The kinetics of acrylamide formation and browning of cookies will possibly allow definition of optimum baking temperatures and times at convectional and steam-assisted baking ovens. The kinetic model can be used by developing baking programs that can automatically control especially a new home-scale steam-assisted hybrid oven producing healthy products, for the use of domestic consumers.
As a novel product, yoghurt powder was produced by freeze drying and with added candied chestnut puree at ratios of 5, 10, and 20 % by weight. During the freeze drying process, mass loss, water activity, and the moisture content of the samples were determined and the colour (Hunter L, a, b) of the yoghurt powder products was measured. Results showed that increasing the percentage of candied chestnut puree resulted in an increase in water activity, moisture content, and colour change values of the end product. The drying behaviour, drying rate versus free moisture content, was also investigated. It was observed that yoghurt with or without added candied chestnut puree could be satisfactorily freezedried. Moreover, the performance of the dried product was observed in a ready-to-use, reconstituted form. For this purpose, the obtained powders were reconstituted to their original moisture contents. Shear stress and apparent viscosity against shear rate in a range of 1-1,000 (1/sec) was then measured by a Haake-Mars rotary viscometer. According to the results, the apparent viscosities of reconstituted products, as plain yoghurt and the one with an added 5 % chestnut puree were lower than that of fresh yoghurt. However, reconstituted yoghurts containing 10 % and 20 % chestnut puree had apparent viscosities higher than fresh yoghurt. Power Law explained well the rheological behaviour of reconstituted yoghurt samples for the applied shear rate range. Based on rheological data and sensory analysis, it was concluded that the freeze dried yoghurt containing 10 % (w/w) candied chestnut puree was an acceptable novel product.
Spinach was baked in steam-assisted hybrid ovens, natural and forced convection ovens, and saturated steam ovens at different temperatures and baking times. The moisture content, water activity, peroxidise activity, colour, ascorbic acid, and chlorophyll content were determined for each baking time and kinetic analysis of thermal degradation of the colour, chlorophyll, and ascorbic acid were evaluated. Degradation of green colour, total chlorophyll, and ascorbic acid in spinach leaves during the baking process was considered as first order reaction kinetics and temperature dependency of degradation was described by the Arrhenius equation. Baking in steam-assisted hybrid ovens resulted in the highest rate of reaction for both colour change and chlorophyll degradation, followed by forced convection and then natural convection ovens. The existence of steam in the baking chamber resulted in an acceleration of the baking process and better ascorbic acid retention in spinach was determined by baking in steam-assisted hybrid ovens. Degradation kinetics could allow definition of optimum baking temperatures and times in different types of ovens and shorter baking times should be preferred in steam-assisted hybrid ovens if fresh appearance (high greenness) is desired.
ARTICLE HISTORY
In this study, convective air drying was applied to tarhana dough using an electric pilot oven. A three‐stage drying process was recommended as a means of shortening the overall drying period. This consisted of the drying of one‐side of a thin layer of tarhana dough, a subsequent drying of the reverse‐side thin layer of tarhana dough, followed by that of flake drying, which is obtained after the flaking of the semi‐dried thin layers. The moisture transfer behavior of the thin layers of tarhana dough and flakes was determined by observing the moisture content and drying rate (kg moisture/m2/s) profiles at air temperatures of 60, 80 and 100C, until the equilibrium of the final moisture content. The moisture diffusivities for each stage were predicted by the analytical solution of Fick's second law of diffusion. At each drying temperature, considerably higher effective diffusivity values were obtained for flake drying (16.3–36.4 × 10−8 m2/s) as compared with thin layer dough drying (0.7–2.6 × 10−8 m2/s; p < 0.05). The convective drying of tarhana in three stages was then simulated by an implicit finite difference numerical solution using the predicted effective moisture diffusivity values as input. A suitable agreement between the numerical and experimental moisture profiles was achieved. The volatile compounds of tarhana powders and their concentrations were determined by headspace solid‐phase micro‐extraction. A sharp reduction in the concentration of specific volatile compounds with applied air temperatures, which are equal to and higher than 80C, was observed.
Practical Applications
Tarhana is a traditional Turkish fermented food and generally consumed as a dry soup mix. Tarhana soup is one of the selected traditional recipes from Turkey, a partner country for inclusion in the work package on “Traditional Foods” of a EuroFIR pilot study, funded under the EU 6th Framework Food Quality and Safety Programme. The drying of tarhana dough is one of the critical steps. In the traditional sun drying method for tarhana dough, a large amount of manual labor is required for homogenous drying. This study recommends mechanical stage‐by‐stage convective oven drying, which can be applied industrially instead of either sun drying or a continual static process. Also presented is the simulation of convective drying of tarhana dough by the implicit finite difference numerical solution, which is a numerical tool to predict the time‐moisture content of the tarhana dough during an industrial convective drying.
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