein isolates treated with temperature or high hydrostatic pressure

The effect of thermal (TT, 70 and 90 °C) and high hydrostatic pressure (HHPTs, 200, 400 and 600 MPa) treatments on physicochemical and functional properties of cowpea protein isolates (CPIs) extracted at pH 8.0 (A8) and pH 10.0 (A10) was analyzed. The pH of protein extraction affected some physicochemical properties (surface hydrophobicity (Ho) and denaturation temperature), without affecting the functional properties. Treatments led to the formation of soluble protein aggregates stabilized by disulfide bonds, especially with TT at 90 °C. TT and HHPTs shifted the wavelengths of maximum emission to red and to blue, respectively. All treatments induced unfolding and denaturation. HHPTs was more efficient than TT to enhance gelation and water holding capacities. Interestingly, treated and untreated CPIs exhibited high values of solubility (72–97%). TT and HHPT induced greater changes in physicochemical and functional properties of A8 than in those of A10. Remarkably, functional properties were improved from the less energetic treatments (70 °C, 200 MPa).Industrial relevanceThe comparison between treatments (one traditional and one corresponding to an emerging technology) gives information about the possibility of obtaining modified proteins for different functional purposes. The modified cowpea protein isolates may be used in beverages because of high solubility, in desserts because of gel formation capacity and/or as additives in other foodstuff because of improved water holding capacity. This knowledge would increase the added value of a local production currently marketed without processing.     

Functional and structural properties and in vitro digestibility of acylated hemp (Cannabis sativa L.) protein isolates

The effects of succinylation and acetylation on some functional, structural properties and in vitro trypsin digestibility of hemp protein isolate (HPI) were investigated. The extent of acylation gradually increased from 0 to 60–70%, with the anhydride‐to‐protein ratio increasing from 0 to 1.0 g g^?1. Size exclusion chromatography showed that succinylation led to formation of more soluble protein aggregate than acetylation, especially at anhydride levels higher than 0.1 g g^?1. Succinylation led to gradual increase in protein solubility (PS) from 30 to 85–90%, while in the acetylation case, the PS was improved only at low anhydride levels, increasing from 30 to about 50% with anhydride‐to‐protein ratio increasing from 0 to 0.2 g g^?1. At neutral pH, the emulsifying activity indexes (EAI) of HPI was 22.1 m² g^?1, and the EAI linearly and significantly increased with the extent of acylation. The EAIs of succinylated and acetylated HPI (1.0 g g^?1) were 119.0 and 54.4 m² g^?1, respectively. Differential scanning calorimetry (DSC) and intrinsic fluorescence spectrum analyses indicated gradual structural unfolding of proteins, or exposure of hydrophobic clusters to the solvent, especially at higher anhydride levels. Additionally, the in vitro trypsin digestibility was significantly improved by the succinylation. The results indicated that the chemical acylation treatment (especially succinylation) could be applied to modify some selected functional properties of hemp proteins, especially PS and emulsifying ability.     

Effect of processing parameters on the properties of transglutaminase-treated soy protein isolate films

The effects of processing parameters, including the applied amount of microbial transglutaminase (MTGase), the pH of film-forming solution, air-drying temperature, as well as the additional pre-incubation, on the properties of MTGase-treated soy protein isolate (SPI) films were investigated. The treatment with low concentration of MTGase (4–10 units per gram of SPI, U g^− 1) significantly increased the tensile strength (TS) values of SPI films, while high concentration of MTGase (over 20 U g^− 1) resulted in significant decrease in the TS values (P ≤ 0.05). The elongation at break (EB) values of corresponding films gradually decreased, and the contact angle values persistently increased with the enzyme concentration. At alkaline pH range, the TS and EB values of MTGase-treated SPI films were significantly higher than that at pH 7.0 (P ≤ 0.05). Meanwhile, the contact angle values significantly decreased with increasing pH from 7.0 to 10.0 (P ≤ 0.05). The TS, EB and contact angle values of MTGase-treated films gradually but insignificantly decreased with increasing the air-drying temperature from 18 to 50 °C (P > 0.05). The properties of MTGase-treated films were also affected by the additional pre-incubation of film-forming solutions with MTGase before casting. Furthermore, the aggregation of SPI or its components induced by MTGase has been proved to mainly account for the influence of processing parameters on the properties of SPI films (MTGase-treated). Thus, low concentration of enzyme, alkaline pH range and low air-drying temperature, at which conditions the MTGase-induced aggregation of SPI in film-forming solutions could be in some extent inhibited or delayed, might facilitate the improvement of the properties of SPI films by MTGase, especially the mechanical and surface hydrophobic properties.Industrial relevanceThe development of biodegradable protein film has attracted a lot of attention worldwide. The enzymatic cross-linking induced by transglutaminase has been confirmed to improve mechanical and surface hydrophobic properties of cast films from most of food proteins, including soy proteins. Results of this study show that, the improvement of properties of cast films of soy proteins by transglutaminase treatment is largely dependent upon many processing parameters, e.g., enzyme concentration, the pH of film-forming solution and temperature.     

