Aspergillus species play a less significant part in the production of fermented foods (at least in foods popular in Western cultures). But they are still a component of some of the fermented foods that are consumed the most around the world. One example of important specie in food is Aspergillus oryzae (A. oryzae). A. oryzae is a filamentous fungus (a mold), also known as “koji” mold, commonly used in Chinese, Japanese, and other East Asian cuisines.

Its primary uses include fermenting soybeans to produce soy sauce and miso (fermented bean paste). It is also used to sweeten rice, barley, other grains, and potatoes to produce alcoholic beverages like hōchū, huangjiu, sake, and makgeolli (Korean rice wine). Billions of people actually consume these Asian fermented foods.

In Japan, this mold is culturally important. In the journal of the Brewing Society of Japan, Dr. Eiji Ichishima of Tohoku University referred to the koji fungus as a “national fungus” (kokkin). This is due to its significance in the production of koji for miso, soy sauce, and a variety of other traditional Japanese foods in addition to koji for sake brewing.

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Studies suggest that the Japanese domesticated Aspergillus flavus. A. flavus is a pathogenic fungus that produces aflatoxins. But what the Japanese used mutated to stop producing the aflatoxins. This eventually gave rise to the beneficial A. oryzae mold.

Let’s discuss further the Aspergillus oryzae genome as well as its various uses in food.

ASPERGILLUS ORYZAE: THE KOJI MOLD

A. oryzae or simply Koji mold, is an aerobic filamentous fungus in the Aspergillus subgenus Circumdati section Flavi. Aspergillus section Flavi also contains industrially important species such A. flavus and A. parasiticus, both of which generate aflatoxins.

While closely related to other Aspergillus species, A. oryzae does not produce aflatoxins. Rather, the ability of Aspergillus oryzae to ferment makes it an important fungus in food manufacturing. In fact, the Food and Drugs Administration (FDA) has listed it as Generally Recognized as Safe (GRAS).

A. oryzae grows best at 89°F (32°C) to 97°F (36°C), and cannot grow over 111°F (44°C). It prefers a pH of 5 to 6 for growth, and can germinate in pH between 2 and 8. Aspergillus Oryzae has been observed to grow in dry food, such as corn flour with a water content of about 16%. It can grow on media with a water activity (aw) greater than 0.8, although it rarely grows below 0.8.

A. oryzae haploid genome contains 37 million base pairs and 12,000 predicted genes organized into 8 chromosomes. A consortium of Japanese biotechnology companies revealed this information in late 2005.

A. oryzae‘s genome is one-third larger than the genomes of two related Aspergillus species, the genetics model organism A. nidulans and the potentially deadly A. fumigatus. Many of the additional genes found in A. oryzae have been linked to secondary metabolism. The sequenced strain, RIB40 or ATCC 42149, was obtained in 1950. The specific increase of genes for amino acid metabolism, secretory hydrolytic enzymes, and amino acid/sugar uptake transporters make A. oryzae an ideal microorganism for fermentation.

SOY SAUCE MANUFACTURING

Soy sauce is a dark brown liquid that is made by fermenting soybeans and wheat in a salt brine. Manufacture starts with the preparation of raw materials. Soybeans or defatted soybean flakes are cooked after being moistened. For each form of soy sauce, the cooked beans are mixed with toasted, cracked wheat in varying proportions.

Soybeans are cooked in a continuous cooker at high temperature and pressure for a short period of time. In koikuchi, usukuchi, and saishikomi shoyu soy sauce manufacture, the same amount of cooked soybeans and roasted wheat is blended. And then the mixture inoculated with an A. oryzae or Aspergillus sojae pure koji starter. Certain Aspergilli species are also utilized in the production of usukuchi and shiro shoyu to prevent the formation of a deep color in the following steps of fermentation.

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After three days of fermentation, a 17% to 19% salt solution is applied to the koji (fermented grains) to create liquid mash called moromi. During the moromi process, osmophilic lactic acid bacteria and yeasts provide a distinct taste, scent, and color in moromi. High concentrations of proteins and carbohydrates from raw materials are significantly destroyed by koji enzymes and microbial action.

To ensure homogenous conditions and accelerate microbial growth, the moromi mash is occasionally stirred and aerated. Lactic acid bacteria, such as Pediococcus soyae or Lb. delbrueckii are permitted to grow on the moromi to make it acidic enough to prevent spoilage and sour taste. Afterwards, yeasts like Saccharomyces rouxii and Torulopsis sp. grow on the moroni to produce alcohol and aid in flavor production. The moromi process takes 4 to 8 months to complete, depending on temperature, agitation, and air supply from an air compressor.

