Bab 11. Produk Fermentasi Susu

FAKULTAS TEKNIK UNIVERSITAS NEGERI YOGYAKARTA

BAHAN AJAR MIKROBIOLOGI PANGAN

Semester 2 BAB XI. PRODUK FERMENTASI

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No. BAK/TBB/BOG6203 Revisi : 00 Tgl. 01 Februari 2015 Hal 1 dari 27

Dibuat oleh : Dilarang memperbanyak sebagian atau seluruh isi dokumen

tanpa ijin tertulis dari Fakultas Teknik Universitas Negeri Yogyakarta

Diperiksa oleh :

Nani R., M.P. Sutriyati P, M.Si.

A. PENDAHULUAN

Milk fermentations must undoubtedly be among the oldest of all fermented foods. Milk obtained from a domesticated cow or camel or goat, some thousands of years ago, would have been fermented within hours by endogenous lactic acid bacteria, creating a yogurt-like product. In fact, the ability to maintain milk in a fresh state before souring and curdling had occurred would have been quite some trick, especially in warm environments. Of course, fermentation and acid formation would have been a good thing since, in the absence of viable lactic acid bacteria, other bacteria, including pathogens, could have grown and caused unpleasant side effects.

Tabel 85. Produk-produk fermentasi susu dari berbagai Negara (Farnworth, 2008)




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Lanjutan Tabel 85. Produk-produk fermentasi susu dari berbagai negara

Milk is particularly suitable as a fermentation substrate owing to its carbohydrate-rich, nutrient-dense composition. Fresh bovine milk contains 5% lactose and 3.3% protein and has a water activity near 1.0 and a pH of 6.6 to 6.7, perfect conditions for most microorganisms. Lactic acid bacteria are saccharolytic and fermentative, and, therefore, are ideally suited for growth in milk. In general, they will out compete other microorganisms for lactose, and by virtue of acidification, will produce an inhospitable environment for would-be competitors. Therefore, when properly made, cultured dairy products have long shelf-lifes and, although growth of acid-tolerant yeast and molds is possible, growth of pathogens rarely occurs.




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Tabel 86. Mikrobia yang berperanan dalam produk fermentasi susu




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The function of lactic acid bacteria in the manufacture of cultured dairy products is quite simplethey should ferment lactose to lactic acid such that the pH decreases and the isoelectric point of casein, the major milk protein, is reached. By definition, the isoelectric point of any protein is that pH at which the net electrical charge is zero and the protein is at its minimum solubility. In other words, as the pH is reduced, acidic amino acids (e.g., aspartic acid and glutamic acid), basic amino acids (e.g., lysine and arginine), and partial charges on other amino acids become protonated and more positive such that at some point (i.e., the isoelectric point), the total number of positive and negative charges on these amino acids (as well as on other amino acids) are in equilibrium. For casein, which ordinarily has a negative charge, the isoelectric point is 4.6. When sufficient acid had been produced to overcome the natural buffering capacity of milk and to cause the pH to reach 4.6, casein precipitates and a coagulum is formed. Along the way, the culture may also produce other small organic molecules, including acetaldehyde, diacetyl, acetic acid, and ethanol. Although these latter compounds are produced in relatively low concentrations, they may still make important contributions to the overall flavor profile of the finished product. The culture may also produce other compounds that contribute to the viscosity, body, and mouth feel of the product. B. PROBIOTIK DAN PREBIOTIK

The term probiotics, as originally used in 1965, referred to the growth-promoting factorsproduced by one microorganism that stimulated growth of another (i.e., the opposite of antibiotics). This definition went through several permutations and by 1989, probiotics were defined as a live microbial feed supplement which beneficially affects the host animal by improving its intestinal balance (Fuller, 1989).The current definition, adopted by the World Health Organization (part of the United Nations Food and Agriculture Organization), defines probiotics as live microorganisms which when administered in adequate amounts confer a health benefit on the host. This latest derivation is important because it recognizes both the relevance of a live and sufficient dose as well as the many reports that indicate probiotics may have health benefits that extend beyond the gastrointestinal tract.

Tabel 87. Sifat fungsional dari bakteri probiotik




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Tabel 88. Strain probiotik yang paling umum digunakan

Tabel 89. Mikrobia probiotik komersial




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Prebiotics are defined as non-digestible food ingredient(s) that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health (Gibson and Roberfroid, 1995). To re-phrase this definition, but with more detail, prebiotics are carbohydrate substances that escape digestion and adsorption in the stomach and small intestine and instead reach the colon.There, they are selectively metabolized by specific members of the colonic microflora. Prebiotics, therefore, enrich the population of those generally desirable commensal organisms such as lactobacilli and bifidobacteria at the expense (theoretically) of their less desirable competition.

C. KEFIR

Kefir is a fermented milk product which originated in the Caucasus Mountain, Tibet or Mongolia, many centuries ago. The Caucasian people discovered that the fresh milk carried in leather pouches would occasionally ferment into an effervescent beverage. In their countries the kefir until now has been produced primarily from sheep milk, whereas in Europe its production on a commercial scale is limited basically to cow milk. Kefir is a beverage produced by the action of lactic acid bacteria (LAB), yeasts, and acetic acid bacteria on milk. This complex mixture of microorganisms produces a distinctive fermented milk product with unique properties.

