EFFECT OF ULTRASOUND BLANCHING ON QUALITY ATTRIBUTES OF CONVECTIVE DEHYDRATED CARROTS Gamboa-Santos, J.1, Soria, A.C.2 , Corzo-Martínez, M.1, Montilla, A.1 and Villamiel, M.1 1Instituto de Investigación en Ciencias de Alimentación (CSIC), Nicolás Cabrera, 9 28049 Madrid (Spain), 2Instituto de Química Orgánica General (CSIC), Juan de la Cierva 3, 28006 Madrid (Spain) INTRODUCTION OBJETIVE Among the different dehydrated vegetables, carrot, due to its organoleptic and bioactive properties, is one of the most used as ingredient in the elaboration of several foodstuffs. Convective dehydration can be carried out at high temperatures for short times or at lower temperatures for longer times. Prior to drying, carrots are usually blanched in hot water or steam for air removal, stabilization of colour, solubilization of protopectin and inactivation of microorganisms and enzymes. Due to the increased consumer’s awareness of the relationship between diet and health, the food industry is interested in the search for mild processing technologies which give rise to final products with improved characteristics as compared to those obtained by conventional thermal treatments. In this respect, high-intensity ultrasound has been used as a pretreatment of vegetables and fruits before conventional drying and to assist osmotic dehydration. 1 However, to the best of our knowledge hardly any is known on the quality parameters of convective dehydrated carrots previously blanched by ultrasound. The present study was undertaken to analyse the effect of conventional and US blanching on both, drying kinetics and quality attributes of carrots, during their convective drying. Analytical determinations 2-FM-AA Maillard reaction indicators MATERIALS AND METHODS a) Acid hydrolyzates ( HCl 8 N,110 ºC, 23 h). 2) RP-HPLC-UV Analysis: C8 column (250 mm x 4.6 mm i.d.) at 37 ºC. Detection: 280 nm. Gradient elution: 0-12 min: 100% A; 20-22.5: 50% A, 50% B; 24.5-30.0: 100%A. 2 different sample geometries Samples and Processing Conditions b) Sliced Carrots (S, 4 mm thickness) Minced Carrots (M, 2 mm thickness) Carbohydrates analysis Raw Carrots 1) Derivatization  Trimethylsilyl oximes Blanching conditions Sample:water ratio = 1:5 Processing conditions Samples Blanching Dehydration (48 ºC – 4.8 m/s) System t (min) T (ºC) Minced (t, min) Sliced (t, min) D-CB-1 Boiling water 1 98.0 420 540 D-CS-2 Steam 2 - D-C95-5 Tempered water 5 95.0 D-C60-40 40 60.0 D-US60-101 Sonication 10 <602 D-US75-151 15 <752 Oven: 200 ºC (11 min) 270 ºC (15 ºC min-1) 300 ºC (3 ºC min-1) 325 ºC (15 ºC min-1) Carrier: N2, 1 ml min-1 Injector: 280 ºC, split 1:40. FID: 325 ºC GC-FID Agilent 7890A HP-5MS (25m x 0.25 i.d., 0.25 um) Protein profiles (SDS Page) Sonication (BRANSON US probe) Drying of selected blanching condition (48 ºC, 4.8 m/s) Extraction Powdered dehydrated carrots (100 mg) + 2 mL 1% sodium metabisulfite solution. Stirring for 2h, 25 ºC. Centrifugation 3000g, 15 min. Standard protein mixture (2.5 to 200 kDa) 1D-US60-10 and D-US75-15: US Probe 0.26 W/cm3 (BRANSON). 2Experimental highest temperature reached during the blanching process. Comparing a) b) D-CS-2 samples a) sliced carrots b) minced carrot. 2)SDS-PAGE Supernatant 12% polyacrylamide NuPAGE Novex Bis-Tris precast Gel and MES SDS running buffer. 120 mA/gel, 200 V, 41 min. Colloidal Blue Staining Kit NuPage LDS 4X sample buffer + DTT (0.5M). Running Loading Dehydrated samples EDIBON Drying Cabinet Rehydration Ability (RR) Microstructural Analysis Gold-palladium (ratio 80:20) metalization. 5mA, 800V. Microstructural analysis by scanning electron microscopy, 25kV. EDIBON data adquisition Inmersion in distilled water (Solid-to-liquid ratio 1:50). Room temperature, 24 hours. Rehydration ratio: RR=mr/md (mr: weight of the rehydrated carrot (g) and md: weight of the dehydrated carrot). a) b) Sputter Coater SC7C40 (POLARON) Scanning Electron Microscope XL30 ESEM (PHILIPS). RESULTS AND DISCUSSION The highest drying rates were obtained after D-60-40 (M) and D-C95-5 (M,S) pretreatments. Slopes during the first period of drying doubled the slopes of the rest of conditions applied. As expected, 2 mm thickness samples showed higher drying rates than those of 4 mm. Drying rates for US pretreated samples were similar to those obtained for D-CB-1 and D-CS-2, the most used conventional industrial blanching conditions. Sliced carrots Minced carrots Drying kinetic Carbohydrate Analysis Dried samples subjected to C95-5 blanching conditions gave rise to the highest 2-FM-AA values. They were significantly higher than those obtained after US pretreatments. Thickness (2 or 4 mm) did not show any influence in D-CB-1 and D-C95-5 samples. Regarding to other processing conditions the relationship between geometry and 2-FM-AA formation was not clear. 