Supercritical carbon dioxide-treated blood orange juice as a new product in the fresh fruit juice market

The work described here deals with the effectiveness of using high-pressure carbon dioxide treatment (HPCD) to stabilise freshly squeezed blood orange juice. Technical planning of a continuous high-pressure supercritical carbon dioxide pilot system, suitable for development on an industrial scale, was carried out in our lab. To determine the optimal operating conditions (temperature, pressure, and CO₂/juice ratio), three different experimental trials were carried out. The first trial was conducted at 230 bar, 36 ± 1 °C, 5.08 L/h juice flow rate, and 3.91 L/h CO₂ flow rate, corresponding to a g_CO2/g_juice ratio of 0.770. The second trial utilised the same conditions except that the operative pressure was reduced (130 bar). The third trial was carried out at 130 bar, 36 ± 1 °C, 5.08 L/h juice flow rate, 1.96 L/h CO₂ flow rate, corresponding to a 0.385 g_CO2/g_juice ratio. The effects of processing were evaluated by determining physicochemical, antioxidant, and microbiological parameters of the treated juices. In addition, once the best operative parameters had been determined, physicochemical, antioxidant, microbiological and sensory evaluation of fresh blood orange juice stabilised by HPCD treatment was carried out during refrigerated storage of juices at 4 ± 1 °C for thirty days. The results showed that HPCD treatment cannot be considered as an alternative to traditional thermal methods but as a new mild technology for producing a stabilised blood orange juice with a shelf-life of 20 days.Industrial relevanceBlood oranges are the main cultivated varieties of Citrus sinensis (L.) Osbeck in Italy. Freshly squeezed blood orange juice exert a high antiradical and antioxidant activity, due to its rich phenolic profile, but its preservation is usually assured by thermal treatment which affects its nutritional and sensory value. In this study we proposed a “milder” continuous HPCD process suitable for implementation on an industrial scale. The HPCD stabilised juice retains its physicochemical, antioxidant, and sensory properties and could be placed within a new retail framework, namely, that of fresh juices with a shelf-life of 20 days.     

Effect of the thermal treatment of the filmogenic solution on the mechanical properties,color and opacity of films based on muscle proteins of two varieties of Tilapia

Myofibrillar and sarcoplasmic proteins are capable of forming a continuous matrix. Therefore, muscle proteins of two varieties of Tilapia were used to study the effect of the thermal treatment of filmogenic solutions (FS) on the mechanical properties, color and opacity of its films as a function of the plasticizer concentration. The mechanical properties of the films were determined by puncture and tensile tests and the color and opacity by colorimetry. In general, the films based on FS treated at 65°C/30 min were more resistant and more rigid, than the films treated at 40°C/30 min. This behavior was more pronounced in the case of FS with 2 g proteins/100 g FS. The color and opacity were mainly affected by the protein concentration in FS. The FS with 2 g proteins/100 g FS produced films more colored and opaque than those made with 1 g proteins/100 g FS.     

Oats protein isolate: Thermal,rheological, surface and functional properties

Oat protein isolate (OPI) was extracted in 0.015 N NaOH and acetylated or succinylated. The thermal analysis of the isolate showed a glass transition (T_g) at 43.4 °C and ΔC_p of 0.102 J/g/°C. The positive net charge of OPI and the positive or neutral charge of the modified OPI were apparent from the free capillary zone electrophoresis (FZCE) profiles. Acetylation significantly lowered foaming and emulsifying properties of OPI, while succinylation showed the highest foaming capacity, foam stability, and emulsion stability. Acetylated OPI showed the highest surface hydrophobicity compared to the other samples, while OPI was the most soluble of all. The water holding capacity of all samples analyzed was the same except for acetylated-crosslinked (ACXL). The surface tension test confirmed that unmodified and modified OPI possessed surface activity and the equilibrium surface tensions decreased sharply with increasing protein concentration and leveled off to a constant value. The elastic modulus, G′, for the acetylated OPI suspension exhibited the highest value, while the G′ of the crosslinked (XLOPI) had the lowest. The plateau of G′, was 2961 Pa, 920 Pa, 223 Pa, 41 Pa, and 1.8 Pa for the ACOPI, ACXL, SOPI, and XL, respectively.     

