Water and steam blanching were investigated as pretreatments of bitter orange peels in order to modulate their bitterness before further formulation processing such as osmotic treatment and drying. The fruit pieces were water blanched at 95°C for 10 min and at 85°C for 60 min and steam blanched at atmospheric pressure during 5 min. The kinetics of water inflow and bitter flavanone losses were established from the variation of moisture and bitter compound contents during the blanching process. The whiteness and the citrus color indexes were adopted to evaluate respectively the color of the flavedo and the albedo. Thin sections of fresh and treated peels were resin embedded for light microscopy evaluation and optical porosity determination. Results revealed that water blanching could partially debitter the peels by removing about 38 and 48 % of bitter flavanones (naringin, neohesperidin, neoeriocitrin) respectively at 95 and 85°C. The citrus color index and the whiteness index decreased during the process denoting a flavedo discoloring and an albedo darkening. By contrast, the steam blanching showed good retention of bitter compounds. The color of the flavedo was unaffected by steaming while the whiteness index decreased.At microscopic level, the water-blanched peels exhibited an extreme swelling of the cell walls and slight disintegration of the tissue. Contrariwise, the steam blanching maintained the structure of the peels and brought about the shrinkage of the albedo tissue and the decrease of porosity.

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This study investigated the use of wet and dry osmotic dehydration for modulating the bitter taste of Citrus aurantium peels, imparted by the predominance of flavanones glycosides in their albedo; namely naringin, neohesperidin, and neoeriocitrin. For this purpose, the peels were subjected to dehydration-impregnation by soaking (DIS) in 40°Brix sucrose solution at 25°C and in 60°Brix sucrose solutions at 25 and 50°C and to dry osmotic dehydration (DOD) at 25°C for 6 h. The peels had not shown the immediate dewatering phenomena in the DIS process but rather an imbibition of sucrose solution, reflected in water and sugar gains. Such a tendency has shown to be ascribed to the porous structure of the albedo which fostered the capillary inflow of external liquid. The imbibition was observed during 6 h of treatment in low concentrated sucrose solution whereas in high concentrated ones, it was followed by the dewatering phenomenon thereby inducing an increase of pore volume together with a decrease of cells size. Conversely, in the DOD process, the expected cross transfers of water and sugar were markedly observed. The water was removed from both albedo and flavedo. Indeed, the essential oil cavities exhibited elongation of their shape in line with shrinkage of the peel. The two techniques allowed loss of bitter compounds and gain of sucrose. Nonetheless, The DIS gave rise to higher gain of sucrose and losses of flavanones glycosides than DOD.