Lactose crystallization delay in model infant foods made with lactose, beta-lactoglobulin, and starch

Handling and storage alter infant food powders due to lactose crystallization and interactions among components. Model infant foods were prepared by colyophilization of lactose, β-lactoglobulin (β-LG), and gelatinized starch. A mixture design was used to define the percentage of each mixture component to simulate a wide range of infant food powders. The kinetics of crystallization was studied by a gravimetric method (dynamic vapor sorption) at 70% relative humidity (RH). After freeze-drying, lactose was amorphous and crystallized at 70% RH. The delay before crystallization depends on the contents of β-LG and starch in the formulations. A mathematical model was proposed to predict crystallization time (delay) at 70% RH. For the formulation containing 50% lactose, 25% β-LG, and 25% starch, lactose was still amorphous after 42 h at 70% RH, whereas pure amorphous lactose crystallized after approximately 70 min. Calculated and experimental results of adsorbed moisture from the formulations were compared. Adsorbed water of formulation containing lactose could not be calculated from moisture sorption properties of each component at a given RH because β-LG and gelatinized starch prevented lactose crystal growth.     

Determining the critical relative humidity at which the glassy to rubbery transition occurs in polydextrose using an automatic water vapor sorption instrument

Similar to an increase in temperature at constant moisture content, water vapor sorption by an amorphous glassy material at constant temperature causes the material to transition into the rubbery state. However, comparatively little research has investigated the measurement of the critical relative humidity (RHc) at which the glass transition occurs at constant temperature. Thus, the central objective of this study was to investigate the relationship between the glass transition temperature (Tg), determined using thermal methods, and the RHc obtained using an automatic water vapor sorption instrument. Dynamic dewpoint isotherms were obtained for amorphous polydextrose from 15 to 40 °C. RHc was determined using an optimized 2nd-derivative method; however, 2 simpler RHc determination methods were also tested as a secondary objective. No statistical difference was found between the 3 RHc methods. Differential scanning calorimetry (DSC) Tg values were determined using polydextrose equilibrated from 11.3% to 57.6% RH. Both standard DSC and modulated DSC (MDSC) methods were employed, since some of the polydextrose thermograms exhibited a physical aging peak. Thus, a tertiary objective was to compare Tg values obtained using 3 different methods (DSC first scan, DSC rescan, and MDSC), to determine which method(s) yielded the most accurate Tg values. In general, onset and midpoint DSC first scan and MDSC Tg values were similar, whereas onset and midpoint DSC rescan values were different. State diagrams of RHc and experimental temperature and Tg and %RH were compared. These state diagrams, though obtained via very different methods, showed relatively good agreement, confirming our hypothesis that water vapor sorption isotherms can be used to directly detect the glassy to rubbery transition. Practical Application: The food polymer science (FPS) approach, pioneered by Slade and Levine, is being successfully applied in the food industry for understanding, improving, and developing food processes and products. However, despite its extreme usefulness, the Tg, a key element of the FPS approach, remains a challenging parameter to routinely measure in amorphous food materials, especially complex materials. This research demonstrates that RHc values, obtained at constant temperature using an automatic water vapor sorption instrument, can be used to detect the glassy to rubbery transition and are similar to the Tg values obtained at constant %RH, especially considering the very different approaches of these 2 methods--a transition from surface adsorption to bulk absorption (water vapor sorption) versus a step change in the heat capacity (DSC thermal method).     

