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File: ■ Purple Corn (Zea mays, Poaceae) ■ ■ Loss

HC 011814-598

Date: August 15, 2018

RE: Effects of Processing on Anthocyanin Content in Purple Corn

Salinas Moreno Y, Jaime Fonseca MR, Díaz-Ramírez JL, Alemán de la Torre I. Factors influencing anthocyanin loss during nixtamalization of blue purple grain. J Food Sci Technol. December 2017;54(13):4493-4500. doi: 10.1007/s13197-017-2932-x.

Nixtamalization refers to a process for the preparation of purple corn (Zea mays, Poaceae) in which the corn is soaked and cooked in an alkaline solution (usually limewater), washed, and then hulled. Purple corn contains , pigments that have antioxidant and anti-inflammatory effects. However, these compounds can degrade during processing. The impact of processing factors on anthocyanin loss (AL) has not been studied in significant detail. The intention of this study was to determine where the greatest AL occurs in the nixtamalization process, and assess the effect of cooking time, alkali concentration, and batch size on AL, and on the color of and tortilla from purple corn.

Purple corn was sourced from Toluca, Mexico. To test the effects of alkali concentration on pericarp solubilization, calcium oxide (CaO) in concentrations of 0.5%, 0.7%, and 1.0% per weight were added to distilled water and heated to boiling. Based on the pericarp solubilization results, CaO 0.7% was used in the determination of AL during cooking and steeping. The cooking time was 25 minutes. [Note: anthocyanins are protected against alkali during nixtamalization by the pericarp.] Samples for anthocyanin testing were taken at regular intervals during the steeping period, which lasted for 16 hours.

The effects of batch sizes on AL were tested using 100 g and 1000 g grain samples. The alkali concentrations evaluated were 0.5%, 0.7%, and 1.0% per volume using a 2:1 water to grain ratio and 25 minutes nixtamalization time and 16 hours steeping period. Color of resultant masa flour was measured using colorimetry. Anthocyanin content was measured using absorbance. All measurements occurred in duplicate.

The anthocyanin content degraded significantly (60%) during the cooking and steeping process due to high pH of the cooking water. CaO concentration decreased anthocyanins, with the greatest loss observed at the highest concentration (CaO 1%, 56% AL). Regardless of batch size used, when the amount of CaO was increased, so did the AL. Major losses were observed with the largest batch size (1000 g vs. 100 g). This was attributed to the fact that the elevated temperature was maintained for a longer time in the larger batch size. The combination of high pH and temperature is known to be highly detrimental to anthocyanins.

Alkali concentration and nixtamalization time affected the color of the resultant masa and tortilla. The green-yellow color of the masa and tortilla increased with increasing alkali concentrations, resulting in a darker appearance. But color did not correlate to anthocyanin content. In the tortillas with 1.0% alkali, anthocyanin content was lower than that of the tortillas with 0.5% alkali. Taken together, these findings corroborate those of previous studies on the nixtamalization process.

These results suggest that anthocyanin content in purple corn can be preserved if manufacturers drain the alkaline water in which the grain was cooked, and add cold water to cool the system (reducing the damaging effects of pH and temperature).

No financial disclosure or conflict of interest was provided.

—Renee Davis RH(AHG)

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