E FECTOS Y FRECUENCIAS DE LOS RESULTADOS EN SALUD

Milk protein concentrate obtained by ultrafiltration of skim milk is a functional ingredient to raise pro- tein level of the mix, but the main reason for its use is to reduce lactose content of the mix to produce “low- carb” yogurt. As yogurt is a Grade A product in the United States, the MPC must be derived from a Grade A process. The labeling for this ingredient is “ultrafil- tered skim milk.” It contains 80–85% water, 10–12% protein,<0.5% fat, <5% lactose, and >2.5% ash.

In the formulation of yogurt, the lactose level can be reduced significantly, as much as 70%, by judi- cious use of lactose-reduced MPC and high-protein WPC in the formulation, replacing milk and NFDM. To conform to the legislation in certain countries or to satisfy the consumer demand, yogurt with no sta- bilizers can be produced. In such products, the con- sistency and stability of texture are accomplished by addition of nonfat dry milk, condensed skim milk, and/or whey protein concentrates. In rare practice,

milk may be partly concentrated by removal of 15–20% water in a vacuum pan. In such a specialty yogurt, the mix is formulated to contain high nonfat solids as much as 12% to provide a desirable body and texture and freedom from syneresis.

Since yogurt is a manufactured product, its chem- ical composition is likely to vary depending on the quality standards established by marketing consider- ations. Nonetheless, it is extremely important to stan- dardize and control the day-to-day product to meet the consumer expectations and regulatory obligations associated with a certain brand or label. The mix is formulated to predetermined milk fat and milk solids- not-fat content and the weights of each ingredient are calculated with the aid of computer software. Most yogurt plants are equipped with computer programs to calculate the amount of each ingredient needed to achieve target levels of milk fat, milk SNF, to- tal solids, sugar, stabilizers, and other ingredients. The program usually also calculates the cost of the mix.

The level of milk fat found in commercial sam- ples of yogurt ranges from 0.05% to 3.60%. Gen- erally, consumers view milk fat negatively from the caloric standpoint. Consequently, 90% of the refrig- erated cup yogurt sold in the United States today is either low fat or nonfat. The fat level in yogurt has a favorable effect on texture quality of the yogurt. Milk fat also has a masking effect on the perception of yo- gurt acidity. It has been observed that nonfat yogurt

(<0.5% fat) tastes more acidic and less mild than the

same pH yogurt with a fat content of>1.5%. There- fore, it is important to use a “mild” yogurt culture in nonfat and 1% low-fat yogurt to maintain the finished pH above 4.2 to please today’s consumer tastes. It has also been concluded that milk fat stabilizes the con- traction of the protein gel formed after fermentation of the yogurt mix and hinders whey separation. Thus,

in yogurt with little or no stabilizer, a low fat content in milk encourages whey separation, while a high fat content prevents the separation. As the fat con- tent is increased, there is a significant improvement in flavor, viscosity, and taste. However, there is also an increase in the caloric value. In most low-fat and nonfat yogurts produced today, stabilizers are used to compensate for the loss of the stabilizing effect of milk fat. For products produced in the United States, the milk fat levels are standardized to a minimum of 3.25% before the addition of bulky flavors for full-fat yogurt. Low-fat yogurt is manufactured from the mix containing not less than 0.5%, nor more than 2.00% milk fat before the addition of bulky flavors. Nonfat yogurt mix has milk fat level not exceeding 0.5%. These fat levels correspond to the Food & Drug Ad- ministration requirement for nutritional labeling of nonfat yogurt, low-fat yogurt and yogurt. (Chandan, 1997, 2004).

Sweeteners

Nutritive Sweeteners

In the manufacture of flavored yogurt, it is usually de- sirable to add a sweetening agent to the yogurt base. The standard of identity for yogurt, low-fat yogurt and nonfat yogurt (FDA CFR Parts 131.200 to 206) specifies the allowable nutritive sweeteners that can be used. The level of sweetness in the yogurt mix will depend on the Brix of the fruit or flavoring ingredi- ent and the desired level of sweetness in the finished product. Most fruit-flavored yogurts contain approx- imately 10–13% sugar equivalent, whereas flavored yogurts (vanilla, lemon, coffee etc.) contain 8–10% sugar. The sweetener most commonly used in the in- dustry is sucrose in either liquid (65–67% total solids) or granulated form. When liquid sugar is used, the added water is taken into consideration to avoid di- lution of the total solids of the mix. The total amount of sugar solids in yogurt mix should not exceed 10–11% because of the inhibitory effect on the tradi- tional yogurt culture. Depending on the culture, some inhibitory effect will be seen with sugar solids con- tent between 7% and 10%. The addition of the sugar generally occurs before pasteurization due to follow- ing reasons:

rHeat treatment of the milk destroys any osmophilic yeasts and molds that might be present in the sugar ingredient.

rPotential source of postpasteurization contamination (HACCP).

rThe consistency of yogurt is better when sugar is added to the milk rather than into the coagulum, unless the formulation has been adjusted to allow for this dilution.

