Plant growth promotion abilities of spent brewer’s yeast (SBY) on Zea mays L.

The global population has reached 8 billion people at the end of 2022 and is supposed to exceed 9 billion by 2045. The increase in population over the last decades induced the raise of food production and therefore the use of fertilizers in agriculture with the aim to sustain the growing food demand. Given the environmental toxicity of chemical products engaged for improving the agricultural yields, the use of more sustainable fertilizers is suggested in the frame of circular economy. In this view, the reutilization of by-products as biofertilizer can be a valid solution in order to limit waste production of agri-food industries and give second life to products that still can be recycled and reused. One of the major producing industries in agri-food chain is represented by brewery, that generates large amounts of by-products that can be easily reutilized for their characteristics, being particularly environment-friendly. The main by-products produced through the brewery process are: spent brewer’s grain (SBG), spent hops (SBH) and spent yeast (SBY). However, they are all unstable and need to be rapidly processed in order to be reused. Despite many papers report the use of these by-products for alternative scopes such as animal nutrition or substrate for microorganisms cultivation, very little is known about the use of SBY as plant growth promoting product. Moreover, a deep investigation in terms of SBY characteristics, biostimulant potential alone and in combination with nutritive solutions is needed to understand its real applicability in agriculture. In this perspective, the goals of the current PhD project were to investigate the physical and chemical features of spent brewer’s yeast extracts obtained by different fractionations (thermic - AUT; centrifuged - CEN; filtered - FIL; ultrafiltered - ULT) by means of laboratory analysis coupled with spectroscopic measurements (DRS) and test the effects of the most promising SBY fraction (ULT) on the germination of corn (Zea mays L.) used as model organism (case study I), and shed light on the morphological and physiological responses of corn towards the yeast application alone and in combination with nutritive solutions and humic acids (case study II). The case study I showed high content of nutrients and amino acids, and a possible good amount of carbohydrates, sugar and vitamins in ULT (laboratory analyses and DRS) that had a biostimulant germination effect on corn at 1.5 and 3% dilutions. The evaluation of corn responses to ULT application showed by the case study II highlighted a plant growth promoting activity in the underground organ in terms of morphological dynamics for ULT alone and mixed to nutrient solutions whereas the mix spent yeast (ULT)-humic acids improved the photosynthesis rate by increasing the pigments efficiency in light use. This research highlights great potentialities for the investigated by-product but further investigations urge for clarifying the specific metabolic pathways or genes involved in these processes with the aim to give more information about the real efficacy of spent brewer’s yeast in agriculture as plant growth promoter.