The objectives of this research are to examine the impact of LED light frequency and intensity on mushroom production bioefficiency (BE) and mushroom nutritional content. It is well known that exposure to UV light (UV-B or UV-C) will increase the vitamin D2 content in mushrooms. While most of this work has been with button mushrooms, specialty mushrooms such as oyster and shiitake have the same response. What is little know is the effect of other light frequencies on both the nutritional content of mushrooms and the production BE.
There is considerable research on the use of LED illumination for plant production in greenhouses with impacts on plant morphology, yield, and nutritional content well documented due to the presence of plant phytochromes and crytochromes sensitive to specific light wavelengths. Fungi also posses phytochromes and crytochromes, however, the impacts of specific wavelengths of light on fungal growth and physiology is not well understood. Our research aims to document the effects of white, red, and blue LED illumination on production BE, total protein content, total antioxidant content, and beta-glucan content for several species of oyster mushroom.
For our studies, straw has been the foundation carbon source to which high nitrogen supplements have been added. The predominant nitrogen sources were either whole cotton seed or mesquite pods. When the two were compared, the use of cotton seed resulted in a 40% increase in BE compared to mesquite pods. The impact of a specific LED illumination during fruiting revealed growth of P. ostreatus, and under all illuminations. Comparing different light frequencies, red LEDs did result in significantly higher BE in most experiments, but not in all repeated experiment with similar temperature, humidity and spawn time conditions. Continued study are needed to fully access these differences.
While LED color did not have a robust impact on BE, it did impact mushroom cluster and cap architecture in P. ostreatus. Growth under red LEDs did not significantly alter the number of clusters produced per bag or the average cluster weight, but red light did result in a significantly larger number of mushroom caps per cluster compared to either blue light or white light and these caps were significantly smaller under red LEDs compared to those grown under blue or white LEDs. This suggest that LED color choice can be used to manipulate P. ostreatus cluster and cap architecture for specific market preferences without sacrificing productivity.
The use of specific LEDs had a significantly impact on several nutritional properties of oyster mushrooms. When grown under red LED, mushrooms contained a higher total antioxidant content compared to either blue or white LED illumination. In contract, when grown under blue LEDs, beta glucan content was significantly increased. Moreover, when grown under high intensity blue LEDs, beta glucan content increased even more.
The use of specific LEDs did not significantly impact the total protein content of the mushroom, but the choice of substrate certainly did and also impacted the percentage of certain amino acids. Mushrooms grown on straw/cotton all contained significantly higher levels of glutamic acid, arginine and histidine compared with straw/mesquite. Given the focus on the nutritional properties of mushrooms, growth of P. ostreatus on a substrate that increases amino acid content is notable. Increased histidine content is particularly critical, given that histidine is both an essential amino acid and a precursor for the antioxidant ergothioneine.
These experiments sought to answer if choice of substrate – straw/cotton or straw/mesquite and choice of LED color influence the BE, nutritional content and antioxidant properties of Pleurotus spp.While the experiments were conducted at similar temperatures, humidity conditions, and fruiting times, findings were at time inconclusive. These studies are continuing with additional focus on maintaining highly uniform environmental conditions.