Lactobacilli as adjunct cultures in a soft cheese model

MARÍA MERCEDES MILESI; ERICA HYNES

Nantes

Congreso; 13th World Congress IUFOST - Food is Life; 2006

IUFOST

Non-starter lactobacilli grow from very low numbers up to 107 cfu g-1 in cheese, and eventually dominate cheese biota in long ripened varieties. As no strategy to avoid wild lactobacilli development is so far available, the use of adjunct starters composed of selected lactobacilli strains has been proposed. The purpose of adjunct cultures in cheesemaking is to improve the control of biochemical processes during ripening and, therefore, the consistency of cheese quality. The objective of the present study was to assess the impact on proteolytic patterns and aroma production of an adjunct culture of Lactobacillus plantarum in a model cheese. We studied a simple ecosystem composed of a thermophilic primary starter and an adjunct culture, in miniature soft cheeses obtained in controlled microbiological conditions.  Cheese milk was pasteurized at 65 ºC 30 min, as stronger heat treatments impaired coagulation properties and did not diminish wild lactobacilli plate counts. Control cheeses contained only primary starter (Streptococcus thermophilus), while in experimental cheeses we also added an adjunct culture of Lactobacillus plantarum (106 cfu ml-1 of cheese milk). Coliform bacteria decreased from 102 cfu g-1 to not detectable numbers after the first week of ripening at 10ºC, but yeast and molds reached 104 cfu g-1 in 60 day-old cheeses, so that a two month period was fixed as the maximum ripening time for this cheese model. Starter population remained about 109 cfu g-1 during all ripening, while adjunct culture population reached 108 cfu g-1 in 3-day old experimental cheeses, then remained constant.  Wild lactobacilli in control cheeses were always lower than 104 cfu g-1 during the 60 days of ripening. Primary proteolysis was similar for both control and experimental cheeses, but significant differences were found in some indexes of secondary proteolysis such as peptide profiles and free amino acids content. A triangular sniffing sensory test showed that the aroma of experimental and control cheeses was significantly different. We concluded that the mini soft cheeses constituted an appropriate model for evaluating the impact of lactobacilli cultures in biochemical reactions during cheese ripening. The adjunct culture of Lactobacillus plantarum studied in this work influenced both proteolysis and aroma development in our cheese model.