Effect of biopolymers on structure and ice recrystallization in dynamically frozen ice cream model systems

Ice crystal growth and microstructure of sugarsolutions prepared with stabilizers (carboxymethyl cellulose [CMC], xanthan gum, locust bean gum [LBG], and gelatin) with or without milk solids-nonfat (MSNF) after freezing in a scraped surface heat exchanger and temperature cycling (5 cycles from -6 degrees C to -20 degrees C) were studied. Ice crystal growth was calculated from brightfield microscopic images acquired from samples before and after cycling. Freeze-substitution and low-temperature embedding (LR-Gold resin) were sample preparation techniques utilized for structure analyses by light microscopy and transmission electron microscopy. Differential staining for carbohydrates and proteins allowed the identification of stabilizer gel-like structures in LBG, gelatin, and gelatin/MSNF solutions. In the absence of milk proteins, xanthan and LBG were the most effective at retarding recrystallization, while in their presence, only xanthan had an effect. Cryo-gelation of the LBG was observed but is not the only mechanism of stabilizer action. Thermodynamic incompatibility between biopolymers was observed to promote localized high concentrations of milk proteins located at the ice crystal interface, probably exerting a water-holding action that significantly enhanced the stabilizer effect. Qualitatively, solution heterogeneity (phase separation) was directly proportional to ice crystal growth inhibition. It is suggested that water-holding by stabilizer and proteins, and in some cases steric hindrance induced by a stabilizer gel-like network, caused a reduction in the kinetics of the ice recrystallization phenomena and promoted mechanisms of melt-regrow instead of melt-diffuse-grow recrystallization, thus resulting in the preservation of the ice crystal size and in a small span of the ice crystal size distribution.     

刺槐豆胶/瓜尔豆胶复合体系的流变学性质研究

研究刺槐豆胶(LBG)/瓜尔豆胶(GG)复合体系的流变学性质,并采用流变学的模型进行拟合分析。实验表明:BG/GG复合体系为非牛顿流体,流动曲线服从Carreau模型,随着LBG比例的增大,其粘度越小,非牛顿性越不明显,触变性越低。LBG与GG复配对粘度的影响可产生协同作用,LBG/GG=1∶9时,复合体系粘度最大。在频率扫描范围内,LBG/GG复合体系同时具有粘性和弹性,随不同的角频率处理展现不同的动态粘弹性行为,LBG/GG=1∶9时,复合体系的动弹粘弹性最大。      

Viscosity of galactomannans during high temperature processing: influence of degradation and solubilisation

The rheological properties of guar gum (GG) and locust bean gum (LBG), in response to high temperature treatments, were measured using a rheometer equipped with a high pressure cell. This has allowed the viscosity to be assessed at temperatures above 100°C and as the polymer suspension is heated from 20 to 121°C and then cooled back to ambient temperature to simulate a food sterilisation cycle. Activation energies for depolymerisation estimated from viscosity changes with time at a series of constant temperatures were estimated as 63 kJ/mol for GG and 98, 104, 110 kJ/mol for three different samples of LBG. A model was developed to interpret the viscosity change through the simulated sterilisation cycle. This took into account the degradation of the polysaccharide and the change in viscosity due to thermal motion. Estimations of molecular weight changes during the heating process suggest that GG is more susceptible to thermal degradation than LBG. It is suggested that this is due to the greater ability of the latter to associate in solution.     

Recrystallization in Aqueous Fructose Solutions as Affected by Locust Bean Gum

Rates of ice recrystallization were measured in aqueous fructose solutions containing locust bean gum (LBG). The effects of temperature, ice phase volume and LBG concentration were determined. Decreasing temperature reduced the recrystallization rate: the dependency followed Williams Landell Ferry kinetics. An increase in ice phase volume resulted in an increase in the recrystallization rate. Addition of LBG reduced the recrystallization rate up to a concentration of 0.3% (w/w); further addition resulted in no further decrease. The hypothesized mechanism of action of LBG is via weak adsorption of the polysaccharide to the ice crystal. Freeze concentrated solution viscosity did not correlate with observed recrystallization rates.     