The traditional kefir manufacturing process, which is still widely practiced, relies on a mixed assortment of bacteria and yeast to initiate the fermentation.The kefir fermentation is unique among all other dairy fermentations in that the culture organisms are added to the milk in the form of insoluble particles called kefir grains directly or a percolate of the grains to milk. Kefir grains are a mass of several different bacteria and yeasts imbedded in a complex matrix of protein and carbohydrate. The microorganisms in the kefir grains ferment the milk, and the grains can be recovered at the end of the fermentation process. The grains have been described as resembling elastic small florets similar to cauliflower in shape, yellow or white in color, and 20 to 30 mm in size. A crude analysis of the grains shows that they are a mass of bacteria, yeasts, polysaccharides, and proteins with a chemical composition of 890 to 900 g/kg water, 2 g/kg lipid, 30 g/kg protein, 60 g/kg sugars, and 7 g/kg ash.

Gambar 52. Electron micrograph dari kefir grain yang menunjukkan simbiosis bakteri dan yeast (Farnworth, 2008)




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Moreover, once the fermentation is complete, the kefir grains can be retrieved from the fermented milk by filtration and reused again and again. The flavor of plain kefir is primarily due to lactic and acetic acids, diacetyl, and acetaldehyde, produced by homofermentative and heterofermentative lactic acid bacteria. However, because kefir grains also contain yeast, in addition to lactic acid bacteria, other end-products are formed that make the finished product quite different from other cultured dairy products. This is because ethanol is produced when the yeasts ferment lactose, such that kefir can contain as much as 2% ethanol. Thus, if yeast are present in the culture (most kefir products made in the United States claim yeasts on their labels), they must be low- or non-ethanol producers. Kefir grains can also contain acetic acid-producing bacteria, such as Acetobacter aceti.

Kefir is the product of the fermentation of milk with kefir grains and mother cultures prepared from grains. Kefir grains are irregularly shaped, gelatinous masses varying in size from 1 to 6 mm in diameter. These grains contain lactic acid bacteria (lactobacilli, lactococci, leuconostocs), acetic acid bacteria and yeast mixture coupled together with casein and complex sugars by a matrix of polyssacharide. Yeast is important in kefir fermentation because of the production of ethanol and carbon dioxide. Kefir grains usually contain lactosefermenting yeast (Kluyveromyces lactis, Kluyveromyces marxianus, Torula kefir), as well as nonlactosefermenting yeasts (Saccharomyces cerevisiae). The principal polyssacharide is a water soluble substance known askefiran. Several homofermentative lactobacillus species including Lb. kefiranofaciens and Lb. kefir produce this polyssacharide. The predominant organisms in kefir grains are lactic acid bacteria, with Lactobacillus species accounting for up to 80% of the total. Other studies have shown that homofermentative species, including Lactobacillus kefirgranum and Lactobacillus kefiranofaciens, were the most frequently isolated species in kefir grains, whereas heterofermentative Lactobacillus kefir and Lactobacillus parakefir were less common. Other lactic acid bacteria that have been identified include species of Lactococcus, Streptococcus, and Leuconostoc.Yeasts are also well represented, and include lactose-fermenting (Saccharomyces kefir) and non-fermenting strains.

Tabel 90. Mikrobia yang berperanan dalam pembuatan kefir

In the United States, kefir is usually made with low-fat or whole milk. The milk is pasteurized at 85C to 90C for up to thirty minutes (like yogurt), then cooled to 20C to 22C. Kefir grains are generally not used in the United States; instead, the milk is inoculated with a kefir starter culture containing Lactobacillus kefiranofaciens and Lactobacillus kefir. The mixture is incubated for sixteen to twenty-four hours or until a pH of 4.2 to 4.6 is




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reached. The coagulum is then gently stirred, flavoring ingredients (usually fruit) are added, and the product is then dispensed. Kefir should contain 0.8% to 1.0% lactic acid along with other heterofermentative end-products (acetic acid, ethanol, and CO2). Acetaldehyde and diacetyl are also usually formed.The kefir will have a tart flavor and a smooth, viscous body. Production of CO2 by the starter culture also provides effervescence and mouth feel.

Gambar 53. Diagram alir pembuatan kefir secara tradisional dan modern (Hutkins, 2006)

The traditional method of kefir making is performed by adding kefir grains directly, as

a starter, to pasteurized, cooled milk. In home production, fermentation temperature and time are not rigidly controlled. The final product cannot be used to inoculate new milk to produce kefir because the original balance of microorganisms in the grains has been disrupted; kefir grains are essential to the process. The large-scale production of kefir making, inoculated milk was filled into bottles, fermented at a controlled temperature until a strong coagulum is formed, and then cooled. However, the kefir produced was of low quality compared to that produced on a smaller scale using traditional methods. Today, kefir is produced by a stirred method where fermentation, coagulum formation, agitation, ripening, and cooling all occur in one vessel. The composition (chemical, organoleptic, microbiological characteristics) of the final product depends on the type of milk used, the source of grains, the preparation of the mother culture (often produced by coarsely sieving the grains and using the percolate), the length of fermentation, the inclusion of a cooling step, and the inclusion of a maturation step.




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A major difference in processing involves the choice of using either kefir grains or a kefir grain-free extract as the mother culture. Traditional artisan production of kefir involved inoculating milk with a quantity of grains (210%), and allowing the fermentation to proceed for approximately 24 h, to a predetermined pH or until a desired taste or texture is obtained. Fermentation is carried out at 20 to 25C. A maturation step, carried out at 8 to 10C for 15 to 20 h, is often added. The grains are then sieved out and can be used for a new fermentation or preserved (17 d) in fresh milk. Leaving the grains in the final product results in excessive acid production and inferior taste.

