مجله علوم غذایی و تغذیه
سال هشتم شماره 4 (پاییز 1390)

Glucose oxidase (β-D-glucose: oxygen-oxidoreductase, EC 1.1.3.4) from Aspergillus niger, is a flavoprotein which catalyses the oxidation of β-D-glucose to D-δ glucono-lactone, which subsequently hydrolyzes spontaneously to gluconic acid using molecular oxygen as the electron acceptor. Apart from being an analytical tool in biosensors for medical applications and environmental monitoring glucose oxidase (GOD) finds application in food and fermentation industry. In this study, glucose oxidase (GOD) was encapsulated within tragacanth gel capsules and the optimal conditions for immobilized GOD were obtained. Glucose oxidase was immobilized on gum tragacanth carrier with Microencapsulation method and the effects of pH, temperature, oxygen, concentrations of substrate (glucose) were studied and the optimal conditions for immobilized GOD were obtained. The enzyme activity was measured through pH- control. The optimal conditions for immobilized enzyme were: T= 36 °C, pH= 6, glucose concentration 0.1 M and the oxygen flow rate = 1 L/min. In optimum condition the activity of immobilized enzyme is preserved up to 75% after 8 repeated uses. As the results are shown gum tragacanth is a proper and economic biopolymer that might be used for immobilization.

The development of probiotics has signaled an important advance in the food industry. Selection for appropriate strain is an important task for production of probiotic dairy products which is usually practiced by industrial companies. The aim of this study was to produce the fermented and non-fermented probiotic milk using UHT(ultra- high temperature) and pasteurized milks with three species of Lactobacillus including Lactobacillus casei, Lactobacillus plantarum and Lactobacillus acidophilus. The number of viable bacteria and also the pH of products were determined during 14 days storage at 4oC. UHT and pasteurized milks were inoculated with one-day old cultures of the individual lactic acid bacteria of Lactobacillus casei, Lactobacillus plantarum and Lactobacillus acidophilus. Microbial concentration at the time of inoculation for sweet and fermented milk was 107 and 104 CFU/ml, respectively. The samples were incubated at 4oC and 37oC to obtain sweet and fermented probiotic milk products, respectively. The number of live bacteria and pH of each product were recorded at different time intervals. All the lactic acid bacteria reached the cell densities of about 107-108 CFU/ml in UHT and pasteurized milks during 24 hours incubation at 37 oC. The pH of fermented UHT milk decreased to 5.7 after 24 hours of incubation, while the pH of fermented pasteurized milk was dropped to 4.5. After 10 hours of incubation, the viable lactic acid bacteria in fermented milks reached to the 106-107 CFU/ml and was transferred to the refrigerator for stability studies. After 2 days of storage at refrigerator, the pasteurized milk was coagulated and was eliminated from the study, whereas during 14 days storage at refrigerator the pH of fermented UHT milk remained constant and the number of individual lactic acid bacteria were increased slowly. The number of viable bacteria in the sweet milk produced by UHT milk was increased by about 1 log during 14 days storage at 4oC, while the pH remained unchanged. The pH of the sweet pasteurized milk dropped from 6.4 to 5 and the number of viable bacteria increased by 1 to 2 log. Each of three species of Lactobacillus including Lactobacillus casei, Lactobacillus plantarum and Lactobacillus acidophilus, were suitable for preparation of sweet and fermented milk. Fermented probiotic milk prepared with UHT milk was stable during 14 days storage at 4oC. Also the pH variation in the sweet probiotic milk prepared with UHT milk was less than pasteurized milk. Sweet and fermented probiotic milk products containing sufficient amount of lactic acid bacteria might be prepared by using UHT milk.

This paper is concerned with rheological behavior of tomato paste from the view point of viscoelasticity and time dependant properties in order to design various units of tomato paste production line. Rheological behavior of tomato paste is determined at Spindle Brookfield viscometer. Experiments were carried out and determined that time dependant category of the samples show thixotropic behavior. Both stress overshoot and step strain tests emphasized the viscoelastic property of the sample, therefore the appropriate model were obtained to define the viscoelastic and time dependent behavior. This work exhibited one model which consisted of time dependent and viscoelastic rheological behavior of tomato paste. The results of the model are compared with experimental data which indicated good correlations between model result and experimental data. The experimental results showed that tomato paste behaves as a non-Newtonian semifluid which follows power law model.

