Ultrasonic monitoring of lard crystallization during storage

This work addresses the use of ultrasonics as a non-destructive technique with which to monitor lard crystallization during cooling and storage. The ultrasonic velocity was measured during both the isothermal crystallization of lard (at 0, 3, 5, 7, 10 and 20 °C) and during the non-isothermal crystallization. In addition, lard crystallization was also studied through Differential Scanning Calorimetry (DSC) and instrumental texture analysis (penetration tests). The measurement of the ultrasonic velocity allowed the bulk crystallization to be detected. The evolution of the ultrasonic velocity and the textural measurements during isothermal crystallization showed two steep increases, which may be explained by the two fractions of triglycerides found in DSC thermograms. At 7, 10 and 20 °C the second fraction did not crystallize within the first 11 days of storage. A two-step crystallization model based on the Avrami model was used to properly describe (% var > 99.9 and RMSE < 1.99 m s^− 1) the relationship between the ultrasonic velocity and the isothermal crystallization time. In addition, a model was developed to estimate the percentage of solid fat content during isothermal crystallization. Therefore, it may be pointed out that ultrasonic techniques could be useful to monitor the crystallization pattern of complex fats during long periods of storage.     

PARAMETERS THAT DETERMINE TRIPALMITIN CRYSTALLIZATION IN SESAME OIL

The crystallization of tripalmitin (TP) in sesame oil (0.98, 1.80 and 2.62% w/v) was investigated under isothermal conditions using a cooling rate similar to the one achieved by industrial crystallizers (1 K/min) and utilizing a modification of the Avrami equation. It was concluded that z, the crystallization rate constant, and the associated energy of activation (Ea) values determined through Avrami's original equation yield erroneous results. Additional results indicated that the increase in supercooling at constant oil phase viscosity (e.g., 5.25–5.5 dynes/cm²) during crystallization, produced a higher degree of nucleation without an appreciable effect on TP crystal size. In contrast, as viscosity of the oil phase decreased at equal supercooling conditions (e.g., 22.0 - 22.5C) the main crystallization process evaluated through z and Ea was crystal growth. It was also concluded that the characteristic crystallization stages of induction time for nucleation, crystal nucleation and growth, and end of crystallization were evident in the viscosity profile of the solid fraction developed during TP crystallization. The predominance of any of these processes (i.e., nucleation or crystal growth) as a function of supercooling and viscosity of the oil phase determines, to a great extent, the rheological profile during crystallization and the final viscosity value of the crystal suspension.     

Crystallization kinetics of palm oil in blends with palm-based diacylglycerol

Crystallization kinetics of palm oil (PO) in the presence of different concentrations (2, 5, 10, 30 and, 50% w/w) of palm-based diacylglycerol (PB-DAG) were investigated over different ranges of crystallization temperatures. Addition of 30 and 50% (w/w) of PB-DAG (high concentrations) increased significantly (P < 0.05) the melting point and crystallization onset while addition of 2 and 5% PB-DAG did not have significant (P > 0.05) effect. PO and PO blends with 2 and 5% of PB-DAG showed crystal transformation at crystallization temperatures (T_Cr) of 26, 26, 26.5 °C, respectively as reflected in corresponding changes of the Avrami parameters at below and above these T_Cr. This was especially evident for the blends containing 2 and 5% of PB-DAG. Individual comparison of induction time (T_i), Avrami exponent (n), Avrami constant (k) and half-time of crystallization (t_1/2) of blends classified under various supercooling ranges based on the supercooling closeness (± 0.1 °C), showed that addition of 5% of PB-DAG in most of the supercooling ranges significantly (P < 0.05) reduced nucleation rate as well as crystal growth velocity of PO. This was reflected in the significantly (P < 0.05) higher T_i and t_1/2 and lower k. Although the presence of 2% of PB-DAG was found to have inhibitory effect on PO crystallization, this effect was not significant (P > 0.05). Mode of crystal growth attributed to n was changed significantly only in presence of 5% of PB-DAG. Furthermore, presence of 10% PB-DAG showed ??'-stabilizing effect on PO. On the other hand, high concentrations of PB-DAG were found to significantly (P < 0.05) reduce T_i as well as t_1/2 and also increase k suggesting their promoting effects on nucleation and crystallization rate of PO even with the close supercoolings. In addition, they changed crystal growth mode of PO. Amongst the different concentrations of PB-DAG investigated, blend containing 50% of PB-DAG as compared to PO, not only, have healthier benefits but also, may have greater potential applications in plastic fat products due to its unique physical properties.     