Gambar 54. Faktor-faktor yang mempengaruhi karakteristik kefir (Farnworth, 2008)

The reported microbiological and chemical composition of kefir varies widely because the fermentation products in the final product are greatly influenced by the source of kefir grains used during fabrication. In addition, different types of milk (various species, various levels of fat) and different production methods (commercial, artisan) can be used. Generally, the pH of kefir is between 4.2 and 4.6. The ingredients most commonly measured as indicators of quality are CO2, protein, lipid (fat), lactose, ethanol, and lactic acid. Yeasts and some heterofermentive lactic acid bacteria are responsible for the production of the CO2 gas in kefir. The CO2 content increases during fermentation as the pH drops. If the fermentation is carried out for longer than 24 h, CO2 production plateaus after 48 h. The gas production leads to fine flake coagulum formation and also imparts a sparkling mouth feel to kefir. The presence of the gas bubbles in the drink has prompted some to refer to kefir as the champagne of fermented milk drinks.

The fat content of kefir can be altered based on the type of milk fermented. In the former Soviet Union, kefirs have been sold that vary from fat free up to 3.2% fat. The lactose found in milk is degraded to lactic acid during fermentation; this causes the pH to drop and the milk to thicken. As much as 30% of the milk lactose is broken down during fermentation. The production of ethanol in kefir is complex; both yeasts and heterofermentative bacteria produce ethanol. The quantity of ethanol produced is dependent on the fermentation process and the type of container used (tightly capped or not). The ethanol concentration can be increased in the final product by increasing the temperature during fermentation. Kefir has the same pattern of amino acids as milk. Kefir proteins are easily digested due to the action of acid coagulation and proteolysis of milk proteins. The taste of unflavored kefir has been




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described as yeasty and the terms prickling and sparkling has been used to describe the mouth feel of kefir caused by the liberation of trapped CO2.

Tabel 91. Komposisi kimia kefir

D. YOGHURT

Yogurt can be made from skim (non-fat), reduced fat, or whole milk. As is true for all dairy products, but especially so for yogurt and other cultured milks, it is important to use good quality milk, free of antibiotics and other inhibitory substances.The first step involves adding nonfat dry milk to the milk to increase the total solids to 12% to 13%, sometimes to as high as 15%. Alternatively, the total milk solids can be increased by concentrating the milk via evaporation. Other permitted ingredients may be added, and the mix (only if it contains fat) is then usually homogenized, although there are some specialty manufacturers that produce unhomogenized, cream-on-the-top whole milk versions.

Yogurt is considered a fluid milk product by the U.S. Food and Drug Administration (FDA) and must be made using pasteurized milk. However, most yogurt mixes receive a heat treatment well above that required for pasteurization. Thus, instead of pasteurizing milk for 71.7C for 15 seconds (the minimum required), mixes are heated to between 85C and 88C for up to 30 minutes. Other time-temperature conditions can also be used, but kinetically they are usually equivalent. Heating can be done in batch mode (i.e., in vats), but continuous




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heating in plate or tube type heat exchangers is far more common. The high temperature treatment not only satisfies all of the normal reasons for pasteurization (i.e., killing pathogens and spoilage organisms and inactivating enzymes), but these severe heating conditions also perform two additional functions. First,even heat-resistant bacteria and their spores are killed, making the mixture essentially free of competing microorganisms. Second, the major whey proteins, -lactalbumin and -lactoglobulin, are nearly 100% denatured at the high pasteurization temperatures. These proteins exist in globular form in their native state but once denatured, amino acid residues are exposed and their ability to bind water, via hydrogen bonding, is significantly enhanced. Denatured whey proteins also reduce the Eh and stabilize the milk gel.

Gambar 55. Diagram alir pembuatan yoghurt

The pasteurized milk is then cooled via a heat exchanger to the desired incubation temperature, usually between 40C and 43C. Alternatively, the milk can be cooled as for conventional processing to 2C to 4C, and then warmed to the higher temperature later. The incubation temperature is critical, since it will influence the activity of the culture and ultimately the properties of the finished yogurt. The route the mix takes next depends on the




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type or style of yogurt being made.There are two general types of yogurt.Yogurt that is mixed with flavors, fruit, or other bulky ingredients is called stirred or Swiss-style yogurt. For this type, the mix is pumped into vats and the culture is added.The mixture is then incubated such that the entire fermentation occurs in the vat. At the end of the fermentation, the mixture is gently agitated and cooled, and the flavor ingredients are introduced. The mixture is then pumped into containers. In contrast, mix can be inoculated with culture, pumped immediately into the container, and then fermented directly in the container. If this so-called fermented-in-the-cup style yogurt is to contain fruit or other bulky flavoring (i.e., fruit-on-the-bottom or sundae-style), the fruit or flavoring material is first dispensed into the cup and the yogurt mix added on top, followed by incubation and fermentation.The consumer must do the stirring and mixing to incorporate the flavoring throughout the product.

Tabel 92. Persyaratan mikrobia untuk pembuatan yoghurt

Gambar 56. Diagram alir pembuatan yoghurt dengan penambahan buah-buahan




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Tabel 93. Jenis-jenis yoghurt komersial

No Jenis yoghurt Definisi

1 Plain Unflavored yogurt may be cultured in individual cups or cultured in a vat and dispensed into cups. No sugar is added to the formulation.

2 Fruit flavored This type of yogurt is cultured in a vat or bulk and then flavored with a fruit preparation. Styles consist of blended/stirred and fruit-on-the bottom.

