Potato Steroidal Glycoalkaloids: Biosynthesis and Genetic Manipulation

Abstract

The potato steroidal glycoalkaloids (SGAs) are important components of plant resistance against pests and pathogens but can be toxic to humans at high levels. SGAs derive their toxicity from anticholinesterase activity affecting the central nervous system and the disruptive effects on cell membrane integrity affecting the digestive system and other organs. Accordingly, current safety regulations limit their content in the edible tuber to 20 mg per 100 g fresh weight. SGA composition and level are genetically determined, with unfavourable growth conditions and inappropriate postharvest management inducing the accumulation of SGAs at levels in the tubers of "safe" cultivars beyond the maximum level set by the industry. Hence, genetic alteration of potato to prevent toxic levels of SGAs in tubers is highly desirable. At the same time, maintaining high SGA levels in other plant organs will contribute to plant resistance against pathogen and pest attacks. To this end, SGA biosynthesis and degradation should be manipulated precisely to exploit tissue-specific expression rather than whole-plant suppression of SGA production, to produce potato cultivars with SGA content enriched in the foliage but diminished in the edible tubers. Only a few details are known about the SGA biosynthetic pathway, its genes and intermediates. Research on factors that regulate SGA biosynthesis and catabolism as well as searches for genetic markers linked to total and specific SGA levels have only recently been pursued. The present review summarizes current data on these issues to encourage further discussion on SGA manipulation for safer food products.

Two Cytochrome P450 Monooxygenases Catalyze Early Hydroxylation Steps in the Potato Steroid Glycoalkaloid Biosynthetic Pathway

“…The results are coincident with that of GAME4-knockdown transgenic potato (Itkin et al, 2013;Umemoto and Sasaki, 2013) and those of SSR2-knockdown and SSR2-disrupted potatoes (Sawai et al, 2014). Characterization of the inheritance of specific SGAs and SGA content has been limited, despite the importance of these phytochemicals (Valkonen et al, 1996;Ginzberg et al, 2009;Manrique-Carpintero et al, 2014). The SGA content of most commercial varieties of potato tubers is well below the human safety limit (200 mg/kg fresh weight), and a high SGA content is frequently associated with the introduction of wild germplasm to the breeding program (Sinden et al, 1984).…”

“…SGAs can be found in most potato plant tissues and are abundant in flowers and tuber sprouts Mizuno, 1985, 1989;Ginzberg et al, 2009). We chose two candidate CYP genes that were most expressed in flowers and tuber sprouts from the potato unigene databases of the Gene Index project (ftp://occams.dfci.harvard.edu/pub/bio/tgi/data/).…”

“…Potato steroidal glycoalkaloids (SGAs) are abundant poisons in tuber sprouts and green tubers and are described as bitter tasting, burning, scratchy, or acrid (Friedman, 2006;Ginzberg et al, 2009;Taylor et al, 2007). SGAs in the tuber are induced by exposure to light, low temperature, and mechanical injury (Valkonen et al, 1996).…”

Efecto del Tiempo de Almacenamiento sobre las Propiedades Fisicoquímicas, Probióticas y Antioxidantes de Yogurt Saborizado con Mortiño (Vaccinium meridionale Sw)

“…Varias estudios han hallado un incremento en el contenido fenólico con el consecuente aumento de la actividades antioxidante de alimentos nutracéuticos almacenados, algunas de las explicaciones al respecto, se presentan a continuación: 1) efecto relacionado con una mayor producción de azúcares reductores durante el almacenamiento a lo que se refieren como "edulcorante en almacenamiento", y que son estos utilizados como sustratos para la síntesis de compuestos polifenólicos futuros aumentó en la actividad fenil alanina monoliasa, que se traduce en un incremento en la concentración de compuestos polifenólicos libres, junto con el bajo nivel de actividad polifenoloxidasa que pueden reducir la oxidación de sustratos fenólicos a quinonas. Incremento de los compuestos polifenólicos y otros componentes bioactivos en respuesta al estrés provocado durante el almacenamiento, se cree que las muestras vegetales comienzan la producción de glicoalcaloides y fenoles (Ginzberg et al, 2009) algunos ácidos fenólicos como el p-coumárico y felúrico durante el almacenamiento, pueden ser liberados de su forma enlazada o esterificada, gracias a la variación en el pH a causa de la acción bioquímica y microbiológica (Ginzberg et al, 2009). …”

Potential Food Safety Concerns in Fried Potato Products in Kenya

“…Injuries during harvesting and poor post-harvest handling practices such as exposing potato tubers to sunlight increase the levels of glykoalkaloids with high concentration in the skin [27]. It is generally agreed that the best raw potato for processing should not have more than 20 mg total glycoalkaloids (TGA) in 100 g of tuber [28]. Higher levels beyond 100 mg/kg are potentially dangerous; some countries have even set the upper limit to be 10 mg/100 g sample [29].…”