Impact of physico-chemical properties of mix on the final quality of ice-cream

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1 Asian J. Dairy & Food Res, 35 (4) 2016 : Print ISSN: / Online ISSN: AGRICULTURAL RESEARCH COMMUNICATION CENTRE Impact of physico-chemical properties of mix on the final quality of ice-cream D.N. Bajad*, S.D. Kalyankar, M.A. Dehmukh, P.R. Bachanti and G.S. Bajad** *MAFSU, Nagpur Camp: College of Dairy Technology, Udgir , India. Received: Accepted: DOI: /ajdfr.v35i ABSTRACT The impact of physico-chemical properties of mix is carried forward in handling of mix, processing including freezing and quality of finished product. With precaution in selection and balancing ingredient viz. Fat, Protein, sugar along with emulsifier, stabilizer and various flavouring components may provide the better quality of the final product. The proper proportion of different ingredients, improved processing can provide better quality and lower cost of Ice-cream with appreciable and acceptable quality. Key words: Physico- chemical properties, Ice-cream mix, Quality. The ice cream s ingredients serve specific functions in supplying the optimum characteristics of the final product. Although many factors, including the flavour, body and texture, melting quality, colour, package, appearance, and influence quality as well as the overall acceptability of the product by consumers, however on textural characteristics of the ice cream which are important and influence by compositional factors. If two different samples of the same ice cream are handled in different way to produce a coarser (icy) texture than another with the same formulations, the sample with the better texture will be considered to a better flavour. In consuming ice cream, one becomes intimately interwoven with flavour sensations, and the ice cream texture, in this case icy or coarse can either complement or detract from the apparent flavour ( dfoods11_new.htm), quality factors in Ice cream (2014). As Per FSSAI regulation 2011, Ice Cream is a product obtained by freezing a pasteurized mix prepared from milk and/or other products derived from milk with or without the addition of nutritive sweetening agents, fruit and fruit products, eggs and egg products, coffee, cocoa, chocolate, condiments, spices, ginger and nuts and it may also contain bakery products such as cake or cookies as a separate layer and or coating. The said product may be frozen hard or frozen to soft consistency the said product shall have pleasant taste and smell, free from off flavour and rancidity. The type of ice-cream shall be clearly indicated on the label otherwise standard for ice-cream shall apply. The prior to FSSAI standard composition of ice cream which is vary from brand to brand with more or less quantum for finish product milk Fat 11-12% MSNF 10-11% Sugar 13-15% Flavouring/Aroma, Preservative % (Total solids 37-39% Moisture % in general, (Sidhu,1998). However, *Corresponding author s dnbajad32@gmail.com. ** Milk Fed Panjab as per recent regulatory document of FSSAI 2011, ice cream can be classified as shown in Table 1. The ice-cream is made up from heterogeneous ingredients which will reflect on the sensory characteristics as well as interaction among the various ingredients/ constituents which ultimately affected or effected by physicochemical properties of ice cream. Moreover the ice cream is complex products which is made up in different pattern in various localities of various countries and accordingly there is impact of preparation method on physico-chemical properties of ice cream mix and reflect on final quality of the product. In the case of ice cream, ice cream stability, acidity and ph, density, viscosity, surface tension, interfacial tension and adsorption will have impact on the final quality of the Ice-cream. ( /dfoods11_new.htm), Mix stability: Compositional control is essential in obtaining and maintaining the quality. The ice cream s ingredients serve specific functions in supplying the characteristic/ properties of the final product. Several ingredients may influence some properties, so that similar results can be obtained by altering the quantities of any or all of them. Other properties of ice cream depends primarily one on other ingredients. The production of ice cream involves mixing the ingredients together, followed by pasteurisation; which reduces the number of non-pathogenic bacteria. After pasteurisation, homogenisation takes place, a process to allow the distribution of fat into as many separate small fat globules as possible. After homogenisation there is a cooling and ageing process. The major ingredients which decides the stability of mix is protein, fat and milk solid not fat during the processing along with impact of minor ingredients including emulsifier, stabilizer and various flavouring component, colour and preservatives.