SAKE FERMENTATION

Alcoholic beverages from East Asia are very distinct, compared to those of Western origin. It is because of two reasons. First, their main ingredient is fermented starchy grains, usually rice. Another reason is that fermentation does not occur from grain enzymes into sugars. Instead, a mold is introduced to start the fermentation process in unison with yeasts. A good example of a product that is produced by this is Japanese sake (rice wine).

This alcoholic beverage is transparent, pale yellow. The substrate food is steamed rice starch, which is hydrolyzed to sugars by Aspergillus oryzae to produce the koji. In general, whole or brown rice is milled to remove 25% to 50% of the surface material (germ and bran), which is required because the fat and protein components are undesired. The rice is then rinsed and steeped for several hours to reach a moisture content of about 30%. The damp rice is then cooked for an hour and chilled to 86°F (30°C) to 95°F (35°C). Three-quarters of this rice are removed and chilled to 41°F (5°C) to 50°F (10°C) for later use. The final fourth is utilized to make koji.

Saccharomyces sake ferments the substance for 30-40 days, giving in a product with 15-20% alcohol and roughly 0.3% lactic acid. The main fermentation takes place in open tanks under cool circumstances, starting at around 50°F (10°C) and rising to around 59°F (15°C). S. cerevisiae strains used in sake production differ from those used in wine and beer production. They have greater osmotic, acid, and ethanol tolerance.

Following fermentation, moromi is separated from the solids to create clarified saké, which is settled, refiltered, pasteurized, mixed, and diluted with water before bottling.

MISO MAKING

Miso originated in China and Korea thousands of years ago. But Japan is today’s leading producer and consumer. Miso is a popular fermented soy bean product. If you have not tasted one before, miso tastes just like soy sauce, but liquid or paste-like, and with a texture similar to that of thick peanut butter. It is used in Japan to make soups and broths. It is also used as a seasoning or flavoring agent. Products similar to miso include doenjang (Korean bean paste), taoco (Indonesian bean paste), and taosi (fermented black soybeans from the Philippines).

Miso is manufactured in a manner similar to that of soy sauce, with one notable exception. Dry salt, rather than brine, is added straight to the koji-soy bean mixture during miso production. For this reason, the product has roughly double the total solids of soy sauce (50% to 60% against 24% to 28%).

The production process begins with the manufacture of koji. Rice, barley, or soybeans can be used as substrate. At 59°F (15°C), the rice or barley is soaked in water overnight before steaming in a batch or continuous cooker. After cooling, a spore culture of specific strains of Aspergillus oryzae and A. sojae is utilized as the inoculum at 0.1%. The koji is then cultured in fermentation chambers at 86°F (30°C) to 104°F (40°C) for 40 to 48 hours.

After that, miso is made by combining salt, koji, steamed soybean, and water, and adding the halo-tolerant yeast, Zygosaccharomyces rouxii or Candida versatilis. The salt is then added to help the yeast and LABs ferment and to prevent any unwanted form of fermentation.

The mixture is allowed to mature for three to twelve months.

References:

M. Shafiur Rahman (2007). Handbook of Food Preservation (2nd edition). CRC Press.

R. Hutkins (2006). Microbiology and Technology of Fermented Foods. Blackwell Publishing.

J. Jay, M. Loessner, D. Golden. (2005). Modern Food Microbiology (7th edition). Springer.

M. Gibson (2018). Food Science and the Culinary Arts. Academic Press.

B. Ray (2005). Fundamental Food Microbiology (3rd edition). CRC Press.

G. Cooper (2018). Food Microbiology. Library Press.

Y. H. Hui (2012). Handbook of Plant-Based Fermented Food and Beverage Technology (2nd edition). CRC Press.

The post Aspergillus Oryzae And Its Uses In Food appeared first on The Food Untold.

For the most of us, whenever we hear the words “bacteria”, “fungi” or “microorganisms”, the first things that come to mind are negative things such as diseases. Well, it is definitely true that there microorganisms that do us harm. But not all the time. Let’s talk about Escherichia coli (E. coli) for example. One particular strain of E. coli is O157:H7. Someone who ingested food that is contaminated with this strain of E. coli may experience food poisoning with severe symptoms. But for most of the time, E. coli does that cause harm or adverse health effects. In fact, this bacteria lives in our intestines and those of animals.