Rheological characterization of experimental dairy creams formulated with locust bean gum (LBG) and λ-carrageenan combinations

The influence of the locust bean gum (LBG)–λ-carrageenan stabilizer combination on the rheology of dairy creams was analyzed. A central composite factorial design was used to choose the LBG–λ-carrageenan ratio, the weight fraction of each gum ranging from 0 to 0.1 g per 100 g cream. Cross’ rheological model was closely fitted to describe the flow curves of the samples and Cross parameters were correlated with gum concentrations. The rheological behaviour of model aqueous gum solutions, with the same pH, ionic strength, and competitive solute concentration as the cream serum, was also examined to analyze gum interactions. Strong interaction of λ-carrageenan with cream components, probably with caseins, may be anticipated based on a great increase in viscosity. The functional role of LBG seems to be associated with an increase in the emulsion shear stability.     

Effects of Locust Bean Gum and Mono‐ and Diglyceride Concentrations on Particle Size and Melting Rates of Ice Cream

The objective of this study was to determine how varying concentrations of the stabilizer, locust bean gum (LBG), and different levels of the emulsifier, mono‐ and diglycerides (MDGs), influenced fat aggregation and melting characteristics of ice cream. Ice creams were made containing MDGs and LBG singly and in combination at concentrations ranging between 0.0% to 0.14% and 0.0% to 0.23%, respectively. Particle size analysis, conducted on both the mixes and ice cream, and melting rate testing on the ice cream were used to determine fat aggregation. No significant differences (P < 0.05) were found between particle size values for experimental ice cream mixes. However, higher concentrations of both LBG and MDG in the ice creams resulted in values that were larger than the control. This study also found an increase in the particle size values when MDG levels were held constant and LBG amounts were increased in the ice cream. Ice creams with higher concentrations of MDG and LBG together had the greatest difference in the rate of melting than the control. The melting rate decreased with increasing LBG concentrations at constant MDG levels. These results illustrated that fat aggregation may not only be affected by emulsifiers, but that stabilizers may play a role in contributing to the destabilization of fat globules.     

THE INFLUENCE OF DIFFERENT TOTAL SOLID, STABILIZER AND OVERRUN LEVELS IN INDUSTRIAL ICE CREAM PRODUCTION USING COCONUT OIL

The purpose of this research was to explain the combined effects of different total solid (TS) contents (20, 30 and 40%), stabilizer types (guar gum [GG], locust bean gum [LBG], carboxymethyl cellulose [CMC]) and overrun rates (OR) (30, 60 and 90%) on mix viscosity, melting time and hardness properties, which are the most important quality characteristics on industrial ice cream production. According to the investigation parameters; GG gave significantly less viscosity to the mix than LBG and CMC. In other words, LBG and CMC may be preferred to increase the viscosity of the mix or to limit the growth rate of ice crystals during recrystallization. Softness of ice creams and melting rapidity were linearly proportional to the increase of TS and ORs.

PRACTICAL APPLICATIONS

The most important parameters affected ice cream structure and quality are total solid, overrun and stabilizers. In many researches, the investigators have been focused of these parameters on only one or rarely two. In this research, the combined effects of different total solids (20, 30 and 40%), stabilizer types (guar gum, locust bean gum, carboxymethyl cellulose) and overrun levels (30, 60 and 90%) were investigated together in same mix and in industrial production conditions.     