2 294 ASIAN JOURNAL OF DAIRY AND FOOD RESEARCH Table 1: Classification of ice cream (FSSR, 2011) Requirement Ice Cream* Medium Fat Ice Cream Low Fat Ice Cream Total Solid Not less than 36.0% Not less than 30.0 % Not less than 26.0 % Wt/Vol (gms/l) Not less than 525 Not less than 475 Not less than 475 Milk Fat Not less than 10.0 % More than 2.5% but Less than 10.0 % Not more than 2.5 % Milk Protein Not less than 3.5 % Not less than 3.5 % Not less than 3.0 % Only the Ice Cream* portion shall conform to the requirements given above. The type of ice-cream shall be clearly indicated on the label otherwise standard for ice-cream shall apply Ice-cream composition. ( It is apparent from this that each ice cream ingredient has specific functions that it alone can perform most effectively. However, there is a definite overlapping of some of the functions. For example, all ingredients influence body and texture, so that a variety of variations can still produce an acceptable product. One must be careful when altering ingredients to assure that the sensory qualities are not impaired. An understanding of the protein-emulsifier interactions at the fat interface is critical to promote the optimal level of partial coalescence during freezing. Excessive protein or insufficient emulsifier can render the emulsion too stable, resulting in reduced rates of partial coalescence. Ice cream consists of a variety of ingredients categories that include air, water, fat, milk-solid-non -fat (MSNF), sugars/sweeteners, stabilizers, emulsifiers, and flavouring/colouring agents. Each category plays an important role on the structure of ice cream Fig 1, which is divided into four main parts: air bubbles, fat droplets, ice crystals, and the matrix. The relationship between each ingredient category and the structural component it affects can be seen below in Figure 2 Fat Stability: Fat plays an important part in the ice cream structure formation. It s responsible for the air stabilization, flavour release, texture and melting properties (Fernando Su, Suzana Lannes ) Milk fat accounts for most of the rich-sensations of ice cream, and only a limited amount of substitution with other ingredients can be made without changing the product s characteristics. Fat provides flavour, body and texture. The type and content of fat in ice cream is used to classify individual products according to certain regulations. Dairy ice cream, must contain a minimum of 10% milk fat and should contain no other fat than milk fat. However Ice cream must contain a minimum of 10% fat except low fat ice cream; however it can contain vegetable fat. The types of vegetable fat most widely used are coconut oil, palm oil and palm kernel oil or a combination. Milk fat contributes mellowness and flavour as no other constituent can. Fat globules in homogenized milk are responsible for stability of mix fat globules in homogenised mix vary from µm with most of globules below 2 µm. It is well know that aeration and freezing of the mix induces certain amounts of fat destabilisation,. Fat destabilisation refers to the process of clustering and clumping (known as partial coalescence) of the fat in an ice cream mix when it is churned in a machine. However, too much churning of the milk fat is associated with weak whipping fat & ice separation in freezer, unsatisfactory extrusion, a buttery texture and does not milk defect in the ice cream stability of milk fat is influenced by factors such as amount type and source of milk fat, amount and quality of MSNF, amount and type of emulsifier, favouring agent and homogenization. Decrease in the drawing temperature and increase in overrun enhances the fat destabilization, protein stability and salt balance of the mix are the other factors influencing the fat stability of Fig 1: Structure of ice cream (Google image ) Fig 2: Relationship of different constituents in ice cream (Athena Casarotto et al, 2015)

3 the mix. Extent of fat destabilization and ice crystal size had the largest effect on melting rate, with the consistency coefficient of the ice cream mix having a lesser effect. Numerous factors (ice crystal content, ice crystal size, and extent of fat destabilization, overrun, and the rheological properties of the mix) were found to influence hardness of ice cream Protein stability: It is the protein that acts to emulsify the ice cream mix by preventing the water and fat from separating, Emulsifiers are used in ice cream because they contribute greatly to smooth and creamy texture by promoting fat destabilisation. Milk proteins contribute three important functional roles to ice cream that can be divided into three categories: emulsification, aeration, and solution behaviour. Milk proteins are present in ice cream as part of the