If it is necessary to add sweeteners after fermenta- tion, only pasteurized liquid sugar or flavored sweet- ened syrups should be used. When using this method, the total solids of the yogurt mix must be adjusted for the dilution associated with these liquid sweeteners. Also, Good Manufacturing Practices and HACCP control should be practiced to minimize the potential risk of microbiological or physical contamination.

Refined crystalline sucrose is manufactured in- dustrially from sugar cane or sugar beet processing. Both sources give identical sucrose with no chemical, physical, or structural differences. Crystalline sugar is either refined from crude raw sugar or is processed from sugar cane juice. The first step is to extract juice from sugar cane using a series of roller presses. Nonsugar impurities are removed by mechanical fil- tration, followed by lime-carbon dioxide purifica- tion step. The juice is allowed to settle and then fil- tered to get purified juice. In some factories, this step involves lime-phosphoric acid floatation procedure. Furthermore, purification of the juice is achieved by treatment with activated charcoal and ion exchange reactors. This juice (12–15% total solids, 91–92% pu- rity) is evaporated in multistage vacuum evaporators to get sugar concentrate containing 65–71% solids. Furthermore, crystallization of sugar is effected in vacuum pans under controlled conditions of temper- ature, pressure, density, and viscosity. The resulting sugar crystals are separated from mother liquor by centrifugation at 1,000–2,500 x g. The semidry sugar is rinsed with water and dried further with hot air in a rotating drum, cooled, classified on vibrating screens, and packaged. The mother liquor goes through a series of crystallization steps to harvest maximum yield of premium quality sugar. The left over liquor is a by-product of sugar industry, called blackstrap molasses.

Refined cane sugar is also manufactured from raw sugar produced at the point of origin. In this case, raw sugar is refined by extracting cane sugar juice, clar- ification, concentration, and crystallization. Other products from raw sugar production are white sugar, turbinado sugar, and various grades of molasses. Raw sugar is then shipped to sugar refineries where it is subjected to a series of purification steps, such as centrifugation, filtration, decolorization, evapora- tion, and crystallization. The by-products of refining

Table 11.5. Various Sugar Products Used in Formulation of Foods

Sucrose Product Sucrose Content(%) Moisture Content(%)

High-purity sucrose 99.90–99.95 0.02–0.04

Brown/soft sugars 92.00–98.00 3.5–4.0

Raw sugar 96.50–97.50 0.5–0.7

Blackstrap molasses 38.00–45.00 12–18

Raw molasses 56.00–62.00 14–18

steps are brown sugar, refinery syrups, liquid sugar, and molasses.

Beet sugar is produced in a single step. Beets are sliced, followed by diffusion of sugar in water, clari- fication, concentration, and crystallization directly to white sugar. Purity and moisture content of various sucrose products are shown in Table 11.5.

When granulated sugar (High Purity) is used for yogurt production, it is purchased in 50–100 pound bags, 1,000–2,000 lb tote bags or in bulk. In large plants, bulk sugar is stored in silos. The color of sugar is measured by procedures approved by Inter- national Commission for Uniform Methods of Sugar Analysis. The procedure involves measuring the ab- sorbance of 50% sugar solution (filtered through 0.45 micron membrane filter) at 420 nm wavelength. The absorbance is converted to International Color Units (ICU). The higher the ICU number, the darker is the sugar color. Generally, most granulated sugars fall below 35 ICU. The inorganic ash content of sugar is approximately 0.02%.

The moisture level in sugar is less than 0.04%. Part of the moisture in sugar results from the syrup trapped within the crystal during its formation, which can be removed only by grinding sugar crystals. Another type of moisture is bound water associated with sat- urated syrup enveloping the crystals. Free moisture is attributed to a supersaturated solution coating the sugar crystal during rapid drying process of sugar manufacture. Furthermore, crystallization of super- saturated solution during the storage of sugar causes the free water to be released in the surrounding air. The dried granulated sugar is conditioned by the man- ufacturer to reach equilibrium with the surrounding atmosphere.

The size of crystals is selected for quick dissolution during the mix preparation. The crystal size distribu- tion is normally defined by the percent of the crystals retained on the standard U.S. mesh screen. The higher the mesh number, the finer would be the crystal size. Regular fine and extra fine grade of sugar has fine crystals. The grain size ranges from U.S. #20/40 and

#100 mesh screens. It is preferred by yogurt proces- sors for its bulk handling properties and resistance to caking or lumping during storage.