Modeling of lactose crystallization and color changes in model infant foods

Lactose crystallization and color changes in formulas containing β-lactoglobulin and gelatinized starch were investigated. Model infant formulas were prepared by colyophilization of 3 components (lactose, β-lactoglobulin, and gelatinized starch). A mixture design was used to choose the percentage of each mixture component. These formulas were stored for 3 mo at different relative humidities (RH), ranging from approximately 0 to 94.6%, to study the lactose crystallization and color changes. Crystallization kinetics was studied by gravimetric methods, and lactose state (crystalline vs. amorphous) was verified before and after storage by differential scanning calorimetry. Before storage, lyophilized lactose was amorphous, but during storage it crystallized, depending on the RH. The lactose crystallization RH depended on the quantity of β-lactoglobulin and gelatinized starch, and by increasing these quantities, the crystallization RH increased. For some formulas, the crystallization RH was noted at 3 different RH during storage. The first was noted after 1 d of storage and the second and third were observed later on, showing that crystallization is a time-dependent phenomenon. Nonenzymatic browning was studied in model infant formulas by yellow color changes of samples at 11.3, 43.2, 54.5, and 75.4% RH. In this study, 7 mathematical models were proposed to predict the moisture sorption properties and color changes at different RH, and the models were validated by experimental results.     

INFLUENCE OF TEMPERATURE AND RELATIVE HUMIDITY ON THE PHYSICAL STATES OF COTTON CANDY

Cotton candy is made by melting crystalline sucrose above 210C in a bowl which shoots molten liquid sucrose into the air where it rapidly cools and dries into an amorphous glassy solid state. As such, it is highly hygroscopic, picking up moisture as %RH increases and becoming rubbery. The glass transition line (T_g vs. %RH) divides the two states. When rubbery, cotton candy should collapse forming crystalline sucrose becoming unsaleable. Cotton candy was stored at 25C and at %RH from ～0% to 75%. Moisture gain/loss, visual observations, and powder X‐ray diffraction using a Seimens 5005‐powder X‐ray diffractometer were used to evaluate collapse and crystallization. At ～0% and 11% RH (below T_g), cotton candy maintained a stable structure for at least 12 months. At 33% RH (just at T_g), it collapsed and crystallized within 3 days while at 45, 54 and 75% RH, collapse and crystallization occurred in less than 1 day.     

Moisture‐Mediated Interactions Between Amorphous Maltodextrins and Crystalline Fructose

The effects of coformulating amorphous maltodextrins (MDs) and crystalline fructose, a deliquescent solid, on the moisture sorption, deliquescence point (RH₀), and glass transition temperature (T_g) behaviors were determined. Moisture sorption profiles of binary fructose:MD mixtures and individual ingredients were generated using controlled relative humidity (RH) desiccators and by dynamic vapor sorption techniques. Blends exhibited synergistic moisture uptake at RHs below the RH₀ of fructose, attributed to partial dissolution of fructose in plasticized MD matrices without a significant reduction in the RH₀ of the undissolved fructose. Increasing storage temperature decreased the onset RH for moisture sorption synergy. At all storage RHs, the measured T_g (2nd scan) was significantly reduced in fructose:MD mixtures compared to individual MDs, and was related to both the synergistic moisture uptake in the blends and heat‐induced ternary fructose–MD–water interactions in the differential scanning calorimeter. Differences were found between the behavior of fructose:MD blends and previous reports of sucrose:MD and NaCl:MD blends, caused in part by the lower RH₀ of fructose. The enhanced moisture sorption in blends of deliquescent and amorphous ingredients could lead to problematic moisture‐induced changes if storage conditions are not controlled.     

Sorption Isotherm and Calorimetric Behavior of Amorphous/Crystalline Raffinose-Water Systems

ABSTRACT: The water adsorption and desorption isotherms at 27 °C of initially amorphous raffinose over a range of relative humidity of 11% to 97% have been determined. Upon adsorption, the isotherm exhibited a "quasi" plateau, and the moisture content at this plateau was found to be very close to the amount required to form the crystalline raffinose pentahydrate (R.5 H2O). Crystallization of raffinose (R.5 H2O) during water adsorption at 52% and 58% RH was indicated by differential scanning calorimetry (DSC); both thermograms showed an endothermal peak of melting corresponding to R.5H2O. The results of the crystallization kinetics at 52% and 58% RH indicated that the time to assess the stable physical state in a sugar system for a given external condition has to be properly defined and depends on the (T-T_g) value.     