MSNF, which has traditionally been supplied by milk, condensed milk, and/or skimmed milk powder. Milk proteins are divided into caseins and whey proteins, with caseins comprising about 80% of the total protein of milk and the remaining 20% comprising of whey protein. Whey proteins are comprised primarily of -lactalbumin and -lactalbumin ( Protein-in-ice-cream) It is the proteins that stabilise the fat emulsion in an ice cream mix, emulsifiers are actually added to ice cream to reduce the stability of this emulsion and encourage some of the fat globules to come together, or partially coalesce. ( The proteins contribute to the structure of the ice cream and to the incorporation of air during processing. Ice cream must contain a minimum of 2.5% milk protein. Instability of milk proteins in the mix lead to the curdling of mix during freezing causing separation of thin watery serum and churning of milk fat, Proteins stability in the mix is dependent on net negative charge which they carry and their extent of hydration. Higher acidity in the mix results in proteins destabilization. Parameter which influences the charge and hydration of proteins in the mix are salt balance, homogenization, previous heat treatment of the MSNF and extent of freezing and ageing of the mix. ( Density of mix: The density or specific gravity (density relative to water) of ice cream mix varies with composition. Increased levels of MSNF, sugars, and stabilizers increase density, whereas increased fat decreases mix density (fat has a density of about 0.9 g/ml compared to 1.0 g/ml for pure water). Measurements of specific gravity are made with a hydrometer, while measurements of density are made by weighing a known volume of mix at a known temperature on a gravimetric balance. The density of ice cream mixes may vary from to gm/ml. The amount of air also has a huge effect on the density of ice cream. A gallon (3.8liter) of ice cream must weigh at least 4.5 pounds, making Volume 35 Issue 4 (2016) 295 the minimum density 0.54 gram per millilitre. This is due to the high fat content of ice cream, however, fat is less dense than water, any ice cream will always be less dense than any aqueous solution. The viscosity of the liquid is playing major role and cannot be neglected at any stage of processing. If the liquid is too viscous, it is difficult to puff and therefore to integrate the air; if it is not viscous enough, the film between the airs bubbles rapidly drain and the bubbles band together Emulsifiers have become more uniform, more versatile, and almost essential to modern ice cream manufacturing. They are especially useful in producing a stiff, dry product for specialty items, but they also have their place in regular manufacturing and packaging operations. The ice cream is smoother, creamier, and more melt-resistant when emulsifiers are used. However, excessive use causes an unnatural slickness, a partially churned appearance, and product that do not melt. In some cases the flavour is adversely affected, too. The effect of the stabilizer on viscosity in relation to temperature and age has very practical significance. If the viscosity is increased immediately and greatly, the mix will be difficult to cool. On the other hand, if the stabilizer imbibes water slowly and takes time to establish a gel structure, an aging period is necessary, and viscosity will vary with age. Constant physical characteristics are important when mix is necessary to freeze the mix immediately after processing. Viscosity of mix is related to resistance to melt and good body and texture. Addition of membrane concentred milk solids caused an increase in the viscosity. Replacement of MSNF with plant protein isolates also lead to an increase in viscosity. The higher degree of polymerization present in the sugar, the more viscous the mix is, Common sugars found in ice cream include sucrose, dextrose, fructose, lactose, corn syrup and sugar alcohol(athena Casarotto et al, 2015) Viscosities of ice cream mixes are affected by temperature; the concentration, type and degree of hydration of the stabilizer, carbohydrates, colloidal salts and proteins of the mix; type of heat treatment; whether the mix is homogenized prior to holding; and the rate of shear in the holding tube. When shear rates varies from 50 to 180 s-1, the viscosities at 80 C ranges from 8.7centipoise (cp) in an unsterilized mix to 103 cp in mix containing 0.25% Carboxy Methyl Cellulose; the mixes had 14% fat and 41% total solids. Gums of various kinds are useful as stabilizers in ice cream because of their characteristic property of imbibing or absorbing large amounts of water. This characteristic is effective in limiting the natural tendency of ice cream to become coarse in texture during storage. Numerous types of animal and vegetable products have been found effective

