Produce Degradation Pathways and Prevention

346 Produce Degradation: Reaction Pathways and their Prevention

as antagonists of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA),
thus causing hyperexcitation of the nervous system. GABA binds to the chloride
channel receptor, increasing the chloride ion permeability of neutrons, which has a
dampening effect on nerve impulse firing.
The environmental hazard associated with the use of certain persistent, bioac-
cumulative organochlorine pesticides, such as DDT (dichlorodiphenyltrichloroethane),
aldrin, or dieldrin, led to the cancellation of these pesticides for crop application
(DDT is still used as a mosquito vector control for the control of malaria in some
tropical countries). Some more biodegradable organochlorines (endosulfan and
methoxychlor) are still employed; however, there is a growing trend toward low-
persistent pesticides that are either naturally occurring compounds with insecticial
properties, such as abamectin or spinosad, or synthetic products derived from nat-
urally occurring insecticides (pyrethroids and neonicotinoids) [23,24].
Abamectin and spinosad are macrocyclic lactones isolated from soil microor-
ganisms Streptomycetes avermitilis and Saccharopolyspora spinosa, respectively.
Abamectin (avermectin) stimulates the release of GABA [25], thus causing paralysis,
whereas spinosad activates the nicotinic acetylcholine receptor, but at a different site
than neonicotinoids [5]. Subspecies of Bacillus thuringiensis represent another group
of relatively popular biopesticides (bacterial insecticides) [26]. At sporulation, this
Gram-positive bacterium forms crystals of protein delta-endotoxins, which cause
damage to the epithelial cells of the insect gut; insects stop feeding and eventually
starve to death [27].

TABLE 11.2
Major Chemical Classes of Insecticides

Chemical Class Mode of Action Representatives

Carbamate Cholinesterase inhibitors Aldicarb, carbaryl, carbofuran, fenoxycarb,
formetanate, methiocarb, methomyl, oxamyl,
pirimicarb, thiodicarb
Organochlorine Antagonists of the GABA
receptor-chloride
channel complex

Chlordane, dieldrin, endosulfan, endrin, heptachlor,

lindane, methoxychlor

Organophosphorus Cholinesterase inhibitors Acephate, azinphos-methyl, chlorpyrifos, diazinon,
dimethoate, disulfoton, malathion, methidathion,
naled, phorate, phosmet
Neonicotinoid Antagonists of the
postsynaptic
acetylcholine receptors

Acetamipirid, imidacloprid, thiamethoxam,

clothianidin, dinotefuran, nitenpyram

Pyrethroid Sodium channel
modulators

Bifenthrin, cyfluthrin, cyhalothrin-lambda,

cypermethrin, deltamethrin, esfenvalerate,

fenpropanthrin, permethrin

Source:Tomlin, C.D.S., Ed., The Pesticide Manual, 12th ed., British Crop Protection Council, Surrey,
UK, 2000.