Energy Value and Nutrients of Ice-Cream.
Energy value can be expressed as the property whereby a food produces both energy and heat within the body. The energy value of ice-cream varies greatly, depending on the food value of ingredients from which it is made. The dairy products which are used to make ice-cream contain the components of milk, but in different amounts. Ice-cream consists of about three – four times more fat, and roughly 13-16% more protein than regular bovine milk does. Ice-cream can contain additional food products such as nuts, fruits and sugars which lead to an enhancement of its nutritive value. In an extension to this, ice-cream contains four times as much carbohydrate as milk does. The milk solids in ice-cream are often subjected to heat treatments which are higher than those of regular pasteurised milk, while also exposed to much lower temperatures in the freezing process. Similar to milk, ice-cream is a poor source of iron and trace minerals. Although it is an excellent source of energy, 50% of ice-creams solid content is sugar, including sucrose, lactose and corn syrup solids.
The amount of energy expected to be derived from milk, per gram of Carbohydrates, is 3.9 Kcal/g, Protein 4.3 Kcal and Fat 8.8 KCal/g (Douglas Goff and Hartel, 2013). These values are the amount of energy which is released from the nutrients as calories or heat units. Carbohydrates and proteins are of equal energy per gram, while fats are about 2.23 times richer in energy (Wendell S. Arbuckle 1986). The total calorific value of ice-cream is dependent on three key factors, first being the amount of carbohydrates, which includes added sweeteners, sugars and lactose that may exist in flavourings and fruits. Second being the percentage of protein, including milk protein and any other protein in nuts, stabilisers and eggs and thirdly, the amount of fat from any source, including eggs, cocoa, emulsifiers, and nuts.
Protein Content in Ice-Cream
Proteins are crucial in animals, as the components of the protoplasm in each living cell.The milk proteins in ice-cream are of great biological value, seeing as they contain all the essential amino acids. Proteins in milk are a very important sources of both tryptophan and lysine, as well as being known as complete, the assimilation of ingested proteins is roughly 5-6% more complete than for other proteins in general. (Douglas Goff and Hartel, 2013). The amount of protein ranges from 2.0-3.5g, on Nutrition Facts labels for a single serving of vanilla ice-cream. Ice-cream has a high concentration of Milk Solid Non-Fat (MSNF) which includes caseins and whey proteins, which are approximately 35% of milk protein. The amount of protein present is normally inversely related to the fat content. Whey solids can be added to replace up to 25% of the MSNF of a mix, the protein level will decrease. There is about 12% protein in dry whey in comparison to 35% in MSNF, as already mentioned above. (Douglas Goff and Hartel, 2013).The values of protein are calculated from the determinations of the nitrogen content in food. The average nitrogen (N) content of proteins is approximately 16%. The nitrogen content is multiplied by the conversion factor of 6.25, in order to find the protein content. The acceptable value for bovine milk protein is 6.38 (Dupont, 2003)
Fat Content in Ice-Cream:
Fat is most commonly referred to as the components of food that are insoluble in water and soluble in either ethyl ether or other solvents used to extract them. Milk from bovines contains an average of »3.8% fat (Mr. Mick O’Sullivan, Class Notes 2018). Milkfat mainly consists of triglycerides of fatty acids. Glycerides are compounds in which either one, two or three fatty-acid molecules are combined by ester linkages with the trihydric alcohol (Arnis Kuksis, 1978) . Milkfat is known to contain almost 400 individual fatty acids; however, it is about 15 or 20 fatty acids which make up around 90% of milk fat. The main fatty acids in milk fat are saturated with a straight chain and have 4 to 18 carbons. From the nutritional point of view, milkfat is interesting primarily for energy, fat-soluble vitamins, essential fatty acids and the proportion of saturated and unsaturated fatty acids. It contains about 65% saturated, 30% monounsaturated and 5% polyunsaturated fatty acids (Wendell S. Arbuckle 1986) Not all fatty acids however are equal. Saturated fatty acids are linked with heart disease and high blood cholesterol, whereas unsaturated fatty acids are not seen as a factor in heart disease.
