The 54th Annual Microwave Power Symposium Impact of Microwave heating on properties and texture in Roua BouOrm12, Vanessa Jury12, Lionel Boillereaux12 , Luc Guihard12 and Alain Le-Bail12 1ONIRIS, BP 82225, 44322 Nantes, France 2UMR GEPEA CNRS 6144 - ONIRIS, 44307 Nantes, France

o Microwave (MW) bread remains one of the most interesting alternatives due to its high volumic power, less baking time and its relatively low space demand. o MW baking was used to provide bread with less acrylamides, which can be considered as more “healthy” [1].Therefore, producing high-quality microwave- baked products is a challenge for food technologists. Since starch is the main component of most baked goods, an in-depth understanding of the effects of MW on starch will play an important role in improving the quality of “MW products”.

Objectives Materials and Methods

o The aim of this study was to compare the effect of MW baking and conventional baking: o on starch structure at different scale o on staling in sandwich bread

SETARAM Micro-Calorimeter (MICRODSC- 7) Drying cabinet : Moisture Content Amylopectin retrogradation and amylose-lipid Baking Heating Modes Réf. AACC method 44-15A (AACC, 1999) crystallization

Scanning Electronic Microscopy TA-XT Texturometer Starch granules Microstructure Crumb Hardness during Staling

Conventional Convection Microwave Oven (MIWE – deck oven) ( Sharp Inverter ) - 220°C for 20 min - 230 watts 10 min

The effect of different baking modes was analyzed at 7°C/min All analyses were performed in triplicate for each bread sample ( Center ) Results v Impact of heating mode on the evolution of Amylopectin Retrogradation and the formation of amylose-lipid Complexes during staling v Starch Granules Microstructure using ESEM in crumbs baked under diffrent heating modes H 7°C/min - MW H 7°C/min - CV H Class-6 °C/min 1.40 4 3.5 1.20 P < 0.05 3 1.00 Vs. dry (J/g 2.5 0.80 Control ) 2

0.60 Flour

Enthalpy 1.5

0.40 1

0.20 0.5 Melting MeltingdryFlour)Enthalpy(J/g 0.00 0 3 6 14 1 6 14 Storage Period (days) Storage Period (Days)

v Moisture Content & Crumb Firminess Evolution 70 9

60 8

50 7 6 40 5 Conventional baked Crumb MW baked Crumb 30 4

3 20

Firminess(N) 2 10 ü MW baking resulted in the formation of superficial cracks and granule

Moisture Content ( g/100 g d.m.) g g/100 ( Content Moisture 1

0 0 deformation while in conventional baking, no ghost of starch granules 1 6 14 1 6 14 Storage (days) Storage (days) were visible, the crumb being made of a continuous starchy gel with üThe evolution of crumb firmness during storage was faster and the crumb very few granules remnants. was firmer in the case of MW baking compared to conventional baking Conclusions üMW produced a more homogenous heating with less baking time üIncreased crumb firmness üDisruption and Severe deformation of most starch granules üFurther tests should be considered with faster heating rates üOptimization of MW heating and Bread Recipe for industrial application

References The 54th Annual Microwave Power Symposium

[1] S. Chandrasekaran, S. Ramanathan, and T. Basak, Microwave food processing-A review, Food Res. Int., vol. 52, no 1, pp. 243–261, 2013