Do enzymatic or non-enzymatic pathways drive the postharvest darkening phenomenon in carioca bean tegument?

Genome-wide association mapping reveals new loci associated with light-colored seed coat at harvest and slow darkening in carioca beans

BACKGROUND

Common bean (Phaseolus vulgaris L.) is a legume whose grain can be stored for months, a common practice among Brazilian growers. Over time, seed coats become darker and harder to cook, traits that are undesirable to consumers, who associate darker-colored beans with greater age. Like commercial pinto and cranberry bean varieties, carioca beans that have darker seeds at harvest time and after storage are subject to decreased market values.

RESULTS

The goal of our study was to identify the genetic control associated with lightness of seed coat color at harvest (HL) and with tolerance to post-harvest seed coat darkening (PHD) by a genome-wide association study. For that purpose, a carioca diversity panel previously validated for association mapping studies was used with 138 genotypes and 1,516 high-quality SNPs. The panel was evaluated in two environments using a colorimeter and the CIELAB scale. Shelf storage for 30 days had the most expressive results and the L* (luminosity) parameter led to the greatest discrimination of genotypes. Three QTL were identified for HL, two on chromosome Pv04 and one on Pv10. Regarding PHD, results showed that genetic control differs for L* after 30 days and for the ΔL* (final L*-initial L*); only ΔL* was able to properly express the PHD trait. Four phenotypic classes were proposed, and five QTL were identified through six significant SNPs.

CONCLUSIONS

Lightness of seed coat color at harvest showed an oligogenic inheritance corroborated by moderate broad-sense heritability and high genotypic correlation among the experiments. Only three QTL were significant for this trait - two were mapped on Pv04 and one on Pv10. Considering the ΔL, six QTL were mapped on four different chromosomes for PHD. The same HL QTL at the beginning of Pv10 was also associated with ΔL* and could be used as a tool in marker-assisted selection. Several candidate genes were identified and may be useful to accelerate the genetic breeding process.

Authentication of carioca common bean cultivars (Phaseolus vulgaris L.) using digital image processing and chemometric tools

Bean authentication can result in higher quality products for commerce. Partial least squares discriminant analysis (PLS-DA) was applied to digital images in order to develop a methodology that allows the non-destructive discrimination of three Phaseolus vulgaris L. cultivars (Agro ANfc9, IPR-Andorinha, and IPR-Sabiá) having different technological characteristics. Principal component analysis resulted in a separation of these cultivars, but with a certain amount of overlap. Supervised analysis showed that three PLS1-DA models, each for two cultivars, was moderately better than the simultaneous treatment of all three cultivars (PLS2-DA). Permutation test evaluated statistical significance of PLS-DA models. The classification models were more accurate for Agro ANfc9 and IPR-Sabiá cultivars than for IPR-Andorinha. The Agro ANfc9-IPR-Sabiá model correctly classified 100% of the two bean classes in both training and test sets. This analytical strategy is fast, inexpensive, environmentally friendly, and can be applied for bean quality control helping cultivar authenticity for commerce.

Effects of refrigeration on biochemical, digestibility, and technological parameters of carioca beans during storage

The objective of this study was to evaluate the effects of grain moisture, temperature, and storage time on biochemical, digestibility, and technological parameters of carioca beans. The grains were stored at 16.7% and 13.8% of moisture at 12, 20, 28, and 36°C for 240 days. It was observed that a reduction in the storage temperature maintained the germination and vigor of the grains. The temperature of 36°C causes between 3.81% and 4.52% reduction in weight of a thousand grains and significant darkening. Carioca beans stored at 36°C exhibited hard-to-cook (HTC) defect at 80 days and increases in hardness after 240 days. The best digestibility indexes of carioca beans were obtained with refrigerated storage. The refrigerated storage (12°C) provides the best preservability of the grains throughout the storage, verified by the parameters biochemical, digestibility, and technological parameters. PRACTICAL APPLICATIONS: Carioca beans are among the most consumed beans in Brazil and their quality for consumption is directly influenced by storage conditions that alter color, nutritional value, bioactive, and cooking properties. Thus, this study seeks to present a practical and viable solution for stockist of bean grains, so that they can store these grains for long periods, maintaining the quality standards for commercialization. In addition, this technology allows the stockist to identify the best time for commercialization of the carioca beans, which has high added value.