Unlike other trans fatty acids, Conjugated Linoleic Acid (CLA) is fatty acid in milk-fat which is beneficial to human health. CLA is an 18-carbon fatty acid with two double bonds which are conjugated. CLA is known to have beneficial anticarcinogenic properties. (Kelsey, Corl, Collier et al 2003).
The milk-fat content in ice-cream is normally found by extracting and weighing the ether-soluble fraction. The fat in milk also contains non-saponifiable fractions, tocopherols, lecithin and cholesterol. From a health and nutritional point of view, it is desirable to use less saturated fat, seeing as high levels of saturates can lead to higher levels of cardiovascular diseases. The contribution of saturated fat from ice-cream should be small, if ice-cream is eaten in moderation.
Carbohydrates in Ice-Cream.
Carbohydrates include dextrin, cellulose, sugars, starch, pectin and gums. Carbohydrates main role is its source of heat and energy in the body. They are broken down in the body into simple sugars under the action of specific enzymes, which are secreted into the digestive tract, with the principal end product being glucose. Many types of sugars can be used in the manufacturing of ice-cream; however, the most commonly used sugar is a disaccharide, sucrose. Sucrose can come from either beet or cane, seeing as they are both identical in composition. Corn sugar, now extensively used is primarily glucose. In majority of fruits the sugars are sucrose, fructose and glucose.
The milk sugar lactose, is a disaccharide that contributes the over 33% of the solid matter in milk and about 20% of the carbohydrate in ice-cream. (Wendell S. Arbuckle 1986). Lactose is unique seeing as it is only found in milk, compared to other sugars which are widely distributed in nature. Moderate quantities of lactose in the diet result in a favourable medium in the intestinal tract, for the growth of Lactobacillus acidophilus, an organism which aids the fermentation of carbohydrates. Lactose also favours phosphorus utilisation and calcium assimilation. Adults, particularly those of African and Asian descent, may produce an insufficient amount of ?-D-galactoside, a lactase enzyme which hydrolyses lactose. Lactose can only be absorbed through the intestinal wall if it has been split from the disaccharide form into the monosaccharide from. This may result in bloating and diarrhoea if too much lactose from ice-cream is consumed by these people. When lactose moves into the large intestine, it raises the osmotic pressure, resulting in water migrating into the intestine (leading to diarrhoea)
In order to calculate the energy values of milk carbohydrates, the coefficient of digestibility is usually 98%, the heat of combustion is usually 3.95 cal/g and ingested-nutrients factor is usually 3.87 cal/g, respectively. (Wendell S. Arbuckle 1986)
Minerals in Ice-Cream
There are certain inorganic elements which are essential for growth and performance. Major minerals include calcium, sodium, potassium and sulfur, while minor minerals which are needed in much smaller amounts include copper, iodine, zinc and fluorine. The inorganic nutrients are interdependent and should be in certain proportions in the diet. Both calcium and phosphorus are of crucial concern, seeing as they are closely related. The best source of dietary calcium is from milk. Milk and its products, which includes ice-cream, are some of the richest sources of calcium, phosphorus and other essential minerals. Approximately 85% of phosphorus in the human body is combined with calcium. (Douglas Goff and Hartel 2013). As already stated above, additional amounts of lactose, favours calcium assimilation in greater quantities, which is essential for growing children and adults.
