Ultrasonic online monitoring of the ham salting process. Methods for signal analysis: Time of flight calculation

Abstract

In the dry-cured ham industry, an accurate control of the dry-salting process is especially complex because of the great heterogeneity of the meat pieces and the effect of different operational variables. The main objective of this study was to evaluate the feasibility of using an ultrasound system and methodology, adapted to the industry requirements, for the online monitoring of the ham dry-salting process. For that purpose, hams were dry salted for different times (4, 10, 11, 14, 16 and 30 days) at 2 °C. The cushion zone of the ham was placed over the transducers during salting and ultrasonic signals were taken automatically (5 min interval by using pulse-echo mode. Several methods of signal analysis were considered in order to assess the time of flight (TOF). TOF estimations by means of the energy threshold and cross-correlation methods (between the initial ultrasonic signal and the remaining signals measured during salting and between consecutive signals 5 min apart without interpolation) were affected by the low signal-to-noise ratio and the pulse distortion and were discarded for the online monitoring of ham salting. Otherwise, the cross-correlation method between consecutive signals (5 min apart) with interpolation n = 3 (CCM-CS n = 3), between non-consecutive signals (1 h apart) (CCM-NCS) and the phase spectrum method (PSM), provided close estimations of the variation of the TOF, which correlated well with the ham salt gain (R2 = 0.83 for CCM-CS n = 3, 0.93 for CCM-NCS and 0.90 for PSM). Consequently, the use of ultrasonic pulse-echo TOF measurements could be considered as a simple, non-invasive, non-destructive and reliable technique for the industrial monitoring of the ham dry-salting process.