2-FM-AA Formation Sliced (S) 4mm Minced (M) 2mm Samples Geometry Fructose (%) Glucose Sucrose Total D-CB-1 Minced 38.83 ±0.44 e1 37.77 ± 0.22 e 16.01 ± 0.22 d 18.09 ± 0.28 d Sliced 14.69 ± 0.11 b 15.36 ± 0.02 b 8.94 ± 0.41 b 9.61 ± 0.41 b D-C95-5 53.75 ± 0.75 d 52.96 ± 0.32 d 37.01 ± 0.48 e 49.55 ± 0.45 e 42.01 ± 1.72 c 43.47 ± 1.77 c 22.24 ± 0.55 c 33.54 ± 0.66 c D-CS-2 0.02 ± 0.00 a 0.03 ± 0.00 a 0.10 ± 0.00 a 0.07 ± 0.00 a 0.13 ± 0.01 a 0.12 ± 0.02 a 0.19 ± 0.00 a 0.18 ± 0.00 a D-C60-40 48.3 ± 4.1 d 40.2 ± 3.4 c 30.7 ± 0.8 c,e 36.0 ± 0.6 c D-US60-10 41.6 ± 0.60 c 44.57 ± 4.43 c 23.50 ± 5.29 c 27.80 ± 4.87 f D-US75-15 52.77 ± 1.31 d 52.10 ± 1.59 d 25.72 ± 0.27c 33.06 ± 0.27 c 1a-f: samples with the same superscript letter within the same column showed no statistically significant differences for their mean values at the 95.0 % confidence level. US blanched samples showed total carbohydrate losses between 27 and 33%. Very higher values, close to 50%, were obtained after D-C95-5 processing conditions. Regardless of blanching conditions and with the exception of D-CS-2 samples, the lowest thickness gave rise to highest carbohydrate losses. D-C95-5 (M,S) and D-C60-40 (S) samples showed the highest rehydration ratios (RR), up to 15%. RR in the range 4-6 were found in the other conventionally treated samples. D-US treatments gave rise to samples with RR higher than 6, values close to those of FD raw samples. Regarding to microstructural analysis, FD samples showed a perfect structure of the vegetal parenquima. On the contrary, D-C95-5 samples showed material deterioration, giving rise to the observed RR. US-treated samples presented pores in the structure due to cavitation effect. Rehydration Ability Microstructural Analysis a) b) c) Sliced (S) 4mm Minced (M) 2mm d) e) f) Protein profiles (1)1 (2) (3) (4) (5) (6) (7) (8) (9) (10) 1 FD : freeze-dried samples. Electron microphotographs of dried minced carrots, a) FD Raw; b) D-CB-1; c) D-CS-2; d) D-C60-40; e) D-US60-10; f) D-C95-5. (400X) SDS-PAGE Electrophoretic profiles of FD carrots showed four major bands with molecular weights of 18, 36.5, 41.2 and 55.4 kDa. All the samples, excepted D-C95-5, presented similar profiles to FD carrots. Diffuse profiles were obtained in D-C95-5 samples due to the formation of aggregates, in agreement with the high values of 2-FM-AA. Regarding to D-US60-10 and D-US75-15 samples, protein profiles indicate that US blanching does not cause important structural changes in carrot proteins. CONCLUSIONS The blanching conditions promote modifications in the samples giving rise to diferent amounts of 2-FM-AA during the dehydration of carrots. Thus, these compounds are very useful indicators during the processing of carrots. In general, the quality attributes of dehydrated carrot samples previously blanched by ultrasound are comparable and, in some cases, better than those obtained in dried samples subjected to conventional blanching. 1SDS-PAGE Analysis of dehydrated carrots: (1) Markers of molecular weight, (2) FD, (3) D-C60-40 (M), (4) D-CB-1 (M), (5) D-C95-5 (M), (6) D-US60-10 (M), (7) D-CS-2 (S), (8) D-CB-1 (S), (9) D-C95-5 (S), (10) D-US75-15 (S). REFERENCES 1García-Perez et al. (2007). Food and Bioproducts Processing Trans IChemE, Part C. Fernandes et al.(2008).Ultrasonics Sonochemistry, 15, 1049-1054. ACKNOWLEDGMENTS: This work has been funded by Ministry of Science and Innovation of Spain (Project AGL2007-63462/ALI), CYTED IBEROFUN (P109AC0302) and by Consolider Ingenio 2010 Fun-C. Food CSD 2007-0063. J.G.S. And A.C.S thank CSIC and the EU for a predoctoral grant and a postdoctoral contract, respectively.