MODELING WATER LOSS DURING FRYING OF POTATO STRIPS: EFFECT OF SOLUTE IMPREGNATION

The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose-NaCl-water, 20-5-75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust.     

Estimation of thermal diffusivity of foods using transfer functions

The effective thermal diffusivity of foodstuffs was estimated from time-temperature histories in the geometric center of samples exposed to heating and cooling processes.Transfer functions methodology was used as an alternative method to estimate the thermal diffusivity assuming that conduction was the main heat transfer mechanism. The samples were characterized as delayed first-order systems with unit gain, dead time (L) and time constant (τ).The results were compared with those obtained from the f_h value and with results reported in the literature.     

马铃薯淀粉渣的羧甲基化研究

研究了马铃薯淀粉渣与氯乙酸进行羧甲基化反应的一般规律，考察了反应温度、反应时间、原料配比等因素对产物取代度的影响，通过正交试验，找到了最佳反应条件，并对产物性能进行了测试。     

种植密度和施肥对马铃薯养分吸收及土壤肥力的影响

在普施２２５ｔ·ｈｍ－２农家肥和固定Ｎ：Ｐ２Ｏ５：Ｋ２Ｏ比例２：１：３的条件下，研究了不同种植密度和施肥量对马铃薯品种“川芋早”矿质养分吸收利用和土壤肥力的影响。结果表明：加大种植密度和提高施肥水平均使植株群体的每生产千公斤薯块的Ｎ，Ｐ２Ｏ５，Ｋ２Ｏ的吸收量增加，提高肥料的利用率，尤其是高密高肥和高密中肥处理显著。农家肥的施用可以增加土壤中有机质和速效养分的含量，特别是与无机化肥配合施用效果更好     

Inactivation kinetics for Salmonella Enteritidis in potato omelet using microwave heating treatments

The aim of this study was to model the inactivation of Salmonella enterica serovar Enteritidis in pasteurized omelet internally inoculated at different microwave heating treatments (300 W; 450 W, 600 W and 800 W). Results indicated a non significant change in Salmonella populations during the first 30 s treatment at 300 W and 450 W, being log reductions lower than 0.5 log CFU g⁻¹. However, after 40 s treatment, log reductions had risen to 4.8 log CFU g⁻¹ at 800 W. Inactivation rates were higher at 600 W and 800 W (0.67 and 0.63 s⁻¹) than at 300 W and 450 W (<0.34 s⁻¹). The temperature-dependent parameters of a Weibull model obtained by Mattick, Legan, Humphrey & Peleg (2001) were evaluated. It was concluded that combinations characterized by a temperature equal or above 70 °C ensured a minimum 4 log reduction of Salmonella population (i.e. 300 W-80 s; 450 W-60 s or 600 W/800 W-40 s). These results may be of value in food service establishments, as target treatments for microwavable potato omelet portions.     

Non-destructive detection of blackspot in potatoes by Vis-NIR and SWIR hyperspectral imaging

Blackspot is a subsurface potato damage resulting from impacts during harvesting. This type of bruising represents substantial economic losses every year. As the tubers do not show external symptoms, bruise detection in potatoes is not straightforward. Therefore, a nondestructive and accurate method capable of identifying bruised tubers is needed. Hyperspectral imaging (HSI) has been shown to be able to detect other subsurface defects such as bruises in apples. This method is nondestructive, fast and can be fully automated. Therefore, its potential for non-destructive detection of blackspot in potatoes has been investigated in this study. Two HSI setups were used, one ranging from 400 to 1000 nm, named Visible-Near Infrared (Vis-NIR) and another covering the 1000–2500 nm range, called Short Wave Infrared (SWIR). 188 samples belonging to 3 different varieties were divided in two groups. Bruises were manually induced and samples were analyzed 1, 5, 9 and 24 h after bruising. PCA, SIMCA and PLS-DA were used to build classifiers. The PLS-DA model performed better than SIMCA, achieving an overall correct classification rate above 94% for both hyperspectral setups. Furthermore, more accurate results were obtained with the SWIR setup at the tuber level (98.56 vs. 95.46% CC), allowing the identification of early bruises within 5 h after bruising. Moreover, the pixel based PLS- DA model achieved better results in the SWIR setup in terms of correctly classified samples (93.71 vs. 90.82% CC) suggesting that it is possible to detect blackspot areas in each potato tuber with high accuracy.     

