Caracterización fisicoquímica y funcional de productos en polvo obtenidos a partir de subproductos de brassicas. efecto de la desestructuración y el secado sobre el contenido en glucosinolatos e isotiocianatos

Abstract

[ES] El cultivo de frutas y hortalizas destinadas a uso industrial genera una gran cantidad de residuos agroindustriales que deben ser gestionados adecuademente, lo que supone un coste para la industria. En general, se trata de residuos ricos en compuestos bioactivos que de ser recuperados y reintroducidos en la cadena productiva, contribuirían al desarrollo de procesos más sostenibles. Del mismo modo, un mejor aprovechamiento de las características nutricionales que ofrecen estos residuos y descartes contribuiría al concepto de dietas sostenibles y saludables definido por la OMS. Los glucosinolatos conforman una familia de compuestos secundarios que pueden encontrarse comúnmente en Crucíferas. Se trata de tioésteres aniónicos de azúcar que están involucrados en la respuesta al estrés biótico. Estos compuestos están sujetos a la actividad hidrolítica del enzima mirosinasa, producida de forma natural como respuesta al daño en tejidos y células, la cual promueve la formación de compuestos como los isotiocianatos sulfuranos a partir de la hidrólisis de los glucosinolatos. Los productos de la hidrólisis resultan en compuestos biológicamente activos y que presentan propiedades de interés por su carácter antimicrobiano, antioxidante y anticancerígeno. Además de sus beneficios para la salud, el carácter antimicrobiano y antifúngico de estos compuestos ha impulsado su aplicación frente al control de plagas (hongos, insectos, arvenses¿). El objetivo del presente trabajo fin de grado es estudiar la influencia del procesado (desestructuración y secado) sobre la conversión de glucosinolatos a isotiocianatos en productos en polvo obtenidos a partir de residuos de col y de brócoli. A tal fin, se obtendrán polvos de tallo de brócoli y hojas externas de col blanca, mediante un proceso que combina una etapa de troceado o triturado y otra de secado por aire caliente (50, 60 ó 70 °C) o liofilización. El contenido en isotiocianatos se determinará por cromatografía líquida de alta resolución (HPLC), tanto en el residuo fresco como en los polvos obtenidos. Adicionalmente, los polvos se caracterizarán fisicoquímicamente en términos de humedad, actividad del agua, contenido en sólidos solubles, tamaño de partícula y propiedades antioxidantes. Como resultado del presente trabajo, se pretende obtener información relevante para poder valorar el empleo de los polvos obtenidos para su uso como plaguicida natural o bien como ingrediente funcional que pueda ser utilizado en la formulación de alimentos.

[EN] The processing of fruit and vegetables generates a large amount of agro-industrial waste rich in bioactive compounds that may be of interest, so their valorisation, aimed at taking advantage of the characteristics they offer, would both improve the management of this waste and add value to the production process. Glucosinolates are a family of secondary compounds involved in the response to biotic stress, commonly found in Cruciferae. These compounds are subject to the hydrolytic activity of the enzyme myrosinase, naturally produced in response to tissue and cell damage, which promotes the hydrolysis of glucosinolates to isothiocyanates. These hydrolysis products are of great interest to human health because of their antioxidant and anticarcinogenic character. Furthermore, the antimicrobial and antifungal nature of these compounds has led to the study of their use in the control of pests (fungi, insects, weeds, etc.). The aim of this final degree project was to develop the process of obtaining powdered products from cabbage (outer leaves) and broccoli (stems) cooperative confectionery waste, and to study the influence of processing (destructuring, dehydration and milling) and the levels of the variables used (intensity of destructuring, drying conditions) on the physicochemical and antioxidant properties of the powders obtained, with special attention to the effect of processing on the conversion of glucosinolates to isothiocyanates. Drying times and temperatures were defined after a first approximation by obtaining the drying and drying rate curves for both residues, for all the set process conditions. Once the drying times were defined, the powdered products were obtained by processes combining a chopping or grinding stage and a hot air drying (50, 60 or 70 °C) or freeze-drying stage, followed by a final grinding to obtain a fine powder. The powders obtained were physicochemically characterised in terms of moisture, water activity, soluble solids content and antioxidant properties (total phenols and flavonoids, antioxidant capacity by DPPH and ABTS methods). During the development of this TFG, the protocol for the determination of isothiocyanate content by high performance liquid chromatography (HPLC) was developed. The isothiocyanate content of products and fresh product was determined in hydrolysed and non-hydrolysed samples. The results showed that the processing of the powders resulted in a reduction in sulforaphane content, attributable to both a possible loss of myrosinase activity during processing and the degradation of sulforaphane during processing. The powders with the best characteristics with respect to this bioactive compound were those obtained by hot air drying at 70 °C or freezedrying. On the other hand, the antioxidant properties were favoured by drying at higher temperatures, with the residues dried at 70 ºC standing out. Regarding the effect of previous destructuring, the previously chopped products showed better antioxidant properties, due to less exposure to drying conditions and less damage caused to the tissue. In general, the products obtained from broccoli showed better characteristics, especially in terms of isothiocyanate content, than the cabbage products. The results of the present work have made it possible to establish the process conditions necessary to obtain stable powdered products from cabbage and broccoli confectionery waste. The powders obtained could be proposed for various uses, including their use as a functional ingredient to be incorporated into foodstuffs, or their use to control the development of weeds.