EFFECT OF GEL FORMATION CONDITIONS ON THE TEXTURE OF DIRECT ACIDIFIEDMILK GELS

Lactic acid bacteria are commonly used in the production of sour milk products in order to give the product its typical aroma and to decreas e the pH. The cultures used determine the parameters of acidification and gelation, steps which take place simultaneously during fermentatio n. This work examines the influence of the gelation conditions on the firmness of milk gels, which were produced by means of direct acidific ation and subsequent gelation. Milk was adjusted to a pH of 4.7 by dir ectly and quickly adding citric acid. It was then warmed at temperatur es between 20 and 50 degrees C for various times. The structural prope rties of the gels were evaluated by considering the firmness, storage module and syneresis. The gel firmness rises with increasing gelation temperature and time. A final value for the firmness is only reached a t after several days. After this gelation time the firmness of the sam ples remains constant during storage at 4 degrees C, which means that there is no subsequent setting. This is not the case if the samples un dergo gelation at 30 degrees C for 2 h. The firmness of these gels inc reases within 4 weeks by a factor 2 approximately, whereby the pH rema ins constant. This increase in firmness during storage was determined for all protein concentrations examined. The warming rate exerts the g reatest influence on the structural properties in direct acidification . The results were established in a rotational viscosimeter as this ap paratus allows steady warming of the cold-acidified sample. High stora ge modulus are achieved by means of fast warming (10 K/min). Such modu les can not be achieved even with long gelation times of a sample whic h has been warmed slowly (0.5 K/min).