JOURNAL OF FOOD RESEARCH (UNIVERSITY OF TABRIZ)
Year:2011 | Volume:21 | Issue:3|Papers Count:11

Microbial transglutaminase (MTG) catalyzes the formation of e – (d glutamyl -) - lysine cross links in proteins via an acyl transfer reaction. In this study, the impact of microbial transglutaminase (MTG) on dough rheological properties of wheat flour supplemented with 20, 35 and 50% of hullless barley flour was investigated. The MTG was added at five different levels (0.0.5%, 1%, 1.5% and 2%; w/w) to increase the concentration of lysyl residues and possibly enhance the extent of cross-linking of protein matrix by MTG, a commercial soy protein isolate (SPI) was added at a level of 3% (w/w) in combination with MTG. Extensography results showed that increasing MTG concentration increases the resistance to extension and decreases the extensibility. Farinography results indicated that in flours with 35 and 50% of hull-less barley flour, with increasing MTG doses, dough development time was increased. Addition of MTG in a concentration of 1% in 20% of hull-less barley led to an increase in dough stability time in farinograph. In 50% of hull-less barley treatment, addition of MTG in concentration up to 1.5% and 2% caused an increase in dough stability time. Mixing tolerance index was decreased with increasing MTG up to 0.5%. In overall, MTG can improve the rheological properties of dough when it is used in an optimum level.

Purslane seeds are rich sources of alpha-lineoic acid (omega-3) in all green plans that ever examined. This plant also contains substantial amounts of lignans, dietary fibre and natural antioxidants such as tocopherols. Health benefit of such components in prevention of certain diseases is the major reason for fortification of functional food products with purslane. In this study, effect of the addition of purslane powder on physicochemical (particle size distribution, protein, fiber, wet gluten and zeleny number) properties of wheat flour as well as rheological properties (in farinograph and extensograph) of the corresponding doughs was investigated. Purslane seeds powder was used to replace 50, 10, 150 and 200 g kg-¹ of wheat flour. Total protein and crude fiber contents of supplemented flours increased while wet gluten content and zeleny number of flour blends decreased as the amount of purslane seeds powder increased. Farinograph results showed lower water absorption, farinograph quality number, shorter stability time a higher softening degree for purslane supplemented flours compared to those of control flour. This indicates the weakening of dough rheological properties upon the addition of purslane seeds powder. Extensograph experiments revealed a significant increase in maximum resistance to extension (Rmax) for supplemented flours, except for 5 and 15% supplementation. Dough extensibility and extension energy were declined for all treatments, except for 5% supplemented flour.

The objective of this study was to determine and compare several physical and hydrodynamic attributes between two commercial pomegranate varieties (Sweet Malase and White Leather) cultivated in Iran. Results showed that the geometric mean diameter (74.61-82.45 mm), volume (176-503 mm3), true density (970.25-1028.3 kgm-3) and packaging coefficient (0.48-0.55) values had statistically significant differences at 1% probability level. Moreover, projected and surface areas of White Leather variety were 15 and 18% higher (P<0.01) than Sweet Malase variety, respectively. Terminal velocity, dropping time and drag force of White Leather variety were -0.17 ms-1, 3.42s and 17 N, respectively, while the corresponding values for Sweet Malase variety were 0.18 ms-1, 3.38 s and 1.94 N, respectively. It was also found that, the difference of buoyancy force value between Sweet Malase (2.41 N) and White Leather (3.25 N) was significant (P<0.01). Determination of these properties is necessary to the design of transportation, grading and processing equipments of the pomegranate varieties.

Introducing a method for separating the shell from kernel by considering the high price difference between kernels is very important from standpoint of color (light to amber). Utilization of the developed method can reduce the requirements of labor force and subsequently will be economically useful. In this purpose, a research was done on Persian walnut (Juglans regia L.). In this study, machine vision technology accompanying with artificial networks were used to study fundamental principals which can be applied for automating the process of separation shell from kernels and kernel classification. Mentioned method includes two phases: separation shell from kernel and classification of kernel. Five invariant moments were applied for separating shell from kernel. After calculating moments an artificial network was used to separate two groups. The results showed that the correct separation rate in the first phase is about 98.6%. In the second phase, to categories walnut kernels, four categories were considered (extra light, light, light amber and amber). By comparing two color spaces HSI and RGB with applying two principal components R and G (RGB) and using discriminant analysis, the process accuracy was obtained about 98.15%. The explained method can be a proper way for classification of walnut kernels from light to amber color.

