Effect of the manufacturing process on Fiore Sardo PDO cheese microstructure by multi-frequency NMR relaxometry.

The quality of Fiore Sardo cheese, a traditional Italian dairy product, was analyzed by means of Multi-frequency Nuclear Magnetic (NMR) relaxometry. Specifically, ten cheese wheels were purchased from different production chains, either industrial (N = 5) or artisanal (N = 5) samples. The former came from large scale productions and the latter were produced by shepherds in small quantities and in very small dairy factories. A preliminary interlaboratory proficiency testing of Time Domain - NMR (TD-NMR, 20 MHz) relaxometry by five laboratories, consistently showed that product quality is significantly different in terms of molecular mobility according to their production chain (i.e. industrial or artisanal). More detailed information about cheese microstructure was obtained by Multi-frequency Fast Field Cycling NMR (FFC-NMR) at lower magnetic fields (0.01-10 MHz). According to the interpretative model adopted to describe FFC-NMR data, industrially processed cheeses showed a higher para-casein hydration, higher protein protons to water protons ratio and a higher disorder (lower fractal dimension df) than artisanal products. It is suggested that differences between artisanal and industrial cheeses generate from the processing steps preceding cheese maturation, and are clearly reflected in the visual appearance of cheeses. This study shows that NMR relaxometry techniques can successfully discriminate Fiore Sardo cheese from different production chains, and paves the way for their implementation in quality control practices of dairy products.

Molecular mobility changes after high-temperature, short-time pasteurization: An extended time-domain nuclear magnetic resonance screening of ewe milk.

This study presents an extensive investigation on the effect of pasteurization on raw whole ewe milk. Milk samples have been analyzed, throughout lactation (from February to July), by time-domain nuclear magnetic resonance (TD-NMR), collecting the characteristic TD-NMR relaxation parameters, proton longitudinal and transverse relaxation times (1H T1 and T2). Collected data aim at integrating previous NMR works, mainly focusing on dairy model systems (casein and whey proteins solutions and gels, reconstituted skim milk) and cheese, with specific reference to the effect of heat treatments. Whole ewe milk, from a single flock (Sarda sheep breed), was daily analyzed both as untreated (raw) and heat treated with a laboratory-scaled high-temperature, short-time treatment (72°C for 15 and 20 s). Moreover, molecular dynamics in milk were investigated by TD-NMR in different periods of lactation for the first time. As a consequence of high-temperature short-time treatment, 1H T1 and T2 consistently shifted to lower values with respect to raw counterparts. Statistical analysis indicated a significant decrease of T2 in treated samples, to an extent dependent on the heat treatment duration. A subset of dedicated experiments demonstrated that the observed T2 shift is largely ascribable to protein molecular rearrangements and, to a lesser extent, to the interaction of fat globules with proteins or other nonfat components (or both). In light of the crucial importance of detecting the application of a heat treatment to milk, the results reported here suggest TD-NMR relaxation parameters were able to describe heat-induced changes in molecular dynamics and interactions of milk components in a water-rich environment. The use of TD-NMR can be considered a potential suitable technique for quality control and assurance practices in the dairy industry. Upon statistical validation of methods, the application of TD-NMR in the dairy industry would take advantage of its low cost, reliability, and robustness.

A low-field Nuclear Magnetic Resonance dataset of whole milk during coagulation and syneresis.

We report the relaxometric dataset obtained on renneted milk during syneresis by Time-Domain Nuclear Magnetic Resonance spectroscopy (TD-NMR). Data were obtained on cow's milk provided by two different producers in two different lactation seasons (April and October) and on a group of goat's milk samples (one season, November-December, one producer). TD-NMR data refer to spin-spin relaxation times (T2) decay curves and distributions measured at 40 °C at seven time points after rennet addition, up to 70 minutes of syneresis. Curd was cut 30 min after rennet addition without removing the NMR tube from the TD-NMR instrument. The dataset here reported is related to the research article entitled "Non invasive monitoring of curd syneresis upon renneting of raw and heat-treated cow's and goat's milk" [E. Curti, A. Pardu, S. Del Vigo, R. Sanna, R. Anedda, Non-invasive monitoring of curd syneresis upon renneting of raw and heat-treated cow's and goat's milk, Int. Dairy J. 90 (2019) 95-97].