Moisture sorption isotherms and isosteric heat of sorption of coffee in different processing levels

The desorption isotherms and thermodynamic properties of coffee from different processing stages were obtained during the drying process of this product. The isotherms were determined by a static gravimetric method for various temperature and humidity conditions. Equilibrium moisture content (M_e) data were correlated by several mathematical models and an artificial neural network (ANN) model. The M_e for coffee fruits, pulped coffee and green coffee increased with an increase in the water activity (a_w) at any particular temperature. At a constant a_w, coffee fruits samples had higher M_e than the remaining coffee samples. Based on statistical parameters, the ANN model, modified Henderson and GAB models were adequate to describe the sorption characteristics of the samples. Isosteric heat of sorption was evaluated by means of the Clausius–Clapeyron equation. It decreased with increasing moisture content. The coffee fruits had higher isosteric heat of sorption than that pulped coffee and green coffee.     

马泡瓜籽油成分分析及氧化稳定性研究北大核心CSCD

采用溶剂浸出法提取马泡瓜籽油,对马泡瓜籽油的理化性质和营养组分进行了分析,通过Rancimat加速氧化实验对其氧化稳定性进行测定。结果表明:马泡瓜籽的粗脂肪含量为(27.96±2.15)%;马泡瓜籽油的酸值(KOH)(0.24 mg/g)、过氧化值(0.036 g/100 g)均达到了食品安全国家标准;马泡瓜籽油中共检测出8种脂肪酸和7种甘油三酯,主要是亚油酸(68.56%)和三不饱和甘油三酯(66.50%);马泡瓜籽油中植物甾醇(总含量619.21 mg/100 g,其中粘霉烯醇140.83 mg/100 g)、角鲨烯(38.01 mg/100 g)和生育酚(546.60 mg/kg)的含量较高;马泡瓜籽油的氧化稳定性优于葵花籽油,运用外推法计算出25℃条件下马泡瓜籽油的氧化诱导时间为582.43 h。研究证明马泡瓜籽油具有很好的应用前景。     

Drying characteristics and sorption isotherms of silverside fish (Atherina)

The aim of this work was to report drying characteristics and sorption isotherms of silverside fish. The sorption isotherm was determined at four temperature levels 40, 50, 60 and 70 °C and at water activities, ranging from 0.058 to 0.89, using the static gravimetric method. Five sorption models were fitted with the desorption data generated from the gravimetric method. It was found that the Peleg model suitably represents the sorption experimental data in the mentioned investigated ranges of temperature and water activities. Sorption isosteric heat was determined from sorption data using the Clausius–Clapeyron equation. The relationship between the net isosteric heat of sorption and the moisture content was best expressed by the Tsami’s equation. The drying characteristic curve and the drying rate expression of silverside fish have been established from experimental convective drying kinetics.     

Scaling approach to water sorption isotherms of hydrogels and foods

Mechanisms affecting water sorption isotherms of foods, at high water activities, were evaluated by the processes of swelling and shrinking of model systems of uncharged and charged hydrogels. Their water activity was found to be determined by the combined effect of their osmotic pressure and the network pressure of the polymeric network. The scaling approach in polymer science indicates that in an uncharged network the osmotic pressure is affected by the mobility of the polymer segments and thus by the degree of cross-linking. However, in charged gels, which behave in a similar manner to many food systems, the counterions play the dominant role in determining the osmotic pressure. The network pressure may shift from a positive to a negative value during shrinking (dehydration), thus counteracting or co-operating with the osmotic pressure in decreasing the water activity. A scaling sorption isotherm, at high water activity, is formulated for a food system with physically significant parameters.     

Water agar-agar equilibrium: determination and correlation of sorption isotherms

Summary Water activity in hygroscopic solids determines the behaviour of many materials in storage as well as in drying and freezing operations. Available data concerning phycocolloid gels, such as those of agar-agar and derivatives, are scarce in spite of their interest for pharmacology and the food industry. Thus, we have determined the isotherms of adsorption and desorption of agar-water gels by means of a gravimetric procedure, at 25, 40, 60 and 80 °C, determining the effect of temperature on the heat of desorption by the isosteric heat method, using the Henderson model.     

The effect of high pressure processing on nutritional value and quality attributes of Cucumis melo L.