Use of ramping and equilibrium water vapor sorption methods to determine the critical relative humidity at which the glassy to rubbery transition occurs in polydextrose

Recent research has demonstrated that the critical relative humidity (RHc) values, obtained using automatic water vapor sorption instruments, can be used to detect the glassy to rubbery transition. However, reported time dependency of these RHc values suggests that additional research be carried out using equilibrium water vapor sorption methods. Thus, the objectives of this study were to: (1) determine the RHc for amorphous polydextrose at various temperatures using both instrumental (Dynamic Vapor Sorption [DVS] ramping and equilibrium) and saturated salt slurry methods, and (2) compare the RHc values obtained via sorption methods to the glass transition temperature (Tg) values obtained via differential scanning calorimetry (DSC). When plotted as a "glass curve" on a state diagram, the RHc values (plotted as a function of temperature) were found to be similar to the Tg values (plotted as a function of relative humidity). Of the 3 sorption methods employed, at 25 °C, the saturated salt slurry exhibited the lowest RHc value (34.3%), followed by the DVS equilibrium method (41.7%), and the DVS ramping method (49.9%). The RHc DVS equilibrium method was closest to the calculated DSC Tg onset RHc value (41.6% at 25 °C). These water sorption methods show promise as practical tools for predicting the quality and stability attributes of amorphous materials by being able to routinely determine the location of the glassy to rubbery transition. Future research applying these sorption methods to more complex amorphous food systems is suggested. Practical Application: Despite its extreme usefulness, the Tg, a key element of the Food Polymer Science approach, remains a challenging parameter to routinely measure in amorphous food materials. Recent research has demonstrated that the RHc values can be used to detect the glassy to rubbery transition. However, reported time dependency of these RHc values suggests that additional research be carried out using equilibrium water vapor sorption methods. Therefore, in this research 2 instrumental (DVS ramping and equilibrium) methods and the traditional saturated salt slurry method were used to obtain RHc values, comparing them to DSC obtained Tg values. The water sorption methods show promise as practical tools for predicting the quality and stability attributes of amorphous materials by being able to routinely determine the location of the glassy to rubbery transition. Future research applying these sorption methods to more complex amorphous food systems is suggested.     

Crystallization Kinetics of Lactose and Sucrose Based On Isothermal Differential Scanning Calorimetry

Isothermal Differential Scanning Calorimetry (DSC) was used to study the crystallization kinetics of freeze-dried samples of lactose and sucrose at several temperatures between Tg and Tm. The sample was rapidly heated to the required temperature. After subtraction of an induction time, the Avrami equation was used to model the data and a Lauritzen-Hoffman like expression used to fit the derived rates of crystallization over the temperature range Tg相似文献   

THERMAL PROPERTIES and MOISTURE SORPTION ISOTHERMS of SPRAY-DRIED ENCAPSULATED MILKFAT

Stable emulsions containing 40 or 60% anhydrous butter oil and carbohydrate encapsulants (sucrose, modified starch or all-purpose flour) were spray dried to produce free-flowing shelf-stable powders, according to a 2 x 3 factorial design, replicated three times. Differential scanning calorimetry profiles showed well-defined melting ranges that were related to encapsulant used. Butter oil was almost completely encapsulated when fat content was 40% and sucrose was used as the wall material. Moisture sorption isotherms of powders with sucrose showed characteristic breaks caused by sugar crystallization followed by moisture desorption, whereas powders with modified starch or all-purpose flour continuously absorbed moisture with increasing relative humidity. the solvent-extractable fat fraction increased with increasing relative humidity in all cases. Scanning electron microscopy showed that sucrose-containing powder particles partially dissolved and fused together as a result of moisture uptake, whereas powders with modified starch or all-purpose flour maintained particle identity, even at 80% relative humidity.     