There is approximately 90-105mg/70g of calcium in Ice-cream according to (Douglas Goff and Hartel 2013) with the recommended daily amount being 1000-1200mg for a normal adult and 700-1000mg for a child. The mineral content of ice-cream is almost entirely derived from the MSNF, so is therefore found in proportion to the content of MSNF, which is usually 9-11%. When the protein content is lowered in MSNF, due to whey powder usage or blended MSNF ingredients with low protein, the mineral content is affected. (Douglas Goff and Hartel 2013)
Other indispensable minerals in ice-cream include, sodium which is roughly 40mg/70g and phosphorus, 70-85mg/70g.The RDA for phosphorus is 1250mg for children and 700mg for adults, it is clear that ice-cream is a good source of phosphorus. (Douglas Goff and Hartel 2013)
Milk used for ice-cream contains very little iron of copper, which are two minerals that can catalyse oxidation. Seeing as ice-cream is often stored for months, it is essential that contamination of any ingredients with these two minerals is prevented. It is because of this, many manufacturers omit copper from dairy equipment.
Vitamins in Ice-Cream
Vitamins are divided into two groups, fat soluble and water soluble. Fat soluble vitamins include vitamins A, D, E and k, whereas water soluble vitamins include vitamins B1, B2, B6, B12 and C. Just like milk, ice-cream is an excellent source if many essential vitamins. Below is a brief description of some vitamins, and their importance in milk and ice-cream in the diet.
Vitamin A- Ice-cream is an excellent source of vitamin A, a vitamin often referred to as the anti-infective vitamin. Its main importance or role is in building a resistance to infection in the respiratory tract and preventing night blindness.
Vitamin B1 (Thiamine)- Ice-cream contains an average of 0.50 mg/kg, with the RDA being about 1.1mg. (Wendell S. Arbuckle 1986). Thiamine is necessary for growth and metabolism.
Vitamin B2 (Riboflavin) -Ice-cream contains an average of 2.3 mg/kg with the RDA being 1.2mg/day (Wendell S. Arbuckle 1986). If someone is deficient from Riboflavin, they may experience lesions of the skin and eyes, mouth and tongue as well as increased sensitivity to light.
Vitamin B12- It is this vitamin which is known to have the most complex structure of any vitamin. Ice-cream contains about 0.0047 mg/kg, with the RDA being roughly 0.0025 mg. (Wendell S. Arbuckle 1986).
Vitamin D- It can be described as an antirachitic vitamin, however it must be noted that there is only a small amount of it in ice-cream, unless it has been fortified with it.
Digestibility and Palatability
Chewing is not necessary for ice-cream with majority of flavours. The smooth texture generally soothes the palate. Ice-creams coolness makes is desirable, especially in warm weather. The digestibility of ice-cream is generally quite high, except those who suffer from lactose malabsorption
Mix properties of practical important
Mix stability can be defined as the resistance to separation of the milk proteins in a colloidal suspension and the milkfat in the emulsion. Instability will result in the separation of protein particles as coagulated or precipitated material from the whey, fat or mix separate. There are many factors which affect mix stability which include, mix acidity, homogenization, ratio of fat to MSNF, freezing, aging time and dehydrating salts. In general, an ice-cream mix will be homogenised in order to reduce the large fat globules to smaller, fine particles ,with a high degree of dispersion. The fat globule distribution ranges from 0.5-2. µm. (Douglas Goff and Hartel 2013
Ice-cream stabilisers are a group of ingredients, usually polysaccharides which are often used in ice-cream formulations. They have many purposes such as ?
1) Increasing mix velocity
2) Stabilising the mix to prevent wheying off
3) Aid in suspension of favouring particles
4) Help in producing a stable foam, that has an easy cut-off and stiffness at the barrel freezer for packaging
5) To reduce ice-crystal growth during storage, especially during periods of temperature change, known as heat shock.
