فصلنامه پژوهش های صنایع غذایی
سال بیست و دوم شماره 4 (زمستان 1391)

In this study, capability to remove cholesterol, acid tolerance, bile salt tolerance and viability in yogurt of Lactobacillus reuteri (DSM 20016) were examined. Results showed that L. reuteri was able to remove 58.96 μg/ml of cholesterol from culture medium containing 100 μg/ml cholesterol and 0.3 % (w/v) of bile salt. Also, after 2 hours at pH 2, the viable count of L. reuteri declined to 3.3 from 8.1 log cfu/ml. In order to study bile tolerance, the growth rate of bacteria was determined in MRS broth containing 0.3% (w/v) bovine bile salt (oxgall). Results illustrated that L. reuteriwas resistant to the bile salts. Finally the viability of L. reuteri in yogurt throughout the storage was examined. Results revealed that L. reuteriadequately maintained its viability throughout the storage period, so that after 3 weeks of storage, the number of viable bacteria was over recommended level of 106cfu/ml. Therefore, L. reuteriwas regarded as a suitable probiotic for production of cholesterol-lowering yogurt.

In this study, response surface methodology was used to optimize the osmotic-ultrasonic drying condition to achieve maximum water loss, phenolic compounds and minimum solid gain and %EC50. Temperature (40, 50 and 60), processing time (4, 7 and 10h), sucrose syrup concentration (40, 50 and 60% v/w) and frequency (0, 35 and 130 KHz) were the investigated factors influencing kumquat properties during the osmotic-ultrasonic drying. The liquid medium to fruit ratio was 10:1 (weight basis). Experiments were designed according to the central composite rotatable design. Results showed that the linear effects of temperature, processing time, sucrose syrup concentration and frequency on water loss, solid gain, phenolic compound and EC50 were statistically significant (p<0.05). For each response, second-order polynomial models were developed using multiple linear regression analysis. Analysis of variance was performed to check the adequacy and accuracy of the fitted models.

For determining the rationale of reducing strength of rice kernels during harvesting and postharvest operations and comparing the quality of rice bulk samples, specially for comercial proposes, a suitable device and method for rice quality measurment is necessary. Rice Breakage susceptible index for bulk samples, is a proposed index which could be determined by a centrifugal impact tester based on weight percent. Therefore, by modification of a laboratory mill, the effect of moisture content, blade rotational speed and duration of test were investigated on a fabricated apparatus performance, based on 50% breakage level and according to a completely randomize factorial test and by conducting 500 milling tests. The results showed that the three independent factors had a significant effect on BSI. According to the results, the speed of 1000rpm and less, and the speed of 5000rpm and more, are not suitable for this kind of test due to very low and very high rate of breakage, respectively. Finally, the speed of 4000 rpm, moisture content of 9% (wb) at 80 seconds of test duration was selected as the best condition for the test, according to 50% rate of breakage with minimum and maximum rate of 23 and 67%.

Despite the popularity and convenience of the box cakes, one of their major problems is poor and fragile texture. The main aim of this study was to use instant wheat starch in the production of box cake powder in order to improve cake quality and to reduce undesirable brittleness of the final cake. Therefore, mixture of wheat starch, 5% gluten powder (based on starch weight) and instant wheat starch at different levels of 0, 5, 10 and 15% (w/w, starch basis) were used in the cake recipe. The results showed that with increasing the level of instant wheat starch, batter consistency and cake volume were increased. Determination of the cake texture using a texture analyser revealed that with increasing the instant wheat starch level, cake hardness decreased while cake cohesiveness increased. The most appropriate dough consistency, cake volume and cohesiveness were obtained when 10% instant wheat starch was used in the cake recipe.

Providing a quick way to predict the activity of yeast in the baking industry in terms of performance and quality is vital. In this paper, seven instant dry yeast samples of domestic and foreign manufacturers were assessed and compared by four methods for fermentative activity of Saccharomyces cerevisiae: Henry -Simon pressure meter, Gasography, microbial tests and baking test results showed a similar trend for yeast activity and demonstrated further power of Iranian yeast. In gasography and pressure tests, Fariman and French samples produced maximum and minimum gas volumes, respectively. The same trend was seen in microbial test (number of colony forming units) and baking test (loaf volume and height) for these two yeasts. Razavi yeast did not show significant differences with Fariman. Dezmayeh, Golmaye, Kelarmaye, Turkish and France yeasts showed significant differences compared with Razavi and Fariman (P<0.05). All tests showed a close correlation with the baking test. Using the pressure meter as the best method to assess the gassing power of bakery yeast was proposed. This quick and simple test can be a suitable alternative to long cooking methods to observe the capability of CO2 production in bakers’ yeasts.

