Low temperature drying (LTD) allows high-quality dried products to be obtained, preserving the nutritional properties of fresh foods better than conventional drying, but it is a time-consuming operation. Power ultrasound (US) could be used to intensify LTD, but it should be taken into account that process variables, such as the level of applied power, have an influence on the magnitude and extension of the ultrasonic effects. Therefore, the aim of this work was to assess the influence of the level of applied ultrasonic power on the LTD of apple, analyzing the drying kinetics and the quality of the dried product. For that purpose, apple (Malus domestica cv. Granny Smith) cubes (8.8mm side) were dried (2m/s) at two different temperatures (10 and -10°C), without and with (25, 50 and 75 W) US application. In the dried apple, the rehydration kinetics, hardness, total phenolic content, antioxidant capacity and microstructure were analyzed to evaluate the impact of the level of applied ultrasonic power. At both temperatures, 10 and -10°C, the higher the ultrasonic power level, the shorter the drying time; the maximum shortening of the drying time achieved was 80.3% (at -10°C and 75 W). The ultrasonic power level did not significantly (p<0.05) affect the quality parameters analyzed. Therefore, US could be considered a non-thermal method of intensifying the LTD of fruits, like apple, with only a mild impact on the quality of the dried product.

Mild thermal treatments could be considered a feasible technique with which to improve the texture of dry-cured ham. This study explores the feasibility of using power ultrasound (PuS) to intensify heat transfer during the mild thermal treatment of dry-cured ham immersed in a liquid medium. For that purpose, a temperature controlled ultrasonic bath was used to avoid the water temperature rise due to cavitation during ultrasonic application, which could mask the actual effect of ultrasound in heat transport mechanisms. Experiments were carried out using dry-cured ham slices (thickness 2 cm), which were heated at different temperatures (40, 45, 50 ºC) with (PuS) and without (conventional mechanical stirring, CV) ultrasonic assistance. Temperature was monitored in the two main muscles of the ham (Biceps femoris and Semimembranosus) and in different positions of the slice. A model that considered heat transfer entirely controlled by conduction was chosen for describing heating kinetics and quantify the influence of temperature and ultrasonic application in the apparent thermal diffusivity. The heat conduction model proposed was adequate to describe both CV and PuS heating kinetics (VAR >98.6%). Ultrasound application sped up the heat transfer by increasing the apparent thermal diffusivity up to 51%, but the higher the temperature, the lower the ultrasonic intensification. The apparent thermal diffusivities identified for the slices were satisfactorily validated (VAR> 98.4%) in independent experiments with ham cylinders. Therefore, PuS could be considered as an effective technology for the purposes of accelerating the heat transfer, thus shortening the heating time of dry-cured ham slices immersed in a liquid medium.

The dry-cured pork ham industry lacks non-destructive quality control techniques able to characterize relevant textural defects, such as pastiness or softness. The aim of this study is to analyze the feasibility of using different destructive and non-destructive techniques to characterize pastiness in dry-cured ham. Dry-cured ham processing was modified in order to induce different pastiness intensities over a wide range of moisture and salt contents. Afterwards, pastiness was assessed by sensory analysis and samples classified as non-pasty, medium-pasty and highly-pasty. Finally, chemical, textural, microstructural (LM and TEM) and ultrasonic analyses (velocity and attenuation coefficient) were carried out. Samples with a high degree of pastiness experienced an increase of 16.8% and 16.7% as regards the proteolysis index and relaxation capacity, respectively, and a 67.7% decrease in hardness compared to non-pasty hams. The microstructural analysis revealed that pastiness brought about great structural degradation. Ultrasonic velocity was significantly related to the salt (r=0.79) and moisture contents (r=0.69), but no influence of pastiness was found on the velocity. However, the attenuation coefficient increased as the pastiness rose and could be considered as a useful parameter for characterizing this complex textural defect. Therefore, ultrasound could be used not only to carry out a non-destructive characterization of dry-cured ham composition but also to assess pastiness.

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Pastiness is a textural defect characterized by an excessive softness and loss of elasticity which lacks corrective actions at industrial level. The objective of this study was to evaluate the textural and microstructural changes of dry-cured pork ham, with different pastiness levels, subjected to conventional and ultrasonically-assisted corrective mild thermal treatments. Pastiness was assessed by an expert sensory panel and hams were classified into three categories: high (HP), medium (MP) and no (NP) pastiness. Ham samples (n=108) were heated (40 and 50 ºC) with power ultrasound (PuS) and without (CV) PuS application. After heating, all of the textural parameters assessed were improved. Hardness increased by 102% and adhesiveness decreased by 55% and the ham became less viscoelastic. The largest modifications were found in the samples heated at 50 ºC and no differences were found between CV and PuS treatments. The microstructure of pasty samples revealed that the treatment produced a shrinkage of the myofibrils, which could explain the increase in hardness and the improvement in texture of defective ham.