Experimental mini-cheeses were made from raw (Ra), microfiltered (MF), pasteurized (Pa) (72 degrees C?, 30 s) or pasteurized mixed with microfiltration retentate (PR) milk to study the influence of the indigenous microflora and pasteurization on the quality of Swiss-type cheese. To estimate biochemical transformations during cheese ripening, several methods were used: nitrogen fractionation (water-soluble fraction and phosphotungstic acid (PTA)-soluble faction), urea-polyacrylamide gel electrophoresis of caseins, reverse phase liquid chromatography of the water-soluble fraction, lactate and volatile fatty acids. Microbial populations were also enumerated. At the end of ripening, in comparison with MF and Pa milk cheeses, Pa and PR milk cheeses exhibited higher overall aroma intensity and pungency, characteristics which correlated with higher populations of facultatively heterofermentative lactobacilli (10(8) cfu g(-1)), propionibacteria (10(8) cfu g(-1)), and enterococci (10(6) cfu g(-1)) These cheeses had high levels of PTA-soluble N and acetic, propionic and isovaleric acids. MF and Pa milk cheeses, although somewhat different from one another, were very different from the two other types of cheese. Pa milk cheese had a lower pH than MF milk cheese, and contained a higher proportion of gamma-caseins due to the activation of plasmin. Moreover, Pa milk cheese was more acidic. but demonstrated a higher overall aroma intensity. The addition of raw milk flora (retentate) to Pa milk restored almost all the biochemical and sensory characteristics of Ra milk cheese measured in this study.