Avrami法研究微量司盘85对棕榈油结晶动力学的影响

采用差示扫描量热仪（differential scanning calorimetry,DSC）分析棕榈油及其与司盘85混合物的等温结晶及熔融行为,通过Hoffman-Weeks法计算出样品的平衡熔点。采用Avrami方程进一步研究样品的等温结晶动力学,从而得到与结晶动力学相关的参数。结果表明：DSC分析显示司盘85可明显降低棕榈油的结晶率和成核速率。通过Hoffman-Weeks法和Avrami方程求得的温度数据具有良好的线性关系,表明Avrami方程适用于棕榈油结晶过程的研究,但在结晶后期出现偏离。拟合得到的Avrami指数（n）在2.37～2.77之间,可知样品二维和三维晶体生长同时存在;结晶速率（k）和半结晶时间（t1/2）随着添加剂的添加均变小。     

Dynamic mathematical model of the crystallization kinetics of fats

A new model able to describe the kinetics of isothermal crystallization is presented: it is a model written in the form of a differential equation allowing use under dynamic temperature variations. It describes the crystallization process as if it is a reversible reaction with a first order forward reaction and a reverse reaction of order n. The model has the advantage of having an analytical solution under isothermal conditions that facilitates parameter estimation. The quality of this model was compared with the more traditional Avrami (with and without induction time) and Gompertz models using different model selection criteria. To show the universality of the model, different fat samples, different crystallization temperatures and different measuring techniques were used for model evaluation. The new model was selected as the best for the majority of the samples and this independent of the model selection criterion used.     

湿面老化动力学研究

利用差示量热扫描仪测定在不同储藏温度条件下(-4、15、25、35℃)的湿面老化焓,应用Avrami模型描述淀粉在回生过程中的结晶行为,研究了贮存温度对湿面淀粉老化速率和淀粉结晶成核方式的影响。通过对模型线性回归后得到结晶速率常数k和Avrami指数n。结果表明,在本实验贮存温度区间内,湿面淀粉的老化结晶速率k随着贮存温度的升高而逐渐减小;在-4～15℃的贮存温度区间内,Avrami指数n均小于1,表明其结晶方式是瞬间成核,在25～35℃区间内,1相似文献   

Rates of Crystallization of Dried Lactose-sucrose Mixtures

The isothermal crystallization kinetics of glassy lactose/sucrose mixtures were studied at several storage temperatures (close to T_g and T_m). The kinetic parameters implicit in the Avrami equation were determined. Activation energies for transport (E_D) and surface nucleation (W*) were also found and correlated to the molar composition of the lactose/sucrose mixtures. A monotonic increase in the half crystallization time (t_1/z), Avrami index (n), % crystallization per day, activation energy for transport (E_D) and surface nucleation energy (W*) and a decrease in the crystallization velocity constants (K) were related to the increase in the lactose content of lactose/sucrose mixtures.     

Crystallization Kinetics of Amorphous Lactose as a Function of Moisture Content Using Isothermal Differential Scanning Calorimetry

Isothermal differential scanning calorimetry (DSC) was used to study the crystallization kinetics of amorphous lactose at 3 moisture contents. Each sample was heated to several temperatures between Tg and Tm. 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 crystallization rates between Tg and Tm. The highest Tm/Tg ratio and crystallization rate were observed for the sample containing the most moisture. Conversely the lowest Tm/Tg ratio and crystallization rate were observed for the sample containing the least moisture. Evidence for multiple transitions was seen. The Avrami equation may not be the best way to model such data.     