The use of nitrogen fertilizers and low enzyme activity of nitrite and nitrate reductase in leaves of plants, causes the accumulation of nitrite and nitrate in leafy plants such as white cabbage (B.o var. alba).Nitrite is a highly carcinogenic substance therefore in this study changes in nitrite concentration during fermentation of fermented cabbage and spontaneous fermentation by inoculation of culture were examined. The strains used in fermented cabbage were Leu.meseneteriodes, subsp.mesenteroids PTCC 1563 and L. plantarum PTCC 1058 (Organization of Scientific and Industrial Research of Iran).The strains and their mixture as active culture, with equal numbers 5.6×106 cfu/gr were selected. Cabbage treatments consisted of inoculation with pure lactic starter (hemofermantative), inoculation with pure lactic starter (hetrofermantative), inoculation with a starter mix and cabbage not inoculated (control) were performed. Significant differences were recorded by the mean values of residual nitrites, pH, total number of lactic acid bacteria in the control samples (not inoculated) and inoculated samples (P<0.05).Residual nitrites in fermented cabbages by L. plantarum, Leu. mesentroides and mixed cultures were reduced up to 67.7%, 68.9%, 84.5% respectively, while it was 51.9% in the control treatment. The best treatment concering residual nitrite was the fermented cabbage by mixed culture. The best treatment concering the pH and the acidity levels was the cabbage inoculated by Leu. mesentroides.

The plants are the main edible oil sources for food, industrial and pharmaceutical uses. Different sources of oil due to their different composition and components might not be effective alone to fulfilled the nutritional needs, therefore various researches in the field of oil recourses is essential. This study is concerned with the evaluation of oils extracted from two varieties of avocado fruit which were obtained from North of Iran (Mazandaran). The pulp of each variety was subjected to oil extraction. The oils extracted from the pulps were subjected to a series of chemical tests consisting of fatty acids composition, free fatty acids content, iodine and saponification values, nonsaponifiable matter content, induction period measurements and qualitative and quantitative analysis of sterols and tocopherols. The results of the fatty acids analysis showed that the predominant fatty acid was oleic followed by palmitic, linoleic and palmitoleic acids. The results indicated that Fuerte variety had the highest amount of free fatty acid and iodine value and Hass variety had the highest amount of nonsaponifiable matter and saponification value. β-sitosterol and α- tocopherol were the predominant sterol and tocopherol present in the oils examined respectively. According to these results, Hass variety has more desirable characteristics and higher oil content and generally the oil might be compared to olive oil in terms of nutritional values.

Aflatoxin M1 (AFM1) is a hepatocarcinogen found in milk of animals that have consumed feeds contaminated with aflatoxin B1 (AFB1). This study was undertaken to determine the presence and levels of aflatoxin M1 (AFM1) in Iranian white cheese consumed in Isfahan and Shahr-e Kord, Iran. A total of 70 cheese samples were randomly obtained from retail outlets. Enzyme Linked Immuno Sorbent Assay (ELISA) technique was used to determine the presence and the level of AFM1. In 45 of the 70 cheese samples examined (64.3%), the presence of AFM1 was detected in concentrations between 44ng/kg and 719ng/kg. The mean level of AFM1 of positive samples was 218.8 ng/kg. AFM1 in 10 samples (14.3%) were higher than the maximum tolerance limit (250 ng/kg) accepted by the European countries. Statistical analysis showed that there were no significant differences (p>0.05) between the mean concentrations of AFM1 in cheese samples produced in spring and summer. It was concluded that widespread occurrence of AFM1 in Iranian white cheese samples were considered to be possible hazards for public health especially children.

Honey is essentially a concentrated aqueous solution of invert sugar, but it also contains a very complex mixture of other carbohydrates, several enzymes, amino and organic acids, minerals, aroma substances, pigments, waxes, pollen grains, etc. The amino acids in honeys are attributable both to animal and vegetable sources, the major of these being pollen. Amino acids account for 1% (w/w), and proline is the major contributor with 50-85% of the total amino acids. In this study, the destructive effect of processing at 55°C for 1 hour on honey Proline has been studied. By the application of spectrophotometer at 510nm the Proline contents before and after processing have been determined and compared. The results of this study indicated that a reduction in Proline content was observed for all the samples and for the samples with high Proline content this wes significant. Proline's reduction in all the samples were observed due to the processing at 55°C for 1 hour. Consequently, processing at the higher temperatures caused higher reduction of Proline.

