Effect of lysozyme and ripening time on in vitro Ca digestibility of Grana Padano DOP cheese

Objectives High Ca content is one of the most important characteristic of dairy products, According to some Authors dairy products have a better Ca digestibility compared to plant foods and this characteristic has been related to the inclusion of Ca in the caseinophosphopeptides (CPP). Because ripening time and lysozyme can affect peptide pattern we decided to study the effect of these two factors on in vitro Ca digestibility. Experimental methods 20 samples of Grana Padano produced with lysozyme and 17 samples produced without lysozyme (total 37 samples), aged between 11 and 25 months were obtained from 2 different cheese-factories. In vitro Ca digestibility (dCa) was determined using the methods of Perales et al (J Agric Food Chem, 2005, 53: 3721). Molecular weight (MW) of peptides was determined by exclusion chromatography and CPP were determined by HPLC-MS. Analysis of variance was carried out with SAS 9.1 using GLM procedure of the SAS 9.1. The correlation between variables was performed with the PROC CORR of SAS 9.1. Results The dCa (%) at ripening time of 12, 15-20 and > 20 months were: 71.75, 76.10, 86.04 for Grana Padano and 73.21, 63.70, 62.59 for lysozyme-free cheese. In Grana Padano dCa and aging were positively related (r2 = 0.27; P<0.05). Since Ca is almost entirely associated with caseins, the difference in dCa could be due to a different proteolysis mediated by the presence of lysozyme as reported by Sforza et al. (Eur J Mass Spectrom, 2004, 10: 421). In the range of MW from 1000 to 2500 D, we observed an higher number of Ca-binding sequences in lysozyme containing cheese compared to Trentin Grana and this fact could explain the different result. Furthermore dCa in lysozyme containing cheese was positively correlated to the concentration of peptides having MW in the range 1000-1500 D and 1500-2500 D. Conclusions A larger number of cheese samples is necessary in order to better describe the effect of ripening and lysozyme addition on Ca digestibility, however our results suggest that the use of lysozyme in cheese-making can affect peptide pattern of cheese and dCa, this could be of nutritional relevance in people with high Ca requirement such as elderly people or pregnant women.