Table of Contents
Sullivan, G.H., L.R. Davenport, and J.W. Julian. 1996.
Precooling: Key factor for assuring quality in new fresh market vegetable
crops. p. 521-524. In: J. Janick (ed.), Progress in new crops. ASHS Press,
Precooling: Key Factor for Assuring Quality in New Fresh Market Vegetable Crops*
Glenn H. Sullivan, Lonni R. Davenport, and James W. Julian
- VALUE-ADDED MARKETING CHAIN
- PRECOOLING TECHNOLOGIES
- COMMERCIAL MARKET SUCCESS
- Table 1
- Fig. 1
Total domestic and export sales of fresh fruits and vegetables produced in the
United States reached $65 billion in 1994-95. Marketplace demands for greater
selection and consistent high quality, combined with consumers' rising
nutritional expectations, have placed increasingly greater performance
pressures on all segments the fresh produce marketing chain (How 1991).
Producer success in the marketplace for fresh fruits and vegetables is highly
correlated with maintaining postharvest quality and shelf-life consistent with
current consumer demands (Sullivan et al. 1991). Precooling technologies that
quickly remove the field heat and reduce internal respiratory processes were
found to be critical in meeting these consumer demands for high quality fresh
produce (USDA/ARS 1986). Forced-air and hydrocooling have been found to be the
most efficient and economical in enhancing product quality for new muskmelon
cultivars and sucrose enhanced bi-color sweet corn. Shelf-life was extended 7
to 14 days, and desired quality characteristics were maintained at near optimum
In the past, the principal market for most fresh produce has been the
traditional family. Today this traditional family unit accounts for only about
13% of all households in the United States. Individuals living alone now
comprise almost 24% of all households, and single parent families account for
nearly 22% of all households with children under 18 years of age. Today 40% of
all shopping is done by men! Point of purchase selections in the fresh produce
departments of retail grocery outlets increased from an average of 67 in 1985
to over 312 in 1995 (Hammel 1995). These trends signal major changes in the
way consumers spend their incomes, and how they make their purchases.
Retail supermarkets are still the principal point of purchase for most fresh
produce consumers, accounting for over two-thirds of all domestic sales (Fig. 1). But how that produce gets to the point of retail purchase has changed
dramatically over the last few decades. Currently, almost 40% of all fresh
produce sold through retail supermarkets comes directly from first-handlers in
the major producing regions (grower-shippers, independent shippers, and
value-added processors) through the retailers' own integrated wholesale
distribution facilities (VanSickle 1985). Historically, central terminal
markets in the major cities throughout the United States were the dominant
assembly points for fresh produce. Today, only about 25% of the volume sold at
retail comes through market wholesale institutions who buy fresh produce both
from the terminal markets and shipping point markets (Hammel 1995). This shift
in the way retail supermarkets source their fresh produce has resulted from the
need to achieve greater control over the postharvest handling functions, and
thereby better meet the changing consumer demands for higher quality and longer
shelf-life at a competitive price. These trends place increasing pressure on
the marketing chain to adopt postharvest technologies that help assure greater
quality control (Sullivan et al. 1991).
When it comes to produce quality, every minute counts. Research confirms that
lowering the respiration rate of fresh vegetables is essential to preserving
market quality. The most important technology for lowering respiration rates
remains proper precooling of produce within hours of harvest (Jones 1996).
Proper precooling preserves product quality by: (1) inhibiting the growth of
decay producing microorganisms, (2) restricting enzymatic and respiratory
activity, (3) inhibiting water loss, and (4) reducing ethylene production
(Hardenburg et al. 1986).
The most efficient methods of postharvest cooling fresh produce were found to
include forced-air cooling, hydrocooling, and vacuum cooling (Table 1) (Junge
et al. 1986). In new muskmelon cultivars and sucrose enhanced bi-color sweet
corn, forced-air cooling and hydrocooling respectively proved to be the most
effective and economical, preserving optimum quality and increasing market life
7 to 14 days depending on the product. Muskmelon cultivars were preserved at
the highest levels of market quality when the internal pulp temperatures
(average 95°F/35°C) were reduced to 42°F/5.5°C within 4 h of
harvest using forced-air cooling technologies. Sweet corn quality was
preserved at optimum levels when harvested at field temperatures below
75°F/24°C and cooled to 32°F/0°>C pulp temperatures using
hydrocooling technologies (Sullivan and Davenport 1995).
