Microwave Drymg of Grapes in a Single Mode Cavity at 2450 Mhz - i: Drying Kinetics

ABSTRACT

Grapes were dried into raisins using combined microwave and convective drying in a single mode cavity specially designed for the studies. Effect of processing parameters, viz.microwave power density (P) air temperature (T) and velocity (u) on drying kinetics was studied in an effort to optimize the operating conditions. The individual and interactive effects of these variables were srudied using three levels of P, four levels of T and two levels of u. Higher drying rates observed with the higher P and T were atuibuted to the increased product temperature and higher partial vapour pressure difference between the surface of the fruit and the air stream. Increase of air velocity increased the drying times. Low drying rate at higher air velocity was attributed to decreased fruit temperature due to rapid convective heat mnsfer at the surface.     

用于面包制作的葡萄天然酵母发酵工艺优化

以葡萄干为发酵原料,研究不同发酵工艺参数对葡萄天然酵母发酵力的影响,为用于面包中的天然酵母发酵优化工艺提供一定的试验数据。以单因素试验为基础,采用响应面分析法对发酵工艺参数进行优化,结果表明:最优发酵条件为培养温度26℃,培养时间4d,葡萄干与白砂糖配比101。该条件下,天然酵母发酵力为0.077 9,与市售的即发干酵母的发酵力较为接近,可代替其用于面包的制作中。     

An After‐School Snack of Raisins Lowers Cumulative Food Intake in Young Children

Snacks are an important part of children's dietary intake, but the role of dried fruit on energy intake in children is unknown. Therefore, the effect of ad libitum consumption of an after‐school snack of raisins, grapes, potato chips, and chocolate chip cookies on appetite and energy intake in twenty‐six 8‐ to 11‐y‐old normal‐weight (15th to 85th percentile) children was examined. On 4 separate weekdays, 1 wk apart, children (11 M, 15 F) were given a standardized breakfast, morning snack (apple), and a standardized lunch. After school, children randomly received 1 of 4 ad libitum snacks and were instructed to eat until “comfortably full.” Appetite was measured before and 15, 30, and 45 min after snack consumption. Children consumed the least calories from raisins and grapes and the most from cookies (P < 0.001). However, weight of raisins consumed was similar to potato chips (about 75 g) and lower compared to grapes and cookies (P < 0.009). Raisins and grapes led to lower cumulative food intake (breakfast + morning snack + lunch + after‐school snack) (P < 0.001), while the cookies increased cumulative food intake (P < 0.001) compared to the other snacks. Grapes lowered appetite compared to all other snacks (P < 0.001) when expressed as a change in appetite per kilocalorie of the snack. Ad libitum consumption of raisins has potential as an after‐school snack to achieve low snack intake prior to dinner, similar to grapes, compared to potato chips, and cookies in children 8 to 11 y old.     

Raisins and Oral Health

Traditionally, raisins have been thought to promote dental caries due to their suspected “stickiness” and sugar content. Current research identifies some evidence contrary to traditional thought, suggesting that raisins may not contribute to dental caries. This article reviews new findings with regards to raisins and the 3 conditions that are thought to contribute to the formation of dental caries; low oral pH, adherence of food to teeth, and biofilm (bacterial) behavior. The studies reviewed concluded that raisin: consumption alone does not drop oral pH below the threshold that contributes to enamel dissolution, do not remain on the teeth longer than other foods, and contain a variety of antioxidants that inhibit Streptococcus Mutans, bacteria that is a primary cause of dental caries. Further research in this area should be considered.     

AN ANALYSIS OF MASS TRANSFER IN AIR-DRYING OF FOODS

A theoretical model for the convective drying of food materials was developed. These materials shrink considerably, as moisture content decreases; for this reason, the proposed model takes shrinkage into account as a fundamental part of the drying operation. This is accomplished by modeling the movement of dry solids and the consequent movement of bound substance during drying. The resulting system of three non-linear partial differential equations is solved numerically and the predicted values of moisture content and temperature are compared with experimental data for the drying of Sultana grapes. The effective moisture diffusivity in the mass of grapes was described by an Arrhenius-type equation. A sensitivity analysis of the predicted values and the examination of the confidence regions of the estimated parameters showed that the activation energy for mass transfer was estimated with a high degree of precision. The agreement between the calculated results and the experimental measurements, using various criteria, was very satisfactory.     

不同葡萄品种加工绿葡萄干的适宜性分析

以36个新疆绿色葡萄品种为试材进行感官、理化指标的检测,运用灰色关联度分析方法,对其主要性状与"理想品种"性状之间的密切程度进行综合分析,依据各品种的加权关联度对参试品种进行聚类分析,研究其加工绿葡萄干的适宜性。结果表明:无核白、底莱特、京早晶、波尔莱特、无核白鸡心等葡萄品种适宜加工绿葡萄干,而苏珊玫瑰、谢克兰格、匈牙利之光等则不适宜加工成绿葡萄干,其他品种居中。此结果与各品种实际表现基本一致,说明该方法可用于我国葡萄干产业加工品种的筛选及其评价体系的建立。     

Iron Bioavailability from Common Raisin-containing Foods Assessed with an In Vitro Digestion/Caco-2 Cell Culture Model: Effects of Raisins

The effects of raisins on iron bioavailability from wheat bran cereal, bread, rice pudding, and granola bars were studied. Iron bioavailability was assessed with an in vitro digestion/Caco‐2 cell culture model. Raisins reduced iron bioavailability from all foods except granola bars. Raisins also reduced iron bioavailability from samples of wheat bran cereal and bread fortified with elemental iron or ferrous sulfate, but this inhibitory effect was less pronounced in samples fortified with sodium iron ethylenediaminetetraacetate (NaFeEDTA). Iron bioavailability was markedly higher for samples fortified with NaFeEDTA, suggesting that iron in the form of NaFeEDTA is more bioavailable than elemental iron or ferrous sulfate in raisin‐containing foods.     

Heat of sorption of water in dried fruits

The heats of moisture adsorption and desorption in four dried fruits (sultana raisins, figs, prunes and apricots) were estimated from equilibrium sorption data, using the Clausius-Clapeyron equation in the temperature range 15–60°C. The net isosteric heat of sorption ( q st) decreased sharply from about 20 kJ mol⁻¹ water to near zero when the moisture content was increased from 0.05 to 0.50kg water kg⁻¹ dry matter. An exponential function was fitted to the experimental q st values at various moisture contents (X) , yielding two characteristic constants ( q 0 and X 0) for each fruit. Mean and total heats of sorption were calculated from the proposed empirical equation, which are useful for enthalpy prediction in food dehydration. The heats of desorption were higher than the heats of adsorption, indicating significant hysteresis in the sorption of water, especially in dried apricots.