ABSTRACT


        The effect of the osmotic treatments until different levels, with and 
without application of vacuum pulse (50 mbar during 5 minutes) and the 
influence of the calcium lactate in the osmotic solution, along with the effect of 
temperature and the storage time, have been analyzed in different properties 
related with the stability and the quality of strawberry and apple. First of all, 
dehydration kinetics has been characterized in halves of strawberry and in apple 
slices to establish the required treatment time. After that, the effect of 
treatments on the mechanical and respiration rate of fruits have been evaluated. 
In strawberry the influence of treatments on the optical properties and ethanol 
and acetaldehyde production have been analyzed. In apple, the effect of 
modified atmosphere in the headspace on the respiration rate has been studied 
and also the effect of treatments in the microbiological stability.
	Osmotic treatments imply changes in the respiration rate of the tissue, 
depending on process conditions. Pulsed vacuum treatments involve greater 
restrictions to oxygen transport, thus leading to higher values of the respiration 
quotient, and favouring anaerobic routs. As a consequence, undesirable volatiles 
are developed as it is observed in strawberry.  From this point of view, the most 
recommendable osmotic treatments are short times of process, at atmospheric 
pressure.
	Osmotic treatments induce changes in mechanical properties of apple 
and strawberry; the greater the dehydration level, the more intense the changes. 
Vacuum pulse implies a reduction in fruit firmness, but contributes to their 
preservation during storage. Vacuum pulse supposes a darkening and chrome 
loss in strawberry, but without hue changes. Structural changes are the 
responsible of colour changes due to treatment and storage. Osmotic treatments 
improve the microbiological stability of apple, especially when vacuum pulse is 
applied, without effect of calcium.