[Studies on the electrostatic interactions between beta -lactoglobulin and tragacanthin: the first step towards fabrication of biopolymeric micro- and nanoparticles]

Investigation of the colloidal behaviour of protein-polysaccharide systems is becoming increasingly important to provide a foundation for their applications in areas such as production of biopolymer micro-and nano-particles, designing food analogues, and microencapsulation technology. The aim of the present study was to investigate the pH-induced critical transitions during associative phase separation between beta -lactoglobulin [BLG] and tragacanthin [T]. The formation of electrostatic complexes in BLG/T dispersions [0.3wt.% total concentration; BLG:T ratio 2:1] was investigated as a function of pH [2.00-6.00] by spectrophotometry and particle size analysis. In addition, coupling of slow in situ acidification of the blend, with gluconodelta-lacton, and rheometry were used to monitor the structural transitions during the associative phase separation. The influence of salt type and concentration on the formation of micro-particles were also determined. The formation of soluble complexes started at pH -5.20, and at pH -4.85 the aggregation of intrapolymeric complexes occurred, followed by a bulk phase separation at pH -4.30. The data indicated that coacervation occurred at pH 4.15. Finally, the mixture returned to a mono-phasic system at pH 2.5. Particle size analysis showed that the assembled structures experienced a contraction process upon complexation. Rheometry provided deeper insights into the colloidal behaviour of the system and the results were in good agreement with quiescent pH-induced transitions established by HCl titration. The formation of the micro-particles was strongly salt-dependent. Under controlled pH conditions, electrostatic interactions between beta -lactoglobulin and tragacanthin can be used to form a variety of biopolymer particles. These biopolymeric micro- and nanoparticles may be used in the food industry as natural delivery systems or fat-replacers

[ effect of two types of Iranian gum tragacanth on some rheological, physical and sensory properties of date milk beverage]

Date syrup, as a native and nutritious additive, is one of the best choices for milk flavoring. In this study, some of the rheological, physical and sensory properties of date milk made from three different concentrations of two types of Iranian gum tragacanth, as a substitute for imported gums, were determined. Rheological properties of samples of date milk containing three different concentrations [0.1%, 0.2%, 0.3% w/w] of two types of gum tragacanth [Astragalus. gossypinus and Astragalus. rahensis] were measured using a rheometer at 3°C, and at three different time periods [one, two and three days] after production. Particle size distribution was determined by laser diffractometry, and colorimetric assays were done by using reflection spectrometer. Sensory analysis was performed by 25 semi trained panelists, using a 5-point hedonic scale. Findings showed that flow behavior parameters, particle size and color parameters [L*, a*,b*] were significantly affected by concentration of the gum tragacanth and the impact severity was influenced by the type of gum. Based on sensory evaluation, samples containing 0.3% A.gossypinus and 0.2% A.rahensis showed higher desirability than others. Using an appropriate type and concentration of gum in date milk formulation can improve the milk texture and mouthfeel by affecting the particle size and flow behavior

[ effect of type of enzyme and activated carbon concenteration on phenylalanine removal from milk]

Phenylketonuria is a hereditary disease caused by a lack or deficiency of the enzyme phenylalanine hydroxylase, its most severe clinical manifestation being irreversible mental retardation. Presently, the only therapy available is the dietary restriction of phenylalanine. The objective of this study was to produce laboratory-scale low-phenylalanine milk to be used as a dietary supplement by phenylketonurics. Low-phenylalanine milk can be used to make a variety of palatable, lowphenylalanine foods and beverages. Three milk hydrolysates were prepared enzymatically [1g of enzyme/100 g of substrate], using a protease from Aspergillus oryzae and papain, separately and in combination [0.5 g of either enzyme/100 g of substrate], followed by adding different amounts of activated carbon [0.3, 0.9, and 1.5 g] to them to remove phenylalanine. The combination of Aspergillus oryzae protease and papain, along with the use of 0.9 g activated carbon in the post-hydrolysis process, resulted in the lowest final phenylalanine content. The best condition for removing phenylalanine from milk was use of a combination of Aspergillus oryzae enzyme[0.5g of enzyme/100g of substrate] and papain [0.5 g of enzyme/100 g of substrate] with 0.9 g activated carbon in the post-hydrolysis process, resulting in removal of 99% of the phenylalanine

