Effects of supplementation on the mycelial ergosterol content of Agaricus bisporus grown on media formulated with olive oil subproducts

Until the last decades of the XXcentury, the growth of mushrooms on an industrial scale was based more on an art of cultivation than on scientific knowledge. It is known that mushroom growth is influenced by the composition of the growth media [1]. Supplementation is one of the most relevant of the different procedures used to modulate mushroom growth. This practice consists of adding specific substances to compost, during composting to increase nutrient availability and/or active substances, which, when consumed, improve performance and/or quality and probably increase the production of metabolites with health benefits. This technique was introduced in the 1960s [2]; [3]; [4], and from a practical point of view, some important aspects should be considered prior to its application, such as the types of nutrients required, the most suitable application time and economic costs and profits [5]. Most of the relatively few studies published on this topic focused on the productivity of the process. These processes result in yields that generally increase by 10–20% and occasionally by more [6], but little is known about the influence of supplementation on the concentration of metabolites with health benefits, such as ergosterol, ergothioneine, glucans, and chitin. Among the different raw materials that can be used for these purposes are agroindustrial subproducts such as cereal grain brands and meals, oilseed meals, cottonseed meal, and peanut oil and its derivatives, which contain varying amounts of the basic nutritional biomolecules, including carbohydrates, proteins, and lipids. In this study, we examined two agroindustrial subproducts of the olive oil industry that are highly abundant in southern Spain: two-phase pomace or alperujo (ALP) and olive leaf (OL), and its derivatives: alperujo meal (ALPM), olive leaf meal (OLM) and olive leaf hydroalcoholic extract (OLHAE).

Experiments leading to fructification (mushrooms) with edible fungi grown on compost require long cultivation times, and since the same components and metabolites with health benefits have been detected in the fruiting bodies and the mycelia [1], the mycelial composition can be assumed to be similar to that of the fruiting bodies. Therefore, in this study, we examined the effect of supplementing minimal defined growth medium with different compounds derived from olive oil industry subproducts, ALPM, OLM and OLHAE, on Agaricus bisporus (A. bisporus) mycelial composition, primarily ergosterol. A. bisporus was grown on liquid and solid media as a preliminary step to the study on fruiting bodies aftergrowth on compost supplemented with the same supplement, in an attempt to obtain mushrooms with higher ergosterol (pro-vitamin D2) concentration.