A study on microbiological and physicochemical properties of homemade and small scale dairy plant buffalo milk yoghurts

In the present study, the physicochemical and microbiological qualities of commercially available yoghurt were investigated. For this purpose, sixty samples of homemade and forty samples of small scale dairy plants buffalo yoghurt were collected, and analyzed in triplicate. The composition of yoghurt samples ranged between for dry matter: 16.93-18.43%, 17.57-18.78%, for fat: 6.76-7.20%, 6.42-760%, for protein: 4.71-5.29%, 5.21-5.45%, for lactose: 3.08-3.25%, 3.11-3.21%, for ash: 0.91-0.93%, 0,91-0.94%, for titratable acidity (TA): 0.91-0.93, 1.07-1.12%, for pH: 4.15-4.17, 3.78-4.15, for the small scale dairy plants and homemade samples, respectively. The microbiological content of homemade and small-scale dairy plants yoghurt samples were investigated for the presence of total aerobic mesophilic bacteria (TAMB) Lactococcus spp. , Lactobacillus spp. , yeast and mould, coliform bacteria, Staphylococcus aureus (S. aureus), Salmonella spp. and E. coli. In general, yeast and mould and coliforms were higher in the homemade buffalo yoghurts. S. aureus, Salmonella spp. and E.coli were not found in any of the buffalo yoghurt samples. The results found do not meet the microbiological criteria of the Turkish Food Codex Communique for fermented milk products in terms of coliform and yeast and mould. Lactococci counts were carried out on M17 medium (Oxoid CM785) at incubation of 30 o C under anaerobic conditions for 48 hours. Lactobacilli counts were performed on deMan Rogosa and Sharpe medium (MRS, Oxoid CM361) at the incubation temperature of 30 o C under anaerobic conditions (5% C0 2 ) for 72 hours. TMAB count was obtained by pour plating 1ml of each dilution into Plate Count Agar (PCA). The colonies were counted after 48 hours of incubation at 35°C[9]. The yeasts and moulds were determined using Potato Dextrose Agar medium (PDA) with 10% tartaric acid. The plates were incubated at 25-28 o C for 48 hours. The CFU’s of yeasts and moulds were counted[10]. For coliform test, one ml of sample was plated onto Mac Conkey Agar media. The plates were incubated at 37 o C for 48 hours. Plates showing positive coliforms were subjected to the confirmed test using Brilliant Green Bile Lactose Broth in test tubes with Durham tubes. The test tubes were then incubated at 44 o C. The total and fecal coliforms were counted, respectively Desoxycholate Lactose Agar (DLA) and Violet Red Bile Lactose Agar (VRBLA) after 24 to 48 hours at 37 and 44 o C for 48 hours. Each subcultured tube was confirmed positive. For the determination of E. coli , a loopful from each positive Lauryl Sulphate Tryptose (LST) tube was streaked on Eosin Methylene Blue Agar (EMB, Oxoid CM69) and incubated at 37 o C for 24-48 hours. Suspicious colonies (dark centered with or without a green metallic sheen) of E. coli on EMB Agar were subjected to confirmation tests (IMVIC). Indole (+), Methyl Red (+), Voges Proskauer (–) and Citrate (–) cultures after 24 to 48 hours incubation at 37 o C were assessed as E. coli type 1[11]. S. aureus was grown on Baird Parker Agar (BPA) (Oxoid, CM0275) supplemented with egg yolk-tellurite emulsion (Merck, 1.03785) at 35 o C for 48 hours. The coagulase activity was performed by using Staphaurex Test[12]. Mannitol Salt Agar (MSA) was used for the isolation of Salmonella spp. count according to BAM[13]. 25 ml of each sample were pre-enriched in 225 ml of Buffered Peptone Water (BPW) for 24 hours at 37°C. 1 of each pre-enrichment culture was used to inoculate 10 ml Muller–Kauffman (MKT) and Selenite–Cystine (SC) broths, which were incubated at 43 and 35–37 o C respectively, for 24 and 48 hours. After each a 3 (10 µ l) loopful removed and streaked result of traditional culture (starter) or contamination of post-production or logistic mishandling. These results might be due to the method of buffalo yoghurt manufacturing, inadequate post-fermentation hygiene, handling, especially prior to sale and packaging which are entirely based on the antiquated (traditional) system.