ABSTRACT
The formulation of a grapefruit-gel product by using osmotic treatments has been considered, trying to extend the fruit-food market supply in order to promote fruit consumption. The study considers the viability of the osmotic solution (OS) re-use in successive dehydration cycles and its final incorporation to the gel development. In this way, the aim was to design a process more economic and environmentally friendly, and to obtain a product with the maximum nutritive and functional value.
The kinetic study performed of the osmotic selected process allowed us to fix in 180 min the time needed to obtain grapefruit with approximately 20ºBrix. For the re-use of the OS during 5 consecutive cycles of osmotic dehydration (OD), which does not affect to the characteristics of the dehydrated fruit, a previous soft thermal treatment (72ºC/15s) before each one of them is recommended. The gel formulation with carrageenan and the re-used OS requires its previous dilution to assure the thermodynamic equilibrium between this one and the dehydrated fruit. The dehydrated grapefruit and the formulated product have been studied from the point of view of their composition in water and soluble solids, acidity, ascorbic acid (AA), respiration rate (RR), colour, mechanical properties and microorganisms growth, considering the evolution of all these aspects during chilling storage. The presence of the gel preserves grapefruit AA loss and delays microorganisms growth, so that the product is safe for at least 12 days. The rest of properties are not affected by the jellied matrix or the storage. The sensory study reveals the acceptability of the formulated product.
The incorporation of calcium lactate to the OS during the OD implies a decrease of the fruit dehydration kinetic and also of the RR, which supposes an increase of the shelf-life of the dehydrated fruit and the fruit-gel product. The calcium improves the colour and therefore of the appearance of the fruit, but it affects negatively to the texture, aroma and flavour. On the other hand, it contributes to the opacity and hardness of the gel. From this point of view, the addition of calcium would not be recommendable for the formulation of the designed grapefruit-gel product.