Effect of protein on sorption characteristics of delactosed permeate

The effects of whey protein isolate (WPI) were investigated on the characteristics of delactosed permeate (DLP) (moisture adsorption/desorption kinetics and glass transition temperature (T_g)) that reflect on the drying ability and shelf stability. The Peleg model showed a good fit to the moisture adsorption/desorption data for the DLP-protein samples. An increase in the protein concentration resulted in a decrease in the initial adsorption rate and adsorption capacity. However, its effect on extent of desorption in DLP-protein mixtures was not significant. T_g increased with an increase in protein concentration. Significant relationships were observed between the Peleg constants for adsorption/desorption kinetics and T_g for the DLP-protein mixtures.     

The effect of delactosed whey permeate on phytochemical content of canned tomatoes

The effect of delactosed whey permeate (DWP) treatment on antioxidant and phyto-chemical components of canned Irish plum tomatoes were investigated. Tomatoes were sterilised for 5 min (F₀) at 120 °C and stored for 6 months. The DWP treatment retained significantly (p < 0.05) higher levels of ascorbic acid and lycopene of tomatoes. The antioxidant activity of DWP treated tomatoes was higher (7%) than the control at the end of storage. The firmness in DWP-treated fruits was around 40% higher than that in control. All the parameters decreased significantly (p < 0.05) during storage except lycopene and total phenols. Lycopene content showed no significant change and total phenols increased during storage. The changes in ascorbic acid, antioxidant activity and texture were fitted well to Weibull kinetic models with high coefficients of determination (R²) and low RMSE (root mean sum of squared error). The results clearly indicate that DWP enhanced the retention of antioxidant compounds in tomatoes during storage.     

Recovery of lactose from simulated delactosed whey permeate by a low-temperature crystallization process

Delactosed whey permeate is the mother liquor/by-product of lactose manufacture, but it still contains around 20 wt% lactose. The high mineral content, stickiness, and hygroscopic behavior prevent further recovery of lactose in the manufacturing process. Therefore, its use is currently limited to low-value applications such as cattle feed, and more often it is seen as waste. This study investigates a new separation technique operating at sub-zero conditions. At low temperature, precipitation of calcium phosphate is expected to be reduced and the lower solubility at sub-zero temperature makes it possible to recover a large portion of the lactose. We found that lactose could be crystallized at sub-zero conditions. The crystals had a tomahawk morphology and an average size of 23 and 31 µm. In the first 24 h, the amount of calcium phosphate precipitated was limited, whereas the lactose concentration was already close to saturation. The overall rate of crystallization was increased compared with the crystals recovered from a pure lactose solution. Mutarotation was rate limiting in the pure system but it did not limit the crystallization of lactose from delactosed whey permeate. This resulted in faster crystallization; after 24 h the yield was 85%.     

The impact of delactosed whey permeate treatment on shelf‐life and antioxidant contents of strawberries

The aim of this study was to investigate the effect of delactosed whey permeate (DWP) treatment on antioxidant and physicochemical properties of strawberries. Fresh strawberries treated with 3% DWP were analysed for different quality, nutritional and microbiological markers during 10 days of storage at 5 °C. The results showed that DWP treatment significantly reduced incidences of decay (70%) and numbers of total aerobic counts (～1.4 Log₁₀ CFU g^?1) and yeast and moulds (～1.8 Log₁₀ CFU g^?1). DWP treatment also inhibited the loss of firmness (15%) and maintained significantly (P ≤ 0.05) higher levels of vitamin C, total phenols and antioxidant activity of strawberries. Sensory scores confirmed that the DWP‐treated strawberries retained a good appearance and overall quality. The aroma and colour attributes were not reduced during storage. These results suggest that DWP treatment has potential to extend the shelf‐life and maintain the quality of strawberries during storage.     

