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.8 to76.4%.A parabolic relationship between the extent of lactose crystallization andstorage relative humidity with a maximum at 70% RH at 24°C was found whenamorphous lactose crystallized in freeze-dried skim milk (13).The correspondingwater content was 17%, and the T Tg value for amorphous lactose was 61°C(13).We assumed that the low extent of crystallization at the lowest relativehumidity resulted from low molecular mobility and restricted diffusion of lactosemolecules within the nonfat milk solids, since the crystallization occurred at atemperature relatively close to the Tg.In addition to the overall extent of crystallization, the extent of crystalliza-tion into various crystal forms may also be dependent on T Tg and relativehumidity at isothermal crystallization conditions (14).The crystal form producedas a result of amorphous sugar crystallization may also affect storage stability,in particular, when the material may crystallize as a hydrate.For example, lactosecrystallization as anhydrous ²-lactose crystals releases a significant amount ofCopyright 2003 by Marcel Dekker, Inc.All Rights Reserved. water compared to crystallization as ±-lactose monohydrate, which containsabout 5% water.4.Crystal Forms of SugarsSugars may exist in anomeric forms, e.g., ±- and ²-glucose, and they may crystal-lize in anomeric crystals, crystals with mixed anomers, and hydrates with differ-ent amounts of water.For example, lactose may crystallize into several crystalforms, e.g., ±-lactose monohydrate (76), anhydrous ²-lactose (77), stable andunstable anhydrous ±-lactose (77), and anhydrous crystals with ±- and ²-lactosein a molar ratio of 5:3 or 4:1 (78).Another example is glucose, which maycrystallize into three crystal forms: ±-glucose monohydrate, anhydrous ±-glu-cose, and anhydrous ²-glucose (79).Crystallization of sucrose usually producesanhydrous sucrose crystals.However, sucrose has been reported to crystallizealso as sucrose hemipentahydrate and hemiheptahydrate at low temperatures (79,80).The crystal forms produced as a result of amorphous lactose crystallizationhave probably been paid most attention.Crystal forms produced from pure amor-phous lactose or lactose in milk powders after storage at various relative humidityconditions have often been determined using X-ray diffraction techniques (e.g.,13, 14, 53, 59, 65, 66, 81).The crystal forms found have been reported to bedependent on the relative humidity and temperature during storage.In severalstudies, spray- and freeze-dried lactose has been reported to have crystallized asa mixture of ±-lactose monohydrate and anhydrous ²-lactose at 53 85% RH atroom temperature (53, 59, 64, 65).Our studies have shown (14) that freeze-driedlactose crystallizes mainly as a mixture of ±-lactose monohydrate and anhydrouscrystals with ±- and ²-lactose in a molar ratio of 5:3 at 44.4 76.4% RH and at24°C, but traces of other crystal forms were also present (Table 2).Bushill et al.(53) studied the crystal forms resulting from amorphous lac-tose crystallization.They found that lactose in freeze-dried skim milk when storedat 25°C and 55% RH crystallized as anhydrous crystals consisting of ±- and ²-lactose in a molar ratio of 5:3.Our results (13) agreed that lactose in freeze-dried skim milk crystallized mainly into the anhydrous 5:3 ±:² crystal formwhen freeze-dried skim milk was stored at 24°C and relative humidity of 53.885.8%.However, as a result of storage at 85.8% RH, traces of ±-lactose monohy-drate crystals were detected.The crystal forms may also be dependent on thecrystallization temperature.Würsch et al.(70) reported that lactose in spray-driedwhole milk with 3.1% water crystallized at 60°C as anhydrous ²-lactose.Saito(66) found that lactose in spray-dried whole milk crystallized as ±-lactose mono-hydrate when stored at 37°C and 75% RH, but as anhydrous ²-lactose whenrelative humidity was less than 20%.Drapier-Beche et al.(59) found that lactosein skim milk powder crystallized mainly as anhydrous ²-lactose at 20°C and 43%Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved. Table 2 Crystal Forms of Lactose Produced in Selected Duplicate Lactose SamplesStored at Vartious RH ConditionsaAnhydrouscrystalsAnhydrous with ±-crystals with and ²-Unstable ±- and ²-lactose lactose in aStorage ±-Lactose anhydrous Anhydrous in a molar molar ratioRH (%) time (h) monohydrate ±-lactoseb ²-lactose ratio of 5:3 of 4:144.4c 7681440216044.4d 7681440216053.8 4819238466.2 247212076.4 213672aApproximate portions of various crystal forms were marked in the following way: predominant crystal form (ap-proximate portion of the crystal form was more than half of sample) with , typical crystal form (approximateportion of the crystal form was less than half of sample but intensity of the typical peaks of crystal form wasmoderate) with , and traces of the crystal form (the typical peaks of crystal form could be detected althoughintensity of the peaks was low) with [ Pobierz caÅ‚ość w formacie PDF ]
