Acta Alimentaria, Vol. 32 (2), pp. 151160 (2003) 0139-3006/2003/$ 20.00  2003 AkadØmiai Kiad, Budapest INFLUENCE OF CULTURE ACTIVITY ON AROMA COMPONENTS IN YOGHURTS PRODUCED FROM GOATS AND COWS MILK R. BO#ANI$, LJ. TRATNIK and M. HRUKAR Faculty of Food Technology and Biotechnology, University of Zagreb, PO Box 625, 10001 Zagreb. Croatia (Received: 3 July 2001; revision received: 12 December 2002; accepted: 15 January 2003) In this paper the experiments on microbiological quality and aroma components of yoghurt samples produced from long life goats and cows milk, and also from milks with 2% milk powder addition, during 9 days of refrigerated storage are described. Milk fermentation was conducted at 42 C for 6 h. During days 1, 3, and 9 of storage the changes in acidity (pH value and lactic acid percent), viable counts of streptococci and lactobacilli and aroma components (acetaldehyde and diacetyl) were determined. Lower pH values and smaller lactic acid concentrations were found in control yoghurt samples. Viable counts of streptococci decreased during storage (from 1.0110 8 to 3.9710 7 CFU ml 1 ), whereas the viable counts of lactobacilli increased in all samples (from 6.9510 6 to 2.3210 7 CFU ml 1 ). The increase in count of lactobacilli was the greatest in goats milk yoghurt samples. On the ninth day of storage, logN between cows and goats milk yoghurt samples was 0.2. Acetaldehyde in yoghurts decreased during storage time from 5.47 mg kg 1 (on day 1) to 1.05 mg kg 1 (on day 9). Both control yoghurt samples had lower acetaldehyde concentration than the supplemented samples. During nine days of storage, a significant increase in diacetyl content of yoghurt samples (from 14.20 mg kg 1 on the first day to 18.65 mg kg 1 on day 9) was noticed. Goats milk yoghurts, especially that manufactured without milk powder addition, had very soft consistency, but no syneresis was observed. Keywords: goats milk yoghurt, microbiology, acetaldehyde, diacetyl, storage In recent years, consumption of yoghurt has increased considerably. Nutritive and health importance of yoghurt consumption includes yoghurts antibiotics influence and relief of gastrointestinal disorders (BUTTRISS, 1997; CHEN et al., 1999; MEYDANI & HA, 2000). Many authors investigated the influence of different kinds of milks (DAVE & SHAH, 1998) and starter cultures (GEORGALA et al., 1995; DAVE & SHAH, 1997) on yoghurt quality. It is well known that goats milk has better digestibility in comparison with cows milk, because of the smaller size of fat globules (ATTAIE & RICHTER, 2000), it has more easily hydrolysable triacylglycerols containing short-chain fatty acids, more essential amino acids (ALICHANIDIS & POLYCHRONIADOU, 1997; HELLIN et al., 1998), higher proportion of soluble minerals (PARK, 2000) and smaller size of casein micelles (JANDAL, 1996; URBIEN, et al., 1997). Although goats milk is used for therapeutic purposes, largely due to its antiallergenic effect (PARK, 1994; SABBAH et al., 1997), it has not been thoroughly investigated yet. As the significance of goat breeding increases in Croatia (SINKOVI$, 2000) this subject is of interest to a segment of the dairy industry.