Effect of Peanut Blanching Protocols on Bed and Seed Temperatures, Seed Moisture, and Blanchability1

Abstract

Abstract Medium commercial size, runner-type peanuts were heated in an air flow direction-controlled lab scale oven to simulate an industrial multizone dryer used in peanut blanching. Nine blanching protocols consisting of three heating times (30,45, and 60 min) factorially paired with three final oven set point temperatures (76.7, 87.8, and 98.9 C achieved from 32.2 C over six heating zones) were tested for effects on blanchability, moisture content, and temperature variation within individual seed and within the bed of peanuts. Temperature through the peanut bed varied as air flow (76.2 m/min) was reversed in alternating zones. Bed temperature variation during the heating process was highest in the 30-min protocols where the maximum difference between the top and bottom of the bed reached 17.6 C. Temperature variations decreased in the 45- and 60-min protocols; however, maximum differences as high as 8.1 C were consistently found. Bed temperature variation was related to air flow direction with higher temperatures in the peanuts nearest the air/heat source. Peanuts opposite the air flow direction did not reach the desired maximum temperature in the last zone of any protocol. Seed temperature variation was as much as 5 C between the seed surface and 3.14 mm into the seed. Seed moisture decreased from ca. 5.5% to a low of 2.94% in the 60 min/ 98.9 C protocol. Blanchability reached an upper limit of 71 to 75% in the 45- and 60-min protocols at 87.7 C and all of the protocols at 98.9 C. Blanchability was unrelated to magnitude of temperature variation in either seed or within the bed. Blanchability correlated positively with final oven set point temperature and negatively with final moisture content when moisture content was above 3.8%.