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تاثیر پوشش چیتوزان بر خواص فیزیکی، مکانیکی و شیمیایی انگور رقم فخری در طول دوره انبارداری مقاله

نویسنده:

نویسنده مسئول:

علمی-پژوهشی (وزارت علوم)/ISC (18 صفحه - از 347 تا 364)

چکیده:

در این تحقیق خواص فیزیکی، شیمیایی، مکانیکی و رئولوژیکی انگور فخری در طول دوره نگهداری مورد بررسی قرار گرفته است. انگور فخری پس از برداشت از باغات استان همدان با استفاده از پوشش چیتوزان در سه غلظت (۵/ ۰، ۱ و ۲ درصد) پوشش دهی شده و در دو دمای محیط و یخچال (۴ درجه سانتی گراد) نگهداری شده است. در طول دوره نگهداری هر ۵ روز یک بار خواص فیزیکی (افت وزن، درصد رطوبت و تغییرات شاخص رنگ)، خواص شیمیایی (pH و TSS)، خواص مکانیکی (نیروی بیشینه، نیروی شکست و مدول الاستیسیته) و خواص رئولوژیکی (زمان تنش آسایی و مقدار تنش آسایی) مورد بررسی قرار گرفته اند. نتایج تجزیه واریانس نشان دهنده آن بود که اثرات اصلی دما، دوره نگهداری و پوشش چیتوزان و برخی از اثرات متقابل آن ها تاثیر معنی داری در سطح ۱ درصد بر خواص فیزیکی و شیمیایی انگور فخری داشته اند. بیشترین افت وزن ۶۶/ ۱۰ درصد در نمونه پوشش دهی شده با چیتوزان ۵/ ۰ درصد نگهداری شده در دمای محیط اتفاق افتاد. کمترین میزان اختلاف رنگ برای نمونه های پوشش دهی شده با چیتوزان ۲ درصد نگهداری شده در دمای یخچال مشاهده شد. کمترین نیروی بیشینه در آخرین روز دوره برای نمونه های شاهد نگهداری شده در دمای محیط بوده است. دوره نگهداری تاثیر معنی داری در سطح ۱ درصد بر مدول الاستیسیته دارد درحالی که تاثیر پوشش بر این پارامتر معنی دار نبوده است. نتایج نشان دهنده آن بود که استفاده از پوشش چیتوزان تاثیر مستقیمی در افزایش زمان و مقدار تنش آسایی انگور فخری داشته است به نحوی که در طول دوره نگهداری کاهش هر دو پارامتر در نمونه های پوشش دهی شده نسبت به نمونه های شاهد کمتر بوده است.

Introduction 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. Materials and Methods 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. Results and Discussion 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. Conclusions 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.

کلیدواژه ها:

خواص کیفی ، انبارداری ، رئولوژی ، انگور فخری ، پوشش چیتوزان

Chitosan coating ، Physical properties ، Chemical ، mechanical ، storage ، Grape


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