[Viscoelastic properties of acid-induced casein gel in a model system]

Nowadays, acid-induced milk protein gels are used extensively in the dairy industry and are the base of many food products. Therefore, a deeper fundamental understanding of the effects of process parameters and system components on the mechanisms of gel formation and final gel properties in real and model systems is important for researchers and industries. The present study was designed to investigate the effects of casein-to-whey protein ratio, incubation temperature, and heating temperature on viscoelasic properties of the final gel in a model system. Samples of solutions with different casein-to-whey protein ratios [2.1:0.9, 2.4:0.6 and 2.7:0.3] were prepared and refrigerated overnight. This was followed by heating the samples at different temperatures [70, 80, or 90°C] for 15 minutes using a water bath and cooling to incubation temperatures [25, 35 or 45 °C]. In the next step lucono-sigma-lactone was added and the samples were transferred to a rheometer. The gelation process was monitored by the time sweep oscillatory test. A second-order polynomial model was fitted to the experimental data and the optimum response was determined using the Minitab15 software. Incubation and heating temperatures influenced significantly [P<0.001 and P<0.01, respectively] the G'200 value [storage modulus value of the final gel measured 200 minutes after addition of GDL]. The casein-to-whey protein ratio had no significant influence on the G'200 value. Increasing the incubation temperature led to a decrease, whereas increasing the heating temperature led to an increase, in the G'200 value. The maximum value of G'200, 268/93 Pa, was obtained at the presence of 2.6152% [w/w] casein and at incubation and heating temperatures of 25 °C and 90 °C, respectively. Smaller quantities of casein and higher incubation and heating temperatures shortened the length of time required for gel formation. Finally, increased incubation temperatures and decreased heating temperatures led to increased the damping factor [tan sigma]. The effects of different process parameters on the viscoelastic properties of dairy gels can be determined and characterized by oscillatory rheometry. The findings of this study show that incubation temperature is the most effective factor, whereas casein-to-whey protein ratio has no significant effect on the final gel strength

[Influence of three types of Iranian gum tragacanths on rheological properties and stabilization of fat-free Doogh, an Iranian yoghurt drink]

Doogh is an Iranian traditional beverage based on yoghurt. In this product, serum separation occurs during storage due to its low pH. In recent years, studies have been conducted on the stabilization of doogh using hydrocolloids. The objective of this study was to compare the effects of different species of gum tragacanth [Astragalus gossypinus, Astragalus rahensis, and Astragalus fluccosus] on the stabilization and rheological properties of this typical Iranian dairy drink during storage. Gum solutions were added to Doogh samples prepared from yoghurt made with skim milk. Phase separation was measured using graduated cylinders during storage [30 days], and particle size distribution at ambient temperature was determined by laser diffractometery. Furthermore, steady and unsteady rheological tests were carried out using a controlled shear rate rheometer [CSR] at 3°C. Finally, sensory analysis was performed with 30 panelists familiar with the product, using a 5-point hedonic scale. In the samples containing 0.3% [w/w] A. gossypinus no phase separation occurred during the 30-day period. The data on particle size distribution indicated that addition of gum tragacanth resulted in a reduction in the size of aggregated particles, specially in the sample containing A. gossypinus. The apparent viscosity in this sample was higher than in the other samples. Also, its sensitivity to frequency [range = 0.01-10 Hz] was much less, which is very important from an industrial point of view. In addition, based on the sensory evaluation data, the sample containing A. gossypinus was the most acceptable product. The higher content of uronic acid and insoluble part of A. gossypinus can be the most probable reasons for the stabilized dispersion caused by A. gossypinus as compared to that caused by the other two species at the same concentration [0.3% w/w] in doogh

