For Consumer Value: New Technologies Extend Shelf Life of Fresh Fruits and Vegetables

by John P. Cherry, Center Director, Gerald M. Sapers, Lead Scientist, Michael F. Kozempel, Lead Scientist, Ching-Hsing Liao, Research Plant Pathologist, John M. Wells, Lead Scientist, and Kevin B. Hicks, Research Leader, Eastern Regional Research Center, ARS, USDA, Philadelphia, PA; Charles L. Wilson, Research Leader, Appalachian Fruit Research Station, ARS, USDA, Kearneysville, WV; Kenneth C. Gross, Plant Pathologist, Beltsville Agricultural Research Center, ARS, USDA, Beltsville, MD; and Attila E. Pavlath, Research Leader, Western Regional Research Center, ARS, USDA, Albany, CA.

Fruits and vegetables are enjoyed by many Americans for their flavors, colors, and textures. They are an important part of a healthy diet, as they provide a number of essential nutrients and dietary fiber. The Dietary Guidelines for Americans, developed by USDA and the U.S. Department of Health and Human Services, recommend that we eat plenty of fruits and vegetables.

With today's fast-paced lifestyles, many people do not have the time to pare, core, slice, or dice fruits and vegetables. Yet, many prefer not to use canned or frozen foods because they want the flavor and texture of fresh commodities. There is a similar trend in hospital, industrial, and school cafeterias. Generally, in such cafeterias, which typically serve 300-500 persons, manual fruit and vegetable preparation is too expensive, and machines for such a small volume are not cost-efficient. The best solution for this food preparation problem is to process produce at some centrally located area and ship the prepared fresh fruit and vegetable products to the consumer or cafeteria.

Considering the time required for packaging, shipping, distributing, and storing, one can estimate that 15-20 days will elapse between the start of processing and the time when the processed produce will reach the consumer. Unfortunately, the removal of the natural outer tissues from agricultural products immediately starts various physical, biochemical, and microbiological processes that will reduce flavor, taste, freshness, and consumer acceptance. If the processed fresh fruits and vegetables could be protected from desiccation, enzymatic and biochemical changes, and microorganisms for 2-3 weeks, it would be possible to process produce on a large scale at a central location and get fresh, nutritious products to consumers, both domestic and foreign, in an aesthetically pleasing form. USDA research is making this possible, without threatening the nutritional quality of the product.

Edible Films

If the surface of the fresh fruit or vegetable could be uniformly covered by an edible material that acts as a barrier to water and oxygen, the stability problems could be diminished. Three major classes of materials are used in edible films: proteins, carbohydrates, and fats. It is not surprising that, individually, these materials do not provide the desirable protection for the preservation of freshness, but scientists at the Western Regional Research Center (WRRC), ARS, Albany, CA, found that their combination, in the right ratio, could be very effective. A composition of 1 percent alginic acid (a carbohydrate), 10 percent casein (a protein), and 15 percent "Myvacet" (a commercially produced fat-derived ingredient) decreased water losses from apple pieces by almost 80 percent. Coated apple, pear, and zucchini pieces retained their freshness for 4-5 days without any noticeable changes. The film does not alter the taste of the coated products, and it does not have to be removed before consumption.

Edible films can also be used on bread, pizza dough, cakes, etc., to prevent these freshly baked products from becoming soggy.

An edible coating compound developed at the ARS Western Regional Research Center in Albany, CA, promises to extend the shelf life of fruits and vegetables. The film does not alter the flavor of the coated products, and it does not have to be removed before consumption.

Keith Weller/USDA 90BW0146- 10A

Preventing Discoloration

Many raw fruits and vegetables become brown or show other kinds of discoloration when they are peeled, sliced, or juiced. To prevent such discolorations in apples and potatoes, scientists at the Eastern Regional Research Center (ERRC), ARS, Philadelphia, PA, have developed treatments that apply "browning inhibitors" to peeled fruit and vegetable surfaces. These inhibitors (ascorbic acid-2-phosphates) are closely related to vitamin C, but will require Food and Drug Administration approval for food use. New approaches have also been developed to control browning in raw fruit and vegetable juices by addition of carbohydrate-like materials called cyclodextrins or vegetable gums such as carrageenan. Other ARS work has eliminated whitening in pre-peeled carrots by means of citric acid dips.

ARS researchers have developed a process for extending the shelf life and improving the quality of fruit juices. Juices can be preserved without heat pasteurization. Keith Weller/USDA 90BW0688-16

Innovative Processes for Juices and Fruits

Research work by ERRC scientists has developed innovative new processing methods for extending the shelf life and improving the quality of fruit juices. Juices can be preserved without heat pasteurization (which detracts from the fresh flavor) by using gentler physical treatments such as membrane filtration and centrifugation, a combined approach called "cold blanching." Unblemished citrus sections can be prepared by treating the fruit with pectinase enzymes to dissolve the "glue" that holds fruit segments together. This approach, developed by the Quality Improvement in Citrus and Subtropical Products Station, ARS, Winter Haven, FL, was recently commercialized by a major citrus processor.

Research conducted at the Appalachian Fruit Research Station (AFRS), ARS, Kearneysville, WV, on the composition and suitability for processing of new berry varieties contributed to the introduction of a new thornless blackberry variety called Chester, which shows superior quality characteristics and is suitable for freezing.

Explosion Puffing-A Preservation Process for the 21st Century

Drying is an ancient yet still excellent method of preserving foods. Since fruits and vegetables consist of 80-97 percent water, removing most of the water not only preserves the food, but also greatly reduces the weight and therefore the cost of shipping. When beans or rice are dried, the product is excellent. Dried grapes are raisins and dried plums are prunes. But, drying also has disadvantages. Produce such as apples, blueberries, potatoes, and carrots, although well preserved when dried, unfortunately are difficult to rehydrate frequently requiring 30 minutes or more.