The rating for sweetness varies according to the crystalline form and size. It is related to the stereo- chemistry of the structural units in the sugar.

Liquid Sugar

Many large yogurt plants prefer using liquid sugar because it lends itself to an efficient handling (meter- ing and pumping ability). Although liquid sugar may be economically priced, conversion from dry sugar to liquid sugar set up requires capital cost for sugar storage tanks, appropriate pumps, heaters, strainers, and meters. The storage space and the inventory con- trol of liquid sugar must be coordinated with plant production volumes. If the delivery of liquid sugar is by tank cars, storage capacity requirements are of the order of at least 1.5 cars or 12,000 gallons. If truck delivery is convenient, the volume per delivery may be in the range of 1,000 to 3,000 gallons. To cope up with emergencies like delays and increased usage, the inventory should be adjusted accordingly.

Liquid sugar is obtained by dissolving refined granulated sugar in water. Some cane sugar refining plants produce liquid sugar directly prior to crystal- lization and drying. It is delivered in tanks and stored in yogurt plant in specific tanks equipped with ultra- violet light to control growth of yeasts and molds. Adequate ventilation of the tanks is necessary to avoid moisture condensation and resulting microbial growth. Storage temperature range is 30–32◦C. This ingredient contains 66–67% solids (67◦Brix) consist- ing of minimum of 99.7% sucrose and invert sugar level<0.35%. The ash content is restricted to less than 0.04% and iron content may not exceed 0.5 ppm. The pH is within the range of 6.7–8.5. A gallon of liq- uid sugar has 7.42–7.55 pounds of solids and weighs 11.08–11.12 pounds. The viscosity of liquid sugar is around 2 poises. The color of liquid sugar is similar to that of granulated sugar (less than 35 ICU).

Conversion of mix formula from dry sugar to liquid sugar can be done as follows:

Pounds of liquid sugar required = Pounds of dry sugar required

Percentage of solids in liquid sugar . Normally, for 100 lbs of dry sugar, 149.25 lbs of liquid sugar is needed to add the same amount of sucrose in the formula.

More often, conversion of dry sugar to gallons of liquid sugar is required. To calculate gallons of liq- uid sugar to replace dry sugar, divide the pounds of dry sugar with pounds of sugar solids per gallon. To replace 100 lbs of dry sugar, gallons of liquid sugar required would be: 100/7.42 = 13.48 gallons of liq- uid sugar.

The level of sucrose in yogurt mix appears to affect the production of lactic acid and flavor by yogurt culture. A decrease in characteristic flavor compound (acetaldehyde) production has been reported at 8% or higher concentration of sucrose (Chandan, 2004), but cultures capable of growth at higher sugar levels are available.

Corn Sweeteners

Corn sweeteners are normally not used in the man- ufacture of yogurt per se, but are commonly the constituents of frozen yogurt mixes, where they are blended after fermentation. They are also sweeten- ers of choice in the preparation of fruit-for-yogurt (Chapter 9). The corn sweeteners offer savings in in- gredient costs. Nonetheless, they do exert much more inhibitory effect on fermentation rate as compared to sucrose. This is attributed to higher osmotic pressure exerted by monosaccharides contained in corn syrup sweeteners. In comparison, sucrose being a disac- charide is less inhibitory to yogurt culture growth. The corn-derived sweeteners, fructose and glucose, usually enter yogurt via the processed fruit flavor in which they are extensively used for cost efficiency and flavor enhancing characteristics. It is desirable for a yogurt manufacturer (especially if frozen yo- gurt is a part of the product profile or fruit-for-yogurt is a part of the plant operation) to be knowledgeable about basics of corn sweeteners.

Sweeteners can be made by hydrolyzing any food starch. In the United States, corn starch is an econom- ical starting material to manufacture corn sweeteners. The 1, 4 glucoside linkages holding together dextrose molecules in starch are broken down to smaller frag- ments and eventually to individual building blocks

consisting of monosaccharide glucose. The hydroly- sis is accomplished by treatment of starch slurry with hydrochloric acid, followed by enzymatic action of ␣-amylase. If the reaction is stopped at an intermedi- ate point, the end products are composed of an assort- ment of sugars and oligosaccharides (maltodextrins). The degree of hydrolysis or conversion is termed by a number “dextrose equivalent,” (D.E.) which is used to signify the percent reducing sugars calculated as dex- trose. Hydrolysis of each glucoside linkage liberates a free aldehyde group that displays the same reducing ability as dextrose (glucose). Thus, reducing ability is an indicator of the progress of starch hydrolysis. For instance, 42 D.E. corn syrup is a product made from corn starch that has reducing sugars in such pro- portions as to be equivalent to 42% dextrose. If the conversion is complete at 100% D.E., the product is dextrose.

