**3.1. Extraction and characterization of AX1 and AX2**

AX1 and AX2 presented yield values of 0.9 and 0.5 % (w/v), respectively. This is consistent with a previous report where poorer AX yield of extraction were registered at lower times of alkaline hydrolysis [20]. Nevertheless, the AX yields found in the present study were smaller than those previously reported [21], which could be related to the maize varieties used in each investigation. The yield found in this study is similar to reported by other sources of AX as wheat flour (0.5 %) [16]. In spite of low yield values, recuperation of AX from wastewater could be an advantage for future industrial applications of this polysaccharide. It could also provide an alternative use this highly alkaline waste generated in large quantities.

The structural features of AX1 and AX2 were analyzed by FT-IR spectroscopy (Figure 1). The spectra were similar for both AX samples indicating a similar chemical structure characteristic of AX from maize and other sources [16, 17]. The region of 1200–850 cm-1 is typical of AX [17, 22, 23]. The maximum absorption band (~1035 cm-1) could be assigned to C-OH bending with signals at 1,070 and 898 cm-1 that were related to the antisymmetric C-O-C stretching mode of the glycosidic bond and β(1-4) linkages between the xylose units [16, 17, 24]. Phenolic com‐ pounds and proteins have specific absorption bands in the 1500 – 1,700 cm-1 [23]. The region from 3500–1800 cm-1 is the fingerprint region of polysaccharides, with two bands (3,400 cm-1 corresponding to stretching of the OH groups and 2,900 cm-1 corresponding to the CH2 groups) [16, 25]. These results suggest that nixtamalization conditions used in the present study do not affect the structural features of AX. However, in this work the effect of two alkaline treatments was also investigated on the FA content and physicochemical characteristics of AX1 and AX2.

The gel permeation chromatography profile of AX1 and AX2 are presented in Figure 2. Molecular weight distribution profiles were similar for both AX showing a major peak at molecular weight region of ~250 kDa (high molecular weight region), a similar behavior has been previously reported for maize AX [17].

FA content in AX1 and AX2 was 0.012 ± 2.7 x 10-5 and 0.008 ± 1.4 x 10-4 (μg/mg polysaccharide), respectively. These values are lower than those reported for other maize wastewater AX (0.23 μg/mg polysaccharide) [4]. Heating temperature, lime concentration, hydrolysis time, and exposure to light could have affected the amount of FA present in AX. In a previous report found that the best conditions of alkaline hydrolysis for FA extraction (from brewer's spent grain) are low NaOH concentration (2.0%), temperature of 120°C, and a short reaction time (90 minutes) [26]. In the present work, maize grains cooking in a lime solution was performed during 90 minutes and 30 minutes for AX1 and AX2, respectively; but after heating, long soaking periods were used (24 hours and 4 hours for AX1 and AX2, respectively), which could explain the lower FA content in the polysaccharide. This is congruent with a previous study where the FA content in AX was dependent of the time of alkaline hydrolysis [20].

**Figure 1.** FT-IR of AX1 and AX2. The arrows indicate the characteristic absorption bands.