Due to the side effects of chemical preservatives and as a support of the idea for consumption of green natural food, demand for studies on the antimicrobial properties of natural preservatives and essential oils on the important food borne pathogensin vitro and in food products has been increased. The goals of the present study included determination of biochemical properties and antimicrobial effects of Allium ascalonicum and Pimpinella anisum essential oils against Listeria monocytogenesin different steps of the ripening White Brined cheese. Results showed that 15 different substances made up 97.2% of its content for Pimpinella anisum essential oil; Longifolene and Benzene had the highest concentrations among these 15 substances; Allium ascalonicum essential oil contained 15 different substances made up 96.62% of its content; organosulfur substances had the highest concentrations among these 15 substances. The results of antimicrobial studies of these essential oils in the administered concentrations (Allium ascalonicum: 0, 0.025, 0.05, 0.1 % and Pimpinella anisum: 0, 0.05, 0.1, 0.2 %) during different steps of production and ripening of Feta cheese showed that Allium ascalonicum essential oils had the highest antimicrobial effects againstListeria monocytogenes. Treatments of 0.1% Allium ascalonicum and 0.2% Pimpinella anisumessential oils at the end of cheese ripening period showed the highest decrease in the mean bacterial colony counts (including 3.79 and 4.65 Log CFU/g, respectively) compared to other treatments (P<0.05). The results demonstrated that 0.025% Allium ascalonicum essential oil maintained the highest acceptable range in cheese organoleptic assessment.

Oil-in-water emulsions have attracted considerable attention in food industry due to their physical and rheological properties. These systems consist of small oil droplets dispersed in an aqueous medium. Numerous factors affect rheological properties of emulsions such as emulsion composition, process and storage conditions. In this study, effect of thermal treatment on oil in water emulsions containing 40 % oil was studied. The emulsions were prepared using xanthan gum, guar gum and carboxymethyl cellulose as stabilizer and polyoxyethylen sorbitan monooleat as emulsifier. A mixture design was used to define the percentage of each stabilizer to simulate wide range of emulsions. The emulsions were pasteurized at 87oC for 15 minutes. Rheological properties were studied using a Brookfield rotational viscometer. Thermal treatment had considerable influence on rheological properties of emulsions. Viscosity of all emulsions decreased after thermal treatment and stabilizers had a positive effect on this response. This behavior could be explained by the structural breakdown of the molecules due to the hydrodynamic forces generated and the increased alignment of the constituent molecules and hydrolization of stabilizers. All model emulsions exhibit non-newtonian pseudoplastic flow behavior often referred to as shear thinning (n<1). A non-linear relation between shear rate and shear stress can be observed. Shear stress versus shear rate data was successfully fitted to the Power-law model. Consistency coefficient (K) of emulsions decreased and flow behavior index (n) increased after thermal processing.

Grapes, both in ripe and unripe forms, are used to produce different food products. This fruit is much sensitive to mechanical damage because of their soft texture and thin skin. This study investigates the effect of the period of maturation of white seedless grapes (Vitis vinifera L.) on changes of some mechanical properties of grape and its skin and flesh. Changes in the value of toughness, ultimate strength, breaking force and energy, stiffness and modulus of elasticity were determined in grapes harvested from a local vineyard during ripening stage. Simultaneously with increasing oBrix and decreasing titrable acidity during ripening, the value of true density of the fruits increased from 1.073±0.004 to 1.106±0.007 g/cm3. Both the value of ultimate strength (spu) and toughness (Upu) of grape flesh, jointly increased in maturation stage with a positive correlation (R2=0.8626, P=0.0025 at a confidence level of 0.99), while the value of modulus of elasticity decreased in the first weeks during ripening then increased in the last weeks of the period. All parameters obtained from tensile test of the skin, including ultimate strength, modulus of elasticity and toughness decreased in the maturation stage. In this period, maximum and minimum of the fruit’s skin ultimate strength were calculated by 3.176 and 2.011 MPa, respectively. Also modulus of elasticity of the skin decreased from 9.515 to 6.127 MPa and toughness changed from 0.876 to 0.413 mJ/mm3 for the duration of ripening. Resistance to rupture (Rupture force) of whole berries was measured using compression test ranged from 7.80 to 9.18 N. The results of penetration test on the whole fruit showed that breaking force, breaking energy and stiffness decrease throughout ripening.

