Biosynthesis and conversion of phenolics and taste active compounds in food fermentations

微生物代谢决定和维持发酵食品的质量和安全。乳酸菌是大多数发酵食品（包括发酵谷物食品）中发酵微生物群的主要代表。申请人的研究项目一般旨在将食品发酵乳酸菌的生态学和生理学与其在谷物发酵中的竞争力及其对食品质量的影响联系起来。拟议的研究计划的长期目标是表征次要代谢物的代谢，特别是味觉活性肽的形成和乳酸菌对酚类化合物的转化，并确定这些代谢物对面包的感官、营养和质地质量的影响。具体地说，拟议的项目旨在阐明形成？-谷氨酰肽和酚酸的转化，以了解这些代谢途径在乳酸菌生态学中的作用，以及它们对改善面包品质的贡献。尝起来活跃吗？-谷氨酰肽通过改变对甜味、咸味和鲜味化合物的感知来影响食物的味道。这种味觉活动被称为“kokumi”活动。？-谷氨酰肽在发酵酱油、长熟奶酪和酵母中积累到活性浓度；然而，它们的形成通常归因于原料中的酶，而不是细菌代谢。申请人最近的工作证明罗伊氏乳杆菌产生？-酵母中的谷氨酰肽。生物信息学分析确定？-谷氨酸-半胱氨酸连接酶和谷氨酰胺酶作为合成酶谷酰基肽。的贡献？-谷氨酰肽对面包味道的影响将通过酵母和酵母面包中这些肽的定量测定，以及用谷氨酰胺酶缺失的野生型菌株和突变菌株生产的面包的感官分析来确定。-glutamate-cysteine合成酶。感官分析将特别针对罗伊氏乳杆菌菌株积累？-谷氨酰肽来生产不影响消费者偏好的减盐面包。酚酸：谷物、蔬菜或水果中通过抗菌活性调节发酵微生物群组成的酚酸；此外，酚酸也是风味挥发物的前体化合物。乳酸菌酚酸代谢对谷物发酵过程中的生态适应性以及发酵谷物食品的质地和感官品质的影响尚不清楚。拟建项目的工作旨在通过比较基因组学确定具有酚酸活性的推定酶。酚酸脱羧酶和还原酶将通过异种表达和等基因缺失突变体的特征来表征，并确定它们在酵母生化和面包品质中的作用。

Microbial metabolism determines and maintains the quality and safety of fermented foods. Lactobacilli are dominant representatives of fermentation microbiota in most fermented foods, including fermented cereal food. The applicant's research program generally aims to link the ecology and physiology of food-fermenting lactobacilli to their competitiveness in cereal fermentations and their impact on food quality. The long term aim of the proposed research programme is to characterize the metabolism of minor metabolites, particularly the formation of taste-active peptides and the conversion of phenolic compounds by lactobacilli, and to determine the impact of these metabolites on the sensory, nutritional, and textural quality of bread. Specifically, the proposed project aims to elucidate the genetic determinants of formation of ?-glutamyl peptides and conversion of phenolic acids, to understand the role of these metabolic pathways in the ecology of lactobacilli, and their contribution to improved bread quality. Taste active ?-glutamyl peptides impact the taste of foods by altering the perception of sweet, salty, and umami tasting compounds. This taste activity has been referred to as "kokumi" activity. ?-Glutamyl peptides accumulate to active concentrations in fermentation of soy sauce, long-ripened cheese, and in sourdough; however, their formation has typically been attributed to enzymes from the raw material rather than bacterial metabolism. Recent work of the applicant demonstrated that L. reuteri produces ?-glutamyl peptides in sourdough. Bioinformatic analyses identified ?-glutamate-cysteine ligases and glutaminases as enzymes that synthesise ?-glutamyl peptides.  The contribution of ?-glutamyl peptides to the taste of bread will be determined by quantification of these peptides in sourdough and sourdough bread, and by sensory analysis of bread produced with wild type strains and mutant strains with deletions in glutaminases or ?-glutamate-cysteine synthase. Sensory analyses will particularly aim to employ strains of L. reuteri that accumulate ?-glutamyl peptides to produce salt-reduced bread without reduction of consumer preference. Phenolic acids that in cereals, vegetables, or fruits modulate the composition of fermentation microbiota through their antimicrobial activity; moreover, phenolic acids also are precursor compounds for flavour volatiles. The contribution of phenolic acid metabolism of lactobacilli to ecological fitness in cereal fermentations and the texture and sensory quality of fermented cereal foods is unknown. Work in the proposed project aims to identify putative enzymes with activity on phenolic acids by comparative genomics. Phenolic acid decarboxylases and reductases will be characterized after heterologous expression, and by characterization of isogenic deletion mutants, and their role for sourdough biochemistry and bread quality will be determined.