3 Blended/stirrer In this style, fermented base containing sugar is blended with fruit preparation to disperse the fruit throughout the body of the yogurt. This style is further subdivided into Swiss- and French-style blended yogurt.

4 Swiss/blended The fermented base is blended with fruit preparation to disperse the fruit throughout and packaged. On cooling, the product thickens and viscous custard-like texture is formed. The product contains stabilizers to assist in texture formation.

5 French/blended Similar to Swiss style, but is characterized by a distinctly less viscous texture. Generally contains no stabilizers other than milk solids.

6 Light Nonfat yogurt in which no sugar is added to yogurt base and high intensity sweeteners are used, resulting in significant reduction in calories.

7 Lo carb Nonfat yogurt in which high intensity sweeteners are used in place of sugar. Fruit preparations are replaced with fruit flavors. Lactose content of nonfat milk is reduced by membrane processing. Milk protein concentrate and whey protein isolate are used to reduce the lactose content further.

8 Custard Designed for children. It has a very viscous body resembling custard. Only fruit puree/juice is used for fruit flavoring. Usually, fermented in the cup.

9 Sundae/fruit on the bottom

The fruit is deposited on the bottom of the cup, followed by a top layer of unfermented or fermented yogurt. Before consumption it requires blending to mix the fruit preparation.

10 Cup-incubated traditional sundae

The fruit is layered in the bottom of the cup and unfermented (inoculated) yogurt mix is deposited on the top. The cups are incubated individually to desired pH and cooled quickly to control further acid production.

11 Vat-incubated sundae

The fruit is layered in the bottom of the cup and white fermented yogurt base is deposited on the top. On cooling, the texture of the top layer is developed.

12 Western sundae The fruit is layered on the bottom of the cup, and yogurt base fermented in vat is deposited on the top. It is characterized by special formulation of yogurt base in that corresponding color and flavor of the fruit-on-the-bottom is included in the top layer.

13 Vanilla flavored The yogurt may be cup- or vat-incubated. Following fermentation, yogurt base is mixed with vanilla flavor.

14 Natural Contains natural ingredients only. Generally, it does not contain stabilizers, artificial colors, or flavors.

15 Organic Contains only ingredients certified as organic.

16 Yoghurt drink/smoothie

Drinkable yogurt is fluid enough to drink. May be sweet and fruit flavored. Smoothies are drinking yogurt, often fortified with minerals and vitamins, prebiotics and probiotics. Some may be designed as a meal replacement.

17 Whips/mousse This yogurt contains up to 50% (by volume) of inert gas/air to create a fluffy/light texture.

18 Yoghurt with topping Sweetened fermented base is packaged separately in a cup and sealed. Topping consisting of cereals, nuts, or fruits and is packaged in a smaller cup and sealed. Then the smaller cup is inverted and placed on the larger yogurt cup. The two cups are tied together by plastic wrap. The consumer mixes the toppings prior to consumption.

19 Concentrated/Greek/ strained

It is relatively high in milk fat and milk solids-not-fat. It has a creamy texture and mild flavor as a result of whey removal by centrifugal/ membrane separation or by straining through cloth.

20 Frozen The fermented yogurt is blended with low fat/nonfat ice cream to obtain pH of 6.0. The yogurt mix is then extruded through a soft serve machine at 50% overrun and garnished with nuts and other foods to get soft serve frozen yogurt. If the extruded frozen yogurt is hardened like ice cream, it is called hard frozen yogurt.




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E. CULTURED BUTTERMILK

Buttermilk is the fluid remaining after cream is churned into butter. It is a thin, watery liquid that is rarely consumed as a fluid drink. Because it is rich in phospholipids (derived from the rupture of milk fat globules during churning), it has excellent functional properties and is an especially good source of natural emulsifiers. It is typically spray dried and used as an ingredient in processed food products. Cultured buttermilk, in contrast, is made from skim or low-fat milk that is fermented by suitable lactic acid bacteria.The only relation this product has to buttermilk is that butter granules or flakes are occasionally added to provide a buttery flavor and mouth feel. How, then, did this product come to be called buttermilk? In the traditional manufacture of butter, it was common practice to add a mixed, undefined lactic culture to cream prior to churning.The lactic acid would provide a pleasant tart flavor, and the cream-ripened butter would be better preserved.The resulting by-product, the buttermilk, would also be fermented.

Gambar 57. Diagram alir pembuatan cultured buttermilk




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Cultured buttermilk is usually made from lowfat milk, although non-fat and whole milk versions also exist. Non-fat milk solids are frequently added to give about 10% to 12% non-fat solids. Next, the milk is heated to 85C to 88C for thirty minutes. This not only pasteurizes the milk, but also satisfies other functional requirements, as described above for yogurt. The mix is then cooled to 21C to 22C and inoculated with a mesophilic starter culture, specific for cultured buttermilk. Following the addition of the culture, the mix is incubated at 21C to 22C for twelve to sixteen hours. At the end of the fermentation, when the titratable acidity has reached 0.85% to 0.90% and the pH has decreased to about 4.5, the product is cooled to 2C and agitated to break up the coagulum. Salt is usually added, and, if desired, butter granules or flakes are added.The finished product should be viscous and pourable. The product is pumped into containers and distributed.

