What happens to a fruit or vegetable after harvest?

It was the summer of ’77. I arrived in Massachusetts from Florida. My mission was to learn about the life of a tomato after detachment from its mother plant. Since tomatoes are difficult to find year-round, my model fruit would be the banana. We could find green bananas year-round including the cold New England winters. But, then, as fate would have it, there was a change in plans. Soon after my arrival in Amherst, my major professor called me into his office. He informed me of his move to the coast. His research direction had changed from fresh fruits and vegetables to fish. He told me that when we get down to the cellular level, it was all about biochemistry and cell physiology. He gave me the option to stay in the department and pursue the banana/tomato connection. OR I could follow him to Gloucester to work with flounder. I opted to follow my mentor to the coast.

tee shirt of the University of Massachusetts Marine Station
Studying lipid oxidation of flounder muscle microsomes for my PhD

Before I could go to the coast, there was the matter of courses. Each MWF that Fall I sat in Dr. Bramlage’s Postharvest Physiology class. I learned answers to the question posed in this post’s title. It was love at first sight. I wanted to be a postharvest physiologist. My mission became studying the mysteries of detached fruits and vegetables. For years I butchered live flounder to study the physiology of their cell membranes. Upon graduation I returned to the sunny South. My research turned back to fruits and vegetables. My favorite field of study, postharvest physiology, became my career. I took a research position at the University of Georgia Experiment Station. My research studied both applied and basic changes in detached plant parts. I started following southern peas and turnip greens from field to processing plant. As part of a research team, we turned our efforts into work with fresh peaches, tomatoes and bell peppers.

It takes a lot of chutzpah to review a book that I co-edited. My goal here is not to sell books. My goal is to describe how fresh fruits and vegetables travel from farm to market. The journey is very different from the one facing processed products. My research focused on fresh foods; my teaching emphasized processed products. I hope you will appreciate important differences between the two.

This year we published the fourth edition of Postharvest Handling: A Systems Approach. The 700+ pages encapsulate what happens to these plant parts as they travel from the field to market. That trip may be to a nearby town or across the world. It is ironic that a defender of processed foods conducted his research on fresh foods. Here are some important messages found in the book:

Fresh fruits and vegetables are alive. Life processes do not stop when the organ separates from the mother plant. Harvested fruits and vegetables continue to respire, the plant form of breathing (1). Metabolic activity proceeds but without nourishment from the plant. These detached, living organisms must rely on their own nutrients to thrive. Some fruits continue to ripen after harvest (2). Flavor, color, and texture are transitory characteristics. To reach their flavor (3) and nutritional (4) peaks depends upon maturity at detachment. The closer a fruit is to peak quality at harvest, the shorter its shelf life. Over-ripe flavors result from an over-accumulation of desirable flavor compounds. 

Vegetables and many fruits do not ripen after harvest. Chemical reactions continue. Some vegetables, like snow peas, reach peak tenderness at an early stage of maturity. Even fresh-cut items maintain the chemical reactions of life (5). We preserve processed foods by physical or chemical means. Processing preserves foods by stopping metabolic reactions. Fresh fruits and vegetables face many challenges during handling and storage (3).

These living organs are also dying as they undergo senescence or programmed death (6, 7). Senescence is a slow process for some items and faster for others. They are also vulnerable to decay by bacteria and molds. Resistance to decay comes from the integrity of the outer layer and a lower moisture content. Protection from rapid deterioration comes from refrigeration and manipulation of atmospheric gases. We also use appropriate humidity and packaging (5, 8, 9, 10). Too low a storage temperature can lead to damage in susceptible fruits or vegetables (8).

Fresh produce travels in value chains instead of supply chains (11). A can of beans is stable and doesn’t need special attention in the supply chain (12). Perishable foods, including detached, plant parts, receive that special attention (13, 14). The faster they respire, the faster they spoil. Slowing respiration is a strategy to keep these living organs fresh longer. Refrigeration lowers respiration. Controlling the atmosphere during storage lowers respiration (15). Fruits that ripen after harvest, like peaches, generate ethylene, a gaseous ripening hormone. Some vegetables like lettuce discolor when exposed to ethylene. Keeping generators of the gas from sensitive items extends shelf life (2, 3, 4, 5).

picture of a peach on a tee shirt
A Georgia peach

Value chains start with understanding the requirements of the consumer. We then study all the steps as we work back to the grower (11, 16). What actions do we need to take at each step in the chain to deliver the quality needed to make a sale? Today’s consumers have become more discerning in their decisions. Many perishable foods proceed through value chains. Shipping fresh fruits and vegetables for long distances requires a value chain. These items must arrive at the market in desirable condition. Most of us select fresh items on the basis of appearance and odor. Also important are credence characteristics such as organic, non-GMO, and health-related properties (17). Other credence attributes include fair trade and sustainable practices (11). At home, consumers judge quality while eating. Consumption characteristics include keeping quality, flavor, and texture (3, 6, 11).