Physico-Chemical and Mechanical Properties of Apple Disks Subjected to Osmotic Dehydration and Different Drying Methods

The effect of sucrose infusion (SI) pretreatment and dehydration methods (freeze and air drying) on physical and textural properties of apple disks were analyzed. Dried samples were humidified between 11% and 43% relative humidity (RH) at 20 °C. Control samples (air- and freeze-dried) behaved similarly regarding water sorption and glass transition temperature. SI process caused important changes in the water sorption behavior of air-dried samples. Nuclear magnetic resonance relaxation times values (T ₂) for freeze-dried apples were higher than those for air-dried samples. Samples subjected to previous SI always presented lower T ₂ values because they had lower water contents. The dehydration method also affected the mechanic behavior. Air-dried samples exhibited higher F _max values during puncture assay than those obtained for freeze-dried samples. SI samples showed higher F _max values for both drying methods. The crust formed during air drying generated crispier materials along the whole RH range, while freeze-dried matrices were more deformable with the increase in RH. SI pretreatment also allowed diminishing browning development. The results obtained are useful in the choice of processing technologies of organoleptically acceptable dehydrated fruits for direct consumption or for their incorporation into compound foods.     

Moisture sorption isotherms and isosteric heat of sorption of leaves and stems of lemon balm (Melissa officinalis L.) established by dynamic vapor sorption

The equilibrium moisture contents (MC) of leaves and stems of lemon balm (Melissa officinalis L.) were determined separately at temperatures of 25, 35 and 45 °C over a stepwise increase of relative humidity (RH) ranging from 3 to 90% by an automatic, gravimetric analyzer (DVS system). Equilibrium was achieved within 6 h for most of the target values of relative humidity. The equilibrium moisture content of leaves was significantly higher than that of stems (p < 0.05). Differences in moisture sorption capacity between the leaves and stems can be attributed to chemical composition and structure of the tissues. Five three-parameter moisture sorption models (modifications of Chung–Pfost, GAB, Halsey, Henderson and Oswin) were tested for their effectiveness to fit the experimental sorption data. The modified Oswin equation was found to be the best model to describe the adsorption isotherms of both leaves and stems of lemon balm. The recommended MC values of leaves and stems for microbial safe storage at 25 °C were 0.124 and 0.113 kg water per kg dry solids, respectively. The net isosteric heat of sorption was computed from the predicted sorption data by applying the integrated form of the Clausius–Clapeyron equation.     

基于不同数学模型的魔芋水分吸湿等温线模拟

根据吸附原理,采用静态调整环境湿度法,测定了魔芋在20、30、40℃3个温度下,0%~98%水活度范围内的平衡含水率,绘出魔芋的吸湿等温线。结果显示,魔芋的吸湿等温线属于II型等温线;在一定的水活度下随着温度的升高魔芋的吸附能力下降。并以平均相对误差和决定系数为评价指标,用八种数学模型对实验数据进行拟合,结果表明Peleg模型对魔芋的吸湿等温线拟合效果最好。      

Equilibrium moisture contents of a medicinal herb (Melissa officinalis) and a medicinal mushroom (Lentinula edodes) determined by dynamic vapour sorption

The measurement of moisture sorption isotherms is of great importance in the fields of food and agricultural engineering. Although the static gravimetric method is still commonly used, automated instruments for the determination of sorption isotherms have been designed to overcome some of the drawbacks associated with the standard method. The dynamic vapour sorption (DVS) is a modern technique which can produce sorption data with high accuracy under controlled conditions in a short period of time. The method was examined and validated by measuring the equilibrium moisture contents of lemon balm herb (Melissa officinalis L.) and Shiitake mushroom [Lentinula edodes (Berk.) Pegl.] at a temperature of 25 °C in the range of 0-95% relative humidity. The experiments were performed in triplicate for a total of fifteen target values of relative humidity. A parallel exponential kinetics model (PEK-model) was used to evaluate the change in mass during the adsorption process of each relative humidity step. Additionally, the GAB model was tested for its effectiveness to describe the equilibrium MC/RH data of both products. The PEK-model fitted adequately to the experimental sorption kinetic data over the entire range of relative humidity. Sigmoid characteristic curves, type II pattern were obtained, as indicated by the C and K values of the GAB model. Differences in the hygroscopic characteristics of the two products tested were ascribed to differences in nature of the material.     