The starter culture for buttermilk usually contains a combination of acid-producing bacteria and flavor-producing bacteria, in a ratio of about 5:1. Many culture suppliers now also offer body-forming (i.e., EPS-producing) strains. The acid producers include strains of L. lactis subsp. lactis and/or L. lactis subsp. cremoris. These bacteria are homolactic, and their function is simply to produce lactic acid and lower the pH. For manufacturers who prefer a decidedly tart, acidic product, the acid-producing strains are sufficient. It is more common, however, to include flavor-producers in the starter culture. Among the flavor-producing bacteria used in buttermilk cultures are L. lactis subsp. Lactis (diacetyl-producing strains), Leuconostoc mesenteroides subsp. cremoris, or Leuc. lactis. The latter organisms are heterofermentative, producing lactic acid, as well as small amounts of acetic acid, ethanol, and carbon dioxide. These metabolic end-products contribute to the flavor and, in the case of the carbon dioxide, to the mouth feel of the product. Importantly, these bacteria also have the metabolic capacity to ferment citric acid and to produce diacetyl, a compound that has major impact on the flavor of cultured buttermilk. Diacetyl has a buttery aroma and flavor, and, according to buttermilk afficionados, imparts a delicate and characteristic flavor. F. SOUR CREAM

Despite the apparent differences in the appearance and texture, sour cream is actually quite similar to cultured buttermilk in several respects.The sour cream culture, for example, is the same as that used for buttermilk. The incubation conditions and the flavor compounds produced by the culture are also similar for both products. There are, however, several notable differences. For sour cream manufacture, cream (containing varying levels of milkfat) is used instead of lowfat or skim milk.The cream is pasteurized, but not quite at the severe conditions used for buttermilk or yogurt. This is because for sour cream, denaturation of protein is not as crucial, since the milk fat will impart the desired creaminess, thickness, and body. The cream is homogenized, which also promotes a desirable heavy body.

In the United States the starting material for sour cream manufacture is cream at 18% to 20% milkfat. Lower-fat versions, such as sour half-and-half (10% milkfat), are produced in some regions, as are higher-fat products (containing as much as 50% milkfat).The latter are generally produced as an ingredient for dips and other sour cream products. There is no need to add additional nonfat dry milk, as for yogurt and buttermilk, since achieving a firm gel and thick body is not an issue for these high-solids products. For the same reason, the cream is pasteurized at more typical time and temperature conditions (85C for twenty-five seconds). However, the cream must be homogenized (usually twice) to produce a smoothtextured product with good viscosity. After the mix is cooled, the sour cream culture is added. The culture, containing mesophilic acid-producing, flavor-producing, and body-




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forming strains, is often the same as that is used for cultured buttermilk. The mix is then either filled into cups and incubated or incubated directly in vats (analogous to the two styles of yogurt). Incubation is at 20C to 25C for ten to sixteen hours. When the pH reaches about 4.4 to 4.6 (about 0.7% to 0.9% lactic acid), the sour cream is cooled, either by moving the cup-fermented product into coolers or, in the case of vat-fermented product, by stirring the product in jacket-cooled vats.The product is then pumped into containers.Sour cream should have a similar flavor profile as cultured buttermilk, with lactic acid and diacetyl predominating. Body characteristics are especially important, and various gums and other stabilizing agents are frequently added to the mix. Some manufacturers even add a small amount of chymosin to provide additional firmness. When defects do occur, they are often due to poor quality ingredients and post-pasteurization contamination by acid-tolerant yeasts and molds and psychrotrophic bacteria.

Gambar 57. Diagram alir pembuatan sour cream

G. KEJU

Cheese is one of the most important products of the dairy industry. Like so many fermented foods, the first cheese made by human beings was almost certainly a result of an accident. Some wandering nomad, as the legend goes, filled up a pouch made from the stomach of a calf or cow with a liter or two of fresh milk. After a few hours, the milk had




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turned into a solid-like material, and when our would-be cheese maker gave the container a bit of a shake, a watery-like fluid quickly separated from the creamy white curd. This moderately acidic, pleasant-tasting curd and whey mixture not only had a good flavor, but it also probably had a longer shelf-life than the fresh milk from which it was made. Today cheese is recognized as having very high nutritional value due to its generally high content in protein, calcium, riboflavin, and vitamins A and D.

There are in excess of 2000 different types of cheese. The Food and Agriculture Organisation (FAO) definition of cheese is the fresh or matured product obtained by the drainage (of liquid) after the coagulation of milk, cream, skimmed or partly skimmed milk, butter milk or a combination thereof. Whey cheese is the product obtained by concentration or coagulation of whey with or without the addition of milk or milk fat.

Tabel 93. Jenis-jenis keju dari berbagai negara

Cows milk consists of, in descending order (and in general concentrations), water (87%), lactose (5%), fat (3.5% to 4%), protein (3.2% to 3.4%), and minerals (




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Gambar 58. Komposisi gizi susu, keju, dan whey

Cheese manufacture essentially involves concentrating the fat and casein of milk by

coagulating the casein enzymatically (rennet cheeses) or by acidic pH (quarg, acidcurd cheeses). Cows milk is used predominantly in industrial cheese making. In Mediterranean countries, sheeps and goats milk are used for cheese making to a large extent. Outside Europe, the milk of water buffaloes, camels, and mares is often used for cheese making. Over the centuries, cheese production has led to the existence of an extensive range of cheese varieties. Although more than a thousand individual varieties exist, some of these differ only in size, packaging, place of origin, or name.

In general, cold storage of milk is necessary before cheese manufacture. Most cheeses are made from pasteurized milk (72C for 15 sec). Pasteurization does not affect the physicochemical parameters of the milk significantly, but it destroys most of the pathogenic and spoilage bacteria contaminating the milk. Some nonstarter lactic acid bacteria (Lactobacillus spp., Streptococcus spp.) and, if present, spore-forming bacteria (Clostridium, Bacillus) can survive pasteurization and affect cheese ripening. Heating of milk before cold storage (63C to 65C for 15 to 20 sec) may be used for prolonged storage; however, the milk is still pasteurized before cheese making.