There is no food system, only a maze of overlapping chains. Two of the editors have a different view of food systems. Nigel Banks introduces us to open and closed systems in the first chapter of the book. Postharvest systems are open. External forces disrupt normal flow of fruits and vegetables in the chain. He guides us through the path fruits, vegetables, and postharvesters face along the way (12).

Stan Prussia brought a systems approach to the handling of fresh produce. He begs to differ with Nigel’s vision. Management and control are necessary for a system. We started applying a systems approach to commercial horticultural operations in the 1980s. At the time we envisioned single chains as systems. It became clear later that our concepts were too simplistic. Stan learned that we were on the right track. He delved deeper into systems thinking and systems management (16). He developed a sophisticated understanding of how fresh foods get to market. Systems thinking constructs a framework for learning about complex inter-relationships. Component parts form a whole system with properties different than any of its parts.

From this vantage point a system has an owner, an established purpose, and boundaries. The whole system has unique properties that none of its parts perform on their own. It exhibits flows of energy, information and materials. By this logic there is no overarching food system and no postharvest system. We can’t sit down and burn down the existing food system and design a new one. A better description than system would be markets, networks or overlapping chains. We need to understand how food flows through chains. Then we can work at the edges of these markets or networks to introduce constructive change. To do so requires systems thinking. In this and following chapters (3, 18), Stan provides an in-depth look at systems theory. The concepts are far too complex for discussion here.

Stan introduces three problems to approach with systems thinking

  • Low per capita consumption of fruits and vegetables,
  • Loss and waste remain high
  • Low income for family farms

More on possible approaches and solutions on this site later this month.

Fresh quality changes over time. Perishability and complexity of fresh produce make quality a moving target (3). Quality at harvest is of particular concern. Maturity at harvest establishes a roof—it’s quality potential will never be higher (1, 12, 16, 18). The quality floor depends on handling in its value chain. Packinghouses assess quality by either human graders or electronic sampling. The criteria here focus on size and appearance including lack of visual defects (9). The environment inside the truck affects changes in quality from one end of the trip to the other. Temperature, relative humidity, gasses, and road vibration all affect quality (8,10, 19). Note the south side of the truck is usually hotter in the Northern Hemisphere. Most fresh fruits and vegetables travel from a growing area to a warehouse closer to the point of sale (3).

Warehouses and other accumulating locations group items by important characteristics (14). They separate chilling-sensitive crops from those that are not. Other items need storage at very cold temperatures above freezing. Ethylene-sensitive vegetables are not stored in the same rooms as ethylene-generating fruits. Operators separate respiring vegetables from fruits that deteriorate in the presence of condensation. Adding ice to greens which lose moisture in a short time is a simple solution. Transport to the supermarket, restaurant, or other market brings together incompatible items (3). Separating incompatible fruits and vegetables occurs in backrooms to keep items fresh. Visual display is important in quality at the point of sale. Savvy consumers focus more on past experiences more than on appearance. Open displays in supermarkets causes loss of moisture and shriveling. Thus, we see periodic spraying on susceptible veggies.

tee shirt displaying a floating market in Thailand
The supermarket is not the only destination for fresh fruits and vegetables

Transportation home presents challenges to fresh fruits and vegetables. Sitting in a hot vehicle for hours before arriving home is not good. Produce shopping should be the last stop before heading home. Fresh items continue to senesce in the back of the refrigerator. It can be a slow lonesome death for that bag of carrots! The quality clock is always ticking. Many fruits continue to ripen during their journey from farm to home. Most fresh fruits and vegetables decline in quality after harvest. Postharvest handling seeks to reduce those changes (6, 10, 14).

Postharvest technologists concern themselves with flavor, safety, and nutrition. Postharvesters fit into two categories. Postharvest physiologists study the complex biological changes occurring in detached plant organs. They understand the basic science of life after harvest. Postharvest technologists learn how to keep produce fresh from plant to market. They handle logistics of value chains.  It is not easy to deliver top flavor (6, 7, 17) through such a complex journey. Safety is a major concern (20). Dangerous microbes don’t play favorites. The lack of a specific kill step makes keeping these foods safe and free from spoilage a challenge (21). Chemical changes during handling decreases certain vitamins and even some dietary fiber (4). Understanding physiology and technology in handling is critical. This information helps deliver the best flavor, safety, and nutrition to a consumer.

Other interesting tidbits appear through the book. Certain points intrigue me. For example, changes in consumer trends shape directions of postharvest research (7). Air transport of fresh fruits and vegetables changes the way fresh foods come to us. The pandemic increased the food delivery business. Meal-kits and imperfect produce delivery pose challenges to produce distributors (14). Meanwhile, food deserts and swamps limit fresh foods consumed by low-income families (6).
 
