Fermentation Process: Making Cassava Tape Fermentation

Indonesia is famous for its abundance of agricultural products such as spices and cassava. Indonesia is also famous for its many special foods in each region, which are called traditional foods. Some traditional foods are processed in various ways, including fermentation. Cassava tape is a fermented food made from cassava that is popular in Indonesia. Cassava is a plant that is widely cultivated in Indonesia and is used as a source of carbohydrates and energy. Tape is produced through a fermentation process involving microorganisms like yeast, fungi, and bacteria. The starter culture used has a round, flat shape. Locals use terms like "ragi tape" or "yeast tape" to refer to it. Fermentation produces alcohols like ethanol from the cassava starch, giving tape its slightly alcoholic taste. The quality of tape depends on the raw cassava, production method, and microbes involved.

Fermentation is a metabolic process used to preserve foods such as tape. These are microbial enzymes that chemically transform organic substrates. As it is a traditional Indonesian food, there is no set standard for how to make tape and it may vary. Starter cultures contain a mixture of rice flour, spices, water, or sugarcane extract. Yeast plays an important role in anaerobically fermenting sugars into CO and ethanol. As primary microorganisms, they determine sensory properties. This action also makes the texture of cassava soft. Saccharomyces cerevisiae can function in the presence or absence of oxygen and can oxidize sugars and ferment. 

Fungi and bacteria also contribute. The fungal amylase enzyme first breaks down starch into glucose. Saccharomyces yeast then converts the sugar into ethanol. Other microorganisms such as Aspergillus, Candida, and Lactobacillus further modify their metabolites. This creates a tape with distinctive fruit, floral esters and acids. There are four main stages in the biochemical changes: 

1. Enzymatic hydrolysis of starch into dextrin and monosaccharides. 

2. Conversion of sugar into ethanol through fermentation. 

3. Oxidation of ethanol into organic acids by lactic acid bacteria.

 4. Formation of esters through the reaction of organic acids with alcohol.

Optimizing the fermentation duration affects the final moisture, sugar, and sensory properties. Controlling the temperature can also impact the rate, time, and product outcome. Proper tools, containers, and sanitization of equipment and workers helps ensure food safety and quality. 

Dok. alodokter.com

Many fermented foods that provide health benefits, such as stimulating gut immunity and improving the balance of microbial populations in the gastrointestinal tract. One of the most well-known fermented foods from Indonesia is "tape." Tape is made from steamed cassava, which is then mixed with a starter commonly referred to as "tape yeast". Tape is produced using traditional methods which have some drawbacks, such as non-standardized manufacturing processes and variability in the products. This could result from in consistencies in the microbial composition of the starter, as well as the influence of environmental factors.

The quality of tape depends on the quality of the cassava, preparation method, and microbes involved. The tape starter comprises a consortium of microbes including fungi, yeast, and bacteria. These microbes determine the quality of the tape due to their roles during the fermentation process. Bacillus species have been reported to play a role in improving the quality of various fermented. Bacillus subtilis has also been reported to determine the quality of cassava tape. However, there is very limited information on the diversity of Bacillus strains present in conventionally prepared tape. 

If observed after 24 hours of fermentation, the tape is white, has a slightly sweet and slightly sour taste with a pH of 4, and has a distinctive sharp tape aroma and a slightly soft texture. Tape fermented for 48 hours has a creamy colour, slightly sweet and slightly sour taste with a pH of 5, the characteristic aroma of tape is more prominent than 24 hours tape, and the texture is softer. Meanwhile, the fermentation time of 72 hours gives the tape a creamy color, sweet and slightly sour taste with a pH of 5, a characteristic sharp tape aroma, and a soft texture.

Observation results show that the length of cassava fermentation affects various parameters of final product quality, including color, taste, aroma, texture and pH. This is probably because the longer the fermentation time will increase the enzymatic activity of microorganisms which will degrade natural cassava root components, changing them and causing changes in the sensory and physicochemical properties of the tape. For example, increased microbial fermentation results in the production of organic acids that lower the pH and the production of new volatile compounds that change the aroma. Texture changes can also be caused by enzymatic degradation of tape and structural components.  In particular, long fermentation times will affect the alcohol content of the tape, because fermenting microorganisms such as yeast produce ethanol through sugar metabolism. The average ethanol content of cassava tape was 0.844% after 24 hours of fermentation, 2.182% after 48 hours of fermentation, and 4.904% after 72 hours of fermentation. The more than two fold increase in ethanol from 24 to 48 h and a further increase after 72 hours indicate that alcohol production continued over the long fermentation times. 