Effect of maltodextrin addition on moisture sorption properties of khoa

Khoa is a popular traditional Indian milk product. It is used as the base material for preparation of variety of popular sweetmeats. The shelf life of this product is limited due to its high water activity (> 0.96). In the present investigation, an attempt was made to lower the a_w of khoa (25.62% moisture, 31.25% fat, 18.21% protein, 3.65% total ash and 21.29% lactose) by using maltodextrin (DE‐16) as a humectant (concentration: 0, 2, 5 and 10%; wt/wt). It was observed that the desorption curves of the product exhibited a sigmoid shape corresponding to type II, typical of many foods. At higher concentrations of maltodextrin, the isotherms shifted to the left compared to control. Among the several models chosen to test the fitness of sorption data, Guggenheim, Anderson and De Boer (GAB) and modified Mizrahi models showed the best fit as indicated by the smallest percentage root mean square values. The monolayer moisture content increased with increasing maltodextrin level, the range being 2.85–3.29 and 3.03–3.81 g/100 g solids for the two models, respectively. Caurie's slope also increased from 0.38 to 0.44, whereas nonfreezable water decreased from 4.98 to 4.01% as the maltodextrin level increased from 2 to 10%. Other critical water sorption parameters such as number of adsorbed monolayers, density of sorbed water and surface area of sorption were also obtained.     

Blends of delactosed permeate and pro-cream in ice cream: Effects on physical,textural and sensory attributes

Various blends of delactosed whey permeate (DLP) and pro-cream, a by-product of microfiltration during whey protein isolate production, were made and assessed for application in ice creams as a source of protein and fat. These blends were compared with control ice cream containing nonfat dried milk (NFDM) as the primary source of protein. Textural properties of ice creams were influenced by partial replacement of NFDM with DLP-pro-cream blends. Compared with control ice cream, those containing DLP-pro-cream blends showed similar mean ice crystal size, relatively higher melt rate, and reduced fat destabilization. Melt rate (based on linear portion of melting curve) correlated well with the fat globule size distribution or extent of fat destabilization. In sensory analysis, ice creams containing the DLP-pro-cream blends (30:70 and 50:50) were slightly less accepted by panelists than the control ice cream for most of the attributes, with an off-flavor more noticeable with increasing DLP content.     

Effect of moisture sorption state on transverse dimensional changes in wood

The purpose of the study was to understand the transverse dimensional changes and corresponding anisotropicity in wood during different states of moisture sorption. Oven dried samples of Erythrina variegata, Lannea coromandelica, Gmelina arborea and Albizia chinensis were adsorbed and subsequently desorbed at constant temperature (35°C). Tangential and radial dimensional changes (swelling) were analysed with respect to relative humidity and moisture content during both the states of sorption. Dimensions in tangential direction were found to change at a relatively greater rate than in radial direction at high humidities. It was observed that transverse dimensions were more during desorption compared to adsorption at a given equilibrium moisture content. This confirms presence a second order effect of moisture sorption on dimensional movement. This effect was found to be more prominent in tangential direction compared to radial direction resulting in higher coefficient of anisotropy ( _T / _R ratio) during desorption. The magnitude of this phenomenon was found to vary from species to species.

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Einfluß der Feuchteaufnahme auf die transversale Dimensionsänderung in Holz

Zusammenfassung Ziel der Arbeit war es, die transversale Dimensionsänderung und die entsprechenden anisotropen Verhältnisse in Holz während unterschiedlicher Grade der Feuchteaufnahme zu untersuchen. Ofengetrocknete Proben von Erythrina variegata, Lannea coromandelica, Gmelina arborea und Albizia chinensis wurden bei konstanter Temperatur (35°C) einer Sorption und anschließender Desorption unterworfen. Tangentiale und radiale Dimensionsänderungen wurden analysiert im Hinblick auf die relative Feuchte und den Wassergehalt in beiden Zuständen. Bei hohen Feuchten änderten sich die tangentialen Dimensionen schneller als in radialer Richtung. Bei einer gegebenen Gleichgewichtsfeuchte war die transversale Dimensionsänderung stärker während der Desorption als während der Sorption. Dies bestätigt einen Effekt zweiter Ordnung für den Einfluss der Feuchteaufnahme auf die Dimensionsänderung. Dieser Effekt war in tangentialer Richtung vorherrschender im Vergleich zur radialen Richtung, woraus sich ein höherer Grad an Anisotropie ( _T / _R -Verhältnis) während der Desorption ergibt. Die Größe dieses Effekts variiert je nach Holzart.