Glass Transition and Crystallization of Amorphous Trehalose-sucrose Mixtures

Our objective was to investigate the glass transition and crystallization of trehalose-sucrose mixtures at various moisture contents. Samples were freeze-dried, rehumidified, and scanned with Differential scanning calorimetry (DSC) to obtain T_g values for all mixtures and pure sugars. Amorphous cotton candy samples for crystallization studies were prepared, humidified, and monitored for crystallinity as a function of time using powder X-ray diffraction (XRD). The T_g of pure dry trehalose was found to be 106 °C, while sucrose had a T_g of 60 °C. Glass transition, as expected, occurred at an intermediate temperature for sucrose-trehalose mixtures. Of the dry samples, only those containing less than 16% trehalose showed sucrose crystallization during scanning. In cotton candy made from a 25% trehalose-75% sucrose mixture, humidified to 33%, sucrose did not crystallize after 30 days, whereas pure sucrose cotton candy at that humidity crystallized completely after 11 days. These data show that trehalose may be a useful crystallization inhibitor in foods with high sucrose content, although small amounts of trehalose did not significantly raise the T_g.     

Moisture Sorption Characteristics of Composite Foods Filled with Chocolate

We compared the moisture sorption isotherms (MSI's) and their temperature dependence of composite foods with those of crust and filling. The MSI were determined on cracker, cookie, chocolate, and two types of composite foods such as CFI (cracker/chocolate/cracker) and CF2 (cookie/chocolate/cookie) at 20,30, and 40°C and 11–85% relative humidity, and fitted into the Guggenheim-Anderson-de Boer (GAB) equation. Chocolate had the lowest monolayer (mo) value, equilibrium moisture content (EMC), and sorption energy levels, followed by cookie and cracker. The CFI had higher EMC values and sorption energy than CF2. The GAB mo values and C1 values decreased with temperature, while C2 values increased with temperature.     

Corn Syrup Solids and Their Saccharide Fractions Affect Crystallization of Amorphous Sucrose

The effects of corn syrup saccharides on the glass transition (Tg) and crystallization of freeze-dried sucrose were studied using differential scanning calorimetry. Corn syrup (CS) solids were fractionated into samples with differing ranges and types of glucose polymers. Tg of the sucrose/CS additive mixtures depended on number-average molecular weight, rather than weight-average molecular weight, of CS material. Additive levels of 10% and 20% (w/w) of CS solids and their fractions interfered with crystallization of amorphous sucrose, whereas levels 50% prevented crystallization. The mechanism by which CS saccharides interfered with crystallization of amorphous sucrose depended not only on Tg but was also influenced by specific interactions between molecules.     

The effects of added sugars and alcohols on the induction of crystallization and the stability of the freeze-dried peki (Caryocar brasiliense Camb.) fruit pulps

Peki (Caryocar brasiliense Camb.) is a Brazilian fruit with an extremely high β-carotene content, but the β-carotene is unstable under dry storage conditions. This work reports on the product development and stability of freeze-dried peki fruit pulp. Freeze-dried products were made by adding alcohols (ethanol and isopropyl alcohol; at concentrations of 0, 5 and 10 mL/100 mL of extract) and sugars (sucrose and fructose; at concentrations of 0, 5 and 10 g/100 mL of extract) to the peki fruit pulps followed by freeze-drying. Scanning electron microscopy was used to analyze the microstructure of the freeze-dried products by visualizing the crystallized forms. The product hardness and total carotenoid content following the different treatments were measured using a texture analyzer and a spectrophotometer, respectively. The stability of these foods was evaluated by their water sorption during their storage in various relative humidity environments at 25 °C. There were characteristic differences in their hygroscopic behaviors. The pretreatment with sucrose and ethanol improved the freeze-dried product and yielded a lower number of collapsed structures. Changes during the storage were observed. The pulp pretreated with sucrose was amorphous and metastable, but the drying process was accelerated by the presence of alcohol (mainly ethanol), which resulted in protected structures without any sign of collapse.     

