INFLUENCE OF CHEMICAL COMPOSITION OF SUBSTRATE ON GROWTH, YIELDS AND SYNTHESIS OF VOLATILE ORGANIC COMPOUNDS IN SOLID-PHASE CULTIVATION OF PLEUROTUS OSTREATUS (JACQ.:FR.) KUMM.

Abstract

Mushrooms of the genus Pleurotus have been used as food and for medicinal purposes since ancient times. To date, Pleurotus mushrooms have been cultivated worldwide since the species of these mushrooms grow relatively easily and have a high degree of adaptability. As a power source they need carbon, nitrogen and inorganic compounds. Various materials containing cellulose, hemicellulose and lignin can be used as growth substrates, such as agricultural waste and waste from the wood processing industry.

The purpose of the study was to determine the features of the growth of Pleurotus ostreatus (Jacq.:Fr.) Kumm. and the synthesis of volatile organic compounds in solid phase cultures on different types of substrates.

Three strains of the edible Pleurotus ostreatus (Jacq.:Fr.) Kumm.: IBK-549, IBK-551 and IBK-1535 from the mushroom collection of the M.G. Kholodny Institute of Botany, National Academy of Sciences of Ukraine were the objects of the study.

Sunflower husk, barley straw, waste from the processing of corn seeds and sawdust of hardwood species were substrates for the production of fruiting bodies. Preparation and sterilization of substrates were carried out according to commonly accepted methods. The cooled substrate was inoculated with P. ostreatus mycelium. Seeding mycelium was obtained on barley grain. Cultivations were carried out at 26±1 °С and 70-80% humidity to the full mycelial overgrowth of the substrate. Then the containers with the substrate were for 24 hours transferred to a growth room with a temperature of 15-16 °С, humidity of 80-90% and 8 hours of illumination. The 1st and 2nd flushes were harvested. Mushrooms were dried at 40-45 °C in a dry oven for 24-48 hours.

Absorption spectra of hexane extracts were recorded using a spectrophotometer SF-2000 in the range of wavelengths of 200-350 nm.

The obtained data were processed statistically using one-way analysis of variance.

The time of overgrowing of the substrate by mycelium was on average 6-7 days, that is, substrates did not have a significant difference in this indicator. On the sawdust only, the term of the substrate overgrown was on average 8 days, which is probably due to the higher density of the substrate. Primordia most likely was formed on sunflower husk, the slowest (for 2-5 days) – on sawdust. No significant difference was observed in the morphology of the fruit bodies of each mushroom strain obtained on different substrates.

By terms of fruiting on different substrates investigated strains had a significant difference. The fastest fruit bodies of all strains appeared on sunflower husk. The latter were fruited with strains IBK-549 and IBK-1535 cultivated on corn waste. The IBK-551 strain has formed fruit bodies almost simultaneously on all of the studied substrates.

There was a certain variation in the number of formed bunches depending on the strain of the mushroom. IBK-551 formed almost identical amount of bunches on all substrates – an average of 13 to 18 pcs. For the strain IBK-549 there was a significant decrease in mushroom bunches during the cultivation on sawdust (17 pcs.) and corn waste (20 pc.) compared to sunflower husk (30 pcs.). And the strain IBK-1535, on the contrary, formed more of them on sawdust (17 pcs.), but on barley straw there was a significant decrease in bunches (on average, 7 pcs.) compared with sunflower husk (13 pcs.).

Yield of the 1st flush was 2-4 times higher for all strains grown on corn waste, and the lowest – on barley straw and sawdust. The 2nd flush was characterized by the highest yield of all investigated strains cultivated on waste from the processing of corn seeds.

The investigated hexane extracts of dried samples of P. ostreatus fruit bodies had light-absorption maxima in the range of 200-210 nm and 260-300 nm. Such spectral properties are characteristic of solutions of unsaturated compounds with unbound double bonds, and saturated and unsaturated aldehydes and ketones, which determine the aroma properties of mushrooms. As it was found in previous studies, the solution of 1-octen-3-ol (the substance that provides the mushroom flavor) in hexane has a maximum absorption at λ = 205 nm.

The intensity of light absorption of hexane extracts of dried fruit bodies of different strains differed during cultivation on different substrates and in different ranges of wavelengths. So, at 205 nm, the extracts of samples of all strains cultivated on sunflower husk had the highest intensity. In the range of 250-290 nm, the highest intensity of light absorption was observed for extracts of strains IBK-549 and IBK-1535 cultivated on corn waste and sawdust, and for the strain IBK-551 grown on sunflower husks and corn waste. That is, on the sunflower husk, a more pronounced mushroom aroma forms in fruit bodies, which is provided by substances with light absorption maxima in the range of 200-210 nm (1-octene-3-ol). On the corn waste and sawdust, the synthesis of saturated and unsaturated aldehydes and ketones increases (light absorption maxima 260-300 nm), which bring sweet and floral notes to the flavor of mushrooms.

The study showed that it is possible to influence the synthesis of mushroom aroma compounds and to increase their characteristic taste and aroma and, accordingly, consumer attractiveness by selecting the substrate composition for solid-phase cultivation of Pleurotus ostreatus (Jacq.:Fr.) Kumm.

Key words: Pleurotus ostreatus, solid phase cultivation, volatile organic compounds, spectrophotometric analysis, sunflower husk, barley straw, corn waste, woody sawdust