Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

POSTHARVEST FACTORS AFFECTING POTATO QUALITY AND STORABILITY 405
19.5.4 Potato sprout inhibitors
Physiological dormancy of the potato tuber is further extended with an artificial environment
consisting of lowered temperature, high relative humidity, adequate oxygen, and by
application of chemical sprout inhibitors. The purpose of sprout inhibitors is to prevent
sprouting in storage as tubers age. Sprout inhibitors work by inhibiting cell division within
the eye region; therefore, they should never be applied to seed potatoes. Ideally, seed storage
should be in separate units with independent air systems; if this is not possible, then care
needs to be taken to avoid drift or movement of sprout inhibitors into areas where seed
potatoes are present. Sprouting causes reduction in the quality of the tuber. This leads to
weight loss due to water loss and disease due to reduced air circulation (Afek et al., 2000).
The more widely used sprout inhibitors are maleic hydrazide and chlorpropham (isopropyl
N-(3-chlorophenyl)carbamate) (CIPC). Substituted naphthalenes are also used as
short-term sprout suppressants on seed. Due to recent Environmental Protection Agency
(EPA) standards and more awareness regarding these chemical suppressants, alternatives
have been explored. Natural compounds, such as carvone and clove oil, have shown effectiveness
in sprout suppression. Ethylene is also gaining popularity as a sprout suppressant
in Europe and Canada for obvious health reasons, but it is also associated with darkening
in french fry color.
19.5.5 CIPC
CIPC is applied as an aerosol by a trained technician for treating potatoes in storage. CIPC
may also be applied as an emulsifiable concentrate on potatoes coming out of storage as they
are packed. It is a potent inhibitor of cell division specifically interrupting spindle formation
during mitosis (Vaughn and Lehnen, 1991). It is advisable to enter treated bins only after 10
complete air exchanges. CIPC application is common after natural tuber dormancy ends and
before sprouting starts. This is typically 75–120 days after harvest depending on cultivar.
CIPC can be effective up to a year after treatment. This irreversible sprout inhibitor is
mostly used on tubers intended for fresh market and the processing industry. Seed potatoes
should not be stored in the same room where CIPC was recently used. CIPC-treated storage
rooms should be cleared thoroughly including the air systems and ducts before storing seed
potatoes. Treated tubers should be held at least 30 days in storage before marketing. The
allowable residue levels of CIPC on tubers is 30 ppm per fresh weight in the United States
(EPA), and this product has been successful for more than 40 years as a sprout inhibitor
(Kleinkopf et al., 2003). In Europe, Australia, and Canada, maximum allowable limit for
CIPC residue is 5–10 ppm per fresh weight. This requires multiple applications for longterm
storage (Kleinkopf et al., 2003). Effective sprout inhibition with CIPC can be achieved
at 1–2 ppm concentration (Kleinkopf et al., 1997). Single CIPC application under ideal
storage conditions maintains tubers for 4–5 months, while a second application is needed
to extend sprout inhibition beyond 8 months (Kleinkopf et al., 2003). The sprout inhibition
response to CIPC application depends on storage temperature, cultivar, and other stress
factors during the growing season (Brandt et al., 2003). Generally, at lower temperatures,
tubers store longer with CIPC application. Even with processing cultivars such as Russet
Burbank that are stored at 10 ◦ C can maintain quality into late April (Kleinkopf et al.,
2003).