Shelf Stability of Peanut Butter Tarts

Summary

Baked tarts filled with peanut butter/strawberry jam were evaluated for shelf life stability. Various packaging regimens were employed, but none protected the product adequately beyond 12 weeks of storage.

Situation

A formula and process for a peanut butter/strawberry jam tart was developed in previous research. This product was very acceptable to consumers, but its shelf life was unknown.

Response

A study to determine the shelf life of baked tarts made with two types of filling—peanut butter alone and peanut butter with strawberry jam—was conducted. The tarts were baked by a commercial bakery on April 25, 2006 and packaged in (a) cardboard box, (b) high barrier film and flushed with nitrogen and (c) high barrier film without nitrogen flushing on April 26, 2006. Samples were stored at 22oC/50% RH and 32oC/70% RH and evaluated at 3-week intervals using physicochemical (moisture, water activity, color, pH, and texture), microbiological (total plate counts, yeast/mold counts), and sensory evaluation analyses. Sufficient samples were processed and packaged for a 24-week storage period.

Impact

At day 0, the total bacterial counts of the crust and filling were 1.47 and 2.48 log10 CFU/g, respectively; yeast and mold counts of the crust and filling were 1.76 and 3.12 log10 CFU/g, respectively. These data indicate that proper sanitary conditions were maintained during processing and handling. The total bacterial counts and yeast/mold counts after 9 weeks of storage were not more than 3.12 log10 CFU/g, which means that the tarts were safe for human consumption. However, results of sensory evaluation by a 4-member, in-house trained panel indicated that the hedonic (liking) ratings for several of the attributes, particularly texture and flavor, had declined to levels of = 5 (neither like nor dislike); products with ratings of 5 or lower were no longer considered acceptable. The initial moisture content of the peanut butter tart crust was 6.7% while that of the peanut butter/strawberry tart crust was 7.3%. The initial moisture content of the peanut butter filling was 4.5% compared to 14.9% in the peanut butter/strawberry tart filling. One of the most notable quality changes which occurred during the storage test was the gradual and considerable loss of moisture from the strawberry jam, from 14.6% initially to 5.9-7.2% after 9 weeks. This storage study was terminated after 12 weeks due to a significant loss of overall product quality, regardless of package type or storage condition. A follow-up study was conducted, using a foil laminate film to individually package the tarts, as is done in commercial packaging of Pop-tarts®. Nitrogen flushing was not employed in the follow-up storage study, since it demonstrated no added benefit in preventing product degradation. Tarts were baked in an impingement oven in the pilot plant of the Department of Food Science and Technology—Griffin Campus on September 19, 2006. They were cooled for 1 hr after baking, held overnight in moisture-vapor-proof containers, individually packaged in air the following day, using foil-like film (metallized oriented opaque polypropylene). Packages were stored at 22oC/50% RH and at 32oC/70% RH for evaluations to be conducted at 0, 6, 12, 18, and 24 weeks. Measurements of color, texture, water activity, moisture content, total bacterial counts, and yeast/mold counts were made as reported in the first study. For sensory evaluation, a 10-member panel of untrained consumers was recruited from the Griffin community. The microbiological data (total bacterial counts, yeast and mold counts) at 6 weeks indicated that the tarts were still acceptable, i.e., the number of colony-forming units (CFU/gram) for both crust and filling were below 3.0. At 12 weeks, however, CFU for some of the samples were greater than 3.0, and there was visible mold on both the surface as well as the interior of the tarts. Therefore, the tarts were considered unsafe for human consumption and were not served to panelists for sensory evaluation. The storage study was terminated at this point due to degradation of the product. It is unfortunate that the air pack/metallized film package employed in this phase of the study did not prevent mold spoilage of the product. A more robust regimen employing the use of mold inhibitors in the crust and filling as well as a modified atmosphere within each individual pouch is warranted to protect the product. A continuous process, such as that employed by commercial bakeries for processing/packaging of Pop-tarts® or other toaster pastries, rather than the batch process/package regimen employed in our pilot plant, may have extended the shelf life of the tarts for more than 12 weeks.

State Issue

Agribusiness Development/Value Added

Details

• Year: 2007
• Geographic Scope: National
• County: Spalding
• Program Areas:
  • Agriculture & Natural Resources