Study on the phenolic composition and antioxidant properties of white, yellow and black corn (Zea mays L.) foodstuffs

Resumen del trabajo presentado al XXII EuroFoodChem Congress, celebrado en Belgrade, Serbia del 14 al 16 de junio de 2023.

Corn, also known as maize (Zea mays L.), is one of the major food sources in the world. Since corn is gluten-free in its natural form, in the last few years there has been a growing interest of people with celiac disease on it. Commonly, corn products are made from white and yellow varieties. However, there is a growing interest in purchasing colored corn foods because of their nutrition related characteristics, which are mainly attributed to their higher content in antioxidants. Corn food products require processing from the raw grain to the consumer final product. However, the potent antioxidant effect of colored corns, can be largely lost during food processing. Among the antioxidant compounds reported in colored corns, it is important to highlight certain phenolics, carotenoids and particularly anthocyanins, which are regarded as very potent antioxidants. Cyanidin-3-O-glucoside is the major anthocyanin in black corn, accounting for approximately 75% of the total anthocyanin content. The present study was undertaken with the aim of reducing the losses of antioxidants, mainly anthocyanins, in black corn food products. With this aim, three different color corns (Zea mays L.) were used: white, yellow and black (Millo corvo). All of them were cultivated and supplied by growers from the same area (Galicia, Spain) during 2021. We evaluated the antioxidant content of two different black, yellow or white corn-based products (ie, tortillas and cookies) subject to moderate processing. The tortilla making process consisted of mixing flour, warm water in a 1:1 (v:v) ratio, and salt. The mixture was heated from 50°C to 90°C progressively until a thick mass was obtained. Then, the dough was cooked on a hot plate at low temperature (120°C) for 5 min on each side. The cookies were prepared by mixing flour, vegetable margarine, eggs and salt. Once prepared, the dough was rolled out into discs 6 cm in diameter and 8 mm in height, and baked in a rotary oven at 183 ºC for 25 min. Polyphenols were extracted from raw flour, tortillas and cookies prepared from white corn, yellow corn and Millo corvo, respectively. For the experiments, 3 g of each sample were used. Extractions were carried out by adding methanol:water (70:30, w:w). The content of phenolic acids and flavonoids in tortillas and cookies made from white corn, yellow corn and Millo corvo flours were determined and quantified by HPLC-QTOF-MS analysis. Additionally, total phenol content was determined in all samples. The method applied was based on that described in the literature with slight modifications. Total anthocyanin content was quantified in all samples using the pH differential method elsewhere reported. Antioxidant activity was studied by DPPH● radical scavenging assay4 with slight modifications and photochemiluminiscence (PCL) antiradical scavenging assay. Raw Millo corvo flour exhibited higher content of phenolic acids, flavonoids and, particularly, anthocyanins than white and yellow flours. Phenolic acids decreased in cookies but they did not in tortillas; flavonoids did not exhibit a clear tendency and anthocyanins were always preserved. Antioxidant activity obtained for Millo corvo samples was twice as high as the value measured in white and yellow corns in terms of DPPH radical scavenging activity. The difference in AA was even more remarkable in terms of (PCL) antiradical activity. The conditions used during the cookie-making process enabled the natural antioxidant characteristics of Millo corvo to be preserved. However, the conditions applied to prepare tortillas resulted in major losses.

This research was financially supported by the Spanish MCIN/AEI/10.13039/501100011033/. Grant number PID2019-107009RB-100.

Peer reviewed