رقیه رمضانی

Lysozyme is a natural enzyme with positive antimicrobial activity against Gram Positive bacteria، but its action is limited on Gram Negative bacteria، which is assumed a restriction for its uses in industry. The purpose of this research was to glycosylate lysozyme with dextran through Maillard-based reaction and to study the antimicrobial characteristics of lysozyme-dextran conjugate. Glycosylation of lysozyme with dextran was performed using a 1:5 weight ratio of protein to dextran، incubated at 60 MC for one week under the relative humidity of 79%. For evaluating conjugation of dextran to lysozyme، SDS-PAGE electrophoresis was conducted. Gel filtration chromatography with sephadox G-100 was used for separation of conjugated enzyme. Lytic activity، free amino group and antimicrobial activity of the modified enzyme were evaluated. SDS-PAGE electrophoresis was used to follow the glycosylation process. Results indicated that 3. 7 moles of dextran were coupled to one mole of lysozyme. The lytic activity of the conjugate was about 62% of that of the native lysozyme. Evaluation of antimicrobial activity of the lysozymedextran conjugate، indicated the effectiveness of modified enzyme against E. coli and a progressive increase in antimicrobial activity with an increase in enzyme-conjugate concentration. The antimicrobial action of lysozyme on S. aureus was not improved by conjugation with dextran as compared with that of E. coli. These results might increase the application of lysozyme as a natural antimicrobial ingredient in different food systems.

In recent years, several oconjugation protocols have been developed to improve the functional properties of the enzyme lysozyme. In this study, the optimum conditions of lysozyme – oxidized inulin conjugation and functional properties of the modified lysozyme were investigated. Initially, inulin (MW about 25 kDa) was oxidized by periodate to provide the reactive carbonyl groups to attach to amino groups of lysozyme for Maillard reaction and was then conjugated to the enzyme at a molar ratio of oxidized inulin to enzyme of 5:1. A number of studies were conducted to investigate the optimization of lysozyme – Inulin conjugation consisting of different pH levels (3, 7, and 9), different temperatures (40, 60, and 80°C), and different reaction times. The degree of modification was determined by SDS-PAGE and sugar analysis of the product. The best condition for conjugation was determined to be 60°C at pH 7.0 for one week. The results showed that under these conditions, the inulin-lysozyme conjugate had 58% of the lytic activity of the native enzyme and had better emulsifying properties and heat stability than native lysozyme. Moreover, there was significantly higher protein solubility at pH 7.0 and 9.0 at different temperatures than heated lysozyme. Taken together, the results of this study indicated that lysozyme modification by oxidized inulin results in a new product with improved functional properties which may be employed for different industrial purposes.

Globally, potatoes are the fourth main food item after wheat, rice and corn. Potato chips are a very popular snack However, due to the high content of oil (40%), consumption of this product is not desirable from a nutritional point of view. The aim of this study was to produce low-fat potato chips by coating with hydrocolloids and investigate the effects of the hydrocolloid coating on chemical, sensory, and shelf-life of potato chips. Potatoes (Agria variety) were sliced, and the slices were then coated by immersion in 1%, 3%, and 5% pectin, 0.5%, 1.0%, and 1.5% sodium alginate, and 0.5%, 1.0%, and 1.5% carboxymethylcellulose (CMC) solutions. The coated samples, as well as an uncoated control sample, were fried in a frying oil. The moisture content, oil uptake, and the total acceptability of all the samples were determined, and then their acid and peroxide values were measured after zero, 2, 4, 6, and 8 weeks of storage. The results showed that hydrocolloid coating caused an increase in moisture content and a reduction in oil uptake in potato chips (p<0.05). Coating with 5% pectin brought about the highest reduction of oil uptake (28.6% oil and 34.4 % reduction), while treatment with 1.5% CMC resulted in the highest retention of moisture (6.06%). Based on the sensory evaluation of the total acceptability and the oil uptake reduction, concentrations of 5% pectin, 1% sodium alginate and 1% CMC for each type of hydrocolloids were selected. The results also showed that hydrocolloid coating causes significant reductions (p<0.05) in peroxide and acid values during 2 months of storage: the lowest peroxide value (61.32% reduction) and the lowest acid value (42.1% reduction) were due to treatment with 5% pectin and 1.5% CMC, respectively. The 5%-pectin coating was selected as the most suitable coating because it brought about the highest reduction in oil uptake, the highest total acceptability, the highest reduction in peroxide value, and a considerable increase in the shelf-life of potato chips.

In this research, sunflower oil that was extracted and refined at Shiraz Narges Oil Company was packed in four different containers, namely, clear PET (polyethylene terephtalate), yellow PET, yellow HDPE (high density polyethylene), and metal can. Samples were kept at ambient temperature in the shelf exposed to normal light for a period of 1 year. Peroxide values were determined at 45-day intervals and TBA and anisidine values were measured at 0, 6 and 12-month periods. In order to determine the effect of artificial light, some samples in PET and HDPE containers were kept in a wooden box equiped with four (20 w) fluorescent lamps and the peroxide values of the samples were determined. Light transmittance properties of the packaging materials were measured using a spectrophotometer over a wavelength range of 350 nm to 800 nm. The data indicated that the greatest variations in peroxide, TBA and anisidine values were observed in samples in HDPE containers (significantly different at 5% level) kept under normal light and ambient temperature for a period of 1 year. It was also shown that the shelf life of sunflower oil in HDPE container was less than 6 months while for the other packaging materials it was more than one year. Samples exposed to artificial light indicated that the highest peroxide values belonged to samples in clear PET while those in yellow PET proved to have the lowest. Finally, PET container proved to be the most suitable container for sunflower oil followed by metal can. Yellow PET with the lowest transmittance percentage (350-800 nm) and peroxide value (when exposed to 20 w fluorescent lamp) could be substituted for clear PET. HDPE container proved to be unsatisfactory for sunflower oil due to high oxidation rate.