Effect of exopolysaccharides and inulin on the proteolytic, angiotensin-I-converting enzyme- and α-glucosidase-inhibitory activities as well as on textural and rheological properties of low-fat yogurt during refrigerated storage

Whey separation during storage continues to be one of the major problems in low-fat yogurts. Exopolysaccharides (EPS) produced by lactic acid bacteria have been recognized as a solution to this problem. Inulin is accepted as a fat replacer in products such as low-fat yogurts, in addition to providing physiological benefits. A combination of EPS and inulin could give both health-and texture-promoting properties to low-fat yogurt. Therefore, the aim of this study was to comprehensively study the influence of using an EPS-producing strain of Streptococcus thermophilus along with inulin (3%, wt/vol) on the viability of S. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus, their proteolytic, ACE-and alpha-glucosidase-inhibitory activities, as well on the textural and rheological properties of low-fat yogurt during storage at 4 C for 28 days. The time to reach a pH of 4.5 was less in the presence of EPS-producing S. thermophilus. However, during storage, EPS and inulin together did not influence the pH and lactic acid, and the effect on ACE-inhibition activity varied with the period of storage. The presence of EPS showed a protective effect on the survival of Lb. delbrueckii ssp. bulgaricus and partially on the extent of proteolysis. The alpha-glucosidase-inhibitory activity was more apparent in EPS-containing yogurt. The yield of EPS varied with the period of storage, being maximal (110.77 mg . 100 g(-1)) at d 14. EPS-containing yogurts showed lower firmness, spontaneous whey separation, storage modulus, yield stress, consistency index and hysteresis area than non-EPS producing yogurts. It was concluded that low-fat yogurt with a stable and compact texture having anti-hypertensive and anti-diabetic potential could be obtained using an EPS-producing strain of S. thermophilus.