The negative connotations associated with microorganisms is undeserving. And on the contrary, many of them are beneficial in different fields or industries. In medicine, without microbes, we would be able to produce vaccines and antibiotic. Soil microbes help farmers recycle plant materials and decompose organic matter.

In the food industry, a lot of food products that we enjoy now would not have existed without them. One species of yeast that we have worked with for thousands of years is Saccharomyces cerevisiae. This fungus is one of the most important in the food industry. It has been used extensively in the manufacture of fermented beverages such as wine and beer, distilled beverages such as vodka and rum, and baked goods. But the strains of Saccharomyces cerevisiae involved in the manufacture of these products vary tremendously.

Let’s discuss further.

WHAT IS SACCHAROMYCES CEREVISIAE?

Like other species of yeasts, Saccharomyces cerevisiae is a eukaryotic, unicellular microorganism. The cells can exist in two forms: haploid or diploid. Most cells exist in diploid form, in which the cells are ellipsoid-shaped with a diameter of 5-6um, Cells in haploid form are spherical with a diameter of 4um.

Cells reproduce both sexually and asexually.

More often, S. cerevisiae reproduce asexually. In a process called budding, a haploid cell undergoes mitosis, forming new haploid cells or daughter cells that bud off the mother cell. The new cell grows bigger until it reaches the size of the mother cell and separates.

During sexual reproduction, two different haploid yeast cell mate, forming a diploid cell. This diploid cell then undergoes mitosis to form zygotes.

S. cerevisiae is a facultative anaerobe—it grows well aerobically and anaerobically. In nature, S. cerevisiae is commonly found in ripe fruits, particularly grapes. All strains can feed aerobically on sugars, including glucose, maltose, and trehalose, but not on disaccharide lactose and cellobiose. Anaerobically, some strains do not grow on trehalose and sucrose. Among these sugars, S. cerevisiae prefers glucose the most.

A 1977 study found out the optimum temperature for rapid growth of all strains of S. cerevisiae to be between 86 °F (30 °C) to 95 °F (35 °C).

Since it is easy to culture, S. cerevisiae is the most studied eukaryote. In fact, S. cerevisiae was the first ever eukaryote genome to be fully sequenced in 1996. The S. cerevisiae genome is made up of over 12 million base pairs and over 6000 genes, packaged in 16 chromosomes. Visit the Saccharomyces Genome Database for more on this.

Brewing

It is hard to pinpoint the exact origin of beer fermentation. But according to history, the oldest piece of evidence was a chemically confirmed barley beer found in modern day Iran.

Basically, beer is produced using germinated cereal grains (referred to as malt), flavoring like hops, water (which accounts for 93% of beer by weight), and yeasts. Yeasts are perhaps the most important ingredient in beer brewing. It is largely responsible for beer’s final characteristics—the alcohol content, appearance, aroma, and flavor—through a process called alcoholic fermentation.

When yeasts are added, they start feeding off the sugar available. The sugars in beers are mostly maltose, a dissacharide. The sugars consumed by yeasts are converted into alcohol and carbon dioxide. The final ethanol content by weight of beers vary from about 3% to 8%. Carbon dioxide is responsible for that fizz sound whenever we open a can of beer. However, CO2 produced during fermentation is allowed to escape. Oftentimes, brewers increase the carbonation by introducing pressurized CO2. Beer fermentation takes a week to several months to complete. This mainly depends on the type of beer (strength) and the yeast involved.

Once fermentation has finished, the beer is conditioned. This is where the yeast settles at the bottom of the fermentation tank, clarifying the beer. The yeast can be collected and reused for the next brewing process.

Around the world, there are over a hundred beer styles that exist. These include lagers, ales, and stouts. One main difference between these beers is how they are fermented. Ale beers are produced using S. cerevisiae yeast at temperatures of 53.6 °F to 64 °F. Whereas lagers are produced using Saccharomyces carlsbergensi yeast at a colder temperature of 46.4 °F to 53.6 °F. Both both ales and lager beers can be dark or light in appearance.

Baking

There are generally 3 main types of leavening agents in baked products. These include physical leaveners such as air or steam, chemical agents such as baking soda and baking powder, and biological agents such as yeast. Unsurprisingly, the species of yeasts more synonymous with baking is S. cerevisiae. This is why S. cerevisiae is also called baker’s yeast.