Effects of D-Tagatose, inulin and stevia as sugar substitutes on the physical, chemical, rheological and sensory properties of dark chocolate

Chocolate is very popular among consumers of all ages. However, its consumption is limited for the obese and diabetic people due to its high energy and sucrose contents. Replacing sucrose by low digestible carbohydrates [LDC[s] will result in lowering its energy content and glycemic index, as well as in preventing tooth decay. The objective of the present study was to investigate the effects of replacing sucrose with 2 sugar substitutes, namely, D-tagatose and inulin, on the physical, chemical, rheological and sensory properties of dark chocolate. Inulin, a dietary fiber, and D-tagatose, a natural keto-hexose with a degree of sweetness similar to that of sucrose, were used as sucrose substitutes in dark chocolate formulas. The inulin:tagatose ratios in the mixtures were 100:0, 75:25, 50:50, 25:75, and 0:100. The physical, chemical, rheological, and sensory properties of chocolate samples prepared with the mixtures were determined. With a reduction in the inulin content and an increase in the tagatose content, the moisture contents of the chocolate samples decreased, while their a[w] increased. Increased D-tagatose resulted in increased hardness of the samples, the sample with 100% being the hardest, comparable to the control [sucrose] value. With regard to color indices, the least amounts of L*,a*,b*,c* and hue° were observed in chocolate samples with 100% inulin. Increasing D-tagatose led to increases in the color indices. The data also showed that reductions in inulin resulted in decreases in apparent and plastic viscosity and increases in ?0 and ?1. Thus, the lowest real and linear yield stresses were found to be in the sample with 100% inulin. The least apparent viscosity and the lowest plastic viscosity were observed in samples with 25% inulin-75% tagatose and 100% tagatose, respectively, with no significant difference with the control value. Overall acceptability of the chocolate samples increased with increasing the D-tagatose level. It can be concluded that in chocolate formula samples an inulin-tagatose ratio of 25%-75% and 100% tagatose are the best sucrose substitutes. As inulin is a dietetic fiber and tagatose and inulin have prebiotic properties, chocolate samples prepared using them are also desirable from a nutritional point of view and can be considered as functional foods

Comparison of some chemical and rheological properties of Iranian gum tragacanth exudate from two Astragalus species [A. floccosus and A. rahensis]

Many studies have been carried out on structural and functional properties of gums from different sources. However, there is not much information available on the properties of gum exudates from different species of Astragalus. The objective of this study was to investigate and compare the chemical composition and rheological properties of two species of Astragalus under different conditions with regard to concentration, temperature and ionic strength. Moisture, ash and protein contents of the samples were determined according to the Iranian official standards, while determinations of minerals were done using ICP-AES. All rheological measurements were made using Physica MCR 301 rheometer [Anton Paar]. In addition, the flow behavior index [n] and consistency index [m] as parameters of power law model were computed, and the temperature dependency of consistency coefficient was assessed by fitting the Arrhenius model. The moisture and ash contents of A. floccosus were higher, and its protein content was lower, than those of A. rahensis. At all concentrations and temperatures, the results of apparent viscosity versus shear rate for each two species were found to exhibit a clearly shear thinning behavior. At all concentrations and temperatures and shear rates, A. floccosus had a higher apparent viscosity. At similar concentrations and temperatures, the magnitudes of parameters [m] and [n] for the A. floccosus was, respectively, higher and lower than that of the A. rahensis. In different food processing operations [stabilizing of soft drinks, using fat replacers, microencapsulation, and appropriate mouthfeel], the use and application of gums is based on the exact knowledge of their functional properties. In this study, it has been shown that different species of gum tragacanth have different characteristics. Therefore, in the processing of different foods [dairy, cereal, soft drinks, sauces, etc.], appropriate species of gum tragacanth should be selected and used