Ice cream generally contains seven categories of ingredients: fat (dairy or nondairy), milk solids-not-fat (MSNF) (the lactose, proteins, minerals, water-soluble vitamins, enzymes, and some minor constituents), sweeteners, stabilisers, emulsifiers, water, and flavours (Goff & Hartel, 2013). In this post, we’ll be looking at the role of sweeteners in ice cream.
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1. SWEETENERS USED IN ICE CREAM PRODUCTION
Sweeteners commonly used in ice cream production include sucrose, glucose (starch sugar or starch syrup), invert sugar (mixture of glucose and fructose), maple sugar, honey, fructose, molasses, malt syrup, brown sugar, and lactose. The most common choice of sweetener is a combination of sucrose (10-12%) and corn starch hydrolysate syrup (CSS) (3-5%) (Goff & Hartel, 2013).
Sucrose (granulated or table sugar) is made from sugar cane or sugar beets and is approximately 99.9% solids. It is also available in liquid form as a sucrose solution with approximately 67% solids (Goff & Hartel, 2013). Sucrose can be used as the sole sweetener in ice cream with excellent results and is arguably the most common sweetener used in homemade ice cream.
1.2. CORN SWEETENERS
Sweeteners derived from corn starch, or other starch sources such as potato, tapioca, rice, oat, or wheat, are extensively used as a replacement for a portion of, or all, the sucrose in ice cream. They are a more economical way to increase the total solids content without increasing the total sweetness.
The use of corn syrups is reported to enhance smoothness by contributing to a firmer and more chewy texture, provide better meltdown characteristics, bring out and accentuate fruit favours, and increase resistance to heat shock, which improves the shelf-life of the finished product (Glazier and Mack, 1941; Keeney, 1962; Goff & Hartel, 2013).
During the hydrolysis process, starch is converted into sugars including glucose, maltose, maltotiose, and dextrose. The extent of starch conversion into sugars is generally expressed as dextrose equivalents (DE value), with a low conversion, 28-38 DE; regular conversion, 39-48 DE; intermediate conversion, 49-58 DE; and high conversion, 59-68 DE (Goff & Hartel, 2013). As the DE increases, the sweetness increases. Lower DE corn syrups are reported to produce a smoother ice cream, increase resistance to heat shock, and improve meltdown (Glazier and Mack, 1941; Keeney, 1962). Ice cream manufacturers usually use liquid or dry corn syrup products with a 28-42 DE (Goff & Hartel, 2013).
With further processing, dextrose can be converted to fructose to produce high fructose corn sweeteners (HFCS). These are much sweeter than sucrose and contribute more to freezing point depression (lower the temperature at which the water in the ice cream mix starts to freeze) than sucrose. Goff & Hartel (2013) note that compared to sucrose, HFCS (42, 55, and 90%) are from 1.8 to 1.9 times as sweet and lower the freezing point nearly twice as much. The most common type is HFCS 42, which contains 42% fructose, 52% dextrose, and 6% higher saccharides (Goff & Hartel, 2013).
2. THE ROLE OF SWEETENERS IN ICE CREAM
The main function of sweeteners is to make the ice cream sweet and enhance the creamy flavour. Lack of sweetness produces a flat or bland taste, but too much tends to subdue other flavours. Sweeteners also improve texture by influencing ice crystal size, increase meltdown, and generally make ice cream softer and easier to scoop.
2.1. ICE CRYSTALS IN ICE CREAM
Ice crystal size is a critical factor in the development of smooth and creamy ice cream (Donhowe et al. 1991). Smooth and creamy ice cream requires the majority of ice crystals to be small, around 10 to 20 µm in size. If many crystals are larger than this, ice cream will be perceived as being coarse or icy (Drewett & Hartel, 2007; Goff & Hartel, 2013).
Ice cream is frozen in two stages: dynamic and static freezing. Ice crystals are formed during dynamic freezing, where the ice cream mix is frozen and agitated to incorporate air, and grow during static freezing, where the partially frozen ice cream mix is hardened in a freezer without agitation. The aim is to promote the formation of as many small ice crystals as possible during dynamic freezing and then to preserve these small crystals during static freezing and storage.
The composition of ice cream has a significant influence on ice crystallisation (Donhowe & Hartel, 1996; Hatley et al., 1991). In particular, sweeteners and stabilisers are the most important composition determinants of ice crystal size (Hagiwara & Hartel, 1996). Sweeteners influence ice crystal formation and growth by two main mechanics: 1. specific effects on ice crystallisation mechanisms (nucleation, growth and ripening) and 2. effect on freezing point depression and recrystallisation (Goff & Hartel, 2013).
2.1.1. NUCLEATION AND GROWTH
During dynamic freezing, ice cream mix enters the ice cream machine slightly above its freezing point. As the freezer bowl absorbs the heat in the mix and brings it below its freezing point, a layer of ice freezes to the wall of the cold freezer bowl causing rapid nucleation, or the birth of small ice crystals (Hartel, 2001). For smooth and creamy ice cream, it’s important to have a high rate of nucleation so as to create as many small ice crystals as possible (Hartel, 1996).
