STUDIES ON THE EFFECT OF SURFACTANT, BLANCHING AND OSMOTIC PRETREATMENTS ON THE CONVECTIVE DRYING OF POTATOES

Moisture removal from solids is an integral part of food processing. To approach the drying process of a given product it is necessary to have a knowledge of the drying kinetics. However, foodstuffs are often subjected to certain chemical and physical treatments, such as surfactant impregnation, osmotic dehydration or blanching, prior to convective drying. The drying behavior of potatoes was monitored within an experimental air tunnel dryer, with the mechanism of internal moisture migration being identified as diffusion. This was subsequently evaluated on the basis of the liquid diffusion theory. Experimental data revealed osmotic concentration as a favorable process. A 29±2% reduction in diffusion coefficient was observed following osmotic dehydration with a salt/sugar solution, however, this provided a 63±3% reduction in drying time. Structural modifications were induced by blanching, with this rendering a 10±1 and 27±2% lowering of the moisture transfer rate during drying at 30 and 60C, respectively.     

INFLUENCE OF COMBINED MICROWAVE‐VACUUM DRYING ON DRYING KINETICS AND QUALITY OF DRIED TOMATO SLICES

ABSTRACT

The study investigated the influence of four microwave powers on the drying kinetics and quality of tomato slices in a microwave‐vacuum dryer at vacuum pressures of 0.04, 0.05 and 0.06 MPa. The results showed that increase in microwave‐vacuum drying conditions increased drying rates and resulted in decreased drying time from 84 to 14 min. The nonenzymatic browning index increased with microwave power whereas the overall flavor degradation was between 18.99 and 20.80%. The brightness and the yellowness of the dried tomatoes generally increased but there was a slight reduction in redness when compared with the fresh. The effective moisture diffusivity increased with microwave power and was 7.22 × 10^?9, 9.10 × 10^?9, 14.99 × 10^?9 and 25.19 × 10^?9 m²/s at respective microwave powers of 200, 300, 500 and 700 W.

PRACTICAL APPLICATIONS

Microwave‐vacuum drying is one of the advanced methods with numerous advantages including high thermal efficiency, shorter drying time and improved product quality. Tomato is the second most important vegetable with enormous health benefits, which include reduction of cholesterol, improvement of vision, maintenance of gut, lowering of hypertension, alleviation of diabetes, and prevention of urinary tract infections and gallstones. The quality of dried products obtained using the microwave‐vacuum dryer provides industries with method that can be used to enhance the quality of dried tomatoes. The dried product is a valuable ingredient in the preparation of soups and sauces, as well as in cosmetics and pharmaceutical formulations.

     

INFLUENCE OF OSMOTIC DEHYDRATION ON THE VOLATILE PROFILE OF GUAVA FRUITS

ABSTRACT

The effect of osmotic dehydration (OD) on the volatile compounds of guava fruits was studied. Osmotic treatments were carried out at atmospheric pressure, at continuous vacuum and by applying a vacuum pulse (5 min under vacuum and the remaining time at atmospheric pressure) at different temperatures (30, 40 and 50C) and times (1, 2 and 3 h). The volatile compounds of fresh and dehydrated samples were obtained by simultaneous distillation–extraction, and were analyzed by gas chromatography/mass spectrometry. In general, OD caused changes in the concentration of volatiles, depending on the process conditions. The use of lower temperatures and shorter treatment times can diminish the loss of volatiles with respect to the fresh samples. The greatest damage to volatiles loss is produced at 50C for up to 2 h under both pulsed and continuous vacuum. The lowest total volatiles loss occurred at 30 and 40C for up to 3 h under pulsed vacuum or atmospheric pressure.

PRACTICAL APPLICATIONS

Consumer demand for high‐quality products with freshlike characteristics has promoted the development of a new category, minimally processed fruits and vegetables. Although these products present, as distinguishing features, simplicity in use and convenience, they generally perish more quickly than the original raw material because of tissue damage caused by mechanical operations. The use of osmotic dehydration process has been presented as a tool for the development of minimally processed fruits. The slight water activity reduction promoted by the process may provide stable products with good nutritional and sensorial quality and with characteristics similar to those of the fresh products. The application of minimal processing to tropical fruits can represent an interesting world market. Fruit flavor is an important quality factor that influences consumer acceptability, and for this reason, its study is relevant in the minimally processed food product.

     

INFLUENCE OF PRETREATMENTS AND BLANCHING TREATMENTS ON THE YIELD AND COLOR OF CANNED MUSHROOMS

Three factors in PSU-3S and SSV processes, i.e. soaking, cold storage, soaking again or vacuum hydration, which might increase the yield of canned mushrooms, were investigated. The results of experiments revealed that only cold storage time in these processes significantly affected the yield of canned mushrooms. The undesirable effect of PSU-3S or SSV processes on the color of canned mushrooms may be significantly remedied by acid blanching.     

THE INFLUENCE OF VACUUM PRESSING ON THE TEXTURE OF CHEDDAR CHEESE*

A study was made of the influence of several factors on the texture of young and mature vacuum-pressed rindless cheese. Pressures greater than 26 lb/in² were required for maximum improvement in texture. A vacuum of 15 in was less effective than a vacuum of 25 in. Vacuum pressing of ‘dressed’ cheese for 5 min was almost as effective as vacuum pressing for 17 h; vacuum pressing after dressing was more effective than before dressing; transfer of vacuum-pressed cheese to a normal press for the completion of pressing did not affect texture. Vacuum treatment of curd before hooping and pressing in the normal way had no beneficial effect on texture; vacuum pressing improved the texture of cheese made with mixed-strain starters although this cheese was not as close as vacuum-pressed cheese made with single strain starters. The distinct improvement in cheese texture which resulted from some combinations of vacuum pressing condition was confirmed in commercial scale trials involving 2,540 rindless cheese. This improvement was evident when cheese were graded at two weeks and when regraded at maturity.     

