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Whey Starter for Grana Padano Cheese: Effect of Technological Parameters on Viability and Composition of the Microbial Community

M. Santarelli^*, M. Gatti^*,1, C. Lazzi^*, V. Bernini^*, G. A. Zapparoli and E. Neviani^*

^* Department of Genetics, Biology of Microorganisms, Anthropology, Evolution, University of Parma, 43100 Parma, Italy
Ente Regionale per i Servizi all’Agricoltura e alle Foreste, Sezione di Mantova, 46010 Mantova Italy

¹ Corresponding author: monica.gatti{at}unipr.it

This work aimed to investigate the effects of thermal treatments and yeast extract addition on the composition of the microbial community of natural whey starters for Grana Padano cheese. Different natural whey starter samples were held at 4°C for 24 h (cooling treatment), or at –20°C for 24 h (freezing treatment) to evaluate the possibility of conservation, or at 54°C for 1 h (heat treatment) to evaluate the effect of the temperature commonly used during curd cooking. Separately, another set of samples was enriched with 0.3, 0.5, and 1.0% (wt/vol) of yeast extract to study its effect on the growth of lactic acid bacteria (LAB) in the starter. The new approach in this study is the use of 2 culture-independent methods: length heterogeneity (LH)-reverse transcription (RT)-PCR and fluorescence microscopy. These techniques allowed us to easily, quickly, and reproducibly assess metabolically active LAB in the control and treated samples. The LH-RT-PCR technique distinguished microorganisms based on natural variations in the length of 16S rRNA amplified by RT-PCR, as analyzed by using an automatic gene sequencer. Fluorescence microscopy counts were performed by using a Live/Dead BacLight bacterial viability kit. The repeatability of LH-RT-PCR showed that this technique has great potential to reveal changes in the microbial community of natural whey starters for Grana Padano cheese. All species showed low sensitivity to cold (4°C). However, after the freezing (–20°C) and heating (54°C) treatments, different behaviors of the species were reported, with significant changes in their viability and relative composition. Heating treatment during curd cooking profoundly affected the viability and composition of the community that remained in the cheese and that consequently modified the microbial population. At the same time, this treatment produced the selection of LAB in whey and could be considered as the first step in natural whey starter production. Addition of yeast extract stimulated the growth of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. lactis to the detriment of Lactobacillus helveticus species. Because the yeast extract altered the microflora balance, whey starter conservation at –20°C and yeast extract addition cannot be suggested as technological innovations.

Key Words: natural whey starter • Grana Padano cheese • length heterogeneity-reverse transcription-polymerase chain reaction • fluorescence microscopy

This article has been cited by other articles:

				M. Gatti, J. De Dea Lindner, A. De Lorentiis, B. Bottari, M. Santarelli, V. Bernini, and E. Neviani Dynamics of Whole and Lysed Bacterial Cells during Parmigiano-Reggiano Cheese Production and Ripening Appl. Envir. Microbiol., October 1, 2008; 74(19): 6161 - 6167. [Abstract] [Full Text] [PDF]