Advances in technology are leading to advances in postharvest handling. Genomics help us better understand the relationship between genetics and physiology (8). Such knowledge helps us understand which items withstand handling in the value chain. Mathematical models aid in predicting changes during handling (1). Better tracing of techniques uncover quality and safety issues in the chain (13). Forensic evaluation of failed cargo shipments allows appropriate settlement of damages (15). Spectral techniques allow us to peak inside of a sample to measure quality without damage (19). New procedures prevent contamination from microbes to ensure better quality in market. The Peach Game, Tomato Game and Fruit Game simulate changes in the market. These games help us understand how roadblocks develop and how to overcome them (16, 18).
 

Bottom line. When reviewing single chapters as part of the editorial process, I saw no unified theme. I went back to read the entire e-book after publication. The flow of the chapters from one to the next brought the topics alive. Postharvest handling within a value chain is more difficult than shipping processed food. Quality changes through the chain defy the simplicity faced by processed products. Safety issues complicate postharvest operations. The kill step in processing is not available to postharvesters. It is a minor miracle that fresh produce arrives in the market as succulent, nutritious food. I don’t expect most of my dedicated readers to rush out and buy a copy of this huge tome for over $100. I hope this review helps clarify the complexity of getting these items from plant to market.

A special thanks to Wojciech Florkowski. He revived the book and guided it through the last three editions. Without his vision and dedication the book would never have been born.

Next week: Designing Value Chains for fresh fruits and vegetables

References:

(1) Tijskens, P. and R. Schouten, 2022. Modeling quality attributes and quality-related product properties. Postharvest Handling: A Systems Approach 99-133.

(2) Wongs-Aree, C. and S. Noichindra, 2022. Postharvest quality properties of potential tropical fruits related to their unique structural characters Postharvest Handling: A Systems Approach 277-316.

(3) Shewfelt, R.L. and S.E. Prussia. 2022.Challenges in handling fresh fruits and vegetables. Postharvest Handling: A Systems Approach 167-186.

(4) Vicente, A.R., G.A. Manganaris, M. Darre, C.M. Ortiz, G.A. Sozzi, and C.H. Crisosto, 2022. Compositional determinants of fruit and vegetable quality and nutritional value. Postharvest Handling: A Systems Approach 565-619.

(5) Nicola, S., G. Cocetta, A. Ferrante, and A. Ertani, 2022. Fresh-cut produce quality: implications for postharvest. Postharvest Handling: A Systems Approach 187-250.

(6) Bowen, A. and A. Grygorczk, 2022. Consumer eating habits and perceptions of fresh produce quality. Postharvest Handling: A Systems Approach 487-515.

(7) Florkowski, W.J. and I. Takács, 2022. What mining the text tells us about mining the consumer: the changing fruit and vegetable consumption patterns and shifting research focus. Postharvest Handling: A Systems Approach 517-564.

(8)  Tonutti, P., C. Bonghi, and S. Brizzolara, 2022. Multiomics approaches for the improvements of postharvest systems. Postharvest Handling: A Systems Approach 251-276.

(9) Bollen, A.F. and S.E. Prussia, 2022. Sorting for defects. Postharvest Handling: A Systems Approach 377-398.

(10) Dodd, M.C. and J.Bouwer, 2022. Cooling fresh produce. Postharvest Handling: A Systems Approach 435-468.

(11) Collins, R. and B. Dent, 2022. Value chain management and postharvest handling. Postharvest Handling: A Systems Approach 319-341.

(12) Banks, N.H., 2022. Postharvest systems—some introductory thoughts. Postharvest Handling: A Systems Approach 3-16.

(13) Bollen, A.F. and M. Adkins, 2022. Plant to plate—achieving effective traceability in the digital age. Postharvest Handling: A Systems Approach 343-361.

(14) Emond, J-P., 2022. Managing product flow through postharvest systems. Postharvest Handling: A Systems Approach 363-375.

(15) Snowden, A.L., 2022. Investigating losses occurring during shipment; forensic aspects of cargo claims. Postharvest Handling: A Systems Approach 469-484.

(16) Aggarwal, D., R.L. Shewfelt, and S.E. Prussia, 2022. Systems approaches for postharvest handling of fresh produce. Postharvest Handling: A Systems Approach 17-49.

(17) Brückner, B., 2022. Measuring consumer acceptability of fruits and vegetables. Postharvest Handling: A Systems Approach 651-666.

(18) Aggarwal, D. and S.E. Prussia, 2022. Models for improving fresh produce chains. Postharvest Handling: A Systems Approach 135-164.

(19) Nicolaï, B. B. De Ketelaere, A.Dizon, N. Wouters, A. Postelmans, W. Saeys, T. Van di Looverbosch, P. Verboven, and M.L.A.T.M. Hertog, 2022. Nondestructive evaluation: detection of external and internal attributes frequently associated with quality and damage. Postharvest Handling: A Systems Approach 399-433.

(20) Walsh, K., 2022. Postharvest regulation and quality standards on fresh produce. Postharvest Handling: A Systems Approach 51-98.

(21) Fallik, E. and Z. Ilic, 2022. Mitigating contamination of fresh and fresh-cut produce. Postharvest Handling: A Systems Approach 621-649.

 

3 thoughts on “What happens to a fruit or vegetable after harvest?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s