Occasionally, bakers use other species of yeast in baking. Saccharomyces exiguus is typically used as sourdough yeast.

Baker’s yeast come in several forms. In commercial baking, where the daily production volume is immense, cream yeast is used. Cream yeast looks similar to a yeast slurry. It is about 85% water and 15% S. cerevisiae yeast. Cream yeast only lasts for up to 10 days, so refrigeration and additional equipment during storage is necessary.

Another form of yeast widely used in commercial baking is compressed yeast. Compressed yeast is similar to cream yeast, but contains less liquid. It is generally 70% water and 30% yeast. Like cream yeast, compressed yeast has a very short life span. For this reason, compressed yeast is now less common, especially in developing countries.

Active dry yeast and instant yeast are common forms of yeast for baking at home. In many home recipes, both forms can be used interchangeably. The main difference between the two is that active dry yeast requires dehydration before use. Whereas instant yeast can be added and mixed directly with other ingredients. Instant yeasts also requires less time to rise.

One advantage of active dry yeast has a longer shelf life than other forms of yeast. It can last for a year at room temperature.

Winemaking

Wine is an alcoholic drink generally made from fermented grape juice. Like in brewing beer, the addition of S. cerevisiae yeast converts the sugar in the fruit into ethanol and carbon dioxide.

Some winemakers use wild yeast to ferment wine for more interesting complex flavors. Thousands of years ago, wines were fermented using wild or “natural” yeasts. They tend to be more active once the grapes have matured enough. However, one major flaw of using wild yeast is its unpredictable nature. And a lot of wild yeasts do not produce quality wine. Most of these yeasts belong in the Kloeckera and Candida genera.

In order to produce quality wines consistently, commercial wineries inoculate strains of S. cerevisiae yeast.

Throughout history, vintners or winemakers have used fruits (apple wine) other than grapes, vegetables, and grains (rice wine such as sake). But wine varieties made from these do not usually produce wine with qualities similar to those made from grapes. The main reason for this is that they contain less fermentable sugars and water to maintain proper fermentation.

Grapes are high in sugars. The initial sugar content of the grape juice dictates the alcohol level of the resulting wine. Unripe grapes contain predominantly glucose. Ripe grapes contain equal amount of glucose and fructose, both of which are fermentable sugars. Other sugars in the grapes in smaller amounts include pentoses, cellobiose, and galactose, all of which are unfermentable sugars.

After fermentation, the wine can have an alcohol or ethanol content between 11-13% on average. This depends on several factors such as the wine variety and the winemaker. For example, some winemakers intentionally stop the fermentation process before the yeast converts of all the sugars into alcohol. This results in a sweeter wine.

Other references

M. Shafiur Rahman (2007). Handbook of Food Preservation (2nd edition). CRC Press.

M. Wallert, K. Colabroy, B. Kelly, J. Provost (2016). The Science of Cooking: Understanding the Biology and Chemistry Behind Food and Cooking. John Wiley & Sons, Inc.

J. Jay, M. Loessner, and D. Golden (2005). Modern Food Microbiology (7th Edition). Springer

O. Zaragoza, A. Casadevall (2021), Encyclopedia of Mycology, Elsevier.

The post Saccharomyces Cerevisiae Yeast In The Food Industry appeared first on The Food Untold.

Kimchi is everywhere—in Korea dramas, served at your local Korean restaurant or in a jar ready for you to pick up at your nearest grocery store. Not bad for a dish that is forever synonymous to South Korea. For the past 20 years, This so-called K-wave has brought this fermented delicacy to a larger audience. In this blog post, we’ll discuss everything you need to know about Kimchi.

History of South Korea’s national dish

Kimchi has been a favorite side dish for a very long time now. Its origin can be traced back to the first century BC until 7 AD, when preservation of food was a norm for people of Korea. The families back then had to find a way to get stock of food readily available especially during winter season when the invention of refrigerator, was far from being realized.

Unlike what we see now usually as red and spicy cabbage in jars, Kimchi was made with radish and not spicy and fermented in pots they called Onggi and buried in the ground.

Only the arrival of Europeans, the Portuguese traders who introduced chili to Asians in the 17th century led Koreans to make spicy Kimchi. Since then, Kimchi has evolved into many variations.