The accumulation of ethanol on the tape had a significant influence on the fermentation time, and the alcohol content gradually increased from 1 to 7 days of fermentation. However, after 7 days, the ethanol content decreased. This phenomenon can be linked to the population dynamics of Saccharomyces cerevisiae, the main alcohol-producing microbial yeast. If fermentation continues for more than 7 days, this yeast enters a quiescent phase and its growth rate decreases due to lack of nutrients and accumulation of waste products. Therefore, S. cerevisiae is reduced, fermentation capacity and ethanol synthesis are reduced. 

In contrast to ethanol, the research results showed that there was no real influence of yeast concentration and fermentation time on cassava tape glucose levels. This lack of change may be explained by the high initial concentration of fermentable cassava starch, a substrate that is converted to glucose by amylase. With this abundant substrate, metabolic processes may take even longer beyond the time points tested. Apart from chemical components such as acids and alcohol, microbial activity during fermentation also has a significant influence on the physical properties of tape products. This includes noticeable effects on texture. For example, for purple sweet potatoes, the longer the fermentation time, the softer the texture of the tape. After 72 hours, the tape becomes completely soft and has a smooth texture. In contrast, a short fermentation of 24 to 48 hours produces a firmer, chunkier texture. 

The biochemical basis of the texture change of fermented tape is the breakdown of complex starch molecules into simpler dextrin and sugars in a process known as enzymatic hydrolysis. Sources of amylase and other enzymes that degrade polysaccharides include fungi, yeast, and bacteria that form mixed starter cultures. By breaking down macrostructure determining components such as starch, the entire matrix is softened by extensive enzymatic action. 

In addition to the preservative effect, the digestibility of the starch produced by this fermentation also contributes to the attractive sensory properties, easy digestion, and higher nutritional value of the final product. The increase in taste and aroma of ribbons can be caused by microbial synthesis of new volatile compounds and increased release of aromatic compounds from the fermented substrate. Additionally, the partially degraded contents of the tape are more easily accessible to consumers' digestive enzymes, thereby increasing digestibility. From a nutritional perspective, monosaccharides and dextrin formed through fermentation hydrolysis are more easily absorbed than original starch. 

Biochemical analysis showed that the fermentation time was correlated with an increase in the acidity of the tape product, which was indicated by a decrease in the pH value. This is related to the production of various volatile fatty acids by microorganisms during fermentation. These include lactic acid from lactic acid bacteria, as well as acetic acid, formic acid, butyric acid, and propionic acid. This acid is produced by the metabolism of carbohydrates and alcohol in cassava. Increased sour taste was noted in sensory analysis of longer fermented tape. It also lowers the pH, because the increase in hydrogen ion concentration is accompanied by an increase in acidity. 

Previous research is consistent with the trend of increasing alcohol content observed with prolonged steaming and fermentation. Although the measured increase was not statistically significant, it suggests a positive relationship facilitated by the longer reaction time of microbial enzymatic processes. During the fermentation period, there are more opportunities for catabolic transformation cascades to occur, which increase the content of final products such as ethanol. These include the direct synthesis of alcohol by yeast and the formation of ethanol from intermediate compounds such as acetaldehyde. 

The choice of culture temperature influences the specific microorganisms that can grow and ferment. For tape, the optimal temperature range for microbial activity is 35C to 40C. If the value is too low then microbial growth will be slow, and if the value is too high there will be negative impacts such as protein denaturation. Acidity, which is regulated by acid accumulation, also influences fermentation microorganisms, with the optimal pH for growth being between 3.5 and 5.5. Since oxygen availability depends on the air tolerance of microorganisms, their activity requires primarily anaerobic conditions, so the space required for movement and contact with air is limited. Finally, the specific strains of yeast, bacteria, and fungi included in the starter inoculum have specific enzymatic capabilities that shape the pattern of acidification, structural damage, and chemical changes that underlie the final characteristics of the tape. 

By adjusting these interdependent parameters, the fermentation progress and quality characteristics of the resulting tape product can be adjusted. For example, if the starter contains too much yeast, microbial activity will become uncontrolled and the tape will become too soft. Overall, this framework of complex interactions between processing methods, environmental factors, and microbial growth highlights the balance required to achieve desired sensory and nutritional properties in fermented foods such as tape. Subtle changes can produce very different tapes, when the tape is fermented for 24, 48, and 72 hours. 

