Ancillary cultures are specific cultures, different from lactic starter cultures, that, when added to the milk or to the intermediate or finish product, are functional to the manufacturing process or to the final products characteristics and/or preservation. Ancillary cultures include both the so-called adjunct cultures and secondary cultures.
Adjunct cultures are mainly composed of other lactic acid bacteria that are typically used in cheeses to provide for additional flavor development, such as thermophilic or mesophilic lactobacilli (e.g., L.casei and L.paracasei used in Cheddar cheese), often defined as NSLAB (non-starter lactic acid bacteria). Lack of flavor in cheese today is often the consequence of high-quality raw milk, pasteurization of cheesemilk, and improved hygiene in cheese plants. Beresford and Williams (2004) reported a summary of NSLAB found in more than 50 cheese varieties.
GHP aim to protect the manufacturing site, equipments, machineries, and products prepared therein from undesired environmental contaminations, particularly from pathogenic bacteria. However, they get rid also of some other microorganisms that in the past selectively colonized the cheesemaking environment (milk, equipments, walls, floors, air, and personnel) and actively contributed to get good organoleptic characteristics and correct balance of all compounds in the final fermented dairy product. Some of these microorganisms, such as Propionibacterium, Brevibacterium, Penicillium and some yeasts, have been recognized to play a fundamental role in the manufacture of several types of cheese (e.g., blue cheeses, Gorgonzola, cheddar cheese, Limburger, Tilsiter cheese, Emmenthaler) and are used as essential secondary cultures.
Ancillary cultures can be added to the milk with the lactic starter or separatedly to the curd or during cheese ripening. Some of them are able to proliferate on the cheese rind, while others grow inside the cheese mass as well, and so they actively contribute to the ripening process (glycolysis, proteolysis, peptidolysis, lipolysis), determining the aroma and flavor of the end product (Aljewicz et al., 2015). The main flavor compounds in cheese are represented by organic acids, aminoacids, free fatty acids, alcohols, aldehydes and ketones, esters, sulphur-containing compounds, lactones, furans, and terpens (Tunik, 2014).
Only microbial species recognized as QPS (qualified presumption status) or GRAS (generally recognized as safe) can be used for food making. Sixty Lactobacillus species are known as microorganisms that may play an important role to confer main organoleptic final positive characteristics.
Brevibacterium linens was isolated for the first time from Romadur cheese, in Germany. Nonmotile, it has an aerobic oxidative metabolism of sugar and is able to hydrolyze casein, gelatin, and milk. B. linens grows well at temperatures between 20°C and 30°C. Thanks to its high salt resistance (15% NaCl), B. linens can easily grow on the surface of cheeses. B. linens plays a big role, when present, in cheese ripening.
The yeasts present in the curd and on the rind utilize lactate as a source of energy, reducing the acidity, increasing the pH and allowing the growth of B. linens. On the rind of surface-ripened cheeses, it is common to find it together with Debaryomyces hanse- nii, Corynebacterium spp. and Micrococcus spp. (Hayaloglu et al., 2015). Brevibacterium linens is used in ripened cheese such as Brick, Limburger, Muenster, and Taleggio, where it develops rapidly, ensuring a good ripening and producing typical flavors. The characteristic smears yellow to orange may take 15 to 20 or even more days to develop. It was reported that B. linens is able to produce several types of proteolytic enzymes thanks to its intracellular and extracellular proteolytic activity. The proteinase system can be considered to have naturally desirable proteolytic characteristics since this microorganism is involved in the ripening of several cheeses. In particular, serine proteinase and aminopeptidase can be considered to be a good mean for accelerating cheese ripening.