###### Abstract  
Current food production methods and consumption behaviours are unsustainable and contribute to environmental harm. One example is food waste--around 38% of food produced is wasted each year. Here, we show that two common food waste products, wheat bran and brewer's spent grain, can successfully be upcycled via miso fermentation. During the fermentation process, kokumi \(\gamma\)-glutamyl peptides, known to increase mouthfulness, are produced; these include \(\gamma\)-ECG (oxidized), \(\gamma\)-EVG, \(\gamma\)-EV, \(\gamma\)-EE, \(\gamma\)-EF, and \(\gamma\)-EL. The profiles of kokumi peptides and volatile aroma compounds are correlated with koji substrate, pH, and enzymatic activity, offering straightforward parameters that can be manipulated to increase the abundance of kokumi peptides during the fermentation process. Correlation analysis demonstrates that some volatile aroma compounds, such as fatty acid ethyl esters, are correlated with kokumi peptide abundance and may be responsible for fatty, greasy, and buttery aromas. Consumer sensory analysis conveys that the bitter taste of vegetables, such as that in endures, can be dampened when miso extract containing kokumi peptides is added. This suggests that kokumi peptides, along with aroma volatile compounds, can enhance the overall flavour of plant-based products. This study opens new opportunities for cereal processing by-product upcycling via fermentation, ultimately having the potential to promote a plant-based diet. kokumi; fermentation; upcycled miso; sustainability; aroma; side stream utilisation; bitterness 2023124297 122323  
products [8]. \"Green\" or \"beany\" aromas such as hexanal, (E)-2-nonenal, and (E,E)-2-4-decadienal in plant-based ingredients present a challenge [9]. Another challenge with many plant ingredients, for example, with vegetables belonging to the Brassica and Cichorium genera, is that they have an inherent bitterness due to the presence of various bitter compounds such as glucosinolates [10; 11], which are often less favoured by consumers [12]. Fermentation has been used to preserve food but also to improve the flavour and the bioavailability of nutrients from raw materials [13]. In particular, \(\gamma\)-glutamyl peptides have been shown to increase'mouthfeel' amongst other desirable qualities and have been proposed as flavour enhancers in food [14]. Additionally, \(\gamma\)-glutamylization is being researched as a means of reducing bitterness by the synthesis of peptides such as \(\gamma\)-Glu-Phe, \(\gamma\)-Glu-Leu, or \(\gamma\)-Glu-Val from bitter amino acids like Phe, Leu, and Val through GGT (gamma-glutamyl transferase) catalysis [15]. These \(\gamma\)-glutamyl peptides cause a sensation called koku, a Japanese word describing the mouthfeels of thickness, richness, complexity, and continuity. These peptides have also been shown to be present in different fermented products like beer, cheese, soy sauce, sake, and miso [15; 16]. Additionally, a concept called the \"unamification\" of plant-based materials suggests that fermentation can increase the concentration of amino acids and simple sugars to improve flavour [7], and kokumi peptides have been shown to increase umami [17], suggesting fermentation as a promising strategy for enhancing the favourable qualities of plant-based foods. Previous studies have shown that kokumi peptides are present in miso prepared with alternative grains [16]. We were, therefore, interested in whether this concept can be expanded to additional substrates, especially cereal processing by-products, as a strategy to revalorise and reduce food waste. Wheat bran, a side product of milling wheat into white flour, and brewer's spent grains (BSG), a by-product of beer filtration, are amongst the most common food production by-products; respectively, around 90 million tons and 32.5 tons are produced annually worldwide [6; 18].