The health properties of fruit are widely known. Powdered fruit may be a practical format to be offered to the consumer. Nevertheless, the process used to obtain the powder must ensure the maximum retention of the bioactive compounds and the functional value of the fruit while retaining adequate physical properties. The aim of this study was to compare freeze-drying and spray drying as the drying technologies to obtain grapefruit powder. The obtained results allow freeze-drying to be proposed as a better technology than spray drying in order to obtain a product with a higher content of vitamin C and total carotenoids. Moreover, all of the edible part of the fruit is used in this case, so a greater quantity of healthy compounds is preserved and by-product generation is avoided. Adding about 6 g water, 4 g Arabic gum and 0.6 g bamboo fibre/100 g grapefruit pulp is recommended before freeze-drying.

Grapefruit is a fruit with interesting nutritional value and functional properties, but a short life. Freeze-drying (FD) is a valuable technique as it produces high-quality dehydrated products. This study is aimed to obtain new food ingredients based on freeze-dried grapefruit formulated with high molecular weight solutes (gum arabic and bamboo fiber) in three different proportions (F1, F2, and F3). To improve the FD, a mild microwave drying pre-treatment was applied. Influence of the water content and the presence of high molecular weight solutes on freeze-drying kinetics was tested by Midilli-Kucuk and Page models. The best FD kinetic model fit on grapefruit powders were Midilli-Kucuk for F2 and F3, and Page for F1, and the adequate freeze-drying times for F1, F2, and F3 were 24, 16, and 18 h, respectively. Final samples were evaluated for nutritional and antioxidant capacity. Gum arabic and bamboo fiber present a protector effect, which results in a significant antioxidant capacity due to the protection of flavonoids and antioxidant vitamins. These novel food ingredients could be of great interest for the food industry in order to develop foods with improved antioxidant capacity as well as enriched in natural fibers and/or micronutrients.

a b s t r a c tDifferent grapefruit powders obtained by freeze drying and spray drying with prior addition of shell materials (arabic gum and bamboo fiber) were studied in order to evaluate the effect of these preservation processes on the retention of antioxidants, in comparison with the freeze-dried fruit with no carriers added. Freeze-dried samples showed above 90% retention of these phytochemicals, while spraydried samples presented good retention of vitamins but a sharp decrease in of phenolic compounds. Pearson's correlation analysis showed that the most significant contribution to DPPH scavenging activity and inhibition of b-carotene bleaching was provided by phenolic compounds, mostly flavonoids, while the contribution to the reducing power was due to ascorbic acid and a-tocopherol. Therefore, the loss of these compounds in the spray-dried samples resulted in products with lower antioxidant activity. Naringin and narirutin were the major phenolic compounds in all grapefruit samples, although other flavanones present in lower concentration, like hesperidin, neohesperidin didymin, poncirin or melitidin, also showed high correlations with the antioxidant value of the samples.

ElsevierAgudelo Sterling, CM.; Igual Ramo, M.; Talens Oliag, P.; Martínez Navarrete, N. (2015). Optical and mechanical properties of cocona chips as affected by the drying process. AbstractThe effect of the application of a pre-osmotic treatment to obtain hot air dried cocona (Solanum sessiliofurum Dunal) chips was studied. The drying kinetics and the optical and mechanical properties of cocona chips obtained by the combined method of osmotic dehydration and hot air drying (OD+HAD) and by only hot air drying (HAD) were compared. Samples were dried by hot air at 60ºC. For the combined method, they were pre-dried to a moisture content of 75 g water /100g, immersed in a 55 ºBrix sucrose solution at 25ºC for 48 minutes. The pre-osmodehydration applied did not influence the subsequent hot air drying kinetics, resulting in a final product with 0.055 ± 0.005 g water /g cocona. The optical properties of OD+HAD chips were more favourable, exhibiting a smaller color change with respect to the fresh fruit (±15 units) than the HAD samples (±23 units). On the other hand, the OD+HAD chips presented more fracture peaks than HAD ones, this related with a structure with a higher degree of crispness, a very desirable property for a chip product.