Acid production during cheese making is essential in the formation of the gel from casein. Starter cultures promote rapid acid development during curd manufacture and contribute to distinct textural and flavor properties in the cheese after ripening. Bacteria used as starter cultures generally belong to the genera Lactococcus, Streptococcus, Leuconostoc, and Lactobacillus. The typical mesophilic starter culture consists of Lactococcus lactis sp. lactis (L. lactis) and L. lactis ssp. Cremoris (L. cremoris). These starters are used for cheeses with moderate scald temperatures (< 40C, Gouda, Edam, etc.). For cheeses requiring higher scald temperatures, thermophilic starter cultures are used (Streptococcus thermophilus, Lactobacillus helveticus, Lactobacillus delbrueckii ssp. bulgaricus, etc.). When eyes are required, the gas-forming species L. lactis ssp. lactis biovar. diacetylactis, Leuconostoc mesenteroides, or Propionibacterium shermanii can be used.




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Tabel 94. Kelompok utama keju




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Tabel 95. Karakteristik beberapa jenis keju

The milk may be pretreated in various ways depending on the cheese that is being made. Such treatments may include: 1) heating (pasteurisation) to destroy pathogens and lower the levels of spoilage bacteria

and enzymes. Such treatment may typically be a regime of 72C for 15 s; 2) reduction of fat by centrifugation or by adding non-fat solids such as concentrated

skimmed milk or non-fat dry milk. However, this may be problematic if lactose levels are too high;

3) concentration, which may be by applying vacuum (for high throughput cheeses) or ultrafiltration (for soft cheeses);

4) clarification, either by high-speed centrifugation or microfiltration. This procedure optimises the number of foci that lead to eyes in the finished cheese. Very high-speed centrifugation will additionally lower the level of undesirable micro-organisms;

5) homogenisation. This involves the application of high-pressure shear to disrupt fat globules, rendering smaller globules that are coated with protein. This is important for rendering consistent texture in blue-veined cheeses and for cream cheese. It also has significance for the levels of free fatty acids and therefore of the flavour-active oxidation products that are made from them;

6) addition of calcium chloride, which promotes clotting; 7) addition of enzymes to enhance flavour or to accelerate maturation. For example, lipases

may be employed in the manufacture of blue veined cheeses; (8) addition of micro-organisms. These microbes may include Propionibacter for Emmental and Swiss cheese, Penicillium roqueforti for blue cheeses and P. camamberti for camembert and brie.




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Tabel 96. Jenis-jenis keju (Bamforth, 2005)

Most of the major international cheese varieties are rennet cheeses. A small

percentage of cheeses are acid curd cheeses (cottage cheese, quarg, feta, Harz cheese) or heat/acid coagulated cheeses (ricotta). For rennet-type cheeses, the gel is formed at a higher pH than achieved by acid alone. The rennet gel is more elastic than an acid gel and shrinks and expels moisture in the presence of heat and acid. Rennet is used in cheese manufacture primarily to coagulate milk. However, residual rennet, which is kept in the curd, also plays an important role in the generation of flavor compounds during cheese ripening. In the past, the principal coagulant used was calf rennet, mainly consisting of chymosin and some pepsin or some microbial proteinases from different mold species. Today a pure recombinant chymosin is increasingly used. Some well-known trade names are Chymogen, Maxiren, and Chy-Max.

After cooking or scalding, the curd, containing the caseins and milk fat, is separated from the whey, containing lactose, whey proteins, and minerals. In the case of Cheddar cheese, the curd may be textured, milled, and salted. The curd of other cheese varieties may be hooped directly into perforated forms, and then an appropriate pressure is applied for draining. After whey removal, cheeses may be salted by applying dry salt to the cheese surface, or by immersing cheese blocks in brines containing 18% or more NaCl. Brining is performed on small-sized soft cheeses for up to 24 h, and for larger cheeses like Gouda, Edam, or Tilsit (> 2.5 kg). Aged brines develop a typical salt- and acid-tolerant microflora (104 to 106 colony forming units (CFU)/mL), often with Debaryomyces hansenii and Staphylococcus equorum as the predominant species. An influence of the brine microflora on




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cheese ripening is significant for surface-ripened cheeses, especially for smear cheese varieties.

Gambar 59. Ringkasan proses pembuatan keju (Bamforth, 2005)

Cheese contains less water and more milk solids, in the form of fat and protein, than

the milk from which it was made. Thus, cheese making can simply be viewed as a concentration process, in which the water portion, or whey, is removed and the solids are concentrated. The conversion of liquid milk into a solid mass of cheese is done via coagulation (or precipitation) of milk protein. Milk, as noted above, contains about 3.3% protein. Of the protein fraction, about 80% is casein (2.5% of the milk), and the remaining 20% are known collectively as whey proteins. For most cheeses, the protein portion consists almost entirely of casein. When milk coagulates and the coagulated material is separated, the soluble whey proteins are released into the water or whey fraction. The casein matrix not only contains some water (and whatever solutes are dissolved or suspended in the water phase), but also a large portion of the lipid fraction that was originally present in the milk, depending on how coagulation occurs.

