Food & Industrial Mycology

The descriptor “food mycology”was first used to describe food manufacture with the aid of fungi by the US microbiologist Dr Larry Beuchat in 1985, with the publication of his book “Food and Beverage Mycology”.  The term “food mycology” has survived, but over time has become used for the study of the role of fungi in food spoilage and the health of human and animals.  Food mycology as we now know it was borne out of the intersection of several existing disciplines: food microbiology – the use of Petri dishes, selective media and dilution counting; seed pathology, which provided direct plating; fungal taxonomy, essential for naming and classifying foodborne fungi; plant pathology as some food spoilage fungi are preharvest pathogens of fruits and vegetables; the fundamental study of water relations, as many foodborne fungi grow under low water activity conditions; and organic chemistry, essential for the study of secondary metabolites, many of which are now known to be toxic and are known as mycotoxins.  International collaboration commenced with the organisation of a meeting called “Standardisation of Methods for the Mycological Examination of Foods” in Boston in 1984.  After a second workshop in Baarn, Netherlands, in 1990, the organisation morphed into the International Commission for Food Mycology, which is still today actively promoting food mycology research.  This paper will describe some of the milestones that occurred among the way, and some of the people who were instrumental in the development of food mycology as a discipline in its own right.

 Sourdough bread has fermented in kitchens globally throughout human history. However, geographic variation in sourdough starter microbial diversity and drivers of this diversity are unknown as our understanding of sourdough microecology is mostly limited to studies of industrial fermentations in Europe. In the largest ever sampling of its kind, 560 starters and background information about fermentation practices were collected from 17 countries, with heavy sampling of North America. Using amplicon sequencing of the 16S rRNA gene (bacteria) and internal transcribed spacer (fungi) amplicon sequencing, we detected 8 yeast and 11 bacterial OTUs occurring at greater than one percent abundance across samples. Samples were dominated by morphologically diverse strains of Saccharomyces cerevisiae as well as Kazachstania spp., Wickerhamomyces anomalus and many non-yeast fungi.  The microbial composition of sourdough starters was poorly explained by fermentation practices or by geography. However, strong patterns of yeast/bacteria co-occurrence emerged under probabilistic analyses and hierarchical clustering revealed 17 sourdough “types” based on microbial community structure.  To test if microbial taxonomic diversity correlates with sourdough functional diversity, eight of these starter “types” were analyzed for the important traits of aroma and rise by analyzing the volatile organic compounds released during fermentation and conducting sensory analysis by an expert sensory panel, and measuring dough rise using time-lapse video. In this relatively simple and ubiquitous ecosystem, we are able to explore broad questions in microecology—including patterns and drivers of microbial community structure.

CBD hemp cultivation is now a very significant industry in North Carolina following its legalization. However, only the flowers of the plant are used for most commercial products, thus the industry generates a significant level of waste in the form of all other parts of the plant not used for CBD products. Mushroom cultivation has the potential of eliminating waste streams, such as the CBD hemp waste, by using the plant matter as a substrate for the mycelial stage of growth in mushroom cultivation. Growing mushrooms on pure hemp material has not always proven to be highly productive. In this study, we formulated five different substrate recipes using hemp material as a dominant ingredient to find the recipe that produced the highest growth rates. We cultivated the following gourmet and medicinal fungi species on the various substrate formulations: Pleurotus ostreatus, Pholiota adiposa, and Ganderma lucidum. Growth rates and mushroom production rates were measured over a period of four weeks. The highest rate of growth was observed with Pleurotus ostreatus on 50% cocoa coir and 50% hemp material. The lowest rate of growth was observed with Pholiota adiposa on 100% hemp material.  The highest rate of mushroom production was also measured with Pleurotus ostreatus on 50% cocoa coir and 50% hemp material. The lowest rate of mushroom production was also measured on Pholiota adisposa on 100% hemp material.

Many outbreaks of human pathogenic bacteria, such as E. coli, are associated with Romaine lettuce. Because lettuce leaves are consumed raw rather than cooked, the phylloplane microbes (fungal and bacterial) are often ingested by the consumer. Despite this, our knowledge about natural bacterial and fungal species associated with the phylloplane of Romaine lettuce is very limited, and yet this knowledge is necessary for understanding how this naturally occurring flora interacts with introduced human pathogens. During this project, we bought 63 Romaine lettuce heads in grocery stores in Illinois, Indiana, Ohio, and Virginia. We plated homogenized samples and isolated individual cultures using axenic techniques. These cultures were DNA barcoded with the internal transcribed spacer (ITS) region of the ribosomal DNA using Sanger sequencing. We isolated 330 cultures and generated ITS sequences for 242 of those, representing 63 unique species of fungi on the lettuce phylloplane. Of these, 9 are undescribed species in diverse genera. Interestingly, the most commonly encountered species in our Romaine lettuce cultures was an undescribed red yeast. Next-generation sequencing was conducted on the same lettuce homogenates, resulting in 630 operational taxonomic units. We compared abundances at different taxonomic levels between treatments. The fungal abundance at all levels was highest in organic lettuces, closely followed by non-organic lettuces. Comparatively, fungal abundance in hydroponic samples was almost non-existent. Our results indicate that certain groups of fungi, like yeasts, in organic samples are replaced by other groups, such as molds, in non-organic samples, likely in response to differing management regimes.

