Pigment loss from semolina to dough: Rapid measurement and relationship with pasta colour

- Developed a method to quantify yellow pigment loss due to enzymatic degradation in semolina.
- The pigment loss from semolina to dough was found to be genotype dependent.
- Durum genotypes with low loss (0-3.8%) were characterized by the absence of a LOX gene duplication at the Lpx-B1 locus.
- The loss was higher (5.5-21.8%) for genotypes carrying the LOX gene duplication.
- The method could be used as a tool to select for reduced colour loss during pasta processing due to enzymatic oxidation.

The yellow colour of pasta is due largely to the presence of carotenoid pigments in semolina. Some of the carotenoids can be degraded during pasta processing through oxidation induced by lipoxygenase (LOX), resulting in pasta colour loss. Measurement of LOX activity is complex and not practical as a screening tool, so there is a need to develop a rapid, cost effective, high throughput method for routine measurement of colour loss in breeding programs and the durum milling and pasta processing industries. After establishing a rapid micro-scale pigment extraction procedure, this study developed a method to quantify pigment loss due to enzymatic degradation in semolina. It can be conducted in parallel with a simple and reliable micro-scale semolina pigment content assay utilizing water saturated 1-butanol extraction. Water (0.15 ml) was added to semolina (200 mg) in a micro centrifuge tube. The mixture was then homogenized to simulate the mixing and kneading processes in pasta-making, and allowed to rest for 1.0 or 2.0 h. Pigments in the resulting dough were extracted by adding 0.85 ml of 1-butanol, followed by homogenization, resting, and centrifugation. Absorption at 435 nm was recorded and converted to yellow pigment concentration. The pigment loss from semolina to dough was found to be genotype dependent. Durum genotypes with low loss (0-3.8%) were characterized by the absence of a LOX gene duplication at the Lpx-B1 locus, which was shown previously to be associated with a strong reduction in LOX activity in semolina. The loss was higher (5.5-21.8%) for genotypes carrying the LOX gene duplication. While the relationship between pigment content in semolina and pasta colour was significant (r2 = 0.55-0.61), the relationship between pigment content in dough after oxidative loss and pasta colour was stronger (r2 = 0.59-0.90). These results suggest that the method developed in this study could be used as a tool to select for reduced colour loss due to LOX activity.