Survey of lactic acid bacteria isolated during the advanced stages of the ripening of Parmigiano Reggiano cheese

Abstract

Parmigiano Reggiano is a hard, cooked cheese produced in specific areas of Northern Italy. The raw material is obtained by mixing the partly skimmed evening milk and whole morning milk. The mixture is then heated to 22°C, and natural whey starter is added at 28–30 g/l after 1–2 min, bringing the pH of the mixture to 6·2–6·3. After coagulation, which takes ∼15 min and occurs at 32–33°C owing to the addition of calf rennet powder, the curd is broken up for 2–4 min, cut into fragments and cooked at a temperature raised gradually to 42–44°C and then more quickly to 55–56°C over 10–15 min. The curd is left undisturbed, covered by the whey, for 40–60 min, then removed and placed inside a circular wooden mould. The cheese is held at ∼20°C for 3 d during which it is turned at frequent intervals to facilitate complete whey drainage. The cheese, which now has its typical shape and size, is then salted by immersion in brine (260–280 g NaCl/l at 16–17°C) for 20–24 d. During this period the cheese absorbs 15–18 g NaCl/kg and its weight decreases by 4%. During the subsequent period of ripening (12–24 months) in store rooms at 16–18°C and 85% moisture, the cheese is frequently turned. At the end of ripening the cheese is cylindrical in shape, with a slightly convex side, 0·22–0·24 m high, 0·40–0·45 m diam. weighs 35–36 kg, has 320–330 g fat/kg dry matter and a minutely granulated internal structure with small holes formed by the activity of some heterofermentative lactic acid bacteria.

Microbiological characteristics of Parmigiano Reggiano cheese during the cheesemaking and the first months of the ripening

“…An undoubtedly important contribution was made by the mesophilic lactic acid bacteria (essentially L. casei, L. paracasei, L. rhamnosus, pediococci) which presented meaningful counts in the fifth month of ageing, thereby showing a significantly higher level compared to what has been reported thus far in literature with specific reference to Grana Padano [1]. This type of microflora undoubtedly played an active role during the entire period of ageing as well as a passive and gradual one, which could be attributed to enzyme release following autolysis of mesophilic lactic acid bacteria cells that takes place in the advanced stages of ageing [4].…”

“…In fact, no strains belonging to L. rhamnosus were isolated from raw milk. This indeed depends on its good thermo-resistance and on its aciduric property [4] (natural whey starter is obtained by incubating the whey from the previous day's production at 54-55 °C with a temperature gradient lowered to 28-30 °C within a 24 h time period and final pH drops to 3.20-3.30 [24]). On the other hand, during cheese ripening, the same species was isolated at 45 °C because of its heat resistance.…”

“…Consequently, knowledge of bacterial flora involved in cheese ripening is of prime importance in predicting and determining final cheese quality. In a previous work conducted during the advanced stages of Parmigiano Reggiano cheese ripening (from 5 to 24 months) we were able to ascertain the presence of lactic acid bacteria throughout the entire period of ageing, with a predominance of facultatively heterofermentative lactobacilli [4].…”

“…Lysozyme does not only significantly influence the growth of butyric acid bacteria but also of lactic acid bacteria, consequently affecting curd acidification during the cheesemaking [9]. Further, significant differences in microbiological composition of the two cheeses during the advanced stages of ripening have been ascertained [4]. Indeed, what is lacking is a study that specifically focuses on the microflora (not only of the lactic acid group) during the entire period of ageing in Parmigiano Reggiano.…”

Antibiotic susceptibility of Lactobacillus rhamnosus strains isolated from Parmigiano Reggiano cheese

“…Within the context of a large-scale research project aimed at isolating and characterising lactic acid bacteria in food, this study examined the antibiotic resistance of Lactobacillus rhamnosus strains of potentially probiotic interest isolated from Parmigiano Reggiano cheese, a hard cooked Italian cheese produced with partly skimmed raw cow milk to which natural whey starter is added and which is then ripened for 12-24 months [15,16,32].…”