Formulation of probiotic dairy fermented drink based containing rice bran extract

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. The aim of ‎this study was to produce a probiotic fermented dairy beverage containing Bifidobacterium ‎bifidum, Lactobacillus casei, and rice bran extract. 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. 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.‎‏ ‏‎ ‎ 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.‎