Diversity of γ- glutamyl peptides and oligosaccharides, the "kokumi" taste enhancers, in seeds from soybean mini core collections

Novel Soybean Variety Lacking Raffinose Synthase 2 Activity

Variation in the raffinose family oligosaccharide (RFO) content in soybean is advantageous for livestock farming and health science. In this study, a soybean variety (GmJMC172) with a significantly low stachyose content in its seeds was identified in the NARO Genebank core collection. The results of the single-nucleotide polymorphism (SNP) analysis suggested that this phenomenon was related to a single-base deletion, inducing a frameshift mutation in raffinose synthase 2 (RS2), rather than the polymorphisms in the RS3, RS4, and stachyose synthase (STS) sequences. Differences in the enzymatic properties between the native RS2 and truncated RS2 were examined by using a three-dimensional model predicted using Alphafold2. In addition to revealing the missing active pocket in truncated RS2, the modeled structure explained the catalytic role of W331* and suggested a sufficient space to bind both sucrose and raffinose in the ligand-binding pocket. The soybean line, with seeds available from the NARO Genebank, could serve as breeding materials for manipulating the RFO content.

Proteometabolomic Analysis Reveals Molecular Features Associated with Grain Size and Antioxidant Properties amongst Chickpea (Cicer arietinum L.) Seeds Genotypes

Legumes are an essential source of nutrients that complement energy and protein requirements in the human diet. They also contribute to the intake of bioactive compounds such as polyphenols, whose content can vary depending on cultivars and genotypes. We conducted a comparative proteomics and metabolomics study to determine if there were significant variations in relevant nutraceutical compounds in the five genotypes of Kabuli-type chickpea grains. We performed an isobaric tandem mass tag (TMT) couple to synchronous precursor selection (SPS)-MS3 method along with a targeted and untargeted metabolomics approach based on accurate mass spectrometry. We observed an association between the overproduction of proteins involved in starch, lipid, and amino acid metabolism with gibberellin accumulation in large grains. In contrast, we visualized the over-accumulation of proteins associated with water deprivation in small grains. It was possible to visualize in small grains the over-accumulation of some phenolics such as vanillin, salicylic acid, protocatechuic acid, 4-coumaric acid, 4-hydroxybenzoic acid, vanillic acid, ferulic acid, and kaempferol 3-O-glucoside as well as the amino acid l-phenylalanine. The activated phenolic pathway was associated with the higher antioxidant capacity of small grains. Small grains consumption could be advantageous due to their nutraceutical properties.

Metabolite Profiling of Soy By-Products: A Comprehensive Approach

Soy is the major oilseed crop as soybeans are widely used to produce biofuel, food, and feed. Other parts of the plant are left on the ground after harvest. The accumulation of such by-products on the soil can cause environmental problems. This work presents for the first time a comprehensive metabolite profiling of soy by-products collected directly from the ground just after mechanical harvesting. A two-liquid-phase extraction using n-heptane and EtOH-H2O 7:3 (v/v) provided extracts with complete characterization by gas chromatography and ultra-high-performance liquid chromatography both coupled to time-of-flight mass spectrometry. A total of 146 metabolites, including flavones, flavonols, isoflavonoids, fatty acids, steroids, mono-, sesqui-, di-, and triterpenoids, were tentatively identified in soy by-products and soybeans. These proved to be sources of a wide range of bioactive metabolites, thus suggesting that they could be valorized while reducing potential environmental damage in line with a circular economy model.

Quantitative determination of kokumi compounds, γ-glutamyl peptides, in Korean traditional fermented foods, ganjang and doenjang, by LC-MS/MS

Recent studies have shown that γ-glutamyl peptides (GGPs) are recognized by the calcium-sensing receptor and induce kokumi taste. The contents of GGP have been reported in some fermented foods such as cheese and Japanese soy sauce but not in ganjang and doenjang which are representative Korean fermented-soybean products. In this study, the qualitative and quantitative analyses of GGPs in several ganjang and doenjang were carried out by LC-MS/MS using 11 synthetic GGPs as reference compounds. The total GGP contents ranged from 92 to 620 μg/mL for ganjang and from 203 to 387 μg/g for doenjang, respectively. Interestingly, the levels of GGPs were not related to manufacturing types of traditional and industrial products. These data provide a basis for the taste of ganjang and doenjang which was expressed abstractly as mouthful and long-lasting taste.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-021-00993-x.

Recent insights in flavor-enhancers: Definition, mechanism of action, taste-enhancing ingredients, analytical techniques and the potential of utilization

The consumers' demand for clean-label food products, lead to the replacement of conventional additives and redesign of the production methods in order to adopt green processes. Many researchers have focused on the identification and isolation of naturally occurring taste and flavor enhancers. The term "taste enhancer" and "flavor enhancer" refer to umami and kokumi components, respectively, and their utilization requires the study of their mechanism of action and the identification of their natural sources. Plants, fungi and dairy products can provide high amounts of naturally occurring taste and flavor enhancers. Thermal or enzymatic treatments of the raw materials intensify taste and flavor properties. Their utilization as taste and flavor enhancers relies on their identification and isolation. All the above-mentioned issues are discussed in this review, from the scope of listing the newest trends and up-to-date technological developments. Additionally, the appropriate sensory analysis protocols of the naturally occurring taste-active components are presented. Moreover, future trends in using such ingredients by the food industry can motivate researchers to study new means for clean-label food production and provide further knowledge to the food industry, in order to respond to consumers' demands.

γ-Glutamyl Cysteine Ligase of Lactobacillus reuteri Synthesizes γ-Glutamyl Dipeptides in Sourdough

Kokumi-active γ-glutamyl dipeptides (γ-GPs) accumulate in fermented food. γ-Glutamyl transferase, glutaminase, glutathione synthetase, and γ-glutamyl cysteine ligase (GCL) may synthesize γ-GPs. The genome of Lactobacillus reuteri encodes GCL but not glutathione synthetase or glutamyl transferase; therefore, this study investigated the role of GCL in γ-GP synthesis by L. reuteri LTH5448. Phylogenomic analysis of gcl in lactobacilli demonstrated that three genes coding for GCL are present in L. reuteri; two of these are present in L. reuteri LTH5448. Two deletion mutants of L. reuteri LTH5448, L. reuteri LTH5448Δ gcl1 and LTH5448Δ gcl1Δ gcl2, were constructed by double crossover mutagenesis. Growth and oxygen resistance of the mutants were comparable to the wild type. γ-Glu-Glu, γ-Glu-Leu, γ-Glu-Ile, γ-Glu-Val, and γ-Glu-Cys were quantified in buffer and sourdough fermentations by liquid chromatography-mass spectrometry. The wild type and L. reuteri Δ gcl1 but not Δ gcl1Δ gcl2 converted amino acids to γ-Glu-Cys. γ-Glu-Ile accumulation was reduced in both mutants; however, the disruption of gcl did not alter the biosynthesis of the other γ-GPs. In conclusion, gcl1 in L. reuteri mediates γ-Glu-Ile synthesis, gcl2 mediates γ-Glu-Cys synthesis, but neither gene affected synthesis of other γ-GPs. This study facilitates selection of starter cultures that synthesize γ-Glu peptides with kokumi activity and, thus, improve the taste of fermented foods.