No abstract

No abstract

No abstract

Summary -A study was carried out on 10 retail samples 01 yoghurt, belonging to 3 different brands (A, Band C), showing a rarely described alteration consisting 01 inward collapse 01 the packs. Microbiological analyses revealed the presence 01 high counts 01 different microbial contaminants: in A sampies Acetobacter aceti was lound at 10 7 clu/g, while in Band C sampies the main contaminants were Mucor hiemalis Mucor racemosus and Penicillium verrucosum var cyc/opium varying between 102 and 105 clu/g. The responsibility 01 isolated strains lor alteration was conlirmed by inoculating cellular suspensions in non-contaminated yoghurt packs kept at 5°C and 25°C: samples inoculated with A aceti showed an inward collapse alter 20 d at 25°C; packs inoculated with M hiemalis, M racemosus and P verrucosum var cyc/opium kept at 25°C showed swelling alter 5-7 d lollowed by inward collapse alter = 20-35 d. In sampies kept at 5°C the delect did not appear even extending the incubation time to 60 d. The explanation lor the evolution 01 this delect is the 101-lowing one; contaminating microorganisms consume oxygen contained in head-space 01 pack and produce CO 2 whose re-absorption into the product causes a partial vacuum involving collapse 01 the pack.

The genus Streptococcus has been rearranged recently into 4 main groups: Pyogenic, Oral, Faecal and Lactic; Streptococcus thermophilus, once ascribed to the Viridans group, is now included in the Lactic group or as unclassified (Sharpe, 1979; Jones, 1978). With the aim of evaluating the best taxonomic criteria to be used for Str. thermophilus and other streptococci isolated from dairy environment a series of strains, some from culture collections and some freshly isolated from different sources (cheese, yoghurt, natural starters, faeces of infants), have been examined, by routine physiological tests and by means of DNA-DNA hybridization techniques. In recent studies on lactic acid bacteria (Dellaglio, Bottazzi & Trovatelli, 1973; Dellaglio, Bottazzi & Vescovo, 1975) genetic homology has proved to be a useful method of classification.