There are three ways the initial coagulation step is accomplished. First, milk can be coagulated by acids produced by lactic acid bacteria, based on the same principle used for yogurt and other cultured dairy products. When the milk pH reaches 4.6, casein is at its isoelectric point and its minimum solubility, and therefore it precipitates. In cheese making, of course, the curds are then further processed, resulting in products such as Cottage cheese and farmerscheese.It is important to realize that casein coagulates at pH 4.6 whether acidification occurs via fermentation-generated acids or simply by addition of food-grade acids direct into the milk. In fact, the latter process is preferred by some producers of Cottage, cream, and other acid-coagulated cheeses, due in part to the ease of manufacture and the elimination of starter cultures as an ingredient.

The second and most common way to effect coagulation is by the addition of the enzyme chymosin (or rennet). In contrast to acid-precipitated casein, the coagulated casein network formed by chymosin treatment traps nearly all of the milkfat within the curd. Most of the cheeses manufactured around the world rely on chymosin coagulation. It is worth emphasizing that even though chymosin, alone, is sufficient to coagulate milk, lactic starter cultures are also absolutely essential for successful manufacture of most hard cheeses.The




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lactic acid bacteria that comprise cheese cultures not only produce acid and reduce the pH, they also contribute to the relevant flavor, texture, and rheological properties of cheese.

Finally, it is possible to form a precipitate by a combination of moderate acid addition (pH 6.0), plus high heat (>85C).Whey proteins are denatured under these conditions, thus the precipitate that form consists not only of casein, but also whey proteins. Fat may also be retained. Even in solutions where casein is absent (i.e., whey), this process can result in enough precipitated whey protein to form a cheese. Examples of precipitated cheeses include Ricotta cheese, the Hispanic-style cheeses queso fresco and queso blanco, and Gjetost, a whey-derived cheese popular in Norway.

Once milk is transformed from a liquid into a solid (actually a gel), the next goal is to remove water.The first step involves increasing the surface area of the single large gel mass by cutting it into literally millions of smaller cubes of curd (e.g., 1 m3 of a cheese gel cut into 1 cm3 particles yields 106 such curd particles). Because the distance the water molecules must travel (from the interior of the gel to the outside environment) decreases as the curd size decreases, this step has the effect of substantially increasing the rate of syneresis. Then, when these curds are stirred, and then heated, the curds shrink and syneresis is further enhanced. Syneresis begins as soon as the curds are cut, and increases during the ensuing minutes when the curds are gently stirred. The initial rate depends on the starting pH of the curd, because prior acid development greatly enhances syneresis. However, the cooking step is the primary means of enhancing syneresis. All other factors being equal, the higher the temperature and the longer the curds are cooked and stirred, the dryer will be the finished cheese.Thus, the cooking step is one of the major variables that cheese manufacturers can manipulate to produce different types of cheese. The more water removed from the curd, the less lactose will be available for fermentation. Cheese manufacturers can, therefore, influence acid production and cheese pH by modulating the cooking time and temperature conditions.

Perhaps the most influential step during the cheese making process involves the means by which the curd is handled during and after the cooking and stirring steps. For many cheeses, the whey is removed when the desired acidity is reached,when the curd has been cooked for a sufficient length of time, or when it is sufficiently firm or dry.There are several means by which the curd is separated and the whey is removed. In traditional Cheddar cheese manufacture, the curds are simply pushed to the sides of the cheese vat and the whey is drained down from the center, with screens in place at the drain end to prevent curd loss. Alternatively, the curds can be collected in cheese cloth and hoisted above the whey, as in traditional Swiss cheese manufacture.In more modern, large production factories, where cheese vats must be cleaned and re-filled, curds and whey are typically pumped to draining tables or Cheddaring machines, where whey separation occurs. Similarly, the curd-whey mixture can be added directly into perforated cheese hoops, where the whey drainage step is completed.

Salt is an essential ingredient that provides flavor, enhances syneresis, and contributes to the preservation of most cheeses. Salt can be applied directly (i.e., in dry form) to the milled curds, as in the case of Cheddar, or salt can be rubbed onto the surface of hooped cheese, as in the case of some blue cheese varieties (e.g., Gorgonzola and Roquefort). Alternatively, some cheeses, such as Swiss, Mozzarella, and Parmesan, can be placed in brines. Obviously, when salting occurs via brining methods, the amount of salt that ends up in the cheese is a function of the diffusion rate into the cheese, as well as the geometry of the cheese block, the duration of brining, and brine strength. If the cheese is




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shaped or cut into small units and left in the brine, as with Feta cheese, salt concentrations can be very high (>3%). In contrast, large blocks or wheels of brined Swiss cheese typically contain less salt (




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inactivating many of the milk-borne bacteria that could otherwise cause problems during the ripening period. Finally, the quality of the cheese also depends heavily on the performance of the bacteria used in the mixed species starter culture, as well as the ratio of those organisms.

Tabel 95. Bakteri asam laktat yang digunakan dalam pembuatan keju

H. PRODUK FERMENTASI SUSU LAINNYA

Tabel 96. Produk fermentasi susu lainnya (Bamforth, 2005)




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1. Kishk

Fermented milkwheat mixtures, known as kishk in the Middle East and tarhana in Greece and Turkey, are important foods in the diet of many populations. In addition to their well-established position in the dietary patterns of the people in the aforementioned countries, these products have been promoted in Mexico and Europe.

