Non-thermal emerging technologies as alternatives to chemical additives to improve the quality of wheat flour for breadmaking: a review

Wheat flour is the main ingredient used in the preparation of bread. Factors such as low gluten content and the addition of nontraditional ingredients in baking affect the quality of wheat flour and may limit its use in baking. With the increasing trend of "clean label" products, it may be interesting to develop and use physical processes to improve the quality of wheat flour and avoid the use of chemical additives. High hydrostatic pressure, non-thermal plasma, ultrasound, ozonation, ultraviolet light, and pulsed light treatments are non-thermal emerging technologies (NTETs) that have been studied for this purpose. They were originally developed to inactivate microorganisms and enzymes in foods. Additionally, these technologies can be used at low temperatures to modify the most important component of wheat flour, i.e., gluten and its fractions, which are responsible for the rheological properties of wheat flour dough. Thus, this review focuses on the effects of these NTETs by considering the following factors: (1) the technological properties of gluten, (2) gluten-starch interactions, (3) possible effects of NTETs on minor components of flours, and (4) the quality of wheat flour and the resulting final products.

Changes in Hydrophobic Interactions among Gluten Proteins during Dough Formation

In this study, changes in hydrophobic interactions among gluten proteins were analyzed during dough mixing. Size-exclusion high-performance chromatography and two-dimensional fluorescence difference gel electrophoresis were performed on proteins extracted with 1-propanol by weakening the hydrophobic interaction. The amount of proteins extracted with 30% 1-propanol increased from the start of mixing to peak consistency, suggesting that the hydrophobic interactions among the strongly aggregated proteins weakened and resulted in disaggregation. The amount of proteins extracted with 10% 1-propanol decreased during hydration, indicating that these proteins aggregated through relatively weak hydrophobic interactions. The proteins that extractability decreased were mainly low molecular weight glutenin, α-gliadin, and γ-gliadin. The amount of monomeric proteins extracted with 30% 1-propanol decreased after peak consistency. The decreased protein was mainly ω-gliadin, indicating that ω-gliadin aggregated with other proteins through hydrophobic interactions. A front-face fluorescence analysis was performed on the dough with the addition of 8-anilino-1-naphthalenesulfonic acid or thioflavin T. The fluorescence intensity increased as a result of exposure to the hydrophobic groups of the gluten proteins and the formation of protein aggregates during dough mixing. These results indicate the importance of hydrophobic interactions in dough formation.

Revealing 3D structure of gluten in wheat dough by optical clearing imaging

Gluten, which makes up 85% of endosperm wheat protein, is considered a crucial quality determinant of wheat-based food products. During wheat dough manufacture, the molecular packing of gluten causes formation of large structures that exceed the millimetre scale. However, due to lack of imaging techniques for complex systems composed of giant macromolecules, the entire gluten structure remains unknown. Here, we develop an optical clearing reagent (termed SoROCS) that makes wheat-based products transparent. Combined with two-photon microscopy, we image the three-dimensional (3D) structure of gluten at the size in the millimetre scale and at submicron resolution. Further, we demonstrate how the 3D structure of gluten dramatically changes from a honeycomb-shaped network to sparse large clumps in wheat noodles, depending on the salt added during dough making, thereby reducing stress when compressing the noodle. Moreover, we show that SoROCS can be used for noodle imaging using confocal laser scanning microscopy.

Transcriptome analysis reveals that the multiple metabolic pathways were related to gluten polymerization in different quality wheats (Triticum aestivum L.)

The rapid development of transcriptome sequencing technology has contributed to the discovery of numerous genes in plant; however, the role of gene expression in postharvest wheat remains largely unexplored. In this study, differentially expressed genes (DEGs) were identified by RNA-seq in different quality wheats. The 102.6 Gb clean reads had been yielded from the nine RNA-seq libraries. Typically, there were 1791 upregulated and 2,677 downregulated DEGs, respectively, in strong-gluten wheat compared with weak-gluten wheat. Specifically, a total of 4,468 DEGs were classified into 286 Gene Ontology (GO) terms and 131 Kyoto Encyclopedia of Genes and Genomes terms (KEGG). Moreover, the storage protein components, starch and sucrose metabolism, and plant hormone signal transduction-related genes were discovered, which had involved 109 DEGs. The wet gluten proteins content was 35.24% and 17.36%, and the glutenin macropolymer content was 6.38% and 5.01% between the strong- and weak-gluten wheat, respectively. The POD activities of the different quality wheats were 6,571.14, 5,341.24, and 4,851.48 U/g/min, respectively. The significant difference of starch and sucrose metabolism, hormone, POD, and CAT enzyme along with the higher ATPase activity might potentially affect gluten polymerization, which might thereby result in the different qualities of wheats.