Research that focused on the market factors influencing commercial success
clearly indicated that vegetable producers must increasingly commit themselves
to meeting the consumers' demand for higher produce quality. Retail buyers in
today's competitive marketplace are increasing their purchases through
direct-from-shipping point deliveries, but only from grower-shippers who
provide the value-added services demanded by increasingly more sophisticated
consumers (Sullivan and Davenport 1991). Product precooling was found to rank
as the most essential of these value-added marketing services.
Given current consumer lifestyles and demand for variety selection in the
produce section of retail supermarkets, new vegetable cultivars represent a
unique opportunity for grower entry into the marketplace. However, research
findings clearly confirm that maintaining an economically viable market
position at retail requires new crop producers to focus increasingly greater
attention on the product quality demands of an increasingly more dietary
diverse consumer population. Precooling is among the most cost-effective and
efficient quality enhancements available to commercial new crop producers.
- Hammel, F. 1995. Produce. Supermarket Business 50(9):87+.
- Hardenburg, R.E., et al. 1986. The commercial storage of fruits, vegetables and
florist and nursery stocks. USDA/ARS, Agr. Handbook 66.
- How, R.B. 1991. Marketing fresh fruits and vegetables. VanNostrand Reinhold
Publ., New York.
- Jones, S. 1996. When time is of the essence. Progressive Grocer 75(2):105.
- Junge, K., M. Weimar, D. Blanton, M. Hayenga, and R. Gladon. 1986. Precooling
methods for commercial vegetable producers, Dept. of Econ. & Hort., Iowa
State Univ., Paper No. 160.
- Sullivan, G.H., et al. 1991. Economic and market feasibility for fruit and
vegetable industry expansion in Southwest Indiana. USDA/VACDC Study Report.
- Sullivan, G.H. and L.R. Davenport. 1991. Fresh vegetable marketing
opportunities in Indiana. Purdue Univ. AES, SB-624.
- Sullivan, G.H. and L.R. Davenport. 1995. Sweet corn: Marketing and postharvest
handling. Purdue Univ. Bul. 707.
- VanSickle, J.J. 1985. Marketing--a requirement for profit with fresh produce.
Univ. of FL, Food & Res. Econ., Staff paper 273.
- USDA, Agricultural Research Service. 1986. The commercial storage of fruits,
vegetables, and florist and nursery stock. Agr. Handb. No. 66.
*Journal Paper No. 15010 Purdue Univ. Agr. Expt. St., West Lafayette, IN
47907-1165. This research was supported in part by grants from the Indiana
Business Modernization and Technology Corporation, Indianapolis, Indiana.
Table 1. Postharvest cooling methods and suitable commodities.
|Cooling method ||Commodities ||Comments|
|Hydrocooling ||Most leafy vegetables, fruits and fruit-type vegetables, sweet corn, snap beans ||Very fast cooling; uniform cooling in bulk if properly used, but may vary extensively in packed shipping containers; daily cleaning and sanitation measures essential; product must tolerate wetting; need water-tolerant shipping containers|
|Forced-air cooling (pressure cooling) ||Most fruits, berries, fruit-type vegetables, tubers, and vegetables not susceptible to chilling injury ||Much faster than room cooling; cooling rates very uniform if properly used. Container venting and stacking requirements are critical to effective cooling. Economical and efficient.|
|Package-icing ||Most vegetables ||Fast cooling; limited to commodities that can tolerate water-ice contact; water-tolerant shipping containers are essential. Economical and efficient.|
|Room cooling ||All commodities ||Too slow for many perishable commodities. Cooling rates vary extensively within loads, pallets, and containers.|
|Vacuum cooling ||Leafy vegetables, iceberg lettuce ||Commodities must have a favorable surface-to-mass ratio for effective cooling. Causes about 1% weight loss for each 6°C cooled. A procedure that adds water during cooling prevents this weight loss, but equipment is more expensive, and water-tolerant shipping containers are needed.|
|Mechanical refrigeration ||All commodities ||Cooling in most available equipment is too slow and variable; generally not effective for field heat removal.|
|Top-icing and channel-icing ||Most vegetables ||Slow and irregular, top-ice weight reduced net pay load; water-tolerant shipping containers needed.|
Fig. 1. United States fresh produce marketing system.
Last update August 24, 1997