Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

POSTHARVEST FACTORS AFFECTING POTATO QUALITY AND STORABILITY 393
potassium and 6% of iron recommended dietary allowance. Iron in a potato is more readily
available because of high vitamin C (45%) and low in oxalates. Potatoes are also a good
source of trace amounts of thiamin, riboflavin, folate, magnesium, phosphorous, iron, and
zinc with natural fiber in the skins. A 6-oz potato can give 3 g of highly digestible, lysinerich
protein. Contrary to the popular notion that potatoes are fattening, a 6-oz potato offers
less than 10% of the daily value of carbohydrates and complex carbohydrates, which are
a great source of energy. Potatoes have also one of the highest overall antioxidant activity
among vegetables (National Potato Council, 2006–2007).
The primary demand of the fresh market and the processing industries is to get highquality
potatoes over the long-storage periods. The chemical composition of the potato
is very important, not only for storage but also for processing and consumption. Storage
conditions vary significantly depending on which type of industry the potatoes are
intended. Storage regimes play a significant role in tuber carbohydrate metabolism and
thereby significantly affect the value of the potatoes depending on their intended use. Dry
matter content, sugars, proteins, and the nitrogen compounds in tubers are important for the
potato-processing industry. Potatoes contain a relatively low dry matter content that renders
them perishable and sensitive to high and low temperatures during storage. The main issues
in potato storage are to minimize sprouting, respiration, dehydration, and disease. Losses
due to the above-mentioned factors can be minimized by designing storages with adequate
ventilation, humidification, and temperature control. The important aspects for long-term
storage are bringing down temperature in a timely systematic manner once tubers are harvested
while allowing sufficient time for wound healing and proper temperature control
during the holding period.
The three primary potato markets are processing, fresh market, and the certified seed
industry. In the United States the processing industry consumes 63% of production, followed
by the fresh market at 31%, and the certified seed industry at 6% (National Potato
Council, 2006–2007). There is an increasing demand for better quality produce and improved
postharvest handling practices. These measures can assist in satisfying some of
these demands, as well as providing a greater window of time for marketing produce. The
goal of this chapter is to bring together recent advances that have been made in understanding
key concepts of tuber postharvest physiology and how that information is applicable
in managing the crop in storage. Tuber dormancy, sprouting, and wound healing are very
important processes that influence postharvest storage conditions. Recent developments in
the above-mentioned processes at biochemical and molecular levels are discussed in the following
pages. Current knowledge on cold-induced sweetening (CIS) and the role of sprout
inhibitors on tuber quality are also discussed.
19.2 Wound healing/curing
The typical injuries associated with mechanical harvesting operations include cuts, bruising,
and periderm loss. Potato tuber sensitivity to mechanical damage and the factors that control
this process is well understood. Most of these damages can be reduced by changing harvester
settings, avoiding harvest during cold weather (below 10 ◦ C), and allowing sufficient time
between defoliation and harvest for skin set to occur. Vine killing (desiccation) is the
standard method for promoting proper skin set and periderm maturation, which reduces
skinning and bruising during harvest operations.