نشریه پژوهش های علوم و صنایع غذایی ایران
سال هشتم شماره 4 (پیاپی 22، زمستان 1391)

Green Tea is prepared from the leaves of Camellia sinensis. Catechins of Green tea are well known as natural antioxidants and have effective beneficial on the body. One of the most important processes in the extraction of catechins and producing green tea beverage is brewing process. The object of this study is to investigating the effect of brewing temperatures (60٫70 and 80˚c) and duration (5٫10 and 15 min) also the season effect of plucking on green tea that was produced in the Tea Research foundation of lahijan. results of total phenolic content on brewed green tea, is showed that plucking in summer and spring seasons samples have much total phenolic content are rather than plucking in autumn season samples also percent extraction of brewing green tea at 15 minuets has most highest total phenolic content than other seasons and brewing times. brewing temperature are not significant effected on the total phenolic content.

In this research, tested factors were margarine types (contractive effects between types of oils in base of margarine such as palm super olein – partially hydrogenated canola oil – 50:50 mixture of palm super olein and partially hydrogenated canola oil and liquid canola) and different moisture (16-8-4%) as the first factor and heating time is the second factor. Every margarines spend 3 times heating and after every heating time, sample was separated to measure of acidite, color, polar compound. Results indicated that margarines based on palm super olein show better heat stability and liquid canola with high moisture have significant different. in acidite and polar compound percent with another margarines during heating steps. Also time of heating have significant effect in changeable factors.

In order to prevent the turbidity during storage of kiwifruit juice, clarification is necessary. Through proper clarification, flavor and taste of the product is also improved. Therefore, the purpose of the present study was to present a method to determine the optimum amount of clarifying agents (Pectinase enzyme, Bentonite and polyvinyl poly pyrolidone) for producing kiwifruit juice with stable clarity. For this purpose, effect of Pectinase enzyme (2-8 g/kg), Bentonite (200-350 g/Ton) and polyvinyl poly pyrolidone (70-110 g/100 lit) on viscosity, turbidity, clarity and total phenolics compound of kiwifruit juice was investigated. For each response a second order polynomial model was developed using a multiple linear regression analysis. Results showed that R2 for viscosity, turbidity, clarity and the total amount of phenolics were more than 0.90. The statistical analysis indicates that viscosity, turbidity and clarity (P

In this study, effects of Guar and Arabic gum on the viability of two common probiotic, Lactobacillus acidophilus and Bifidobacterium lactis, in frozen yogurt during 60 days were investigated. Results of survival evaluation of probiotics showed that although during storage time bacteria counts decreased significantly, this product could maintain 107 cfu/gr of probiotic at the end of storage. Maximum death rate of lactobacillus acidophilus was observed in control sample. Best viability of this microorganism was seen in samples containing 0.2% guar gum and 0.1% Arabic gum that these two treatments had no significant difference. The highest loss of bifidobacterium lactis belonged to sample containing 0.3% guar and lowest was seen in samples containing 0.1% Guar and 0.1% Arabic gum.

The objective of this work was to determine the effect of pre-frying elimination through the addition of methylcellulose and the influence of wheat flour partial replacement with corn flour (5 and 10%) on some quality factors of deep fat fried shrimp nuggets and compare the results with traditional process including pre-frying step. All batters showed shear-thinning behavior (n ≤ 0.624) and provided a good fit with power law model (R2 ≥ 0.979). Methylcellulose produced a significant increase in the consistency index of the batters. The highest pick-up value (57.68%) and the lowest oil content were found in 2% MC added batters that contained 5% corn flour, which was consistent with its high apparent viscosity. Results showed that the pre-frying elimination is an effective way in reducing oil content (%46) in deep fat fried shrimp nuggets.

Corn tortiilas are flat breads made from corn dough (masa) which is prepared through the nixtamalization process (alkaline cooking). Corn, in nixtamalization, is cooked in a lime solution then the boiled maize is steeped in cooked liquor, following by washing out and milling to obtain wet masa flour. Drying wet masa flour in air oven produce dry masa flour. Cooking temperature, cooking time, lime concentration, and steeping time significantly affect the quality of masa flour and final product(tortilla). In this research the cross effects of these four factors, to determine the best treatment for production of masa flour, were studied. Effects of cooking temperature (75,85,95°C), cooking time (0,30,60 min), lime concentration(0, 0.5, 1%) and steeping time (10,14,18 hr) by measuring pH, protein content, ash content, color parameters, water absorption index (WAI) and using central composite design were investigated. Statistical analysis revealed the best treatment for production of masa flour as: cooking temperature 85°C, cooking time 30 min, lime concentration 0.5%, and steeping time 14 hr.

