فصلنامه پژوهش های صنایع غذایی
سال بیست و سوم شماره 3 (پاییز 1392)

The effect of microbial transglutaminase (MTGase)، and sodium cholorid (NaCl) on chemical، and textural quality of chicken nugget was investigated in current study، using response surface methodology (RSM). The soluble peptide، fat absorption، expressible water and textural properties (breaking force، hardness، chewiness، adhesiveness and springiness) were assessed. Treatments had no significant effects on soluble peptide content، and fat absorption. The results indicated that enzyme and salt both were effective factors on expressible water (P<0. 05). Furthermore، increasing in MTGase and salt level had significant linear effect on springiness and deformation (P<0. 05). MTGase and time of incubation had synergistic effect on deformation (P<0. 05). Under higher activity of MTGase and incubation time، nugget deformation increased significantly. The higher level of MTGase، salt and incubation time were caused the higher hardness، chewiness and adhesiveness. The optimum condition for this experiment was MTGase activity، NaCl concentration، and incubation time of 1. 48%، 0. 85% and 25min، respectively. On the basis of the results، it can be concluded that MTGase can improve chemical and textural quality of low salt chicken nuggets.

Full-fat cheese (FFC) contains high amounts of saturated fatty acids and cholesterol، which have been known as a risk factor for health، particularly in cardiovascular diseases. Low-fat cheeses have problems such as undesirable flavor، texture and sensorial properties. In this study، functional low-fat white brined cheeses were made from bovine skim milk containing walnut (5، 10 or 15% w/w of curd) or linseed (1، 2 or 3% w/w of curd) powders and a full-fat cheese (control sample). Physicochemical properties، lipolysis patterns، total fatty acids، total count of lactic acid bacteria، sensorial properties were evaluated during 80 days of storage at intervals of 20 days. Results showed that low-fat white brined cheese containing walnut or linseed powders had significantly (P<0. 05) lower amounts of saturated fatty acids and higher levels of unsaturated fatty acids compared to FFC. Lipolysis index increased in all samples during ripening (P<0. 05) and the control cheese had lower lipolysis value than the cheeses containing walnut or linseed powders at the end of ripening period (80 days) (P<0. 05). Number of Lactococcus bacteria increased during 40 days of ripening but then decreased slightly، whereas number of Lactobacillus bacteria was different between all the cheese samplesduring ripening. Sensory properties of fortified cheeses were different (P<0. 05) compared with control sample; the cheese containing 15% walnut powder or 1% linseed powder was more acceptable than the control sample. In conclusion، results obtained showed the possibility of making healthy and functional low-fat white brined cheese with walnut or linseed powders with increased sensory scores and high amounts of unsaturated fatty acids.

Food borne diseases are the most important public health concerns worldwide. Escherichia coli O157: H7 is the most common member of a group of entropathogenic E. coli strains that is food and water borne pathogen and cause diarrhea، hemorrhagic colitis and hemolytic uremic syndrome in humans. Plant essential oils and Nisin have been known as antimicrobial agents that could be used to control food spoilage and food borne pathogenic bacteria. In this study the antimicrobial activity of combination of Nisin and Mentha spicata essential oil (EO) against Escherichia coli O157: H7 was determined by Minimal Inhibitory Concentration (MIC). The MIC value of EO was 40µl/ml. The synergism effects of Mentha spicata essential oil and Nisin depended on the parameters such as temperature storage، NaCl concentration and pH. Our results revealed that the numbers of surviving E. coli O157: H7 following exposure to Mentha spicata oil and Nisin was differed significantly (P<0. 05) with group 1:20μl/ml EO + 5IU/ml Nisin; group 2:20μl/ml EO + 2. 5IU/ml Nisin and group 3:10μl/ml EO + 5IU/ml Nisin، 10μl/ml EO + 2. 5IU/ml Nisin. The encouraging results indicate the essential oil of M. Spicata might be used as natural preservative for the control of E. coli O157: H7.

