Physical characteristics of set yogurts as affected by co-culturing with non-EPS and EPS starter cultures and supplementation with WPC

In our earlier study, co-culturing with non-exopolysaccharide (EPS)- and EPS starter cultures and fortification with whey protein concentrate (WPC) were shown to increase EPS production by S. thermophilus during fermentation. The current study investigated physical characteristics of non-fat set yogurts as affected by the use of non-EPS- and EPS starter cultures, as well as by co-culturing with non-EPS- and EPS starter cultures and supplementation with 0.5% WPC. The set yogurts were evaluated for viable counts of starter cultures, EPS concentration, syneresis, firmness, yield stress and apparent viscosity. The use of EPS starter cultures or co-culturing with non-EPS- and EPS starter cultures decreased the firmness, apparent viscosity and syneresis, but increased the yield stress of the yogurts. The products supplemented with 0.5% WPC showed firmer texture than those made from reconstituted skim milk (RSM). The EPS concentration increased in products that contained WPC. A further increase in EPS concentration was observed upon co-culturing with non-EPS- and EPS starter cultures in RSM containing 0.5% WPC. The viable counts of L. delbrueckii ssp. bulgaricus were lower in products containing WPC than those made using RSM only.