Integrated Roles of Lactate, Ammonia, and Calcium in Texture Development of Mold Surface-Ripened Cheese

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Abstract
Pure cultures of Penicillium caseicolum and Geotrichum candidum each rapidly metabolized lactic acid from an acidified milk-agar medium. P. caseicolum rapidly produced ammonia on milk agar (within 1 wk) but G. candidum elaborated ammonia only in older cultures (>3 wk). Brevibacterium linens showed little metabolic activity on milk agar systems because of inhibition by low pH or lack of proteases or essential nutrients. Analysis of samples (center, corner, surface locations) from wheels of a lot of ripening Brie cheese (227 g each) held at 17.degree. C over 57 d also showed metabolic depletion of lactic acid and the production of ammonia by the surface microflora. During ripening, calcium concentrations became elevated in surface locations and diminished in interior locations of Brie wheels. An integrated model is proposed that incorporates a pH mediation of systems for calcium migration and insolubilization, proteolytic enzyme activity, and casein solubilization whose combined activities control texture development in mold surface-ripened cheeses.