Science Digested pieces provide concise summaries of important research on microbial foods. In addition to introducing the science, these summaries will emphasise the practical implications of the findings.
When you buy an aged cheese at the store, you expect it to have a specific appearance. Camembert should be white and fuzzy. Limburger should be orange and sticky. Cheese makers work hard to manage aesthetics, but sometimes unplanned colors or textures cause cheese defects. In the past few years, cheese rinds around the world have started turning an unusual purple color. In this Science Digested, I’ll explain how my lab discovered the microbial cause of this purple rind defect.
Various attributes of a cheese, including both flavor and appearance, contribute to the final quality of the product. During the production of some cheeses, microbial processes can cause strange quality defects, often with colorful outcomes. Researchers in University College in Cork, Ireland identified the microbial culprit behind a notorious pink cheese defect. In this Science Digested, Adam Shutes from the Boston Cheese Cellar explains what they found.
Have you ever noticed those goat’s milk cheeses with the wrinkly surface at the cheese shop? They look like a fuzzy white brain or a dusty grey coral and they smell like sweet, buttery flatulence. Those aesthetics and aromas come from the growth of the fungus Geotrichum candidum. Using in-depth genomic sequencing, French scientists recently unlocked the evolutionary history of this important cheese microbe and revealed a fungus with an identity crisis.
It’s difficult to connect the dots throughout our complex food system. Although it is rarely demonstrated scientifically, we generally accept that what happens on farms impacts the quality of our food. For microbial foods, the raw materials we use in fermentation can introduce different microbes depending on how those materials were produced. A recent study in Italy of sourdough fermentation demonstrated that organic vs. conventional farming can affect the quality of sourdough bread. This exciting new research highlights the role that microbes play in shaping food quality as it moves along the path from farm to fork.
Our last Science Digested piece on kimchi looked at the effect of red pepper powder on the progress of fermentation, and its impact on which bacteria dominate at the end. This paper backs up a step and asks: where do these lactic acid bacteria come from in the first place? Which ingredients bring microbial life to kimchi?
When making fermented vegetables, we often add different kinds or amounts of spices. Their impacts on flavor may be obvious, but what do these spices do at the microbial level? A recent study took a careful look at how the addition of red pepper changes the course of microbial development in kimchi.
Our world is full of organisms that scientists have yet to discover and officially describe as a species. You may have heard in the news about a new species of amphibian discovered in a remote rainforest or new species of fish discovered at the bottom of the sea. But you don’t have to travel to far flung places to find new species. Sometimes they are right under our noses…. growing on salami.
Henriet et al., International Journal of Food Microbiology. 2014. 191: 36-44. Full text available here.
Within the world of fermented food, salt is usually regarded as a tool for controlling microbial activity rather than as a source of microbial diversity. But recent studies are beginning to reveal that unrefined salts can carry viable and diverse microbial communities. This paper explores the incidence of members of the domain Archaea in a selection of food-grade salts from around the world. [click to view the full story]
Kefir is a thick, sour, and sometimes slightly spritzy fermented milk drink produced through the action of the bacteria and fungi within kefir ‘grains’, a classic example of a SCOBY (Symbiotic Community of Bacteria and Yeasts). Despite a history that dates back several millennia, kefir and the microbes that produce it remain little-understood. Two recent papers from China and Ireland set out to explore the microbial diversity of kefir samples collected from a wide geographical area. One also provides insight into the physical structure of the kefir grain, and the distribution of yeast and bacteria across it. [click to view the full story]