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.     

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.     

Developments in glass transition determination in foods using moisture sorption isotherms

The food polymer science (FPS) approach has been effectively used to investigate the physical stability of amorphous food materials. The glass transition, a key FPS parameter, has traditionally been determined using thermal techniques that scan temperature while holding the plasticizer (moisture) content constant. Moisture sorption isotherms provide information about the physical properties of food as the plasticizer level is adjusted and temperature is held constant. New automatic isotherm generators can be used to produce high resolution, dynamic isotherms much faster than traditional static methods. Dynamic isotherms for a small selection of amorphous materials have been investigated and shown to experience distinct inflection points in the water activity region where the glass transition temperature is close to the experimental temperature. Several studies on amorphous spray dried milk powder and amorphous polydextrose indicate very good agreement between glass transitions determined using thermal techniques and dynamic isotherm methods. This agreement suggests that dynamic isotherms are a viable alternative to traditional thermal methods for investigating glass transitions of amorphous foods.     

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。      

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。     

Application of the GAB model to the moisture sorption isotherms for dried fruits

The moisture adsorption isotherms for dried raisins, figs, prunes, and apricots were determined at 15, 30, 45 and 60°C, using the gravimetric static equilibrium method. The applicability of the GAB (Guggenheim-Anderson-de Boer) model to the experimental results was found to depend on the regression method employed. So, using direct non-linear regression analysis, five constants of the GAB model were estimated which enables the equilibrium moisture content of each dried fruit in the temperature range 15–60°C to be predicted with reasonable accuracy. The indirect (successive) non-linear regression method is not recommended since the basic three constants of the GAB equation are interrelated.     

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.     

响应面法优化羊胎粉中抗氧化多肽制备工艺的研究

选用胃蛋白酶为水解酶,采用响应面法(RSM)优化羊胎粉水解条件,制备抗氧化多肽。研究反应温度、pH、酶与底物浓度比(w/w)对水解度(DH)和产物还原能力的影响,水解条件不同对水解度和铁还原力都有显著性影响(p<0.05)。结果表明,水解产物还原力最强的工艺条件为:温度36.48℃,pH1.05,酶与底物浓度比(w/w)2.03%。     

陕西生鲜羊奶及其加工羊奶粉品质调研分析及相关性研究

为调查陕西省生鲜羊奶及羊奶粉品质随月份的变化规律,明确生鲜羊奶和羊奶粉品质之间的相关关系,该研究以2020年4月至11月某乳品企业在陕西不同地区的奶站收购的生鲜羊奶及其加工羊奶粉为试验样品,对其感官、理化和安全指标进行分析.结果表明,生鲜羊奶和羊奶粉在感官指标方面均符合国家标准要求;在理化指标方面,生鲜羊奶脂肪含量为3...     

Mathematical modelling of moisture sorption isotherms and determination of isosteric heat of blueberry variety O'Neil

The sorption isotherms of blueberry variety O'Neil were determined at 20, 40 and 60 °C, for a range of water activity of 0.10–0.95. The isotherms showed that the equilibrium moisture content increased when temperature decreased at constant water activity. The BET, GAB, Halsey, Henderson, Caurie, Smith, Oswin and Iglesias-Chirife equations were tested for modelling the sorption isotherms. The results showed that GAB, BET and Halsey models gave the best fit quality for the experimental desorption data, and BET, Oswin and Henderson for adsorption data as suggested by the statistical tests employed. The net sorption heat was calculated using the Clausius–Clapeyron equation giving 38.62 kJ mol⁻¹ (desorption) and 30.88 kJ mol⁻¹ (adsorption) at a moisture content of 0.01 g water (g d.m.⁻¹). Tsami equation was applied to estimate the net isosteric heat of sorption as function of equilibrium moisture content with satisfactory results.     

Comparison between moisture sorption isotherms obtained using the new Vapor Sorption Analyzer and those obtained using the standard saturated salt slurry method

The moisture sorption isotherm is an important tool, useful for both processing and product stability applications. The saturated salt slurry method has been a standard method of generating isotherms for many years. Recently, the Vapor Sorption Analyzer (VSA) has been introduced as a new type of isotherm generating instrument and is the first instrument specifically designed to produce both equilibrium and non-equilibrium isotherms. This research compared the equilibrium isotherms generated by these two methods for five food materials and found no significant differences, demonstrating that the VSA can obtain saturated salt slurry equivalent isotherms in much less time and without visible mold growth.     