Influence of chemical interesterification on thermal behavior,microstructure, polymorphism and crystallization properties of canola oil and fully hydrogenated cottonseed oil blends

This work evaluated chemical interesterification of canola oil (CaO) and fully hydrogenated cottonseed oil (FHCSO) blends, with 20%, 25%, 30%, 35% and 40% (w/w) FHCSO content. Interesterification produced reduction of trisaturated and increase in monounsaturated and diunsaturated triacylglycerols contents, which caused important changes in temperatures and enthalpies associated with the crystallization and melting thermograms. It was verified reduction in medium crystal diameter in all blends, in addition crystal morphology modification. Crystallization kinetics revealed that crystal formation induction period and maximum solid fat content were altered according to FHCSO content in original blends and as a result of random rearrangement. Changes in Avrami constant (k) and exponent (n) indicated, respectively, that interesterification decreased crystallization rates and altered crystalline morphology. However, X-ray diffraction analyses showed randomization did not change the original crystalline polymorphism. The original and interesterified blends had significant predominance of β′ polymorph, which is interesting for several food applications.     

新型长碳链聚酰胺1211的非等温结晶动力学

针对聚合物力学性能受微观晶型结构影响的问题, 采用一步聚合法制备了聚酰胺1211, 通过调节聚酰胺1211 的微观晶型结构来调控其力学性能。借助差示扫描量热仪对聚酰胺1211 进行非等温结晶研究, 表征其在非等温情况下晶型变化方式, 分别用Jeziorny 法和莫志深法修正的Avrami 方程分析聚酰胺1211 的非等温结晶行为。结果表明:通过Jeziorny 法修正后的Avrami 方程处理时,其非等温结晶过程由2 个阶段组成, 在主结晶期阶段Avrami 指数为2. 51 ~3. 22, 晶体为二维盘状方式生长, 在次结晶期阶段指数为0. 99 ~2. 14, 晶体为一维纤维状方式生长; 用莫志深法修正的Avrami 方程得到冷却速率值为14. 91 ~37. 57; 利用Kissinger 方法求得聚酰胺1211 非等温结晶的结晶活化能为-115 kJ/ mol。     

糙米重组米的回生特性

采用差示扫描量热仪和质构仪研究了糙米重组米的Avrami方程及硬度,探讨了糙米重组米的回生特性。结果表明：糙米重组米的Avrami参数n值均小于1,以一次成核的方式结晶;糙米重组米淀粉中的直链淀粉含量对Avrami参数n有非常显著的影响,对支链淀粉的最大回生度没有显著的影响;参数n和结晶速率k之间成极显著负相关;最大回生度与结晶速率k成显著负相关;硬度可以有效地反映出糙米重组米的回生程度。     

Enzymatic interesterification of tripalmitin with vegetable oil blends for formulation of caprine milk infant formula analogs

The structure of triacylglycerols in vegetable oil blends was enzymatically modified, and the blends were incorporated into skim caprine milk to produce goat milk-based infant formula analogs, homologous to human milk. A modified lipid containing palmitic, oleic, and linoleic acids, resembling the composition of human milk fat, was synthesized by enzymatic interesterification reactions between tripalmitin and a vegetable oil blend containing a 2.5:1.1:0.8 ratio of coconut, safflower, and soybean oils. A commercial sn-1,3-specific lipase obtained from Rhyzomucor miehei, Lipozyme RM IM, was used as the biocatalyst. The effects of substrate molar ratio and reaction time on the incorporation of palmitic, oleic, and linoleic acids at the sn-2 position of the triacylglycerols were investigated. The fatty acid composition and sn-2 position of the experimental formulas were analyzed using gas chromatography. Results showed that the highest incorporation of palmitic acid was obtained at 12 h of incubation at 55°C with a substrate molar ratio of 1:0.4 of tripalmitin to vegetable oil blend. However, the modified milk interesterified for 12 h at a 1:1 molar ratio had a greater resemblance to human milk compared with the other formulas. The level of oleic acid incorporation at the sn-2 position increased with the molar ratio of tripalmitin to vegetable oil blend. It was concluded that, unlike the original goat milk and other formulas, the formulated caprine milk with a molar ratio of 1:1 and a 12-h incubation was similar to the fatty acid composition of human milk.     

