Individual Shrink-wrapping of Sweet Potatoes: An Emerging Value-added Marketing Technique

Linda Benedict, Picha, David H.  |  6/11/2009 10:50:57 PM

About 3 percent of the fresh-market sweet potatoes sold in U.S. supermarkets are in the form of microwavable, shrink-wrapped roots.(Photo by Mark Claesgens)

David Picha has conducted numerous tests to identify the appropriate film type and thickness for maximizing the retail market life of shrink-wrapped sweet potatoes. These tests have continued with the advent of new film types and formulations.(Photo by Mark Claesgens)

David H. Picha

The majority of sweet potatoes consumed in the United States are purchased through retail fresh market outlets. They have traditionally been marketed in the form of individual roots stacked in bulk displays and priced per pound. When purchased as a fresh product, sweet potatoes are most commonly prepared as a baked root. However, product convenience and ease-of-preparation are becoming increasingly important among time-stressed consumers.

A value-added form of marketing sweet potatoes involves packaging individual roots in shrink-wrap film, followed by heat-sealing the film to adhere it tightly to the skin. Consumers may then conveniently prepare the roots by microwave with a cooking time of approximately eight minutes for a 6-ounce root.

Although individual shrink-wrapping technology in the fresh produce industry has been available for years, it was mostly confined to use on greenhouse-grown cucumbers. The potato industry began using this packaging technology about 20 years ago, followed by a slow adoption with other crops.

Research on developing a value-added shrink-wrapped sweet potato product began in the LSU AgCenter in the early 1990s. Numerous tests were conducted to identify the appropriate film type and thickness for maximizing the retail market life of shrink-wrapped sweet potatoes. These tests have continued with the advent of new film types and formulations.

The sweet potato industry in the United States has adopted this technology for marketing a small but significant portion of its fresh product sold through retail channels. Louisiana growers and shippers began to offer this value-added product in 2004 with small-sized U.S. No. 1 grade Beauregard roots.

According to trade industry sources, about 3 percent of the fresh-market sweet potatoes sold in U.S. supermarkets are in the form of microwavable, shrink-wrapped roots. Sales of this convenience-type sweet potato are increasing annually. The most common root sizes used for individual shrink-wrapping are 6, 7 and 8 ounces. Retail prices within the United States typically range from $0.99 to $1.59 per root, depending on the store and location.

Shrink-wrapping Process

The sweet potato root surface must be completely dry before wrapping to prevent surface mold from forming on the skin during extended periods of storage or marketing. The shrink-wrapping process involves enclosing individual sweet potato roots in polyolefin or other type polymer shrink films. The film is readily available from package-supply vendors and usually arrives on rolls cut to the desired length and width. Film thickness typically ranges from 40 to 100 microns.

The sweet potatoes are put in a feeder assembly with a spacer to separate the roots. The film is wrapped around the root and cut to the proper size by a heat-sealing device. Manual, semi-automatic and automatic film-cutting and heat-sealing equipment are available. The root with the loosely fitting film is then conveyed through a heat tunnel to create a tightly sealed package. Fully automated commercial equipment approaches a speed of one wrapped root per second. The individual roots can be conveniently labeled with product-preparation, nutritional-value and other marketing information.

Benefits of Shrink-wrapping

Shrink-wrapping adds value to fresh-market sweet potatoes by enhancing appearance, reducing weight loss and allowing for individual labeling. Weight loss by shrink-wrapped roots during reta Beauregard roots lost about 0.5 percent of their weight after three weeks of simulated retail market conditions at room temperature compared with 2.5 percent weight loss by unwrapped roots.

Film thickness and weight loss showed an inverse relationship, with the thicker-gauge films allowing the least amount of weight loss. Taste-panel test results indicated that film type and thickness did not influence overall root flavor or sweetness.

Economics

The purchase price of an automatic, sweet potato shrink-wrapping system – which includes the root feeding device, cutter/heat sealer and heat tunnel – is approximately $100,000 for a unit that will process about 60 roots per minute. Lower-capacity processing systems cost less, but the packaging cost per root is higher. Manual labor is needed to place the sweet potatoes on the feeding device, continually monitor the flow of roots, make necessary adjustments and repairs to maintain a continuous flow, and put the wrapped roots into cartons for shipping. In addition, the cost of the shrink-wrap film (not including equipment or labor) is about a half cent per root.

Although shrink-wrapping equipment does represent a major investment, grower/packers around the country generally receive a two- to three-fold premium price per pound for shrink-wrapped sweet potatoes compared with bulk-packed roots.

Significant market growth potential exists for convenient-to-prepare, value-added forms of sweet potatoes, such as individually shrink-wrapped roots in microwavable films. The technology for packaging sweet potatoes in this manner is widely available from multiple commercial vendors. Shrink-wrap packaging and heat-sealing equipment can be obtained to match any size of operation, from small gift-pack enterprises to large grower-shippers who market sizeable volumes to large retail supermarket chains.

Added benefits of packaging sweet potatoes in this way include product cleanliness, ease of labeling, traceability, reduced shrivel and the ability to include advertising and preparation information on each root. Buyers and consumers alike pay a premium price for this value-added fresh product.

David H. Picha, Professor, School of Plant, Environmental & Soil Sciences, LSU AgCenter, Baton Rouge, La.

(This article was published in the spring 2009 issue of Louisiana Agriculture.)

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