高蛋白低聚肽奶粉生产过程中的风味控制

研究了高蛋白低聚肽奶粉的生产过程中的各种因素对产品风味的影响。结果表明,脱酰胺反应会使产品具有氨味和辛辣味;还原处理和加热处理,对脱脂乳粉和乳清浓缩蛋白的酶解速度和水解液风味都无明显影响;不同的酶解顺序对乳蛋白水解液的风味影响显著;用风味剂不能有效地掩盖酶解液的不良风味。因此,工艺过程中酶的种类、水解度的控制以及酶的水解顺序对产品的风味影响很大。     

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.     

Microbial dynamics during the ripening of a mixed cow and goat milk cheese manufactured using frozen goat milk curd

To overcome the seasonal shortage of goat milk in mixed milk cheese manufacture, pasteurized goat milk curd and high-pressure-treated raw goat milk curd manufactured in the spring were held at −24°C for 4 mo, thawed, and mixed with fresh cow milk curd for the manufacture of experimental cheeses. Control cheeses were made from a mixture of pasteurized cow and goat milk. The microbiota of experimental and control cheeses was studied using culture-dependent and culture-independent techniques. Bacterial enumeration by classical methods showed lactic acid bacteria to be the dominant population in both control and experimental cheeses. In total, 681 isolates were grouped by partial amplified rDNA restriction analysis (ARDRA) into 4 groups and identified by 16S rRNA gene sequencing as Lactococcus lactis ssp. lactis (563 isolates), Leuconostoc pseudomesenteroides (72 isolates), Lactobacillus spp. (34 isolates), and Lc. lactis ssp. cremoris (12 isolates). Temporal temperature gradient gel electrophoresis (TTGE) analysis of cheese showed (1) the predominance of Lc. lactis in all cheeses; (2) the presence of Leu. pseudomesenteroides population in all cheeses from d 15 onward; (3) the presence of a Lactobacillus plantarum population in control cheese until d 15 and in experimental cheeses throughout the ripening period. Due to the most diverse and complete set of peptidases present in the genus Lactobacillus, the prevalence of this population in experimental cheeses could give rise to differences in cheese flavor between experimental and control cheeses.     

Calculation of water sorption isotherms for multicomponent protein-containing mixtures

This paper presents a method of calculating water sorption isotherms for multicomponent mixtures from the mass fractions and sorption isotherms of the particular components. Interactions between the components are also considered. to compare experimental and calculated data, investigations on protein concentrates produced from blood plasma, baker's yeast and whey were carried out. Calcium carbonate, molecular sieves, cellulose, wheat bran and some types of flour were used as additives.     

Determination of safe storage moisture content of soybean expeller by means of sorption isotherms and product respiration

Soybean expeller (SBE) is rich in protein and has a relatively high and variable oil composition (7–15%). With the increasing use of the SBE for animal nutrition there arose a need for understanding the quality deterioration during storage. The goal of this research was to determine the storability of SBE by developing a model for predicting its equilibrium moisture content (EMC), using the EMC model to determine its safe storage moisture content (SSMC), and by measuring dry matter loss (DML) for SBE incubated at 10 °C and 20 °C for 46 days. Samples of SBE with different residual oil contents were collected and an EMC experiment was carried out to determine the sorption isotherms at 65, 70, 75 and 80% RH; at 10 and 20 °C for samples with 6.2, 9.6 and 15.3% oil content. A second set of samples was used for determining the respiration rate at 20 °C. The Enhanced Halsey model was fitted to the SBE EMC/equilibrium relative humidity (ERH) data and it was established that the residual oil content significantly affected the sorption isotherms. By considering an ERH of 67% or below to be a safe storage condition, the SBE should be stored at or below 12.2% moisture content (m.c.) if the temperature is at or below 20 °C and an the oil content is 7%. However, according to the respiration experiments it would be safe to store SBE up to 16% m.c. (equivalent to 75% ERH). Considering a DML limit of 0.1%, the allowable storage time of SBE at a m.c. lower than 15.4% (ERH of 75%) was at least 46 days. The widely accepted practice of incorporating the gums present in the extracted oil, diluted in water, back into the SBE should be avoided since it increases the m.c. of the product and substantially reduces the allowable storage time.