The importance of probiotic-containing products to maintenance of health and well-being is becoming a key factor affecting consumer choice, resulting in rapid growth and expansion of the market for such products, in addition to increased commercial interest in exploiting their proposed health attributes. The majority of probiotic foods already on the market, such as fermented milks and yoghurt are fresh products and are generally consumed within days or weeks of manufacture. In contrast, hard cheeses, such as Cheddar have long ripening times of up to two years.
Probiotic bacteria are described as ‘living’ micro-organisms, which upon ingestion in certain numbers exert health benefits beyond inherent basic nutrition. Probiotics may be consumed either as a food component or as a non-food preparation. Foods containing such bacteria fall within the ‘functional foods’ category and these are described as ‘foods claimed to have a positive effect on health’. Such products are gaining more widespread popularity and acceptance throughout the developed world and are already well accepted in Japan and the USA. Furthermore, increased commercial interest in exploiting the proposed health attributes of probiotics has contributed in a significant way to the rapid growth and expansion of this sector of the market.
The potential health-promoting effects of dairy products which incorporate probiotic organisms such as Lactobacillus and Bifidobacterium spp. has stimulated a major research effort in recent years. To date, the most popular food delivery systems for these cultures have been freshly fermented dairy foods, such as yoghurts and fermented milks, as well as unfermented milks with cultures added.
There are relatively few reports concerning cheese as a carrier of probiotic organisms, even though there are a small number of ‘probiotic cheeses’ currently on the market.
In 1994, Dinakar and Mistry (J. Dairy Sci. 77:2854-2864) incorporated Bifidobacterium bifidum into Cheddar cheese as a starter adjunct. This strain survived well in the cheese and retained a viability of approximately 2×107 cfu/g even after 6 months of ripening, without adversely affecting cheese flavour, texture or appearance. This example suggested that Cheddar could provide a suitable environment for the maintenance of probiotic organisms at high levels over long time periods. However, no growth of the B. bifidum was observed in the cheese during the ripening period and thus it is important to emphasise that the Bifidobacterium strain did not grow during manufacture and/or ripening and thus had to be added at a relatively high inoculum. In another study, bifidobacteria were used in combination with Lb. acidophilus strain Ki as a starter in Gouda cheese manufacture (Gomes, A. M. P. et al. (1995); Neth. Milk Dairy J. 49:71-95). The two strains were used as sole starters, requiring relatively large inocula (3%) of both strains and adaptation of cheese making technology. In this case, there was a significant effect on cheese flavour in the resultant product after 9 weeks of ripening, possibly due to acetic acid production by the bifidobacteria.
In order to exert a probiotic effect, cultures must maintain their viability in food products through to the time of consumption, which for Cheddar cheese is many months after manufacture.
Cheese is a milk product in which the whey protein/casein ratio does not exceed that of milk and which is obtained by coagulation of milk by the action of rennet, followed by whey drainage. Starter cultures containing lactic acid bacteria are initially required during cheese making to metabolise lactose, thereby producing lactic acid and reducing the pH. During Cheddar cheese manufacture for example, the starter lactococci grow, reaching maximum levels of approximately 109 to 1010 cfu/g at salting. Conditions in the cheese however, such as high salt in moisture (S/M), low pH, lack of a fermentable carbohydrate and low temperature of ripening can result in a dramatic decline in starter numbers during the early weeks of ripening. The rate of decline depends on a number of characteristics of the strain, including autolytic properties, salt tolerance and phage resistance. In the meantime, a population of non-pathogenic organisms, referred to as non-starter-lactic acid bacteria (NSLAB), chiefly composed of lactobacilli (Lb. plantarum, casei and brevis) and pediococci (Pediococcus pentosaceus) proliferate as the cheese ripens, a process that is generally performed at 2-16° C. It is believed that NSLAB gain access tothe cheesemilk during the manufacturing stage or that they survive pasteurisation in an attenuated state. Regardless, their numbers increase rapidly reaching maximum levels of 107 to 108 cfu/g in ripened Cheddar cheese. Indeed, in mature cheese, NSLAB may represent the principal flora. Their role in determining cheese quality remains unclear. NSLAB are generally enumerated using an aerobic plate count on Rogosa or Lactobacillus Selective (LBS) agar.
It may not be cost-effective to add probiotic strains to cheese in amounts corresponding to that finally required for a probiotic product at time of consumption. Rather what is required is a probiotic strain which can be added as a starter adjunct at a low inoculum to cheese and which grows to the required values of ˜>107 cfu/g.
What is required, therefore, for a probiotic cheese with a long ripening time such as Cheddar is a probiotic strain which can survive and grow throughout manufacture and the ripening period.