Abstract

The effect of different drying techniques (freeze, convective, vacuum-microwave and combined drying) on the drying kinetics, the phytochemical compounds and sensory characteristics in loquat cultivar ‘Algar’ was studied. The convective drying resulted in the highest amount of total hydroxycinnamic acids (5077 mg/kg wet weight (ww)), with 3-caffeoyl quinic acid and 5-caffeoyl quinic acid being the greatest carotenoids. The highest values of total carotenoids were obtained by the freeze-drying technique (2601 mg/kg ww), followed by all convective treatments and vacuum-microwave at 360 W. The highest carotenoid was β-carotene. The ABTS+• (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and FRAP (Ferric Ion Reducing Antioxidant Power) values ranged from 2.04 up to 3.27 mmol Trolox/100 g ww, and from 1.89 up to 2.29 mmol Trolox/100 g ww, respectively. As expected, the color difference of freeze-dried samples was the lowest (7.06), similar to combined drying conditions (9.63), whilst the highest value was found after convective drying (37.0). All treatments were sensory acceptable (no off-flavors). However, still, further research is needed to fully optimize these studied drying treatments because the freeze-dried sample still had higher carotenoid content and better instrumental color parameters. Although recently the impact of microwave drying has been studied, this is the first work comparing phytochemical composition of loquat fruit under the different drying methods mentioned above.

Highlights

  • The loquat species (Eriobotrya japonica Lindl.) comes from China and it was introduced into Europe in the XVIII century, but only as an ornamental tree in Botanical Gardens

  • The changes in the moisture ratio (MR) of loquat samples dehydrated by convective drying (CD) at 50, 60 or 70 ◦ C, vacuum-microwave drying (VMD) at 240, 360 and

  • It is worth mentioning that there are no previous data about drying kinetics of loquat fruit

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Summary

Introduction

The loquat species (Eriobotrya japonica Lindl.) comes from China and it was introduced into Europe in the XVIII century, but only as an ornamental tree in Botanical Gardens. In Spain, it was introduced two hundred years ago, and it was already used for productive ends, as well as for ornamental [1]. There are no FAO (The Food and Agriculture Organization) statistics available for world loquat fruit production, Lin [2] reported 550,000 t for 2006 [2], with China being the main producing country followed by the Mediterranean basin, especially Spain [3]. Spain is the world’s major exporter, and more than 50% of Spanish loquat production (28,522 t in 2017) is cultivated in the southeastern region of the country. The most important Spanish production area is Alicante (14,160 t in 2017), followed by Granada (10,716 t in 2017) [4]. The most popular are ‘Nísperos Callosa d’En Sarriá’, for which production has been safeguarded by a Protected Designation of Origin (DOP) since 1992

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