FST 140 Lecture (Week 1-2) PDF

1 FOOD FERMENTATION According to Prescott and Dunn, and Doelle, as cited by Jay (2000), fermentation is “a process in which chemical changes a...

1 FOOD FERMENTATION According to Prescott and Dunn, and Doelle, as cited by Jay (2000), fermentation is “a process in which chemical changes are brought about in an organic substrate through the action of enzymes elaborated by microorganisms”. Biochemically, it is the metabolic process in which carbohydrates and related compounds are partially oxidized. External electron acceptor is absent, and the final electron acceptors are organic compounds produced directly from the breakdown of the carbohydrates. Food fermentation is a method of processing food with the use of microorganisms or enzymes which alter the physical and chemical components of the raw materials. This results in the modification of the quality of foods, and to some extent, improve its nutritive value. Food fermentation is an important aspect of food science and technology because of the following reasons: 1. Helps minimize the nutritional deficiency and food shortage. 2. Coverts the raw materials into a new product. 3. Improves the properties and storage stability. 4. Converts high molecular compounds into simple compounds. A. Microorganisms Involved in Fermentation 1. Molds Molds are multicellular, filamentous fungi that has fuzzy or cottony appearance. This group of microorganisms reproduce chiefly by means of asexual spores and require oxygen for growth. Figure 1 shows some parts of a mold. : Figure 1.1. Some parts of a mold used in fermentation. Source: http://www.brainkart.com/article/Rhizopus---Fungi_32856/ This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.  2 Importance on Molds 1. Molds are important in conversion of complex compounds into simpler compounds. Take for example, tempeh (Figure 2) is produced by inoculating softened soybeans with Rhizopus oligosporus. In the process of fermentation, its protein is broken into amino acids and starch to glucose. Figure 1.2. Tempeh covered with mold. Source: https://thejapanstore.jp/blogs/column/all-about-tempeh 2. Mold species such as Aspergillus and Trichoderma are known to produce cellulase, the enzyme responsible for hydrolysis of the polysaccharide cellulose to form glucose (Figure 3). Figure 1.3. Hydrolysis of cellulose by cellulase. Source: https://www.biotek.com/resources/application-notes/enzymatic-digestion-of- polysaccharides-part-ii/ This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.  3 3. Some commercially available antibiotics are produced by molds such as penicillin. Please check this link to know more about this antibiotic: https://www.youtube.com/watch?v=CNbnLgetqHs 4. Some molds produce colored pigments which can be used in food processing. An example of this is the red pigment produced by Monascus purpureus. In the process of colorant production, Monascus purpureus is inoculated in rice to form angkak. Afterwards, the pigment is extracted using food grade ethanol then concentrated using rotational evaporator. The produced colorant can be used as alternative to nitrite in processing of meat products such as tocino, ham, and longganisa. 5. Certain large industries are entirely or partly dependent on the activities of mold to produce enzymes. For example, invertase enzyme, which is responsible for the hydrolysis of sucrose into glucose and fructose, can be produced by Aspergillus and Penicillium. 6. On the downside, some molds cause spoilage on food products with low water activity such as bread. 7. Some molds can cause infections in humans, including not only people at particular risk, such as those having a compromised immune system, but also people who are normal and healthy. In general, mold-related illnesses that are classed as mycoses result from a fungus that grow on or in tissues. Aspergillus flavus, Aspergillus fumigatus, Cryptococcus neoformans, and Histoplasma capsulatum are some known pathogenic molds. 2. Yeasts Yeasts (Figure 4) are eukaryotic unicellular micro fungi that are widely distributed in the natural environment. Around 1000 yeast species are known, but this represents only a fraction of yeast biodiversity on Earth. The fermentative activities of yeasts have been exploited by humans for millennia in the production of beer, wine, and bread. This fungus has different forms ranging from spherical, lemon-shaped, pear shaped, cylindrical, triangular, or even elongated into false or true mycelium. Yeasts commonly reproduce asexually by budding or division. This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.  4 Figure 1.4. Main features of a typical yeast cell Source: https://www.sciencedirect.com/topics/agricultural-and-biological- sciences/yeasts Technological Behaviors of Yeast Top fermenting yeasts can produce higher alcohol concentrations and prefer higher temperatures. Example of this is the Saccharomyces cerevisiae var. ellipsoideus which is known to brewers as ale yeast. It produces fruiter, sweeter, ale- type beers. Bottom fermenting yeasts produce fewer of the esters that cause the fruity taste in the ale and work well at low temperature. Saccharomyces pastorianus, formerly known as Saccharomyces carlsburgensis are used in producing lager type beers. Flocculation is the tendency of yeast cells to aggregate together, forming a multicellular mass and sedimenting rapidly from the suspended medium or rising to the surface. Yeast flocculation is a complex phenomenon occurring in brewer's yeast under various conditions near the end of the fermentation process. Flocculation of yeasts can be classified as either clumping or highly flocculative or powdery or poorly flocculative. o Clumping yeasts separate early from suspension in fermenting wort, thus, result in beers which are less fully fermented, sweeter, and having “palate fullness”. Prompt removal of these yeast cells tend to avoid harsh flavor (yeast “bite”/ aftertaste), which is contributed by yeast if it is allowed to remain in contact with the mash. However, beer or alcoholic This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.  