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DOCTORAL THESIS Effect of ultraviolet/visible radiation processing on the quality of fruit juices Karla Aguilar Lara Dissertation presented to fulfil the requirements to obtain the degree of Doctor by The University of Lleida Doctoral Program of Agricultural and Food Science and Technology Directors Albert Ibarz Ribas Alfonso Garvín Arnés 2017 II A los mexicanos que trabajan por una vida mejor III IV ¿En perseguirme, mundo, qué interesas? ¿En qué te ofendo, cuando sólo intento poner bellezas en mi entendimiento y no mi entendimiento en las bellezas? Sor Juana Inés de la Cruz V VI This thesis was undertaken in the Department of Food Technology of the Technical Superior School of Agricultural Engineering at the University of Lleida (Lleida, Catalonia, Spain). The research was funded by the Ministry of Science and Innovation of the Spanish Government in the CTQ2011-26569 project. Part of the research was performed with the Group of Studies on Processing and Engineering (Ge2P) in the Department of Agrifood Industry, Food and Nutrition (LAN) of the Luiz de Queiroz College of Agriculture (ESALQ) at the University of São Paulo (USP, Brazil). This piece of work was part of project no.º 2014/16998-3, funded by the São Paulo Research Foundation (FAPESP, Brazil), and project no.° 401004/2014-7, funded by The National Council for Scientific and Technological Development (CNPq, Brazil). My doctoral studies were sponsored by the National Council of Science and Technology of the Mexican Government (CONACyT, Mexico) by means of a fellowship for post-graduate foreign studies. The stay at the University of São Paulo was supported by the Research Vice-chancellor’s Office of the University of Lleida. Finally, this thesis has received a grant for its linguistic revision from the Language Institute of the University of Lleida (2017 call). VII VIII SUMMARY Fresh fruit juices are nutritious refreshing beverages. For commercialization, they need to be submitted to a process to inactivate microorganisms and enzymes. Thermal pasteurization, commonly used for this purpose, alters the organoleptic and nutritional quality of food. Besides, it does not eliminate mycotoxins and induces the formation of the potentially toxic 5-hydroxymethylfurfural (HMF). Ultraviolet irradiation is an alternative for fruit juice pasteurization due to its effectiveness at inactivating microorganisms and enzymes as well as destroying mycotoxins. This work studied the effect of ultraviolet-visible (UV-Vis) irradiation processing on the quality attributes of clarified fruit juices. The results showed that UV irradiation does not produce HMF and is capable of degrading it. A three-stage mechanism related to the radiation absorbed by the liquid sample was proposed to describe the photo-degradation of this compound. From this mechanism, three kinetic models were developed to describe this process: first-order, zero-order and/or pseudo-first-order. The fitness to the model depended on the initial concentration of HMF. On applying the kinetic and thermodynamic compensation theory, it was concluded that the HMF photo-degradation process is entropically controlled and can be speeded up by changing non-thermal parameters such as agitation. On the contrary, when a multi-wavelenght emission lamp was used, the photo-degradation of L-ascorbic acid was insignificant. After the UV-Vis treatments, most of the physicochemical parameters of the fruit juices were practically unaltered. The enzymes polyphenoloxidase and peroxidase were totally or partially inactivated, the higher the temperature the higher the inactivation. To sum up, UV-Vis processing combined with mild-heating for fruit juice pasteurization is an alternative to traditional methods, since it is effective inactivating enzymes, preserves quality attributes of the product and does not produce HMF. 1
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