Solanine is a green-colored pigmented glycoalkaloid and acts as natural pesticide, also known as α-solanine (Fig. 12.2B). α-Solanine is naturally produced in the plants of the solanaceae family and other plants such as potatoes, tomatoes, apples, bell peppers, cherries, and sugar beets. It is found in high concentrations at areal and the green part of the plant but also is found in potato tubers at low concentration (Shibamoto and Bjeldanes, 1993). Synthesis of α-solanine in potato tubers is stimulated by sunlight exposure, mechanical injury, and tuber aging. High concentration of α-solanine is unsafe for human consumption (Dalvi and Bowie, 1983; Jones, 1995) as it leads to inhibition of acetylcholinesterase, cell membrane disruption. Manifestations include itchiness in the neck region, increased sensitivity called hyperesthesia, drowsiness, stomach pain, labored breathing, nausea, vomiting, and diarrhea (Shibamoto and Bjeldanes, 1993). A 1–5 mg/kg dose of α-solanine is highly toxic for humans, and 3–6 mg/kg doses leads to death (Tice, 1998).
Potato and Tomato
Solanine (8) from potato (Solanum tuberosum) and α-tomatine (9) from tomato (Solanum lycopersicum) are both steroidal saponins. They contribute to the protection of the plants against attack by phytopathogenic fungi. In vitro, both solanine and tomatine caused the disruption of model membranes, possibly by the insertion of the aglycone moiety into the lipid bilayer. Solanine is toxic and has fungicidal and pesticidal properties, and it is one of the plant’s natural defenses. It can occur naturally in any part of the plant, including the leaves, fruits, and tubers. Tomatine, which has fungicidal properties, is toxic and found in the stems and leaves of tomato plants. Some microbes produce an enzyme called tomatinase, which can degrade tomatine, rendering it ineffective as an antimicrobial.