Estudo da bebida do café utilizando a espectroscopia de lente térmica e a interferometria óptica

• Autor(a) principal: Sato, Francielle
• Data de Publicação: 2005
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Estadual de Maringá (RI-UEM)
• Texto Completo: http://repositorio.uem.br:8080/jspui/handle/1/2685
• topic: Espectroscopia óptica; Lente térmica; Interferometria óptica; Coeficiente Térmico da Refração; Condutividade térmica; Ciências Exatas e da Terra; Física

The aim of this work is to apply the thermal lens and the optical interferometry to study the thermal and optical properties of coffee as a function of temperature. The data will be explored in terms of using the techniques for the coffee adulteration and species classification purposes. pH measurements were also performed as complementary information. From the optical interferometry, the parameter dn/dT (coefficient of temperature of the refraction index, n) was measured as a function of temperature. From the thermal lens data we obtained the parameter q (describes TL signal amplitude) and tc (characteristic time for the TL formation) and then the coefficient K-1 (dn/dT)(T) and the thermal diffusivity, D(T), were determined. The measurements were performed as a function of temperature, in the range between 25ºC and 65ºC in pure cocamar coffee (blend with 85% of arabic coffee and 15% of robust coffee), arabic coffee and robust coffee. Commercial roasted corn meal was used as the adulterant by mixing it with cocamar coffee in several proportions. The samples were prepared in the american rostead standard, clearer color than that of Brazilian roasted coffee. The results showed that dn/dT (T) increased, in module, with the temperature. We performed a theoretical fitting with a linear finction fot the thermal lens TLS data, while an exponential treatment was used in the dn/dT values. We observed that the temperature dependence of the measured parameters did not allow the detection of the presence of corn meal in the coffee samples. On the other hand, both methods provide values for the measured parameters that could be used to differenciate two types of coffee. In summary, the use of TLS and the optical interferometry showed to be efficient to investigate coffee brew and may be promising methods to be used for foodstuffs certification.