Mazafati date is a wet and semi-dried date fruit type with dark red to black color that has premier quality. Because of its high moisture content, date fruits of this variety are very perishable at room temperature and therefore must be refrigerated during storage. In this study, effect of air temperature (50, 60, 70, 80 and 90 ˚C) and air flow rate (1, 1.5 and 2 m/s) in hot air drying of Mazafati date were investigated. The results showed that for all samples, drying occurred at the falling rate stage of drying and the main factor affecting the drying rate was air temperature. Air flow rate did not have significant effect on drying rate. Overall, it was concluded that moisture of Mazafati dates can be reduced by cabinet drying and therefore using drying process, the need for their cold storage can be eliminated.

The high hydrophilic property of biopolymer based plastics is one of the most important defects of them. Blending biopolymers with compatible synthetic polymers and using nano particles such as nanoclay as nanofiller are improving methods that have been extensively considered in recent years. Carboxymethyl cellulose (CMC) is one of the lowest cost biopolymers that have enormous applications in different industries and polyvinyl alcohol (PVA) is a synthetic polymer which has a high compatibility with biopolymers. In this research, CMC-PVA nanocomposites containing 3-10% Montmorillonite (W/W CMC) were prepared by casting method. The X-ray diffraction (XRD) results indicated the formation of an exfoliated nanostructure in all MMT content samples. Nanocomposites containing 10% MMT exhibited 29.06% reduction in water vapor permeability (WVP) compared to the blend film without nanoclay. Samples with 10% MMT, showed the lowest surface hydrophilisity (contact angle = 65.1o). The differential scanning calorimetry (DSC) results indicate that by increasing of MMT contents, the glass transition disappeared gradually and no glass transition was observed in the thermograms of the films containing 5, 7 and 10% MMT.

The sorption isotherm and state diagram of sundried, golden and sultana raisins were constructed for investigation and comparison of the product stability. The isotherms were measured at 15, 25 and 35 °C using an isopiestic method and the data were modeled with GAB model. Glass transition temperatures of the products were measured by differential scanning calorimetery (DSC) and fitted to Gordon Taylor model. Moisture sorption results indicated that the amount of moisture adsorption and the GAB monolayer moisture contents were the highest in sultana and the lowest in sundried raisins, at all of investigated temperature levels. Critical water activity (CWA) and critical water content (CWC) were estimated from the state diagram and the relationship between water activity, the glass transition and the equilibrium moisture content. According to the state diagram specification, CWC (dry basis) and CWA of raisins were estimated lower than 0.03 and 0.05, respectively.

Physical properties are often required for designing post harvest handling and processing equipment for agricultural products. Persimmon (khormandy cultivar) is rich in vitamin A, calcium, potassium, tannic acid and antioxidant phenolic compounds. In this study changes in the physical properties of persimmon fruit during storage were studied. Properties such as fruit dimensions, mass, geometric mean diameter, arithmetic mean diameter, equivalent diameter, sphericity, aspect ratio, surface area, volume and the static coefficient of friction on three surfaces (plywood, glass, and the galvanized iron sheet) were investigated. The results showed that the mean values of all physical properties decreased with increasing storage time. Experiments were carried out at initial moisture content of 44.26% d.b. Dimensions decreased from 56.01 to 52.57 mm in length, 54.19 to 50.01 mm in width, and 36.72 to 32.48 mm in thickness during storage time. Arithmetic mean diameter, geometric mean diameter and equivalent diameter varied from 48.07 to 44.06 mm, 48.95 to 45.06 mm, and 48.7 to 44.75 mm, respectively. The results also revealed that with increasing in storage time, the sphericity, the aspect ratio and the surface area of persimmon fruits were decreased from 0.859 to 0.8383, 0.6548 to 0.6211 and 72.99 to 61.41 mm2, respectively, while average volume and mass ranged from 59.18 to 45.79 mm3 and 72.8 to 65.45 g, respectively. Also, the static coefficient of friction on all surfaces increased significantly during the storage time.