LINEAR AND NONLINEAR VISCOELASTIC BEHAVIOR OF OIL-IN-WATER EMULSIONS STABILIZED WITH POLYSACCHARIDES

The rheological behavior and stability of oil-in-water emulsions stabilized by different thickening agents were analyzed. Food emulsions were prepared with commercial sunflower oil (40% w/w oil-in-water) and stabilized with 1% emulsifier. The tested thickeners were: (1) 1% w/w xanthan gum (XG), (2) 5% w/w potato starch (PS), (3) 5% PS + 0.5% XG, (4) 1% w/w guar gum (GG), and (5) 0.5% XG + 0.5% GG. Mean droplet size and droplet size distribution (DSD) of emulsions were determined by static light scattering. Steady flow (viscosity versus shear rate), transient flow (viscosity versus time) and oscillatory shear tests (linear viscoelasticity) were performed. The addition of thickening agents improved the stability of the emulsions, the effect was less marked in systems containing only GG. DSD was not significantly modified in emulsions containing starch or hydrocolloids. Microscopic observations showed that all the tested emulsions were flocculated due to the presence of hydrocolloids. The observed shear thinning behavior was attributed to the molecular structure of the polysaccharides and to the flocculation/deflocculation process; viscosity data were satisfactorily fitted to the Cross model. Frequency sweeps showed that emulsions with PS or XG have a weak gel structural network (G' > G); those with GG correspond to a polymeric solution where G' and G" curves intersect within the range of tested frequencies. The viscoelastic linear behavior was described according to the Maxwell generalized model. The discrete relaxation spectrum and relaxation times were estimated from the experimental values of G' and G" for emulsions with PS, PS + XG, and XG. Nonlinear viscoelasticity was also studied from stress relaxation curves at different shear strains. The damping function was calculated and the Soskey-Winter parameters were determined. Transient flow viscosities at different shear rates were comparable to the values estimated from stress relaxation measurements.     

Droplet characterization and stability of soybean oil/palm kernel olein O/W emulsions with the presence of selected polysaccharides

Droplet characteristics, flow properties and stability of egg yolk-stabilized oil-in-water (O/W) emulsions as affected by the presence of xanthan gum (XG), carboxymethyl cellulose (CMC), guar gum (GG), locust bean gum (LBG) and gum Arabic (AG) were studied. The dispersed phase (40%) of the emulsions was based on soybean oil/palm kernel olein blend (70:30) that partially crystallized during extended storage at 5 °C. In freshly prepared emulsions, the presence of XG, CMC, GG and LBG had significantly decreased the droplet mean diameters. XG, LBG, GG and CMC emulsions exhibited a shear-thinning behavior but AG emulsion exhibited a Bingham plastic behavior and control (without gum) emulsion almost exhibited a Newtonian behavior. Both control and AG emulsions exhibited a severe phase separation after storage (30 days, 5 °C). The microstructure of stored XG emulsion showed the presence of partially coalesced droplets, explaining a large increase in its droplet mean diameters. Increases in droplet mean diameters and decreases in flow properties found for stored GG and LBG emulsions were attributed to droplet coalescence. Nevertheless, the occurrence of droplet coalescence in these emulsions was considered to be small as no free oil could be separated under centrifugation force. Increases in flow properties and excellent stability towards phase separation found for stored CMC emulsion suggested that CMC could retard partial coalescence. Thus, the results support the ability of CMC, GG and LBG in reducing partial coalescence either by providing a sufficiently thick continuous phase or by acting as a protective coating for oil droplets.     

Effect of Some Stabilizers on Textural and Sensory Characteristics of Yogurt Ice Cream from Sheep's Milk

Yogurt ice cream made of 6.5% sheep's milk fat and 11.5% of nonfat milk solids (MSNF) derived by 83% from sheeps milk contained decreased lactose and increased protein by approximately 20% and 25%, respectively, compared to the conventional product from cow's milk. Acidity of the final product was from pH 4.4 to 4.9. Stabilizers that were tried were xanthan gum, guar gum and a commercial stabilizer at concentrations 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5%. Based on determinations of physical qualities as well as on the sensory evaluation of the yogurt ice cream, xanthan gum gave optimum results at 0.2% concentration, guar gum at 0.3% while the commercial stabilizer was partially satisfactory up to 0.5% concentration.     

Recrystallization in Ice Cream as Affected by Stabilizers

Addition of locust bean gum (LBG) or guar gum to ice cream mixes gave products with smaller ice crystals after heatshock than control samples without either stabilizer. LBG was more effective at inhibiting recrystallization than guar. Increasing stabilizer concentration resulted in greater inhibition. With LBG we found some evidence for an optimum concentration above which no further inhibition occurred. We found no evidence for phase volume effects.     