Maltodextrins

Maltodextrins are products of very low hydrolysis of starch. Their D.E. ranges from 4 to 20. They are only slightly sweet. Hydrolysis of starch is random result- ing in the formation of smaller chain oligosaccharides to saccharide polymers of varying chain length. They are made from common corn starch, as well as from waxy starch. The maltodextrins from each of these starting materials display slightly different function- ality. In general, their pH value ranges from 4.4 to 5.0 and moisture level is 5–6%. Maltodextrin 5 D.E. from waxy starch has an actual D.E. range of 5–8, contains<0.5% dextrose, 1% maltose, and >98.5% higher polymers of dextrose. On the other hand, Mal- todextrin 5 D.E. derived from common starch has an actual D.E. range of 4–7 and contains<1% dex- trose,<1% maltose, and >98% higher polymers of dextrose. Maltodextrins of 10 D.E. have actual D.E. range of 9–13 and contain 0.5–1.0% dextrose, 2% maltose, and 96–97% higher polymers of dextrose. Finally, maltodextrins D.E.15 have an actual D.E. range of 13–18 and contain 2% dextrose, 3% maltose,

and>94% higher polymers of dextrose (Alexander,

1997). It is good to remember that lower the D.E., the higher the molecular weight of the product and lower the intensity of sweetness. To enhance dispersability, maltodextrins are agglomerated. Agglomeration of corn-derived 10 D.E. maltodextrins reduces the bulk density from 0.54 to 0.34 g/cc. In dry mixes, they promote flowablity and reduce dust during handling. They are also good bulking agents in the formulation of low/non fat frozen yogurt.

Table 11.6. Properties of Liquid and Dry Corn Sugars

Relative Sweetness: Type Actual DE % Moisture % Dextrose % Maltose DP3a _{Higher DP}b _{Sucrose= 1}

Corn syrup 36 D.E. 35–37 20 13–14 11–12 10 64–66 0.40

Corn syrup 42 D.E. 41–43 18–20 19 13–14 12 55 0.50

Corn syrup solids 36 D.E.

34–38 4–5 13–14 11–12 10 64–66 0.40

Corn syrup solids 42 D.E.

40–44 4–5 19 12–14 11–12 55–58 0.50

Dextrose 100 0.5 99.5 0 0 0 0.8

Adapted from Alexander, 1997.

a_{Degree of polymerization, 3 dextrose units.} b_{Degree of polymerization.}

Corn syrups are defined as the products in which 20–70% of the glucoside linkages have been hydrolyzed. Three types of corn sweeteners are com- mon in the frozen yogurt industry. They are classified as low conversion (28–38 D.E.), regular conversion (38–48 D.E.), intermediate conversion (48–58 D.E.) and high conversion (58–68 D.E.). High-conversion syrups may be obtained by a combination of acid and enzyme action on starch. High maltose syrup is made from a combination of acid and␤-amylase hy- drolysis. The disaccharide maltose consists of two molecules of glucose. Dry corn syrups are obtained by spray drying partially hydrolyzed corn starch of various D.E. Crystalline dry forms of refined dextrose and fructose are available. Generally, frozen yogurt producers use 36 or 42 D.E. corn syrup in liquid form or as dry corn syrup solids. Since the liquid form is very viscous, to facilitate their pumping and meter- ing, this ingredient is stored in heated tanks at 32◦C. Corn syrup solids are economical to use. They contribute firmness and extend the shelf life of the frozen dessert. The sweetness and other proper- ties of corn sweeteners are shown in Tables 11.6. The high-polymer content contributes adhesive and cohesive properties to mix (Marshall and Arbuckle,

1996). The corn syrup solids ingredient is a white powder and is susceptible to caking when exposed to moist air. Since too much corn syrup in the mix may impart a flavor defect, its use in frozen dessert is limited to one-third of the total sweetener level. Crystalline dextrose is a white powder with 80% of the sweetening power of sucrose. Dextrose, being a monosaccharide of molecular weight nearly one-half of sucrose, depresses the freezing point of the mix twice as much as sucrose. Frozen yogurt from a mix containing corn syrup displays less stiff consistency as it extrudes from the ice cream freezer. Accord- ingly, its usage level is adjusted not to exceed 25% of the total sweetener level.

High fructose corn syrups (HFCS) and crystalline fructose equal or exceed the sweetness of sucrose (Table 11.7). HFCS production involves dextrose conversion to fructose in corn syrup by enzymatic means. They also lower the freezing point of frozen dessert mixes to the same extent as the original corn