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| Author(s): |
Bianca Cristine Marques
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Escola Politécnica (EP/BC) |
| Defense date: | 2023-07-10 |
| Examining board members: |
Carmen Cecilia Tadini;
Livia Chaguri e Carvalho;
Gabriela Alves Macedo;
Caciano Pelayo Zapata Noreña
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| Advisor: | Carmen Cecilia Tadini |
| Abstract | |
Yacón (Smallanthus sonchifolius) roots are used as alternatives in sugar-restrictive diets. Due to the presence of fructans, such as fructo-oligossacharides (FOS) and inulin, they taste sweet, but when consumed, results in a low glycemic index. There is evidence that, depending on the drying conditions, the FOS and inulin are hydrolyzed and converted into simple sugars. The motivation of this work was to study the processs of yacón drying, to identify the temperature and humidity distrobutions in the product, relevant factors for fructan hydrolysis. This objective was accomplished in three steps: pilot-scale drying, laboratory-scale drying, and simulation. In the literature, no works about yacón drying mentioning relative humidity (RH) control were found. In this pilot-scale work, this gap was filled. Data about the drying kinetics of yacón were obtained in four conditons: (50-60 °C; 20-30 % RH), with control and real-time registration of the drying air conditions and sample mass. Yacón slices underwent considerable shrinkage, that was measured during the process; at the end of the drying period, the slices had on average a fifth of the height and two thirds of the original radius. The drying kinetics was described using several models; applying the classic Lewis (1921) model, the initial drying rate parameter, k1, ranges from (1,37-1,75) s-1. On the laboratory-scale step, also with control of the drying air conditions and real-time sample mass recording, images of the yacón sample were obtained as projections. From this step, using macroscopic and microscopic (by environmental scanning electron microscopy) measurements, it was possible to conclude that the pore formation during drying is negligible. This information, along with drying kinetics and shrinkage data obtained during the pilot-scale step, was essential to develop the simulation. It was possible to estimate the temperature, moisture, water activity and water diffusivity spatial distributions along the drying period, and the simulation was able to satisfactorily predict the experimental average sample moisture content. It was observed that, despite the swift temperature uniformization, the moisture content in the center of the sample remains high unitl the end of the drying process, so it is necessary to closely monitor the final hours of the drying process. Finally, thermograms and sorption isotherms were obtained to describe the dried product, and the fructan content was measured; the latter ranged from (29.61-40.74)g fructans/ gram of dry matter. The best drying condition for fructan preservation was 60 °C and 30 % RH. The thermograms and vapor sorption isotherms were used to build a state diagram, which took a typical shape for carbohydrate-rich products. (AU) | |
| FAPESP's process: | 18/21327-1 - Mathematical modeling of convective drying of yacon slices (Smallanthus sonchifolius) |
| Grantee: | Bianca Cristine Marques |
| Support Opportunities: | Scholarships in Brazil - Doctorate |