Acetic acid and starch are two highly consumed components in preparation of foods such as sauces، soups and fermented bread dough. Therefore، determination of the starch functional properties in presence of acetic acid can be useful in determination of the characteristics of such products. In this study، the effects of acetic acid (150 mg/k) on the functional properties of wheat starch were investigated. Scanning electron microscopy images revealed the appearance of some spots on the surface of starch granules. Starch water solubility increased from 4. 70 to 5. 43% but water absorption reduced from 4. 96 to 4. 53 (g/g). Intrinsic viscosity as an indication of molecular size and weight reduced from 174. 08 to 152. 75 (mL/g) that is an indication of starch molecular weight reduction in the presence of acetic acid. Gelatinization temperature decreased from 64. 50 to 64. 41 °C and enthalpy of gelatinization reduced from 9. 17 to 8. 14 (J/g). Using a Rapid Visco Analyser it became clear that the peak and final viscosities and peak time decreased significantly (P<0. 05). Overall، the results showed some partial degradation of starch molecules in the presence of acetic acid resulting in changes in physicochemical properties of wheat starch.

Ice cream is frozen mixture of milk materials، sweeteners، stabilizers، emulsifiers and flavor which has a variety of colloidal features because of different component in its structure such as ice crystals and dispersed air cells in serum phase. In this study، physicochemical properties of ice-cream were studied by using different ratios of sucralose as a substitute of sugar in the ice cream formulation. Vanilla ice cream with 19% sugar was used as a control sample and sucralose in five levels (20، 40، 60، 80 and 100%) was used as a substitute for sugar in the formulation، then its physicochemical properties were investigated. Results showed that by increasing sucralose overrun، viscosity، specific gravity and melting temperature of ice cream decreased.

The viability of Lactobacillus acidophilus and Bifidobacterium lactis was monitored during the storage of probiotic Doogh for 21 days as influenced by incubation and storage temperatures and product’s final pH value. Samples were fermented at various temperatures (37، 40 and 44°C) till the pH value dropped to 4. 6، 4. 4 or 4. 0. The highest viability of probiotics was achieved at fermentation temperature 37°C and final pH values 4. 4 and 4. 6. Storage of these two best treatments in various temperatures (5، 10 and 15°C) for 21 days resulted a rapid decrease in B. lactis population in the first 7 days after which the bacteria became compatible with the harsh condition. The highest viability occurred for L. acidophilus merely at pH lower than 4. 05 ± 0. 05 and its growth was observed in first week of storage. Samples stored at 5°C showed the highest viability and samples at 15°C had the best sensory properties.

Oxidation of oils during processing and subsequent storing decreases quality and produce oxidative products which cause various diseases. Therefore، use of antioxidants is drawn attention. One of the innovations in food packaging technology is active packaging in which an antioxidant is incorporated into the package. This kind of package increases shelf life of food without direct addition of antioxidant to the food as a result of gradual releasing of antioxidant from package to food surface and reducing compounds formed by the oxidation. In the current study، BHT with 0. 01 and 0. 02 % and 0. 37 and 1. 7 % concentration were added to pure soy bean oil and polyethylene bottles، respectively. They were put in oven set at 40 °C up to 2 months and their physicochemical properties were tested every 15 days. Results showed that BHT concentration in oil containing antioxidant decreased during storage due to oxidation but it was observed that BHT in oil without antioxidant were in contact with active packages increased by migration over time. BHT in package delayed the oxidation better than BHT in oil significantly. Generally، the use of active packaging containing synthetic antioxidant instead of direct addition of antioxidant to oil can be suggested.

