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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Blanching on Peanut Shelf Life

Authors
item Sanders, Timothy
item Adelsberg, Gordon - MASTERPIECE ICE CREAM CO
item Hendrix, Keith
item Mcmichael, Jr, Robert - UTS

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 26, 1999
Publication Date: N/A

Interpretive Summary: Blanched peanuts, peanuts with seed coats removed, are required in many manufacturing operations and the blanching process, in conjunction with color sorting, is effective in removing damaged/discolored seed associated with aflatoxin contamination. Although blanching is often a necessary processing step, the general peanut industry consensus is that significant shelf life reduction occurs as a result of the process. The process consists of gentle heating followed by mechanical removal of the seed coat. To evaluate the effect of blanching on peanut shelf life, virginia-type peanuts were exposed to nine heating protocols consisting of three heating times (30, 45, and 60 min) paired with three final temperatures (76.6, 87.8, and 98.9 C beginning from 32.2 C and increasing over six heating zones). Blanched peanuts from each protocol and unblanched controls were stored at 30 C and ambient relative humidity over a 28-wk period. Blanched dpeanuts from all protocols had similar storage stability as unblanched peanuts as determined by oil stability and development of lipid degradation products. Descriptive sensory analysis of roasted peanuts which had been stored as blanched from each protocol or unblanched control samples indicated no significant differences in intensity of either positive (roasted peanutty) or negative (painty) descriptors. This study demonstrated that blanching as performed in this study does not reduce shelf life of high quality peanuts. The study should result in industry reexamination of the perception of lowered quality from blanching and greater acceptance of blanched peanuts in domestic and export markets.

Technical Abstract: Blanched peanuts are required in many manufacturing operations and the blanching process, in conjunction with color sorting, is effective in removing damaged/discolored seed associated with aflatoxin contamination. Although blanching is often a necessary processing step, the general peanut industry consensus is that significant shelf life reduction occurs as a result of the process. To evaluate the effect of blanching on peanut shel life, virginia-type peanuts were exposed to nine heating protocols consisting of three heating times (30, 45, and 60 min) factorially paired with three final temperatures (76.6, 87.8, and 98.9 C achieved from 32.2 C over six heating zones). Lipoxygenase activity in peanuts decreased with increasing time and temperature of heating. Blanched peanuts from each protocol and unblanched controls were stored at 30 C and ambient relative humidity over a 28-wk period. Blanched peanuts from all protocols had similar or better storage stability than unblanched peanuts as determined by oil stability index (OSI) and peroxide valude (PV). OSI was ca. 10 hr for blanched and unblanched peanuts and did not change significantly over the storage period. PV's for blanched peanuts from the nine protocols varied from 0.2-0.8 and were significantly different from the PV of 1.3 for unblanched peanuts. Descriptive sensory analysis of roasted peanuts which had been stored as blanched from each protocol or unblanched indicated no significant differences in intensity of roasted peanutty and painty descriptors.

Last Modified: 4/20/2014
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