The Effects of Fat Structures and Ice Cream Mix Viscosity on Physical and Sensory Properties of Ice Cream

The purpose of this work was to investigate iciness perception and other sensory textural attributes of ice cream due to ice and fat structures and mix viscosity. Two studies were carried out varying processing conditions and mix formulation. In the 1st study, ice creams were collected at ?3, ?5, and ?7.5 °C draw temperatures. These ice creams contained 0%, 0.1%, or 0.2% emulsifier, an 80:20 blend of mono‐ and diglycerides: polysorbate 80. In the 2nd study, ice creams were collected at ?3 °C draw temperature and contained 0%, 0.2%, or 0.4% stabilizer, a blend of guar gum, locust bean gum, and carrageenan. Multiple linear regressions were used to determine relationships between ice crystal size, destabilized fat, and sensory iciness. In the ice and fat structure study, an inverse correlation was found between fat destabilization and sensory iciness. Ice creams with no difference in ice crystal size were perceived to be less icy with increasing amounts of destabilized fat. Destabilized fat correlated inversely with drip‐through rate and sensory greasiness. In the ice cream mix viscosity study, an inverse correlation was found between mix viscosity and sensory iciness. Ice creams with no difference in ice crystal size were perceived to be less icy when formulated with higher mix viscosity. A positive correlation was found between mix viscosity and sensory greasiness. These results indicate that fat structures and mix viscosity have significant effects on ice cream microstructure and sensory texture including the reduction of iciness perception.     

冰淇淋复合乳化稳定剂流变特性及其应用的研究

本通过对不同溶液表观粘度的测定,研究了冰淇淋用原辅料的流变特性,表明了混合料粘度是控制冰淇淋质量的重要参考指标,并通过对不同复合肥化稳定剂配方所生产的冰淇淋样品的品质检验,发现在主要成分保持一致（含脂量10％,非脂乳固体含量10％,糖含量15％）的情况下,改变乳化稳定剂的配方,可得到不同的产品特点,其中最佳复合乳化稳定剂的配方为：瓜尔事前交0．2％;CMC0．1％;蒸馏单甘脂0．1％;蔗糖酯0．1％。     

黄原胶和瓜尔豆胶的复配稳定剂对冰淇淋品质和流变性的影响

研究了黄原胶和瓜尔豆胶的复配胶作为冰淇淋稳定剂对冰淇淋品质和流变性的影响,测定了冰淇淋浆料的粘度,应用小幅振荡测定经硬化后冰淇淋成品的动态粘弹性,以及硬化冰淇淋的硬度和粘结度.结果表明,随复配胶用量的增加,冰淇淋浆料的粘度也随之增加,另外,Power law模型的流动指数和粘度指数、冰淇淋成品储能模量、及硬度、粘结度均呈增加趋势.实验结果还表明,随复配胶用量的增加,冰淇淋的弹性模量和稳定性得以提高.通过测定冰淇淋的膨胀率和抗融性,得出冰淇淋中复配胶的最佳添加量质量分数为0.35%.     

Application of decolourised hsian‐tsao leaf gum to low‐fat salad dressing model emulsions: a rheological study

The effects of mixed gums, including decolourised hsian‐tsao leaf gum (dHG) mixed with propylene glycol alginate (PGA) or xanthan gum (XG), and egg yolk concentration on the rheological properties of low‐fat salad dressing model emulsions were studied. All model emulsions showed pseudoplastic flow behaviour. Model emulsions with PGA addition showed the lowest pseudoplasticity, followed by those with dHG and then XG addition. Increasing the PGA level in the dHG/PGA system reduced the pseudoplasticity. Increasing the XG level in the dHG/XG system did not change the pseudoplasticity significantly but imparted a significant increase in viscosity. Dynamic viscoelasticity measurements indicated that model emulsions with dHG or XG addition could be classified as elastic gels. However, model emulsions with PGA addition essentially belonged to the class of either dilute or concentrated solutions rheologically, depending on the egg yolk concentration. The rheological characteristics of individual gums were found to be confounded in generating the rheological characteristics of model emulsions containing them. Copyright © 2004 Society of Chemical Industry     