     

孔隙结构和脂肪含量对饼干水分吸附特性的影响

采用动态水分吸附法研究不同孔隙率和脂肪含量的发酵饼干在25℃下的水分吸附动力学特性,基于GAB模型和无限大平板模型确定其等温吸湿曲线和有效水分扩散系数。结果表明:孔隙率对饼干平衡水分含量几乎没有影响,而随着脂肪含量的增加,饼干的平衡水分含量逐渐下降。GAB模型能成功拟合饼干的等温吸湿数据。饼干的有效水分扩散系数随含水量变化先增大而后逐渐减小,有效水分扩散系数在水分含量为10 g/100 g(干基)左右时达到最大值。初始孔隙率87%、76%和68%的最大有效水分扩散系数分别为7.8×10-10m2/s、5.6×10-10和3.4×10-10m2/s,这与水分扩散机理从以气态传输为主向以液态传输为主的转变有关。增加脂肪含量会显著降低水分扩散系数,有效水分扩散系数从最大值5.6×10-10m2/s下降到2.3×10-10m2/s。     

动态水分吸附法研究发酵饼干水分吸附特性

以发酵饼干为研究对象,采用动态水分吸附法研究发酵饼干在25℃的水分吸附等温线与水分吸附动力学特性,同时与饱和盐溶液法得到的水分吸附等温线进行对比,并基于常用的等温吸湿模型对实验数据进行拟合。结果表明:动态水分吸附仪能在更短的时间里采集更多的数据,高频率的实时数据采集能够更准确地获得食品的水分吸附动力学特性;其从水分活度适用范围和拟合精度方面来看,GAB模型拟合饼干的等温吸湿的效果最佳。与饱和盐溶液法结果相比,动态水分吸附法得到的饼干平衡含水率略低。      

Effect of drying method on the moisture sorption isotherms for Inonotus obliquus mushroom

Moisture sorption isotherms of Inonotus obliquus mushroom were studied over a selected temperature range (20-50 °C). Sigmoid sorption isotherms were observed for these samples. The sorption data were analyzed using various conventional models. The Oswin model was found to be the best model for predicting the equilibrium moisture content of mushroom in the range of water activity 0.08-0.96. The monolayer moisture content decreased as temperature increased and was affected by the drying method used. The net isosteric heat of sorption was determined using the Clausius-Clapeyron equation and the value decreased with increase in moisture content of mushroom.     

芝麻平衡水分及吸着等热研究

采用静态称重法测定了我国4个芝麻品种的平衡水分等温线,并采用CAE、修正Chung-Pfost（MCPE）、修正Halsey（MHAE）、修正Henderson（MHE）、修正Guggenheim-Anderson-deBoer（MGAB）、修正Oswin（MOE）及StrohmanYoerger（STYE）7个水分吸着方程进行拟合,指出MOE最适合描述芝麻平衡含水率（EMC）-平衡相对湿度（ERH）之间的关系,并用于计算芝麻吸着等热。在含水率<7.5%湿基,芝麻吸着等热均随含水率增大而快速减少,同一温度下的解吸等热显著高于吸附等热。在含水率7.5%以上,芝麻吸着等热随含水率增大而变化平缓,同一温度下的解吸等热趋同于吸附等热。在含水率<7.5%湿基条件下,较低温度下的芝麻吸附等热与解吸等热均高于较高温度。在含水率10%湿基的自由水点,芝麻的吸着等热（汽化热）接近纯水的潜热,约是2450kJ/kg。在测定温度10³5℃范围,黑芝麻吸着等热数值类似白芝麻吸着等热数值。计算的25℃芝麻储运绝对安全水分是6.46%,相对安全水分是6.94%。      

Modelling moisture sorption isotherms for maize flour

The sorption isotherm of food material is pertinent in the processing and storage of food products. Adsorption and desorption isotherms for maize flour were investigated using the static gravimetric method over the range of temperature (27–40 °C) and water activity (a_w) (0.10–0.80) commonly experienced in the tropical environment. The experimental data were compared with five widely recommended models in the literature for food sorption isotherms (GAB, modified GAB (MGAB), modified Oswin (MOE), modified Henderson (MHDE), and modified Chung–Pfost (MCE)). The GAB, MGAB, and MOE models were found to be acceptable in predicting the moisture sorption isotherms for maize flour. Overall, the MGAB appears to be most suitable for fitting the adsorption and desorption moisture isotherms data for the maize flour.     

Effect of temperature and initial moisture content on sorption isotherms of banana dried by tunnel drier

Sorption isotherms of intermediate moisture content (IMC) products are essential to predict shelf-life of packaged moisture-sensitive product by modelling moisture uptake during storage and distribution. The effect of temperature and initial moisture content (MC) of IMC banana on the relationship between MC and water activity were investigated. Raw bananas were dried in a tunnel dryer at 2% relative humidity (RH), 70 °C, and a 3.2 ± 0.2 m s^–1 air velocity. Drying procedure was carried out a number of times until various IMC levels were obtained (5%, 14%, 22% and 33% db for banana). Sorption isotherms of bananas were determined at 10, 20, 30 and 40 °C. The initial MC of IMC banana had no significant effect on the relationship between MC and water activity according to statistical analysis. All the sorption curves were found to be Type II. BET, GAB, modified GAB, Oswin, Halsey and modified Freundlich models were fitted to the data and it was found that the best results were obtained with a modified Freundlich equation. A secondary modified Freundlich model was built accounting for the effect of a _w and temperature on the sample MC.     