4 296 ASIAN JOURNAL OF DAIRY AND FOOD RESEARCH in ice cream and as a result a considerable range of stabilizers is available on the market. The primary purpose of stabilizers is to maintain the smooth texture by inhibiting the formation and growth of ice crystals, but other considerations are also important. Their effect on flavour, colour, viscosity, whipping ability and meltdown should also be considered.( drinc.ucdavis.edu/dfoods11_new.htm ) Finally Viscosity, or the resistance of a liquid to flow, is the internal friction that tends to resist the sliding of one element of fluid over another. It is defined as the shear stress (the imposed force per area) divided by the rate of shear (the velocity gradient resulting in the liquid as a result of the applied shear stress). If the shear stress-shear rate relationship is linear (viscosity is constant regardless of applied stress), the liquid is said to be Newtonian. Examples of Newtonian fluids include water and sugar syrups (e.g., corn syrup). Ice cream mix, however, is not a Newtonian fluid. It is pseudo-plastic, where the viscosity decreases as shear rate increases. Thus, to characterize the viscous behaviour of an ice cream mix, knowledge of the shear rate dependence is necessary. Apparent viscosity is defined as the ratio of shear stress to shear rate at a specified shear rate and is often used to describe the viscosity of a pseudo-plastic material, such as ice cream mix. For a pseudo-plastic (shear-thinning) fluid like ice cream mix, apparent viscosity decreases as shear rate increases. This is important in mix handling since pump size is strongly influenced by fluid viscosity. Ice cream mix also exhibits thixotropy, which means that the apparent viscosity decreases with time applied with a constant shear stress. Thixotropy is common in colloidal-type liquids such as an ice cream mix and is due to rupture of interactions and associations (weak bonding) among the different components of mix. ( Athena Casarotto et al, 2015) Surface tension of ice-cream mix: Surface Tension of icecream mix has been considered as an important attribute with the belief that lowers surface tension is conducive for better whipping of the mix. However, no correlation has been observed between the surface tension and whipping ability. Also, the ageing and homogenization which increase the surface tension of mix help to improve whipping properties.(sidhu J. S. 1998) Ice cream is an oil-in-water emulsion in which an oil phase, usually consisting of milk fat, is dispersed into a continuous aqueous phase. Emulsions are thermodynamically unstable, meaning that the oil and water will separate due to high interfacial tension between oil and water surfaces. Immediately following homogenisation, where the fat phase is broken down into numerous small droplets, proteins quickly adsorb to the surface of the small fat droplets, forming a membrane around them. This membrane reduces the interfacial tension between the oil and water surfaces, stabilising the fat droplets and preventing them from coming together ( cream Science.com) The lower force of attraction between serum and oil phase causes the interfacial tension which in turn lead to adsorption of surface active substances. This adsorption causes the lowering of interfacial tension. Interfacial tension destabilized the emulsion of butterfat in the mix fat Adsorption on the interface is influenced by the temperature and lowering of the temperature caused an increase in adsorption. The beneficial effect of ageing the mix on the stability of the milk fat and whipping ability of mix may be explained on the basis of enhanced adsorption of natural and commercial emulsifiers. The use of anhydrous milk fat emulsion on which the proteins are absorbed on the fat globule surface has been removed. Acidity and ph of the mix: The normal acidity of the mix varies with percentage of MSNF. Acidity of mix is generally normal when fresh milk component and various ingredients of excellent quality are used in the preparation of mix. A higher acidity or lower ph is undesirable as it contributes to the excess viscosity, decreased whipping ability, inferior flavour and less stable mix leading to it coagulation during processing. As the normal titratable acidity of mixes varies with the percentage of MSNF and it may be calculated by multiplying the percentage of MSNF by the factor Thus, a mix containing 11% MSNF would have a normal titratable acidity of 0.187% lactic acid. The normal ph of ice cream mix is about 6.3. The acidity and ph are related to the composition of the mix, an increase in MSNF raises acidity and lowers ph. The apparent or natural acidity of ice cream mix is caused