Sweeteners have been shown to reduce the rate of ice nucleation (Schwartzberg, 1990). Arbuckle (1940) concluded that sugar improved the texture of ice cream by reducing the amount of ice that was formed and Berger & White (1979) found that, in general, a higher sucrose content produced smaller ice crystals. Similarly, Haddad Amamou et al. (2010) found that the average crystal size decreased with increased sucrose concentration. Arbuckle (1986) notes that an increase in sugar content from 12 to 18% decreases ice crystal size by about 25%. Drewett & Hartel (2007), however, found that sweetener did not significantly affect mean ice crystal size. These studies suggest that although sucrose may reduce the rate of ice nucleation, resulting in fewer crystals, a higher sucrose content improves texture by producing smaller crystals.
2.1.2. FREEZING POINT DEPRESSION AND RECRYSTALLISATION
Ice crystal growth during static freezing and storage, or recrystallisation, can result in coarse or grainy texture. Arbuckle (1986) notes that the mean size of ice crystals may increase to as large as 65 µm during static freezing because of growth. Sweeteners affect recrystallisation by depressing the freezing point, or lowering the temperature at which the water in an ice cream mix starts to freeze (Harper & Shoemaker, 1983; Wittinger & Smith, 1986). For an ice cream mix with a lower freezing point, less water is frozen at a given temperature.
Hagiwara & Hartel (1996) found that the lower the freezing point, or the larger the amount of unfrozen water in ice cream, the higher was the recrystallisation rate. Harper & Shoemaker (1983) found similar effects of freezing point for the effect of sweeteners on recrystallisation rates. These results suggest that ice cream formulations with the highest possible freezing point and the least amount of unfrozen water, should have the greatest resistance to recrystallisation.
Different sweeteners depress the freezing point of water to different extents. The freezing point of mixes with a high sugar content may range downward to -3°C (26.5°F) while mixes with high fat, low sugar content may range upward to -1.4°C (20.5°F) (Goff & Hartel, 2013). Corn syrup of either 42 or 63 DE lowers the freezing point of ice cream mix more than sucrose, producing a softer ice cream that is easier to scoop at lower temperatures. The use of low DE CSS (20DE) causes an increase in freezing point compared with that for sucrose (Hagiwara & Hartel, 1996).
Miller-Livney & Hartel (1997) found that the highest freezing points were exhibited by mixes containing 20 DE CSS, and mixes containing 42 HFCS had the lowest freezing point. They also found that recrystallisation rates were lowest for ice creams made with 20 DE CSS and the highest for ice creams made with HFCS. Similarly, Hagiwara & Hartel (1996) found that ice creams containing HFCS exhibited the highest recrystallisation rates. Ice creams made with 20 DE CSS and 42 DE CSS gave the lowest recrystallisation rates, and ice creams made with sucrose were intermediate in recrystallisation rate.
The type and amount of sweetener also affects the melting rate of ice cream, with a lower freezing point leading to an increased rate of melting (Muse & Hartel, 2004; Goff & Hartel, 2013). Junior & Lannes (2011) found that formulations added with fructose syrup generally presented a higher melting rate when compared to ice creams made with glucose syrup, a probable cause being the impact of fructose syrup on the freezing point of the mixes.
Muse & Hartel (2004) tested the effects of three types of sweeteners, sucrose, 42 DE HFCS, and 20 DE corn syrup, and three levels of the emulsifier (0, 0.05, and 0.1%) polysorbate 80 on melting rate and hardness. They found that ice cream made with 20 DE corn syrup had the slowest melting rate, whereas ice ream made with 42 DE HFCS had the fastest melting rates.
The hardness of ice cream is affected by overrun, ice crystal size, ice phase volume, and extent of fat destabilisation (Muse & Hartel, 2004). Higher overrun in ice cream has been found to lead to softer the ice cream (Tanaka et al., 1972; Goff et al., 1995; Wilbey et al., 1998), and Sakurai et al. (1996) found that ice creams with more large ice crystals were harder than ice creams that had fewer large ice crystals.
Muse & Hartel (2004) found that the ice phase volume (the amount of frozen water) significantly impacts the hardness of the ice creams: the more ice in the ice cream, the harder the sample. They found that ice creams made with 20 DE CSS had the greatest ice phase volumes and were the hardest. A positive correlation between hardness of ice cream and the amount of ice was also found by Wilbey et al (1998). Sweeteners affect the hardness of ice cream by depressing the freezing point and reducing the ice phase volume, resulting in softer ice cream that is easier scoop.
The main function of sweeteners in ice cream is to make ice cream sweet and enhance the creamy flavour. Sweeteners also play a significant role in improving ice cream texture by producing smaller ice crystals and retarding ice crystal growth during hardening and storage.
A higher sweetener content depresses freezing point, resulting in ice cream that is softer and easier to scoop but melts quicker. 42 HFCS produces mixes with the lowest freezing points and ice cream with the softest texture, whilst lower DE corn syrups (20 DE) are reported to produce a smoother, but harder, ice cream, increase resistance to heat shock, and improve meltdown.
I hope that helps. I’d be happy to answer any questions so do get in touch and say hi! All the best, Ruben 🙂
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