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.8 to76.4%.A parabolic relationship between the extent of lactose crystallization andstorage relative humidity with a maximum at 70% RH at 24°C was found whenamorphous lactose crystallized in freeze-dried skim milk (13).The correspondingwater content was 17%, and the T Tg value for amorphous lactose was 61°C(13).We assumed that the low extent of crystallization at the lowest relativehumidity resulted from low molecular mobility and restricted diffusion of lactosemolecules within the nonfat milk solids, since the crystallization occurred at atemperature relatively close to the Tg.In addition to the overall extent of crystallization, the extent of crystalliza-tion into various crystal forms may also be dependent on T Tg and relativehumidity at isothermal crystallization conditions (14).The crystal form producedas a result of amorphous sugar crystallization may also affect storage stability,in particular, when the material may crystallize as a hydrate.For example, lactosecrystallization as anhydrous ²-lactose crystals releases a significant amount ofCopyright 2003 by Marcel Dekker, Inc.All Rights Reserved. water compared to crystallization as ±-lactose monohydrate, which containsabout 5% water.4.Crystal Forms of SugarsSugars may exist in anomeric forms, e.g., ±- and ²-glucose, and they may crystal-lize in anomeric crystals, crystals with mixed anomers, and hydrates with differ-ent amounts of water.For example, lactose may crystallize into several crystalforms, e.g., ±-lactose monohydrate (76), anhydrous ²-lactose (77), stable andunstable anhydrous ±-lactose (77), and anhydrous crystals with ±- and ²-lactosein a molar ratio of 5:3 or 4:1 (78).Another example is glucose, which maycrystallize into three crystal forms: ±-glucose monohydrate, anhydrous ±-glu-cose, and anhydrous ²-glucose (79).Crystallization of sucrose usually producesanhydrous sucrose crystals.However, sucrose has been reported to crystallizealso as sucrose hemipentahydrate and hemiheptahydrate at low temperatures (79,80).The crystal forms produced as a result of amorphous lactose crystallizationhave probably been paid most attention.Crystal forms produced from pure amor-phous lactose or lactose in milk powders after storage at various relative humidityconditions have often been determined using X-ray diffraction techniques (e.g.,13, 14, 53, 59, 65, 66, 81).The crystal forms found have been reported to bedependent on the relative humidity and temperature during storage.In severalstudies, spray- and freeze-dried lactose has been reported to have crystallized asa mixture of ±-lactose monohydrate and anhydrous ²-lactose at 53 85% RH atroom temperature (53, 59, 64, 65).Our studies have shown (14) that freeze-driedlactose crystallizes mainly as a mixture of ±-lactose monohydrate and anhydrouscrystals with ±- and ²-lactose in a molar ratio of 5:3 at 44.4 76.4% RH and at24°C, but traces of other crystal forms were also present (Table 2).Bushill et al.(53) studied the crystal forms resulting from amorphous lac-tose crystallization.They found that lactose in freeze-dried skim milk when storedat 25°C and 55% RH crystallized as anhydrous crystals consisting of ±- and ²-lactose in a molar ratio of 5:3.Our results (13) agreed that lactose in freeze-dried skim milk crystallized mainly into the anhydrous 5:3 ±:² crystal formwhen freeze-dried skim milk was stored at 24°C and relative humidity of 53.885.8%.However, as a result of storage at 85.8% RH, traces of ±-lactose monohy-drate crystals were detected.The crystal forms may also be dependent on thecrystallization temperature.Würsch et al.(70) reported that lactose in spray-driedwhole milk with 3.1% water crystallized at 60°C as anhydrous ²-lactose.Saito(66) found that lactose in spray-dried whole milk crystallized as ±-lactose mono-hydrate when stored at 37°C and 75% RH, but as anhydrous ²-lactose whenrelative humidity was less than 20%.Drapier-Beche et al.(59) found that lactosein skim milk powder crystallized mainly as anhydrous ²-lactose at 20°C and 43%Copyright 2003 by Marcel Dekker, Inc.All Rights Reserved. Table 2 Crystal Forms of Lactose Produced in Selected Duplicate Lactose SamplesStored at Vartious RH ConditionsaAnhydrouscrystalsAnhydrous with ±-crystals with and ²-Unstable ±- and ²-lactose lactose in aStorage ±-Lactose anhydrous Anhydrous in a molar molar ratioRH (%) time (h) monohydrate ±-lactoseb ²-lactose ratio of 5:3 of 4:144.4c 7681440216044.4d 7681440216053.8 4819238466.2 247212076.4 213672aApproximate portions of various crystal forms were marked in the following way: predominant crystal form (ap-proximate portion of the crystal form was more than half of sample) with , typical crystal form (approximateportion of the crystal form was less than half of sample but intensity of the typical peaks of crystal form wasmoderate) with , and traces of the crystal form (the typical peaks of crystal form could be detected althoughintensity of the peaks was low) with [ Pobierz caÅ‚ość w formacie PDF ]