Putting produce to sleep
You can improve the shelflife of your fruit by reducing its metabolic activity.
DURING postharvest handling of perishable commodities, one will sometimes hear the phrase “putting the commodity to sleep.” In this article, we will discuss what this means and how to accomplish it.
It is important to remember that there is a relationship between a commodity’s shelflife and its rate of respiration. The chemical reactions that occur within a commodity are referred to as its metabolism. These reactions both create important chemical molecules (e.g., sugars or color pigments) and break down molecules to release energy.
As part of this, respiration represents a key series of reactions whereby cells use oxygen to completely break down carbohydrates (e.g., sugars) and produce energy, carbon dioxide, water, and heat. Respiration supplies the energy for all the other metabolic reactions, so its rate reflects the overall metabolic rate of the commodity.
Produce ages both physiologically (how fast metabolic processes are taking place) and in regard to time (hours, days, months). The relative shelflife of a commodity is tied more to its physiological age than to its temporal age. Thus, by reducing the metabolism (respiration) of a commodity, its quality is maintained longer, resulting in an extended shelflife. This is sometimes called “putting the commodity to sleep.”
Many factors influence how fast metabolic processes occur in produce. Among the most important factors are temperature and oxygen/carbon dioxide concentrations.
Maintain Proper Temperatures
Proper temperature management is the most effective way to reduce respiration and prolong shelflife. As a general rule, for every 18 deg F (10’C) increase in temperature, respiration increases two- to threefold with a corresponding decrease in shelflife.
Use of temperature to reduce respiration also applies to how fast the commodity is cooled after harvest. For some, an hour at 90 deg F can equal a week at 32 deg F. Other benefits of rapid cooling and maintaining these temperatures include slowing the growth of pathogens and reducing water loss.
Never expose tissue to temperatures below freezing. This will kill the tissue. For maximum quality and shelflife, always store produce at a low temperature that does not result in chilling or freezing injury.
Oxygen & Carbon Dioxide
Oxygen (O2) and carbon dioxide (CO2) are key gasses involved in respiration and other metabolic processes within commodities. In general, reducing O2 levels and/or increasing CO2 levels around a commodity (called modified or controlled atmospheres) reduces its rate of respiration.
Each commodity has its own level of tolerance to changes in O2 and CO2 levels before injury occurs. Because plant tissues consume O2 and give off CO2, simply sealing a commodity in an airtight container will begin to lower the O2 and raise the CO2 levels within the container.
Modified or controlled atmospheres are used for different commodities ranging from large, specially designed apple storage facilities, to sealed packages of fresh-cut salad mixes. Though modified or controlled atmospheres can be an effective means of reducing respiration and increasing shelflife, they are not a replacement for good temperature management and must be managed to prevent O2 or CO2 from reaching levels that cause injury.
Recommended storage and shipping temperatures and O2 and/or CO2 levels for specific crops can be found online at the UC-Davis Postharvest Product Facts Web site
(postharvest. ucdavis.edu/Produce/ ProduceFacts/index.html) and at the Worldwidefresh Web site (18.104.22.168/
Jeffrey Brecht and Steven Sargent are in the Horticultural Sciences Department, University of Florida, Gainesville, FL; Mark Ritenour is at the Indian River Research & Education Center, Ft. Pierce, FL; e-mail MRitenour@mail.ifas.ufl.edu.
Copyright Meister Publishing Company Jun 2002
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