J. of Food and Dairy Sci., Mansoura Univ., Vol 10 (12):447- 452, 2019 Journal of Food and Dairy Sciences Journal homepage: www.jfds.mans.edu.eg Available online at: www. jfds.journals.ekb.eg * Corresponding author. E-mail address: sehamswelam9@gmail.com DOI: 10.21608/jfds.2019.71333 Properties of Non-Fat Yoghurt as Influenced by The Incubation Temperature of Exopolysaccharide Producing Culture Seham Swelam 1* ; M. A. Rashed 1 ; H. E. Hatem 2 and Eman F. khames 2 1 Dairy Dept., Fac. Agric. Kafr El- Sheikh ,Egypt. 2 Animal Prod. Res. Institute, Agric. Res. Center, Egypt Cross Mark ABSTRACT Different incubation temperatures (40°C, 42°C and 45°C) were used in making non-fat yoghurt. Exopolysaccharides producing culture consists of Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus and Lactobacillus fermentum with (1:1) or without commercial yoghurt starter culture (YC- x11) were used. Treatments were examined during the storage. Results showed that, the fermentation time decreased significantly by increasing the incubation temperature, further decrease of the incubation period was observed by using a combination of YC and EPS cultures. The higher pH value and lower acidity were observed by using EPS instead of YC cultures, while using higher incubation temperature improved development of the acidity. The highest acetaldehyde content and water holding capacity were achieved by using a mixture of the tested cultures at 42°C., followed by 45°C. The same trend was noticed for the viscosity parameter; as compared with the control (YC culture at 42°C), which had lowest value. Yoghurt made using EPS culture at 40°C resulted in a very high wheying-off, but it could be treated by the combination of EPS and YC cultures at the same temperature. More improvement, however, could be achieved by increasing the incubation temperature to 42°C. Panelists gave the highest sensory scores to the yoghurt made by a mixture of EPS and YC cultures at 42 and 45°C. The results revealed that the yoghurt made with EPS and YC starter cultures (1:1) at 42°C was the most accepted and were of the best rheological properties, compared with the other treated samples. Keywords: Exopolysaccharides, Fermentation temperature, Yoghurt. INTRODUCTION Exopolysaccharides (EPS) are high molecular- weight carbohydrates consist mainly from D-galactose, D- glucose and L-rhamnose. D-mannose can also be found in some EPS as well as in acetylated aminosugars, glucuronic acid, phosphate groups and acetyl groups. EPS are naturally produced by some lactic acid bacteria (LAB) during the fermentation process. Some bacteria produce only capsular EPS and some produce only slime (ropy) form whereas, in some cases, bacteria can produce both forms of EPSs (Yang, et al. 1999, Broadbent, et al. 2003).The EPS play an important role in the improvement of physical properties of fermented milks, which can be efficiently used as commercial stabilizers for preventing or reducing syneresis. In addition, it provides the fermented milk products with suitable structure and viscosity. Usually, it acts like a stabilizer, viscosifier, emulsifier or gelling agent providing a product with natural thickness (Ruas-Madiedo and Reyes- Gavilan 2005). EPS produced by LAB cultures offer a natural way for making low- fat or fat-free fermented milks with more acceptable flavour and sensory attributes as well as an increased water-binding capacity. Furthermore, EPS of LAB are thought to have beneficial effects on human health such as cholesterol- lowering ability, anticanceral, immunomodulation and antitumoral activities and prebiotic effect (Dal Bello et al . 2001, Korakli et al. 2002 and Pigeon et al. 2002).The quantity of EPS depending on type of the lactic acid bacteria (LAB) and growing conditions (pH, temperature and incubation time) (De Vuyst, et al., 2001and Broadbent et al ., 2003). The fermentation temperature and type of the used culture usually have a crucial role for the development of yoghurt quality and functional properties. Increased incubation temperature and EPS culture led to a higher water-holding capacity but lower syneresis, storage (G') and loss moduli (G''). Using EPS producing starter culture resulted in decreased syneresis, G' and G'' and increased water holding capacity (WHC) of yoghurt gels compared with the non-EPS culture. (Abbasi et al. 2009). The fermentation temperature significantly contributes to EPS concentration because the increased rate of fermentation temperature was attributed to increased metabolic activity of LAB (Feldmane et al. 2014). Chemical, rheological and sensory properties of non-fat yoghurt was studied as affected with incubation temperature. MATERIALS AND METHODS Cow's skim milk powder was taken from ValioLapinlahti Plant - Finland. It contains 1.25% fat, 52% lactose, 36% protein, 4% moisture and 8% ash. Yoghurt starter culture (YC-x11) consisting of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus was obtained from Chr. Hansen, Copenhagen, Denmark. Commercial exopolysaccharides producing cultures (EPS) Yo-Flex starter: Harmony 1.0 composed of Streptococcus thermophilus, Lactobacillus