| چکیده انگلیسی مقاله |
Inroduction: Rice is one of the main food crops consumed by a huge global population. The by-products of rice after milling are germs, broken rice, and bran. Bran is the most favorable by-products of rice and wheat. Rice bran is a source of fiber with the balance level of soluble and insoluble dietary fiber, high amount of minerals, and vitamin. Rice bran is rich in nutrients such as protein (15%), fat (20%), and fiber (10%). It also provides a rich source of vitamins and minerals such as thiamin, niacin, aluminum, chlorine, iron, magnesium, phosphorus, potassium, and sodium. Also rice bran has some antioxidants such as ferrulic acid, tocopherol, oryzanol, and tocotrienol. It contains lysine nearly 4 times higher than rice due to having the out layer of rice. On the other hand, the use of probiotic foods, especially probiotic dairy products, in the consumers community is much preferred rather than probiotic pharmaceutical products, therefore, the development of probiotic food products seems necessary. Objectives: The aim of this study was to produce a probiotic fermented dairy beverage containing Bifidobacterium bifidum, Lactobacillus casei, and rice bran extract. Methods: Rice bran was obtained from a rice milling complex in Amol and sterilized in an autoclave at 160°C for 1 hour. Then, 100 grams of bran was mixed with acetate buffer solution with pH equal to 5, 200 ml of distilled water along with 5% (weight/volume) of phytase enzyme and heated at 37 degrees Celsius for 60 minutes. The liquid phase was separated from the solid phase by filter paper and the bran extract was separated by a centrifuge (6000 g, 15 minutes). Formulation of dairy drink containing rice bran extract was prepared using the following components: 50% (v/v) skim milk containing 5% (w/v) sucrose and 0.5% (w/v) pectin with low methoxylation degree, 20 % (v/v) of cheese juice and 30% (v/v) of rice bran extract. In formula A, the bacterial culture only contains starter cultures (Streptococcus thermophilus and Lactococcus lactis, 0.01% by volume/volume), and in formulas B and C, it includes probiotic culture (Lactobacillus casei or Bifidobacterium bifidum, 0.01% by volume/volume and The final population was 7 logcfu/ml). The control sample was prepared without adding rice bran extract. After preparing the base formulation and before adding the bacterial culture, the thermal process was performed at 90°C for 5 minutes and cooling to 42°C. The starter culture was added and mixed, cooled to 37°C, and then probiotic bacteria were added. The formulation was kept in a greenhouse at 37°C for 3-4 hours until the pH reached 4.5. In the next step, homogenization was done with a homemade stirrer to break the clots. Drinks were stored in 250 ml glass bottles with lids at refrigerator temperature (4±0.5 °C) for 21 days and tested at 7-day intervals.Survival of probiotic bacteria, chemical and physical properties, the content of phenolic compounds (TPC), antiradical activity, and sensory properties were evaluated. Results:The results showed that incorporating rice bran extract in a dairy beverage containing probiotics increases the activity of bacteria to produce acid and reduce pH. The activity of Bifidobacterium bifidum in acid production was higher than that of Lactobacillus casei, and samples containing rice bran extract and Bifidobacterium bifidum have lower pH and higher titratable acidity. The samples containing Bifidobacterium bifidum showed lower total solids and viscosity than the samples containing Lactobacillus casei, which indicates higher activity in the production of enzymes that decompose substrates in the culture medium. TPC and free radical scavenging potential in probiotic beverages increased during the storage period and its level was higher in the beverage containing Bifidobacterium bifidum (74% radical scavenging) than the samples containing Lactobacillus casei (70% radical scavenging). The addition of rice bran extract to the milk based medium improved the survival of both probiotic bacteria by more than 20% due to the prebiotic activity of the extract. The physical stability of the samples was checked using the precipitation formation technique (coagulation technique). No significant difference was observed between the control samples containing Bifidobacterium bifidum and Lactobacillus casei, but the amount of sediment formed in the samples containing rice bran extract was slightly higher than the control samples .The amount of precipitation increased slightly with increasing storage time, which could be due to the presence of suspended bran particles in the product, despite the two-stage filtration of the extract. Therefore, in order to solve the phenomenon of phase separation between the soluble component and the insoluble component, stabilize the product and stabilize the colloidal systems, an emulsifier or stabilizer such as carboxymethyl cellulose should be used. Conclusion: The results of this study showed that rice bran (agricultural waste) extract acts as a prebiotic in the presence of probiotic bacteria (symbiotic and synergistic effects are observed), and this synbiotic product has a high potential to be presented to the consumer market as a functional food due to its significant content of phenolic compounds, antioxidant activity and high survival and activity of probiotics. |