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Abstract
Nowadays, Polysaccharides are used to improve the nutritional and physicochemical properties of dairy products. The identification of natural compounds such as polysaccharides with antidiabetic and antioxidant properties has become important due to the relationship between diabetes and oxidative stress. Therefore, the present study aimed to evaluate the influence of pectin on the antidiabetic and antioxidant activity of milk fermented by lactic acid bacteria (LAB) isolated from traditional Iranian dairy products. Pectin (1%) was added to the samples following milk fermentation by Lactobacillus helveticus and Lactobacillus para-casei strains, and antidiabetic activity was assessed by considering the inhibitory effects on α-amylase and α-glucosidase. The antioxidant activity was determined by evaluating inhibition of 2,2-Diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and hydroxyl radicals. Samples included pectin solution (0.5-3.5 mg/ml and 0.5-10 mg/ml for evaluation of anti-diabetic and antioxidant activity, respectively), whey of fermented and non-fermented milk with (1%) and without pectin. The results indicated the role of  pectin on  inhibition of  α-glucosidase enzyme activity (IC₅₀=2.38 mg/ml), as well as scavenging the DPPH (44.57%), ABTS (28.7%), and Hydroxyl (38.85%) radicals (P<0.05) a concentration of 10 mg/ml. Pectin added to the whey of non-fermented milk sample boosted antioxidant properties and the maximum rate of free radical scavenging activity (35%) was obtained for DPPH radicals. Furthermore, adding pectin to the whey of milk fermented with Lactobacillus helveticus strain improved the activity of the product on inhibition of α-glucosidase enzyme (29%), scavenging of DPPH (41.26 %), ABTS (2.5%), and hydroxyl radicals (7.64%) (P<0.05). The results indicated the potential of pectin to be used in the formulation of beneficial food products due to its ability to improve the antioxidant and anti-diabetic properties of fermented milk products.

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Today, the use of Lactobacill strains and their metabolites is the new strategies in control of diabetes and oxidative stress. Therefore, the present study aimed to investigate the antidiabetic and antioxidant properties of metabolites obtained from of Lactobacillus delbrueckii ssp. bulgaricus culture media. The samples were evaluated including cell free supernatant (CFS), cell free extracts (CFE), cell free supernatant of fermented milk (CFS-FM) and bioactive peptides separated from ultrafiltration (3,5,10 kDa). The ability of bacteria in proteolysis of protein of  fermented milk (FM) was evaluated by O-phthaldialdehyde method compared with non-fermented milk (NFM). The antidiabetic activity was measured based on inhibition of α-amylase and α-glucosidase. The antioxidant activity was evaluated by inhibition of 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS). The results showed that the sample of CFS-FM inhibited α-amylase (25%) and α-glucosidase (26.6%) enzymes. Among the peptide fractions, fraction  of >10 kDa with higher protein content (13.816 mg (had the highest inhibition of α-amylase (80.64%) and α-glucosidase enzyme (54%) (p<0.05). The inhibitory efficiency ratio (IER) showed that the 3-5 kDa fraction had more inhibitory than other peptide fractions (p<0.05). Also, the CFS and CFE inhibited α-glucosidase enzyme by 50% and 25%, respectively. In case of antioxidant properties, it was observed that the free radicals scavenging of CFS-FM increased compared with NFM (p<0.05). Also, the peptide fractions of 3-5 kDa (80.85%) and >10 kDa (43.63%) had the highest DPPH and ABTS free radicals scavenging. The antioxidant capacity of trolox equivalent from peptide fractions (µmTE/mg protein) showed that the <3 kDa fraction had the highest antioxidant activity (p<0.05). The ability to free radicals scavenging in CFS and CFE was observed. Results indicate the importance of  Lactobacillus delbrueckii as a starter culture and its functional role.