Artificial neural network and mathematical modeling comparative analysis of nonisothermal diffusion of moisture in wood

The objective of this study was to develop an optimum artificial neural network (ANN) capable of predicting the direction and magnitude of the moisture flux through wood under nonisothermal steady-state diffusion. A comparison between experimental measurements and the predicted values of three mathematical models reported in the literature and of the proposed neural network is presented and discussed. When developing the ANN model, several configurations were evaluated. The optimal ANN model was found to be a network with six neurons in one hidden layer. This well-trained network correlated the forecasted to the experimental data with low-level errors compared to previously developed models and also predicted the flux-reversal phenomenon thus confirming that ANN modeling has a much better predictive performance. It was also shown that the numbers of the training data were linked to the performance of the network during estimation. However, the powerful predictive capacity of this modeling method was still supported although a limited experimental data set was trained.     

玉木耳多糖对杂粮粥糊化、流变及老化特性的影响

以糯玉米、燕麦、小米、红豆、绿豆、芸豆为原料,玉木耳多糖为稳定剂,研制一款罐装杂粮粥.通过快速黏度分析仪、流变仪、差示扫描量热仪结合Avrami模型对杂粮粥进行测定分析,研究玉木耳多糖对杂粮粥加工过程中糊化特性、流变特性和贮藏期间老化特性的影响.结果 表明:玉木耳多糖添加量与杂粮粥体系峰值黏度、最终黏度呈正相关,与回生...     

Mutual effect of fat and β-carotene on fat crystal network structure and carotenoid bleaching

In this study the mutual effect of fat type and β-carotene on fat crystallization behavior and carotenoid bleaching was investigated. To this aim, β-carotene was added to tripalmitin (PPP), tristearin (SSS) and saturated monoglycerides (MG). Phase transition properties of fats with and without β-carotene were studied by differential scanning calorimetry, synchrotron X-ray diffraction and polarized light microscopy. The color fading of β-carotene containing fat matrices was followed by measuring color changes during storage at 20 °C.Structural information acquired at different length scales highlighted that the presence of β-carotene in fats greatly affected crystal morphology, crystal network structure and thermal properties of the lipid matrices. Depending on fats molecular characteristics, β-carotene participated (PPP and SSS) or withdrew (MG) from the fat crystallization. The presence of β-carotene probably altered the triacylglycerol crystal morphology through its incorporation into the solid phase. Contrarily, β-carotene formed clusters inside the solid matrix when added to MG. Results appear of considerable interest in the attempt to improve the stability of β-carotene in lipid containing foods as well as to design efficient delivery systems, for which the choice of the lipid carrier could be crucial. In fact, preliminary results showed that the kinetics of β-carotene bleaching were higher in PPP and SSS than in MG, suggesting that β-carotene location inside the crystal network as well as lipid structure organization might affect the carotenoid chemical stability.     

