properties of ice cream and effect of processing
- 1. Presented by Dharani . M MTM19002 Department of Dairy Chemistry College of food and dairy technology Chennai- 52. Properties of ice cream mix
- 2. 2. Density 4. Mix Viscosity 1. Mix stability 3. Acidity of Mixes 5. Interfacial characteristics
- 3. Mix stability refers to the resistance to separation of the milk proteins in colloidal suspension and the milk fat in emulsion. Instability results in separation of (1) fat globules due to creaming, (2) protein particles as coagulated or precipitated material, or (3) a clear serum or whey from mix or melted ice cream.
- 4. No creaming due to homogenization due to small size of fat globules. increased density due to the newly adsorbed surface layer high viscosity in the mix due to the addition of proteins and stabilizers The emulsion of the mix can be too stable - leading to reduced rates of partial coalescence during freezing. This stability is also important for the whipping and freezing process to fat. Whey separation from mix or from melted ice cream is another example of mix stability problems. Due to phase separation between milk proteins and polysaccharide stabilizers. milk proteins and polysaccharide stabilizers , both are hydrophilic. tend to move apart from each other, leading to formation of a clear serum layer in the mix after standing Carrageenan is normally added to stabilizer blends to reduce phase separation
- 5. Increased by added MSNF, sugars, and stabilizers increased fat decreases mix density vary from 1.0544 to 1.1232 g/mL average for a 10% fat mix of approximately 1.1 g/mL (kg/L). hydrometer and of density by weighing a known and very exact volume of mix at a known temperature on a gravimetric balance.
- 6. varies with the percentage of MSNF calculated by multiplying the MSNF% by the factor 0.017. The normal pH of ice cream mix is about 6.3. an increase in MSNF raises acidity and lowers the pH. A high acidity is undesirable - to excess mix viscosity, decreased whipping rate, inferior flavor, and a less stable mix. may contribute to “cook on” during processing and pasteurization, because heat and acidity accelerate the denaturation of proteins.
- 7. Ice cream mix is pseudoplastic, where the viscosity decreases as shear rate increases. essential for proper whipping and retention of air, and for good body and texture . Composition—viscosity increases with increasing concentration of stabilizer, protein, corn syrup solids, fat and total solids, with the contribution of each decreasing in that order (i.e., stabilizer has more influence on mix viscosity than does fat). Also, heat and salts (such as calcium, sodium, citrates, phosphates) can affect the viscosity due to their effect on casein and whey proteins. Processing and handling of the mix—elevated pasteurization temperatures, increasing homogenization pressures, and aging for up to about 4 h will each increase mix viscosity. Temperature— viscosity is temperature dependent, so lowering ageing temperature will result in increased mix viscosity.
- 8. fast freezing (rapid whipping) in modern equipment a lower viscosity seems desirable. viscosity increases, the resistance to melting and the smoothness of texture increases, but the rate of whipping decreases. varies greatly, especially due to stabilizer addition, values between 0.1 and 0.8 Pa.s are normally found at 4°C, after aging. viscosity values in low fat mixes 0.02 to 0.15 Pa.s at 100 s −1 and 4°C
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- 10. Interfacial characteristics between fat globule surfaces, air bubble surfaces, and serum are critical for converting ice cream mix into ice cream. Determined by the type and quantity of material adsorbed at the air interface. Addition of emulsifiers in ice cream mix lowers the interfacial tension. Sample – without emulsifier - 6.2 mN/m addition of monoglycerides - 5.0 or 5.5 mN/m polysorbate 80 - 2.2 mN/m This decrease is because emulsifier displace proteins adsorbed to fat globules. Mixes with lower surface tension values tend to produce higher overrun and smaller air bubbles. Mixes with too low surface tension values caused by the addition of emulsifie r have shown excessive rates of whipping, fluffy and short body characteristics, and high susceptibility to shrinkage. Small fat globules enhance whipping. Nonfat mixes whip more rapidly than those containing fat, but when frozen, they possess a foam structure that is susceptible to shrinkage. Emulsifiers also improve whipping ability.
- 11. Freezing point Dependent on the concentration of the soluble constituents and varies with the composition. Initial freezing point - highly dependent on the sweetener content and MSNF of the mix, specifically the lactose and mineral salts content. Higher concentrations of lactose and salts, especially those derived from or making high use of whey powder, the effect on freezing point can be extreme . The freezing point of mixes with high sugar and lactose content may range downward to −3°C (26.5 °F) while for mixes with high fat, low lactose, or low sugar content it may range upward to −1.4°C (29.5 °F).