5 beverages remain so clean of yeast cells thus only few remains for the second stage of fermentation to have adequate activity. Also, early separation of yeasts leave beer relatively rich in nutrients on which spoilage microorganisms can thrive. o On the other hand, powdery of poorly flocculative yeasts produce drier beer or wines with better biological stability. Also, sufficient number of yeasts remain at the end of the primary fermentation to ensure adequate secondary fermentation for conditioning and maturing. However, slow clarification process and possibility of acquiring “yeasty” flavor are some disadvantages of using poorly flocculative yeast. Types of Yeasts Based on their Purpose 1. Baker’s yeast is mainly used in bakery for dough fermentation. 2. Brewer’s yeast, on the other hand, is essential for beer production in alcoholic fermentation of brewer’s hopped malt extract. 3. Food yeast is classified as “dried” yeasts. These are non-fermenting, stable whole yeasts cells which carefully dehydrated to yield flakes and powder for nutritious factor. Examples of yeast under this type are Candida guilliermondii, C. utilis, C. lipolytica, and C. tropicalis; Debaryomyces kloeckeri; Candida famata, C. methanosorbosa; Pichia spp.; Kluyveromyces fragilis; Hansenula polymorpha; Rhodotorula spp.; and Saccharomyces spp. Single cell protein (SCP) is an example of food yeast product. It refers to protein derived from cells of microorganisms such as yeast, fungi, algae, and bacteria, which are grown on various carbon sources for synthesis. Figure below shows substrate materials needed to produce SCP. This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.  6 Figure 1.5. Substrate materials needed to produce SCP.. Source: Lifted from JAY, J.M. 2000, Modern Food Microbiology, 6th ed., Gaithersburg, Maryland: Aspen Publishers, Inc. p. 173 4. Distillery yeasts are used in alcoholic beverages production. It is utilized to ferment substrates like fruit juice, cereals, sugar cane, and others. 3. Bacteria Bacteria is a large group of single-celled, prokaryotic microorganisms. It can multiply rapidly by simple fission while some species develop a highly resistant resting (spore) phase. Bacterial shapes could be spherical, rod-like, spiral, or filamentous (Figure 1.6). Also, bacterial colonies have different colors which can aid in identification (Figure 1.7). This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.  7 Figure 1.6. Typical shapes of bacteria. Source: https://biologydictionary.net/bacteria/ Figure 1.7. Color of bacterial colonies. Source: https://www.researchgate.net/publication/283303851 This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.  8 Importance of bacteria 1. Source of enzymes 2. Source of pigments 3. Production of amino acids 4. Production of lactic acid 5. Production of acetic acid 6. As spoilage microorganisms 7. As pathogenic microorganisms B. Types of Food Fermentation There are four main types of food fermentation. It includes lactic acid fermentation, acetic acid fermentation, yeast fermentation and mold fermentation. 1. Lactic Acid Fermentation Lactic acid fermentation is a bacterial process that takes place during the production of numerous food products. It provides the final products with characteristic aromas and textures and plays a crucial role in food safety and hygiene. Among the bacteria responsible for lactic fermentation are lactic acid bacteria, which display high morphological and physiological diversity. The term lactic acid bacteria, also called lactics, emerged at the beginning of the twentieth century to describe a heterogeneous group of bacteria that are currently defined as spherical (cocci) or rod-shaped (bacilli), gram-positive, catalase-negative, immobile, nonsporulating, anaerobic, aerotolerant, and producers of lactic acid. The lactics are also known to be important in the fermentation of fruits and vegetables and dairy products such as kimchi, sauerkraut, pickles, and yoghurt, among others. There are two major classifications of lactic acid fermentation. These are the homolactic and heterolactic fermentation. In homolactic fermentation, the product of sugar fermentation is chiefly lactic acid with small amounts of acetic acid and CO 2. Examples of homofermentative lactics are Pediococcus cerevisiae, Streptococcus thermophilus, Pediococcus halophilus, Streptococcus faecalis, Pediococcus pentocaceous, Streptococcus lactis, Lactobacillus bulgaricus, Lactobacillus plantarum, and Lactobacillus casei. On the other hand, heterolactic fermentation happens when the microorganisms produce considerable amounts of acetic acid, alcohol, and carbon dioxide, in addition to lactic acid. Some known heterofermentative lactics are Lactobacillus buchnerii, Leuconostoc mesenteroides, Lactobacillus brevis, Leuconostoc lactis, Lactobacillus pasteurianum, and Leuconostoc citreum. This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.  9 2. Acetic Acid Fermentation Acetic acid fermentation is used in vinegar production. It involves two processes to convert sugar into acetic acid. The first step is the fermentation of sugar into ethanol by the action of yeast under anaerobic condition. It will be followed by the oxidation of ethanol into acetic acid by bacteria under aerobic condition (Figure 1.8). Some examples of microorganisms which can perform this conversion are Acetobacter aceti, Acetobacter xylinum, Acetobacterium woodii, and Acetobacter pasteurianus. Figure 1.8. Conversion of ethanol to acetic acid. Source: http://entrancechemistry.blogspot.com/2012/04/oxidation-test-to-distinguish- alcohol.html 3. Yeast Fermentation Yeast fermentation involves the action of yeast to produce bread and alcoholic products. Alcoholic fermentation is a complex biochemical process during which yeasts anaerobically breakdown sugars to ethanol, carbon dioxide, and other metabolic byproducts that contribute to the chemical composition and sensorial properties of the fermented foodstuffs. Alcoholic fermentation is the basis for the manufacturing of alcoholic beverages such as wine and beer. 4. Mold Fermentation Molds are sources of hydrolytic enzymes which break down high molecular weight compounds into simpler ones. Examples of mold fermentation are the process of starch saccharification to simple sugars in soy sauce (Aspergillus oryzae), and tempeh (Rhizopus oligosporus) fermentation. Please check this link to know more about types of fermentation: https://www.youtube.com/watch?v=eksagPy5tmQ This course material is for exclusive use of FST 140 students registered during the 2nd Semester 2020-2021.