Addition of fruit purees to enhance quality characteristics of sheep yogurt with selected strains

The aim of this research was to assess the effects of fruit purees of banana, kiwi, mango, red berry, and strawberry on the microbiological, physicochemical, antioxidant, and sensory properties of sheep yogurt. The fruit purees were characterized for their microbiological profile before yogurt production, and no spoilage or pathogenic microorganisms were detected in any of the purees analyzed. Yogurt productions were carried out under industrial conditions using pasteurized sheep's milk and selected starter cultures of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Five experimental yogurt productions (EYP) were made by adding 10% (w/w) of each fruit puree, while the control yogurt production (CYP) was puree-free. Plate counts revealed that levels of viable Lb. delbrueckii subsp. bulgaricus and S. thermophilus exceeded 8.0 log cfu/g in all CYP and EYP samples after 3 d of refrigerated storage. The addition of fruit purees reduced fat percentage until to 7% and increased of antioxidant activity, especially with red berry puree. Except for banana, the addition of fruit purees resulted in a statistically significant increase (p < 0.0001) in the total terpene VOC profiles of EYP. Notably, the terpene content in mango-flavored yogurt was eightfold greater than that observed in the control trial. Sensory evaluation revealed a reduction in unpleasant odor and off-flavor, and an increase of about 50% in overall acceptance for all EYP in comparison to CYP. Therefore, adding fruit purees to sheep yogurt is a promising strategy for the valorization of Sicilian sheep's milk.