ORIGINAL RESEARCH The effect of adding sour cherry pulp into yoghurt on the physicochemical properties, phenolic content and antioxidant activity during storage MEMNUNE S ¸ ENGU ¨ L, 1 TUBA ERKAYA, 1 MUSTAFA S ¸ ENGU ¨ L 1 * and HILAL YILDIZ 2 1 Department of Food Engineering, College of Agriculture, Ataturk University, Erzurum 25240, and 2 Department of Food Engineering, College of Engineering, Gumushane University, Gumushane 29100, Turkey *Author for correspondence. E-mail: msengul@atauni.edu.tr Ó 2012 Society of Dairy Technology This study investigated the effect of adding sour cherry pulp into yoghurt on its physicochemical proper- ties, phenolic content, antioxidant activity and sensory characteristics. Sour cherry pulp was added at 0%, 8%, 12% and 16% into the yoghurt, and measures were checked through 14 days cold storage. The increasing sour cherry pulp concentration in yoghurt resulted in increasing pH and whey separation, whereas the values of the other parameters, total solid, fat, protein, ash, titratable acidity and viscosity decreased. During storage, total phenolic contents and antioxidant activity in yoghurts ranged from 20 to 81 lg gallic acid equivalent per mg of sample and from 48% to 86%, respectively. Keywords Sour cherry yoghurt, Phenolic content, Antioxidant activity, DPPH. INTRODUCTION Recently, functional foods have been gaining more attention by consumers and manufacturers because of their additional health benefits beyond normal nutritional value. Functional foods are diverse groups, including conventional foods, such as yoghurt, or they can be specifically enhanced, such as fortified yoghurt with probiotics and fruit (Gonz- alez et al. 2011). Yoghurt is known for its thera- peutic, nutritional and sensory properties for a long time, and it is obtained by the lactic acid fermenta- tion of milk by addition of homofermentative yoghurt starter culture. It is the most well-known and consumed fermented dairy product around the world (Tamime and Robinson 1999). Yoghurt and yoghurt-like products have been marketing and modifying successfully to meet consumers’ demands (Gonzalez et al. 2011). It is one of the most widely consumed dairy products because of its availability in different forms. In European countries, yoghurt consumption per person in a year is about 20 kg and this amount is reported as 36 kg per person per year in Turkey (Hutkins 2006). The increasing yoghurt consumption trends in many countries have been attributed to increase the variety of fruit-flavoured yoghurt in markets. It comes in a number of fruity flavours such as straw- berry, banana, blueberry and peach, as well as des- sert flavours such as key lime pie, chocolate, vanilla and peanut butter. To create these flavours, a number of ingredients are incorporated in the yoghurt recipe. This includes whole foods, juices, jams, herbs, spices and sweeteners. The addition of different fruits into milk may enhance the taste and the therapeutical values of milk products as well. Fruit-flavoured yoghurts are manufactured by adding fruit concentrates or flavoured syrups to the cultured milk after or before the incubation pro- cess. Sour cherries (Prunus cerasus L.) are good sources of natural antioxidants (Gao and Mazza 1995; Wang et al. 1997, 1999; Friedrich and Lee 1998). Sour cherries are also rich in anthocyanins and polyphenolics compounds as well as their usual nutrients, such as vitamins and minerals (Robards et al. 1999; Kaur and Kapoor 2001). Therefore, the consumption of foods containing these compounds as a part of diet may also be healthful for people. In recent years, there has been increasing interest in the use of natural food addi- tives into the diet. Epidemiological studies also show that fruit and vegetable consumption are asso- ciated with the reduced risk of several lifestyle- related diseases such as cancer, cardiovascular Vol 65, No 3 August 2012 International Journal of Dairy Technology 429 doi: 10.1111/j.1471-0307.2012.00838.x