Irradiation as a method of meat and poultry preservation has excellent potential to improve meat safety and extend the shelf life. The main concern of irradiating meat, however, is the organoleptic quality changes that occur. The present study was conducted to evaluate the combined effect of low-dose gamma irradiation (2/5 kGy) and chitosan edible coating (2%) on the shelf life of chicken breast meat. Samples were separated into four groups; uncoated and unirradiated control (C), coated with chitosan (CH), irradiated and uncoated (I) and coated with chitosan and irradiated (ICH). Samples were stored at 0-4oC and evaluated periodically for microbiological (aerobic mesophilic and psychrotrophic counts), chemical (TBA, pH, aw) and sensory (odor, appearance and overall acceptability) characteristics. Microbial analysis indicated that gamma irradiation and coating had significant effects (P<0.05) in reducing the mesophilic and psychrotrophic counts with at least a 14-day extension of shelf life. The chitosan-coated products showed lower TBA and pH values than the uncoated samples for up to 21day of storage at 0-4oC. No significant (P>0.05) differences in TBA values of samples were observed due to irradiation. The results indicated that the application of chitosan coating significantly improved (P<0.05) sensory quality of samples. None of the sensorial characteristics (odor, appearance, overall acceptability) was significantly affected by gamma irradiation (P>0.05). This study thus clearly indicated that the effect of chitosan coating plus irradiation on samples was to retain their good quality characteristics and extend the shelf life during refrigerated storage, which was supported by the results of microbiological, chemical, and sensory evaluation analyses.

In this research, duo to increasing importance of producing low fat meat products such as hamburger and in order to developing new and safe product with low fat and cholesterol content and high fiber, effect of different levels of microcrystalline cellulose as a fat replacer on physicochemical, textural and sensory properties of low fat hamburgers were compared with high fat control samples. Control with 12% fat and 0% MCC, and low fat hamburgers with %6 fat and %1, %1.25 and %1.5 MCC were produced. Results showed that it is possible to reduce the fat content of the hamburger samples up to 50 percent without significant effects on protein, carbohydrate, salt and ash. There was a direct correlation between MCC level and moisture content of samples but MCC content didn’t show any significant effects on the loss of the weight of samples after cooking. Sensory analysis were highly favorable and all samples gained acceptable score .Findings of all textural parameters revealed that low fat samples with %1 MCC, were more similar to control than others and could imitate textural properties of high fat products.

The seeds of Shahi, Qodumeh Shahri, Qodumeh Shirazi and Marve were selected as the new sources of hydrocolloids and the extraction yield and some functional properties such as time independent rheological properties, emulsion capacity (EC), emulsion stability (ES), gelling properties, foaming capacity (FC) and foaming stability (FS) were determined. The results showed that the yield of hydrocolloid extraction from selected seeds was in the range of 8% to 15% (w/w) and Qodumeh Shirazi and Shahi seeds had the highest and the lowest yield, respectively. All samples exhibited shear thinning behavior (n<0.43). Marve seed extract showed the highest apparent viscosity followed by Qodumeh Shirazi, Shahi and Qodumeh Shirazi. EC and ES values of Marve seed extract were obtained more than other extracts at 1% concentration, whereas Marve seed extract and Shahi seed extract at 0.5% concentration had the highest EC and ES, respectively. Qodumeh Shahri seed extract and Qodumeh Shirazi seed extract showed the greatest FC and FS, respectively.

Spoilage of bakery products is mainly caused by molds. Nowadays, consumers demand for minimal use of chemical preservatives in foods. Thus, researchers attempted to use lactic acid bacteria as biopreservatives in food. Lactic acid bacteria produce a number of antifungal metabolites, e.g. organic acids, diacetyl, acetone, hydrogen peroxide, antifungal peptides and bacteriocin, by which the shelf-life of food is prolonged. In this study antifungal properties of lactic acid bacteria includingL. plantarum and L. reuteri in sourdough in inhibition of Aspergillus niger and two Aspergillusspecies (yellow and black molds) isolated from bread was investigated. Results showed THAT after 2nd day, Aspergillus niger growth was significantly (P<0.05) higher in control culture than that of sourdough supernatants cultures. In case of yellow and black molds, sourdough supernatant cultures did not retard mold growth.