CHARACTERISTICS OF CHAMBER TEMPERATURE CHANGE DURING VACUUM COOLING

In order to investigate the dynamic changing pattern of the chamber temperature with chamber pressure during vacuum cooling, 10 repeated experiments were conducted to evaluate the time-dependent temperature and pressure in the vacuum chamber during vacuum cooling of water. Water was chosen in the experiment as it is the main component of most foods. The results showed that the temperature in the vacuum chamber significantly depended on variation in pressure at different pumping stages. The temperature changes in the chamber generally followed a certain pattern. In the early stage of vacuum cooling, the chamber temperature dropped very quickly (0.26 K/s), while at the end of vacuum cooling, it increased rapidly (0.22 K/s), and was about 11.8 K higher than the ambient temperature when the vacuum was released with ambient air flowing back to the chamber.

PRACTICAL APPLICATIONS

Vacuum cooling is a rapid cooling method for the food industry; further understanding of the vacuum cooling mechanism can help to control and improve this cooling process. Temperature changing pattern and distribution affects the quality of the food product in vacuum cooling process. As the main component of most foods is water, it is necessary to investigate the dynamic temperature changing pattern and distribution with vacuum pressure during vacuum cooling of water so that the information obtained could be used as a reference for vacuum cooling of food products.     

INFLUENCE OF SAMPLE SIZE AND SHAPE ON TRANSPORT PARAMETERS DURING DRYING OF SHRINKING BODIES

An experimental investigation on the influence of sample size and shape on heat and mass transport parameters under natural convection air‐drying is presented. Potato cylinders with length of 0.05 m and thicknesses of 0.005, 0.008, 0.010 and 0.016 m, and circular slices with diameter of 0.05 m and thickness of 0.01 m were dried in a laboratory scale hot‐air cabinet dryer. Results indicate that each transport parameter exhibits a linear relationship with sample thickness. Convective heat and mass transfer coefficients (h_cand h_m) decreased whereas moisture diffusion coefficient (D_eff) increased with increasing thickness. Considering no sample shrinkage effect in the parameter analysis, for the thickness range considered, the values of h_care found to be underestimated in the range of 29.0–30.6%, whereas those of h_mand D_eff are overestimated in the range of 33.7–38.0% and 75.9–128.1%, respectively. Using Levenberg–Marquardt algorithm for optimization, a correlation for Biot number for mass transfer (Bi_m) as a function of drying time and sample thickness is proposed. A close agreement was observed between dimensionless moisture contents predicted by this relation and those obtained from experiments for different sample thicknesses at drying air temperature of 60C. For the same thickness and drying conditions, circular slices caused an increase in each transport parameter significantly.     

INFLUENCE OF DRYING TEMPERATURE AT HARVEST ON MAJOR VOLATILES RELEASED DURING ROASTING OF PEANUTS

Sound mature kernels of Spanish and Runner-type peanuts harvested from two crop years were dried at four different temperatures (stack cured, 110, 135 and 160°F). Immediately after drying, the peanuts were shelled and roasted; the volatiles released during the roasting process were collected and quantified. Higher drying temperatures resulted in an increase in hydrogen sulfide, total base, dicarbonyl compounds and total carbonyls (hydrazones). Total volatile carbonyls appeared to be the best indicator of the effects o drying temperatures.     

油炸与真空干燥结合加工菠萝蜜脆片工艺研究

通过在棕榈油油炸定型的条件下,分别比较不同真空度、不同温度对菠萝蜜干燥效果的影响,从Vc含量,亮度值和外观,口感,香味等感官评定各项指标进行比较分析,得出在真空度0.09MPa条件下,采用50℃的温度真空干燥菠萝蜜效果最好。     

STUDIES ON FLAVOR CHANGES DURING DRYING OF DILL (Anethum sowa Roxb.) LEAVES

Indian dill (Anethum sowa Roxb.) is a popular herb widely used in culinary preparations and is characterized by a persistent cineolic flavor. To study the flavor quality of the fresh and dried herb, it was subjected to through-flow, cross-flow, vacuum and freeze drying procedures. The volatile oils obtained from the fresh and dried samples were examined by gas chromatography and gas chromatography-mass spectrometry and the changes in their flavor compositions determined. Seventeen compounds have been identified in Indian dill leaf oil, of which β-cubebene is being reported for the first time. The proximate composition of the dried herb is also reported.     

番茄片真空干燥参数研究

将新鲜番茄切片进行真空干燥和超微粉碎加工成果蔬粉,研究番茄真空干燥的工艺参数.通过双因素试验设计,考察真空干燥过程中干燥室温度和番茄切片厚度对真空干燥制得番茄粉品质的影响.结果显示,干燥室温度对番茄粉品质的影响极为显著;最优工艺参数为真空干燥室温度60℃、番茄切片厚度7mm,相应的Vc保存率为148.48 mg/100 g.     

冷冻干燥海蓬子的品质分析

研究采用真空冷冻干燥加工海蓬子以及分析冻干品的营养品质.以新鲜海蓬子作为对照,通过感官品质、复水性、营养成分、卫生指标等方面对海蓬子经冷冻干燥所得干菜品进行了分析.结果表明,真空冷冻干燥海蓬子干品的感官接近新鲜海蓬子;经95℃热水浸泡2 min基本恢复鲜品状态;营养成分得到很好保持;卫生指标符合NY/T 1045-2006(绿色食品脱水蔬菜)质量安全要求.真空冷冻干燥很好地解决了海蓬子长期保存、保鲜的技术难题.