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Rheological characterization of nixtamalized corn doughs

14/11/2019 14:49

PRESENTATION

Corn can be nixtamalized (soaked and cooked in an alkaline solution) for improving its nutritional value, flavor and aroma and for reducing mycotoxins. The nixtamalized corn is then grinded in order to obtain a dough (masa) which will be used to produce tortilla chips (nacho type). Nowadays, no satisfying rheological method is known to analyze nixtamalized corn dough. As a result, industrial producers encounter problems during process due to a lack of prior characterization. The objective is to find a rheological method able to analyze nixtamalized corn dough in a repeatable and discriminative way.

MATERIALS AND METHODS

3 nixtamalized corn doughs of various quality (good, medium and bad) were tested with the Mixolab thanks to a tool called the dough kit which allows to directly analyze already formed dough. The dough kit is made up of:
• a fully mounted lid equipped with a "chimney" to facilitate the incorporation of doughs.
• An adapted nozzle (Picture1).
A protocol called "Chopin+90g" has been applied. This protocol is similar to the standard protocol (AACC 54-60.01) but is conducted with 90 grams of dough (Table 1).
All analyses were made in duplicate to evaluate the repeatability of the method.
In order to evaluate the significance of the results, an ANOVA test coupled to an HSD interval of Tukey will be used. The Tukey HSD test allows to compare all pairs of averages and to show significant differences with a 95% confidence level. This test provides groups named by letters (group A, B, C ...). The averages that do not share letters are significantly different.

RESULTS AND DISCUSSION

The results showed this protocol allowed the assessment of Nixtamalized corn dough:
• A complete curve is obtained whatever the tested sample. The results seem well discriminated (Figure 2)
• The repeatability results are very good given the low coefficients of variation obtained (4.7% in average taking into account all parameters and all samples) (Table 2).
• The statistical analysis proves that the method is discriminative: C2, C3 and C4 torques are parameters that allow to differentiate efficiently the different qualities of doughs (Table 3).
• Finally, the results are consistent with the quality of the masas: when the dough is heated, the lower the torques, the better the sample is, according to the process performances. For example, the lower the C3 parameter is, the better the behavior of the dough during process is (2.67 Nm for bad quality dough, 2.37 Nm for good quality dough) (Figures 3 to 5).

CONCLUSION

Thanks to a slight adjustment of the standard protocol, the Mixolab is able to analyze nixtamalized corn doughs.
This analysis is repeatable and discriminative:
• The method is able to differentiate a good quality sample, from a medium quality and from a bad quality in a repeatable way.
• The Mixolab results show a good link with the quality of the samples (the lowest the curve, the better the quality of the dough).
Rheological properties of nixtamalized corn doughs can be evaluated and the quality of such products can be predicted thanks to the Mixolab. Further tests will be needed to validate the protocol or adjust it if necessary.

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