Chemical composition and nutritive value of spray dried permeate powder

Reconstituted skimmed milk (10% TS) was ultrafiltered, and the permeate was concentrated threefold by reverse osmosis and then spray dried at different temperatures (145–195° C). The drying conditions had no effect on the moisture content or the major constituents of permeate powder. The powder was mainly lactose (85%) with 6.35460% ash. A small percentage of the lactose in the permeate powder was present as a-lactose. Sodium, potassium and citrate were present in high concentrations nearly equivalent to their average percentage in skimmed milk. The calcium, magnesium and inorganic phosphorus contents of permeate powder were also determined. The thiamine, riboflavin and niacin contents of permeate powder averaged 0.445, 0.947 and 0.729 mg/100 g respectively. The drying temperatures had no effect on the vitamin contents of the powder. The permeate powder had average Fe, Zn, Mn and Cu contents of 94.7, 21.1, 3.1 and 9.5 Fg/100 g respectively.     

油菜籽平衡水分及吸着等热研究

采用静态称重法测定了我国8个油菜籽品种的平衡水分,指出修正3参数Guggenheim-Anderson-de Boer方程(MGAB)、修正Halsey(MHAE)、修正Oswin(MOE)等方程均适合描述油菜籽平衡含水量(EMC)—平衡相对湿度(ERH)之间的关系,并计算了油菜籽水分吸着(吸附／解吸)等热和安全水分值.在含水率＜12.5％湿基,油菜籽吸着等热均随含水率增加而快速减少,同一温度下的解吸等热显著高于吸附等热.在含水率12.5％以上,油菜籽吸着等热随含水率增加而变化平缓,同一温度下的解吸等热趋同于吸附等热.在含水率＜12.5％条件下,较低温度下的油菜籽吸附等热与解吸等热均高于较高温度.在含水率12.5％的自由水点,油菜籽的吸着等热接近纯水的潜在热.计算的20℃油菜籽储存绝对安全水分是8.09％,相对安全水分是8.98％.     

The prediction of moisture sorption isotherms for dairy powders

Moisture sorption isotherms were measured for whey protein isolate, high micellar casein and a milk protein concentrate powder. No temperature dependence was observed over the temperature range of 4–37 °C. At 50 °C the powders absorbed less moisture than observed at the lower temperatures. These isotherms were used to predict the isotherms for freeze-dried amorphous lactose/casein/whey protein powders. An isotherm for micellar casein was predicted using a simple additive isotherm model and was used along with isotherms for whey protein and amorphous lactose to predict moisture sorption isotherms for commercial dairy powders. Predicted isotherms compared well with measured isotherms indicating that this simple additive isotherm model is suitable for predicting moisture sorption isotherms of dairy powders. Delayed lactose crystallisation was observed in lactose/whey protein powders when compared to lactose/casein powders over the same water activity range.     

豆粕平衡水分及吸着等热研究

采用静态称重法测定了国产6个豆粕样品的平衡水分吸附/解吸等温线,并采用修正MCPE、MHAE、MHE、MGAB、MOE及STYE 6个方程进行拟合,得出MGAB、MHAE、MOE均适合描述豆粕平衡水分-平衡相对湿度之间的关系,并可用于分析豆粕水分吸附/解吸等热。当水分小于15%时,豆粕吸附/解吸等热均随水分增大而快速减小,同温度下的解吸吸着等热显著高于吸附吸着等热。当水分大于15%时,豆粕吸附/解吸等热均随水分增大而变化平缓,同温度下的解吸吸着等热趋同于吸附吸着等热。当水分小于15%时,较低温度下的豆粕吸附吸着等热与解吸吸着等热均高于较高温度下的。在水分17.5%的游离水临界点,豆粕的吸着等热(汽化热)接近纯水的潜热,约为2 500 kJ/kg。由等温线分析的25℃豆粕绝对安全水分为12.48%,相对安全水分为13.90%。     

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。