- 13. A well balanced mix should always ensure:- A correct fat to sugar ratio – to prevent fatty mouth feel in high fat ice cream. For instances 16% fat ice cream should ideally have 17% sugar as against 15% sugar for economy (10% fat) ice cream. A correct total solids to water ratio – if too high, sandiness and rough texture and if too low, glassy or icy texture with weak body. Usually total solids of 36.0 to 40.0% will result in acceptable ice cream. Inverse relation between fat and SNF in ice cream mix for e.g. super premium ice cream (high fat) will have lower SNF than good average (moderate fat) ice cream. To calculate the mixes: Pearson square method, Serum point method, Formula tables / graphics method, Algebraic method and Computer developed formulations. To standardize the mix (a) Algebraic method, (b) Serum Point method. 1. Standardization/Formulation
- 14. Liquefying dry ingredients well ahead of time for their use permits foam to dissipate and colloidal substances to hydrate fully. Proper suspension to avoid lumpiness of the dry ingredients can be obtained by (1) mixing the dry ingredients with part of the crystalline sugar before adding it slowly to the liquid, or (2) sifting it slowly into the liquid. The liquid should be cool (<30°C, <86 °F) when milk solids-not-fat (MSNF), cocoa, or similar ingredients are added. addition of stabilizer/ emulsifier blends are capable of dissolving at relatively low temperatures, whereas others should not be added to a mix until the temperature reaches about 65°C (149 °F). Added frozen products, e.g., butter or frozen cream - small pieces - sufficient melting time before pasteurization starts. coloring and flavoring materials are added after pasteurization at the time the mix is frozen. 2. Blending
- 15. Destroys all pathogenic microorganisms, thereby safeguarding the health of consumers. Necessary to heat mix to dissolve or hydrate dry ingredients . Reasons for higher heat treatment include the following: (1) it reduces the amount of stabilizer needed by up to 25%, (2) it improves body and texture because of the denaturation of proteins and the consequent increase in their water-holding capacity, and (3) it increases resistance to oxidation because it exposes additional reducing groups as heat causes proteins to unfold. Excessive heat - change the conformation of the whey proteins (denaturation), leading to their adsorption to the casein micelle and their precipitation. breaks disulfide bonds (-S-S-) in whey proteins, exposing sulfhydryl (-SH) groups - the cooked flavor. 3. Pasteurization
- 16. Make a stable and uniform suspension of the fat by reducing the size of fat globules to less than about 2 micrometer. Homogenized fat destabilizes very slowly in the freezer so that emulsifiers are usually required to provide the amount of controlled fat destabilization that results in a frozen product that is dry in appearance and slow to melt. Natural fat globules are coated with phospholipids to which are adsorbed other lipids and proteins. The amount of phospholipid available to be adsorbed will reduce, and added emulsifiers are adsorbed to the fat. Fat globules is reduced to one-half the original diameter, the number of globules increases by eight times and the total surface area is doubled, amount of materials adsorbed increases . Since proteins are adsorbed on the outer surfaces of the newly formed membranes, the amount of hydrated surface area is greatly increased by the treatment. This may account for the increased smoothness of texture associated with homogenization of mixes. Inadequate homogenization can lead to fat churning in the freezer. Chocolate mixes – low pressures - 500 psi g (3.45 mPa) lower than plain mixes - cocoa solids increases the viscosity. Fat globules readily adsorb protein during homogenization to create a fat globule membrane and enhance stability. 4. Homogenization
- 17. Major changes – fat crystallization hydration of molecules rearrangement of molecules at the fat globule interface. Fat crystallization - depends on the type of fat and emulsifier used , requires up to 4 h for complete crystallization Hydration of proteins - hydrocolloid stabilizers require time for full hydration to provide significant increases in viscosity. Sodium carboxymethyl cellulose and guar gum, commonly used stabilizers, hydrate well. Freezing of improperly aged (“green”) mixes leads to less retention of shape and relatively fast meltdown due to less than optimal destabilization of fat during freezing. 5. Aging
- 18. Flavours are added by experience to obtain pleasing flavour and colours should correspond to the flavour. Fresh or canned fruits should be used as pulp or cut into pieces and added to partially frozen ice cream or as top dressing Nuts after cut into pieces, roasted / unroasted, should be added to partially frozen ice cream while it is in the freezer. Chocolate flavorings are usually added to mixes prior to processing. In the case of batch freezer operations, the most common practice is to flavor plain mix after it is placed in the freezer, just prior to freezing. For solid ingredients, time of addition in the batch freezer depends on the amount of breakup of the materials that will produce the optimal size and distribution of the flavoring material. 6. Flavoring
- 19. 7. Freezing 1. first phase of freezing process - 33 to 67 %of the water 2. Initially temperature drops very rapidly –sensible heat removed 3. Formation of ice crystals 4. agitation reduces the viscosity 5. partially destroying the gel structure 6. breaking up the fat-globule clusters 7. incorporation of air into the mix To freeze a portion of the water in the mix and to incorporate air into the mix. 1. second phase (hardening process) - 23-57 % of water 2. Ice crstallization of water continues 3. Other solutes concentrates 4. slightly depressesion the freezing point 5. Further formation of ice crystals 6. Further solute concentration , until that further freezing will not occur 7. even after long periods in the hardening room, all water does not freeze