酰化对芸豆分离蛋白热学特性的影响研究

从参与酰化反应基团的视角,运用热分析(DSC)技术,研究了不同酰化阶段芸豆分离蛋白热学性质的变化规律。芸豆分离蛋白(KPI)的酰化过程存在两个主要的酰化阶段,酸酐-蛋白比为0～0.1(乙酰化)和0～0.2(琥珀酰化)g/g,为ε-氨基(Lys)酰化阶段(N-酰化);再增加酸酐与蛋白比,ε-氨基酰化基本完成,反应进入羟基(Thr,Ser)酰化阶段(O-酰化)。在N-酰化阶段,琥珀酰化诱导KPI的热稳定性增加,而焓变(ΔH)略有降低,乙酰化不影响KPI的热稳定性和焓变(ΔH);羟基酰化阶段,酰化导致KPI变性温度(Td)降低,伴随焓变(ΔH)急剧下降。     

Heat-induced modifications in the functional and structural properties of vicilin-rich protein isolate from kidney (Phaseolus vulgaris L.) bean

Heat-induced changes in the physico-chemical (and/or functional) and structural properties of protein isolate from kidney beans (KPI) were characterised. The extent of protein denaturation, free sulphydryl contents, surface hydrophobicity, as well as structural characteristics of the proteins were evaluated. Analyses of size-exclusion chromatography combined with laser scattering showed that the heating at 95 °C led to transformation of 7S-form vicilin to its 11S-form, and even higher molar mass (MW) oligomers or polymers. Moderate heating (for 15–30 min) significantly improved protein solubility, emulsifying and foaming activities (at neutral pH), whilst extensive heating (for 60–120 min) on the contrary decreased these properties. Spectral analyses of fluorescence and/or Raman spectroscopy showed that tertiary and secondary conformations of protein in KPI were remarkably affected to a varying extent by the heating. The results suggested a close relationship between functional properties of the vicilin from kidney bean and its conformational characteristics.     

Production of traditional Greek yoghurt using Lactobacillus strains with probiotic potential as starter adjuncts

Lactobacillus plantarum ACA-DC 146 and L. paracasei subsp. tolerans ACA-DC 4037 were examined for their potential application as adjuncts in the production of traditional Greek set-type yoghurt. Both strains displayed low milk acidification activity, while no inhibition was observed towards or from the yoghurt starters used. Yoghurt produced with L. paracasei subsp. tolerans ACA-DC 4037 exhibited the best sensory properties, with a rich traditional smooth taste, and the strain was selected for further trials. Yoghurt produced with this strain as an adjunct had good physicochemical properties. After 2 weeks of refrigerated storage, microbial loads (>7.0 log cfu g⁻¹) were in accordance with international recommendations and guidelines for probiotic and starter cultures in milk products. Increasing the microbial load further, using concentrated and encapsulated inocula (10–11 log cfu g⁻¹), gave yoghurt with long fermentation times and poor organoleptic properties.     

Brining of cod fillets: effects of phosphate,salt, glucose,ascorbate and starch on yield,sensory quality and consumers liking

In order to study how triphosphate, salt, glucose, ascorbate and starch, both separately and in mixture, could affect the quality and the yield of brined cod fillets, an experimental design was applied. Salt was the variable with highest pronounced effect on yield and appearance, followed by triphosphate, glucose, starch and sodium ascorbate. By treating skinless frozen/thawed cod fillets with brine consisting of 25 g salt/l, 10 g triphosphate/l, 5 g glucose/l, 5 g sodium ascorbate/l and 5 g starch/l in a vacuum tumbler for 15 min, a 35% weight increase was obtained. The products retained a natural appearance with a homogenous surface. Next, an experiment was carried out to assess the effect of this brining mixture on sensory properties and consumers liking of both fresh and frozen/thawed cod fillets. Sensory analyses showed that the intensity of the sensory attributes cod taste, cod smell, juiciness, whiteness and glossiness could be heightened by brining, while the intensities of old/stale taste and smell could be lowered. The effects were prominent for products subjected to freezing before and/or after processing, while the characteristics of the fresh products were little influenced by brining. Using an in-house consumer panel, it was shown that the frozen/thawed products were the less preferred products. However, brining considerably enhanced the preferences for frozen and thawed cod fillets, obtaining preferences similar to the fresh, nonbrined product (F).     

