Enzymatic activity of variously preserved extracts from spent mushroom substrate (Pleurotus ostreatus) and in vitro rumen degradation of extract-treated wheat straw.

White rot fungi obtain nutrients from fibrous substrates through the radical secretion of extracellular ligninolytic enzymes (LE) and spent mushroom substrate (SMS), a by-product of commercial cultivation, is a valuable bioresource of LE. This study aims to compare various techniques for dehydrating and preserving the Pleurotus ostreatus SMS extract in terms of enzymatic activity and ability to improve the fiber rumen degradability (NDFD) of extract-treated wheat straw. To convert the extract into stable enzyme powder, it was concentrated before being dried using freeze, spray and vacuum drying processes. The different extracts reconstituted from powders were evaluated for residual LE activity after multiple successive freeze-thaw cycles, as well as their ability to improve wheat straw NDFD. To produce extracts, fresh SMS was suspended in acetate buffer, homogenized and filtered. A portion of the original extract was stored (- 20 °C) and the remainder was concentrated up to 50% of volume by cross-flow filtration. The concentrated extract was divided into four aliquots to be used without processing or spray, vacuum or freeze drying. Extracts were evaluated for total, Mn and lignin peroxidases and laccases (LAs) enzymatic activity and were subjected to four freezing-thawing cycles. Wheat straw was incubated in reconstituted extracts before being tested for in vitro NDFD. Compared to the original extract, reductions of LE were 2-30% in concentrated and 10-36, 4-48 and 74-84% in freeze, vacuum and spray dried, respectively. LE of extracts decreased with the number of freeze-thaw cycles, apart from the spray dried extract. The NDFD of all extract-treated straws resulted higher (P < 0.05) than the control, apart from the spray-dried extract and had a high linear relationship with LAs of extracts (R