by milk proteins, mineral salts (mostly citrates and phosphates) and dissolved carbon dioxide. Developed acidity is caused by the production of lactic acid by bacterial fermentation of the lactose in dairy products. When the acidity of the mix or ice cream is above normal, developed acidity is probably present in the dairy products used in the mix. The latter may contribute to cook on during processing and pasteurization, because heat and acidity accelerates the denaturation of proteins. Freezing point of mix: Before focusing the freezing point study, it is essential to have to study of some thumb rules. When a solute is added to water the physical properties of freezing point and boiling point is bound to change. Water normally freezes at 0 o C and boils at 100 o C. As more solute is added, the freezing point drops ( freezing point depression ). The freezing point depression T f is a colligative property of the solution and for dilute solution is found to be proportional to the molar concentration cm of the solution: T f = K f cm

5 Where, K f is called the freezing-point-depression constant. A usual mix of ice cream containing 10% milk fat, 11% MSNF, 15% sugar, 0.3% stabilizer and 61.7% water has a freezing point of approximately 2.5 C. The freezing point of mixes with higher sugar and MSNF contents may range downward to 3 C while for mixes with high fat, low MSNF or low sugar content it may range upward to 1.4 C. Generally, the differences in type and quantity of sweetener solids and lactose concentration used in the mixes are primarily responsible for the differences in freezing points of mixes (Ecourse NAIP) The initial freezing point of ice cream mix is highly dependent on the sweetener content of the mix. When latent heat is removed from water and ice crystals are formed, a new freezing point is established for the left over solution since it has become more concentrated in respect to the soluble constituents. Whipping ability of mix: Whipping ability of the mix refers to those properties which determine the rate of air incorporation and maximum overrun that can be achieved. The overall rheological behaviour is also determine by the air cells and fineness their uniform distribution and also reflect whipping ability of the mix. Whipping ability is related with quality and cost of the finished product. Higher whipping ability of the mix enables the finished ice-cream to be frozen to proper stiffness, consistence without compromise to the overrun in the form of smaller air cells. Both of these factors are conducive to a smooth texture and Volume 35 Issue 4 (2016) 297 lower cost. Several factors are responsible to decide whipping ability of mix like ingredients, source and amount of fat, MSNF and specifically salt balance. As use of eggs, sodium caseinate, whey protein concentrate/replacement of milk fat with palm or palm kernel oil and sodium salt of phosphate or citrate, stabilizer and emulsifier sodium salt of fruit, nuts and chocolate have adverse effect. Whipping ability also influenced by method processed and freezing, type of freezer and refrigeration Ageing and homogenization are beneficial combining freezing and whipping machine and the replacement of a part (8-12%) MSNF with WPC lead to better wiping ability. Whipping ability is also influenced by the type of emulsifier. Glycerol monocaprate, glycerolmonolaurate and polyxyethyline sorbitan monooleate (Tween 80) depresses, glycerol monooleate diglycerides and spares have no effect while monoglycerides of mystric, palmatic and stearic acids (Tween 40, 60 and 65) cause better whipping ability of mix (Sidhu 1998) CONCLUSION The optimum Physico-chemical properties of ice cream mix can improve by selecting fresh milk component and other ingredients which imparts the rheological behaviour of Ice cream. Prior selection of specific quality, quantity and balancing of ingredients with optimum concentration of various constituents can improve the quality of mix which can reflect final quality of ice cream REFERENCES Athena Casarotto et.al. (2015) Effects of composition and flavour on viscoelastic properties of ice cream en.wikipedia.org/wiki/worcester_ Polytechnic_Institute E-Course NAIP (2012) Ice-Cream and Frozen Desserts Physico-chemical properties of ice cream mixes and ice cream ecourses.ndri.res.in/moodle/ mod/resource/vie 17. Fernando Su, Suzana Lannes. (2012). Rheological evaluation of the structure of ice Cream mixes varying fat base, 22:6 / usp.br/handle/bdpi/ Ice-cream composition. (2011). pp 296 Sidhu J. S. (1998), Physico-chemical properties of ice-cream mix, Compendium,CAS, NDRI, Karnal pp Sidhu J. S. (1998), Composition and properties of ice-cream, Compendium, CAS, NDRI, Karnal pp Quality factors in Ice cream(2014) : cream Science.com