Puff amaranth seeds using a single-screw extruder.

Amaranth (Amaranthus cruentus) is a pseudocereal that has excellent nutritional properties. It is a very good source of squalene and tocotrielnols, which are proven nutraceuticals. Amaranth seeds are generally puffed or roasted. Puffing is carried out on a hot skillet, which unfortunately affords no control over the temperature used and the residence time.

Rutgers University scientists attempted to develop and optimize a puffing technique in which they would accurately control temperature and residence time. To puff the seeds, they used a single-screw extruder with a tapered screw without a die. A tapered screw provided better contact between the seeds and the hot barrel, as compared to a straight screw.

To puff the seeds, the researchers applied different combinations of barrel temperature (250 C to 290 C) and screw speed (75 rpm to 150 rpm) at a constant feed rate of 16 g per minute to 18 g per minute. The efficiency of puffing--based on the mass fraction of puffed seeds--decreased with increases in screw speed at a constant temperature. The efficiency increased with a rise in temperature at constant screw speed. Efficiency increased from 10% to 85%. At certain temperature-rpm combinations, the efficiency was extremely low. The maximum efficiency (at certain screw speeds and temperatures) reached 85%.

The technique yielded a maximum efficiency in a range of 84% to 86%. The final moisture content of the puffed seeds declined with an increase in temperature at a constant screw speed. Preliminary sensory analyses were undertaken with an untrained 12-member panel using samples produced at maximum efficiency: 290 C, 125 rpm; 270 C, 100 rpm; and 250 C, 75 rpm. The analyses showed that 58% of the subjects best liked the sample processed at 250 C and 75 rpm. All of the panelists found the sample processed at 270 C and 100 rpm to be the darkest.

Bulk density was in the range of 240 kg per m3 to 280 kg per m3 for all of the samples and could not be correlated with the different processing conditions. The technique developed will be useful for the large-scale puffing of amaranth, when it is required to control temperature and residence time. Continuous operation can increase profitability and energy savings. Researchers have not quantified the profitability or energy savings, but it is generally regarded that continuous processes are more efficient and better controlled than batch processes.

Further information. Mukund Karwe, Department of Food Science, 65 Dudley Rd., Cook College, Rutgers University, New Brunswick, NJ 08901; phone: [phone]; fax: [phone]; email: [e-mail].