Physicochemical characterization of protein isolates of amaranth and common bean and a study of their compatibility with xanthan gum.

Vegetables are considered to be a sustainable source of promising biomaterials such as proteins and polysaccharides. In this study, four protein isolates (amaranth protein isolate API, amaranth globulin-rich protein isolate AGR, bean protein isolate BPI, and bean phaseolin-rich protein isolate BPR) were structurally characterized under different pH conditions (2-12) and their compatibility behavior with xanthan gum (XG) in aqueous medium was described. All protein isolates showed ß turn and ß sheet (78.24-81.11%), as the major secondary structures without statistically significant difference under the pH conditions surveyed. Protein isolates show solubility at pH ≤ 3 (40.4-85.1%) and pH ≥ 8 (57.6-99.9%) and surface hydrophobicity results suggest protein denaturation at pH ≤ 3. In the compatibility study, API/XG ratios between 1:1 and 5:1 at pH from 7 to 9 and the BPI/XG ratios from 1:1 to 20:1 at pH 7 form gels that do not require heating nor crosslinking agent addition. Zeta potential results, on the other hand, evidenced that formation of gels is driven by attractive electrostatic interaction of the charged regions of both biopolymers and intermolecular interactions such as hydrogen bonds.

Effect of Pleurotus agaves mushroom addition on the physicochemical and sensory properties of blue maize tortillas produced with traditional and ecological nixtamalization.

The physicochemical, nutritional and sensory properties of flours, doughs and tortillas made with traditional nixtamalization (TN) and ecological nixtamalization (EN) and enriched (9%) with the traditional maguey mushroom (Pleurotus agaves) were analysed. EN resulted in flours and tortillas having a greater content of bioactive compounds than that of TN flours, which represents a production process of maize tortillas containing high amounts of antioxidants. The addition of mushrooms to EN flours improved their sensory properties, whereas the addition of mushrooms to TN flours decreased them. The amount of P. agaves added to tortillas was equivalent to 3% enrichment with ß-glucans. The edible mushroom P. agaves, highly appreciated in many Mexican regions, improved the nutritional and sensory quality of blue maize tortillas when added to flours prepared by EN. A new product was developed using local traditional foods of complementary nutritional value.

Chemical acetylation of nixtamalized maize flour and structural, rheological and physicochemical properties of flour, dough and tortillas.

Nixtamalized maize tortilla is a basic food for the Mexican population. It has high energy due to high starch, which may be modified to decrease its bioavailability and to produce changes in the characteristics of flours. For this research, nixtamalized maize flour was prepared and subjected to an acetylation chemical process, with and without prior hydrolysis. Raw maize flour, traditionally nixtamalized maize flour, acetylated-nixtamalized maize flour (AF) and acetylated-hydrolyzed nixtamalized maize flour (AHF) were prepared and evaluated. These flours were used for dough and tortilla preparation and analyzed for degree of substitution (DS), physicochemical properties, structure, thermal, rheological, morphological and texture properties. FTIR spectra and DS showed the presence of acetyl groups. AHF showed the highest value for water absorption index. The resistant starch increased 0.27 and 0.42% for AF and AHF samples. The gelatinization enthalpy (∆Hg) for AF was greater than other flours. AF tortillas showed better characteristics than the traditional ones and their consumption was recommended since showed better RS.

Comparison of nixtamalization and extrusion processes for a reduction in aflatoxin content.

Traditional nixtamalization and an extrusion method for making the dough (masa) for corn tortillas that requires using lime and hydrogen peroxide were evaluated for the detoxification of aflatoxins. The traditional nixtamalization process reduced levels of aflatoxin B(1) (AFB(1)) by 94%, aflatoxin M(1) (AFM(1)) by 90% and aflatoxin B(1)-8,9-dihydrodiol (AFB(1)-dihydrodiol) by 93%. The extrusion process reduced levels of AFB(1) by 46%, AFM(1) by 20% and AFB(1)-dihydrodiol by 53%. Extrusion treatments with 0, 0.3 and 0.5% lime reduced AFB(1) levels by 46, 74 and 85%, respectively. The inactivation of AFB(1), AFM(1) and AFB(1)-dihydrodiol in the extrusion process using lime together with hydrogen peroxide showed higher elimination of AFB(1) than treatments with lime or hydrogen peroxide alone. The extrusion process with 0.3% lime and 1.5% hydrogen peroxide was the most effective process to detoxify aflatoxins in corn tortillas, but a high level of those reagents negatively affected the taste and aroma of the corn tortilla as compared with tortillas elaborated by the traditional nixtamalization process.

[Fortification and evaluation of the nixtamal tortillas]. / Fortificacion y evaluacion de tortillas de nixtamal.

The effect of the addition of vitamins and soy protein on the quality characteristics of nixtamal tortillas (TN) and the losses of nutrients during the nixtamalization process were evaluated. Vitamins (0.15% as is) and defatted soy (4% as is) were added to the tortillas without affecting their sensory characteristics. Higher values of those nutrients had a negative effect on the color and flavor of the product. During the production of the tortilla the corn lost approximately 1.5% of proteins. The nixtamal tortilla fortified with 4% of defatted soy (TNS) showed 3% higher protein content than the TN. The calcium content in the samples was 7.7, 114 and 212.5 mg/100 g for the corn, the TN and the TNS respectively. In the process of producing the nixtamal tortillas from corn 28.9% of the niacin, 46.3% of the folic acid, 36.3% of the thiamin and 80% of the riboflavin were lost. During the washing and rinsing of the nixtamal there were losses of 18.2% of the thiamin, 16.6% of the riboflavin and 20.7% of the folic acid. Although the niacin showed a 28.9% loss, the alkaline process caused an important release of that vitamin. The losses during the cooking of the tortillas were high especially for riboflavin which showed a total loss of 80% in comparison with the original corn. Of the total, 63% was lost during cooking and 16.6% was lost during washing of the nixtamal.

[Chemical and nutritional changes during preparation of whole corn tortillas prepared with instant flour obtained by extrusion process]. / Cambios en algunos componentes químicos y nutricionales durante la preparación de tortillas de maíz elaboradas con harinas instantáneas obtenidas por extrusión continua.

Chemical changes of some nutritional components (protein, total dietary fiber, vitamins, lysine, tryptophan, ether extract and fatty acids) of tortillas made from instant whole corn flour prepared by extrusion process (CINVESTAV process) were evaluated. The tortillas prepared by extrusion process were compared with tortillas made by traditional process and raw corn. The protein content of tortillas from both processes were statistically similar to those of the raw corn, although the traditional tortillas showed the lowest actual values. Tortillas from traditional process contained the lowest amount of total dietary fiber and available lysine. The loss of protein, crude fiber, total dietary fiber, available lysine, tryptophan, and vitamin contents during traditional tortillas process, was attributable to the partial loss of pericarp, aleurone and germ tissue during the process. Tortillas prepared by both processes showed loss of vitamins. The thermal treatment in both processes (traditional and extrusion) decreased the ether extract and fatty acids contents. Tortillas prepared by extrusion process showed better nutritional characteristics than traditional tortillas prepared by nixtamalization process.