米饭回生研究（Ⅱ）米饭回生动力学

回生动力学研究在淀粉及谷物食品的贮存保鲜方面具有重要意义。Avrami模型可用于描述淀粉回生过程中的结晶行为,通过对模型参数k（结晶速率常数）和n(Avrami指数）的确定与分析,可以了解在结晶过程中直链及支链淀粉分子对晶体的成核方式、晶核密度和晶体生长方式的影响。在此基础上,本文研究了含水量对米粉糊及米饭回生速率的影响。结果表明在实验范围内,体系中含水量的减少主要是通过提高瞬时成核的强度（使n降低）和提高晶核密度（使k提高）来提高淀粉回生速率的。     

Thermal,structural and rheological characteristics of dark chocolate with different compositions

The effect of different cocoa composition of dark chocolate samples and their ingredients on their thermal, structural and rheological characteristics was investigated. Thermal behavior was evaluated by means of differential scanning calorimetry (DSC), while the crystal morphology was observed by polarized light optical microscopy. The rheological measurements were carried out using both continuous and oscillatory experiments. The formation of more stable polymorphic structures was time and temperature dependent; and it was not affected by either cocoa composition or particle sizes. The kinetics of crystallization was determined by a step crystallization method and modeled by the Avrami equation, it was accelerated by solid particles concentration, lower particle size and lower crystallization temperatures. Negative spherulites with featherlike microstructures defined the time dependent crystal growth and were consistent with Avrami indexes of 3–4. Under continuous shear, cocoa butter was well described by the Bingham rheological model, while Casson and Carreau equations modeled the flow of cocoa liquor and chocolate samples. However the Carreau model was preferred for presenting better fittings and for predicting apparent viscosities at low and at high shear rates. From both, continuous and oscillatory experiments, it was found that composition of chocolate samples in terms of fat and nonfat cocoa solids, and sugar content, affected their rheological behavior. The solid liquid transition of chocolate samples and cocoa liquor was obtained at a yield stress of around 1 Pa from both continuous and oscillatory shear experiments.     

EFFECT OF SALTING AND SMOKING METHOD ON THE STABILITY OF LIPID AND MICROBIOLOGICAL QUALITY OF NILE PERCH (Lates niloticus)

Nile perch fillets treated with two brine concentrations (250g/L and 80g/L) and smoked by two different methods (hot and cold smoking) were stored at 2C for a period of three weeks. The rate of lipid oxidation during storage was observed to be a function of brine concentration and method of smoking. Lipids were more stable in cold than hot smoked fillet. Total phenolic compounds were inversely correlated with the degree of lipid oxidation. The strength of brine affected the bacterial profile of the stored fish; temperature affected both bacterial growth and lipid oxidation during storage.     

Influence of a commercial monoacylglycerol on the crystallization mechanism of palm oil as compared to its pure constituents

The effect of a commercial monoacylglycerol (MAG), Myverol™ 18 04-PK (Myverol), on the non-isothermal crystallization mechanism of palm oil (PO) was investigated and compared to the effect of the two main constituents of Myverol, monopalmitin and monostearin. The MAGs were added to PO in concentrations up to 8% and the blends were studied using different techniques (differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarized light microscopy (PLM)). The DSC crystallization profiles revealed an earlier onset of crystallization along with extra crystallization peaks when MAGs were added to PO. Combined with X-ray results, it could be concluded that the crystallization process of the blends is initiated by the MAGs crystallizing in the α form and then transforming to sub-α. The effect on the non-isothermal crystallization of the PO TAGs is confined to an earlier onset of crystallization, probably through a template effect, and an effect on the crystal structure coarseness.     

司盘85对棕榈油结晶过程动力学的影响分析

采用核磁共振仪测定棕榈油及添加0.01%~0.1%司盘85棕榈油的等温结晶行为。采用Avrami方程进一步探究样品的等温结晶动力学,研究司盘85对棕榈油结晶行为的影响。结果表明:棕榈油及添加0.01%~0.1%司盘85棕榈油的Avrami指数在1.422~1.912之间,可知样品的晶体生长为二维;司盘85对棕榈油的结晶过程具有抑制作用,且随着司盘85添加量的增大,其抑制作用增强,表现为结晶速率常数减小,半结晶时间延长。