The production of tape is considered traditional biotechnology as it uses limited conventional methods. When producing tape, yeast consumes the glucose contained in cassava as food for growth. This softens the cassava and allows the mushrooms to convert glucose into alcohol. During fermentation, the yeast Saccharomyces cerevisiae produces enzymes that break down carbohydrates in cassava into simple sugars. This means that ripe tape is sweet without the need for added sugar. Fermentation time on influence the alcohol content, pH, and sensory properties of cassava tape, such as taste, aroma, and texture. This indicates that fermentation time influences physicochemical and sensory properties. On the other hand, yeast concentration affects moisture more than sugar content. 

The cassava tape fermentation process begins with the microbial enzyme amylase which converts cassava starch into maltose. It is then broken down into glucose, which is converted into alcohol by yeast enzymes. Fermentation converts alcohol into acetic, pyruvic and lactic acids. This acid production is caused by acetic acid bacteria which are common in starter cultures. Pyruvate is an intermediate in the breakdown of glucose into ethanol. Pyruvate is converted into ethanol and lactic acid. These organic acids react with alcohol to form aromatic esters, creating the tape's characteristic taste. Microorganisms that promote tape fermentation include fungi, yeast, and bacteria that hydrolyze and carry out bioconversion cassava carbohydrates. Initial amylase activity releases maltose sugar and glucose for metabolism. Yeast such as S. cerevisiae then convert the sugar into ethanol anaerobically. Acetobacter aerobically oxidizes ethanol to acetic acid to obtain energy.

These microbes originate from the starter culture added to initiate fermentation. Traditional starter consists of remnants from previous batches, containing accumulated microbial communities. Modern pure cultures of defined species aim to standardize quality but traditional starters continue in small-scale production. Environmental bacteria also contribute. The microbes' enzymes and metabolic pathway interact to break down cassava components and generate new compounds. However, excess microbial growth can spoil tape through over softening or not good. Thus, processing controls like limited oxygen exposure aim to balance activity. Temperature similarly affects microbiology and biochemistry. 

As fermentation progresses, the dynamics of the growing microbial population change the process of cassava metamorphosis. First, amylolytic bacteria multiply and contribute strong amylase activity to carbohydrate digestion. When glucose levels rise, rapidly multiplying yeasts such as Saccharomyces cerevisiae displace the fungus and switch to alcohol production. In the next step, acetic acid bacteria oxidize ethanol into acid, thereby lowering the pH value. These community variations were the basis for changes in tape quality observed after 24, 48, and 72 hours of fermentation. 

Besides microbes, the cassava substrate impacts process efficiency. High quality cassava has increased starch reserves to fuel fermentation. Pre-treatment like grating increases surface area for microbial access. Insufficient grinding limits carbohydrate breakdown by physical barrier. Conversely, overly disrupted cassava accelerates microbiological spoilage. Finding the right surface area balance helps optimize starch conversion versus microbial overgrowth. Apart from microbes, the cassava substrate also has an impact on process efficiency. High quality cassava has increased starch reserves to fuel fermentation. Pretreatment such as a grid increases the surface area for microbial access. Inadequate grinding limits carbohydrate breakdown by physical barriers. On the other hand, cassava that is too processed will accelerate microbiological spoilage. Finding the right surface area balance helps optimize starch conversion with microbial overgrowth. 

Environmental factors like humidity also mediate activity. Drier conditions slow fungal amylase production and alcohol generation, while moisture supports yeast and bacterial growth. Oxygen controls aerobic versus anaerobic metabolism, altering microbial efficiency. Temperature adjusts reaction rates. This tape process optimization demands factor integration for ideal fermentative balance maximizing flavor and texture while minimizing spoilage compounds. Combining new omics tools with empirical quality testing has enabled detailed studies of the biochemical changes underlying cassava microbial community dynamics and tape fermentation. Metagenomics characterizes starter cultures and environmental biodiversity through high-throughput DNA sequencing. Metatranscriptomics captures changes in gene expression of key members of a community. Metabolomics tracks degradation and fermentation products over time. When combined with bioinformatics, a systems-level understanding of the interconnected biology underlying fermentation can refine production strategies. 

Integrating traditional knowledge with modern molecular insights provides a deeper understanding of in a biocultural way important fermentation processes and improves traditional methods. These advances can be applied to large-scale tape production, helping to maintain the practice while expanding its economic reach. More broadly, ribbon fermentation describes how microbial communities transform agricultural raw materials into high-quality food through ancient yet sophisticated metabolic processes.