Use of ultrasound for the characterization and correction of textural defects in dry-cured ham

Abstract

Dry-cured ham is a product highly appreciated by consumers, nevertheless, one of the main problems in the quality of dry-cured ham is the appearance of textural defects, in particular, the development of pastiness. This defect is characterized by an excessive softness and loss of elastic behavior of the ham, making slicing difficult and promoting the adhesiveness between slices. Currently, the methods available to measure ham pastiness are time-consuming and destructive. In this context, the main goals of this thesis were to determine the feasibility of using low intensity ultrasound to non-destructively detect the appearance of pastiness during ham manufacturing, as well as to explore the feasibility of mild ultrasonic assisted thermal treatments to correct this textural defect. To meet these goals, a customized dry-cured ham manufacturing was designed in order to obtain hams with different levels of pastiness. During ham manufacturing, the feasibility of using contact ultrasound to monitor the appearance of pastiness was addressed. As the manufacturing progressed, a progressive increase in the ultrasonic velocity was found. Notwithstanding, the increase in the ultrasonic velocity was not related with the pastiness defect. Contact ultrasound was also used to monitor the compositional and textural changes taking place along the ham post-salting stage. The variation in the ham hardness during post-salting was negligible and hence, the velocity increase was mainly attributed to the compositional changes. The hams obtained after the customized manufacturing were sliced and the ultrasonic velocity and attenuation were measured with the aim of non-destructively finding out its pastiness level. The non-destructive assessment performed with ultrasound revealed that ultrasonic attenuation could be successfully applied for the grading of dry-cured ham slices according to its pastiness level. Thus, the greater the pastiness, the higher the ultrasonic attenuation. Air-coupled ultrasonic techniques were developed for the characterization of dry-cured ham texture since the non-invasive nature of air-coupled ultrasound allows a contactless measurement, which makes easier its industrial implementation. As for corrective actions of the texture defects in dry-cured ham, mild thermal treatments in two different heating media (water and air) were evaluated. Furthermore, the feasibility of intensifying these mild thermal treatments with the assistance of power ultrasound was considered. The experiments showed that power ultrasound application sped up the heat transfer, significantly shortening the heating time and increasing the apparent thermal diffusivity up to 51 and 37% for water and air heat treatments, respectively. As regards the changes in the textural properties of ham after the mild thermal treatments at short times, an increase in hardness and elastic behavior was observed. Finally, the texture correction in dry-cured ham with different levels of pastiness was tackled. After the mild thermal treatments, the texture of ham was improved since the hardness was increased (102%) and the viscous behavior and the adhesiveness diminished (11% and 55%, respectively). In conclusion, pastiness is a relevant and highly complex textural defect in dry-cured ham. The measurement of the ultrasonic attenuation could be considered a potential technology to non-destructively detect and characterize pastiness in sliced dry-cured ham. Moreover, the use of mild thermal treatments in liquid or gas media could be a feasible method to correct the defective texture of dry-cured hams and the application of power ultrasound during the heating phase could be a relevant means of speeding up the thermal treatments.