Kishk (Fugush) is typically prepared by adding strained yoghurt to bulgur (cracked and bran-free parboiled wheat) and allow the mix to ferment at ambient temperature for different periods of time. The wheat grains are boiled until soft, dried, milled and sieved in order to remove the bran. Milk is separately soured in a container, concentrated and mixed with the moistened wheat flour. The milk undergoes a lactic fermentation and the resulting paste is dried to a moisture content of 1013% and then ground into a powder. The product is stored in the form of dried balls, brownish in colour with a rough surface and hard texture. The microorganisms responsible for the fermentation include Lactobacillus plantarum, Lactobacillus casei and Lactobacillus brevis, Bacillus subtilis and yeasts.

Kishk is a balanced food with excellent preservation quality, richer in B vitamins than either wheat or milk, and well adapted to hot climates by its content of lactic acid. Some modifications, such as the substitution of whole wheat-meal for bulgur, have been proposed in the formulation of kishk. It has been found that substitution of whole wheat-meal for bulgur enhances the availability of Ca, Fe, Mg and Zn and provides a better means for the utilization of wheat nutrients, without undue effects on the acceptability of the final product. Sensorily, the whole wheat-meal kishk is sourer, less cohesive, less gritty, contains more bran particles and is more yellowish in colour than the traditional bulgur kishk. The production costs are lower and whole wheat meal is nowadays an ingredient in the formulation of kishk.

2. Tarhana

Tarhana (Trahanas) is prepared by mixing wheat flour, sheep milk yoghurt, yeast and a variety of cooked vegetables and spices (tomatoes, onions, salt, mint, paprika) followed by fermentation for 17 days. The fermented matter is dried and stored in the form of biscuits. The fermentation process and the type of product obtained is very similar to kishk. The sheep milk yoghurt contains Steptococcus thermophilus and Lactobacillus bulgaricus as the major fermenting organisms.

Tarhana has an acidic and sour taste with a strong yeasty flavour, and is a good source of protein and vitamins. While tarhana soup can be used as a part of any meal, it is often eaten for breakfast. The practical nutritional importance of tarhana is the improvement of the basic cereal protein diet by adding dairy protein in a highly acceptable form. The low pH (3.84.2) and low moisture content (69%) make tarhana a poor medium for pathogens and spoilage organisms. In addition, tarhana powder is not hygroscopic and it can be stored for 12 years without any sign of deterioration.

3. Vili

Villi is widely consumed in Finland is known for its high viscosity and musty flavor and aroma.The ropy texture is due to capsular EPS production by L. lactis subsp. lactis and L. lactis subsp. cremoris, and the musty flavor is caused by growth of the fungal organism Geotrichum candidum.




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4. Koumiss Koumiss was traditionally produced from mares milk. Similar to kefir in that lactic

acid and ethanol are both present, this product owes much of its popularity to its putative therapeutic properties. Koumiss is a fizzy, greyish white drink produced traditionally from mares milk in eastern Europe and central Asia. It can have an acidity up to 1.4% and an ethanol content up to 2.5%. A mixed yeast/LAB flora is responsible for the fermentation comprising Lb. delbrueckii subsp. bulgaricus and a number of lactose fermenting yeasts. These are dispersed throughout the product and do not form discrete particles as in kefir. Cows milk is a more convenient raw material to use nowadays and this is usually modified to resemble more closely the composition of mares milk which has a lower fat content and higher carbohydrate levels.

5. Gaio

Gaio was first produced by the Danish dairy corporation MD Foods A/S established in Aarhus in Denmark. Recently, MD Foods merged with Arla Foods, and the product is only produced by Arla Foods and consumed in Denmark and Sweden. The production of Gaio uses a fermentation of milk at a temperature of 37C. The level of starter inoculated is approximately 5 1012 CFU/1000 L of milk. The fermentation time is approximately 9 h, to a final pH of 4.5. The final product is very viscous and has a mild, slightly acid taste. The product is sold in plastic containers of 500 g as natural and with different fruit flavors. The product is distributed and sold refrigerated. The original Ukrainian bacterial culture (Causido) is used to produce Gaio. This culture contains one human species of E. faecium and two strains of S. thermophilus. The CFUs of the fresh product are 105 to 109/mL for E. faecium and 5 to 20 108/mL for S. thermophilus. One hundred grams of the product has an energy content of 240 kJ and contains 4.9 g of protein, 5.4 g of carbohydrate, and 1.5 g of fat (66% as milk fat and 33% as soybean fat). The cholesterol content is about 5 mg for every 100 g of the product. Vitamins E and C are added in accordance with the original Ukrainian recipe, giving final concentrations of 0.5 mg and 10 mg, respectively, per 100 g.

6. Dadih

Susu kerbau mempunyai kandungan protein dan lemak lebih tinggi dibandingkan susu sapi sehingga lebih mudah rusak. Secara tradisional, dadih dibuat melalui proses fermentasi alamiah dan spontan dari susu kerbau mentah di dalam wadah bambu gombong (Gigantochola verticilliata). Jenis bambu ini telah digunakan secara turun temurun karena di dalamnya terdapat beberapa jenis mikrobia yang secara alamiah dapat memfermentasi susu menjadi dadih. Salah satu alasan menggunakan bambu ini adalah karena menimbulkan rasa pahit sehingga tidak dikerumuni oleh semut selama proses fermentasi.

7. Dali

Dali adalah produk olahan susu berasal dari Tapanuli Utara. Pembuatan dali dilakukan dengan cara mengkoagulasikan susu menggunakan enzim yang berasal dari tumbuh-tumbuhan, yaitu enzim papain dari pohon pepaya. Produk yang diperoleh berupa padatan/gumpalan menyerupai tahu, dan biasa dikonsumsi sebagai lauk-pauk pada waktu makan.

Documents

Bab 11. Produk Fermentasi Susu