عنوان مقاله [English]
Introduction: Nowadays, many types of probiotic dairy products are available worldwide. Probiotic yogurt is still among the most popular probiotic products (Shori, 2016). To provide health benefits related to probiotic organisms, the minimum viable counts of each probiotic strain in gram or milliliter of probiotic products is a critical value. Generally, the amount of 106cfu/mL or cfu/g has been accepted as minimum level and the amounts of 107 and 108cfu/mL or cfu/g as satisfactory levels (Sidira et al., 2017). Prebiotics are non-viable and non-digestible (or very low digestible) food ingredients selectively metabolized by beneficial intestinal bacteria and enhance their growth and/or activity. They are mostly sugar-like compounds comprising between two and ten monomers that largely resist digestion by pancreatic and brush board enzymes. The term “symbiotic” is used to describe products that contain both probiotics and prebiotics (kumar et al., 2015). Prebiotic compounds are used for the survival and growth and higher activity of probiotic bacteria in the formulation of these products. Inulins are storage polymers of many plants consisting of b-2, 1-linked fructosyl units with a terminal glucosyl unit. The main source of commercial inulin for food application is the chicory roots. The functional attributes of inulin are dependent on its degree of polymerization (Delavari et al., 2014). Because they are indigestible and not absorbed in the human small intestine, they arrive intact in the large intestine where they promote the proliferation of beneficial probiotic bacteria (Crispín-Isidro et al., 2015; Shori et al., 2016). Moreover use of herbs and flavors in dairy products increases nutritional, medicinal value and consumption of these products (Elsayed and yousef, 2019). Shallot is an important part of the diet of many populations and there is long-held belief in their health enhancing properties. Shallot (Allium ascalonicum L.) is a major component of many Asian diets and is widely believed to be beneficial to health. This bulb is darker than garlic and has a stronger odor that correlates with its sulfide content. Analysis of shallot extracts has confirmed the presence of flavone and polyphenolic derivatives. This study is aimed to assay the physicochemical and antioxidative properties of probiotic yoghurts containing inulin as prebiotic and shallot.
Material and methods: For the preparation of yogurt, firstly the solid fat content of the raw milk with 3.3% fat content, heightened through addition of 3% skim milk powder. Secondly inulin was mixed at different concentration (0, 0.5 and 1.5%). Homogenization and heating process were applied and after that, cooling was performed until starter culture inoculation temperature (42°C). Inoculation was carried out with yogurt starter culture (Lactobacillus bulgaricus and Streptococcus thermophilus) and Lactobacillus acidophilus as probiotic bacteria. At the end of fermentation, the cured cooled and stirred gently, then shallot in two levels (0.6 and 0.3%) and salt (0.5%) were added to the mixture. Finally filling was conducted and yogurt samples stored at 4°C until analysis. The prepared probiotic yoghurt samples were evaluated for chemical properties (pH, acidity based on Dornic degree), texture properties (water holding capacity and viscosity), total phenolic content based on gallic acid equivalent, antioxidative property based on DPPH scavenging capacity and survival of probiotic bacteria during storage period (0, 7, 14 and 21 days of storage). The sensory evaluation of probiotic yogurt samples enriched with inulin and shallot was performed 7 days after production with 30 semi-trained panelists (15 males and 15 females, 35 years old). Sensory analysis consisting of appearance and texture (abnormal color, gel strength or weakness, whey-off, mouth-feel), aroma (unusual odor), taste (bitter, too high or low acid), and overall acceptability were based on 5-point hedonic scales (1: dislike extremely; 7: like extremely). Preparation of treatments were carried out in triplicate and the data obtained from the above mentioned evaluation parameters were analyzed based on Factorial design and Duncan's multiple range comparison test.
Results and discussion: The results showed that acidity increased and pH decreased during storage of treatments as a result of lactic acid production by lactose consuming bacteria (p < 0.05). Addition of shallot accelerated pH reduction rate. Due to the ability of inulin to form a gel network and absorbing water, it increases the water holding capacity and viscosity of yogurt samples at all storage times. Similar results have been reported by Silva et al., (2018). Shallot containing samples had higher acidity in comparison to others so it leads to decreasing effect on water holding capacity. The addition of shallot also increased the total phenol content of samples because shallot contained sulfur compounds that increase DPPH radical scavenging capacity (Lu et al., 2011) and the highest total phenol content and antioxidant activity related to 1.5 inulin + 0.6 shallot treatments. At the end of the storage period, all of the probiotic yogurts had an acceptable number of Lactobacillus acidophilus bacteria (more than 106cfu/ml). Shallot with sulfur compounds provided the conditions for the growth of probiotic bacteria; moreover inulin supported survival of probiotic bacteria too as a result of gelling properties and oxygen depletion in samples. Sensory properties analysis showed that inulin addition lead to significantly improvement of surveyed parameters except aroma. Inulin containing yogurt had a creamy and pleasant texture based on panelist comments. Inulin 1.5% + shallot 0.3% and inulin 0.5% + shallot 0.3% treatments had the highest and lowest overall acceptability, respectively. Overall, the addition of shallots and inulin could lead to the production of probiotic yogurt with an acceptable microbial population until 21 days of storage through with acceptable sensory and higher nutritional characteristics.