Influence of enzymatic cross-linking on milk fat globules and emulsifying properties of milk proteins

The enzyme transglutaminase (TGase) can modify dairy protein functionality through cross-linking of proteins. This study examined the effects of TGase treatment on milk fat globules and the emulsifying properties of milk proteins. The extent of TGase-induced cross-linking of caseins increased with incubation time, with no differences between whole and skim milk. Extensive clustering of fat globules in extensively cross-linked raw whole milk occurred on homogenisation at 400 or 800 bar. Considerably less clustering of fat globules was observed when recombined milk (90 g fat L^–1) was prepared from TGase-treated skim milk and homogenised at 400 or 800 bar. TGase treatment did not affect fat globule size in cream, but prevented coalescence of fat globules therein, possibly through cross-linking of milk fat globule membrane components. TGase-induced cross-linking of milk proteins affected their emulsifying properties and may increase the stability of natural milk fat globules against coalescence.     

Polysaccharides influence on the interaction between tannic acid and haze active proteins in beer

Colloidal instability in beer is mainly caused by interactions between proteins and polyphenols. These two combine producing a visible haze that reduces the physical shelf life of beer. The haze active proteins (HAPs) react with tannic acid (TA); therefore, this reaction provides a way to determine HAP concentrations in beer. Beers also contain a number of constituents that may influence the protein–polyphenol haze formation. We used a response surface methodology to predict the influence of total polysaccharides (TPS) and proteins on beer haze. Experiments were carried out using the Central Composite Design (CCD) methodology. Samples of beer were prepared with variable concentrations of TPS and proteins. TPS concentrations ranged between 1.34 and 2.23 g L^− 1 and proteins concentrations between 0.11 and 0.18 g L^− 1. Results show that the increase in turbidity in response to TPS addition was similar to that in response to protein addition. Our regression analyses indicate a significant dependency and correlation between the observed values and the predicted response values (R² = 97.87% and R²[adj] = 95.75%). Furthermore, these values indicate that our experimental model can explain 95.75% of the total variation. Therefore, using TA as an indicator of the interaction of TPS with proteins, as commonly done, can lead to considerable errors, since the polysaccharides also react with TA, and this reaction actually causes a considerable increase in turbidity.     

Chemical composition and potential of some underutilized tropical biomass. I: fluted pumpkin (telfairia occidentalis)

The seeds of Telfairia occidentalis have been subjected to standard chemical analysis to evaluate their properties. Proximate analysis indicated a low moisture content (6.30 ± 0.50%). The ash content was slightly higher than the range recommended for compounding of animal feed (3.44 ± 0.06%). The carbohydrate content was low (16.5 ± 0.12%). Starch, however, constituted the dominant carbohydrate (62.5 ± 0.48), while three sugars, glucose, fructose and sucrose were detected in the seed. The crude protein in the seed was high (16.0 ± 0.03%), a value which compared favourably with high protein seeds and nuts. In all, 16 amino acids were detected in the protein. Glutamic acid showed the highest concentration (16.4 g 100 g⁻¹), while lysine showed the lowest (2.6 g 100 g⁻¹). The brown oil extracted from the seed (yield 48.6 ± 0.94) had the following physicochemical properties; acid value, 3.05 ± 0.80 g, saponification value 166 ± 1.34 mg/KOH g⁻¹, free fatty acids, 0.3 g and peroxide value 3.02 ± 0.07 mg Eq kg⁻¹. The iodine value (80.1 ± 0.10)g 100 g⁻¹ indicated a preponderance of unsaturated fatty acid. Four fatty acids were detected whilst unsaturated acids constituted 61.3 g. Triglyceride was the dominant lipid species while hydrocarbons, waxes, sterols and sterol esters and higher alcohols, were detected in the unsaponifable matter. Results of nutritionally valuable mineral elements indicated that potassium occurred at the highest concentration.     

Incorporation of microbial transglutaminase into non-fat yogurt production

This study investigated the physical, chemical and sensory characteristics of non-fat yogurts treated with microbial transglutaminase (MTGase) at varying concentrations from 0 to 0.5 g L⁻¹. Also, the effect of enzyme inactivation prior to fermentation on the selected properties of the yogurts was studied. Acid development rate was reduced with increasing MTGase doses. Cross-linking of milk proteins by MTGase had a growth-slowing effect on yogurt starter bacteria, which was more pronounced at higher concentrations. Physical properties of the yogurts were improved by MTGase throughout 21-day storage; on the contrary, the production of acetaldehyde was slowed down by increasing MTGase concentrations during the same period. Principal component analysis (PCA) and hierarchial cluster analysis (HCA) clearly differentiated the samples with added MTGase at lower (⩽0.3 g L⁻¹) and higher (0.4–0.5 g L⁻¹) concentrations regarding the physical and sensory properties. The physical and sensory properties of non-fat set yogurt could be improved by incorporating MTGase up to a level of 0.3 g L⁻¹.