جستجوی مقالات مرتبط با کلیدواژه « رئولوژی » در نشریات گروه « مکانیزاسیون کشاورزی »

Grape fruit set its fruits and shortly after planting and due to high nutritious value and excellent food quality has been welcomed by many people in the world, but considering its soft tissue and high softening velocity and sensitivity to fungi attack it is known as an extensively vulnerable fruit. One of the most important ways to maintain fruit quality, decrease vulnerably and assist more appropriate storage, is the use of coating method and proper packing of agricultural products and combining these procedures to decrease damages in storage. Edible coatings provide a replacement and fortification of the natural layers at the product surface to prevent moisture losses, gas aromas, and solute movements out of the food, while selectively allowing for controlled exchange of important gases, such as oxygen, carbon dioxide, and ethylene, which are involved in fruit respiration. Chitosan is the most common polysaccharide-based coatings. Chitosan films have been successfully applied as edible material in films and coatings for the quality preservation of different fruit. In this study, the effects of the application of chitosan edible coatings and storage time on some physical, chemical, mechanical and rheological properties of grape were investigated during storage. Grape fruits were screened for physical damages, fungal infections, and size homogeneity after harvesting from the farm. Then fruits were divided into without coating and fruits with coating. Fruits being coated, prepared in chitosan emulsion and submerged for two minutes and kept at 20°C for one hour for drying the surface coating via airflow. In order to calculate the weight loss, three containers of each grape fruits (treatment and control) collected and after weighing and averaging weight loss were compared to initial weight during storage expressed as a percent. Color intensities were determined using colorimeter samples. In order to determine soluble solids from each sample, refract meter was used and pH amount of each sample was determined. Mechanical traits and fruit stiffness were measured through penetration test using materials test machine Zowick/ Roell having 500 N loadcell in line with the small diameter with concave probe (5 mm diameter), the penetration depth of 2 mm and loading rate of 10 mm s-1. Mechanical traits including stiffness and elasticity module calculated from the force-deformation curve. Viscoelastic materials have the properties of both viscous and elastic materials and can be modeled by combining elements that represent these characteristics. A viscoelastic model, called the Maxwell model which can predict behavior was evaluated. In this current study, the application of chitosan coating significantly reduced the fresh grape decay. Fruit decay of grape increased with storage time, but the coating reduced the rate of decay with the length of storage. According to the results, the application of these coatings has a positive impact on yield stress and energy of rupture product texture during the storage. Results of variance analysis showed that temperature, coating and storage time has a significant effect (1% level) on some of the engineering properties of the grape. Storage time has a significant effect on elasticity, while the coating does not have a significant effect on this parameter. Finally, results showed that the application of chitosan coating has an effect on relaxation time and stress. So during storage of coated samples these parameters decreased compared to uncoated. Edible films and coatings may reduce the moisture transfer, the rate of oxidation and respiration which are considered important to prolong the shelf-life of these products. This investigation showed that the chitosan coatings are effective for grape shelf life extension and retarded the senescence process compared with control. The coat has been as a physical barrier for the gas exchange between the fruit and the environment. It was demonstrated that the coating reduced the loss of firmness and delayed the softening of fruit and texture change.

A foodstuff response evaluating at different forces such as shear, compress, tensile and chewing force is in fact product texture evaluating which is relying on rheological characteristic. In this research, the relaxation behavior of various chicken parts was perused based on Generalized Maxwell Model at different regimes. The effects of three types of treatments as Control (without additives), Antibiotics of 650 ppm and 2 g/g of a medicinal plant named Coneflower on relaxation behavior of chicken part (two groups of thigh and breast) were surveyed in room temperature. The relaxation times of different samples were compared with each other basis a six element Maxwell model. Results showed that this model was suitable fitted with the experimental data and with the addition of antibiotics and coneflower the elastic coefficient of General Maxwell model changes. Moreover, the relaxation times of samples were significantly different with each other under different regimes.

In order to improve food texture, hydrocolloids are used widely as gelling material in food systems. Wild sage seed has remarkable amounts of gum (mucilage) with good functional properties. This mucilage also improves the rheological, textural and functional properties of foods. In this study the effects of different drying methods including hot air drying (40, 50, 60, 70 and 80°C), freeze drying and vacuum oven drying on rheological and textural properties of wild sage seed gum were investigated. The apparent viscosity of dried gum solutions at shear rate 60 s-1 was varied from 0.162 to 0.344 Pa.s. With increasing oven temperature from 40 to 80°C, the apparent viscosity of gums decreased from 0.271 to 0.162 (shear rate 60 s-1). The Heschel-Bulkley’s model was found the most suitable to describe the flow behavior of wild sage seed gum over the whole experiment.Drying method of mucilage has a significant effect on the change of textural characteristics of prepared gel from the dried gum and the highest value of hardness, stickiness, consistency and adhesiveness of gum texture were for freeze-dried gum, that were 78.2 g, 17.0 g, 794.8 g.s and 159.2 g.s, respectively.

Flaxseed is rich in omega-3 essential fatty acids, lignans, dietary fiber and natural antioxidants such as tocopherols. Because of its functional effect in preventing disease, flaxseed is used as an ingredient to fortify food formulations. Bread is a major food product in Iran. Fortification of wheat flour with ground flaxseed makes use of the healthy benefits of flaxseed. This study investigated the rheological properties of dough prepared using flaxseed-supplemented flour. Flaxseed flour was used to replace 5, 10, 150 and 200 g.kg-¹ of the wheat flour. Farinograph results showed greater water absorption, longer development time, increased softening and a higher farinograph quality number for the flaxseed supplemented flours over the control flour. Dough stability time for all blends decreased except for that with 5% flaxseed. Extensograph testing revealed a significant increase in maximum resistance of dough to extension and a substantial decrease in dough extensibility and extension energy. Despite the beneficial health effects of flaxseed in fortification of bread, the negative effects of high concentrations of flaxseed powder on dough quality and rheological properties must be considered and precautions taken to compensate for these adverse effects.