琼脂-刺槐豆胶协同作用及其凝胶骨架材料缓释性能

对由琼脂与刺槐豆胶组成的复合胶液进行了流变性能,旋光性能测试,对其形成的凝胶进行了力学性能与负载盐酸二甲双胍药物的缓释性能测试。测试结果表明:随着复合胶液温度的降低,琼脂分子与刺槐豆胶分子发生了相互作用;随着复合胶液中刺槐豆胶含量的增加,复合胶液的表观黏度明显增大,温度降低过程中表观黏度突增时温度点移向高温区;复合胶液的旋光度值在降温过程中明显增大;复合凝胶的硬度、耐咀性明显降低,内聚性增大,凝胶骨架结构网孔更加致密细小,药物突释现象减弱,药物缓释效果更加明显。其中样品25/75(琼/刺)效果最佳,5h达到最大溶胀率,溶胀过程吸水率可达22倍,其载药率为16.59%,载药样品的缓释过程符合一级动力学模型,T50时间为88min,整个缓释过程可持续5h以上。     

Phase separation in soft-serve ice cream mixes: rheology and microstructure

Soft-serve ice cream mixes containing 4% milk protein and 0.14% locust bean gum (LBG) showed extensive visual phase-separation after 21 days at 5 °C, unless κ-carrageenan was added to the formulation. Addition of κ-carrageenan (0–0.02%) did not inhibit microscopic phase separation between protein and polysaccharide. A higher degree of “emulsification” of the protein-enriched phase into the continuous serum phase was observed as the κ-carrageenan concentration increased, which correlated with inhibition of macroscopic serum separation in the mix. After macroscopic separation, the serum phase of mixes with different κ-carrageenan concentrations showed similar microstructural and rheological characteristics, implying no concentration of LBG and no presence of κ-carrageenan in the serum phase. The rheological behaviour of the protein-enriched phases indicated κ-carrageenan/casein interactions. There was no evidence of “weak-gel” formation through the addition of κ-carrageenan as a means for macroscopic stability in the system.     

Optimising the ice cream formulation using basil seed gum (Ocimum basilicum L.) as a novel stabiliser to deliver improved processing quality

Mixture design was used to determine the optimum ratio as well as concentration of basil seed gum (BSG), guar gum (GG) and carboxymethyl cellulose (CMC) in the formulation of ice cream stabilisers. Predicted equations and contour plots of physicochemical responses were also generated. Generally, increasing the ratio of BSG in gums mixture increased the apparent viscosity of ice cream mixes and decreased the melting rate. Increasing the proportion of GG at concentration of 0.35% enhanced overrun of samples. High ratios of BSG at concentration of 0.35% and CMC at concentration of 0.15% increased the fat destabilisation in ice creams. Combination of 84.31% BSG and 15.69% CMC at concentration of 0.35% proposed as optimum formulation which verified in practice. Introducing BSG as a novel source of stabiliser could be promising as alternative and improve the quality and diversity of ice cream and related products.     

Effects of xanthan and galactomannan on the freeze/thaw properties of starch gels

Three starches (maize, rice and wheat), and the two non-starch polysaccharides xanthan and locust bean gum galactomannan (LBG) were examined in gel and dough systems for texture and stability properties during freezing and low temperature storage. Xanthan and LBG were found to confer increased resistance to freeze/thaw cycling on rice starch gels but the non-starch polysaccharides had little effect on the performance of maize and wheat starch gels or on wheat dough.     

STRUCTURAL DEVELOPMENT IN ICE CREAM—DYNAMIC RHEOLOGICAL MEASUREMENTS

The influences of temperature, polysaccharide stabilizing agents and overrun on the rheological properties of ice cream mix and ice cream were measured using dynamic rheological techniques with a controlled stress rheometer. Storage and loss moduli and tan δ all decreased significantly with increasing temperature. Unstabilized samples demonstrated significantly greater storage and loss moduli at temperatures < –8C and tan δ at all temperatures than stabilized samples, however, polysaccharides increased mix viscosity and resulted in significant increases in viscosity as the mix was concentrated. This indicated the importance of considering both ice and unfrozen phases in determining the impact of stabilizers on ice cream rheology. Increasing overrun from 20 to 60% increased the storage modulus significantly but had less effect on the loss modulus, especially in the stabilized samples. However, as overrun increased, the maximum force required for large deformation decreased, emphasizing the need to consider the effects of small-scale versus large-scale deformation testing on structure. Dynamic rheological measurements can provide insights into the development of ice cream structure and are useful in complementing other techniques.