Surface-ripened cheeses are simple microbiomes—bacteria, yeast, and filamentous fungi—that form in cheese aging facilities around the world. The molds that grow in the rinds of these cheeses are celebrated for their role in shaping their flavors, aromas, and aesthetics. Natural rind cheeses have ‘wild’ rinds (not inoculated with fungal starter cultures) and rely on fungi introduced from the environment or raw ingredients. Despite the importance of wild molds in cheese production, the ecological processes that determine fungal community development have yet to be identified. To understand how fungal communities develop in aging facilities, we partnered with a small U.S. cheesemaker in the fall of 2018. We began a long-term monitoring project using settle plates isolate culturable fungi that colonize cheese. We sampled the airborne fungi from post-construction through the addition of cheese. Early sampling, before aging occurred, indicated variable fungi species—both in composition and abundance. After cheese was added to the facility, cheese-associated fungi increased and, eventually, outnumbered the indoor air species—with Penicillium spp. becoming most prevalent. Interestingly, after the addition of cheese, white phenotypes of Penicillium became more common—suggesting a potential phenotypic switch (blue-white transition), or an increase in abundance of white species or strains. This ongoing project will provide key insights into the development of fungal communities and more opportunities to monitor the real-time domestication of wild molds, in cheese production environments.

Marshall Islands is a coconut producing country of the Pacific Region with an abundant source of coconut husk and copra cake that are commonly used by farmers for soil amendment. The study aims to explore the potential alternative use of coconut husk and copra cake for mushroom cultivation. Mycelial growth, fruiting body, cap diameter and biological efficiency conversion (BEC) of Pleurotus sajor-caju (PSC) were evaluated to determine the most suitable coconut husk-copra cake ratio combination. Ten grams of PSC were grown separately on a 600g substrate and incubated at 28^○C for 35 days. The substrates used for this study were composed of shredded coconut husk (73-98%), dolomitic lime (1%), brown sugar (1%) and copra cake (0%, 5%, 10%, 15%, 20%, 25%) with moisture content at field capacity. Treatments were distributed in 10 replications and data gathered were analyzed using DMRT (p<.05). Results revealed the following patterns: mycelial growth and BEC (10%> 15%>5%, >20% >25%>0%), number of fruiting body and cap diameter (10%>5%>15%>20%>25=0%) Thin and slowest mycelial growth occurred at 0% and 25%. No significant difference was observed among treatments 0%, 20%, 25% and between 5% and 15% of copra cake supplementation. The overall growth performance was observed to be feasible at 10% copra cake supplementation (BEC=58.4%). Results suggest that coconut husk supplemented with the right amount of copra cake could be utilized effectively as locally available alternative substrates for mushroom cultivation.This work is supported by Hatch Program (accession number: 1010361) from the USDA National Institute of Food and Agriculture 

Citrus Black Spot (CBS) is a disease caused by Phyllosticta citricarpa (Botryosphaeriales, Dothideomycetes) and currently effects citrus groves in five counties in southwest Florida (Charlotte, Collier, Hendry, Lee and Polk). This disease has a unique cycle in Florida as the fungus cannot reproduce sexually due to the presence of only one mating type (MAT1-2), but rather reproduces exclusively via asexual sporulation, which confers limited dispersal ability. Here we present a novel qPCR assay to distinguish both mating types (MAT1-1 and MAT1-2) and to monitor for the possible introduction of the MAT1-1 mating type. During 2017-2019, we surveyed fruit lesions, asymptomatic leaves from tree canopy and leaf litter from previously known and newly detected CBS-positive trees, and from asymptomatic trees adjacent to CBS-positive trees. To date, we have detected only the MAT1-2 mating type in Florida, after surveying more than 850 citrus fruit lesions and 205 asymptomatic canopy and leaf litter samples from 30 groves. Our findings confirm the low dispersal ability of the asexual state of P. citricarpa in Florida.

Anthracnose is a postharvest disease of banana caused by the fungus Colletotrichum musae that results in major economic losses during transportation and storage. For the management of banana anthracnose, antifungal effects of three medicinal plants (Azadirachta indica, Calotropis procera and Anacardium occidentale) were assessed in this study. The extracts of the plants were prepared using water, the phytochemical constituents were determined and agar well diffusion method was used to assess the toxicity of each extract at 50mg/mL100mg/mL and 150mg/mL. The pathogen was isolated from banana infected with anthracnose disease. The results revealed the presence of one or more phytochemicals in each of the plant extracts. Among these were alkaloids, saponnin, tannins, anthocyannin, phenol and flavonoids. All the extracts inhibited mycelia growth of Colletotrichum musae. The inhibition of mycelia growth of the pathogen increased with increase in concentration and days of incubation. At the end of day 5 of incubation, the inhibition at 150mg/mL of all the extracts was significantly different(P<0.05) from other concentrations. However, in all, C. procera extracts gave the highest percentage growth inhibition of the pathogen at all levels of concentrations tested while A. indica extracts though effective was the least but not significantly different from A. occidentale. Therefore, since these plants are cheap, easy to obtain and extract with a simple process of maceration or infusion, more trials on the dosage and formulation on the control of banana anthracnose disease are recommended.