Determination of dry matter content in potato tubers by low-field nuclear magnetic resonance (LF-NMR).

The objective of this study was to develop a calibration model between time-domain low-field nuclear magnetic resonance (LF-NMR) measurements and dry matter (DM) content in single potatoes. An extensive sampling procedure was used to collect 210 potatoes from eight cultivars with a wide range in DM content, ranging from 16 to 28%. The exponential NMR relaxation curves were resolved into four mono-exponential components using a number of solution diagnostics. Partial least-squares (PLS) regression between NMR parameters (relaxation time constants T(2,1-4) and magnitudes M(0,1-4)) and DM content resulted in a model with low error (RMSECV, 0.71; RMSEP, 0.60) and high correlation (r(CV), 0.97; r(test), 0.98) between predicted and actual DM content. Correlation between DM content and each of the proton populations revealed that M(0,1) (T(2,1), 3.6 ms; SD, 0.3 ms; r, 0.95) and M(0,4) (T(2,4), 508 ms; SD, 53 ms; r, -0.90) were the major contributors to the PLS regression model.

Effect of gel firmness at cutting time, pH, and temperature on rennet coagulation and syneresis: an in situ 1H NMR relaxation study.

The objective of this study was to monitor rennet-induced milk gel formation and mechanically induced gel syneresis in situ by low-field NMR. pH, temperature, and gel firmness at cutting time were varied in a factorial design. The new curve-fitting method Doubleslicing revealed that during coagulation two proton populations with distinct transverse relaxation times (T2,1=181, T2,2=465 ms) were present in fractions (f1=98.9%, f2=1.1%). Mechanical cutting of the gel in the NMR tube induced macrosyneresis, which led to the appearance of an additional proton population (T2,3=1500-2200 ms) identified as whey. On the basis of NMR quantification of whey water the syneresis rate was calculated and found to be significantly dependent on pH and temperature.