Ultrasound-assisted drying of orange peel in atmospheric freeze-dryer and convective dryer operated at moderate temperature

This is an Author's Accepted Manuscript of an article published in Ronaldo E. Mello, Alessia Fontana, Antonio Mulet, Jefferson Luiz, G. Correa & Juan A. Cárcel (2020) Ultrasound-assisted drying of orange peel in atmospheric freeze-dryer and convective dryer operated at moderate temperature, Drying Technology, 38:1-2, 259-267, DOI: 10.1080/07373937.2019.1645685 [copyright Taylor & Francis], available online at: http://www.tandfonline.com/10.1080/07373937.2019.1645685[EN] Atmospheric freeze-drying (AFD) at -10 degrees C and moderate temperature convective drying (MTD) at 50 degrees C without and with ultrasound application (20.5 kW/m(3)) were carried out. Alcohol insoluble residue (AIR) and its swelling capacity (SC), water retention capacity (WRC) and fat retention capacity (FRC) were measured in the dried product. Ultrasound significantly shortened the drying time in both processes, the intensification effect being more significant in atmospheric freeze-drying (57% and 27% reduction in atmospheric freeze-drying and convective drying, respectively). As regards AIR and WRC, no effect was observed of either the drying temperature or ultrasound application. On the contrary, SC was significantly lower in AFD samples. The FRC of MTD samples was similar to that of the fresh ones and higher than the values obtained for atmospheric freeze-dried samples. Therefore, convective drying at moderate temperature preserved the AIR properties better than atmospheric freeze-drying.The authors acknowledge the financial support of INIA-ERDF through project RTA2015-00060-C04-02. We are also grateful for the economic support of the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior - Brasil (Capes)- Finance Code 001, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) and Fundacao de Amparo a Pesquisa de Minas Gerais (FAPEMIG).Mello, RE.; Fontana, A.; Mulet Pons, A.; Correa, J.; Carcel, JA. (2020). Ultrasound-assisted drying of orange peel in atmospheric freeze-dryer and convective dryer operated at moderate temperature. Drying Technology. 38(1-2):259-267. https://doi.org/10.1080/07373937.2019.1645685S259267381-2Freire, F. B., Atxutegi, A., Freire, F. B., Freire, J. T., Aguado, R., & Olazar, M. (2016). An adaptive lumped parameter cascade model for orange juice solid waste drying in spouted bed. Drying Technology, 35(5), 577-584. doi:10.1080/07373937.2016.1190937Tasirin, S. M., Puspasari, I., Sahalan, A. Z., Mokhtar, M., Ghani, M. K. A., & Yaakob, Z. (2014). 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A systems approach to model the relationship between aflatoxin gene cluster expression, environmental factors, growth and toxin production by Aspergillus flavus.

A microarray analysis was used to examine the effect of combinations of water activity (a(w), 0.995-0.90) and temperature (20-42°C) on the activation of aflatoxin biosynthetic genes (30 genes) in Aspergillus flavus grown on a conducive YES (20 g yeast extract, 150 g sucrose, 1 g MgSO(4)·7H(2)O) medium. The relative expression of 10 key genes (aflF, aflD, aflE, aflM, aflO, aflP, aflQ, aflX, aflR and aflS) in the biosynthetic pathway was examined in relation to different environmental factors and phenotypic aflatoxin B(1) (AFB(1)) production. These data, plus data on relative growth rates and AFB(1) production under different a(w) × temperature conditions were used to develop a mixed-growth-associated product formation model. The gene expression data were normalized and then used as a linear combination of the data for all 10 genes and combined with the physical model. This was used to relate gene expression to a(w) and temperature conditions to predict AFB(1) production. The relationship between the observed AFB(1) production provided a good linear regression fit to the predicted production based in the model. The model was then validated by examining datasets outside the model fitting conditions used (37°C, 40°C and different a(w) levels). The relationship between structural genes (aflD, aflM) in the biosynthetic pathway and the regulatory genes (aflS, aflJ) was examined in relation to a(w) and temperature by developing ternary diagrams of relative expression. These findings are important in developing a more integrated systems approach by combining gene expression, ecophysiological influences and growth data to predict mycotoxin production. This could help in developing a more targeted approach to develop prevention strategies to control such carcinogenic natural metabolites that are prevalent in many staple food products. The model could also be used to predict the impact of climate change on toxin production