Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

POSTHARVEST FACTORS AFFECTING POTATO QUALITY AND STORABILITY 407
synergistic mode of action between these two compounds for sprout suppression was reported
by Riggle and Schafer (1997) and Beaver et al. (2003). This approach led to reducing
the required concentration of CIPC to achieve effective sprout suppression in potato storages.
The study conducted by Beaver et al. (2003) showed a 50% reduction in CIPC levels
when applied at 1:1 ratio with DIPN with the same sprout-suppressant activity.
Multiple application of 1,4-DMN delayed the emergence in most of the cultivars studied
and also reduced tuber size and increased stem number. The effect and extent of increase
in tuber number and reduction in size depends on the cultivar (Knowles et al., 2005). Nolte
conducted a similar study with 1,4-DMN using a single application (P. Nolte, personal
communication). His results also showed delay in plant emergence, but did not find any
change in tuber size distribution.
19.5.8 Irradiation
High-energy irradiation to inhibit potato sprouts is in limited usage in a few countries like
Japan, the Netherlands, and Canada (Thomas, 1984). The widespread use of this technology
has been impeded by consumer acceptance to irradiated produce. Burton and Hannan
(1957) reported 50–100 Gy or even lower doses were highly effective in total sprout inhibition.
Exposing potato tubers to high-energy radiation causes an increase in starch solubility,
decrease in starch swelling power, and viscosity (Farkas et al., 1987, 1988). These changes
in starch are attributed to depolymerization of starch and modification of amylose and amylopectin
structure (Duparte and Rupnow, 1994). Al-Kahtani et al. (2000) conducted a similar
study using a Co60 gamma ray semicommercial irradiator at a dose rate of 900 rads/min
(0.05–0.20 kGy) on potato tubers. The study revealed changes in starch characteristics,
which are dependent on irradiation dose, timing, cultivar, and postirradiation conditions.
Frazer et al. (2006) reported successful sprout suppression with 40–50 Gy dosage using
an 18-MeV industrial-type linear accelerator on Russet Burbank. Sprout suppression was
observed for 6–8 months in storage at 7.2 ◦ C. Immediately after irradiation, glucose levels
were higher, but storing at a slightly high temperature for 2–6 months reduced the effect.
Tubers recovered quickly when irradiated with a higher dosage for a shorter time compared
a lower dosage for a longer time. Tubers treated with the higher dosage (100 Gy)
showed higher soft rot and dry rot incidence. This is attributed to the inhibition of the
wound periderm process (Thomas, 1982). Tuber lots with high disease susceptibility may
not be suitable for irradiation, and freshly harvested tubers tend to do better with irradiation
treatment.
19.5.9 Alternative sprout inhibitors
Essential oils, monoterpenes, and other volatile organic compounds extracted from plants
were tested to find alternative and more environment-friendly sprout inhibitors for their
effectiveness on sprout inhibition (Oosterhaven et al., 1995b; Sorce et al., 1997). These
alternative sprout suppressants are most effective when they are applied at “peeping,” or
before sprouts are one-eighth of inch long (Kleinkopf et al., 2003). These materials need
to be applied multiple times during storage to maintain tuber dormancy. Application timing
is critical for the success of sprout inhibition. Added advantages with these materials
are that they also suppress disease in storage (Farag, 1989; Thompson, 1989; Vokou,