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Pyrrolizidine alkaloids
Alkaloids are natural plant products that contain a heterocyclic nitrogen atom, are basic in character and are sometimes toxic to animals when eaten (Holstege et al. 1995). Thebiological role of alkaloids in plants is largely unknown, but is thought to have evolved as a feeding deterrent (Ober and Hartmann 1999). Direct evidence of this protective role in the plants is rare, but it is well known that many insect herbivores have developed various adaptations, even utilizing alkaloids for defense against predators (Boppre 1990; Lindigkeit et al. 1997).
Pyrrolizidine alkaloids are mainly present in the families Boraginaceae (many genera), Asteraceae (tribes Senecioneae and Eupatorieae), Orchidaceae (nine genera) and Fabaceae (mainly the genus Crotalaria) (Dharmananda 2002). More than 95% of the PA containing plants investigated thus far belonged to these four families (Ober and Hartmann 1999).
Pyrrolizidine alkaloids are a major cause of livestock losses each year and can also enter the human food chain as contaminants of grain. Contamination of grain is particularly likely to occur in parts of the world with arid climates and poor rainfall, which promote the growth of PAcontaining plants, growing as weeds among cultivated crops. The first recorded instance of PA poisoning in humans was in 1920 in South Africa when many people in the Western Cape suffered from liver cirrhosis after eating bread made with wheat, probably contaminated with Senecio burchellii (Willmot and Robertson 1920). To date the largest reported outbreak of human intoxication by PAs was in Afghanistan in 1974 when an estimated 35 000 people were affected after grain was contaminated with Heliotropium plant material. Among 7 200 cases examined, 1 600 were affected and many died 3-9 months after the onset of clinical signs (Mohabbat et al. 1976).
Pyrrolizidine alkaloid contaminated animal products can also enter the human food chain and although these exposure incidences may not cause immediate toxic effects in humans, the effect of long-term, low-level, chronic exposure is still uncertain. The most frequently encountered source of residues is the milk of animals that have ingested PA-containing plants (Dickinson et al. 1976). Chickens can also transfer PAs to their eggs after eating contaminated grain (Edgar and Smith 2000) and honey has been found to contain high PA levels, up to 1 mg.kg-1, causing a risk to those who consume large amounts of honey (Deinzer et al. 1977). Pyrrolizidine alkaloid residues are, however, unlikely to be present in meat from animals ingesting plants containing PAs, since the compounds are rapidly cleared from the tissues and slaughter would have to occur within a few hours after grazing on contaminated pastures (Mattocks et al. 1988).
CHAPTER 1: LITERATURE REVIEW
1.1 Pyrrolizidine alkaloids
1.2 Absorption and biotransformation
1.3 Toxicity of pyrrolizidine alkaloids
1.4 Clinical signs and pathology of toxicosis in livestock
1.5 Crotalaria species (rattle pods)
1.6 Risks
1.7 Regulation criteria
1.8 Conclusion.
1.9 Aim and objectives .
1.10 Envisaged results .
CHAPTER 2: ANALYSIS OF PYRROLIZIDINE ALKALOIDS
2.1 Background
2.2 Sample preparation procedure
2.3 Analytical techniques
CHAPTER 3: LC-MS/MS SCREENING METHOD FOR THE DETECTION OF
TOXIC PYRROLIZIDINE ALKALOIDS.
3.1 Introduction
3.2 Method development
3.3 Results .
3.4 Discussion .
CHAPTER 4: STABILITY OF PYRROLIZIDINE ALKALOIDS DURING FOOD
PREPARATION.
4.1 Introduction .
4.2 Experimental procedure.
CHAPTER 5: OTHER ANALYTICAL METHODS .
5.1 Background
5.2 Ehrlich’s screening methods.
CHAPTER 6: ANALYSIS OF OTHER PLANTS CONTAINING PYRROLIZIDINE
ALKALOIDS
CHAPTER 7: GENERAL DISCUSSION AND RECOMMENDATIONS.