In this study, the physicochemical, rheological and sensory properties of stirred strawberry yoghurt enriched by wheat fiber in different levels and particle size were investigated during storage for 28 days at 5 ±1 °C. The fiber was used at 5 levels (0 as control, 0.3, 0.6, 0.9 and 1.2 g in 100 ml) at two different particle size of 0.22-0.42 and 0.17-0.20 mm. The statistical analysis of the results showed that the acidity and viscosity were increased and moisture content and syneresis were decreased with increasing the amounts of fiber in yoghurt significantly (P<0.05).The minimum syneresis rate (23 to 25%) and maximum amount of viscosity (4000-4500 Cp) were observed in samples contain-ing higher than 0.6 percent fiber. The samples containing smaller fiber particle size showed higher viscosity and acidity than the other samples (P<0.05). The pH of sample was decreased and the acidity and syneresis were increased during storage period (P<0.05). The results also showed that the amount of wheat fiber Used and its particle size had no effect on color index (a*, b* and L*) and sensory evaluation (color and flavor). Therefore it was concluded that the wheat fiber can be used successfully in the production of stirred yoghurt at the rate of 1.2%.

Staling of the bread prepared from the flour of various kinds of newly developed rice cultivars (Tarom, Shiroodi, Neda, Fajr, Ghaem and Binam) was investigated. To prepare free gluten bread, rice flour with 2% hydroxylpropylmethylcellulose (HPMC) as gluten substitute were used. Moisture content, enthalpy changes (ΔH) and firmness of bread were monitored and found to be significantly affected during storage at room temperature. Crumb moisture content was found to decrease steadily during staling and crust moisture content increase during storage time. Enthalpy changes (ΔH) as measured by differential scanning calorimeter (DSC) increased over the time in Binam, Fajr, Tarom, Shiroodi and Neda cultivars. Ghaem, Binam and Tarom cultivars had lower amylose content than the others and showed lower values of ΔH. Staling of gluten-free rice bread results in increasing firmness of crumb and decrease firmness of crust, therefore, the crumb texture of this bread became progressively harder with storage. The lowest value of crumb firmness was reported for Binam cultivars in four days of storage.

Seeded pumpkin is cultivated for its seeds to be used as snack. After removing seeds at harvest time, the residual including fruit peel and pulp are left in the field which causes pollution of the environment. The amount of wastage is considerable, thus it can be used as a pectin source. Pectin is an important structural constituent of plant cell wall. It is widely used as a gelling, thickening and stabilizing agent in food industries. In this study, pectin of seeded pumpkin was extracted under various conditions: pH (1, 2, 3 and 4), temperature (60, 75 and 90° C) and time (1, 2 and 3 hour). The extraction yield, degree of esterification and galacturonic acid of the extracted pectins were evaluated. In this study, yield of pectin was considerable and extracted pectins were high methoxyl pectins with high purity. The results showed that drastic condition of acidic extraction (lower pH, higher temperature and time) increased extraction yield and galacturonic acid content of pectin whereas it caused a decrease in the esterification degree of pectins. Analysis of variance showed that the temperature of extraction was the most significant factor on the pectin extraction yield while pH was the most influencing factor on the degree of esterification and galacturonic acid content of pectin.

Several strains of lactic acid bacteria, used as starter culture to produce yoghurt and other fermented products, produce exopolysaccharides which can improve textural properties of products. In this study, physical (syneresis), rheological (viscosity and firmness) and sensory properties of yoghurt samples produced with exopolysaccharide producing starter culture were investigated in comparison with nonexopolysaccharide producing starter culture CH-1 during 30 days of storage. Samples with exopolysaccharide producing starter culture had lower syneresis and were more viscous and firmer than those made with nonexopolysaccharide producing starter culture. Storage time had significant (P<0.001) effect on mentioned properties. Panelists expressed that yoghurts produced with YF-L811 were whiter, firmer and had lower syneresis before and after inserting spoon into them, stronger flavor and tended to be creaminess, more cohesive and adhesive than samples produced with CH-1. Difference between unpleasant sourness of samples produced with exopolysaccharide producing starter culture and nonexopolysaccharide producing starter culture was not significant (P>0.05).

Patulin is a mycotoxin mainly found in apples and apple products, and has become one of the most important quality criteria for apple juice. In most country the maximum level of patulin recommended concentration of 50 μg.L-1 for adult and 10 μg.L-1 for infants and young children, respectively. In this study, effects of adding different concentrations of folic and pantothenic acids, as well as effects of storage temperature and storage time on reduction of the patulin content and qualitative characteristics such as colour, clarity and turbidity of apple juice concentrate were investigated. The results indicated that by adding the folic and pantothenic acids to the samples with an initial patulin concentration of 170 μg.L-1 and storage temperatures of 5 °C and 27 °C, the mycotoxin content decreased to less than 50 μg.L-1. The storage of samples without any acids at these two temperatures is also an alternative to reducing the mycotoxin content if the storage period is increased which can reduce the other quality parameters of product. Addition of acid has a positive effect on reduction of patulin. However, these samples have the lowest amount of patulin, but they have the lowest transparency and highest turbidity. The highest transparency and lowest turbidity is related to the samples without acid and sample that contains pantothenic acid, 500 mg/kg in 5 °C with 10 days storage time, wich amount of patulin can be reduced by 71%.