This study examined the applicability of pomegranate peel extracts (PPE) and microencapsulated pomegranate peel extracts (MPE) in yogurts made with cow’s milk and soy drink mixtures. For preparing PPE, pomegranate peel powders were extracted by 50% ethanol in an ultrasonic water bath. PPE was encapsulated by using a spray dryer. Phytochemical composition and antioxidant activity of PPE and MPE were determined and 0.5% and 1% PPE and MPE were used in yogurt production. Physicochemical, rheological, microbial and sensory properties of the yogurt samples stored at 4 °C were determined during storage. Extract addition affected storage modulus (G') values and lost tangent (tanδ) values. The extract additive prevented the growth of yeasts and moulds and extended the shelf life of the samples. The favorable effect of the extract on taste and aroma was determined in sensory tests. However, the extract contributed to the loss of textural properties such as syneresis and visible viscosity.

This study surveyed the effect of the addition of microbial transglutaminase (m-TGs) on textural, microstructural, FTIR spectra and SDS-PAGE electrophotogram parameters of probiotic yoghurts made with mixture of cows' milk and soy drink during refrigerated storage for 28 days. Mixture was treated with different rates of m-TGs (0, 0.5, 1, 1.5 U/g protein) and incubated with Lactobacillus acidophilus La-5, Bifidobacterium lactis Bb-12, Streptococcus thermophilus probiotic starter cultures. Yoghurts prepared with m-TGs had higher textural parameters than samples without m-TGs. SDS-PAGE patterns, SEM imagines and FTIR spectra demonstrated that milk caseins were well cross-linked by transglutaminase. Scanning electron microscopic studies showed that the microstructure of m-TGs added probiotic yoghurt samples appeared denser than that of control. Results of this study indicated that the textural and microstructural properties of probiotic yoghurt prepared with soy drink could be improved by incorporating m-TGs up to a level of 1.5 U/g protein.