Raw materials
The corn hybrids used in this study is the best of six white maize crosses selected according to their superiority in grain yield assessed in the field experiment and the commercial hybrid Single Cross Giza 10 as a control hybrid. These hybrids were obtained from hybridization between parental inbred lines imported from The International Maize and Wheat Improvement Center (CIMMYET). These hybrids were planted under normal and drought conditions in the Experimental Farm of Agric. Res. Center (ARC), Delta region, EL-Kalyubia Governorate, Egypt. Sucrose, shortening, sun flower oil, salt, sodium, and ammonium bicarbonate were purchased from local market, Dokki, Egypt.
Chemical composition
Moisture, protein, ash, fiber, and fat contents of corn hybrids were determined according to AOAC (2005). Total carbohydrates were calculated by difference.
Preparation of NCF
The traditional cooking method was used to prepare NFC according to Vidal-Quintanar et al. (2001) with some modification as follows: The whole corn grains (1 kg) were soaked in 3 L of 1% calcium hydroxide solution then cooked at 95 °C for 95 min. The nixtamal was steeped for about 15 h at room temperature then washed with excess water (three times) followed by decantation using a sieve. The wet masa was dried in an air oven at 85 °C for about 6 h. The dry masa was ground using Brabender mill to pass through a 60 mesh screen. The prepared masa were packed in polyethylene bags and stored in a refrigerator until used.
Pasting properties of corn flours
Pasting properties of NCF and raw Single Cross Giza 10 (SC10) flour were determined using a rapid visco analyser (RVA) starch master R&D pack V 3.0 (Newport Scientific Narrabeen, Australia) according to AACC (2000). The RVA parameters measured were peak time, peak viscosity, trough viscosity, final viscosity, break down viscosity, and set back.
Preparation of biscuits
Biscuit was manufactured using the standard procedure (AACC 2000) as follows: NCF (100 g), sugar (30 g), shortening (15 g), sodium bicarbonate (1.11 g), salt (0.93 g), dextrose solution (14.66 ml), and the required water. All dry ingredients were mixed together then all liquid ingredients were added to the dry mixture and mixed in a dough mixer at low speed for 3 min. The water, required to obtain smooth dough, was added and the obtained dough was left to rest for 5 min. Dough was sheeted to 3-mm thickness then cut to circle pieces using templates with an outer diameter of 50 mm. The biscuits were baked at 180 °C for 12 min, and allowed to cool at room temperature for 1 h. Raw SC 10 flour was used to prepare the control sample.
Evaluation of biscuits
Diameter and thickness of biscuits were recorded and spread ratio was calculated. Organoleptic properties (color, flavor, taste, texture, appearance, and overall acceptability) of biscuits were evaluated according to Hoojjat and Zabik (1984) by ten panelists from the staff of Food Technology Department, National Research Centre, Cairo. Samples were served to the panelists and they were asked to assign scores from 0 to 10 for each parameter.
Color attributes of processed biscuits
The color parameter were evaluated using Hunter, Lab Scan XE, Reston VA., calibrated with a white standard tile of Hunter Lab color standard (LX No. 16379) x = 77.26, y = 81.94, and z = 88.14 (L* = 92.43, a* = − 0.88, b* = 0.21). The results were expressed in accordance with the CIELAB system where L* (L = 0 [black], L = 100[white]), a* (− a = greenness, + a = redness), b* (− b = blueness, + b = yellowness).
Statistical analysis
All samples were analyzed in triplicates, except pasting properties (n = 1) and sensory evaluation (n = 10). The obtained data were subjected to one way analysis of variance (ANOVA) and the differences among the means were evaluated for significant at 5% level using the least significant difference test (LSD). Statistical analysis was carried out using the SAS Systems for Windows software, version 6.12 TS020 (SAS, Statistical Analysis System, Institute Inc., Cary, NC, 1996).