Cabbage is not the only vegetable you can use in kimchi making

Kimchi is made with many selections of spices and vegetables. By 1820’s, there had already been 92 different types of Kimchi . At present, there are already over a hundred types of Kimchi. Pretty long list, huh?

Here are 2 more prominent kimchi versions according to Brittanica:

Kkakdugi is Kimchi made of diced radish mixed with different spices. It is fermented for around 2 weeks inside a large pot locally called onggi or jangdok. Just like Kimchi, Kkakdugi is a Korean side dish favorite.

Oi Sobagi is cucumber Kimchi. Used to snacking on pickles? Oi Sobagi can not different.This version is not that known elsewhere but in Korea, known for being crunchy and refreshing, the cucumber Kimchi is a summer favorite.

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Kimchi made with eggplant; bamboo shoot; sugar beets; lotus roots; pumpkin; spinach; Korean wild chive; sweet potato vines; and cilantro are some of the lesser known versions of Kimchi, outside Korea, at least.

How is Kimchi Made?

Lacto-fermentation or natural fermentation through use of brining, is the most important stage in making Kimchi. Brining is the process of submerging the vegetables in brine solution that only good bacteria (Lactobacillus bacteria or LABs) can survive in. Similar products that undergo lacto-fermentation include yogurt, pickles and Kimchi.

After the brining process, the LABs convert the sugars present in the food into lactic acid, thus creating an acidic environment that gives Kimchi the distinct flavor and aroma.

To make brine solution for making Kimchi, high concentration of salt ranging from 3% to 26 % is needed but for traditional making of cabbage kimchi, 15% brine solution is the standard.

Want to make your own Kimchi Korean-style?

Here is a recipe of Kimchi according to Sook Jong Rhee, Jang-Eun Lee & Cherl-Ho Lee of Department of Food Technology of Korea University in Seoul, South Korea.

Cabbage Kimchi

Ingredients:

• 100 g Korean cabbage
• 2 g of garlic
• 2 g of red pepper powder
• 0.5 g of ginger
• 2 g of green onion
• 10% brine solution

Cut the fresh cabbage in half or shredded. Afterwards, soak it in brine of approximately 10% salt concentration overnight (or 15% salt brine for 5 to 10 hours) and then wash and drain. Chop and mix the minor ingredients, with shredded radish stuffed between the salted cabbage leaves. Pack the Kimchi in an earthen jar, Onggi or Dok and bury it in the ground and press it with a stone in order to submerge them in the juice. Ferment the Winter Kimchi for 1-2 months.

Shelflife of Kimchi

Yes, though fermented, Kimchi will still spoil and go bad, and quickly when stored improperly.

Once opened, a jar of kimchi stored at room temperature lasts about a week. Keeping Kimchi in the refrigerator lengthens the shelf life for months (3 months to 12 months) and Kimchi will continue to ferment. Just ensure that refrigerator’s temperature must be at 40° F (4° C) or lower, as per FDA. Higher temperature increases the rate of spoilage.

How to tell if it is Kimchi is spoiled? As long as the normal smell of Kimchi is there and it doesn’t have mold, it is safe to consume. When in doubt, do not consume it—better be safe.

Health benefits of eating kimchi

Should you consume Kimchi? Picky eaters, particularly who do not like eating veggies, may find Kimchi a very good tasting side dish. That sourness, spiciness and umami just perfectly blend together. But is its favorable taste the only reason why you should get a jar of it? Definitely not!

Depending on the ingredients used, kimchi can give you a lot of healthy benefits.

Considered a super healthy food, the presence of lactic-acid bacteria in Kimchi makes it a probiotic, like yogurt. It’s good bacteria help you maintain a healthy digestive system and immune system.

For the skin conscious, I’ve got great news for you.

Ever wondered how Koreans have managed to look younger than they actually are? Because Kimchi is rich in antioxidants such as carotenoids, flavonoids, vitamins and other phenolic compounds. And on average, Korean adults eat at least 1 serving (100 grams) of Kimchi each day. So?

Although I’ve listed some here, might wanna check this post out from University Health Post for a detailed list of everything you need to know about Kimchi and its health benefits.

Right! That’s everything You Need To Know About Kimchi.

Reference:

Rhee, S.J., Lee, J. & Lee, C. Importance of lactic acid bacteria in Asian fermented foods. Microb Cell Fact 10, S5 (2011). https://doi.org/10.1186/1475-2859-10-S1-S5

The post Everything You Need To Know About Kimchi appeared first on The Food Untold.