To determine the effect of cultivar on high pressure processing (HPP) performance three commercial melon varieties were assessed before and after HPP for vitamin C and β-carotene by HPLC and for ferric ion reducing capacity (FIRC) using the Ferric Reducing Ability of Plasma (FRAP) assay. Total titrable acids (TTA), °Brix and colour were also recorded for fresh,−HPP (material cut and packaged) and +HPP samples (material cut, packaged and subject to HPP). The HP process was non-thermal so as to determine the effect of pressure alone on these phytochemicals. There were significant differences between cultivars in vitamin C, β-carotene, TTA, °Brix and colour parameters in fresh samples prior to HPP. HPP did not have an effect on TTA or °Brix, but colour was adversely affected. FIRC and vitamin C concentrations were decreased by HPP and these losses were cultivar dependent for vitamin C. Levels of β-carotene were significantly increased. Cultivar was identified as an important parameter in raw material selection for HPP and retention of vitamin C as a good measure of both quality and cultivar suitability.Industrial relevanceThere is an increasing consumer demand for fresh, natural and healthy fruit and vegetable products with an extended shelf life. This demand is driving industry to look at alternative preservation technologies. HPP has the potential to deliver safe, preserved fruit and vegetables through enzyme inactivation of microbe destruction. HPP removes the need for additives or preservatives and the process is therefore viewed as closer to “natural” by consumers. We show that HPP results in minimal loss of sensorial properties and health-promoting phytochemicals; thus providing consumers a high quality, healthy product with extended shelf life. The introduction of non-thermal processing techniques has the potential to move the focus of the Australian food processing industry from safety to the dual aims of safety and health, resulting in an increase of health-promoting phytochemicals in highly consumed processed foods.     

The applicability of the GAB model to food water sorption isotherms

Summary  The fitting ability of the GAB equation has been analysed. It has been shown that the GAB model describes well sigmoidal type isotherms when parameters are kept in the following regions: 0.24 7lt; k ≤ 1 and 5.67 ≤ c ≤∞. Outside these regions the isotherm is either no longer sigmoidal or the monolayer capacity is estimated with the error larger than ± 15.5%. Moreover, keeping constants in the above regions fulfils the requirements of the BET model.     

Impact of high-pressure processing on microbial shelf-life and protein stability of refrigerated soymilk

The effects of pressure (400, 500 and 600 MPa), dwell time (1 and 5 min) and temperature (25 and 75 °C) on microbial quality and protein stability of soymilk during 28 days of storage (4 °C) were evaluated under aerobic and anaerobic conditions. After processing and during storage, there were significant differences in total bacterial count (TBC), numbers of psychrotrophs (PSY) and Enterobacteriaceae (ENT), and protein stability between untreated (control) and pressurized samples (P < 0.05). Pressure applied at an initial temperature of 75 °C resulted in a greater suppression in growth of PSY compared to TBC. No ENT was detected in pressurized samples throughout the storage period tested. Dwell time had no significant effect on log reduction of TBC at 25 or 75 °C (P > 0.05). Pressure at 400 MPa (5 min), 500 and 600 MPa (1 and 5 min) produced 100% sub-lethal injury in surviving bacterial populations irrespective of temperature. After 28 days of refrigerated storage, both aerobic and anaerobic pressurized samples had better or similar stability as the control on day one of storage. Soymilk control samples were spoiled after 7 days whereas pressurization increased soymilk shelf-life by at least 2 weeks. Pressure (600 MPa) at 75 °C for 1 min not only significantly reduced initial microbial populations and increased the microbial shelf-life but also extended the protein stability of soymilk (P < 0.05).     

Survival analysis methodology to predict the shelf-life of probiotic flavored yogurt

The feasibility of survival analysis methodology was used to determine the shelf-life of probiotic strawberry flavored yogurt supplemented with Bifidobacteirum animalis DN 173010 W was investigated. The quality parameters of probiotic yogurts were related to storage conditions which they are submitted. The consumers were shown sensitive to changes towards sensory characteristics introduced into the products. Using the survival analysis and considering 25% and 50% probability of consumer rejection, the shelf-life of the probiotic yogurt was estimated at 38 and 53 days, respectively. The findings of this research highlighted the feasibility this technique to determine the shelf-life of foods, in particular, functional foods, as probiotic yogurts.     

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.     

Spectrophotometric assay of POE nonionic surfactants and its application to surfactant sorption isotherms

The operational range and suitability toward environmental samples of an iodine-iodide (I-I) assay for nonionic surfactants were assessed. The I-I assay provides a rapid and repeatable method for determining aqueous nonionic surfactant concentrations. Through a systematic examination of surfactant structure, the operational range of the assay was shown to be on the order of 10(-6) to 10(-3) MEO, where the concentration unit MEO is defined as the molar surfactant concentration multiplied by the number of ethylene oxide units in the surfactant molecule. For environmental samples, it was shown that the I-I assay can be applied to measurement of surfactant sorption isotherms to aquifer sands and bacteria cultures. A potential limitation of the I-I assay is interference with humic acids, with the magnitude of the interference dependent on the concentration of humic acids present. The main benefit of the I-I assay is that its high accuracy and ease of application allows measurement of low levels of surfactant sorption. Surfactant sorption to aquifer sand could be measured down to the range of 10(-9) mol/g.     