A Mathematical Model for Vacuum Far-Infrared Drying of Potato Slices

A mathematical model of mass and heat transfer for vacuum far-infrared drying of potato slices is introduced in this study on the basis of energy and diffusion equations. The finite difference method is used to mathematically simulate the sample temperature and moisture content in different drying conditions. Calculated results are compared with the experimental findings at varying conditions of heater temperature (120°C, 140°C, and 160°C), chamber pressure (1500, 8000, and 15000 Pa), sample thickness (0.004, 0.006, and 0.008 m), and radiation distance (0.08, 0.12, and 0.16 m). Comparison results show that the model fits well the changes in sample temperature and moisture content at different times of drying, with the values of the coefficient of determination close to 1.0 and the relative error values less than 10%.     

Changes in glycoalkaloid and nitrate content in potatoes during dehydrated dice processing

The aim of this experiment was the determination of glycoalkaloid and nitrate content in potatoes during stages of processing into dry potato dice.Samples obtained from the tubers of three potato varieties were used: a very early Denar variety of Polish origin; Innovator, an early Dutch variety; and a Polish medium early Pasat variety. There were sampled three times from the factory store in 2009 and 2010. The potatoes were diced in laboratory conditions, by first peeling with a carborundum peeler, dicing into 10 × 10 × 10 mm pieces and rinsing with water at a temperature of 20 °C. In the next stages, the diced potatoes were blanched in water at a temperature of 75 °C for 5 min then dried in a laboratory drier for 1 h at 120 °C. After 1 h of drying, the temperature was lowered to 55-60 °C in order to obtain a defined final moisture content of 8-11%.In the raw material, intermediates and finished products, the concentrations of glycoalkaloids (α-chaconine and α-solanine) were determined using an HPLC method, and nitrates were determined colorimetrically using an RQflex analyser.It was found that the processes used in dried potato dice production significantly decreased concentrations of glycoalkaloids (α-chaconine and α-solanine) in intermediate and finished products when compared to raw material. The highest decrease in the quantity of glycoalkaloids occurred during peeling (33%) and after blanching (17%) of peeled potato. Nitrate content fell the most after cutting and rinsing with water (13%), and after blanching (23%). On average, dry potato dice contained 44% of the initial quantity of glycoalkaloids and 40% nitrate content in the final dried product.     

DMA thermal analysis of different parts of potato tuber

Dynamic mechanical analysis (DMA) was applied to three potato tissues (‘cortex’, ‘pith’, and ‘side’ surface) of two cultivars (more waxy ‘Nicola’ and more mealy ‘Saturna’) in temperature scans in the range 30–90 °C and constant air humidity of 90%. The obtained scans indicate peaks in both storage and loss module of elasticity (SM and LM, respectively) at temperatures higher than 70 °C – so called ‘starch’ peak (SP) – as was observed previously. The peak value increase with increasing potato dry matter (DM) content, below DM content approximately 14% no SP is observed (‘Nicola pith’). Slope analysis of the basic parameters: SM, LM, and loss tangent (LT) was performed and further characteristic points on the temperature plots were found: (i) in temperature range A (30–40 °C) maximum of SM and LM and minimum of LT, (ii) in temperature range B (40–50 °C) minimum of SM and LM slopes corresponding to point of inflection on SM-T and LM-T plots, (iii) at about 50 °C, big peak in LT in side tissue only, (iv) at about 70 °C just prior the ‘starch’ peak, big peak in LT that is more marked in ‘pith’; this peak denoted as ‘I’ influenced the ‘starch’ peak ‘II’. It was found that both cultivar and part of the tuber influences the DMA temperature plots.     

Where to for Brazil's Cities? Citizen Empowerment or Global Marketing?

An awakening interest in public space in Brazilian cities is emphasising the value of existing civic areas. Guilherme Wisnik , a critic, curator and professor at the Faculty of Architecture and Urbanism of the University of São Paulo, looks at the history and potential future of Brazil's urban spaces. He highlights how despite the introduction of innovative Modernist design in the mid-20th century, which forged ‘a new relationship between architecture, urbanism and landscape design’, more recently the country's cities have been subject to the vicissitudes of market and political forces.