ORIGINAL RESEARCH Influence of inulin and demineralised whey powder addition on the organic acid profiles of probiotic yoghurts ARZU KAVAZ 1 * and IHSAN BAKIRCI 2 1 Department of Food Engineering, Engineering Faculty, Adıyaman University, 02040 Adıyaman Turkey, and 2 Department of Food Engineering, Faculty of Agricultural, Atat€ urk University, 25240 Erzurum, Turkey In this study, the effect of the different concentrations of inulin and demineralised whey (d-whey) powder on the chemical characteristics and organic acid profiles of probiotic yoghurts were investi- gated. Analysis of chemical composition was performed on the first day, while pH and organic acid profiles were carried out during storage. The results indicated that different proportions of inulin and d-whey powder significantly influenced the levels of the organic acids, produced while the duration of storage affected the orotic, pyruvic, citric, lactic and acetic acid levels. There was a direct relationship between the level of d-whey powder and organic acid (except for butyric acid) concentration in the probiotic yoghurt. Keywords Probiotic, Inulin, Demineralised whey powder, Organic acid. INTRODUCTION Yoghurt plays an important role in the human diet. It is obtained from lactic acid fermentation of milk by homofermentative yoghurt starter cul- tures comprising Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (Tamime and Robinson 1985, 1999). Recently, the use of probiotic micro-organisms such as Lactobacillus acidophilus and Bifidobacterium sp. has increased in yoghurt and other fermented dairy products, due mainly to their perceived additional health benefits beyond normal nutri- tional value and because they produce a less acidic aroma. The characteristic flavour of fer- mented dairy products is mainly the result of the metabolism of the starter cultures (Kneifel 1992; Lourens-Hattingh and Viljoen 2001a; Sodini et al. 2002; Gonzalez et al. 2011). In order to obtain a specific desired aroma profile in fer- mented milk products, the application of the appropriate strains and prebiotics is highly important. The composition of the product and the availability of prebiotics are also reported to affect the growth and viability of probiotic starter cultures (Dave and Shah 1998). In recent years, inulin and whey powder have probably been the most commonly used additives in fermented milks (Holzapfel and Schillinger 2002; O’Brein et al. 2003; Zimeri and Kokini 2003). Inulin is a good source of dietary fibre, and it consists of a mixture of oligomers and long polymer chains with a variable number of fructose molecules. When inulin is used as a prebiotic agent, it stim- ulates the growth and viability of the useful micro-organisms, increases calcium and magne- sium absorption, stimulates the immune function and reduces the level of cholesterol (Izco and Franck 1998; Holzapfel and Schillinger 2002; O’Brein et al. 2003; Zimeri and Kokini 2003; Dello Stafollo et al. 2004; Ohr 2004). On the other hand, whey powder contains biologically active proteins or peptides, minerals and vita- mins (especially vitamin B2). It has many bene- fits when added to yoghurt. These benefits include: textural improvement, nutritional enrich- ment, reduced syneresis, extended shelf life, mild flavour development and potential prebiotic and nutraceutical effects (Kailasapathy and Supriadi 1998; Antunes et al. 2004). Organic acids play an important role as pre- servatives and contribute to the sensory charac- teristics of the yoghurt. The majority of organic acids are formed as a result of carbohydrate metabolism by lactic acid bacteria (lactic acid, acetic acid, pyruvic acid, propionic acid and *Author for correspondence. E-mails: arzu-kavaz23@hotmail. com, akavaz@adiyaman. edu.tr © 2014 Society of Dairy Technology Vol 67, No 4 November 2014 International Journal of Dairy Technology 577 doi: 10.1111/1471-0307.12152