A new method for predicting sorption isotherms at different temperatures: Extension to the GAB model

In this work, the new methodology for parameter estimation using less experimental data proposed in Staudt et al. (2013) is extended to be used with the GAB model. In addition, a modification in the Arrhenius form for temperature dependency of the energetic constant C is proposed in order to avoid numerical instabilities during parameter estimation. When compared to the original work, one additional parameter, k needs to be estimated but still only one isotherm and one value of net isosteric heat of sorption is required to build the whole set of sorption isotherms. Different food materials were successfully tested providing good fitting and prediction results attesting that the advantages of the methodology originally developed for the BET model are kept with the GAB model.     

Thermodynamic analysis of the sorption isotherms of pure and blended carbohydrate polymers

The adsorption isotherms of gum Arabic (GA), mesquite gum (MG), and maltodextrin DE 10 (MD), and a blend of the three gums (17%GA–66%MG–17%MD) were determined at 25, 35, and 40 °C. All isotherms were fitted using the GAB model and the thermodynamic properties (enthalpies and entropies, differential and integral) were estimated by the Clausius–Clapeyron method. The minimum integral entropy was considered as the point of maximum stability where strong bonds between the adsorbate and adsorbent occurred, and water is less available and likely to participate in spoilage reactions. The point of maximum stability was found between 12.24 and 14.68 kg H₂O/100 kg d.s. (corresponding to water activity, a_w, of 0.32–0.57) for GA, 12.12–14.27 kg H₂O/100 kg d.s. (a_w = 0.33–0.55) for MG, and 11.37–13.84 kg H₂O/100 kg d.s. (a_w = 0.28–0.55) for the biopolymer blend, in the temperature range studied.     

水果果皮的加工利用现状及研究进展

我国是水果生产大国,但水果加工副产物果皮等废弃物丢弃严重,未能得到充分利用。水果果皮中含有多种活性成分且具有特殊的多孔结构和巨大的比表面积,水果果皮作为水果加工的副产物,对其多种活性成分进行提取和加工利用,可变废为宝,提高原料的利用率,具有较大的利用价值。本文以橘子皮、柚子皮、柠檬皮、香蕉皮为主要原料,对这几种水果果皮活性成分的功效和提取方法以及其综合开发利用等几个方面进行了综述,以期为合理利用资源、避免对环境造成污染提供借鉴。     

Water sorption isotherms of freeze-dried milk products: applicability of linear and non-linear regression analysis in modelling

Summary  Water sorption of various freeze-dried milk products was modelled using several water sorption isotherm models, most of which proved to be applicable. Sorption models were fitted to experimental data using linear and non-linear regression analysis. Both methods gave almost the same prediction of water sorption when the model had a good fit. The GAB model was considered to be the most applicable in predicting water sorption in practical applications, as the use of one universal model is desirable. Time-dependent changes, e.g. lactose crystallization above glass transition, were taken into account in the water sorption modelling. Water contents and relative humidities which allowed changes in physico-chemical properties were not included in the modelling, because of unsteady amounts of sorbed water.     

Optimization of processing conditions and evaluation of shelf-life for jeonbokjang products

The objectives of this study were to identify appropriate manufacturing conditions and determine the shelf-life of cold-stored jeonbokjang, and to study the functional properties of oriental herbal jeonbokjang. Blanching abalone at 100°C for 1 min produced the highest sensory scores, and the optimum formulation of jeonbokjang sauce was 49.56% water and 18.62% starch syrup along with other fixed ingredients. During the storage time of 4 weeks at 5°C, the texture of jeonbokjang became firmer, and salinity, total acidity, and L value decreased, whereas pH, volatile basic nitrogen (VBN), and the number of microorganisms increased. The storage experiment indicated that the shelf-life of cold-stored jeonbokjang was 3 weeks at 5°C. Another optimum formulation for oriental herbal jeonbokjang was identified using optimizing technique; 50% water, 12.5% starch syrup, and 8.33% oriental herbs. Oriental herbal jeonbokjang (100 g) had 122.44 mg vitamin C equivalent (VCE) of antioxidant capacity and 140.89 mg garlic acid equivalent (GAE) of total phenolics.