Amino acid profile and Maillard compounds of sun-dried pears ...

Eur Food Res Technol (2011) 233:637–646 639at the village of Ervedal da Beira (Oliveira do Hospital,Portugal) at the commercial maturity stage (Fig. 1a). Onaverage, the fresh fruits had a mass of 64 g, with a diameterof 4.3 cm and height of 6.5 cm. The moisture content was78%.For fresh pear analysis, some fruits were frozen justafter harvesting. The remaining fruits were processedaccording to the different methodologies under study.According to the traditional sun-drying process, thefresh fruits were peeled and allowed to dry in an openspace with sunshine incidence, as described by Ferreiraet al. [5] (Fig. 1b). After being peeled, fresh pears werealso allowed to dry in two greenhouses that differed in theirsize, structure and location. GH1 was provided with airconvection, with a flux of 900 m 3 h -1 , it was located atground level and, in comparison to GH2, had the largestcargo capacity. Its area was 6.3 m 2 (3.19 m long by 1.93 mwide), and the height in the sides was 1.24 m, whereas inthe middle was 1.97 m. The structure was aluminium withhorticulture glass and there were two roof windows for airextraction. The drying time for GH1 was approximately7 days (Fig. 1c). The GH2 greenhouse consisted of insulatedglass panels and had the form of a box (1.20 m heightby 1.20 m long and 1.00 m wide). Inside, it was composedby a U-shaped structure, parallel to the floor, where pearswere let to dry. GH2 was located on a roof of a buildingand contained a step structure coated with reflective film,where pears were allowed to dry. This interior structureallowed a greater incidence of the light and consequentlypromoted the drying process by natural air convection, withthe air entering in the lower level (first step) and leaving inthe higher level, by means of a girandole. The drying timefor GH2 was approximately 5 days (Fig. 1d), 2 days lessthat the drying time of GH1.For hot air tunnel drying (HAT), after peeled, pears werelet to dry at a constant temperature of 40 °C and an air flowof 1.2 m s -1 for about 7 days (Fig. 1e). The drying tunnelwas 2 m long, and the air convection was promoted by aventilator placed at the entrance of the tunnel. In thisstructure, pears were not exposed to light, although the airwas heated by a solar collector, and therefore the sun wasalso the main source of energy.Independently of the type of processing used, the processedfruits reached a mass of 10–14 g with a moisturecontent of 20% and had a maximum width of 2.5–3.4 cm,height of 3.9–4.7 cm and thickness of 1.2–1.5 cm. Thesensory descriptive profile of the traditional product, whenevaluated by a sensory panel test, is the following: brown–red uniform colour (Fig. 1b), sweet and slight acid, with anot too hard–not too soft texture and presenting elasticity.Concerning GH1, it was considered very similar to thetraditional product, with the same rate of global appreciation,but with lower colour uniformity (Fig. 1c), sweetnessand elasticity. GH2 was similar to GH1, although obtaininga lower global appreciation, possibly due to an even loweracidity (Fig. 1d). HAT presented the sensory profile closeto the traditional product concerning colour uniformity,sweetness and toughness but it was not appreciated due tothe colour tonality (yellow-orange) (Fig. 1e) and slight lessacidity. This product, although having the accurate organolepticcharacteristics except the colour, was rejected bythe panellists due to the inaccurate colour when comparedwith the traditional product.Before analysis, the pulp of the fresh and dried pearswas collected, ground and freeze-dried.Amino acids analysisThe methodology for acid hydrolysis of protein materialwas adapted from Zumwalt et al. [22]. To a test tube with ascrew cap with PTFE coating was rigorously weighed10 mg of freeze-dried material. To each sample, 2 mLhydrochloric acid (HCl) 6 M was added; the content of thetubes was frozen in liquid nitrogen, evacuated during 1 minwith a vacuum pump and refilled with nitrogen. Afterthawing, the suspension was sonicated for 5 min in anultrasound bath at room temperature. The procedure offreezing–vacuum–sonication was repeated twice. Thehydrolysis took place during 24 h at 110 °C using a heatingblock. After cooling to room temperature, 500 lL of theFig. 1 The S. Bartolomeu pear.a Fresh pears and pears dried bydifferent technologies:b Traditional, c GH1, d GH2and e HAT123