Evaluation of pasting and dough rheological properties of composite flours made from flour varied in gluten strength

Flours from various wheat varieties varied in gluten strength were blended in varying proportions and evaluated for pasting and dough rheological properties. The different blends of strong: very weak/weak/medium flour (100:0, 75:25, 50:50, 25:75 and 0:100) (w/w) were prepared. Two strong and three weak wheat varieties were selected for this study on the basis of Farinograph dough stability (DS). Strong wheat (HUW468 and HP1761), medium weak (HUW234), weak (HD2894) and very weak (WH1021) wheat variety had DS of 11.4-13.5 min, 9.9 min, 6.2 min, and 2.8 min, respectively. Protein content of the flour decreased with increase in proportion of weak wheat flours in the blends. The lowest values of protein content, paste viscosities and mixographic parameters were observed for blend of strong and very weak wheat flour (25:75). The blending of strong wheat flour with weaker wheat flour decreased the protein content and mixographic properties. The regression equations for blending of weak wheat with strong wheat flour had the highest regression coefficient for paste viscosities (Peak, final, breakdown and setback) and pasting temperature indicated that the greatest change in these properties with increase in blending level of weak wheat. The blending of weak wheat with strong wheat flour had the highest regression coefficient indicating the greatest change in MPT as the blending level was increased. The blending of very weak, weak and medium wheat flour with strong wheat flour showed significant effect on G' and G″. The flours with variable dough rheological properties suitable for different products can be produced by blending strong and weak wheat flour.

Recombinant Wheat Endoplasmic Reticulum Oxidoreductin 1 Improved Wheat Dough Properties and Bread Quality

Recombinant wheat endoplasmic reticulum oxidoreductin 1 (wEro1) with considerable ability was expressed in Escherichia coli. The functional roles of wEro1 in flour processing quality were investigated by farinographic, rheological, texture profile analysis, electrophoresis, size exclusion chromatography, scanning electron microscopy, and Fourier transform infrared spectroscopy. wEro1 exhibited an obvious oxidation activity of sulfhydryl groups in small molecule and protein. Addition of wEro1 could strengthen the processing quality of dough, indicated by the improved mixing characteristics, viscoelastic properties, and bread qualities. These improvement effects of wEro1 could be attributed to the formation of macromolecular gluten polymers and massive gluten networks by disulfide cross-linking. Additionally, the increased β-turn structure further demonstrated the enhancement of dough strength. Moreover, the amount of peroxide in dough was improved significantly from 2.36 to 2.82 μmol/g of flour with 0.15% wEro1 treatment. Therefore, the results suggested that wEro1 is a promising novel flour improver.

Effect of Condensed Tannin Profile on Wheat Flour Dough Rheology

Proanthocyanidins (PA) cross-link proteins and could expand wheat gluten functionality; however, how the PA MW or gluten profile affect these interactions is unknown. Effect of PA MW profile (sorghum versus grape seed PA) on dough rheology of high versus low insoluble polymeric protein (IPP) wheat flour was evaluated using mixograph, large (TA.XT2i) and small (HAAKE Rheostress 6000) deformation rheometry. Sorghum PA (93% polymeric) more effectively (p < 0.05) strengthened both glutens than grape seed PA (45% polymeric), without reducing gluten extensibility. These effects were higher in low IPP (weak gluten) flour, e.g., sorghum PA doubled IPP, increased mix time by 75%, dough elasticity by 82%, and peak angle by 17° versus control. Grape seed PA increased IPP by 75% and elasticity by 36%, but reduced peak angle by 15°, indicating reduced mixing tolerance. Sorghum PA, but not grape seed PA, increased (p < 0.05) all above parameters in high IPP dough. Polymeric PA more effectively strengthened gluten than oligomeric PA, likely via more efficient protein cross-linking to overcome strong antioxidant effect of PA. High MW PA may be useful natural gluten strengtheners for diverse applications.

From raw material to dish: pasta quality step by step

Pasta is a traditional Italian cereal-based food that is popular worldwide because of its convenience, versatility, sensory and nutritional value. The aim of this review is to present a step-by-step guide to facilitate the understanding of the most important events that can affect pasta characteristics, directing the reader to the appropriate production steps. Owing to its unique flavor, color, composition and rheological properties, durum wheat semolina is the best raw material for pasta production. Although pasta is traditionally made from only two ingredients, sensory quality and chemical/physical characteristics of the final product may vary greatly. Starting from the same ingredients, there are a lot of different events in each step of pasta production that can result in the development of varieties of pasta with different characteristics. In particular, numerous studies have demonstrated the importance of temperature and humidity conditions of the pasta drying operation as well as the significance of the choice of raw material and operating conditions on pasta quality.