Food Technology
Shokohfeh Taziki; Seyed Mohammad Ali Razavi
Abstract
Introduction Wheat starch granules are composed of amylose and amylopectin, which are responsible for the functions of starch such as swelling, gelatinization, pasting, gel formation, and retrogradation. The retrogradation changes the functional properties, it is an undesirable phenomenon in some ...
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Introduction Wheat starch granules are composed of amylose and amylopectin, which are responsible for the functions of starch such as swelling, gelatinization, pasting, gel formation, and retrogradation. The retrogradation changes the functional properties, it is an undesirable phenomenon in some starch-based foods which reduces the acceptability of food, and shortens the shelf life. Delaying or preventing of starch retrogradation is a major challenge in the food industry. Various ingredients such as carbohydrates imply an important role in improving the functional properties, decreasing amylose leaching and retarding the retrogradation of starch gels. Cress seed gum (CSG), as an emerging galactomannan, has shown the ability to improve the textural and rheological features of food systems based on its unique properties. Addition of CSG to the composite wheat-rice bread increased dough stability and improved the staleness of bread compared to guar gum. Also, the addition of CSG and xanthan gum to gluten-free bread stabilized the texture of bread during storage. Sucrose (SUC) is a common additive in food formulations which is useful as a sweetening agent and textural modification. Sugars have been able to reduce amylose leaching and accelerate or delay starch gel formation. They also delay retrogradation of starch gels during storage. Therefore, the objectives of this study were to determine the impact of different substitution levels of CSG (0, 5, 10 and 15%), SUC (0, 5 and 10%), and their blend on the functional properties (swelling strength and solubility), microstructure features, retrogradation kinetics and synthesis of native wheat starch (NWS) gel (4% w/w).Materials and Methods Cress seeds were purchased from a local medicinal market. NWS and SUC were supplied from Sigma Aldrich (Spain) and Merck (Germany) respectively. Starch suspensions (0.6 gr powder/20 ml water) substituted with CSG (0, 5, 10, and 15% w/w) and SUC (0, 5, and 10% w/w) were prepared to estimate the swelling power and solubility index. To produce starch gel, the 4% w/w suspensions of NWS-CSG-SUC were prepared by dissolving the appropriate amount of CSG powder and SUC in deionized water. Then, each suspension was poured into a stainless-steel cylindrical container and was heated to 95 oC and held at 95 oC for 3 min and then cooled to 50 oC while stirring continuously at 160 rpm with a mechanical mixer. Finally, the pastes were kept at ambient temperature (25 oC) for 1 h. To assess gel structure, imaging of the gels was performed by scanning electron microscopy (SEM). The retrogradation kinetics and syneresis of gel samples were determined after storage at 4 oC for 0, 1, 7 and 14 days.Results and Discussions The swelling power and solubility index of NWS increased with increasing the replacement level of CSG. CSG promotes adhesive interactions among the gelatinized granules. This can enhance the forces applied to them, facilitating water entering (increasing swelling), amylose solubilization and its exudation. In contrast, SUC compete with starch molecules for water in the system and thus preventing gelatinization and mobility of starch molecules reduced the swelling power. The starch-gum-sugar mixtures had a higher swelling power compared to the starch and starch-sugar samples. The mixed samples had higher solubility values than each of them individually. SEM images showed that the pore size of starch gel decreased and increased from 33.01 to 29.44 µm and to 45.37 µm with increasing the substitution levels of CSG and SUC, respectively. NWS-15% CSG-5% SUC gel had 31.34 µm pore size. After storage for 14 days at 4 oC, the CSG substitution with NWS reduced the rate of retrogradation and syneresis from 0.101 to 0.52 (s-1) and from 50% to 23%, respectively. It could be related to creating a film around the granules by the leaked amylose and the CSG in the continuous phase, so inhibiting further swelling and polymers leaking out and related to high water holding capacity of CSG. The addition of SUC reduced the rate of the process to 0.096 (s-1) but because of its low water holding capacity, the value of syneresis enhanced to 57%. In the mixed gels, more reduction of the retrogradation rate and syneresis was observed which was clearly at high CSG replacement. The retrogradation rate of the NWS-15%CSG-5%SUC was 0.057 (s-1) and its syneresis was 45%. According to the results, it can be concluded that 15% CSG and 5% SUC replacement levels can effectively improve the functional properties and reduce the rate of retrogradation and syneresis of NWS during storage.