The majority of these functions are attributed to increased velocity of the unfrozen phase in ice-cream. Any stabiliser used in ice-cream production must have a clean/neutral flavour, contribute to an acceptable meltdown of the ice-cream, they must not bind to ice-cream flavours and they must also provide a desirable texture. Stabilisers have little or no effect on freezing point depression. It is common for ice-cream manufacturers to use commercial stabilisers or emulsifier blends. The most popular used ingredients in normal ice-cream mixes is guar and locust bean gums, cellulose gum which is a primary hydrocolloids, carrageenan which is the secondary hydrocolloid and polysorbate 80, which is the emulsifier. Stabilisers are quite bulky macromolecules, which have a great ability to interact with water through hydration. (Douglas Goff and Hartel 2013)
The hydrophilic suspension is the most stable mix particle seeing as it is charged and hydrated. The least stable is a suspension in which the particle is neither hydrated or carrying a charge, resulting in unstable mixes. (Wendell S. Arbuckle 1986). Salts, acidity, temperature, previous heat-treatments and homogenization all affect the hydration of milk proteins. Colloidal substances in ice-cream are more hydrated at lower temperatures. Calcium salts are known to result in a greater depressing effect on the hydration of proteins in comparison to potassium or sodium. Hydration is at a maximum when the pH is between 6.2-6.4.
Mix stability is reliant on emulsion (fat) and colloid (protein) stability. Ice-cream is homogenized, so to reduce the fat to fine particles, that have a high degree of dispersion. An interfacial layer surrounds the fat globules in a homogenized mix, which can be hydrated and is thick in regard to the dimensions of fat globules. The interfacial layer is made up of mainly complexed milk proteins. If the internal liquid cohesion is increased, it will stabilise the fat emulsion against partial churning in the freezer and increases the resistance to foam destruction when the mix is extended into the lamellae during shipping.
Shattering, explosive effects and shearing of the homogenizing valve are forces that tend to drive the fat globules apart in the state of dispersion of butterfat in ice-cream, and the mutual repulsion of the globules because of their electric charges. Collisions of the globules as they emerge from the valve of the homogenizer tend to bring the globules together. High temperatures result in the increases of the electric charge on fat globules, which decreases clumping. Low temperatures increase the positive charge which will lead to an increase in clumping.
The process of freezing is one of the factors which affect the stability of fat in ice-cream. Agitation and concentration of freezing causes fat globules to agglomerate. The rate of coalescence and agglomeration is a function mainly of the degree of agitation, however it is also affected by factors such as, melting point of the fat, emulsifiers, sugars and protein stability.
Dryness in ice-cream is directly inked with emulsion instability. A greater degree of fat destabilization is seen, seeing as ice-cream in manufactured under low freezing temperatures and with long agitation periods. The best dryness is obtained in ice-cream where the maximum fat clumping has taken place short of churning. Dryness and stiffness is mainly due to agglomeration of butter fat globules, which is a beneficial, especially in the case of the continuous freezer. (Wendell S. Arbuckle 1986)
The density or specific value of ice-cream can change relative to its composition. High levels of MSNF, stabilisers and sugars results in a higher density. Increased fat levels will decrease mix density. The density of various ice-cream mixes vary from 1.05 to 1.12 g/ml, with an average for a 10% fat mix, 1.1g/ml. (Douglas Goff and Hartel 2013)
Acidity of Mixes
If fresh dairy products of a high standard are, an ice-cream mix can be expected to have normal acidity. The normal pH of ice-cream is about 6.3. (Wendell S. Arbuckle 1986). If the Milk Solid Non-Fat (MSNF), is increased there is an increase in acidity. The natural acidity of ice-cream is due to mineral salts, milk proteins and dissolved Co2. The production of lactic acid by bacterial action in milk is the cause of developed acidity. A high acidity leads to excess mix viscosity, inferior flavour, and a less stable mix, which is undesirable. A less stable mix can lead to “cook on” during both processing and pasteurisation, seeing as heat and acidity increase the denaturation of proteins. (Douglas Goff and Hartel 2013)
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W.S Arbuckle (1986) ‘Ice-cream’ 4th edition
Christophe Dupont (2003) ‘The American Journal of Clinical Nutrition’, Volume 77, Issue 6
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