The aim of this study was to determine the effects of cardiac rehabilitation (endurance and resistance exercise training, nutrition and psychological interventions) on metabolic syndrome indexes and exercise capacity in patient with coronery artery disease (CAD). We studied 31 patients (21 men and 10 women with mean age of 54.45±7.8 who were participating in the recovery phase II cardiac rehabilitation program and 15 patients (9 men and 6 women with mean age of 55.35±5.7 who were assigned as the control group. Cardiac rehabilitation program (CRP) consists of Exercise program and Dietitian and Psychiatric Counseling. All 46 patients underwent plasma lipids test and Functional capacity was assessed by a maximal exercise test before and after CRP. Both groups were comparable regarding baseline clinical characteristics. Post CRP, functional parameters and plasma lipids criteria improved significantly in the case group as compared to the control. After rehabilitation, the case group demonstrated significant improvements in estimated metabolic equivalents (METs) (8.5+/-1.8 vs. 11.8+/-1.5, p < 0.001), body weight (73.55+/-12.84 vs. 70.93 +/- 12.08 Kg, p < 0.001), body mass index (26.63+/-3.29 vs. 25.6+/-2.93 kg/m2, p < 0.01), percent body fat (27.6+/-9.17 vs. 25.88 +/- 8.78%, p < 0.001), high density lipoprotein (34.08+/-7.44 vs. 52.8+/-5.03 mg/dl, p < 0.001), low density lipoprotein (131.87+/-34.9 vs. 101+/-21.7, p<0.001), a decrease in triglycerides (167.06+/-54.86 vs. 115.71+/-25.68 mg/dl, p < 0.001), total cholesterol (186.45 +/- 43.04 vs. 135.45 +/- 23.07, p < 0.001) and blood glucose (107.25 +/- 26.5 vs. 92.06 +/- 11.09, p < 0.0001). There were no changes in any variables for control group. The proposed CRP is effective and might be applied after acute coronary events. The program can be also used as a method of secondary prophylaxis as it lowers total cholesterol, atherogenic index, and body mass index.

Yogurt is a fermented dairy product consumed world wide. In the recent years, a novel product has been produced using probiotic bacteria known as probiotic yogurt which is beneficial and functional. Prebiotics are added to its formulation to increase probiotics survival and growth and to improve technological properties of probiotic yogurt. The aim of this study was to evaluate the effect of prebiotics on probiotic yogurt containing lactobacillus casei. In this study prebiotics including Lactulose, Inulin, and Oligofructose as single, double and triple mixtures, and lactobacillus casei were used to produce probiotic yogurt. The samples were assessed for pH value, acidity, synersis, total count of probitics, and sensory characteristics (flavor, color and texture) and compared to control sample (probiotic yogurt without prebiotics). Next, the best samples based on sensory properties were chosen and then stored at 4°C for 21 d. During cold storage, physico – chemical properties and total count of probiotics of these samplese were evaluated. The results showed that the samples containing Inulin, Lactulos – Inulin, and Lactulose – Oligofructose had the best sensory characteristics. These samples and control sample were refrigerated for 3 w. According to the results of this study the sample contained Lactulose – Inulin had the lowest synersis percentage and the highest total count of live probiotic at the end of storage period. The results imply the positive effect of prebiotics on probiotic yogurt. The study showed that prebiotics can be used for improving quality and survival of probiotics in the yogurt.

The aim of this research was to determine the scale of contamination to heat resistant spores in common spices that are utilized in food preparation. Spices namly cinnamon (Cinnamomum cassia), white pepper (Pepper linnaeus migrum), red pepper (Capsicum annuum linnaeus), turmeric (Curcuma longa), garlic powder (Allium Sativum), and hindi Nutmeg (Myristica fragrans Houtt) were obtained from the food supplying centers in Tehran. Successive dilutions were prepared followed by pasteurization of dilutions at 65oC for 10 minutes. This is conducted in order to destroy the vegetative forms of bacteria. The counting of the existing spores were carried out by the application of blending plantation method. The results of this investigation revealed the contamination in the order of 22×101cfu g for hindi nutmeg,18×102cfu/g for red pepper, 18×103cfu/g for cinnamon, 26×102cfu/g for white pepper, 16×103cfu/g for garlic powder, and 18×103cfu/g for turmeric. The results of this investigation indicated that heating the suspension in vinegar is the most effective and more economic to eliminate the contaminated spores.