Whey Protein-Sucrose Coating Gloss and Integrity Stabilization by Crystallization Inhibitors

ABSTRACT: Whey protein coatings protect foods from change and deterioration and can extend product shelf life. However, because they are also made from food materials, whey protein coatings may also change over time if not properly formulated. Whey protein isolate (WPI)-sucrose high-gloss coatings, with and without crystallization inhibitors, were formed on chocolate-covered peanuts. The objective was to determine the effectiveness of crystallization inhibitors on preventing cracking of coatings and loss of coating gloss caused by sucrose crystallization during product storage. The 4 inhibitors tested were lactose, modified starch, polyvinylpyrrolidone, and raffinose. The WPI-coated chocolate-covered peanuts were stored for 119 d in 23%, 33%, and 44% relative humidity (RH) at 25°C. Gloss of the WPI coatings was measured periodically with a gloss-analysis system. It was found that raffinose is the most effective inhibitor of sucrose crystallization in whey protein-sucrose coatings. WPI coatings containing raffinose had significantly higher gloss values than all other coatings. For raffinose-containing samples stored in 23% and 33% RH environments, less than 3% of gloss was lost during storage. In 44% RH, the raffinose coating system had significantly less gloss fade than other WPI-sucrose coatings. This information can be used to improve the effectiveness of water-based high-gloss edible coatings.     

The Stability of Poly(lactic acid) Packaging Films as Influenced by Humidity and Temperature

The effect of moisture sorption on stability of poly(lactic acid) (PLA) films at food‐packaging conditions, obtained by different humidities (11% to 98% RH) and temperatures (5 °C and 25 °C), was investigated by decrease in number average molecular weight (M_n) and loss of tensile strength. Hydrolysis of the PLA ester linkages resulted in a 75% decrease over 130 d at 25 °C and 98% RH. At cooling conditions the decrease amounted to 35%. An equilibrium moisture sorption isotherm could not be determined as the irreversible hydrolysis of PLA induced an ongoing moisture uptake. The rate increased when the humidity and temperature increased from 5 °C to 25 °C. After 189 d at 98% RH, moisture sorption was 7 g/100 g and 86 g/100 g at 5 °C and 25 °C, respectively. Loss of tensile strength was minor and primarily due to reversible plastization by moisture. Only at 98% RH and 25 °C, loss of tensile strength became pronounced (45%). Consequently, the present PLA material is in general expected to be mechanically stable when packaging foods covering the region from dry to moist food and storage conditions from chill to ambient temperatures.     

Effects of anticaking agents and storage conditions on the moisture sorption,caking, and flowability of deliquescent ingredients

Deliquescent highly soluble crystalline ingredients are prone to caking and dissolution when they are stored above a certain relative humidity (RH) but exhibit minimal moisture adsorption below this RH. Anticaking agents are added to improve the flowability of powders and to prevent or reduce caking. The objective of this study was to determine the effects of anticaking agents on the moisture sorption behavior, flowability, and caking characteristics of deliquescent ingredients and blends thereof. Single deliquescent food ingredients (sodium chloride, sucrose, fructose, and citric acid) and binary systems (sodium chloride blended with sucrose, fructose, or citric acid) were used as the host powders, and silicon dioxide, calcium silicate, and calcium stearate were the three anticaking agents studied. Moisture sorption isotherms were generated to investigate the water–solid interactions of the anticaking and host powders. Following controlled RH storage treatments, caking was assessed by the sieve test and flowability by avalanche power and avalanche angle measurements. Formulation had variable effects on deliquescence behavior and moisture sorption, while formulation, storage RH, length of storage, and RH cycling all significantly affected the physical stability of the powder blends. Calcium stearate was the most effective anticaking agent at reducing moisture sorption and delaying the onset of deliquescence, as well as maintaining the flowability properties of all powders tested. In particular, calcium stearate was able to substantially alter the moisture sorption behavior of blends of deliquescent ingredients, which are inherently more susceptible to the deleterious effects of moisture due to deliquescence lowering. The results are of great significance because they show that the effectiveness of an anticaking agent in preventing moisture-induced caking depends on the complexity of the host powders as well as on the interaction with environmental moisture. Thus, the type of anticaking agent added to a deliquescent ingredient must be tailored to the host powder to enhance product quality and stability.