In this study، the effect of different pretreatments on oil uptake and sensory characteristics of fried potato slices was investigated and also oil uptake of the samples was modeled. Ultrasound pre-treatment was performed at 28 and 40 kHz for 15 min and drying pretreatments were conducted at 80°C for 8 and 15 min. Then، the frying process was done at 150، 170 and 190°C for 60، 120، 180 and 240 seconds. In order to model the oil uptake، experimental data were fitted with six empirical models (2 models from published literature works and 4 models proposed in this study). The results showed that ultrasound-pretreated samples achieved the best result in decreasing oil uptake at the frying temperature of 150°C، compared to the control samples (rectangular slices with dimensions of 4×1. 2×1. 2 cm3) fried at similar frying time and temperature conditions; although the decrease was not statistically significant. Moreover، the samples pretreated with drying as well as combination of ultrasound and drying reduced oil uptake in comparison with the control samples. The decrease was significant in some samples and insignificant in some others. In addition، all the models used were well fitted to the experimental data. On the other hand، through multiple regression analysis، various models with high R2 were proposed to be applied at different circumstances of time and temperature during deep-fat frying process. Between different fried samples، in terms of sensory evaluation، no statistical significant difference was observed among the evaluated factors.

Color is one of the most important quality indices and this necessitates its rapid control during process progress and storage. In this study، capability of image processing method as a measurement tool for L*، a* and b* indices were evaluated. Six different imaging procedures were compared with hunterlab results using paired t-student test (α=0. 01) and only one imaging procedure (with sensor light sensitivity of ISO 400، shutter velocity of 1/40 s and diaphragm of f4. 0) did not show significant difference with hunterlab readings، therefore، this procedure was selected for imaging. Maximum standard error (SE) of this method for L*، a* and b* was equal to 2. 3، 2. 8 and 6. 5، respectively and maximum TCD between the readings of hunterlab instrument and this method was equal 11.

Response surface methodology was employed to investigate the combined effects of sodium caseinate (0–4%)، peppermint extract (0-0. 2 %) and refrigerated storage on functional، chemical and antioxidant activity of nonfat-set yogurt. The second-order polynomial model was fitted to the physicochemical properties of runs as the responses. Analysis of variance revealed that the quadratic models are well adjusted to predict the experimental data. Lack-of-fit tests were not significant and determination coefficients (R2) and adjust determination coefficient were high. The statistical analysis of the results showed that addition of sodium caseiante had significant effect on syneresis، water holding capacity (WHC)، apparent viscosity and L. casei counts (P<0. 05) and also addition of peppermint extract showed significant effect on apparent viscosity، L. casei counts (P<0. 05) and refrigerate storage had significant effect on pH، acidity، syneresis، WHC، apparent viscosity، probiotic count and antioxidant activity (P<0. 05).

In this study، the possibility of total and partial replacement of sucrose with xylitol was investigated. For this purpose، xylitol was used for total replacement of sucrose and in combination with oligofructose، sucrose or as a mixture of all. Physical properties of the cake batter such as specific gravity and viscosity، physical properties of the cake such as volume، specific volume، apparent density، solid density، porosity، moisture، water activity، symmetry، and firmness (first، 7th and 14th day after production) and final score of sensory evaluation (first، 7th and 14th day after production) were evaluated. Results indicated that cakes prepared with 25% xylitol - 25% oligofructose - 50% sucrose had the highest volume and porosity and the least apparent density. The least volume، specific volume and porosity and the most apparent density were observed in the cakes containing 100% xylitol. Less symmetry was observed in the cakes containing 100% xylitol whereas the cakes containing 25% xylitol - 25% oligofructose -50% sucrose and 100% sucrose showed more symmetry. In the first day، moisture content and water activity was lower in the samples prepared with 100% xylitol and 75% xylitol -25% sucrose، while the highest moisture content and water activity was observed in the samples with 100% sucrose. Cakes with 100% sucrose and 75% sucrose - 25% xylitol showed the maximum hardening rate of texture، whereas samples produced with different concentration of xylitol had the least hardening rate. Samples replaced with 50%sucrose – 50% xylitol and 25%xylitol-25%oligofructose -50%sucrose gave the most sensory evaluation score، however، the cake produced with 75%xylitol-25%oligofructose gave the least sensory evaluation score.