Sima Shamsaei; Seyed Mohammad Ali Razavi; Bahareh Emadzadeh; Esmaeil Atayesalehi
Abstract
Introduction: An emulsion is made of dispersed particles through the continuous phase, while not dissolving happens between two phases. Mayonnaise is oil-in- water emulsion (James and Dakin, 1962), as one of the most sauces used in the world. It has a mild odor and taste, creamy to pale yellow color ...
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Introduction: An emulsion is made of dispersed particles through the continuous phase, while not dissolving happens between two phases. Mayonnaise is oil-in- water emulsion (James and Dakin, 1962), as one of the most sauces used in the world. It has a mild odor and taste, creamy to pale yellow color and a pH in the range of 3.6- 4.0, which does not exceed 4.1 (Iranian National Standard, No 2454). Emulsion products are naturally instable. Different factors such as temperature, particles size, stirring, mechanical movements, constituents’ concentration, presence or absence of stabilizers and thickeners may affect the emulsion stability (David, 1999). Ocimum basilicum L., known as basil (or ‘‘Reyhan” in Iran), is a common herb plant grown in Iran. Soaking in water, basil seeds become gelatinous. The high mucilage content of basil seeds can make it a novel source of edible gum (Razavi et al., 2008). The objective of this paper was to investigate the effect of basil seed gum as well as xanthan as fat replacers on some physical and rheological properties of low fat mayonnaise. Materials and methods: Emulsion stability determination: Mayonnaise samples were centrifuged at 5000 rpm for 30 minutes. Emulsion stability (ES) was then determined using the following relation (Worrasinchai S et al., 2006): Stability index= (Total volume/ Volume of emulsion remaining)100. Particle size measurement: Particle size distribution of low-fat mayonnaise samples was determined using laser light diffraction technique (Fritsch Analysette 22, Germany). Rheological measurements: A rotational viscometer (Visco 88, Malvern, UK) equipped with a thermal circulator was used to measure the steady shear rheological properties of samples at the shear range of 14-300 s-1 and constant temperature of 25 oC. Power law, Bingham, Casson, and Herschel-Bulkley models were fitted on the experimental data and the rheological parameters of these models were determined using Slidewrite plus-bar Graph software (1983, Advanced Graphics Software, Inc, USA). Image processing: A scanner was used to capture the samples’ image and the scanner resolution was set to 300 dpi. 7g sample was placed onto a plate and then 152×210 Pixel parts was cut from the obtained image. All images were stored in JPEG format for further analysis. The Clemex image processing software (Clemex Vision Professional, PE4, Canada) was used to determine the color parameters (L*, a* and b*). Results and Discussion: Steady shear flow behavior: The results showed that all samples are classified rheologically as non-Newtonian shear thinning fluids. According to R2 values, Power law was considered as the best rheological model to describe the flow behavior of samples. The maximum and the minimum consistency coefficients of Power law model were observed for the formulation containing 0.75% xanthan gum and 0.45% basil seed gum, respectively. In this study, the apparent viscosity of mayonnaise (in shear rate 42 s-1) raised with increasing gum concentration that this increase in samples 4 and 5 were not significant (P>0.01). The highest apparent viscosity was observed in sample 3 that was prepared with a concentration 0.75% of xanthan gum, while the lowest viscosity was related to sample 4 that was contained of 0.45% basil seed gum. With increasing gum concentration, Bingham viscosity of the samples increased, but this increase in the samples (1, 7, 8) and (2, 6, 9) was not significant (P> 0.01). Yield stress values of Herschel-Bulkley (τH), Bingham (τB) and Casson (τC) models raised with the increasing of gum concentration. Highest yield stress value was related to mayonnaise containing 0.45% xanthan gum and the lowest yield stress value related to mayonnaise prepared with 0.45% basil seed gum. Particle size distribution: Particle size distribution of mayonnaise at concentration of 0.6 % xanthan gum, basil seed gum and mixture of xanthan- basil seed gum had mono-modal particle size distribution. Emulsion stability: Among samples, formulations of 1, 2, 3, 8, and 9 were quite stable and there was no instability (two-phase state). Higher stability in emulsions containing xanthan gum was probably due to higher viscosity of this gum compared to basil seed gum. Color: The best color was observed in sample 6. In this study, with increasing concentration of gum in three samples (1, 2, 3), the amount of L* decreased, it means that the brightness of the product was reduced while in samples containing a mixture of gums (xanthan- basil seed gum), increasing the gum concentration resulted in an increase in L* parameter.
